3 ms·

My calculations (http://daniellefong.com/2008/11/15/tick-tock/ http://daniellefong.com/2008/11/15/tick-tock/) give about 4 kwhr per 100 miles of city driving wi

My calculations (http://daniellefong.com/2008/11/15/tick-tock/ http://daniellefong.com/2008/11/15/tick-tock/) give about 4 kwhr per 100 miles of city driving without regenerative breaking at about a 70% efficiency. Most of the US ranges between 2 to 4 kwhr a day of impinging sunlight - let's call it 3. High efficiency PV panels are about 30% efficient, so this is about 1 kwhr per m^2 of charge per day. This would give about 25 miles of city driving, which is well in the range of many urban commutes, but not most. To do better you need regenerative braking or higher efficiencies or more solar panels or all three.

jwilliams 18y ago
Thanks! So if you add in the weight of the panels, and the occasional patch of cloudy days - I think it might be a bit marginal... Would you agree? I hadn't really considered regenerative braking. I can see how it would be useful in a place like San Francisco, but I'd wonder how effective it would be in places like NY (where you need to slam on the brakes instead of just curb your speed). I recall reading about a mine in Peru (?) that used regenerative braking on all their hauling vehicles. They were all hooked up via a quite clever bumper-car style grid. When one was going downhill, it was helping power something going uphill. Apparently the regenerative braking in that case resulted >50% efficiency - which seemed like a very good figure to me. Do you know any figures for cars/bikes/scooters in more regular practice?
- DaniFong 18y ago
  To make quick regenerative braking efficient, you need something other than batteries to store the energy -- they can't absorb that much power so quickly. They're working on ultracapacitors, which seem like an expensive solution to me. Our strategy, which is also used by so called hydraulic hybrids (in garbage trucks, most notably, which are constantly stopping and starting), is to compress air during braking: this can be done quite quickly and efficiently, and avoids conversion losses. We were expecting a cycle efficiency of between 70% and 80%. We're not working on vehicle technology at present, though.

jwilliams 18y ago

Thanks! So if you add in the weight of the panels, and the occasional patch of cloudy days - I think it might be a bit marginal... Would you agree? I hadn't really considered regenerative braking. I can see how it would be useful in a place like San Francisco, but I'd wonder how effective it would be in places like NY (where you need to slam on the brakes instead of just curb your speed). I recall reading about a mine in Peru (?) that used regenerative braking on all their hauling vehicles. They were all hooked up via a quite clever bumper-car style grid. When one was going downhill, it was helping power something going uphill. Apparently the regenerative braking in that case resulted >50% efficiency - which seemed like a very good figure to me. Do you know any figures for cars/bikes/scooters in more regular practice?

DaniFong 18y ago
To make quick regenerative braking efficient, you need something other than batteries to store the energy -- they can't absorb that much power so quickly. They're working on ultracapacitors, which seem like an expensive solution to me. Our strategy, which is also used by so called hydraulic hybrids (in garbage trucks, most notably, which are constantly stopping and starting), is to compress air during braking: this can be done quite quickly and efficiently, and avoids conversion losses. We were expecting a cycle efficiency of between 70% and 80%. We're not working on vehicle technology at present, though.