PV Panels On Vehicle Roof

[Antipodean Bucket Farmer]

I am quite interested in the idea of mounting
photovoltaic panels on the roof of a van (e.g. standard
Volkswagon Vanagon, Toyota HiAce, etc.)

I am guessing that the best choice would be flexible
panels designed for marine/boating installations. And
that the panel would be best mounted directly on the
roof surface (as opposed to on raised brackets.)

Does anybody have any info on estimating how much
wattage of panels could fit onto a van roof? And
generally how to use this small space most efficiently?

Any recommendations for manufacturers/models?

BTW, the specific power requirements are vague at the
moment. Hopefully panel and battery capacity for, say,
four hours of laptop computer use per day, with one
autonomous (zero-sunshine) day reserve.

Any references, Web sites, personal experiences?

Thanks...

 

[Bernd Felsche]

I am quite interested in the idea of mounting
photovoltaic panels on the roof of a van (e.g. standard
Volkswagon Vanagon, Toyota HiAce, etc.)

Flush-fitting, low-profile.

Does anybody have any info on estimating how much
wattage of panels could fit onto a van roof? And
generally how to use this small space most efficiently?

Depends on where you are, and what the weather is like.

Daily insolation onto a horizontal panel is about 30MJ per day
around here this time of year when it's not cloudy. Expect to get
about 10% of that from the PV cells.

If you budget for about a third of that, you'll not be disappointed
too often. i.e. 1 MJ per square metre of horizontal PV array.

Any recommendations for manufacturers/models?

BTW, the specific power requirements are vague at the
moment. Hopefully panel and battery capacity for, say,
four hours of laptop computer use per day, with one
autonomous (zero-sunshine) day reserve.

Any references, Web sites, personal experiences?

The best reference i have is a book on my shelf. Not much use to
you... try this one:
http://www.solarserver.de/wissen/photovoltaik-e.html

Google for "daily insolation"

http://www.self-reliance.co.nz

Oh... you're in NZ.... better budget on 0.5MJ/day per square metre.

 

[Ecnerwal]

BTW, the specific power requirements are vague at the
moment. Hopefully panel and battery capacity for, say,
four hours of laptop computer use per day, with one
autonomous (zero-sunshine) day reserve.

As for use, an article in Home Power magazine some years back covered a
person who put a solar panel on the roof of their car and disconnected
the alternator, which resulted in considerable fuel economy improvement.
Did end up reconnecting the alternator in the depths of winter, however,
IIRC.

 

[[email protected]]

...an article in Home Power magazine some years back covered a person
who put a solar panel on the roof of their car and disconnected the
alternator, which resulted in considerable fuel economy improvement.

Cool. I wonder how many watts the panel made.

Did end up reconnecting the alternator in the depths of winter...

Maybe he needed a reflective wall above the north edge.

Nick

 

[[email protected]]

Cool. I wonder how many watts the panel made.

If you can fit a square yard (apx equivalent square meter) of panels on
the car's roof, figure on around 100 watts.

 

[[email protected]]

http://shop.altenergystore.com

They have a flexible 32 watt PV panel. It would put out about 1.5 amps. per
hour max.

What do you mean by amps per hour?

Nick

 

[Anthony Matonak]

I am quite interested in the idea of mounting
photovoltaic panels on the roof of a van (e.g. standard
Volkswagon Vanagon, Toyota HiAce, etc.)

Well, autotrader.com lists the Vanagon as 15 by 6 feet but the
windshield slopes and makes the roof area somewhat smaller.
I would say you could probably use at least 11 feet of that.
This gives you a useable roof area around 66 square feet.

I am guessing that the best choice would be flexible
panels designed for marine/boating installations. And
that the panel would be best mounted directly on the
roof surface (as opposed to on raised brackets.)

Flush mounting will likely help with MPG but being able to
tilt the panels will help with performance. Judging from
your application (and the fact that you have an alternator
for backup power generation) I'd say performance is not
the most critical requirement.

Does anybody have any info on estimating how much
wattage of panels could fit onto a van roof? And
generally how to use this small space most efficiently?

The flexible panels are rated around 5 watts per square foot.
Figure 80% of ratings for the real world and maybe 3 sun-hours
a day and you could expect around 790 watt-hours a day if you
cover the roof with these. Double that if you use crystalline
panels.

BTW, the specific power requirements are vague at the
moment. Hopefully panel and battery capacity for, say,
four hours of laptop computer use per day, with one
autonomous (zero-sunshine) day reserve.

Laptops vary but generally they seem to run in the 20 to 50
watt range. Let's say 50 watts for 4 hours of use and you
would need 200 watt-hours. If you get around 3 sun-hours
a day then you could get by with 83 watts of panels.

If you use flexible panels they would require some 16.6 square
feet of the roof. Unisolar sells 32 watt panels so you might
use 3 of these costing some $850 USD.

On the other hand, if you use a glass panel then you could
buy a 90 watt unit for around $320 and it would only take
up around 9 square feet.

Anthony

 

[[email protected]]

Take such claims with a large grain of salt, as the math says otherwise.
Let's do a little. The typical daylight load on an alternator of an
older car is about 25 amps (number is experience from many, many tests).

I worked with a frugal man who had a car with a bad alternator. He drove
to work every day and only charged his battery from the grid once a week.
I would guess his car consumed about 12Vx100Ah = 1200 Wh in about 5 hours
of driving, ie about 240 watts while driving during the day.

25 amps at 14 volts is 350 watts. Someone more into solar electricity
can do the analysis but I don't think 350 watts' worth of solar panels
could be fit to a car.

T'would be tight, but people don't drive cars 24 hours per day.
A 1 watt panel might produce 5 Wh/day.

Assume that an alternator is about 50% efficient. That means that 700 watts
of motive power would be required of the engine. 746 watts is a horsepower.
That's 0.94 hp. A trivial amount of power.

My Honda CRX got 55 mpg when it was new. That's about 120K/55 = 2182 Btu
or 640 watt-hours per mile...

Nick

 

[Anthony Matonak]

During the span of one hour it puts out 1.5 amps.

....

I think Nick was more concerned with your use of an instantaneous
measurement (amps) over time (hours). A PV panel that puts out 1.5
amps will do that over 1 minute, 1 hour or 1 millisecond. If it does
so for 1 hour then you have 1.5 amp-hours produced.

I'll leave it up to you to figure out how using the wrong units can
mess up both calculations and communication.

Anthony

 

[Robert Morein]

I am quite interested in the idea of mounting
photovoltaic panels on the roof of a van (e.g. standard
Volkswagon Vanagon, Toyota HiAce, etc.)

I am guessing that the best choice would be flexible
panels designed for marine/boating installations. And
that the panel would be best mounted directly on the
roof surface (as opposed to on raised brackets.)

Does anybody have any info on estimating how much
wattage of panels could fit onto a van roof? And
generally how to use this small space most efficiently?

Any recommendations for manufacturers/models?

Take a look at:
http://www.rvpartscenter.com/Produc...96&DepartmentID=&CategoryID=&BasketID=&RepID=

They run auctions:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=41981&item=5902489780&rd=1
and
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=41981&item=5902021782&rd=1
The 150 watt job, I was told, is actually two 75 watt panels.