EEVblog 1502 - Is Home Battery Storage Financially Viable?

[@johnwest7993]

I found comparing grid power costs to my own PV power costs was silly. Instead of spending a lot of money on a backup generator for emergencies I have my PV/battery system that requires almost no maintenance. And for the years I lived in an RV my PV panel /battery energy system was priceless. A friend told me that PV panels simply didn't pay for themselves. I replied that he wouldn't say that in the dead of winter at a campsite in the national forest. ANY money I put into the system just made my life better, and it saved me over $1000 a month in rent. So the RV and the PV/battery system entirely paid for itself in the first 2 years, ALL of it. So it's entirely a situational thing, as you mentioned.

[@spikester]

Nobody is objecting to offgrid use of PV & batteries, it certainly works very well in an RV when you have backup/propane heat in the winter. The problem is industrializing this at grid level with GWh of batteries so the environmentalists can game the rates system & charge ratepayers double just so they can pocket the rest. Offgrid is a real practical solution for 'household' uses of power.

[@spikester]

This is why they have to use households as a metric; as its a totally useless one when it comes to grid demand; but it looks extremely good on paper to power 10,000 'households' with a 'solar farm'. In theory...

[@SHREDTILLDEAD]

Umm so this video is about rv usage now ?

[@sporefergieboy10]

LIVE IN A VAN DOWN BY THE RIVER

[@johnwest7993]

@@SHREDTILLDEAD, nope. My comment was about how many different applications and values there are for PV panels, so the cost/benefit comparison has to be entirely a case by case comparison with the items that matter being identified by the owner of the installation. A fixed site application where value is only determined by a dollar for dollar comparison vs grid cost is an absolute worst case and simplest comparison that leaves out many factors in a typical installation. 'Can I undercut the grid price?' is only a starting point in calculating whether or not to do a PV and battery installation.

[@401ksolar]

I have lived off grid for quite a while and I have learned that the word battery can mean several different methods, some are electrical in nature however the larger ones are usually water, air, and even larger ones are large tank batteries for sweet crude oil, I like the idea of heat storage, as far as the electrical devices that I use most are one off which I have repurposed from other devices and redesign their power supplies to a softer mode to the lightest power usage needed, as an example instead of using one Pelletier device at 12 volts I will connect to in series and run them using the load control on the solar charge controller.

[@autohmae]

It's amazing how few people realize heat and electricity can have different source too. Converting heat to electricity isn't always a great idea.

[@erbse1178]

You could take a small 5kwh battery to power the house if your electric car is on its way and install a system that takes the energy from your parked car. Then you would have a 60+ kwh battery at no additional cost other then the setup. (Hyunday Ioniq 5 has a 58 kwh battery with bi-directional output of max 3.6 kwatts)

[@casemodder89]

the additional cost is the shortened life span of the fckn expensive car battery you wear out prematurely ! no free beer on planet earth !

[@haveaseatplease]

Source?

[@erbse1178]

@@casemodder89 Maybe. But most of old car batteries get decommisioned to home storage batteries in a second life these days before real recycling comes into play. Of course it would wear down the car battery by an additional certain level, BUT car batteries (btw. battery is the wrong word, it is technically and by chemical properties an accumulator) wear down most, when charged or uncharged in a short period of time, involving heavy loads in and out. That is not the case here. Second: modern car batteries (FeS based like in the China Model 3) have around 6k-8k full charges until they are supposed to reach their end of life as a car battery. Assuming a complete charge-discharge cycle per day ( I doubt a house needs that much energy or your house solar can supply that loads during a day) this leaves us around 16 years until worn down to 70% (which is the value from where it should be change in a car.)

[@sokolum]

Lithium Iron Phosphate is way to go to have a grid/house battery. And i would buy 12~15kWh, a bit overhead will have less stress on your batteries and better live span, in my opinion.

[@eddwhite12345]

Even though the feed-in tariff is a pittance, if you factor it into the calculations it reduces the yearly saving to ~$1170. Because you're no longer selling the excess energy to the grid and instead storing it in a battery, then you need to subtract that loss of revenue from the savings made on your electricity bill. I still think the battery system is a good way to go, as feed-in tariffs only seem to be going down, so I don't think you can rely on it for long term investments like this.

[@PietroZambon]

Did you account for the excess over the 15kwh of the battery? Any energy produced ovet that limit would still go in the grid, once the batteries are full

[@haveaseatplease]

Your correction does not account for the savings you have by using those stored kW's and not pay 30 cents for each kW to your provider.

[@eddwhite12345]

@@haveaseatplease I believe it does, so let me try explaining it again. Instead of selling excess to the grid, the plan is to store this power for later to reduce our electricity bill. So every kwh stored reduces the electricity bill by 30 cents, however that was power that previously would have been sold to the grid for 7 cents prior to having the battery. So the net gain for installing the battery per kwh is actually 23 cents (ignoring storage and conversion losses etc) I hope this makes more sense 🙏

[@haveaseatplease]

@@eddwhite12345 This was exactly what I was trying to write down, but was to lazy to do it. Thank you.

[@rootbox27]

These hybrid inverters are "whole house" too as they can measure the energy in and out of the total house and make decisions based on that to for example charge or discharge their battery. A transfer switch like you showed could also be handy

[@smsn13act85]

Just wanted to second this comment but add the gotcha of DNSP inverter limits. Mine limits to 10kW of inverter per phase so that sets engineering limits on the combinations. I've got 7.8kW of solar and 5kW of battery behind a 6kW hybrid inverter and still a bit of room to add more later. Not sure how hard it is to get exemptions approved but could imagine trying to validate stability and islanding of any weird mix of inverters being challenging.

[@EEVblog]

Yes, but usually not as standard. And certainly not in the case a retrofit of an existing grid tied inverter. You have to specifically have them set up and wired as a whole house solution.

[@crissd8283]

I think there is a misunderstanding. Hybrid inverters are tied into the house and can attempt to use zero grid energy using CTs to monitor grid current. However, if their is a power outage, a hybrid system won't power the entire house as it can only be tied to selective circuits unless you have a whole house transfer switch. I think this is what he is referring to.

[@IreBrezOvire]

@@EEVblog We're in the process of installing a PV system here in Slovenia and I ordered 2 SolarEdge SE10K-RWB48 (the completly new model) and they have 9 kW backup output (10 kW when on grid) - but only pull 5 kW off the battery. Will also install 1 BYD LVS batteries for each inverter. Took me a lot of time to research this (at least here in the EU) SolarEdge + BYD is the best € per kW/kWh combo you can get that is just plug&play (Huawei has a complete hybrid system but it kinda sucks). Order fast tho, prices are rising :(

[@cloudysky3614]

@@EEVblog It's quite wide spread, at least from all the models I checked for my installation. And the list of hybrid with full backup is growing. But factor in the power draw of the inverter when running on battery power. This can be between 50-130W at idle load for three phases. So always factor in the idle power consumption which is not something the manufacturer includes in their specifications) There are lots of details if you dig deeper into this topic but most of them are not relevant if you don't care about backup power that much. Here the gap between what you pay and what you get per kWh ist quite big as well. 0.41€ vs ~0.075€. When I planend my installation most people said that a battery is useless. I got my battery 12.8k for 3.8k€ after incentives and with my power habbits / power consumption during the day it'll actually pay off in about 6 years. And since our power supply here in europe could be critical during this winter I am happy to at least have a full backup option.

[@raymondcasso7966]

Wow... about time this made sense. I've been off-grid for 4 years now and I paid $2000 usd for a 10kw lifepo4 24v battery plus $800 usd for a hybrid inverter. Best purchase so far!

[@Stealthsilent1337]

The

[@raymondcasso7966]

@@Stealthsilent1337 ?

[@randomelectronicsanddispla1765]

How much storage did that $2000 get you?

