 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Solar : Cooling solar panels might pay (well?).
Page 1 of 2   |
|||||
| Author | Message | ||||
| neil0mac Senior Member  Joined: 26/12/2009 Location: AustraliaPosts: 210 |
I know 'everyone' doubts the economics of panel cooling, but have these factors actually been considered - or even calculated? 1. Keeping them (and the inverter!) cool can increase power by 'up to' 20(?) percent. 2. The inverter won't shut down during peak insolstion periods. 3. Panel degradation over '20 years' is (largely?) due to overheating, so that even half of that loss (0.5% per year) is surely worth preventing? A rough calculation suggests that half that 1% loss is about one years total production over time. When you add the actual lost output per day (the '20%'(?) so called 'system losses') you are losing around 6 years (~ 1/3) of power production? Or have I got it wrong somewhere? |
||||
Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Sound like just another good reason for a solar tracker to get them off the hot roof and out in the breeze to me. Pete. Sometimes it just works |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
A sort of 'Frying pan OR Fire' situation? Methinks, tracker AND cooling is the way to go! I'll wait for evidence to the contrary. Neil. |
||||
KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Neil you are fast becoming quite the expert. if you have the time (and could be bothered) panels are as you know rated at 25degC and loose 0.5% of output per degree of temp rise now, panel typically runs at between 25-35deg hotter than ambient thus calculation would be along the lines of reduction in that rise of say 1/2 thus moving sufficient air (how much could be calculated I guess based on insolation level) thus instead of the panel running 1KW at 25deg its running at 60 degrees and output is down 17% or 170W (over a day that adds up really quickly!) you get the idea, given its your post, i look forward to your results!! 
The maths could get quite messy i think, almost easier to have a working model for results! Luck favours the well prepared |
||||
Loomberah Regular Member  Joined: 11/06/2008 Location: AustraliaPosts: 43 |
I have often given my panels a spray of ~20C water on a hot day when the panels are over 60C on front and rear surface, and always gained 20-25% output. Of course not long after I stop spraying, the output decreases again. ~20 litres of water only gives a short period of cooling and the water is lost. As Neil and I discussed the other day when he called in, you would have to use a closed loop system for the coolant, otherwise there would be too much demand for water. A large dam or very long underground pipe to disperse the heat would do it though. I've looked at the logistics of doing that on my trackers, but the weight of even a 5mm depth of water and the 1.2mm sheet of Aluminium to enclose it gets a bit prohibitive, weight and cost wise. Loomberah weather +solar&UV, astronomy, photography, organic farm |
||||
MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
As long as everyone is cool with using trackers, why not use a tracking flat-plate heliostat (mirror) on a gimbal and hit the panels with 'reflected' light? By using a second-surface flat mirror, it would capture much of the solar radiation within itself and pass on the rest of the energy to the photovoltaic panel. That means the panel(s) could remain in a fixed position, making them more easily serviceable and likely at ground level and overall cooler than if they were bombarded with direct sunlight. I've never actually tried it, but I threw up a post somewhere back in the day and everyone seemed to think reflected light would do as well as direct light as far as producing electricity from the photo cells, so this might be worth a try just to allow the panels to operate at a lower overall temperature. Just an idea. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
||||
| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
What percentage of the incident radiation would a good mirror actually absorb? If you reflected 100% of the light off a mirror and all of it hit the solar panel why would it run cooler? Have a look at this project here and use the cooling water to heat a swimming pool. |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Gordon, you might like to comment on the scale an glass comments above somewhere. I do have the option of running a closed reticulation system by using the submersible on the bore with an open return pipe. No resevior, and a constant supply of cool water at around 18 deg. C. As you well know, mate, I can hang another tonne off my tracker (with its six 'legs' and five feet' - no further comments at this stage of development!), so weight isn't a problem. The problems with an aluminium sheet are to do with water in contact with the electrics one of and sealing it to the panel frame, as well as the cost and weight. I am seriously looking at using a 'plastic bladder' with a light internal frame to keep it taut so that there is minimal pressure on the glass. BTW, the glass in solar panels is far too thin to withstand the water pressure is any 'simple' add-on. You could need glass around the 12 to 16mm thick mark to prevent a disaster. (Think domestic 'fish tanks' and they have considerably smaller glass areas!) |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
