Stick on solar panels for camper shells?

[whatcharterboat]

Another question: How critical is dirt and dust to the comparative output of the panels? I'm know how quickly my roof gets dirty while travelling - not absolutely filthy, but it certainly doesn't stay pristine for any length of time!

Without writing another War & Peace , "Environmental" or "soil" derating might be around 0.90 but there is alot of variables and this figure is really only a ballpark so you get the idea. Obviously Keep them as clean as possible.

Riparious must have gone. That was getting interesting.

Thanks Michael

 

[michaelgroves]

Apologies to you too Michael. I skipped around that one. Expect to pay around $10AuD per watt for amorphous panel in Oz. Polys are around the same money.

No apology necessary, and sorry if I put you in an awkward position!

That's a great way to put it - one can get an idea of what one's particular requirements would cost for any given situation. Presumably they're a little more expensive per watt when one goes for smaller panels, and cheaper for bigger panels, other things being equal.

Though any battery charging is useful, we found when we camped for several days at a stretch, that we required about 150A-hrs from our 12V system, per 24hr period. This covered the use of our freezer, 12 fluorescent lighting, occasional computer use, and various other sundry bits. If we assume 12 hours of sunlight per day, a 150watt (actual output) panel would be adequate. This probably translates to a nominal 200W panel, I would imagine, if we wanted to be independent on other sources of power.

 

[whatcharterboat]

Michael. No >> this is way off. Just on my way to work. Will reply tonight in detail

 

[michaelgroves]

Michael. No >> this is way off. Just on my way to work. Will reply tonight in detail

Ok, thanks!

Just to clarify my calculations: 150Ah @ 12V = 1.8kWh per day.
Power generated at a continuous rate of 150W, produces 1.8kWh in a 12 hour period.

No?

Or are you thinking my assumption of power consumption of 150Ah / day is unrealistic?

 

[bigreen505]

Thank you all for your responses and clarification.

I think Riparious makes a great point about the need to have solar panels in the sun. If you are camping in the sun it makes sense for them to be permanently mounted to the vehicle, but if you are camping in the shade, they need to be portable.

$10/w is a good rule of thumb for finding the balance between output and cost -- thanks for that!

 

[whatcharterboat]

Just to clarify my calculations: 150Ah @ 12V = 1.8kWh per day.
Power generated at a continuous rate of 150W, produces 1.8kWh in a 12 hour period.

OK Michael. The calculations are exactly right but you are saying that there is 12 hours in a day when a panel will be making rated power. That’s what is way off.

We said earlier that at the earths surface at midday we get about we get about 1 kw /m2 and in outer space it’s 1.353 kw/m2. That’s the solar constant >>> 1.353 kw/m2. As the sun’s rays pass through the atmosphere (air mass) they lose that 0.353kw/m2 at midday. As the day moves on and the sun gets lower in the sky, the rays have to pass through even more air mass to reach the panel than when the sun was directly above. Pretty simple heh?

Any way this would be so much easier if I could draw a graph on here but if you imagine a graph with the Iraddiance on the vertical axis from 0 up to 1 kw/m2 and a time clock at the bottom say from sunrise at 6AM, 7Am, etc, all the way accross to sunset at 6 PM. Now obviously at sunrise the power will start from zero and slowly rise to the highest point at midday and drop back to zero at sunset 12hours later. That’s where you got your 12 hours from isn’t it?. Your graph should look like a hill with everything under the line shaded in. Bare with me.

When you’re designing a solar system you need to know how much solar energy you can expect from the sun for a given location. Well a panel is rated at STC (as Ruparious explained ) based on 1kw/m2. So (how do I explain this?) if you take the area of the shaded section of your graph and squash it up so that it looks like a rectangle 1kw/m2 high on the graph , it will only around 6 hours long . These are called Peak Sun Hours (PSH). I’m around latitude 27. 5 deg South and PSH here vary between 5.2PSH in December to 4.4 PSH in Jun but I work on an average of 5 PSH because I design more for Summer months when the truck’s fridge/s ( usually the biggest DC load on a truck) will be working harder.

