Making Solar More Effiecient by cooling the panels

[Rock-N-Ruth]

This is our bus:

These are some of our solar panels:

This is our home and it is a work in progress. We have been depending on the sun for our electricity since 2011. One of the factors that affects solar panel efficiency is heat. Kinda funny that it takes sunlight to make the electricity but the heat from that sunlight slows the process. I have an idea that might add some efficiency and produce some hot water.
On any given day the temperature on the underside of the panels runs about 110 to 125 degrees Fahrenheit. For more than a year we collected hot water by laying a roll of black irrigation pipe on the ground and letting the sun heat it up. It gave us nice hot showers by 11 am. No fancy solar collectors, just $15.00 worth of plastic pipe and a garden hose. So, why not do the same with our solar panels?
I haven’t got the whole thing worked out but I am thinking using the same cheap irrigation pipe to make a heat sink under each solar panel and connect them together in series. Circulate water with a low volume pump to a storage tank. The storage tank can feed my hot water tank and thus any captured heat can be used to wash dishes and take showers. In the mean time it is also reducing the temp of the panels a bit allowing them to produce just a little better.

 

[john61ct-SKO]

There are commercial products designed to do exactly that.

Never caught on that much

 

[Rock-N-Ruth]

Perhaps price may have been a factor in them never catching on. I think asside from my labor the heat sink will run about 20 bucks per panel. Most of the cost will be the materials I use to attach the pipe to the underside of the panel.

 

[Iceni John]

If you want to harvest more power from your panels, tilt them! In the summer it won't make much difference, but in the winter with low sun and shorter daylight hours it will be useful, and the further north you are in winter the better it will be to tilt them. It's really not that difficult to make an effective tilting system for curved-roof buses: I made a walkway between my two roof hatches, then hinged the panels to the walkway. When stowed down for travel they are at 21 degrees below horizontal, but either side can be raised to 21, 33 or 45 degrees up for better insolation. Just as importantly, the panels always have good airflow under them so they never get much hotter than ambient air temperature; they shouldn't derate much on hot summer days.

I'm also going to make two water heating solar panels that will tilt just like the PV panels, but my biggest concern is how to prevent the water flashing into steam on hot days. Some sort of drainback system will be needed, but as these are used in RE setups for houses it shouldn't be hard to find a design that will work for the bus.

John

 

[joeblack5]

Doubt if you will see any gain.. Probably your batteries are full by 2 pm in that weather.. It is nice to use the heat .. At least the overall efficiency gets a lot higher.

Can not see enough detail from you solar racking but I would brace at least the outsides. if the wind from an oncoming truck hits you the wrong way that might come of.

Good luck. Johan
We heated our thee water to a boil like this.
Line reflector and vacuum tube..

 

[Rock-N-Ruth]

Lol. Thanks for your concern about the racking. The rear system is made out of 2x6s and was meant to be temporary last July. Depending on which way we park here in New Mexico, we often have 30-5mph crosswinds. Ocasionaly we get Gail force wind gusts from dust devil's. The panels hold fine. Though there is no side bracing as we have seen others do, 5000+ highway miles and a year in the desert indicate stability. We used 1" EMT for the front racks, but again no side brackets or stabilizers. They get the full head of wind from 75mph travel and not an indicator of dress. I was originally worried about vibration and cracking the glass.

 

[joeblack5]

Your call, I would not trust emt to handle shock loads since it buckles. I am less worried with the 2x6 as long as they do not rot.
People had large solar panels blow out before, even when sturdily mounted.
If you have a good insurance that covers the person driving behind you when it goes wrong then I am all good, Life is a risk..
You 74 MPH, the 18 wheeler 75mph and the geo metro behind you. The energy in the wind goes up with the third power of the velocity.
That is the reason why windmills are so hard to build.

Good luck,
johan

 

[naes14]

So you are wanting to water-cool your panels? That's interesting, I haven't really looked into how cooling the panels affect efficiency. The byproduct from this endeavor would effectively be solar hot water. My question would be about the interface from the panel to the irrigation pipe. What kind of conductor could you use to wick heat from the panels?

 

[Rock-N-Ruth]

So you are wanting to water-cool your panels? That's interesting, I haven't really looked into how cooling the panels affect efficiency. The byproduct from this endeavor would effectively be solar hot water. My question would be about the interface from the panel to the irrigation pipe. What kind of conductor could you use to wick heat from the panels?

Dare I say, nail, head, right on it? This is the part of not quite worked out that I'm am currently thinking on. The intention is low cost, simple and light. I have considered simply using epoxy and fiberglass cloth to attach the pipe to the backside of the panel. Still in the planning stages. Suggestion?

