Results of Solar Thermal vs. PV Experiment in Heating Water

[@flussoincrociato]

I loved the way you gave the solution just a minute after the start and only then explaining reasons. It's clear that you are not doing it for bucks. Thanks.

[@funny-video-YouTube-channel]

*Go for both.* A small solar-thermal to pre-heat, and the electric one to boil the water. Great experiment !

[@DavidPozEnergy]

Thanks. I was just talking with my wife tonight about what a duel system might look like. I'm not 100% there right now, but maybe. I'll be sure to make videos about it if I do. Thanks for watching.

[@obiecanobie919]

@@DavidPozEnergy What about glueing pex tubing in the back of the pv panels and harvesting that heat ,that will also keep panels cooler and more efficient in wormer days .

[@DavidPozEnergy]

@Steve Slade Response to both Steve and Obie: What you are asking about is a hybrid panel, electric on the front and hydronic on the back. Manufacturers of panels have been trying to sell this concept for at least 40 years. There always seems to be some issue and it doesn't take off. Let's think of the temperatures. The hotter a PV cell is, the less efficient it is. This is quite dramatic. So a PV cell wants to be cold, practically speaking as close to ambient air temperature as possible. In my area we rarely get over 100°F. However, we want out hot water faucet to spit out 130°F water. I want my own thermal storage tank to heat to 180°F. So we want the hydronic side of the panel to get HOTTER than ambient air temperature. But our PV to be at ambient. The two goals are working against each other. If I build a hybrid panel that favors getting hot water then I'm sacrificing electrical production. If I build a hybrid panel to stay at ambient then the water will never be hot enough for a shower. At best the system can warm a pre-heating tank before water goes into my real hot water tank. It's simply not worth the added cost and complexity at the sacrifice of efficiency. Instead concentrate on keeping your PV (electric) system working as optimally as possible and there will be plenty of electricity to heat water. There is a solar house a couple towns over from me built about 10 years ago. It was half funded by grant money from state and federal. They had hybrid panels. Unfortunately, the hot water side of the panels never worked quite right and had leaks constantly popping up. Eventually the developer drained that side of the panels and left the array as PV only. I went on a tour of the house one year after being moved in and the homeowners were so relieved to not have to worry about the leaks on the roof any more.

[@toraguchitoraguchi9154]

Waste of time.

[@Psi-Storm]

@@DavidPozEnergy It could be done with a water/water heat pump. The primary circuit runs through those Hybrid PV panels and the heat pump removes the energy to heat the secondary hot water circuit. The problem is the efficiency of the panels would only profit from it in the summer, where you don't need heating, just hot water. For a system like this you would need really high hot water consumption, like a heated pool, sport club house or gymnasium.

[@fourzerofour7860]

I definitely advocate using the PV panels when you have the area. As some other people have pointed out, the PV panels can be set up to dual purpose for both water heating AND electrical power to charge your batteries or run loads. Because people's needs vary from day to day, and season to season, the PV panels give, at least in my opinion, the 'best of both worlds'; provided there is space to accommodate them. It also seriously gets to be cheaper when you consider the cost of potentially running pipes from an array in your yard or on your roof, to your hot water storage tank. Wiring can be much cheaper, and is less subject to leaking. XD

[@flampy1]

When the water is hot via PV, you can route those panels to power other things like charging batteries, where as the solar thermal can only heat water.

[@rupe53]

flampy1... excellent point, especially when the weather warms up and the heat isn't needed. The next level would be to sell power pack to the grid when all systems are satisfied.

[@geneselah]

Or when you're charging batteries and they get full, you can continue heating water :)

[@philtimmons722]

@@rupe53 -- he noted he could also use the Thermal for Space Heat. Solar Thermal with a heated concrete floor works GREAT. Once the Concrete is warm, it will keep the whole building warm for DAYS, even with Cloudy Weather.

[@rkan2]

Yet going further and avoiding the "saturation temperature" problem is you can increase the water volume and heat more of the stuff when compared to PV.. While being at it, might as well buy a heat pump!

[@TheRainHarvester]

Heat water, or charge batteries? Well water is cheaper, but batteries are smaller. Are batteries smaller per btu stored?

[@ArthurDent0042]

Well, that was a completely surprising result! I expected that PV would have been the worse option. But a big plus is ease in construction (wires are certainly easier than pipes). And you avoid problems like collector stagnation overheating in warmer weather. And that's one cute kid you have.

[@5th_decile]

Yes! There are also many rumours concerning leaks and maintenance costs being much worse for collectors (I have some personal bad experience in that regard).

[@randyretired8443]

Love your video! Thermal solar is mostly ignored today. We use solar thermal to heat. We have 30" of soil under our 6" concrete slab that is insulated on the sides and underneath with pex running through it and the concrete slab. I also have a 600 gallon insulated tank with copper pipe as a heat exchanger. Cooper is the way to go. We are in Colorado and sunshine is abundant. That massive thermal mass keeps the house warm for many cloudy days. The solar thermal panels are significantly more efficient at the lower temperatures used for this. With a well insulated house the floor temps rarely get to 80F to maintain comfort. Our thermal panels were old new stock and 4'x8' panels were $150. I have a backhoe so that also helped with costs.