[@Passco666]

Its impossible to buy 10kWh for 2000 USD

[@randomelectronicsanddispla1765]

@@Passco666 my guess would be a 10kW output capable system but I'm curious to what capacity battery it has. Or it could be second hand, I get second hand backup lead acid batteries for about $1000 (AUD) per 10kWh

[@JBoy340a]

We have a Tesla system, Solarroof and Powerwalls. We got it to do 2 things. First, ensure we had power all the time. We have 3-5 power shutoffs per year some lasting upwards of 18 hours, and since we work from home, no power means no work and associated billings. Second, to reduce our power costs. The system has done very well at both. The system has pretty much removed our electrical power bill. We used to pay upwards of $600 USD/mo. in the summer. Now we usually only pay the minimal connection fee amount, about $12/mo. And as far as backup goes, we have not lost power, even when the neighborhood is out. We usually just get a message in the app that says the grid is down. And we verify this by looking out the windows and see the lights are out at in the neighborhood. We usually don't even see our lights flicker.

[@billjohnson3344]

Nice video Dave. One thing you also need to consider is your best and worst solar days combined with worst and best home usage - not just average for the seasons. For example, if you have many days in the summer where your solar is pumping but your house load is light, that energy can't all get saved with your battery system - you will hit max state of charge. At which case you still have to give back to the grid (at your lower feed-in rate). But if you then have rainy days where you need more power than the battery could have banked, you have to get that from the grid at your higher consumption rate. If it turns out you have an overall surplus, that's not a big deal. But you really need to look at your daily worst cases to size the battery - not just average within the seasons. Otherwise your calculations are giving you a best case, and you'll be 'clipped' by your battery state of charge in reality and not achieve that. Seems super easy to have many days where your solar provides more than 10kWh surplus over your home usage (which would be your 0-100% battery SOC for a 10kWh battery) - and that extra energy can't be banked by the battery and goes back to your current grid feed in/out pricing. And conversely, on a rainy but high consumption day, you won't get your battery charged to last through the night - so need power from the grid. If you do a day to day analysis, you'd probably see that both these scenarios happen fairly often, and you have to either go with a bigger battery - or just factor in the grid in/out cost for those daily over / under consumption scenarios. And also, when sizing the battery, you also want to consider how far you want to dip down. Battery life is extended if you aren't cycling 0-100%, so you generally want to oversize capacity to account for that as well. I think in your case a battery system is a tough call. You probably won't reclaim your expenditure if you figure a 10 year life on the batteries. Unless you have some incentives in your area to help with the price. If you have time-of-use billing, or zero credit for feed-in, then a different story.

[@andyjdhurley]

I was thinking there was a small mistake here too. Dave uses the average daily usage from the grid to work out what size battery to go for but in the worst cases that is getting on for double what the panels are producing so if you sized for the usage it would never fill up. 'Course, in Dave's case, he is planning for more solar so that is probably why he ignored that little point.

[@mostlyguesses8385]

Yeah, weather can be bad for 4 days, no sun, so need 4x maybe in batts. Theres a reason why people stick with $2,000 power grid, to go off grid is like $80,000 which at 8%,20yrs is $8,000 a year financed. .. which is a tech miracle but going off grid is not for any but elite 10% earning over $200,000.......... Compared to 1990 batt and solar has progressed but still need lower

[@ThisRandomUsername]

I think Dave isn't trying to go completely off grid here. He wants to see if he can run his own battery power for a reasonable cost which will pay itself back quickly. That's why in winter he uses a lot more than he puts back into the grid, but he isn't adding the cost of extra solar panels into this equation. It's most economical to price for your average consumption. Honestly with LiFePO4 you may as well use them to 80-90% of their capacity every day because eventually they will die of calendar age anyway.

[@billjohnson3344]

@@ThisRandomUsername Agree Dave isn't looking to go full off grid. But by using average daily usage, the calcs for savings / payback are much too optimistic and not realistic. He's going to need to lean on the grid much more than that shows. He can see/prove that if he uses his past yearly data for each day and plots things out for when his battery reaches max and min state-of charge. His calc would have been ok if his grid feed in/out was the same price, but where he lives it is not. He also needs to factor in not using all of the battery to keep it happy, and some system inefficiencies into the calc. And you are right, he did talk about adding more panels. That will also factor into this, and he'll need to amortize that cost. For energy output, he can even add that into his past data to see the impact. Although neat to have the battery system, it doesn't look financially sound in his case.

[@zazugee]

he is sizing for on-grid case, I'm familiar with this for total off-grid you think about the worst cases

[@horsreseauquebec]

Nice analysis, thanks! I live off more or less 8 kWh usable, off grid (14 kWh SiO2 total). I like when the batteries go full, then the charge controllers will lower the input for float stage. Then I can turn on more loads such as boiling water or cooking. The charge controllers will instantly adjust and pull the exact quantity of required power, you can see the stats of the load by looking at the difference of the input before/after! Going off grid requires a lot of optimization and compromises, let's call it degrowth.

[@nateb3105]

The Deye inverters Dave mentioned have a "smart load port" which will turn on when batteries reach a state of charge & there's enough solar power for exactly this!

[@darrenthompson3696]

Hi Dave, I do a slightly different system. Rather than export, I import limit. I have 8 truck batteries feeding a couple of inverters that feed lighting and general supplies to the house. The system swiches through an ATS switch so at 8am we go off grid and run on the batteries. 8pm switch back to grid where Leccy is then at off peak level and that what I do to charge the batteries is to start recharging through midnight to 6am. As long as you have loads of battery capacity recharging is minimal. Have cut my import cost by 35 to 40%

[@EngineersFear]

I noticed that a fair share of energy that I used to pull from the grid was down to pulling energy at the wrong instant (clouds) or the solar not providing sufficient power. So now with the battery system I can bridge those cloud gaps and boost the solar system on high power loads. So it's not just night and day that matters.

[@lilblackduc7312]

Some geographical locations (South Georgia) are overcast 2 out of 3 days.

[@MikkoRantalainen]

1:15 The price of electricity here in Finland is about 38 cents/kWh right now and some estimates put the price over 50 cents/kWh before the end of the year already. It used to be about 6 cents/kWh only a year ago! Everybody thinks this is just temporary market error but nobody knows for sure. As far as I know, in 2021 any plant that had estimated costs above 55 EUR/MWh was cancelled for not being profitable. If end of the year estimates are actually correct, any power source with price less than 500 EUR/MWh is going to be profitable!

[@kimmer6]

We pay 32 cents for the first 292kwh in a month, then it rises to 39 cents, eventually to 49 cents per kwh for ''excessive'' use. This is in the San Francisco area. The UN Agenda 30 and the WEF are working to substantially reduce the use of natural gas, coal, and oil by 2030. The mechanism is to price fossil fuel so high that people can't afford it. This affects abundant ''green'' hydroelectric power prices as well as it can be blended in with the high cost of fossil fuel. I believe that this high priced energy is permanent and will increase with time.

[@ctechbob]

Not sure what Heat Pump water heaters you have down under, but I replaced my 50 gallon (190 Liter) electric resistive heater with a heat pump model in April. According to my records I'm using a smidgen less than 1/4 the electricity to heat water. Bonus is that it pulls moisture out of the garage, and keeps it a bit cooler out there as well. Best case scenario for me. The heater sits in the garage, and I'm in the Southeast US, so it gets HOT out there. Plenty of heat to pull from the air and pump into the water. Highly recommend!

[@TomJones-tx7pb]

Not so good in the Pacific Northwest where the garage is cool and damp.

[@ctechbob]

@@TomJones-tx7pb They can still be more efficient than a resistive heater, perhaps not gas though.

[@TomJones-tx7pb]

@@ctechbob They are usually hybrids in these locations, but the recovery times are poor. I used a gas continuous water heater for many years which are really efficient. Currently using a resistive heater powered mostly by solar panels.

[@cmuller1441]

If the size of the battery is just 1 average day then often you won't have enough energy if there's under average weather. To really eliminate most of the sell/buy electricity from the grid you must have a battery capable of smoothing/averaging the production of multiple days. I guess there's an optimal level using a big enough battery to have an effect without costing too much. You could simulate the effect by just doing the analysis on a day by day instead of a 3 months level.

