Let me illustrate with the energy storage that most of us are familiar with, even if we don't recognise it as such; the fuel in the tank of our car! The typical fuel tank holds 50 to 60 litres of fuel that gives us both instant flexibility even on a cold morning (modern cars start so good at starting nowadays!) and a couple of weeks worth of resilience assuming average mileage. Indeed, if we knew there was a supply crunch most of us could probably stretch that full tank for a month or so by car sharing, using public transport and the like.
So that unseen energy storage which comes free when you buy a car and only ties up £50 to £60 in fuel gives us a lot of resilience and flexibility in our mobility. The energy system that has evolved over the last hundred years or so has embedded within it quite a lot of hidden resilience and flexibility. As well as our car fuel tanks we have petrol and diesel at filling stations and tank farms, we have piles of coal at our diminishing number of coal fired powers stations and we have natural gas in the network of pipes (the jargon for this is linepack), in dedicated storage facilities like Rough and Hornsea and offshore where at some fields production can be ramped up quite quickly.
However, the energy world is changing. We need to decarbonise our electricity system and then the rest of our energy system. This second stage is likely to increase the role of electricity in meeting our heating and transport needs. The problems are that firstly our current electricity system only has embedded in it the resilience and flexibility that the current uses of electricity need and secondly what little already exists is in decline principally as old coal stations shut. This is exacerbated by the fact that low carbon forms of energy, be they renewables, nuclear or clean fossil fuels, are not currently known for their inherent flexibility or resilience. So we will be faced with less of what we need just when we start needing more. What will happen when our electric car battery needs to be recharged at the same time as our heat pump needs to work and we want all our lights and gadgets to function but it's a still calm night?
This is the reason why so many energy professionals put energy storage at the top of their innovation agenda. In deciding on where that innovation should be targeted we need to think about what level in the electricity system we can best provide resilience and flexibility. There are four possible levels, the source of demand (our home for example), the local area (think of the transformer at the end of your street), the generator itself or the grid as a whole. The answer may be a combination of all four levels and, importantly, may be different for resilience than it is for flexibility. It will be determined by things like economies of scale, the efficiency of sharing the capabilities with others (we don't all need to meet our own maximum flexibility, if we can pool with others the flexibility needs of the system will be less than the sum of all the indivdual needs) and the value of providing security close to demand. I have a hunch that the answer may involve local or even domestic level resilience but generator or grid level flexibility but time will tell.
Debate about energy storage tends to get dominated, right from the start, about technology be it batteries, phase change material or pumped storage hydro. However, we need to separately assess our current and future needs for resilience and flexibility, then decide at what level in the system that need can be most efficiently meet and only then determine the choice of technology. We have to put needs before technology.