[@bobcole3852]

Can you tell me about your controls? A friend gave me a solar thermal panel, I want to make some coils of pex under my big plant bags (15 gallon) that are in rubber lined long trays in my greenhouse. Just getting started, really appreciate any shortcuts/time and money saving ideas. Wr are in mountains of western NM, 7600+ Elevation. Thanks!

[@SuperJamster1]

I really appreciate all the work and math you've put into these projects. I've wondered about this for a long time, and when i put my future system together, you'll have done all the work.

[@DavidPozEnergy]

Your welcome, thanks for watching.

[@ek9772]

Eleanor is the best balance between electric cuteness and thermal warmth.

[@MagivaIT]

awh man, i thought id get a clever message in, you beat me by miles, and dead right

[@UnknownIdaho]

Love the kiddos!

[@fxm5715]

Thanks for the followup, David. The actual performance of your two systems was closer than I had expected. For me, personally, simplicity and long-term reliability won the contest when I was researching my own solar hot water system. I don't want to have to spend my time monitoring and keeping everything working well. Sure, you need more square feet of collection surface for PV, but that's not at all an issue for me. A few panels, some wire, the DC heating element, a thermal switch and a fuse; when it comes to real-world applications, the KISS rule is king. :)

[@DavidPozEnergy]

I agree, KISS.

[@MaximumEfficiency]

why not use solar air heater, simplest, cheapest and most efficient?

[@RetroDawn]

@@MaximumEfficiency Ever try washing yourself or dishes using hot air? Also, hot air blowing heating systems are worse for air quality, comfort, *and* efficiency than radiant floor heating. You can set the thermostat lower on a radiant system for the same comfort.

[@bilk2521]

David, Thank you so much for this series of vids. You did all the physical work of my mind experiment!! I found your channel by doing a search on YT to see if someone had tried comparing these two methods of making hot water, in the simplest way, and you did!!!! Thank you so much. Thanks also for the time spent on matching heater elements to PV panel output. Years ago I trained/worked as an aircraft mechanic and recently converted a 36v golf cart to 72v ac with LiFePo batts. I like to think I know a bit about electricity but might have messed up at first as well, if I had actually done what you had done and so conveniently posted on your channel for other to learn from. I'm a fan now of your channel and will probably be watching a good bit of your content.

[@DavidPozEnergy]

Thanks for your comment and watching the videos.

[@bobirving7460]

David, while Evacuated Tube solar HW is more expensive still, it has the following advantages: 1. It does not need to be a drain back system, as the water only passes through the heavily insulated header, not the tubes. This removes all sorts of design constraints. 2. Because of this, it is not affected by the ambient air temperature as your flat plate setup is. 3. It is many times more efficient than the flat plate setup. 4. It generally comes with a sophisticated controller that varies pump speed etc. For these reasons, nobody has fitted flat plate setups here in NZ for a number of years.

[@Zamolxes77]

The best is probably do both ! They seem to compensate each other very well, and you can feed the electric pump for the thermal off your PV, so you have a nice closed system. Suggestion: get a "heat camera" or hire someone to test your system. Around here (Romania), building inspectors thermal image a new house, in order to give it an energy rating. On the thermal imaging camera, you can clearly see how hot are the parts and where the heat is escaping. Those areas need attention - extra insulation. My guess is that the insulation you put on the tanks (saw the video where you built them) is insufficient for the kinds of temperatures you get. Around here, the insulation is about 5 times thicker than what you used, about 3-4 inches thick. Sidenote: cost is subjective, depending in what area of the world you live. A thermal panel is dirt cheap around here, while a PV one is extremely expensive - one of the reasons my brother only installed a thermal panel. It feeds a 1200 liter boiler - aprox. 350 gallons.

[@BrainStormAcres]

Thanks for sharing the results! Really like that you got real operational data. The BTU per unit area didn’t surprise me, but the cost comparison really did. Assuming my free thermal panels don’t leak, the price is hard to beat - maybe a hybrid system with a two stage PV over thermal .... thanks again!

[@DavidPozEnergy]

I've got some "Free" thermal collectors too. Every one that I got free had a leak. But it doesn't take that much effort to fix them. They are currently heating my garage. Worth it!

[@BrainStormAcres]

DavidPoz we’re in N Arizona and I wish I had the panels installed right now - we’ve had too many single digit nights this winter. Hope the next storm treats you gently.

[@Speak_Out_and_Remove_All_Doubt]

Brilliant video thank you so much. I have been looking into solar heating for my Dad's very very cold house and I had wondered this very question PV vs thermal. What I have been seeing in the last few days though is in cold locations like yours you are much better off using evacuated tubes as they don't lose the heat to the cold anywhere near as much.

[@TimG...]

Thank you for the time, money, and effort you put into this comparison!

[@DavidPozEnergy]

Your welcome. Thank you for watching.

[@_CAT-lg4sr]

I'm impressed. You really did an outstanding test and analysis. Thank you for all your hard work and explanations. (P.S.- Your daughter is absolutely darling, what a blessing she is!)

[@vincentrobinette1507]

Awesome Data!!!! When you showed the data, the results came back exactly as I predicted. If you run the same experiment during the hot summer, the thermal will win. When cold, The photovoltaic wins. The graphs and spread sheets clearly show, thermal the fastest out of the gate, but PV finishing at a higher temperature. Thanks for posting the results!❤ (Cute kid, by the way)

[@nicklappos]

and electric driven heat pumps always win. Dave's experiment was a big waste of time.