[@cmuller1441]

Also if it's a sunny day (above average) the battery is filled then you'll have to sell the extra power

[@Alexander-qz6px]

Shouldn't you aim for at least 20kwh if you want to pull 15kwh out each day so you don't have to deep cycle the cells?

[@markae0]

What is using the 20Kwh? I would find the individual items and fix it. I think it is winter heating.

[@johncoops6897]

@@markae0 - Nothing is using 20kWh. Watch the video and pay attention.

[@johncoops6897]

Yes, theoretically with a 10kWh battery he's very often 100% discharging and hammering the cells, so their life will be shorter. The question is whether there is enough savings in electricity and longer cell life to justify buying another 5 or 10kWh worth of cells. The reason being that in 10 years the cells will be much better and potentially cheaper too.

[@AntonioCunningham]

Power in my neighborhood used to go out once every 2 months or when it's stormed. I got tired of looking out of my window doing one of these blackouts and seeing the next door neighborhood have power. So I went out and bought a few power stations. The following year the power company buried the power cables in my city. Now the power only goes out twice a year. However I'm still glad I bought my power station because over half my power usage is now from solar power.

[@svenqnerd1338]

Great Video, thanks. But I think u missed to mention, that every kwh you store in your battery, you wont export to the grid. Therefore you "loose" an income of about ~400$ per year, isnt it? Here in Germany our winters are quite bad for PV, which leads to a situation, where in some days, the battery has to be charged from the grid, to prevent deep discharge. Maybe that isnt relevant in your country?

[@jonathanrees3765]

Here in South Australia we have all been (forcibly with no options) moved off flat rate charges - so we now pay off peak, shoulder and peak. All properties get/got a smart meter when solar is installed so easy for the suppliers to do this. Expect this will come to NSW over the next year? This will significantly increase your bills. There is so much BS re the grid - solar power distributed across the network actually lowers grid cost, and improves reliability. Current best feed in I have been able to get is 7.5cents - which is straight forward theft, maybe a class action against the AEMO? Tesla 13.5Kw battery has cost me $11,529.00 (actual cost). Went to this solution because of install options and location. This is currently working as part of the Tesla virtual power plant - which I can leave at any time, but does give additional rebates and extends battery warranty if you stay on the plan. Waiting to see what real costs are.

[@drstefankrank]

Did I miss something in the video? On long summer days you generate way more than your battery can store and you are only using a fraction of it during the short night. The next day starts with a pre filled battery already. So you are going to export the excess most of the time. In winter it's hardly possible to fill up the battery to store enough for the longer night. Especially if you got a heat pump that needs the most energy during these cold days. I created a battery simulator from my hourly data on my sold/bought values of my main meter for the last >400 days and came to the conclusion that no matter what size of battery I buy at this time, I get ROI dates of around 15 years. As soon as I get

[@stusue9733]

So you want him to buy a big enough battery to supply his needs in winter with power generated in summer? I cant help but think more panels would be a better answer, but of course that just makes the summer problem worse :)

[@drstefankrank]

@@stusue9733 No, that won't work, but the calculation he does assumes an inifinite size of the battery to store all energy of these 4 timeframes. Having a battery that can store all summer energy for the winter may require 500kWh to 1MWh.

[@Sylvan_dB]

Did I miss how you accounted for the different rate for generated vs. purchased electricity? The question needing answered is if it is more cost effective to store your electricity or sell it at the 7cent/kwh rate.

[@dv1858]

He currently sells basically what he buys when the sun is not shining. With 30 cents buying vs 7 Cent selling he has to have roughly 4 times more power to be generated and sold to break even. Adding the risk of not getting money at all for the selling and rising costs buying power I would also invest in storage rather than in generating more for selling

[@NautilusCL]

Dave, with the Victron gear (a Multiplus II for example) you can AC couple your Enphase system and at the same time can hook up your string. The Multiplus II is inverter and charger, so you can charge your battery via AC. With regular MPPT solar controllers you can feed your string to the battery via DC, so you have the best of both worlds. The Multiplus can also act as a grid tie inverter and sell the excess solar power generated with the DC side. I have one and during the morning it charges the battery and power the loads directly from solar, and sell the excess power to the grid on the afternoon, at night it it power your loads until the battery reach a SOC that you set.

[@ohmannhey]

Nice system but two limitations: 1. It gets expensive when you go for 3 phase. 2. The power of the MPPTs is very limited.

[@NautilusCL]

@@ohmannhey yes you're correct, I don't know if they use 3 phase on homes in Australia, here in Chile is only single phase. There are very powerful MPPT controllers, mine can do 4kW without problem, and you can parallel these, so no big deal. You can install a Victron GX device to monitor and manage all the system.

[@nateb3105]

Twice the price of the Deye inverters... they're nice sure, but pricey

[@NautilusCL]

@@nateb3105 they are low frequency inverters, with a giant toroidal transformer inside, another league

[@snawsomes]

This was helpful good sir. Thank you. This is an upvote from me.

[@_general_error]

The viability of batery storage lies in self-sufficiency - if the grid goes don;t for whatever reason, you still can fill up those batteries with your solar panel.

[@Squat5000]

That's the whole point for us. Screw the grid. We're off. Well, septic, power. Gas can be imported for my forge but that's it. But the only reason that's feasible is because of a great deal of battery storage. All lead acid vrla because I'm after a 20 year design life

[@_general_error]

When will small modular reactor be in every house!?

[@flexairz]

As long as the weather cooperates.. mostly in summer not so much in winter

[@flagmichael]

If you have that large a system you should be off-grid anyway. But that would require enormous storage in harsh winter areas. Not practical at all in Phoenix (lived there for 25 years.)

[@rilosvideos877]

It really depends on so many parameters you didn't (and probably can't take) into account - so its all kind of a milkmaid bill in the end. You can't predict daily solar power, charge cycles, energy consumption - its all an average attempt and a prognose of the future behavior. It will pay off in good conditions and won't in the worse ones. But you have good chance that it will in the end!

[@geoninja8971]

With rising power prices, the sums are moving towards batteries..... we picked up a Powerwall in Jan 2021 with the proceeds of a couple of Covid-cancelled holidays, so a reasonable investment.... getting power bills sub $100 is pretty cool. The daily supply charges are a killer, especially in winter when you don't produce much grid excess (or any) to pay for them.

[@EEVblog]

I pay 62c/day supply charge. That was removed from these calcs BTW.

[@vincei4252]

@@EEVblog Here in CT USA I am charged 2-3 times the supply rate for every killowatt as "delivery". Going off grid was a no brainer for me. I don't sell back and use my excess to charge batteries during the day.

[@geoninja8971]

@@EEVblog ours is over a dollar.... who are you with? Apologies if you mentioned it already! :)

[@nateb3105]

A Tesla battery will INCREASE your power bills. They're expensive with short cycle life as they use the dangerous NMC chemistry - you just pay upfront

[@cidercreekranch]

Where we live, Northern San Diego County, the power grid is not that reliable and we've had frequent outages. Some as long as 34 hours and being without power for that long is a real PIA. After looking at our options, this was several years ago, we went with a solar/battery system from Tesla. We chose this over getting a gas/diesel/propane generate since there is little to no maintenance, other than periodic cleaning of the solar panels, transfer to battery is quick and it's hands-off. Since we've installed the system we have not needed to pay for electricity, other than the fixed admin costs. Paying for itself was never a selection criteria. Looking at the outage data since the system was installed, we've had 44 outages, for a total of 7 days, with the longest being 34 hours.

[@hxhdfjifzirstc894]

California has the power grid of a third world country. It's pretty funny how they think they're going to all drive electric cars very, very soon. Don't forget to set your AC to 87°.

[@BinaryCounter]

Have you considered building the battery yourself? Good quality EVE LiFePo cells can be purchased pretty affordably nowadays and you can pretty easily build a 10KWH system for under 2000 bucks. Just add a BMS and a hybrid inverter and you're good to go. Also look into server rack batteries, very affordable too.

