EEVblog 1630 - Solar Panels for Water Pre-Heating? - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: July 15, 2024, 08:24:09 am
content: Is it worthwhile to run water through your solar panels to cool them down while pre-heating your hot water? Also solar air and water heaters.Answering a Twitter question:https://x.com/axion2003/status/1812740667367460971As always, YMMV.

author: nctnico
author_rank: Super Contributor
timestamp: July 15, 2024, 08:35:46 am
content: Looks complicated indeed. I have been wondering about installing a water mist system (which basically are a few plastic pipes which run under the panels) to cool the panels using tap water and up the production of the panels on a hot day. It could make a difference of 50W per panel.

author: EEVblog
author_rank: Unknown
timestamp: July 15, 2024, 12:06:03 pm
content: Quote from: nctnico on July 15, 2024, 08:35:46 amCheaper and simpler to just install a few more panels to compensate?Bonus in that you get more output on cooler days.K.I.S.S

author: nctnico
author_rank: Super Contributor
timestamp: July 15, 2024, 02:34:03 pm
content: Quote from: EEVblog on July 15, 2024, 12:06:03 pmThat only works if you have space left on the roof. An advantage of a misting system could be that the interior of the house doesn't get so warm so the AC has less work to do. But I didn't run any numbers on the amount of water (cost) is needed.

author: BarrowBoy
author_rank: Contributor
timestamp: July 15, 2024, 03:03:21 pm
content: Lack of roof space....bifacial solar modules?

author: thm_w
author_rank: Super Contributor
timestamp: July 17, 2024, 10:08:29 pm
content: Cooling panels with water won't make sense in Netherlands. Maybe in Australia or Dubai.Roof temperature won't be significantly affected because panels are air-gapped from the roof, so that is multiple layers of insulation (unless you use tesla solar roof or something).Anyway simpler options like aluminum cooling fins, phase change materials, etc. that don't need pumps to operate or waste water can be viable in hot climates. But only if they are easily available, and I don't really see many manufacturers offering them.There was actually one with build in piping, but again super complex:https://dualsun.com/en/products/dualsun-spring/https://www.mdpi.com/1996-1073/17/3/713https://www.mdpi.com/1996-1073/16/18/6706

author: coppice
author_rank: Super Contributor
timestamp: July 17, 2024, 11:35:13 pm
content: Quote from: nctnico on July 15, 2024, 02:34:03 pmYeah, its annoying when one of the tiny minority of people who have excess space suitable for solar panels says this. The vast majority of people interested in producing solar energy are severely limited by the amount of space they can use, whether its limited roof space, or an awkwardly shaped roof that offers little space facing in a suitable direction where large rectangles will fit. Those people stand to gain a lot from more efficient panels, or more efficient ways to use them.

author: EEVblog
author_rank: Unknown
timestamp: July 18, 2024, 01:26:45 am
content: Quote from: coppice on July 17, 2024, 11:35:13 pmObviously if you don't have the space then you don't have the space, so the comment is not relevant. Don't take it as some sort of attack.I for one have plenty of roof space left, and yet people are asking me why I don't implement complex efficiency improvements on existing panels.As for "tiny minority of people who have excess space suitable for solar panels", take just Australia for example. Almost every solar installation has excess roof space.Tell me your local town and we can look on Google satellite and I'd be wiling to bet that the majority of existing solar installations do not utilise all the roof space. Want to take that bet?

author: coppice
author_rank: Super Contributor
timestamp: July 18, 2024, 08:18:09 pm
content: Quote from: EEVblog on July 18, 2024, 01:26:45 amI'm in the UK. Look at any area you like, and apart from a few large houses for the wealthy, and some low population areas with sprawling bungalows, you won't find many solar installations using only part of the available roof space.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 18, 2024, 09:15:10 pm
content: The effort for water cooling is quite high and the chance for leaks / faster aging is also there.Another point it that cooling mainly helps for the time with high power - this may not be the main issue, as the inverter may be smaller than peak power anyway. The simple calculation looking only at the peak power case will overestimate the gained effciency from cooling.If at all it would be cases where the waste heat is still good for somehing (e.g. a pool), where cooling the PV cells makes sense.