[@agrxdrowflow958]

You're using the wrong type of thermal panel. People in Northern latitudes typically use vacuum tubes. Tube insulation is way better than flat panel insulation.

[@AtlantisArch]

That's not the only (or even bigger) flaw of this experiment, but that is true.

[@Flightstar]

Well, everything is an evolution. It will be fascinating if and when, he may do the same comparison with a vac tube system. Hopefully as the channel grows and the economics make it feasible to run out and buy thousands of dollars worth of equipment, we will may a video on it. I hope so. Ive seen vac tube systems in action in below freezing temps and their performance is very good, so good that water cannot be left stagnant in the set up on warmer days for risk of boiling. Excess heat must get dumped if it cannot be stored. swimming pools and hot tubs are good for that.

[@davidianmusic4869]

PV thermal was an option for my tiny house, with this it’s a certainty. You’ve really helped me out, thanks. And, what a great experience for your daughter, being involved in your projects.

[@opera5714]

I think that is a wrong conclusion. I have PV at my camp and heat a 6 gallon tank with excess solar which isn't used for other needs. MY PV efficiency using a controller is twice what was achieved in this test.

[@nokhuthulamuzemba7313]

Well done David. I watched this experiment sometime ago. And it made me design a hybrid solar thermal and electric water heating system. I have fabulous results!!! So the solar thermal heater is connected in series with the electric gyser. No circulation pumps!!!

[@DavidPozEnergy]

That's great. Please let me know if you upload a video about it. I'd love to see.

[@cescargot]

Great job ! Would be great to see a dual panel (both featuring a thermal and a PV in a single panel) beeing tested the same way.

[@brianjackson38]

One positive to note is that, you don't need power for a pump to move water about when heating with a PV panel system. It can heat the tank even when the panels and the water are in 2 different locations.

[@garthhowe297]

Your kid is going to steal the show ... cute kid!

[@kylesvids]

Fantastic. This is what I have been telling my customers for years, now I have a video to send them to.

[@Woodyjims-shack]

Chiming in late here David, great video btw 👍 One thing you may not have taken into account which will be relevant on many systems. In winter, late spring and early autumn solar water systems can be irrelevant if there is a single tank with multiple coils. What happens is the solar water system never runs because other heat sources keep the tank temp too high to trigger the system to switch on and pump heat from the solar panels. Solar electric water heating does not have this problem.

[@Chris-ie9os]

I know you've had bad luck with heat pumps... but they usually work and magnify the energy of PV 3-4x. So even if you're space constrained the ideal solution would be HP+PV. I sort of use my HPWH as a thermal battery... it only turns on when the sun is up and my batteries are full.

[@Cerberus984]

While your statement is true to an extent it's limitation is hit when the outside coil freezes vastly decreasing thermal conductivity. Hence, why some heat pumps have electric heat coils to supplement. Where solar thermal shines is cost efficiency when you build it yourself. I've seen functional solar thermal water heating systems simply using pex tubing wrapped in form fitted aluminum sheets meant for hydronic floor heating. Alternatively, aluminum gutter down spouts for solar thermal air heating.

[@TheRainHarvester]

Christopher Dizon , but then the "best cost ribbon" might go back to the solar thermal. Decisions decisions! Is it cheaper to buy 4x panels than one heat pump?

[@motalasuger]

There is a catch with heat pumps though, in that they require a determined amount of power to operate, where if it’s slightly cloudy a direct heating element would still just produce less heat but the heat pump would probably not operate (properly?) if it dips below it’s required power.

[@nicklappos]

@@motalasuger Short sighted answer. A simple PV-heat pump system with batteries and charge controller has all the power needed to beat Dave's experiment by a factor of three or four. That is what my new off grid house has. It is a shame that Dave gets the publicity he does based on how little he actually knows.

[@matija3791]

@@nicklappos What is the efficiency in of a air-water heat pump when the surrounding temperature is about -10°C and you want to pump up the tank up to +80°C? I'm not an expert but I expect it not to be working quite well with this high of a delta...

[@cubecgae]

Excellent experimentI messed around with several pv heating setups and finally hit the winnerTwo 4 panel series arrays in parallel ( 275 w panels ) wired direct into a 2000 w 120 vac element. Simple, simple , simple. I peaked at 1900 w ( 118v and 16 amps )Steamed a 265 L tank in 8 hrs from 10 degrees C start temperature

[@joetothemail]

David, you are a remarkable young man! You have a unique skill of explaining the process of your project efficiently and succinctly. I hope you're getting some sponsorship in what you're doing because you are well worth it!

[@DavidPozEnergy]

I'd love to get a sponsor, but none so far. Thanks for watching.

[@etienneetienne9054]

Great job! The PV has surely an attractive advantage with flexibiitity in uses (satisfy specific needs of electricity; heating; ...). But not really for heating and storing heat: - I'm just sceptic about the prices comparison. Even if commercial solar heaters are abusively expensive when we know what is inside, a 4m2 solar heater (+pump) does no reach the price of 20m2 of PV (+ electronics, electric heating device). And can cost +10 times less if DIY (with 20-30% lower yield). - Also the shelf life of PV is 20years with declining output, and environmental costs up- and down-stream exploitation are much higher. Solar Thermal pannels last >30-50 years, and are easily and fully recyclable. If you like energy autonomy, you are concerned with that. -A PV pannel has typically at its level a 10-16% electric yield, then lets say 99% yield at the electric heater step. Thermal solar Pannels reach typically 50-80% (to heat - depends on the technology). Then all difference come how they are connected to the heat storage (water tank). Your experiment clearly shows that a wise guy can build corresponding set-ups (PV system or Solar Thermal System) at small scale with very interesting and similar performances. There is more space for optimization for the solar thermal system beacuse of scaling, isolation, ... Also heat lost by the solar thermal pannels and tubings and water tank can be recovered at low cost to warm air! = PV+heater remains great if the goal is to achieve higher temperature. Thermic is sufficient an in fact better for domestic uses (water a 40-60°C, and air at 30°C).