[@EEVblog]

No. Not Mrs EEVblog approved.

[@jpjay1584]

@@EEVblog you could protect yourself and place (one of both) outside the house, then nothing really can happen and you would be fine.

[@nateb3105]

Its ~$2,500 here in Aus... just got another 15kw in myself.. shipping & prices are up. Add BMS, cabling, switchgear too

[@ithames2753]

@@jpjay1584 I've ordered 16 EVE 280Ah batteries ($110ea) + Seplos 280 kit enclosure and BMS ($800) a bit extra expense there but it comes with all the cabling included. Andy at the Off grid garagre reports some good results.

[@darkworlddenizen]

I'd rather use a set of marine batteries. Cheaper and safer than lithium.

[@hojnikb]

I'm so happy, that we have yearly accumulation of solar production in our country. Whatever you produce during the year gets fed into the grid (minus what you can use urself at the moment) and that MWh then transfers to the next year. So if you size your solar panels right, so the yearly total production is equal or higher than your yearly consumption, you're pretty much golden and you have almost free electricity. Grid is really the best kind of battery there is.

[@niempi2]

I am not sure if using average production/consumption figures gives you the actual pontential savings. I mean on sunny day you might charge your battery quickly and have to sell rest of the power to grid and on a overcast day you might actually have to buy some power from the grid. I assume that you have saved your actual daily production/consumption data so you could run a "simulation" with that and see how much would a battery actually saved in the last year for instance.

[@billjohnson3344]

I like your idea of a simulation from a year's worth of actual daily data. I think Dave will see that a small 10kWh battery will hit max SOC often, and conversely not support those rainy / high consumption days. He does have the grid to lean on for those scenarios, but the financials aren't as good as he's predicted (given the different feed in/out rates). Battery depth of discharge and AC/DC/AC efficiencies also needed for true numbers.

[@DudleyToolwright]

I am in California and we do have to pay a grid fee under So Cal Edison. It costs me $15 if i generate $0.01 in excess energy for the month.

[@heyarno]

At 1.49€/kWh from the grid and 0.086€ to the grid, pretty much every battery becomes economically viable where I live.

[@cauf6182]

In Belgium 55-65 eurocent/kWh and ( in the winter) 25-30 eurocent in to the grid

[@freundron]

Dave, your situation mimics mine here in Si Valley CA w/ a newer and older PV, annual consumption and overall needs. Excellent discussion, highlighting some basic considerations. Well done, thanks!

[@jackykoning]

To calculate the real number you will need to do a continuous test. There is a Domoticz script that will add a virtual battery. I have had this script running since 26 august so not too long. However since then it would have stopped about 263 kWh from flowing into the grid. With a price of 0.3 euro per kWh that would be about 79 euro. However until some point next year we can freely export power and take that number off of our used numbers ("Salderen"). At that point we can only do that to 50% so Theoretically right now there was 0 gained or lost. Next year it would be 40 euro lost during this same time. (Not exactly we would have to calculate the payback for return power after the 50%.) But even at 80 euro a month that seems not worth it. At least not right now. There is an elephant in the room though. It is no longer 0.3 euro kWh it is going closer to like 0.7 euro soon. Which all of the sudden makes it 184 euro per month. Perhaps those prices are interesting. But how long will that last? So if these prices keep up we would be doing 92 euro a month in potential recuperated costs next year. With those prices it would still take 10 years to get a return on investment. Which likely means... knowing lithium, that there is no real return on investment as the thing will die before that. Extra information: I set the script to 12.5 kWh battery capacity and during this last month the battery "overflowed" for 92.917 kWh so that power would get exported to the grid because the battery would have been full. Also it couldn't supply 83.404 kWh which had to be imported because the battery was empty. (58.3828 euro in import costs and 8.3625 euro for the returned. Meaning with this system it would still cost 50 euro a month.) Then lastly I set the maximum power the inverter can give to 5.8 kW and it only went over that number twice which would have taken 0.012 kWh from the grid.

[@haveaseatplease]

It is no longer 0.3 euro kWh it is going closer to like 0.7 euro soon. Which all of the sudden makes it 184 euro per month. Perhaps those prices are interesting. But how long will that last? That will last for the whole transition towards sustainable energy, after the transition is complete, prices will stabilize or decline.

[@andrewmclauchlan9205]

Interesting that you mentioned Greenbank. A lot of their stuff is showing as 'out of stock'. But their warranty looks good and the cells they use are CATL - good cells

[@martinlutherkingjr.5582]

You forgot to factor in the rampant inflation over the next decade.

[@exshvezdickou]

10kWh is sweet spot for most residential houses. Problem is if you started without hybrid inverter, then you need to buy more power electronic or replace inverters you have. Then if you do investment to battery it is good to have islanding option. You can also take a look on Solax, but for you take look on Victron, you can play with it a lot, it also accept some string inverter on island output. With Victron you can choose battery you want and easily replace and expand it in future.

[@CharlesGregory]

Great video Dave. You mentioned you aren’t on a time-of-use plan. Have you looked at that to see if it would save you anything? Or is it hard to know without the hourly usage data?

[@willynebula6193]

Without even looking it would cost him more. The only way those time of use plans save you money is if you work night shift and don't have kids.

[@oambrosia]

@@willynebula6193 Agreed. Power is cheapest during daylight hours.

[@nateb3105]

With Battery - time of use is by far the cheapest, you top up off peak each morning to a minimum level (i.e. 60%) & you're at most paying off-peak for elec. I've done insane levels of analysis - the biggest factors: #1 - daily connection fee, #2 - off peak rates, after that nothing else matters :)

[@johncoops6897]

As far as I am aware, off peak rate in Sydney can only used for Hot Water heating. And they inspect your meter box and wiring if they detect "unusual activity" on the off-peak meter.

[@nateb3105]

@@johncoops6897 I *think* it states "hard wired appliances only" and mentions water heating & pool pumps. My pool pump used to run with off peak no issues for a few years

[@robert574]

I've often thought of this. If you could control the startup of all the motors and compressors switch off your inverter and then back in (a useful feature if you're temporarily on a generator, to bring them on in sequence) and use the grid for startups. Your inverter is sized more to actual loads and more efficient. Then maybe bring in DC to your house for lights or whatever else you can power with it. Are li-ion batteries better than lead acid for storage and cost?

[@dh2032]

the what talk doing something similar the freezes and similar goods, at grid peak demand powering down, freezes and such, but to make ready work you would, hand the full time so it not cutting power just before it moter power the get back down to temperature cycle starts

[@johndododoe1411]

I was also going to comment about the lead acid option, as weight isn't a problem in most stationary buildings (exception would be if there was something hollow underneath that could turn your land into sinkhole).

[@robert574]

@@johndododoe1411They seem to think they are, but how many li-ion fork trucks have you seen lately? Maybe they're common now.

[@PhillipParr]

This is fab - I've recently done my own maths and it's just on the other side of the "not yet" line for me (town house so roof a bit small and high up, leading to expensive install price and lower possible generation capacity). I could go without solar and make use of the cheap night rate of power, but I'd still need around a decade to make that break even. But the good news is that's down from about 17 years only a couple of years ago, so I live in hope it'll happen very shortly 😀

[@echelonrank3927]

since installing solar, the power bills went up to what they used to be as the feed in tariff became extremely low. if im going to produce more energy than i consume then why is my power bill so high? i know ive been a total idiot to jump on the solar bandwagon, what im doing now is keeping solar off no matter how counter intuitive it seems. the slightly higher power bill does hurt a bit, but at least i know im starving the grid a lot more than its ripping me off. a solar/battery off grid system is a completely different story. we should all have those and the the grid should only serve as emergency backup or maybe a 24/7 connection for those who dont mind paying the associated overinflated costs. you people are being had.

