Intermittency of Renewable Energy

2005 October 7
by Chris Vernon

Wind turbineOne of the common complaints levelled against the deployment of renewable energy like wind and solar on the national grid is that of intermittency. What good is a source of energy if you can’t rely on it to be there when you need it? Intermittency is managed today by ensuring that intermittent sources only provide a tiny fraction of the total supply or by keeping reserve generation capacity ticking over in the background ready to step in on short notice as the wind drops.

This situation isn’t ideal and isn’t necessary. Today you and I sitting at home in front of our grid-connected computers expect the moon on a stick, we expect to be able to use any and all of our electrical appliances for as long as and whenever we want. This grade of service is difficult to maintain and will become impossible as we decommission our ageing nuclear fleet and burn through the last of our indigenous North Sea gas. In the future we will be left reliant on more intermittent sources of energy leaving us with the challenge of maintaining our comfort and utility from this new source of energy.

We must adjust our energy consumption is such a way that we don’t all, up and down the country, make demands on the grid at the same time or when the wind isn’t blowing.

My first (and totally impractical but I mention it here to illustrate the point) idea of how this could be accomplished involves having two circuits in the home, a red circuit and a green circuit. The electricity to each circuit would be metered separately and charged at different rates, for example the ‘red electricity’ might be 10 pence per kWh and ‘green electricity’ might be only 2 pence per kWh. The difference between the two would be reliability. The red circuit would be virtually 100% reliable, into this circuit you would plug the freezer, fridge, some lighting, central heating pumps etc. The important appliances. The green circuit would be less reliable, it might regularly cut out at times of peak load, advert breaks in Coronation Street, unusually cold weather or when the wind wasn’t blowing. The important point here is that really important appliances wouldn’t be lost when there wasn’t enough power. A power cut on the green circuit wouldn’t really matter that much, we would be more tolerant of the intermittent supply than we are now where a power cut means lights out, game over.

Of course no one actually wants two circuits in the house and just having two circuits doesn’t provide a very smooth response. What we really need is for demand to automatically shape itself to match instantaneous supply and we want this to happen without us even noticing. Not possible? Well maybe it is. This is where Dynamic Demand and appliances that can continuously monitor the condition of the grid and adjust their usage accordingly come in.

To quote straight from their site:

Dynamic Demand aims to promote the introduction of “dynamic demand control” technologies on the UK power grid by advocating institutional change and stimulating research and discussion.
Demand control technologies could provide significant stability and peak demand management for the electricity network. This could lead to significant carbon dioxide savings and may help facilitate the connection of greater amounts of intermittent renewable energy generation, such as solar and wind power.

This is a snapshot of a meter monitoring the power balance of the UK electricity grid (click the meter to see the live status of the grid).

The meter shows the grid’s “frequency”, which is related to the speed of rotation of generators all over the country. When there is too little power available, the whole grid “slows down” and the needle moves to the left.

This can be measured from any power socket by any electrical appliance; the appliance would know the instantaneous imbalance on the grid. These dynamic demand appliances would react to this information, switching on and off or just adjusting their consumption with respect to how much power was available.

Millions of such devices acting together would act like a huge, fast-reacting back-up system mitigating the problem of intermittency.

What is happening?
There is Early Day Motion 388 tabled by Colin Challen MP and the “Management of Energy in Buildings” Bill which introduces dynamic demand is being introduced by Alan Whitehead MP.

There is information on how you can ask your MP to support Dynamic Demand here.

Dynamic Demand looks to me to as a fantastic way to address the inevitable problems facing our electricity supply and the enabling technology for greater use of renewable intermittent energy sources whilst avoiding the threat of complete blackouts at peak load. Maybe at peak load your Dynamic Demand electrical shower, oven or hair dryer wouldn’t work but losing the utility of a few devices like that for a short while is far better than the alternative of widespread blackouts.

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