[@Bugkiller666]

I wanna say Thank you for sharing your experiment! I learned something today. And as usual Eleanor is the Winner. Well done David!

[@uprightfossil6673]

Your videos are by far the best explanation of what I am looking for. All the information is there and the explanation is clear and concise. Thanks

[@DavidPozEnergy]

Your welcome, thanks for watching.

[@marcfruchtman9473]

This is really great information. I really like how you can focus on both efficiency per unit area vs efficiency per dollar. Thanks for making this video. I also find it super interesting how the solar thermal capped out so quickly. This suggests that the design could benefit from lens concentrators inside the panel itself for the thermal panel, to boost the incoming maximum temperature.

[@peters972]

Thanks! I was quite interested in these panels are a hybrid of both ways! In summer, the water circulating keeps the Pv cooler, and also provides the heated water.

[@jimh712]

Excellent comparison... For the winter the photo voltaic seems to be the choice 👍👍👍👍👍👍

[@junkerzn7312]

Makes a whole lot of sense, particularly the fact that the solar thermal is only more efficient under ideal conditions whereas the solar PV can be productive across a wider set of conditions. And I would think just being able to run the PV-produced eletricity over to the house without any further (serious) losses is also quite important. That gives you a lot of flexibility in situating the tank in a location where even its waste heat would help heat the garage or home. I'll bet the PV solution would work as well for the garage as for the home using the same heat-exchanger method. For that matter, even a single-loop heat exchanger with a small fan ought to work pretty well for heating the garage. Now, since its a closed-loop system, what about using something other than water? Something that doesn't suffer from corrosion or mineral deposits and perhaps can handle higher temperatures and/or have more heat mass? -Matt

[@davidbateman5805]

Hey David, this is amazing work. You know, I think you should write a scientific paper. The world needs to know this stuff!!

[@briandbeaudin9166]

Your assistant is so sweet! Great video!

[@brucekahn6083]

Hey thanks for putting all this together - very useful, however, I wonder about other factors. Firstly, could not the thermal system work more efficiently at lower temperature with additional insulation? Also, over time, PV panels loose efficiency, producing 10-20% less power by age 15 or so, thermals don't. Hence, second - hand thermal panels, which can be had for as little as $100, change the equation entirely I'm still working on a solar system design for electricity and heat, in my radiant - floor heated barn in Pennsylvania thanks again

[@gramos9115]

Great work David , thank you for doing all the experiments we all think about doing ! Anther point about the PV vs ST systems is there is more risk involved in the Solar Thermal systems failing due to expansion causing burst pipes / joints and tanks . I have seen the various parts blow after overheating causing scalding water to escape . One pretty dangerous situation !! I will use the PV / heating element system for certain .

[@alexandreesquenet3736]

Cool. And the other best: with the PV is that you can power devices, not with the heat panel ^^

[@bobirving7460]

And 5. It works extraordinarily well in overcast conditions: the tubes are individual heat pumps, scavenging whatever energy arrives at the tubes and transferring it up to the header.

[@paulgracey4697]

I have had a thermal system for my home hot water for more than 10 years now here in SoCal. At the time I installed it from a kit, the price was far cheaper than PV. Now you show me that the cost of PV has dropped so low that you can get twice the area for less. Great news. I should mention that the pump on my thermal system was powered by a small (2.5 Sq.ft.) PV panel. At first I thought this was clever as it only pumped when the sun was shining, but I soon discovered a difference between the two solar collection schemes. Both panels, like your array, were at the same angle and orientation towards the south. Both were optimized for the winter sun angle, and because I live near the coast with its morning fog, I cheated it 15 degrees towards the west for more afternoon exposure. What I discovered, was that on clear mornings, the PV panel would start the pump, but the sun had not reached the right angle to bring the thermal panel temperatures up above the tank top temperature, so what would happen was the tank hot water would be cooled for a while by radiation back out into space. Of course I then had to get the temperature controller which would stop that inversion of function, especially in winter.

[@maxmachin4894]

It would be better to run it via a differential solar controller to avoid this issue

[@opera5714]

The future of energy is controls. What almost no one understands is controls. IN SoCal you don't need anything to be somewhat successful with solar.

[@TrackGeeks]

As an alternative you could use a simple thermal sensitive mechanical switch to delay the pump operating until the panel began to warm up. That is what I do with mine. It is the same kind of switch that is used when converting older cars to electric fans on the radiator. Works very well.

[@offgridwanabe]

Amazing so what you need is a hybrid using thermal to start and finish it with solar electric

[@DavidPozEnergy]

LOL. I was thinking more of just thermal for space heating and electric for DHW.