[@peteparadis1619]

Everyone wants a free lunch, it doesn’t exist

[@TDOBrandano]

If you use any hot water in the summer you can probably save some gas with a thermal solar panel for that. And it should still help at least pre-heat the water before feeding it to an heat pump during a mild winter.

[@flagmichael]

Not so much here in Flagstaff. Water coming from the pipes is warmer than it would be going through a heat exchanger sitting out in freezing temperatures. Similarly, very few heat pumps here. We replaced our 35 year old furnace with a new gas furnace with refrigeration for summer after we looked into a heat pump. There just isn't enough heat in winter to pump economically.

[@bjorn_moren]

Excellent video, very interesting. I live alone in a small off-grid house, and I have 2 kW solar panels connected to 9.6 kWh batteries (8 x 12 V 100 Ah lead acid deep cycle). This is more than enough during spring and summer. My use averages around 3.5 kWh/day. But during fall and winter, I have to be very careful about my energy use. I turn off the fridge, which is the biggest consumer, and instead lead outside cold air via a duct into the fridge. Frozen items are put outside. I run a gas powered generator sometimes in the winter to top up the batteries. I've spent a lot of time trying to come up with cost effective energy storage. My first idea was to make my own led acid batteries by buying the lead keel off of a second hand sail boat. However this is very toxic and dirty work. My second idea was to build my own LiFePo battery bank from individual cells and a balancer circuit. I've also looked into DIY super capacitors. Although there are videos online about various methods, they all look too good to be true. Instead of focusing on the weak link (the batteries), I've decided to just throw a lot of overcapacity of solar panels at the problem. A week of rainy over cast skies is normally a big headache for my energy system, but if I had several fold more panels it wouldn't be a problem anymore, because they would give enough power even at bad conditions. And unlike batteries they virtually never wear out. So I'm looking to purchase around 6 kW of panels to install. But right now with the European energy crisis they are hard to find at bargain prices. My energy system: www.bjornmoren.com/Solar-power-for-homes.html Different ways of storing energy: www.bjornmoren.com/Optimizing-energy-storage.html

[@erg0centric]

Off-grid gasoline powered home.

[@bjorn_moren]

@@erg0centric Cool. What kind of generator do you use?

[@mosfet500]

I have two systems very7 close to Dave's and I have 15kW of LiFePo4 batteries on it. I do run all summer off grid because I refuse to sell energy back to the grid for a pittance! I'll see this winter how well it goes but right now I have ~14,650 watts of PV built up over the last 15 years. Hey Dave, that looks like an HP71B calculator from the 80's - ask me how I know!

[@CLuengas]

Nah. It's an hp41C. I still use mine occasionally :)

[@mosfet500]

@@CLuengas That's the first one, look later around 7:30, that's a 71B.

[@rasmusvergo]

Hi Dave. You should look in to Victron Energy Quattro. It will work as the ones you call “AC battery” but you can choose what battery you will like to use.

[@nateb3105]

Nope - they cannot be installed as they're not on the CEC approved list & they're twice the price of the Deye units he mentioned.

[@Speed00007]

Having a battery bank with solar panels is a no brainer. I have 4 server rack batteries that store 20k Kilowatt hours. Cost me $9500 U.S dollars. I'm 100% grid independent. BEST money I have ever spent.

[@flymypg]

So long as I can control my backfeed to the grid, I'm good with almost any battery solution, as I can disconnect from the grid whenever desired. I'm planning to do a 9KW home system when the new US incentives kick in next January, which includes battery incentives. I only plan to feed the grid when I'm paid well to do so, and I hope something like Tesla's "Virtual Power Plant" becomes an industry standard.

[@markm0000]

Your batteries will be long gone when that happens. There is no incentive for government to pay customers good money for back feeding.

[@terrydennis467]

Being part of a Virtual Power Plant (VPP) removes the flexibility to disconnect from the grid when desired and choice on when to feed the grid. The VPP operator can call on your battery to discharge to the grid as they see fit, and also to pre-charge your battery from the grid in advance of an anticipated power shortage/outage event.

[@markm0000]

@@terrydennis467 You see that’s called socialism and I don’t want any part of that.

[@abitofabitofabit4404]

@@markm0000 Actually, that's just the capitalist freedom to contract, even (especially!) when you don't happen to like it.

[@uksa007]

Dave, check out Goodwe GW5000S-BP it's a whole of house AC coupled battery inverter, allows you to use any combination of solar with most LV 48V batteries. It can even support 3-phase with solar inverters on different phase (like me). Goodwe is huge with the like of GE rebranding them. Note the Tesla only has a backup circuit if the grid goes down.

[@SomnolentFudge]

definitely swap out the gas water heater, I recently switched to a heatpump water heater and I can't recommend it enough. we (3 person household) saved ~70usd / month over the old resistance heater. A trap for young players though, make sure the model you buy allows you complete control over the mode it runs in (all heatpump water heaters have a resistance heater backup and many will use them for fast water temperature recovery even when you think it's in heatpump only mode). If you can space out the major uses of hot water, like showers you can turn down the setpoint on the heater I was able to set mine at 112f (~44c) from the default 120f (~49c). Heatpumps are a lot more efficient the lower the temperature differential is.

[@stusue9733]

yeah but, Living in a nanny country we have regulated things like this. Minimum 60C tank temp, with a tempering valve for bathrooms and such ;)

[@Bob_Lob_Law]

You can also look into Drain Water Heat Recovery, a simple heat exchanger pipe that uses hot drain water to preheat the water entering your hot water tank. They run ~67% Efficiency, and can reduce your whole hot water energy usage by 25-33%.

[@simon7719]

Do consider the risk of legionella growth in your pipes if you do this though. AIUI infected water droplets (like in showers for instance) can give you bad cases of pneumonia. Potentially fatal even.

[@simon7719]

@@Bob_Lob_Law How about dirt solidifying in the exchanger due to the temperature reduction, is it a problem?

[@stusue9733]

@@simon7719 The heat exchangers I have seen are along the lines of 1/2" copper pipe wrapped around and solders to around a 4" copper pipe that the waste water runs through. So I would assume pretty much self cleaning.

[@HighTechLab]

Have you seen SOKbattery in the states? 5.12kwh for $1789 @48vdc

[@FailTrainS]

Cool video. One nice thing about my Tesla powerwall system is that they're part of the Virtual Power Plant program. So when there is a grid event coming they act as a distributed grid stabilization force and whenever my system participates in those we get 2$ per kwh. So far this year it has been several hundred dollars. Pretty nifty little unforeseen benefit that might reduce the payoff time substantially for my system. I believe they pioneered the VPP program in Australia a few years ago by having a local utility subsidize the installation cost in exchange for future participation. I just like the idea that I'm helping the grid be more resilient.

[@echelonrank3927]

imagine having a look and there is a few extra dollars in your bank account. not bad huh? everyone likes a few dollars. until you realize theres no energy left in your battery, its all been sucked out by the grid, and you will have to endure the same blackout as people who cant afford a battery at all LOL nice going chief. enjoy the resilience in the dark and silence.

[@TheCablebill]

@@echelonrank3927 or use those dollars to purchase additional independent battery/solar/generator capacity that can be isolated for emergency circumstances. Set distribution/apportionment thresholds to one's own preferences/needs - thus contributing to grid reliability while still protecting oneself. Chief.

[@echelonrank3927]

@@TheCablebill great smoke signal, i like the sound of builiding up independent capacity, but we still need the grid as a reliable backup emergency energy system when all else fails. the grid looks set to become obsolete technology similar to wired phones. i mean it will still exist if the mobiles fail, but the available capacity will be small, no? shaman.

[@eDoc2020]

@@echelonrank3927 In my area the draw events are max two hours each and there is a limit of X events per year (I think 50). Size the system accordingly and only enroll an amount of your storage you are willing to risk. Here they also won't schedule the events during storms where outages are most likely, minimizing the risk. Also keep in mind you can still recharge from solar during a blackout. And one last thing, it does not make sense to use the grid as a backup emergency energy system. It's the primary system for moving electricity and the battery systems are backups for when the grid can't do enough.