These PV panels (see PVCool.com.au) were quoted last year as 90 Watters, now they are 140 with the same specs. as far as I can tell (so the mirror only adds 50% in reflected light?) but it also adds heat too. They are a Russian design and. up there. they have aluminium fins on the backs of the panels and draw warm air down into the building. Ummm. Now folks will see why I am 'obsessed' with cooling! |
||||
| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
|
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Food for thought! (I must confess, I thought the glass thickness 'story' from a (Tamworth) glazier was a bit far fetched - but he was the 'expert' - so I didn't argue.) |
||||
| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=Davef]What percentage of the incident radiation would a good mirror actually absorb? If you reflected 100% of the light off a mirror and all of it hit the solar panel why would it run cooler? I dunno! I used to have a concentrating solar collector that I used for fractional distillation of wood chips to make ethanol. The mirror array was stationary facing north (I live in Southern California, USA). I used a flat-plate, second-surface mirror to track the sun and bisect the angle between it and my target (the mirror array with fixed focal length) and the flat mirror got pretty hot, while the concentrator array didn't. "How much" hotter or cooler wasn't an issue, so I never measured it. Now, I don't know if reflected sunlight will create as much or as high quality electricity from a PV array as using direct sunlight. This was "Just an idea" I thought I'd throw out. If anyone knows the answer to this, now's the time to step up to the plate! As for Davef's second question, it's been my experience that 100% of the light DOESN'T get reflected and therein lies the rub. Like I said, I don't know about the quality of the PV-generated electricity from a secondary source (a reflection in this case). . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
||||
| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
Back surface mirrors generally relect about 80% of the incident light. 2 reflections puts you down in 60-70% territory, so you'd expect 60-70% of the output. [quote] Like I said, I don't know about the quality of the PV-generated electricity from a secondary source (a reflection in this case). [/quote] The electricity will be of the same quality, but there wont be quite so much of it ;) Loomberah weather +solar&UV, astronomy, photography, organic farm |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Does anyone know where Mylar fits within the 'reflective index' (for want of a better term!) range? |
||||
| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
Various above 90% I suspect. Loomberah weather +solar&UV, astronomy, photography, organic farm |
||||
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
The problem with mirrors, is that these get dirty as well. we need a dustrophobic surface for the panels, combined with a decent air cooled heatsink on each panel. :) I just increased the number of panels to get more power. the panel temperature problem may be of significance in central AUS, but for most coastal areas, there would not be too many really hot days, and the other days, there may be a few hours around midday with a reduced output due to cell temps. The cell derating with temperature, flattens the daily peak power output, during periods of maximum solar irradiation. There may be a short period of the day when the maximum power was reduced by up to say 15%, but a lot of the day, the derating would be between 5 & 10%. To me the jury is still out, and I will leave my system alone, wrt a water cooled/washed option. Gordon. become more energy aware |
||||
| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
On long summer days of 35C+ that "short period" might be 6-8 hours long, ie a large proportion of the day. Neil gets plenty of days like that in summer. I'm up in the hills with my panels at nearly 700m ASL, so a few degrees cooler than Neil, and I see long periods of low output in summer too. The gains are quite immediate and dramatic when I cool my panels, so I think Neil's proposed array would benefit if he can make a reliable cooling system that doesn't consume too much power. Loomberah weather +solar&UV, astronomy, photography, organic farm |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
So the mylar needs to be 'grounded'? Since the Array/tracker should be grounded, that isn't difficult. Just for the record, we've had periods where the minimum temp over 24 hours has been 35 deg. plus for days at a time. Not every summer, of course! |
||||
| Loomberah Regular Member Joined: 11/06/2008 Location: AustraliaPosts: 43 |
I'm not sure how successful you would be trying to Earth a sheet of Mylar, given that it is mostly an insulator- the reason it gets charged up in the first place. The Al coating is extremely thin, and I'm not sure how reliably you could make contact with it in the long term. Loomberah weather +solar&UV, astronomy, photography, organic farm |
||||
| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
I'm thinking that it might be attached to a (slightly convex) metal sheet ... or ... held in place with (mylar covered?) metal straps (provides security against wind damage as well). |
||||
| Page 1 of 2 |
|||||
 Print this page |