[@philtimmons722]

@@DavidPozEnergy -- add some concentration on the Thermal. Makes a HUGE difference on the delta T.

[@Cerberus984]

@@DavidPozEnergy Go the DIY solar thermal route and save a good chunk of change. For solar thermal air aluminum gutter downspouts with solar powered mixed flow fan. With it having less mass and specific heat capacity it will ramp up faster with less losses during night time as you close the entrance / exit ducting to the house. If you oversize it just duct the excess heated air to a heat exchange to your thermal water battery. For solar thermal water pex tubing form fitted into aluminum hydronic heat transfer plates meant for hydronic flooring. It is honestly more of a headache in colder climates but ideal in regions similar in latitude as North Carolina or closer to equator.

[@TheRainHarvester]

I don't think it changes the cost equation. Does it? But if you already have the solar thermal, it's a win.

[@benjaminlewis671]

Great Minds think alike!!

[@antontoyra5071]

Gerat vid, thank you. How about using the Thermal to preheat the water before going into the PV tank? You'll gett all the water to your prefered temperature and increase the Thermals efficiency do to the air/water temperature variable.

[@roymunson8365]

Great stuff. Do you have any comparative videos about in floor heat with Thermal solar compared to PV?

[@buixote]

My folks got solar thermal back in the 70s. It was a 2-story house, and when time came to overhaul the system, the cost was significant, so they decommissioned the system... I don't know how the solar thermal systems are today, but it seems like the plumbing might be more failure prone than wiring... also weight, maybe? Another thing to think about if you're doing a heat-pump water heater... a friend of mine has a duct leading to the *attic*, to get extra-toasty air for the unit to extract heat from!

[@DavidPozEnergy]

I don't know if plumbing is more prone to failures, but it's definitely more tricky to install. I like the PV approach.

[@MagivaIT]

another awesome video, loved the sticker off and bamb its back on... video cut. its the small things that amuse me and that make your videos worth returning to time and again

[@DavidPozEnergy]

Thanks, I'm still learning how to do editing.

[@Jonb01z28]

Awesome info and exactly what I was looking for. I have been tossing around this exact thing either going solar thermal or pv to heat my water heater. Been on a quest to cut my homes energy and have already cut about 50% and now its time to shut off that hot water heater once and for all and heat it will solar panels. Should have a pretty good return on investment as I figure it cost me about $30 a month to heat water, so at a cost of around $500-600 to install a pv system myself im' looking about about a 2yr return which is pretty damn good.

[@royamberg9177]

The solar thermal is better for large volume of hot water. The solar thermal need bright sun light to do much. The pv will produce a little in lower light condition. On a smaller System the pv is less intense to install no pumps and pipes but on a yearly average thermal will out do the pv.

[@energycrafts8206]

Roy and David Poz, I have only solar thermal using pool panels to heat water. Been working perfectly for over a year with zero maintenance. The panel glazing is stained and dirty. Yet I get right now here in Feb hot water so hot I have to mix with cold in the shower. This is true daily whether the sky is clear, mixed clouds or hazy. Yep hazy, as in no bright sun light between 10am and 3pm. For me solar thermal install was way cheaper than just adding more PV as I got the pool panels on CL for free and I do not use any pumps or electronic controls. Plumbing only cost (one time expense) around $100. For that money I could only buy one 100W PV and in no way could supply the same amount usable hot water. Can see on my channel.

[@benssolarandbattery]

You will need a thermostat to shut off the element in a DHW or heating scenario. (One that's rated for DC voltage) You could also use a second thermostat to run a relay and transfer the PV over to a Charge controller when it's not heating water.

[@SolarSteve]

Glad to see the results on this... question for you, and this is something I've thought about often - could you convert a PV panel into a thermal panel so that it's a hybrid? Given that the PV panels get hot, that's just wasted heat... presumably you'd get better performance out of the PV because it'd be cooler, and you'd collect the BTUs that would have been wasted. The ultimate PV/thermal panel!

[@DavidPozEnergy]

Hi Solar Steve, It's totally cool if you want to experiment with that, but personally, I"m not planning to do it. Several manufacturers have tried bringing products to market doing this. They are all off the market now.

[@scec85]

@@DavidPozEnergy Do you remember any of the manufacturers? I wonder if I can find one of their panels...

[@Laser2120]

It would be nice to see you do this experiment in the summer months, also a combined solar and thermal. I am sure you could decrease the price of thermal heater by making your own to.

[@GoingOffGrid101]

loved the video! I already have everything I need for pv hot water installing soon!

[@DavidPozEnergy]

Thanks for watching.

[@robertbogan225]

Ive seen work with solar thermal in roads and ive been thinking that designing a driveway around it could be the best way to hide the panel and also your driveway usually goes right next to the house so it would be easy to pipe it into the basement. Lol at 8:00 when you said the pv was so simple yet you goofed it at the beggining.

[@rupe53]

Might be slightly off topic for this video, but very much on topic for your heating in general. Do you know what the BTU requirements are for your garage? Do you know what the BTU capability is for the radiant heating system? A little math from your chart says the PV system can easily go over 15,000 BTU per day so that's a bit over 600 BTUs per hour. IOW, not much as far as heating systems go. OTOH, knowing how many BTUs per hour are needed (that's the standard for expressing heating needs) will allow you to calculate the size and scope of future improvements. Maybe the next update would be a system to follow the sun? Might be cheaper than adding more panels.