[@echelonrank3927]

@@eDoc2020 1.glad to find out the customer has control. 2. primary today, secondary tomorrow. such is the fate of all technologies, i dont see why the grid will be the exception. eventually roads too...ok i should stop now before i appear even more ridiculous. its like talking about a global information grid 60 years ago when libraries are still the primary sources of information. one extremely last bit, if we start using hydrogen will there be a hydrogen grid? high pressure pipes down every street?

[@bramdevoogd2226]

Nice Video, Dave. But you forgot the payback from the exported solar. Over the year this would be close to $500. So actual budget for your battery storage is roughly $11k. Cheers

[@iskinmind7020]

The 1 day power storage is impractical in the extreme and can not be considered an "off grid" solution. At least around my parts. Around my area, a week or 2 of constant rain and heavy clouds is normal. We are using around 8kwh per day on average, and an actual longest blackout was for around a week (a tractor vs an underground cable incident). Basically, "off grid" would require an enormous redundancy in both - power production AND storage. Like an x10 redundancy. Assuming a 15% efficiency (North Europe) my 8kwh consumption would require a 100kw solar cell setup(double daily use to compensate for weather) and at least a 50 kwh of storage (blackouts are frequent and sometimes last days). That will never pay for itself. The most practical solution for me (and most europeans north of Italy) is getting a gas generator for emergencies.

[@harshbarj]

Where I live you can generally expect to lose power for at least an hour yearly. Generally we have 2-3 mini "blackouts" that last a few minutes every year. The record for me was just 2 years ago where a monster storm took out power to virtually the entire city (500,000 people, over a million in the area) for DAYS. Some were without for a week. I was without for about 3 days. In general if you are producing more than consuming and can afford it I'd suggest a battery backup "just in case".

[@thomasa5619]

Are you in a third world country like texas?

[@jake1021]

I was out last year here in northern U.S. for 12 days in the last weeks of winter. Thank God for gasoline and diesel.

[@djlorenz11]

Sounds to me that the first move should be getting rid of the gas boiler and use an electric boiler or solar water heater as a big thermal battery. Hopefully in the meantime battery prices will go down (or electricity will go up like here in Europe) and then it will be an easier ROI. In the meantime hopefully EV bidirectional chargers will become interesting and then you could even use your EV as battery storage

[@nateb3105]

Never use your battery as storage... You're wearing down your EV battery which is the most expensive irreplaceable part... Stationary LiFePO4 storage is SO much cheaper than an EV battery...

[@billjohnson3344]

@@nateb3105 Actually no - stationary storage solutions cost more than EV solutions. Example: Ford F-150 Lightning standard range: 98kWh for $47K ($480 / kWh). 5 Tesla power walls 50kWh for $50K ($1000 / kWh). You'd save double the price using the truck battery instead of the power wall - and you also have a truck.

[@nateb3105]

@@billjohnson3344you chose the worst stationary storage system & most $$$. $30k for 50kw of lifepo4 retail, $15k DIY for 50kw

[@billjohnson3344]

@@nateb3105 Even with choosing a different low cost stationary storage system as you suggest, the EV truck still beats that cost per kWh. Of course DIY, is cheaper.

[@djlorenz11]

@@nateb3105 comparing apples with potatoes is difficult. First DIY is another story, a car or a truck is certified and your home system is certified, so that is not comparable. Yes there are some storage systems that might be cheaper, but you can not go to the supermarket with your storage system. There are plenty of households in the world with two cars, the secondary car is usually barely used in some occasions. Having one or both connected to the house means a lot of storage available, even using 40% of the capacity (in order to not fully discharge it and keep it between the healthy 20/80%) is probably more kWh than your storage system. Used it right and with the right electricity rates for selling on peak times it can be a valuable asset with the good ROI in the future. Stationary storage is very valuable, but it can only do one job, if you can invest that money in EV you can have two features for the same energy storage, why not!

[@jeffreyparker9396]

I have batteries, Tesla powerwalls to be specific. The biggest reason I got that is because the grid here is really bad. I am in Texas and in addition to the 3 days without power in February 2021, I have seen so many more outages than I had when I lived in Arizona. So, for me it is about not being able to trust the grid so trying to account for power outages and keep solar generating power during those outages.

[@austinfarley4971]

I was so confused for a minute. I always forget that not everyone has the same summer/winter/spring/autumn.

[@masaharumorimoto4761]

Excellent presentation!!! My power literally never goes out, I'm lucky to live in a sub division directly beside the 4 reactor Darlington Nuclear Plant so we even get generator backup from the plant LOL.

[@AIM54A]

You'll probably increase the battery life if you go with a bigger pack that you only use maybe 80% of its capacity.

[@nateb3105]

Look at Andy at Off Grid Garage channel... Its voltage that is the important factor, playing it safe/conservative you're dropping to 95% at most from memory. You also go with a bigger battery pack - so you're not pushing the cells to hard. 5kw pack = 100Ah batteries 10kw pack = 200Ah batteries etc...

[@davenz000]

Curveball what about swapping the car for one that does vehicle to grid or whatever marketing malarkey they're calling it? Use on the E.V battery too much?

[@EnricoConca]

Reportedly, some Goodwe Hybrid inverters may be able to charge using not only their solar input, but also from the output of other inverters in the house, as they use a simple nullying algorithm that just tries to zero the current entering/exiting the house. I can't check it but some forums say that.

[@derickson1656]

Have you consider some form of thermal floor heating ? Heat a concrete floor during the day and have it radiate the heat over night.

[@World_Theory]

Have you looked at alternate energy storage systems? Like a big ol' flywheel? Or a gravity or thermal system? I wonder what kind of free space you have on your property you have for such things. Personally, I like the concept of a flywheel. I doubt it would wear out anywhere near as fast as an electro-chemical battery. You may have to do maintenance on certain parts periodically though. Parts like the bearing. But if it's made right, it should be simple to yank the bearing out and replace it. Lubricant may need changing too. I hear there are magnet bearings for flywheels too, but I suspect those wear out too, because force and motion is still being applied to them constantly. I haven't really looked into them too closely, so I don't know enough to give useful details.

[@Shadowdncer]

Almost regardless of financial viability, I do think that for a moderately efficient PV array, say 6+kW real peak production, a battery should be mandatory. I'm running almost independent (the setup doesn't allow grid independence and the battery "only" has a ~3.3kW inverter) for around 7 to 8 months a year, and with some "intelligence", a bit of capacity can even be used for grid stabilisation.

[@simonupton-millard]

7c pkwh is good here in the UK I get 0.05p pkwh, I have 2x tesla powerwalls and a 10kw pv system mainly because its all there was back in 2018 when my system was installed my system dosnt have the ability to run if the power fails as it wasn't available yet, but after 4 years my system has half paid for itself the biggest saver for my has been able to charge the battery off the cheaper night power 7.5p pkwh and run the house off it in the day when it's 31p pkwh

[@zukjeff]

people need to consider their options depending on how many phases their property uses. This changes the hybrid system installation or our household power circuits.

[@nateb3105]

Rabbithole there! I ran 2 single phase inverters on my old 3phase setup really well, put my water heater on the 3rd phase, A/C ran on all 3... worked a dream!

[@petr6542]

It's not as simple as it looks. Allow for losses when storing and drawing from the battery. The capacity will also be needed at least double, and even then sometimes in the summer it will happen that the battery will be full. But the most important omission is the own consumption of the entire system, which is normally around 200-300 W. Here it depends on the installed power of the solar panels, but for routine installations it pays to completely disconnect the battery in winter.

[@Psi105]

Wonder what the efficiency loss is. If you push 10kwh of solar energy into the battery do you get 9kwh out?

[@EEVblog]

This is the "round trip efficiency" and may system will quote that figure. Hybrid is better because it has one less AC-DC conversion step.

[@theshedmahal937]

@@EEVblog please check compatibility of your zappi with dc coupled systems. I believe you will see it can’t monitor battery usage. But it can with ac coupled systems ( it uses an extra CT clamp). So you either lose efficiency by going AC, or you lose some zappi capability by going DC.

