By Barney Smith

If de-carbonisation and ending overwhelming reliance on fossil fuels are given aims, as is an increased role for electricity from renewable sources, then perhaps it is time for us to say a little about why we think that intermittence is a handicap in the rise of renewables? Put another way, how are renewables to be integrated into an electricity system when it is also important to retain a secure and predictable energy environment?

On the assumption that renewables effectively means solar and wind, the fact is that the wind does not always blow and the sun does not always shine. The difficulty of storing electricity means that sufficient capacity has to be provided to cope with demand when electricity from renewables is inadequate or absent. This could mean the installation of expensive back-up power, which is idle much of the time, but stands ready to be switched on when needed. Another option would be more batteries, but at the moment their practical/economic range is a day, or possibly two. A further option would be the conversion of electricity to hydrogen or nitrogen for storage. But for all these, the questions remain: how much and who pays?

UK wind output 2018 at 5 min intervals,

It is, I suppose, possible to argue that a sufficient multiplicity of sites should mean that the sun is always shining somewhere and the wind is always blowing on a turbine somewhere. But this is at best a very partial, not to say very risky, solution. Arguably it may reduce the extent of the gap, but it certainly does not eliminate it.  An alternative is to suggest that intermittence is not the problem of the owner of the wind or solar farm, but rather the problem of the regulator, or the grid operator, or the infrastructure provider, in a word-someone else. But wherever responsibility falls, this argument admits that an intermittence problem exists.

 Then there is an issue which surfaced first in Germany: if the network needs to take each and every megawatt of renewable electricity generated, the problem becomes steadily more serious as renewables assume a greater percentage of overall energy provision. For it becomes more and more difficult to construct a business case for, say, a new gas-fired power station. Basic assumptions are increasingly unclear. No-one can say whether the new station will be producing base load electricity or just peak load electricity. The economics, and thus the economic justification, are very different. But once nuclear generation has been abandoned,  it cannot be right that an existing coal-fired station turns out to be the cheapest option.

Yet at the root of all this is essentially a comparison of apples and oranges. A centralised grid using fossil fuel is very different from a decentralised system reliant on renewables. Hence a central systemic question: how far are our current systems going to have to adapt to enable cleaner technologies to provide reliable energy for a society concerned about de-carbonisation. Fossil fuel sources have been successful for many reasons. One of them is their relative simplicity.  A renewable-based system will not mirror this. For one thing, entry costs for a renewable installation can be much smaller (that is not to say that total costs are much smaller); for another, power sources will be much more diffuse and more numerous. They will also need more active management than the old centralised electricity generating model ever did. A changed system will be much more complex. The modern ability to digitalise information is an advantage, but organisations will face a big challenge in adapting to a system which makes it possible to manage all that data.