The b-bug project will try to estimate the carbon savings which could accrue from replacing a percentage of visitor car journeys in the Brecon Beacons with b-bug journeys. To figure that out, we need to take two things into account:
1. The amount of fossil CO2 a particular source of energy creates over the whole energy production cycle – measured in grammes or kilogrammes per kilowatt hour – g/kWh.
2. How efficiently we use that energy to achieve our transport goal – usually measured in kWh per 100 passenger kilometres – kWh/100p-km.
It’s very hard to nail down hard figures in this area. We are currently working with figures from David Mackay‘s excellent book andwebsite.
Petrol and diesel emit about 250g of CO2 for every kWh, and a typical petrol or diesel car needs about 80kWh/100p-km.
The current electricity generation mix for the UK grid emits between 500g and 600g of CO2 for every kWh – it’s over 900g for a coal-fired power station, while the EU average is under 400g because of France’s nuclear capacity and Germany’s renewables. “First generation” electric cars like the G-Wizz use around 20kWh/100p-km, and future lightweight electric cars
should do even better. The G-Wizz manages this by being more efficient in its use of energy, by being lighter, and by going more slowly. So while the best combustion-engined cars can now manage over 80mpg, lightweight electric cars already manage the equivalent of 200mpg.
The b-bug is intended to be at the most efficient end of the electric car spectrum, because it is even lighter than a G-Wizz, doesn’t go as fast, and doesn’t go as far. Because it doesn’t go as fast, it wastes less energy overcoming air resistance (the major consumer of transport energy above about 15mph). Because it doesn’t go as far, it carries less battery, making it even lighter.
So while it would indeed be better if b-bugs were re-charged entirely from renewable sources of electricity (and we will certainly seek to encourage that wherever we can), they will already produce much lower carbon emissions, and will do even better as more and more of the grid capacity comes from renewable sources.
A light weight, low speed, short range vehicle like the b-bug can hope to be about 4 times as efficient as the best combustion-engined cars, saving even more.
The main purpose of the 2011 b-bug trial, however, is to establish whether a significant proportion of visitor journeys in the Brecon Beacons National Park could be met satisfactorily by a light weight, low speed, short range vehicle, if packaged and presented in the right way.