author: tszaboo
author_rank: Super Contributor
timestamp: July 18, 2024, 10:54:41 pm
content: Quote from: nctnico on July 15, 2024, 02:34:03 pmA neighbor of my parents tried something like this. Though he was trying to cool down the house, and thought it's a good idea. His was the only house I've ever seen with water scale on the roof.Quote from: Kleinstein on July 18, 2024, 09:15:10 pmI don't get this either. Fir this year, I had maybe 2 days that were actually optimal, and then I might be loosing 4-500W for 2-3 hours. Everything else was weather limited. Certainly not enough to worth the effort to run water pipes to the roof.

author: EEVblog
author_rank: Unknown
timestamp: July 20, 2024, 11:00:45 am
content: Quote from: Kleinstein on July 18, 2024, 09:15:10 pmYes, majority of inverters are underrated anyway. Solar panels are pretty awesome these days, so adding a complex system to try and eek out an extra 10-20% from them on a limited numbers of hot days just seems silly. There is a reason why it's very niche.

author: EEVblog
author_rank: Unknown
timestamp: July 20, 2024, 11:06:10 am
content: Quote from: coppice on July 18, 2024, 08:18:09 pmCrikey, I had a hard tiem finding ANY houses wiht solar panels.This is the first one I found, and nope, plenty of roof space left.Can you give me an example of a town that has a large uptake of solar?

author: EEVblog
author_rank: Unknown
timestamp: July 20, 2024, 11:09:35 am
content: Random suburb in Sydney, about half the houses have solar. My street has 100% of the houses.

author: EEVblog
author_rank: Unknown
timestamp: July 20, 2024, 11:12:33 am
content: Quote from: EEVblog on July 20, 2024, 11:06:10 amPlymouth has the highest uptake of solar:https://www.greenmatch.co.uk/blog/solar-power-hotspots-in-ukThis wasn't easy to find, but here is my first fine, plenty of roof space left.

author: tszaboo
author_rank: Super Contributor
timestamp: July 20, 2024, 11:25:55 am
content: In the EU, Netherlands is the leader with something like 1KW/person.And I see plenty of empty roof spaces.Though keep in mind that Google maps lies about the date of the highres images.

author: themadhippy
author_rank: Super Contributor
timestamp: July 20, 2024, 11:50:09 am
content: QuoteThat because its the uk, not really known for its abundant sunshine.What we need is a wet panel ,one that converts rain to electricity.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 20, 2024, 01:17:14 pm
content: The angled and relatively steep roofs shown in the picture from the UK are not ideal for PV panels. Unless you get triangular panels, there is not that much useful south facing roof. Some of it may also so shadows from neighbors.The other points is the steep angle that does not give ideal power and makes mounting more tricky.

author: tszaboo
author_rank: Super Contributor
timestamp: July 20, 2024, 01:26:06 pm
content: Quote from: Kleinstein on July 20, 2024, 01:17:14 pmIt's very easy to mount panels to angled roofs. I have 45 degree, and they installed it in an afternoon.Because of solar insolation, you get surprisingly large amount of power out of a roof even if it faces North. The difference will be ~20-30%, more or less, depending where you live of course. Better if it's not directly North. I suggest calculating it with solar calculators for each case. And the difference in production can be easily overcome with just a few extra panels (and same inverter), that is a few hundred EUR extra cost.

author: nctnico
author_rank: Super Contributor
timestamp: July 20, 2024, 02:35:45 pm
content: Quote from: tszaboo on July 20, 2024, 11:25:55 amAgreed. In 2022 / 2023 / 2024 a lot of new solar panels have been installed across the EU due to high electricity prices but Google's images lack behind. From looking from my office window, I notice half of the solar panel installations aren't visible on Google yet.I disagree on North facing panels though. You get like 50% output (or less) compared to the ideal position. I could add more panels on the rear side of my roof (facing North-North-West) but the ROI just isn't there.

