The importance of balance
We aren’t suddenly extolling the benefits of wellness (although a spot of yoga is never a bad idea). We’re talking about the delicate balance on the electricity grid, which plays out minute by minute and day by day.
As we work towards Net Zero, grid balancing is something we need to consider, but not because of tired tropes about ‘intermittent’ renewables — rather, because this always has been and always will be a feature of our energy system.
Behind the scenes of your energy supply
In the UK we are fortunate that when we flick the switch on the kettle we can assume that it will boil. What we tend not to give much thought to is the work that goes on behind the scenes to ensure that there is enough power available to meet demand as it shifts throughout the day — this was brought into sharp relief following a brief power outage in early August 2019, which threw rail operators into chaos for days.
The National Grid buys energy in half-hour slots 24 hours in advance. The reason energy is bought and sold in this way is that our demands vary throughout the day and seasons, allowing the National Grid to make reasonable predictions based on changeable factors such as the weather forecast and time of year (the longer days in summer meaning we turn the lights on later, for example, and vice versa in winter). They can also take into account fluctuations based on predictable one-off large-scale events such as major televised sports finals, when people traditionally get up and start using more energy in the home during half time and immediately after the end of a match.
Last week’s power outage came about after a gas fired power plant tripped, followed shortly after by an offshore wind farm, and both at a peak time. In the aftermath debate has sprung up about supporting more renewables on the grid, despite the fact that a fossil fuel powered plant was equally liable. As you will see, this type of event is almost impossible to plan for — yet more renewables could help solve rather than exacerbate the problem.
The reason we have an energy mix
The varying demands on the grid are met by a range of energy generating technologies, some of which are better suited to a particular demand. Nuclear power, for instance, is traditionally part of the baseload (which is the lowest level of constant demand on the grid) because it is expensive and slow to power up and down.
Coal, too, has historically generated a significant proportion of baseload power for the same reason. Thankfully its use has fallen considerably and after 2020 there will be only four coal plants in use in the UK, all of which are due to be phased out by 2025. The benefits of baseload are the same as the problems it presents. As a large, centralised source of power it can deliver constantly. However when a plant fails, as happened on Friday 9 August, a significant source of energy generation is immediately lost.
On top of baseload we use a number of technologies and tools to meet variations in power demand in the medium term, when the National Grid can confidently predict that we will need a sustained chunk more power. For example, energy use tends to be lower at weekends than during the working week when most people are in offices or factories are operating. Intra-day, power tends to peak in the early evening when people get home from work and start cooking tea, tailing off at bedtime. The graph below shows the variations in demand over a week in 2012. As you can see, the lowest level of demand was around 30,000 MW, while the highest was between circa 49,000 MW and 57,000 MW — a 40% variation.
Meeting unexpected peaks or short term demand
Finally, short term demand fills the gap between the longer periods of high demand and the difficult to forecast ‘peaks’ of ultra high demand, which as shown above do not last very long. Currently we use generation, not storage, to meet this demand. Most options can power up in a couple of minutes and then be shut off as soon as the peak starts to fall, a common example of which is gas peaker plants. Peaker plants use reciprocating gas engines to produce power and typically run on natural gas. They are also modular, offering greater flexibility in size and site options. They are able to supply standby support to the grid as they can power up in as little as 5–7 minutes, so are often called upon as demand begins to rise.
The only low carbon technology we currently have for grid balancing is pumped storage hydro, which offers a way to use excess power on the grid when it is cheap and release it at peak periods later on. Large-scale batteries will also play an increasing role in future.
Dealing with a changing grid
The way we balance the grid needs to change. First, because the increasing proportion of renewables on the grid are currently having to be turned off, instead of being allowed to generate additional cheap power on particularly sunny or windy days. Second because renewables are variable, and don’t always sync with our daily rhythm — e.g. wind power is often highest in the evenings and at night, during which electricity demand can be lower for long stretches of time. Similarly, solar peaks during the middle of the day at a time when our consumption is lower than others. Third, because we need to decarbonise and that means turning further away from fossil fuels, including gas.
For the grid we have today, gas peakers are an essential part of the power mix. Exciting developments in technology, and particularly battery storage, mean that could change rapidly in the years to come.
Batteries give even greater flexibility than gas peakers. Instead of 5–7 minutes, batteries can release power in a matter of seconds. They can store the energy generated by renewables if it isn’t required at the precise moment it is generated (which in itself is a symptom of the grid we have, since it must be so finely balanced at all times). They can be situated beside renewables to quickly and efficiently store excess generation, and deliver it later so that we can use green energy instead of brown more of the time.
Supporting a changing energy mix
As you can see the grid is a finely balanced operation, one which we undoubtedly take for granted. More renewables can certainly be supported, and indeed need to be if we are to achieve Net Zero emissions. Our power mix is changing rapidly and as it does so the need for greater flexibility and new balancing solutions becomes more pressing.
The planned shut down of traditional baseload power from fossil fuels means we need more sustainable baseload, which could take the form of energy from waste or nuclear. We could also decide to take the large scale storage route, or invest in a Smart Grid — both of these options are covered in more detail in this blog. There may even be solutions we have not found yet.
What is abundantly clear is that how we balance the grid in 10 or 20 years will look very different to how it does today. At Abundance we see it as our responsibility to ensure we back the solutions that can get us to a greener grid fit for the next 100 years to help save our planet.
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