Have a look at this world chart. http://www.oksolar.com/abctech/images/world_solar_radiation_large.gif It will give you an idea how PSH can vary. Instead of PSH some maps show KWh per square metre. Same thing and still relates to how much solar energy will go into your panel over the period of a day. So you see it’s not as simple as saying there is 12 hours of sunshine in a day. Your 150watt panel at my location would average about 750watt/hrs/day or 62.5amp/hrs/day

Not sure where you got you DC load of 150amphours from but if its accurate and you were trying to meet that load purely with solar (not usually done on a truck) then you also have to factor in the regulator efficiency although most of them are very good now ( 95% plus) and your overall system efficiency or in other words, battery charging efficiency. Unfortunately if you put 100 amphours into a battery you might only be able to get 85 back. Don’t want to sound like an alarmist but that’s the way it is. This efficiency varies and older lead acid battery systems I ‘ve worked on were as bad 0.80 efficiency.

All this needs to be considered. Actually 150AH/day sounds a little high for a 12v compressor fridge, a couple of lights and a computer. If your fridge has a Danfoss pump it’ll run around 4.5A and if the insulation is allright on a day with average ambient temperatures it might have a duty cycle of 10 or 12 hours??? I don’t know how hot it is were you live. Man , it’s hot here right now. Anyway that ‘s only about 45 to 54 ah/day, throw in some lights, etc and you might be around 75ah/day. What am I missing??

 

[whatcharterboat]

I think Riparious makes a great point about the need to have solar panels in the sun. If you are camping in the sun it makes sense for them to be permanently mounted to the vehicle, but if you are camping in the shade, they need to be portable.

Bigreen505, This is so true. A company here actually makes a panel arrangement just for this purpose. Don't have any pics but have seen them up the beach. I've fitted external solar input sockets to a few trucks and caravans over the years but never actually supplied the panels. The ones I've seen are 2 panels hinged together. About 48watts each I guess. They have a carry handle like a briefcase and when you unfold them there is an adjustable leg at the back so that you can alter the angle. I suppose they come with a travel bag or box to protect them in transit.

Would be simple to make anyway.

 

[michaelgroves]

Your post makes sense to me. Actually, I was only making the assumption of 12hrs of sunlight per day - the actual number of hours it will obviously depend on where one is travelling!

I also had it somewhere in my mind that a solar panel's performance is roughly related to the amount of visible light (brightness), rather than the total radiation, which would mean that there would be considerably less variation between direct and angled sunlight. I guess that even if that's true, it's all relative. Either way, I take your point about the early morning and late afternoon sun not being as effective as the midday sun. I tend to try and follow the summer, so mostly I would expect to have more than 12 hours sunlight on average - though I suppose a cloudy day would take away a chunk of output, too.

One part I hadn't factored in at all was the inefficiency of charging the battery!

With regard to the usage, it may well be that I'm overestimating. We didn't keep an accurate log of what was used and for how long - my estimate was partly based on how frequently we would drain the deep cycle batteries. It would be a relatively simple thing to keep track of electrical items are in use, and what the typical usage period would be. A worthwhile exercise and discipline in any case.

Thanks again for the interesting info!

 

[whatcharterboat]

Either way, I take your point about the early morning and late afternoon sun not being as effective as the midday sun. I tend to try and follow the summer, so mostly I would expect to have more than 12 hours sunlight on average - though I suppose a cloudy day would take away a chunk of output, too.

Michael If this helps . Australia being the driest continent is probably one of the best places in the world to travel with solar. Most of it would be like the Sahara. The Kimberly region in West Oz has the highest Peak Sun Hours in this country IIRC at about 7.5 PSH in mid summer. So that's the most I can expect a panel to output at full wattage here, 7.5 hours average in the middle of summer in a dry desert. That chart I gave you in the link, takes into account the average number of cloudy days. So it isn't just calculated by the latitude. Use that to get your PSH for your calculations for a given location.

It would be a relatively simple thing to keep track of electrical items are in use, and what the typical usage period would be. A worthwhile exercise and discipline in any case.

A lot of good digital regulators now have data logging capabilities with the ability to check daily operation for the previous 30 days. Usually at least daily data such as Amphrs in, Amphrs out, max and min voltage. It's a good way to analyse your system and determine wether or not you need more panels or batteries, etc.

Michael, really enjoyed posting this info. Thanks for asking all the right questions.
John.

 

[michaelgroves]

Having guys like you write about your field of expertise is what makes ExPo such a terrific board. Your sharing your knowledge and experience here is much appreciated!

M...

 

[Bogo]

Somethings to think about.

Given solar panels are relatively dark they are good heat absorbers. Having your solar panels above the roof by a couple inches allows for an air gap. Not knowing numbers, roughly 1/2 the heat gained by the solar panel will be radiated up and 1/2 will be radiated down. That halves the source heat for heat gain for the section of roof shaded by the solar panel. That means an easier to keep cool interior.

