Friday, July 25, 2008

Performance data for a GWiz in London

This article is by Kele Baker and David MacKay, based on data collected by Kele

The performance of the G-Wiz varies with driving conditions and the weather. The G-Wiz can be driven on 'high' or 'low' power. The lights may be on or off. And the efficiency of the battery appears to depend on the temperature. The graph shows data for 19 charging events: the distance travelled in miles is on the horizontal axis and the energy required from the grid to recharge the battery (measured at the socket with a Maplin meter) is on the vertical axis.

The best performance was 16 kWh per 100 km. The worst was 33 kWh per 100 km. The average was 21 kWh per 100 km. This number is roughly four times better than the energy consumption of an average petrol car doing 33 miles per gallon, which uses 80 kWh per 100 km. In money terms, the electricity cost of the G-Wiz is 2.1 pence per km (assuming 10 p per kWh).

Tuesday, July 22, 2008

Mysterious cheap electricity generated in Nevada

There is a strange violation of economics going on on the Nellis Solar Power Plant wikipedia page. It asserts that the US air force are paying 2.2 c per kWh for electricity from a solar PV farm that happens to be on their land. This sounds far too cheap. The article says the '14MW' farm cost $100M to build (that's 7 dollars per watt, peak) and will generate 25M kWh per year. That means it will generate an income of $0.55M per year for the owners of the farm (who paid $100M, remember). That corresponds to a pay-back time of 180 years. So what's going on? Is it a strange Nevada phenomenon? Did aliens subsidise the farm? Or did wikipedia get the numbers wrong?