[@jstro-hobbytech]

5 or six hours. That's crazy. I just went through 8 days haha. Very informed breakdown. Great video.

[@mrbmp09]

You need to factor in 15 -20% conversion losses for charging/ discharging storage batteries.

[@MrRfries]

7.9 cents per KWH sounds like a fair generation rate. There is of course also the delivery fee which pays for the grid. Since a grid tie system which depends on the grid, it only seems fair to pay for the grid use. Perhaps the rates are dramatically different where you live, but it seems like a fair generation rate to me.

[@fairhall001]

As people are at work during the day, it is unlikely that a solar system can return on the investment to an e-car owner in the same way as someone that can charge their vehicle directly from their own solar system during the day. Also three phase homes won't be able to capitalise on the whole of house power style battery and will have to lose air conditioning and heating. Also historical anecdotes surrounding blackouts can be dismissed as speculation considering the added load on the grid that is expected by the e-vehicle and holus bolus dumping of gas alternatives. Adding 5-50kW/hrs a day to charge every electric vehicle per house (for a single vehicle) will add strain on the grid that has not been taken into account by ideologues of e-vehicles.

[@josephallen2655]

I like the idea of standardizing on "Group 31" sized LiFePO4 batteries since there are many brands supporting this standard, so you can easily replace them in the future. An example is Renogy 12V, 100 AH: these are around $3750 USD for 10 KWH. An issue is that not all batteries can be put in series. I would rather trust parallel only, but there are 24V, 50 AH commonly available in this size as well. Strictly for emergency backup, there are RV inverters that will charge the batteries with "shore power"- basically turns your batteries into a UPS (plus you can add a cheap MPPT if you have solar). This is good for some applications: I want to keep a sump pump powered on during storm outages, otherwise my basement floods.

[@ecospider5]

Renogy has different versions of that battery depending on features. How many you can put in series, does it have Bluetooth, ect. The extra features cost more of course.

[@karlm9584]

Two words: Demand Tariffs. With demand tariffs being applied to residential customers now, and if you don't have gas (which is also rising in price) then batteries are probably going to be as "worth it" as solar panels used to be 10 or 15 years ago. And they will only get more "worth it" as the retailers increase their demand tariffs. (Presently around 10 to 15c/kWh/day)

[@gonzo_the_great1675]

On seasons where the import exceedes the export, should you not use the export value in the savings calculation, rather than the import value?

[@topduk]

There is a cost to store the batteries where they aren't going to be hazardous (space/property), and also a good possibility that you would never be able to collect on any warranty offered.

[@manolistsikalakis5751]

Try Victron ESS System.. Quatro or Multiplus II, AC coupled with your existing enphase system . Use DC strings to charge directly a "low" voltage 48V DIY Battery (i.e. 14 KWh ~ US$ 2500 with a descent BMS ..) using external Solar Charge Controller.. Include a raspberry PI, with Venus OS as "GX" Control Center, visible and configurable from anywhere in the world... Works like a charm..

[@StormsandSaugeye]

The charging people to export energy to the grid thing actually has happened where I live. If you want to get solar panels and have it set up to supply voltage back to the grid that's fine but you have to pay 5 grand a month to do so.

[@flagmichael]

The public at large does not understand the economics of bulk electric power at all; I blame NERC for failing to educate consumers. (I retired from 34 years with a Fortune 100 electric company, so I got a real education there!) As I explained in a much longer comment, no electric retailer wants unsolicited energy. It is by far the most expensive and unreliable source of energy. Imagine being required to buy something you already paid for from reliable sources, and in unlimited amounts.

[@StormsandSaugeye]

@@flagmichael oh no the decision has nothing to do with available energy. Multiple chairpeople of the electric coop are currently under investigation and the city has moved to reject their renewal of supply rights for the city due to a long term practice of illicit activities. Especially since they charge twice what surrounding communities charge.

[@TheOwenMajor]

It's almost like "renewable" energy is largely driven by political zealots and not actual market forces... Everyone knew this was going to happen, because is a pain in the butt for grid systems. It produces the most power during one of the lowest demand periods of the day, all while being incredibly variable and season dependent. Nobody wants this power, it was hosted on them because it was politically driven.

[@StormsandSaugeye]

@@TheOwenMajor my comment actually deals more with corruption at the electrical coop

[@TheOwenMajor]

@@StormsandSaugeye Where are you from?

[@themurman01]

Do they sell the Schneider XWPro 6848 in Aus? Built in transfer switch with battery charging inverter, will ac couple to your existing inverters, and use frequency shift to shut them down in an islanding situation. Not affiliated, just thought the product seemed cool.

[@SteveGuidi]

In Washington State, USA, we have "net-metering" system where the grid is essentially your battery. A separate meter tracks your PV system production and keeps a balance; anything you consume is taken away from your existing balance and you are billed for the excess. The two drawbacks are that your balance resets to zero in the spring, and the utility will remotely disconnect your PV system from the grid when they work on the power lines. We had a subsidy that expired a few years ago where the state paid electricity production ~50 cents/kWh for systems manufactured locally. This was great as our fixed-rate costs are about 10-11 cents/kWh! Other states have/had similar incentives, but the laws vary in every state with some promoting PV systems and others stifling them (go USA!).

[@ThisRandomUsername]

Are those prices all in AUD? Those Greenbank are really price competitive. A few months ago I imported some raw 280Ah LiFePO4 cells from Alibaba into South Africa for the equivalent of $1800 AU for 7.1kWh (8 cells) including a BMS. I will probably double it to a 48V bank sometime. Also, does your recently installed inverter not support connecting batteries to it?

[@stevedotrsa]

Have you looked at the Redflow zbm3 zinc bromine flow batteries? Do the numbers stack up?

[@EEVblog]

I heard they exited the consumer retail space?

[@saintmichael2931]

Dave - did you consider using the battery from your EV in the analysis? I am told that some EVs give you the option to extract up to 6 or 7kW from the battery, as AC mains power, which would be enough to run most average homes.

[@hojnikb]

i don't think his ioniq has that option.

[@PsiQ]

i've been thinking and looking around for the battery (and hot water tank) storage options for months now. Our house is from 1960 and my gramps planned ambivalent back then. 2 "and a half" apartments for living. Diesel based heater (modernized) for the house heating only, so only running in winter. large underground tank outside. 2x fresh water gas direct heater for shower/bathtub. + added a few years ago 3phase electricshower +back then 1960 also gas stove in kitchen. +back then 1960 also wood fired stove (with water tank) in washing room basement. Small electric tank (around 5 Liter) heaters under the kitchen sinks. No central water heating/tank for drinking water. And we have solar (electric only) for about over 20 years now, peaking at 5.7kW. Roof got new/better insulated before solar got installed. Now the problem is to use PV-solar for warm water, "hotwater" panels would be better, combined with a large hot water tank/pump in the basement which does not exist yet. Then new plumbing over 3 stories and 3x heat exchangers in the bathrooms, instead of the 2x old gas +1x electric heaters. Combined with an input into the diesel heater (which can be used for drinking water, 2 loops standard) .. then adding also more solar-PV panels and a heat-pump (in combo with the hot water roof collector) to stock up energy during day into hot water tank. With all that (above 30k euro investment with luck and lots of optional problems, noise and dirt), we might be able to reduce consumed fuel during winter time. On the other hand central water heating+pumps would need to run all year round. And there would still not be enough power overhead to charge the EV for the daily work round 80km, charging every 3 days (

[@rklauco]

You are a bit wrong about the hybrid inverter - it can also charge battery from "grid" and if the grid is fed from your Enphase, you have double conversion, but you can still charge it. So it won't be wasted.

[@rockpadstudios]

"brown stuff hits the fan" - nice, I'm going to start using that :)

[@_B_K_]

It's worth doing in California, where lovely PG&E thinks it's fine to go days without power a few times per year.

