re: i have an idea, i just need some help SOLAR.KnowledgePublications.com

re: i have an idea, i just need some help
17 jul 1998
dupleklus@aol.com wrote:

>...why must it be impossible for these large trucks to carry solar panels
>on their roof, enabling the truck to operate solely on this energy
>absorbed from the sun....

like many pv applications, this one is probably uneconomical, at today's
oil and gas and pv and battery prices. you might put 400 ft^2 (5.5 kw
or $28k's worth) of pvs on top of a 40' trailer, with some batteries
inside. suppose the truck gets 10 mpg at 30% efficiency, so it needs
about 1 kwh/mile, and the pvs gather 22 kwh/day, enough to drive 22
miles per day. this could be a poor modern-day pony express, with lots
of union drivers moving each trailer 22 miles a day...

or, we could let the trailers sit a long time between drives, but then
we have to put more and more batteries inside, and pretty soon they weigh
a lot, which increases the energy needed to haul them...

suppose we store enough energy to pull a trailer 8 hours, say 400 miles
or 400 kwh. a trojan t105 220 ah 6v battery stores about 1.32x0.9 = 1.2
kwh at a cost of about $50/kwh, so we'd need about 337 of them at a cost
of about $20k. they would weigh about 19,000 pounds. at their 60% optimal
life-cycle cost discharge depth, they would deliver about 1200 discharges
at a cost of $60/(1200x1.32x0.9x0.6) = $0.07 per kwh, ie about 7 cents per
mile. the trailers would need to sit idle about 400/22 = 18 days between
drives, as someone pays interest on their extra $48k's worth of hardware.

nick