[@patrickdegenaar9495]

Excellent surprising vid! It's amazing that photovoltaics are cheaper than solar thermal given the water's simplicity. Mass production always wins!

[@jb65270]

David LOVE your videos, have rewatched several over the years. I have a question: How does pv compare against thermal on overcast/cloudy days? We had a 17x10 room on the S side of the house, with an entire glass wall on the S. side. I hung 1/16" Alum flat sheets painted flat Blk 6" from the glass inside, along 10' of that wall. 21*F outside 110*F inside with cheap recycled DBL pane... most had broken seals. Overcast days, they still generated SOME heat, but not alot. I saw a PV system recently which on an overcast day was still producing well. I thought I would get your feedback on whether you have found PV to be significantly more effective when considering overcast days.

[@filetdelumiere5037]

Very interesting video ! But it should be very useful to do the same test in summer. In this case, the winner could be the thermal panel. The efficiency of solar panels decreases a lot when the ambient temperature increases.

[@thefreckster1038]

I have several extra PV panels. I would love to utilize them for heating water. Do you have the design specifications and instructions for building your system?

[@HumbleServant3777]

New subscriber here. You're doing a great job, I love these videos. Very informative. Keep up the good work!

[@avid0g]

The problem with cold ambient temperature can be offset with more glazing insulation layers or with evacuated insulated tube collectors. It also helps to set the thermal collector angle to optimize winter absorption. Furthermore, when using Geothermal heat pumps, the deep ground temperature output can be further heated by the solar thermal collectors before the heat pump. This significantly increases efficiency of the heat pump, and the solar collector can operate far cooler than a _hot water_ collector would require.

[@avid0g]

One way to cheaply improve the temperature of solar thermal is to preheat some *air* in a lower collector and run this _over_ the glazing of the upper water thermal collector. This lower collector can be much simpler and cheaper than the copper assembly used for heating water. Since it is heating the air to above outdoor ambient, but not as hot as the main collector, it does not have to have as perfect an absorber. Of course, this requires another glazing layer, but you can use an inexpensive plastic film that covers both collectors. If you build your own thermal collectors, the cost can be significantly lower than prefab, and you can incorporate the air heater into the water heater box.

[@kevinroberts781]

After seeing this I'm pondering using PV to help heat my water! I need to design a hybrid system. Off grid when the sun is out on grid when the sun goes down. Thank you for doing this!

[@DavidPozEnergy]

Cool. If you size it well, you can store enough hot water for night time. And, in case you are new to my channel, I have a free calculator on my website to help match the pv to heating element. www.davidpoz.com

[@warrenbrooke2402]

Great work! Important information came out of this compare and contrast, so thanks for doing the experiment

[@rustusandroid]

Would be interesting to do a hybrid, where the thermal does most of the heating and then you top it off with the electric.

[@77Trev617]

I think the thermal has potential, if there is a medium inside the water with a greater thermal capacity then it might hold the water temps more stable, that is until you have a big drop in temps along with clouds. Great video

[@rkan2]

77Trev617 The most cost efficient way to store energy is to store it in to a insulated rock! Of course heat transfer is going yo be very slow, but say you have a tank that is half full of gravel and half full of water, then you already have a feasible system for hot water storage.. Of course there might then be a need for a heat exchange, so the more rock you have and the cleaner you can keep the "coolant" the more directly it can be used.

[@marscan1]

@@rkan2 ; The specific heat of rock is approx .2 and the specific heat of water is 1, that means that the for the same weight, (say 1 pound) you need 5 times(1/.2) as much rock to store the same amount of heat. Specific heat = the amount of heat required to raise 1lb of water 1 degree F., or to raise 1 gram, 1 degree C. It also means that, if you have the same weight of water and rock, it takes 5 times as much heat to raise the temperature of the water, which makes it such a good thermal storage media. And to store the same amount of energy you would need 5 times as much weight in rock as you would in water.

[@rhiantaylor3446]

Great outcome - really clear. Of course if you are going to need to store the energy you are harvesting, the cost of storage comparison you did earlier becomes a factor - storing hot water is way cheaper than storing electricity in batteries. Next project - even larger mega insulated thermal water store ?

[@WaemYt]

amazing documented comparison. Have you considered to ad a wind turbine to the comparison?

[@DavidPozEnergy]

A wind turbine would be a lot of fun to add, but I have no immediate plans to do so. Thanks for watching.

[@hedleypepper1838]

Interesting comparison.. but on cost of panels, you can make solar thermal panels very simply for a fraction of the cost of solar pv panels, you can also insulate the solar thermal panel to reduce losses on cold days, losses from the barrel on cold days will be the same for either system 😉

[@bjleau76]

awesome head to head comparison, love the real world data . As the efficiency man once said “In God we trust....all else bring data” Demming.

[@EdouardStenger]

Great video, thank you for sharing all your hard work! I would love to see a video of what would happen during summer. Would the PV / thermal comparison still hold up?

[@DavidPozEnergy]

In the summer the solar thermal collector will produce far more hot water than the PV. About 4x more. I live in Massachusetts and want to produce hot water for both DHW (showers) and space heating. I have surplus hot water in the summer, but was running this experiment to decide how best to make hot water in winter. Thanks for watching.

[@EdouardStenger]

@@DavidPozEnergy Thank you for taking the time to answer David! Keep up the great work!