 

[kazetsukai]

Aside from weight, think about the energy needed to circulate liquid. I hate to pile on with pragmatic challenges to this idea, but a few key questions:

• Have you measured panel output?
• Have you determined that heat is significantly enough diminishing your yield to warrant this?
• Why not build a solar water heater panel? Its fairly easy to DIY.

I considered doing this, and tilt, until some of the data started coming in. For recovering energy, not worth it. For hot water, _maybe_. If that's the primary objective.

 

[joeblack5]

I used to experiment a lot with solar collectors..
Experimented with corrugated plastic sheet used in the packing industry.
The problem was sealing and reconnecting the ends. But with the now better and easy available adhesive/sealant this might not be so difficult.

If you take the 6MM thick stuff then the water channels will be square . The advantage is that almost no conduction has to happen besides directly thru the thin plastic.

We used to slice plastic pipe and wedge it open, then insert the corrugated sheet and seal around it.

I think it would be important to get a sheet the same size as the collector to absorb the heat as evenly as possible .

Then there still is how to press it evenly against the back of the panel. Or glue it?

Maybe I will do an experiment myself with an old panel.

The thought is intriguing.

Having separate hot water panels instead of solar panels does not seem
effective use of your roof space . It is easy to make hot water with a heat pump and that efficiency is pretty on par with a hot water collector.

Just looked some up, not packing industry but green houses.
6MM x 48" X 96" white twinwall polycarbonate sheet
$81.86 eplastics.com

Here is someone who put up an article about what we experimented with in the 80's

https://www.instructables.com/id/Build-your-own-flat-panel-solar-thermal-collector/


Good luck.

Johan

 

[Mudhutwarrior]

Your call, I would not trust emt to handle shock loads since it buckles. I am less worried with the 2x6 as long as they do not rot.
People had large solar panels blow out before, even when sturdily mounted.
If you have a good insurance that covers the person driving behind you when it goes wrong then I am all good, Life is a risk..
You 74 MPH, the 18 wheeler 75mph and the geo metro behind you. The energy in the wind goes up with the third power of the velocity.
That is the reason why windmills are so hard to build.

Good luck,
johan

I remember reading where an RV lost a panel and it nearly killed someone and some poor woman here just got killed by a tire on the back of a trailer poorly secured. Its pretty irresponsible to secure panels haphazard and guess if they will hold.
And people wonder why its hard to get buses insured.


Other issue is many old timers on the board encourage this kind of thing.
Crazy

 

[djmitzlplick]

Solar on Bus

Nice Setup! I wanted to be able to use more of my roof, so chose a slightly different configuration for my 8 panels.

Where did you get your panels?
What is your capacity?
Are you using any battery backup?

 

[Rock-N-Ruth]

Nice Setup! I wanted to be able to use more of my roof, so chose a slightly different configuration for my 8 panels.

Where did you get your panels?
What is your capacity?
Are you using any battery backup?

I like the arrangement. Got 8 of my 12 sunpower 327W panels from a wholesaler in Albuquerque @ $140.00 each.
Got the last four from these guys. https://phoenix.craigslist.org/nph/fod/d/phoenix-sunpower-solar-panels-new-30/7140533171.html They are new old stock. At .30/watt it's a steal. You bet we have batteries. We have three systems. 12v 8 Everlast 29D in parallel. With a 2500W modified sine wave inverters. This is our tertiary system for when the clouds stay for 3 or four days. Our secondary system runs on the front four panels. It has a 432 AH ATM bank with a 5kw true sine inveter. Runs the freezer an charges the 12v backup system. By the way our alternator failed a year ago and we tied the 12v backup to the bus bank. Was meant to be temporary but we have about 5000 miles without an alternator. Our primary system runs off of 8 solar panels. It powers air conditioning, fans, tv, lights, chargers, and bi-pap machines. 440 AH LiFePo4 batteries we got last month from these guys https://www.ebay.com/itm/2-matched-BYD-LiFePO4-24-volts-Battery-Packs-FREE-SHIPPING-/392798230109 we love em.
I have been thinking about maybe doing something like you have done and filling the under deck with foam insulation.

 

[Rock-N-Ruth]

I remember reading where an RV lost a panel and it nearly killed someone and some poor woman here just got killed by a tire on the back of a trailer poorly secured. Its pretty irresponsible to secure panels haphazard and guess if they will hold.
And people wonder why its hard to get buses insured.


Other issue is many old timers on the board encourage this kind of thing.
Crazy

What's crazy is people with out experience and stories they heard or read about making disparaging comments without any basis. You call my structural engineering haphazard and insult my work,sensibility and even ethics, without so much as a moment of practicle application. I call that crazy.

 

[FatBoySTL]

Instead of a home built water heater setup, have you considered running something like this?

Home Depot: Above Ground Pool Solar Heater

This would save you a LOT of time in engineering if you could figure out how to secure them to the underside of your panels.