author: nctnico
author_rank: Super Contributor
timestamp: July 20, 2024, 02:59:42 pm
content: Quote from: EEVblog on July 20, 2024, 11:12:33 amThat is too optimistic. Look at numbers 31 and 32 Eastfield cres. Number 31's roof is full. 32 has a dorm and roof windows. For sure you can fit a few panels on number 32's roof, but not that many. Especially if the dorm hasn't been constructed to deal with the weight of the ballast needed to mount solar panels on a flat roof. In general the roofs of these houses are rather oddly shaped making it hard to do a straightforward install; it takes more effort to mount rails and wiring. And as has been pointed out before, the state of the roof needs to be good enough for a succesful installation of solar panels. IOW: just looking at Google maps and pointing to empty roofs is not good enough. For example: where my father lives nobody has solar panels. Not because they don't want to as the roof is at the perfect angle for solar panels, but because the state of the roofs is too poor (note: as typical for the NL, these homes are build in series so all the home in the street are identical where it comes to construction and age).

author: coppice
author_rank: Super Contributor
timestamp: July 20, 2024, 03:51:01 pm
content: Quote from: EEVblog on July 20, 2024, 11:12:33 amHuh? The one house in that picture with solar seems to have used 100% of their roof which is facing in a practical direction. You do realise they can't start putting solar panels on other people's rooves, don't you?

author: coppercone2
author_rank: Super Contributor
timestamp: July 20, 2024, 03:59:02 pm
content: I have very low faith in the integrity of rooftop hydraulicsI consider the industry is full of bullshitters that just claim something wont leakpersonally, to have a array of heat exchangers on the roof, I would need to have VERY nice profit from this addon

author: tszaboo
author_rank: Super Contributor
timestamp: July 21, 2024, 01:13:27 pm
content: Quote from: nctnico on July 20, 2024, 02:35:45 pmHere is a report for a randomly selected house (King's Palace) in the Netherlands showing that at 30 degree angled roof, a exactly North facing roof would make ~60% of the South facing roof.The south facing system generates 4.4 MWh with 10 panels, the North facing 3.2 with 12. This is as bad as it gets for Azimuth. And of course elevation can get worse.Assuming 4K installation cost, and 25 cent electricity price the North facing panels have a ROI of 5 years, or 20% per year.

author: EEVblog
author_rank: Unknown
timestamp: July 22, 2024, 01:10:45 am
content: Quote from: coppice on July 20, 2024, 03:51:01 pmErr, if you can't fit some more panels on that roof then you aren't trying.There are panels on both east and west sides, and room to fit a bunch of extra on both sides.

author: EEVblog
author_rank: Unknown
timestamp: July 22, 2024, 01:15:04 am
content: eBay auction: #Quote from: nctnico on July 20, 2024, 02:59:42 pmDifferent argument entirely. We are talking about houses thatalreadyhave solar panels, and whether or not it is better to simply find some space to fit a few more panels, or to install a complex piping system to cool down the existing ones to improve the efficiency.

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2024, 11:15:21 am
content: That is a semi-detached house, and they can only use their half of the roof. The panel of their own roof they haven't used appears to be facing away from the sun, so it would be useless at the UK's latitude.

author: tszaboo
author_rank: Super Contributor
timestamp: July 22, 2024, 11:21:12 am
content: Quote from: coppice on July 22, 2024, 11:15:21 amMost of the UK is the same latitude as here, not useless, 60% of south facing (see above), probably 80% as good as the east or west facing. There is a second shed. There is a second roof a bit lower. Plenty of space.100% of the time it comes down to: "But I dont wanna install panels"

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2024, 11:45:35 am
content: Quote from: tszaboo on July 22, 2024, 11:21:12 amPutting panel on a shed seems a bit desperate, considering how flimsy most sheds are. The strip of lower roof on the left is probably in shadow a lot of the time. They usually are. That reduces the benefit.i think they would have got more out of half width panels to use the last bit of the main roof space on the left hand side in the picture. Half width, half length, and triangular panels wouid allow a lot of fill-in on a typical UK roof, but you don't see them. Unless people live in a simple terraced house the utilisation of their roof is considerably limited by the types of panel available. That is something solar tiles might be a lot better for, if someone can eventually provide them in an effective form.

author: nctnico
author_rank: Super Contributor
timestamp: July 22, 2024, 06:10:41 pm
content: Quote from: EEVblog on July 22, 2024, 01:15:04 amActually you don't need a super complex piping system to just cool solar panels. You can buy a misting system for a few dollars which sources water from your tap water supply.https://aliexpress.com/item/1005007122639641.htmlPut it under your solar panels and done. The ROI depends on how much the misting system costs to operate in terms of tap water use. For hot water a seperate system with tubes + collectors is likely a better (more cost effective) option.