[@olqu1352]

thumbs up for going with the results at the beginning of the video. No time wasted. Topic was just what I was looking for. Some Questions though: Are you using water only or glycol for the thermal and are you using a AC converter for the pv or are they wired directly to the heater?

[@DavidPozEnergy]

This setup is water only. It's a drain-back design, so when the pump shuts off the panel drains back down into the tank. The PV panels are wired directly to the water heater element.

[@jsbrads1]

The baby's yodel during the intro makes me chuckle every time

[@disneyjoe7]

Have you considered doing both systems to heat your home hot water?

[@elmafudd9703]

This is good stuff. Thank you for your time sir.

[@johnward5890]

If your Solar electric panels have a bypass diode so the shading doesn't limit the voltage output because of the series circuit of many panels being hooked in series to get higher voltages like 240 volt DC 15 amps for a series /parallel setup, you could use regular AC elements out of a Hot water tank because it doesn't matter if it is AC or DC with resistive loads. 240 x 15= 3600 watts element. Solar panels can handle up to a 1000 volts passing through them for some of the newer panels with lower amps. When in series the volts add together but amps stay the same.

[@adrielrowley]

Or have both and use the thermal to pre heat the water. Then you have the best of both. What hope to utilize on my dream home.

[@guygrotke7476]

The heat loss from cold air temperature is from the thermal panel, not the tank. Both tanks have the same insulation. This would not really be a problem for me since I live in Southern California. It snowed once here about 10 years ago for 15 minutes. Another problem is how much you paid for your solar thermal panel. Most any DIYer can make their own solar thermal panels for much, much less. Much harder to make your own solar electric panels! You can also get rid of the water pump if you can put the tank above the thermal panel on a Southern-facing slope.

[@andrewwaters2354]

Great video!Have always wondered which was better, but i installed solar PV because 2nd hand pv panels can be bought extremely cheaply and its a lot simpler to install, no pipes freezing on the roof, no leaks to worry about. But one thing would be good to do some further investigation, in the UK most days are cloudy, i wonder if PV is better in cloudy conditions? If you have a direct connected system with PV you will notice on the cloudy days you will get virtually no power out (the heating element pulls the voltage too low past the max power point) this is why im developing a MPPT controller for use on solar pv heating systems. The system will limit the current to keep the voltage at its max power point, increasing efficiency.

[@DavidPozEnergy]

It would be wonderful to bring a proven MPPT controller to market that needs no batteries. I hope you do. Especially if you can incorporate a thermister in your package. The thermistor can be attached to the steel tank in place of the AC version.

[@dantyler6907]

As PV has gotten more efficient over the last few years (as well as cost has gone down, big time) similar comparisons have lost to PV. A few years ago, I looked at thermoelectric generation, similar in concept to Voyager I & Ii, current PV won out. Years before PV, some looked into extracting electric current from cold and hot fluid run over a central Be conductor. Top efficiency was 2-4%. Crazy how far PV has come, pretty much eclipsing all other solar energy methods. And I have to believe the progress will not stop. I put solar panels on my house just 3 years ago, 300 W/panel. Now, not uncommon to read about some panels that generate 350W!!! I have begun looking into DC voltage, since more and more homes have panels on their roof, no need for AC. Most electric powered devices have AC compensation first in the schematic. Since AC to DC conversion is never 100%, many (if not all) appliances are generating heat from the conversion. Seems we would enjoy lower electric needs if we eliminated AC...

[@xubiwilson7654]

Getting higher temperatures to your crawlspace tank can be achieved by slowing the flow rate, although it does so at a small reduction in efficiency.

[@carlossaroufim]

Evacuated tubes are way more efficient, also its interesting that you mentioned cost, solar panels dont have longevity they have to be replaced much sooner.

[@mr.somebody1493]

Combine the two, use the solar thermal as a pre-heater for the PV panels.

[@rkan2]

Colorado Clyde Heater? Why would heat silicon or copper? Cooling is where it is! I wonder if pumping water under the panels would be efficient enough to power using PV. You could then use the waste heat for anything!

[@TheRainHarvester]

Nice idea!

[@wkzeier]

Great content great analysis quick question what was the wattage on the PV panel?

[@DavidPozEnergy]

Each PV panel is 365 watts. Thanks for watching.

[@titusm9837]

Interesting experiment. IT would be very interesting to compare a heat pump vs presurized thermal panels. The flat thermal is at least 30% less eficient than presurized models.

[@dr2944]

Thank you. was a big help in making a choice.

[@j.patrickmoore9137]

It would be interesting to see how the numbers compare in the summer. From what I've read, PV efficiency drops a bit when the panels are hot. On the other hand, you wouldn't be needing the thermal heating in the summer, either. So, the PV might overall be more helpful. But, if I was going to heat a swimming pool in the summer, I'd probably stick to the solar thermal.

[@DavidPozEnergy]

Solar thermal is the perfect choice for heating a pool.

[@fignon]

Great video! ive a 20 evac tube system which is 15 years old and due to leakes needs £800 worth of repairs to repalce pipe worth. THe solar guy said it would be better to replace them with 3kw solar pv, costing £5000 but with a water heater diveter, there is not enough rooom for both. Do you think we shoud repair or switch to pv?

