With the arrival of the Nissan LEAF, the (much derided) G-Wiz, the Tesla, and other Electric Vehicles(EV’s) there is no doubt that these are here to stay and will play a major role in the lowering of transport emissions. Even if the emissions that are lowered are particulates and CO in the short term, this is a good thing for urban dwellers and air quality. The use of EV’s as a long term strategy means that as the Grid emissions are lowered, the emissions of drivers is lowered also leading to lower CO2 in the long term. Other benefits such as quieter engines, are less easy to quantify, and for some people, might even be considered a disadvantage.
For about a decade now, the mantra has been to reduce parking in proximity to dwellings, to aim to improve the use of public transport, that cars are BAD, and almost anything else is better, walking, cycling, buses, etc., do these ideas still hold good with the introduction of the EV? Or have we reached the future promised us by the Jetsons?
Well, EV’s are efficient, but not quite as efficient as public transport. Professor McKays book Sustainable Energy – without the hot air contains some useful rules of thumb:
See fig 20.23 on P128 where he compares the energy used per person per km.
The figure for a ‘normal’ car is 80, an electric car is 15, cycle is 2, electric train 4 and bus is 32. This tells us that electric cars are extremely efficient, but not quite as good as an electric train. But in suburbia, where electric trains are pretty rare in the UK, the electric car is a good second place behind cycling/walking.
Of course there are other issues to do with congestion and the undesirability of commuting that I am not going to deal with here, but we can safely conclude that the introduction of the EV into new UK housing is a big step forward in terms of energy efficiency. Even if the emissions from electricity were to remain constant the actual energy use of EV’s is approximately 25% of those of other vehicles. This is not quite the 80% of emissions reductions that we need from transport, but a 75% reduction in energy use is a start. In terms of CO2 emissions the average UK car produces about 168 g/km whereas an EV will produce about 100g/km and this will reduce over time with the improvements to the Grid, about a 40% reduction in CO2 without making any changes to the grid.
But in order for these cars to function at all they have to be charged, the Nissan Leaf will take 8 hours to charge on a 13amp supply, this can be halved by using a 16 amp supply installed by a specialist supplier, and 40 minutes using one of their special charging units.
But all of these require the car to be near the charger, otherwise there is the problem of cables snaking over pavements.
This means the return of the in-curtilage parking space or the car in the garage for new suburban housing, or alternatively a network of on-street charging stations with networked credit card systems. Neither of these is particularly desirable. One is rewarding suburban residents for owning cars and taking up lot of space, the other is cluttering up the pavement and making the introduction of street trees more difficult.
Perhaps the ideal scenario is to retrofit charging stations onto street lighting columns and parking meters, these are already there, have electrical supplies, and in the case of the parking meters, have networks as well. But having only one or two of these per street will still produce the problem of snaking cables and clutter, as well as the problem of there simply not being enough of them to go around.
Where the new dwellings have PhotoVoltaic arrays on their roofs there should be a presumption in favour of in-curtilage parking, as these arrays can contribute to charging a car during the day. The output of a 4kW array per day is around 4kWhs on an average day, but the Nissan Leaf can store 25kWhs in its battery, so it helps but on its own it isn’t enough. In the winter it isn’t so good, the output is likely to be only 0.5-1Kwhs so not enough in winter to charge the car. We need more efficient cells and we need some of them on the car itself. The economics of charging will depend on the use of the car, if the car is used for commuting and isn’t at home for much of the time, then the energy would need to be stored somehow and used to charge the car at night. This looks like a problem looking for a neat technical solution. A duplicate set of batteries that can be swapped out by the owner every day?
What this does highlight is the fact that low carbon homes that incorporate renewable systems can have a large impact on the lifestyle and emissions of their residents, a fact that is missed in the recent changes to the zero-carbon definition.