jaraczs said:
However, technology is improving. I have made my calculation based on:
1) pricing of 15.7 sq. feet PV panels at $295 for 205W:
http://www.solarsystemsusa.net/solar-panels/panels/vikram/elv-205/
2) area of iMiEV roof = 20 sq. feet
3) solar day = 8 hours
This gives 2.09 kWh per day for $375 (PV only), which in my hands provides 10 miles of range per day, which in turn covers exactly my daily RT commute. So, if we manage to mount PV on the roof at reasonable cost, low weight and hook it up to the battery, this would provide very appealing claim.
First, if your vehicle can make the daily round trip you need it to, why put panels on the car? On the car you cannot aim them and they'll be giving you maybe 1/3rd of what they would if they were on a fixed structure, properly aimed at the sun
It's difficult to come up with actual numbers when you're talking solar - You surely cannot do it by multiplying the panel's theoretical best output times the number of hours you're going to set it in the sun. For one, panel manufacturers all quote best possible case scenarios when giving you the panel output. Clear, cloudless day, panel oriented so the sunlight strikes it at a 90 degree, perpendicular angle and the panel well ventilated so it generates minimal heat
On a building, you orient the panels at an angle which is a compromise of a best case average over the angle of the sun at your particular latitude for all 4 seasons of the year - Sometimes you fudge it a little toward the winter angles because the panel does pretty well in full summer sun being off angle a bit and since it's already compromised by the lower winter angle, you try to improve the winter efficiency by giving up just a little summer efficiency. At any rate, for that half hour when the sun is exactly where you want it to be, the panel actually comes pretty darned close to what the manufacturers spec says it will, but that's the only time - The average over an 8 hour day might be only 50 or 60% of the advertised output. Most operators of fixed panels properly aimed use some number around 60% of maximum in their calculations for a day's total output . . . . even if they don't calculate it that way, that's closer to what they'll actually get
Mount the panel flat on a vehicle roof where you cannot set it for your latitude and your output goes way down, which is why your theoretical outputs look so much better than those reported for the Fisker Karma - They are giving you actual, real world numbers and you're comparing them to pie in the sky numbers you're never going to come close to getting. When we use panels on sailboats, we can aim them a bit for better output . . . . nothing nearly as good as fixed panels on your garage roof, but we can get much better numbers than you're ever going to see with the panels flat on your car's roof. If you lived where I do, the gain you'd see from leaving your car sit in the sun charging all day would be almost entirely offset by what the A/C is going to use cooling the car off when I get into it to drive . . . . I'm about as well off by leaving the car parked in the shade. I'd be much better off leaving it parked in shade provided by 150 to 200 sq ft of solar panels and then I don't need to mount them on the car :mrgreen:
So, when running the numbers for use on a car, I would plan on getting about 1/3rd of what you're currently thinking and then decide if the modification costs are worth the gains - Not to discouragfe you from going forward . . . . I love it when anyone does these sorts of mods and then has the capability to generate real world numbers as it helps everybody who follows in their footsteps. The very idea of a vehicle which can drive even partly powered by the sun is EXOTIC and it's certainly worth pursuing . . . . but I wouldn't go into it expecting to get anywhere near 8 times the theoretical maximum instant output of the numbers printed on the panel
Don