Roof space on an RV is very limited. When amorphous silicon panels are running only 8 to 9 percent and multi-junction cell panels are easily available at 17% it really tilts the advantage to the multi-junction cell panels.

Having said all that I really wish I could get a flexible panel I could stick on the hood of my mini truck. I don't feel the hood would work for the placement of a rigid solar panel. It could be done, but.

 

[saburai]

Somethings to think about.

Given solar panels are relatively dark they are good heat absorbers. Having your solar panels above the roof by a couple inches allows for an air gap. Not knowing numbers, roughly 1/2" the heat gained by the solar panel will be radiated up and 1/2" will be radiated down. That halves the source heat for heat gain for the section of roof shaded by the solar panel. That means an easier to keep cool interior.

Roof space on an RV is very limited. When amorphous silicon panels are running only 8 to 9 percent and multi-junction cell panels are easily available at 17% it really tilts the advantage to the multi-junction cell panels.

Having said all that I really wish I could get a flexible panel I could stick on the hood of my mini truck. I don't feel the hood would work for the placement of a rigid solar panel. It could be done, but.

Great idea!

Thanks. I think I will build a take down mount for my new Global Solar 62 watt foldable panel. I make it so that it mounts on stand offs on top of the Autohome Extreme (when I get it)...

 

[Chris]

I have a Solara 68 W. thin flexable marine solar panel mounted to the top of my yakima cargo box. molds to the shape just fine. You can walk on them!!


I Am NOT a solar dude, here ya go:

Solara semi-flexible solar panels

Solara M-series (marine-series) solar panels and modules for boats, yachts and general use within the marine environment are premium quality semi-flexible modules manufactured in Germany to the highest standards. They are an ideal alternative to all oversized, rigid or inflexible glass panels. All materials are high quality and have been subjected to numerous stress tests, are robust, durable and completely weatherproof.

The V4A stainless steel backing is seawater proof and acid resistant, the cable outlet is potted and screwed to the solar panel which rules out cable oxidisation and penetration of moisture into the panel. The cable is also made of weatherproof material and does not become brittle when exposed to strong solar radiation, wind and water.

This range can be fixed with adhesive or screwed and due to the synthetic surface will shape around slight curves, they can also be walked upon with no fear of broken glass or damage. The Solara 'M' series also has an additional black edge-protection (optional) made of uv-resistant synthetic with stainless steel reinforcement. An attractive way and useful way to finish the panels edge. All solara panels are individually tested for high performance and long service life.

http://www.ekmpowershop11.com/ekmps/shops/sbsboats/solara-semi-flexible-solar-panels-767-p.asp

 

[JIMBO]

:sombrero: My 60 watt rigid panel has been fine each time I've used it, even once on top the trailer, in a wind

I'm sure the flex type have uses, but I don't need that and my panel weighs about 3 lbs and packs easily with my trailer gear, I have a 25 foot 10 ga line for hookup

:wings::costumed-smiley-007:safari-rig::safari-rig: JIMBO

 

[saburai]

I have a Solara 68 W. thin flexable marine solar panel mounted to the top of my yakima cargo box. molds to the shape just fine. You can walk on them!!


I Am NOT a solar dude, here ya go:

Solara semi-flexible solar panels

Solara M-series (marine-series) solar panels and modules for boats, yachts and general use within the marine environment are premium quality semi-flexible modules manufactured in Germany to the highest standards. They are an ideal alternative to all oversized, rigid or inflexible glass panels. All materials are high quality and have been subjected to numerous stress tests, are robust, durable and completely weatherproof.

The V4A stainless steel backing is seawater proof and acid resistant, the cable outlet is potted and screwed to the solar panel which rules out cable oxidisation and penetration of moisture into the panel. The cable is also made of weatherproof material and does not become brittle when exposed to strong solar radiation, wind and water.

This range can be fixed with adhesive or screwed and due to the synthetic surface will shape around slight curves, they can also be walked upon with no fear of broken glass or damage. The Solara 'M' series also has an additional black edge-protection (optional) made of uv-resistant synthetic with stainless steel reinforcement. An attractive way and useful way to finish the panels edge. All solara panels are individually tested for high performance and long service life.

http://www.ekmpowershop11.com/ekmps/shops/sbsboats/solara-semi-flexible-solar-panels-767-p.asp

I'd be careful with them. Seem CS is a bit sketchy. Durability may also be an issue.
Look here: http://www.geoffschultz.org/Solara/e-mail.shtml