Stick on solar panels for camper shells?

[Metcalf]

I have started looking around for some solar power options for my new Dodge expedition truck project.

Has anyone seen a thin film solar panel that was designed to cover the top of a camper shell?

I know a lot of people like having a rack on top, but I think it would be very sweet if the entire top of the camper shell and/or the truck cab could be covered in a flexiable thin film solar panel. If you did it right you wouldn't even know it was there.....

This company makes a nice large 4'x8' panel that sticks on. Its semi-ridgid though and designed to be stuck on a flat surface. I e-mailed them asking if the panel could be stuck to something with a slight radius like a camper shell.



http://www.lumetasolar.com/products/powerply

This company also has some nice stick on solar panels. All the production models are too long for a standard long box camper shell though.

http://www.uni-solar.com


http://www.uni-solar.com

[adventureduo]

Im not aware of any stick ons , but what you post is very cool., i wonder what highway speed they'd hold up too. Not like we do 90mph anyways.

[whatcharterboat]

I’ve mentioned them on here before but we’ve been mainly fitting Uni Solar since I started at Allterrainwarriors 7 years ago. As you say they are sometimes an inconvenient size if you have other roof protrusions to work around such as roof vents or hatches The 68watt laminates are about 2800mm long and 400mm wide. The advantages on a camper are fantastic. First choice every time if the space is there. Again, only if the space is there



IMO the advantages are :
· Non-skid surface you can walk on. One of our guys even loads a canoe on his with some padding although it’s not really recommended. So they are definitely hail proof and generally indestructable.
· The non skid is a result of a prismatic surface designed to increase power output at low sun angles.
· They are Amorphous cells which are (albeit much bigger) very efficient in cloudy conditions and partial shading.
· I work on de-rating a normal poly or mono panel down 20% when mounted flat on an RV roof. The Uni-solar seem to give close to rated output even when mounted flat. Very important consideration for a camper. (Especially when sizing any system)
· Theft proof. As long as the surface is clean and smooth, once you stick them down they are there for good. No second chance.

“i wonder what highway speed they'd hold up too.”

You could never go that fast to be a problem in your DD let alone a camper. As long as it’s done right.
· They can be mounted on a curved surface. Not sure exactly but I once mounted them around a 6” radius “s” over a hump in a roof with out dramas. Perfect for a yacht roof for example. They are very flexible in one direction only. Lengthways OR width ways.
· Did I mention they’re cheap? Here anyway.

Disadvantages:
· Weird size may not be suitable
· Non – transferable to another vehicle.
· Overall Amorphous cells take up much more area than Poly - crystalline or Mono - crystalline Panels for the same power output
· Wiring comes out the top (sunny side) of the panel, which has to be considered, and the supplied junction boxes are rubbish. Don’t use them.
Just a late edit: wiring can now be provided exiting the under side of the laminates

[whatcharterboat]

Mistake. That should have been

"Disadvantages:
Weird size may NOT be suitable"

And what are those guys doing mounting these panels flat anyway? Are they on the Equator, do they like throwing money away, did they leave the rack in the truck, loose the plans?




I'm sure they have a logical excuse. Going to have a look at lumetsolar.com and find out.

[michaelgroves]

· Did I mention they’re cheap? Here anyway.

What sort of money would a 68W panel be - ball park figure?

[bigreen505]

I’ve mentioned them on here before but we’ve been mainly fitting Uni Solar since I started at Allterrainwarriors 7 years ago. As you say they are sometimes an inconvenient size if you have other roof protrusions to work around such as roof vents or hatches The 68watt laminates are about 2800mm long and 400mm wide.

That seems very inefficient for the size. I guess if the price is right that could be a good way to go.

[whatcharterboat]

That seems very inefficient for the size.

Very inefficient for their size. No question about it. About 8 or 9% compared to 12 to 17 for poly or mono.

But over the period of a day I bet a 68w Amorphous PVL will put in considerably more power than a Poly or Mono. There is also temp de rating of a panel to consider as well . I never even mentioned that. Amorphous cell have negligible de rating for temp. This is another thing to consider if you are in hot desert country.

As for price > check how they compare in the US. They're very good price wise here.

[bigreen505]

But over the period of a day I bet a 68w Amorphous PVL will put in considerably more power than a Poly or Mono. There is also temp de rating of a panel to consider as well .

Care to clarify that comment for those of us who frankly haven't got a clue. Or perhaps just me.

First, what is a temp de rating? Second, I'm thinking at a PV panel of that size should be at least double the output, but that may be totally off base.

[riparious]

Warning: I am a solar weenie, so this is kind of long.

Whatcharterboat
Module mounting angle - Most commercial scale grid-tied roof systems are mounted nearly flat for two reasons. First, rows of angled racks require shade spacing between each row. The flatter the modules, the less shade spacing required, which means more modules and thus more power production in given roof area (Though less power per module). Second, in warm climates with high AC loads, electricity is much more valuable in the summer than the winter, which happens to coincide with the sun being at a very high angle in the sky, so the economics often favor flatter mounting angles. If you just have one or two modules as you would with an expedition rig, you want to squeeze every watt out of them, so point them as directly to sun as you can. You make good points about the advantages of thin film for expedition use.

BiGreen505
Temperature derating - This is counterintuitive, but photovoltaic modules actually product less power when they get hotter. The energy is produced from the light, not the heat. Typically they lose about ˝ percent per degree C for mono- or polycrystalline cells, and much less for thin film systems. Manufacturer spec sheet will usually have this information for their modules.

