The power system is run by a complicated mix of agents. On top of that, different countries organise themselves differently, and both economics and engineering skills are needed to provide consumers with electricity. Nevertheless, the nature of electricity is such that it needs to be utilised, or consumed, when it is generated. This means that when you turn on the light in your apartment, the power that lights up your home needs to come from some generating unit which is connected to the same grid as the one you draw your power from. In theory, this needs to be instantaneous, but mechanical energy stored in rotating masses and the size of the energy system means that the small change in consumption you trigger by turning on your light doesn’t really matter in the big scale of things.

If the consumption increases significantly though, for example if many people start up their electrical appliances at the same time, and the generation doesn’t follow, the frequency of the grid will drop. Similarly, if a power plant fails, the frequency will also drop. Conversely, if an additional generating unit is connected and the demand drops relatively, the frequency will increase. Thus, the grid frequency provides a measure of how well the power supply always matches the power demand. In Europe, the nominal grid frequency is 50 Hz, and it needs to be kept close to this value to avoid damaging equipment or triggering disconnections.

Keeping this balance has become more difficult with more renewable generation from wind and solar power. Traditional renewable generation from hydro power and other generation from fossil fuels can largely be controlled and adjusted to yield a higher or lower power output according to the demand. The dominant solar and wind power technologies, however, are intermittent and depend on the meteorological condition, generating when the sun shines or the wind blows, respectively. They also differ from traditional technologies in not contributing with inertia from big rotating masses, which, as I briefly mentioned, cushion the impact of changes in power generation or demand.

Now this is where the need for flexibility comes into the picture. In general system operators are responsible for maintaining a stable grid frequency. When the generation can be controlled to a lesser extent, several countries have explored making use of flexibility among the consumers, affecting when they use electricity. This can be by temporarily disconnecting electrical heating systems for example or deciding when an electric car draws its power. Another solution is to make use of energy storage technologies, which makes it possible to save energy for shorter or longer amounts of time. Different approaches are still being tested, and I’m following the development eagerly. Hopefully, transitioning to a fully renewable energy mix won’t prove to be too much of a stretch.

Do you want to work on the integration between renewable energy and the electric systems? Check out the EIT InnoEnergy programme that I completed: Master’s in Smart Electrical Networks and Systems!

 

 

By Maria Isabel Bipop Bang Jensen, EIT InnoEnergy Master School alumna

Photo credit: Eric Griess