Results of Solar Thermal vs. PV Experiment in Heating Water
ฝัง
- เผยแพร่เมื่อ 19 ก.พ. 2019
- After three long weeks we finally have the results of our test. This was an experiment comparing solar PV vs. solar Thermal panels in heating water.
I have been heating water with my solar thermal collectors for years, and then storing that hot water in a thermal battery. However, I have found that the tank never seems to get super hot. Also, a few months ago, I had a leak in one of my thermal panels. Those things motivated me to see if there was a better way. Everyone says heating water with PV is crazy. But why? I set up an experiment to find out if it is a dumb idea, or holds merit.
I was very surprised to find that the PV panels did a fantastic job. Not only did they create more heat (BTU's) but they also got the tank of water hotter compared with the solar thermal collectors. I think I'm in love with solar PV panels!
It's important to me to learn all I can about heating water without grid power. I'm trying to move my family's energy needs off-grid so that we are more energy independent.
I've got a lot of videos about this whole experiment. Here are a few:
Storing 180°F water: • Cheapest Energy Storag...
Introduction to the experiment: • Solar PV vs. Solar The...
Building the experiment: • Building a Solar Hot W...
Wiring the PV panels: • Matching Water Heater ...
Thank you for your support on Patreon: / davidpoz
DC Power Meter: amzn.to/2Nl6SGI
DC Hot Water Pump: amzn.to/2GWq5Nx
DC Electric Heating Element: amzn.to/2E1Bngk
“As an Amazon Associate I earn from qualifying purchases.” - แนวปฏิบัติและการใช้ชีวิต
Eleanor is the best balance between electric cuteness and thermal warmth.
awh man, i thought id get a clever message in, you beat me by miles, and dead right
Love the kiddos!
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.
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!
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.
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
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.
Your welcome, thanks for watching.
I wanna say Thank you for sharing your experiment! I learned something today. And as usual Eleanor is the Winner. Well done David!
Fantastic. This is what I have been telling my customers for years, now I have a video to send them to.
Great series! Thanks for the info
Great work! Important information came out of this compare and contrast, so thanks for doing the experiment
This is good stuff. Thank you for your time sir.
Thank you for the time, money, and effort you put into this comparison!
Your welcome. Thank you for watching.
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!)
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.
Nicely done.
Thanks for the comparaison :)
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.
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.
Or when you're charging batteries and they get full, you can continue heating water :)
@@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.
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!
Heat water, or charge batteries? Well water is cheaper, but batteries are smaller. Are batteries smaller per btu stored?
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.
Thanks for your comment and watching the videos.
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.
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).
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
Your welcome, thanks for watching.
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.
terrific data driven video, thank you
Thank you , valuable experiment
Thank you. was a big help in making a choice.
New subscriber here. You're doing a great job, I love these videos. Very informative. Keep up the good work!
Excellent comparison...
For the winter the photo voltaic seems to be the choice
👍👍👍👍👍👍
Great work!
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 .
Great job, very informative well presented and explained, Cheers
Thanks, this video was very useful in the research/decision process for my installation.
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!
I'd love to get a sponsor, but none so far. Thanks for watching.
Nice analysis!!
Your assistant is so sweet! Great video!
good show as always .thank you. keep making the vids. I have learned more from you than anyone ,
loved the video! I already have everything I need for pv hot water installing soon!
Thanks for watching.
*Go for both.* A small solar-thermal to pre-heat, and the electric one to boil the water.
Great experiment !
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.
@@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 .
@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.
Waste of time.
@@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.
Great info! Thanks!
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.
Thank you for doing this. Great info.
Your welcome, thanks for watching.
Thank you, I find your experiment well done, the results interesting and valuable - thank you.
Thanks for watching.
Thx for your time and effort
Your welcome, thanks for watching.
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.
Your kid is going to steal the show ... cute kid!
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.
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.
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.
The baby's yodel during the intro makes me chuckle every time
Subscribed and rang the bell! Great info!
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
Thanks, I'm still learning how to do editing.
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!
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!
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.
Nice experiment! Awesome kid as well
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.
Great job 👍,, love info 😁
Amazing thx! Great work
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.
great video , David
Thanks.
Seriously. You Rock! Thank you.
Your welcome, thanks for watching.
Great video!
Hey David, this is amazing work. You know, I think you should write a scientific paper. The world needs to know this stuff!!
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
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.
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).
You do the best videos thank you for what you do
Thanks for watching.
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. :)
I agree, KISS.
why not use solar air heater, simplest, cheapest and most efficient?
@@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.
Thank´s for show us your data.
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)
and electric driven heat pumps always win. Dave's experiment was a big waste of time.
Great stuff 👍🏼
Thanks.
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!!!
That's great. Please let me know if you upload a video about it. I'd love to see.
Thank you for this. 🙏👌💪
great effort :)
Thanks good job.🇨🇦
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?
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.
@@DavidPozEnergy Thank you for taking the time to answer David! Keep up the great work!
Cool.
And the other best: with the PV is that you can power devices, not with the heat panel ^^
the baby is adorable!!!
Brilliant video and your daughter is so cute ❤️
Excelente canal
Felicidades porque el idioma para entender no es problema.
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.
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.
HOWdy D-P
thanks for the COMPARISON
COOP
...
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.
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.
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.
Congratulations you have got a new subscriber.
Thanks
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!
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
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?
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.
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 ?
Well done, you have a new sub!
Thanks for the sub. You have a beautiful system and I enjoy your videos. Thanks for posting them.
enjoyed this
Excellent surprising vid! It's amazing that photovoltaics are cheaper than solar thermal given the water's simplicity. Mass production always wins!
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!
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.
@@DavidPozEnergy Do you remember any of the manufacturers? I wonder if I can find one of their panels...
Have you considered doing both systems to heat your home hot water?
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.
heya nice comparicing have been thinging about this myself pv again thermal thank you for this so I haven't to do it myself
Great stuff. Do you have any comparative videos about in floor heat with Thermal solar compared to PV?
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.
thank you for solar energy video
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.
That's not the only (or even bigger) flaw of this experiment, but that is true.
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.
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.
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"
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.
The raw data is all on Patreon: www.patreon.com/DavidPoz and I live in MA, 42.5°N
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!
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.
hey man keep up!!! you doing well.. i m in a mediteranean zone !!!! 3/4 months a year a family needs heat and 2 months a year a bit cool down..!!! its a bless i guess .. makes me think of a project with a tank that heats water for use and a bigger tank for heat and cool for those months!!!!! the solar ones can do easier both but a few companies out there do it already in more tropic zones cause they need the cool water for massairconditioning projects!!!!..
Hi David - I think that's a fair result and what I always expected. Especially in a cold climate. Seeing as how you already have the solar thermal have you thought about a hybrid system with a diverter for the solar panels to power the element? As I already have a solar thermal system I'm seriously considering that course myself instead of investing more money in tubes. It might make sense for you as well as you won't have to expand your solar panels as much. For my money those flat panel collectors are nowhere near as efficient as the evacuated tubes, but that can be somebody else's experiment..
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.
It would be better to run it via a differential solar controller to avoid this issue
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.
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.