[@DavidPozEnergy]

That's a tough call. If the evac tube system was newer (say less than 10 years) then I'd go with the repair. But, at 15 years old I'd be concerned that another leak will pop up again next year, and so on. If the prediction is that you can get another 5+ years out of the system with just the 800 repair, then I'd go that way. But if it's a sign of things to come I'd lean to the PV. In my mind it depends on what is leaking, and the condition of the rest of the parts.

[@Throughthebit2000]

Thank you for sharing your efforts in this comparison, it’s very interesting. I may have missed it, but did you record electrical power produced from the PVs for the same 15 days as your thermal comparison? Also, what was the “rated” power of the thermal panel? From your data, it seems as though you obtained only about 92 W/m2 useable for heat from the PVs, but 157 W/m2 from the thermal.

[@DavidPozEnergy]

I did not record the electrical watts. I recorded the tank temperatures. The data plate on the side of the thermal panel says "Thermal Performance Efficiency (ASHRAE 93-77) 81 BTU/ft2-hr-°F"

[@Throughthebit2000]

OK, thank you Sir. So that’s 2590 BTU/hr or 760 W (per degree F)...I guess that’s a delta T between the inlet and outlet. Was there much of a difference between the top and bottom tank temperatures? The angle of your panels means you live pretty far North, I guessed about 6 hrs of sunlight per day in Feb...at least when it wasn’t snowing! Thanks again for your efforts and reply! There is a ton of “stuff” out there, I really appreciate it when someone is willing to share the numbers.

[@DavidPozEnergy]

The raw data is all on Patreon: www.patreon.com/DavidPoz and I live in MA, 42.5°N

[@Throughthebit2000]

Thanks man. So, about 2 degrees F delta T, which gives your thermal panel around 1.5 kW, or 500 W/m2, and made it close to 30% eff. at heating h20. That’s awesome! The PV’s were about 18% eff. Thank You!

[@oldporkchops]

Hi David, when factoring in costs, did you include the cost of storing the electricity generated from the PV panels (that is, the cost of the lithium batteries)? Thanks. How often do Lithium batteries need to be replaced? Thanks.

[@DavidPozEnergy]

Not in this test. This test is using the solar PV (electric) panel connected directly to a water heating element. So there is no inverter, batteries, charge controller involved. It's extremely simple compared to a battery based system. In this case we are using the hot water as a "Thermal battery".

[@S3l3ct1ve]

What can you tell about using a system like this (electric heating) to heat the whole house? Well of course on the bigger scale, both number of panels and bigger water tank. Placing the tank inside the basement of the house. Would it be worth it in your oppinion?

[@Uglydollsrises23132]

#hiddenbattery This is a great video for helping us understand that solar Electric is more cost efficient. This helps demonstrate the benefit of Solar electric (PV) AC-Coupled to a battery system.

[@0900McShizzle]

N

[@markperry6660]

nice but heating a barrel is alot different than real world usage, just curious if it was heating a large storage tank that is being used for dhw

[@billhulstrunk7308]

Thank you for running this experiment, before this I had no idea that you could run your PV panel directly into a electric hot element. I love the simplicity, and lack of things to break down and go wrong.

[@DavidPozEnergy]

I also love the simplicity, KISS

[@climatechangepreppersfaceb2148]

You can't do it long term. DC will result in electrolysis. A new tank can corrode in 2-3 years

[@TheRainHarvester]

Nevada Forensics LLC , I just saw this video. No others yet. Dumping the current into the resistive heating element will cause electrolysis? Or did he do something different?

[@markthomasson5077]

@@climatechangepreppersfaceb2148 . Why? Surely the element is electrically sealed from the water.

[@XRinger]

I didn't notice if you took the temperature of the PV array into consideration in your study. PV panels perform better on really cold days. On hot summer days, they are at the worst. But if it's under 20F (air-temp) outside, you can count on more power from the sun.

[@Leggir]

I wonder how this would work for a stock tank. I only have to keep the water a few degrees above freezing, but there's going to be a 12" circular hole in the top for the horses to water at any time. Perhaps changing from a 100-gallon tank to a 5-gallon tank and put insulated barrel next to it to cycle the water to and from, and pump water from the well into the barrel when the level gets low. Most commercial systems have insulated walls, but a steel bowl that's heated with 1000W, and when it's cold, it's on 24/7.

[@dgmenace73]

I really enjoyed watching these videos. Thanks! ......What size is the size of thermal panel? I luckily got three (3×6ft) before a demolition crew sent them to be recycled. I "think" two should be enough for my needs but I do still have the 3rd. Like you, I have a garage that just ran water to and use a small 6.7gal RV water heater but I don't use water in the garage that much and just keep it on its lowest setting (for now). I really would like to see a video of someone that may have used 2-3 thermal panels and how they used them in junction with their regular water heater. If you know of any links, please let me know. For me, the electrical shouldn't be an issue, just the design & configuration of a storage tank and or circulation pump. Again, thanks for your vids.

[@5th_decile]

Thanks, this video was very useful in the research/decision process for my installation.

[@swampcastle8142]

Nicely done.

[@sammyjimsmith6100]

Interesting project. The pv are more efficient in the winter and less for heating a pool in a hot summer, I suppose.

[@1202Sid]

Solar thermal evaluated tubes outperforms solar thermal flat panels in the cold by a large margin. But initial cost and setup complexity is greater. In the long run, if the system is setup properly, evacuated tubes will be more cost effective. Specially as the prices go down.