Power per surface area - Since PV output varies greatly with light intensity and temperature, Standard Test Conditions (STC) have been developed to rate modules – 1000 watts of light per square meter at 25 C. So a ’65 watt’ module will produce 65 watts at STC, and less as temperature climbs or light intensity drops.

So at STC:
Thin film at 8% efficiency will produce 80 watts per square meter.
Polycrystalline at 14% will produce 140 watts per square meter.
Top of the line mono-crystalline at 20% will produce 200 watts per square meter.

You rig will rarely if ever see STC, so in the real world you will probably see significant losses due to temperature and partial shading with the mono/polycrystalline module. Also, even though the glass modules are about as durable as a windshield (both are laminated safety glass) the flexible thin film will probably survive the harsh conditions of being permanently mounted on an expedition rig much longer.

My ideal system would be a thin film module on the roof as a ‘set it and forget it’ power source, supplemented with a mono-crystalline module that I set up on a portable stand when camped in one location for a while. This would add flexibility as I prefer to park and camp in the shade, but have my solar in the sun.

[whatcharterboat]

Care to clarify that comment for those of us who frankly haven't got a clue. Or perhaps just me.

Not at all. They’re very valid questions and I should be able to support any comments I make anyway. Especially a bold one such as this. Just hope you don’t get bored. And I have to talk in metric so you may have to go to www.onlineconversion.com if you want to check what I’m saying.

Let me answer this one first.

“I'm thinking at a PV panel of that size should be at least double the output, but that may be totally off base.”

OK IIRC at the earth’s surface a we get about 1 kw of solar energy per square metre and in space it’s about 1.33kw per sq.m. Therefore if a solar panel is about 1 sq.metre and is rated output is 80watts, it is said to be 8% efficient. If it is more like 130watts it could be said to be 13% efficient. This is a rough guide but you should get the idea.

BTW When I say if a solar panel is a certain size I mean the area of the cells on the panel not the length and width of the outer frame. There are two trains of thought here. One is to maximize the area used by filling the entire panel with cells so no space is wasted. The other is to give the individual cells a border around them of a reflective material to aid in cooling the overall panel and reduce the cell temps. More about that in a sec but you often see this on more efficient and costly mono crystalline panels.

So typically Amorphous cells are 8 or 9% efficient, poly crystalline are 13 or 14%. And mono maybe 17 to 19% plus. I haven’t looked this up. Just what I remember from early study so I hope it’s still accurate. I often have people in the solar industry say “why do you use the most inefficient panels” (probably because they have their own sales agendas). “Panel efficiency” as a term is only relevant to the size of the panel, not how much they put out or more importantly how they actually perform on the roof of a camper in offroad conditions.

“what is a temp de rating?”

Ok this may not sound logical but solar panels put out more power in more sunlight but they put out less power as the temperature increases. Crazy, I know. Luckily the solar energy is usually going up at the same time. But the big thing is that if you can lower a solar cells temp you can increase the output. Actually I talked to a guy here who is developing a solar mat that has glycol tubes running through it. The idea is that the panel is cooled slightly by the glycol and the heat is transferred to the hot water tank. So more efficient solar electricity and solar hot water in one mat. He’s hoping to have one available for the RV market in the not too distant future.

(BTW if you are using polys or monos I always thought you should leave a space under them to allow airflow to reduce temps.

Anyway this is probably not critical to the system design of an Expedition truck, so don’t get too wrapped up in it. An Expo trucks electrical system usually has very fluid needs and multiple charging sources. At the very least, an expo truck with solar will also have the ability to charge from the engine and / or possibly a small generator. So worst case scenario, if your solar can’t keep up due to the conditions then you may have to run the genset or if you are moving on that day, the truck will charge your house batteries without any dramas. However if you are designing a remote area power system, say for a shack in Baja, things may need to be a little more carefully thought out. Actually if you aren’t getting the rated output from a panel on your truck and you want to know why, cell temp de rating is one factor that needs to be considered.

So to calculate cell temp de rating

F temp = 1 - (y x (ECT day – T stc))

f temp = temperature de rating factor
y = power temperature co-efficient per degree Celsius (typically 0.5% for poly crystalline, 0.4% for mono crystalline, where as amorphous are less than 0.2% ).
ECT day = average daily cell temperature in degrees Celsius
T stc = cell temperature at standard test conditions in degrees Celsius

BTW as a general rule (from the Aust Standards) the average daily cell temp is the daytime average ambient temperature plus 25 degrees C. Tstc should be given on the solar panel data and on the BP panel I looked at recently it was 25 deg. C. That is also a general rule Tstc = 25deg C.

So to give you an example, on a 30deg C day (86deg F) with a 100watt poly panel

F temp = 1 – (0.5% x ((30 + 25) – 25))
F temp = 1 – ( 0.5% x 30) = 1 – 15% = 85% = 0.85

So theoretically your 100watt panel can now be reduced to 85watts through temperature. For the same conditions an amorphous panel might go like this

F temp = 1 – (0.1% x ((30 + 25) – 25))
F temp = 1 – (0.1 % x 30) = 0.97

Or worst case maybe F temp = 1 – (0.2% x 30) = 0.94

So the amorphous on the same day is only temp de rated down to between 94 to 97 watts.

To sum up, cell temperature is only one of half a dozen different factors to de rate for and consider when comparing different types of panels but still worthy of note. Remember factoring this into a design is far more critical in a fixed system purely dependent on solar and not a camper. If the solar on the truck isn’t right, well it means you will just spend more on fuel. However I hope this backs up my original claim about an amorphous panel outperforming others when mounted flat on the roof of a truck out in the hot desert.