jameskb said:
Too bad the Honda designers didn't build the 144v-12v charging circuit to work both ways, not too hard to do and wouldn't cost much. Then you could get one of those 12V dashboard panels and just plug into the 12v power point.
I love appropriate technology. That's why I love the Insight. The dark side of that is that I have an inappropriately passionate response to technological ideas that I honestly believe are not well thought out.
I want to be concise here, so as not to annoy people more than necessary. First, the Insight obviously works well without solar panels. Before a company could justify paying the money to develop a solar electric charger for the Insight, they'd have to see a sufficient benefit.
I like solar power. I've lived with it and am building a woodworking shop that will be powered by it. Having a stable site, clear of trees and buildings is possible for the shop, but not for a car. The building doesn't care if the panels are not aerodynamic. Flat, non-aerodynamic panels are already expensive. Making them integrated into the Insight's sleek body would be quite expensive.
Given those basic problems, the idea is already too impractical to then have to think about voltage levels, SOC calculations, the inefficient angle of the panels to sunlight in a parked car, and the simple fact that there isn't enough surface area on an Insight to collect enough solar electricity to improve the performance of a car that is already doing just fine without the panels, especially considering the remarkable cost of such a system.
It's really easy to pull out a paper napkin, draw an Insight and put some panels on it, labeling them and then talk the idea up to other people who are clueless as to the impracticality of the idea. It's really hard to make the idea work at all, even if you don't consider the cost, and in the real world, engineers have to consider the cost.
jameskb said:
Your thought about putting the cells in the back cargo area is good: it saves the need to drill somewhere to pass wiring into the battery, plus, that puts the cells right on top of the 144V module. Short wiring would really help.
You are ignoring the rather dramatic loss of solar-electric power you get when sunlight goes through the glass of the rear window. Hold your hand out in the sunlight and notice the color and brightness of your skin. Now partially hold open the tailgate and look at your hand illuminated through the rear window. The tint is darker and there are all those little shadows of the defroster lines. In terms of solar electric production, this is a big deal. It wouldn't work. Most sunlight on panels is consumed bringing the voltage up to that of the system you are attempting to charge. It is only the brightest, most direct exposure to the sun that pushes the panel up high enough to charge the system. You can't afford the loss of going through that rear window.
jameskb said:
Two problems to think about. First, it renders your cargo area hard to use for anything else. This could be helped by a panel that could fold up like an accordion.
At this point, you are either talking about a panel that produces so little power that it is a joke, or you are talking one that is so expensive that it is a joke.
jameskb said:
Second is heat gain. The dark solar cells will enhance interior heat gain and solar cells lose a couple percent efficiency when they get hot.
Your calculations here are focussing on a few small details while ignoring factors much greater than a couple of percent efficiency. You'll lose much more than that just going through the back window. Then there are tracking issues. You have to aim the panels fairly directly at the Sun and hope that the shadow from the edge of the window doesn't cover any of your cells.
jameskb said:
What kind of power gain? Say you've got a 50W panel.
Do you actually know of a 50W panel that is small enough to fit in a Honda Insight trunk and be fully illuminated, without shadow? I honestly didn't know that such a panel exists. I find it startling how much more efficient that panels have become since I bought my 75-watt panels that are quite a bit too long to fit in the trunk without being well in shadow, even at noon in summer. I think they are about 4' long and a foot and a half wide, though that's from memory.
jameskb said:
Probably about 4A at 12V. You could up-convert that to 144V at about 1/3rd amp. Not a bad charge rate for, say, 6 hours conservatively.
The engineer who helped me design my solar electric system explained that I should plan on a maximum 4 hour solar day. Without an active solar-tracking system aiming the panels directly at the Sun, this is what you can expect, given that the panels are pointed at one spot and most of the time the solar angle is too poor to generate significant power. Add clouds part of the time. It's a good solar day if you collect the amp hours you'd get from 4 hours at the rated output of the panel. This assumes that the one spot you aim the panels is well chosen. In a car in a parking lot, it won't be.
jameskb said:
Might get you "a few bars" with the 300-400 Watt-hrs you'd gain during the day.
I think your math is startlingly optimistic. It also doesn't include any talk of cost. I honestly believe that you'd spend a bunch of money, risk screwing up a remarkable car and not get anything close to a benefit from it at all.