This is part of a series on electric vehicles (here are parts 1, 2, 3 and 4). It’s been 18 months since the last post – I feel like George R. R. Martin, except no one has really been asking me about when the next post is coming. Sorry, anyway, and I promise to get better. Today, I’m looking at the impact of these vehicles on NZ’s power supply. Again, I’ll abbreviate plug-in hybrid electric vehicles to PHEVs, and battery electric vehicles to BEVs – these are the “full” electric vehicles which don’t have an engine for backup.
In part 2 of this series, we saw that EVs are much more energy efficient than “conventional” cars. But instead of the established infrastructure for supplying and fuelling petrol, we’re going to need to rely on our electricity networks. Can the power grid cope?
The government’s Energy Strategy, written in 2007, argues that “switching to electricity as a fuel for our vehicles would make the most of New Zealand’s abundant renewable electricity supplies, particularly if transport was not competing for supply at times of peak demand”.
New Zealand’s car fleet travelled 39 billion kilometres in 2014. If the fleet was entirely replaced by BEVs using 20 kWh/ 100 km, it would require 7,800 GWh of electricity. That’s 18% of New Zealand’s 2014 electricity generation.
This might seem like a fair chunk of our nationwide electricity, and it is. But that analysis assumes that every car in the country is replaced by a BEV running only on electricity. In practise, it will take years or even decades for EVs to become firmly established in the market, and PHEVs – which will probably outnumber the “pure” BEVs – will only use electricity for part of their travel, running on petrol or diesel the rest of the time.
Additionally, the power companies have scoped out a large number of new plants (mainly renewable – wind and geothermal) which they could build in the future. The only reason they aren’t building them already is that electricity demand has been flat for the last few years. So the industry has plenty of room to boost supply to meet any new demand from electric cars (a number of academic studies have reached the same conclusion).
Overall, the power grid can certainly handle New Zealand’s car fleet being partially or even entirely replaced with electric vehicles.
Feeding power back to the grid?
Potentially, PHEVs and BEVs could even feed power back into the grid. The idea is that during low-demand times – e.g. in the middle of the night – EVs will charge their batteries, and then they’ll stay plugged in and send power back the other way during high-demand times. In theory, this could help to smooth daily fluctuations in power demand, i.e. the daily peak/ trough cycle. At least one paper (Smith, 2009) suggests that EVs could actually reduce New Zealand’s requirements for new diesel and gas peaker plants (which only run during high or “peak” demand periods) as a result.
However, there are a number of issues with using electric vehicles to provide “security of supply” for electricity. These include the slow charge/ discharge times for vehicle batteries, and the energy losses involved in transforming the battery’s energy back into electricity.
The biggest issue is that in New Zealand, our main “security of supply” concerns are for dry years rather than daily demand cycles. Half of our electricity generation comes from hydro, and the problems arise when there’s low rainfall and the lakes and rivers supplying the power plants are depleted. EVs won’t help with this problem, and I tend to agree with Clive Matthew-Wilson that “the times and situations when [advanced vehicles feeding electricity into the grid] would be of much practical help would be few indeed”.
This is a NZ-specific issue, so for most countries EVs may be much more useful for feeding power back to the grid. Even in New Zealand, our power generation profile will change over the next few decades, with wind (and maybe solar) becoming more important. The output of wind and solar plants tends to fluctuate, and EVs that can feed electricity back to the grid would be an excellent complement, smoothing out these variations. This could help us kick our dependence on fossil-fuelled electricity – the main advantage those plants have in NZ is that they can scale their production up or down quickly as demand changes. I’ve written previously that New Zealand can get to 100% renewable electricity even with current technology, but better power storage would only make that easier. Batteries for homes, like Tesla’s Powerwall, would help too, although as for EVs there’s a long way to go before they’re cost competitive.
Even in New Zealand, there are advantages to charging EVs outside of peak times; this allows for better use of existing grid capacity. Schafer (2011) cites two studies which suggests that if EVs are charged off-peak, they won’t have much effect on New Zealand’s electricity demand or the need for new power plant capacity. This will of course depend on the number of vehicles, and an all-electric car fleet would probably require some level of increase in capacity. The key takeaway from this post, though, is that the electricity market can definitely handle EVs, even if uptake is fairly rapid.