Commercial Battery Management
Another great one from Sam Kitching…
Renewable energy has a variable-output simply due to the very nature of weather, and in the UK, renewable energy capacity has grown dramatically surpassing fossil fuels for the first time in October-18 as part of the UK’s commitments to carbon reduction.
What does more renewable energy have to do with batteries?
In the simplest terms, most renewable generation such as wind or solar are highly variable – the wind doesn’t always blow and at night the sun doesn’t shine. In detail, introducing intermittent generation reduces system inertia, a property of the transmission system that provides robustness against any frequency disturbances due to traditional generation involving a large rotating mass like that in a generator or motor. This poses a big challenge for National Grid as the system is now more susceptible to a quicker change in frequency. This means we require balancing services to act quicker and at greater capacity to maintain the system frequency within statutory limits and thereby security and quality of electricity supply across Britain’s transmission and distribution systems. This is one avenue for battery use.
How are batteries used to balance grids? A case example.
One of the ways batteries can be used is alongside renewable generation assets. On the river Ruhr in Herdecke, Germany, a new large scale battery storage facility is used in primary frequency control alongside an existing pumped-storage asset via a fully automated load control system. It is composed of over 550 battery modules that each weigh over 120 kilos. They are actually produced by Daimler and are actually the same as those found in some Daimler and Mercedes electric cars. The facility is able to conduct, store and discharge 7 MWh.
The attached hydro plant works quite simply. When supply is higher than demand, water is pumped into a storage reservoir and relieves the system stress. When supply is lower than demand, water is released downwards through a pipe to generate electricity. At all times, the power is monitored and the batteries can compensate for any imbalance on the grid to reduce system stress.
It can also be used to reduce the effect of renewable generation’s variable output on the grid (more applicable with Wind or PV) providing balancing services.
What is the future?
In a small grid, a single device could be used for balancing, but in a larger grid, several devices must be distributed and synchronised. The Enhanced Frequency Control Capability (EFCC) is a three-year project by National Grid where battery storage is central to the monitoring and control system that will coordinate fast responses from generation and balancing services based on central and local signals (shown in the graphic below)(3). It can also be used to tackle National Grid’s inertia problem by combining a battery with a fast reacting inverter to provide a “virtual inertia”.
NG EFCC Control System Architecture – EFCC National Grid Paper
There are numerous types of batteries including flow, lithium Ion and lead acid. Important to consider when deciding is the target rate of change of frequency (RoCoF) events as this typically defines requirements such as response time, battery recycle rate, power to capacity ratio and a C Rating, an indicator of the continuous discharge rate. For example, flow batteries are not applicable for EFCC as they have a response time greater than 0.5s due to time it takes electrolytes to mix.
Not just local grids
It also does not need to be exclusive to the grid and big companies; Telsa, Mercedes and others supply high-capacity lithium-ion batteries for domestic customers, like you and me, to store energy produced from solar panels. This tackles the fact that energy usage is generally higher in the evenings when PV does not work well, therefore addressing supply and demand.
Companies are also producing Smart Home applications and devices that will utilise the battery capacity of your car and other devices to manage your energy usage with increasing sophistication to reduce customer costs whilst increasing efficiency of supply and demand. Services such as demand side response in which participants manage usage on the grid to reduce energy costs could generate consumer savings of £2.9-8.1 billion per year by 2030 due to increasing network and policy costs.
In the future, we would expect to see both the industrial and domestic systems coordinating supply and demand to reduce the increased risk a system with low inertia has on security of supply. This is already happening with new auctions for balancing services and start-up companies developing systems, such as Piclo Flex, that function as flexibility marketplaces for Distribution System Operators (DSOs).