[@dancevideo2]

With one person I know, there was one requirement that made even very expensive backup power a requirement- they had a whole year of food in their deep freezer. The system proved its worth after a grid outage for 10 days(!) following a huge severe weather event, but a combination of solar power plus some quickly added tractor batteries to hold over a cloudy day, kept the freezer working through it all. A backup generator could have worked too, but sometimes I find seldom-used complex mechanical things end up not working when you need them most. Also, during that event, generators were unobtanium because everyone else wanted them too.

[@pemtek1]

The enphase inverters would not need wiring through the hybrid inverter. The inverter will charge the battery with anything it can on the inside of the property before the inverters power measurement point. It doesn't matter that its not generated in the inverter.

[@bfth121]

Should you not be counting usage > 10kwh, since once you use that stored 10kwh from the battery you will be going back to grid use? In that case, should your budget be $3 per day (0.30/kWh * 10kWh)?

[@ptarcher86]

I also believe this, $3.00 per day is the maximum to be saved. But its worse than that. Also need to take into account the efficiency of system, lets say 80% round trip. Finally you need to also take into account that he would have exported the 10kWh to the grid. This gives. $0.30/kWh * 10kWh - $0.07 * 10kWh / 0.80 = $2.13 per day or $775 per year. If we take the 5 year pay off period, you can now only spend less than $4,000 on the system (battery and also the hybrid inverter) I think the bigger financial payoff will be with disconnecting the gas, and going with an electric heat pump hot water, for a few reasons: 1) You'll now have "solar" hot water (just like your solar car :) 2) You're doing a reno, so its probably easy enough to replace it 3) You'll use more of your export energy, which is only paying you $0.07/kWh 4) You'll be able to disconnect from the gas, and avoid the daily access charge. Now, if you take that into account, that a family your size probably uses > 10kWh of hot water a day, and lets assume a low 200% efficient heat pump. 1) You'll get approximately $3.00 saving each day from gas costs 2) You'll also get a saving of your gas access fee (lets call it $0.50 per day) 3) You'll only use 5kWh of electricity to heat the water (10kWh / 2) Total = $3.00 + $0.50 - $0.07*5 = $3.15 per day = $1149 per year. Heat pump is a huge winner.

[@katbryce]

If you sell for $0.07 and buy back for $0.30, then your budget is $0.23/kWh.

[@wiegeroord9822]

I don't know what the weather is in Sidney on a day to day basis but here in Ireland we might not see the sun for 3 weeks so you need a back-up for that. In your case that would be a lot more than 15kWh. What you are suggesting covers only one day.

[@peterhargrave2246]

I think you had best check out hybrid/multimode inverters as some do AC couple to other inverters

[@Trojansteel-hh5xd]

Have you had a looked at the Redflow batteries?

[@mattlee3044]

Absolutely LOVE the intelligent ‘walkthrough’ of your “Shall I buy a battery” question. Don’t beat yourself up about your ‘wacky’ system, nor your decisions. Score highly for making decisions around sensible reasoning. I have the same question over here in the UK, but I have different sums to do, as my government decided to PAY ME to generate electricity, whether I use it or not !! They pay something called a FIT payment. They did this ages ago, and their payments from my (maximum domestic micro generation system allowed) 4kW system covers ALL my utility bills. This is very different to the offer down under, as you describe. So, what’s my problem ? I have a couple of puzzles I’d love to answer. 1) how can I show I am using my generated power 1st, before my electricity meter charges me for any electricity? An electrician came over to fix a ‘fault to earth’ problem on one panel string, and he found something unusual by clipping current meters onto various cables in my supply cabinet. I wondered if the electricity meter - (which shows the statement RED on it’s screen for Reverse Energy Detected, when the solar is driving power back up the grid) is then charging me for some proportion of the electricity I’m generating ! In other words, my power is going into the grid and then I’m being charged for it via the meter as I use it ! I can’t see why this is a daft idea, and I can’t see what gadget to design to prove what’ happening. If I have a current coils on the solar generation output, on the grid supply and on the house supply from the grid’s meter; can I watch current/voltage waveforms (Raspberry Pi-type project) to see where power is going? If the solar is winning, I should see it’s power output being partially sent to the grid (reversed through the meter) and partially consumed by the house (via the meter) But how can I tell if the meter is registering input power to the house? That would be a naughty thing, and great fun to prove. Does anyone see what I mean? I’m quite content to be branded a) paranoid and b) bonkers, but it’s bugging me. The government is generously giving me X for generating, and the electricity company takes a cut Y by billing me for the same electricity ! 2) Is it worth grabbing unused power in a battery system? Typical answers may include, “why the hell do you care? The government is paying your utility bills, anyway!” Well, I’m a degreed electrical techie, and it would be fun to power the house when the solar was not. Lastly, I have daily data (manually logged - good grief!) since to system was installed. If you’d like a copy, let me know. Like you, I have 1/2 my solar panels NOT oriented optimally. Here, 52N, I need South facing panels, and 1/2 are N facing. I can’t tinker with this, as the FIT scheme requires a ‘licensed installation’ which I can’t change. (Not unreasonably) Any-road-up, great video. Matt Lee (old computer and electrical hack - BBC micro era !)

[@vk3fbab]

If your EV had V2L you could augment it with your battery to cover those very rare days of low production to consumption but would the installation costs pass the economics test? Though if it allowed you to live the dream and go off-grid it might make financial sense. I pay approx 400 Aussie rubels a year here in Vic for poles and wires.

[@andrewradford3953]

V2L seems to work for conservative overnight power use. 2400W is plenty for a fridge, chargers, TV, and led lights. Currently around $10k for V2H inverter to access our Leafs 40kWh. I think that's a 5kW inverter.

[@mikefochtman7164]

Seems like, considering the seasonal variation, you'd really want to be able to store summer/spring production for fall/winter usage. So instead of daily cycling, it's a much longer term storage problem. Storing something like a few hundred watt-hours every day, building up to 1000 kW-hrs, and saving that for a few months seems different than the typical daily cycle.

[@tiemenfiat1321]

In the Netherlands you sell and buy for exactly the same price (for now at least), then it does not make sense to store it local. Price is going up to 75 eurocent per kWh.

[@briangray5921]

Correct me if I’m wrong but last time I checked the Tesla power wall will not provide any power if the utility power goes out (in USA) which makes it useless for power backup.

[@billjohnson3344]

Of course it does - and always has. It even switches over so fast in a grid outage that many people don't realize the power went out. Comes with a separate gateway box (auto-transfer switch) that disconnects the grid power, and makes the house a micro grid (island) during an outage.

[@neilwilson984]

Another thing worth looking at if your installing a battery is the ability for the system to be included as part of a virtual power plant rather than just directly feeding into the grid. in this case, the company aggregates the capacity and uses a % of your capacity within agreed limits, this means they can sell onto the market at the standard generators rate or higher on spot market and pay you a higher feed in rate.

[@fredygump5578]

An issue that is not often discussed is the cost of maintaining the electrical grid you are connected to. Some people naively think the grid is free and they just pay for energy. That point of view makes sense until you produce a surplus of energy. Ideally the electrical bills would be structured so the cost of the energy and the cost of maintaining the grid are separate. That would avoid confusion about why you can produce a surplus of energy and still have a bill to pay.

[@stusue9733]

I saw a news article just the other day that stated maintaining the grid was more than 50% the price of power and going to increase.(talking about WA grid)

[@petehiggins33]

Here in the UK we do pay a separate standing charge that's supposed to pay for the upkeep of the grid. My new charges from next month are 49.1 pence per day plus 33.7 pence per kwhr. So the standing cost is equivalent to about 1.4 kWhr. Each energy supplier charges a different amount for both the standing charge and the energy but the total cost to an average consumer is currently government controlled and subsidised to control the cost of living.

[@ehsnils]

HP41 - that's nice, or rather awesome! Where I live the electricity price swings wildly right now, the price is changing every hour based on trade done the day before. It's wilder than the stock market in 1929.