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June 15, 2018

Electric vehicles as Frequency Containment Reserves

Energy solutions

Electric vehicles hold a promise of becoming a key component in providing ancillary services for the power grid. Using the frequency of the grid is a concrete example on how the vehicle-to-grid (V2G) vision becomes reality.

As the amount of intermittent renewable energy production increases, the need for stabilizing the elements in the grid becomes greater. Simultaneous rise of electric vehicles means that the vast majority of future energy storage capacity will have four wheels.

Using EV's for demand response is fairly easy: you either throttle down charging power or take electricity out of the battery with bidirectional charging. Process just has to be based on a signal from the energy system.

 

The grid frequency contains information about supply and demand

Frequency containment reserveThe frequency of the grid (utility frequency, power line frequency, mains frequency) is the nominal frequency of changes in alternating current (AC) in an electrical grid. Typically it is 50 Hz (e.g. Europe and Asia) or 60 Hz (e.g. US).

The actual frequency varies around this nominal value. It drops down when the grid is heavily loaded (high demand and/or low supply) and increases when lightly loaded (low demand and/or high supply).

Simply put, the grid frequency contains information about the supply and demand balance. If the balance is not maintained, the grid can suffer from power outages.  

 

Controlling EV charging with grid frequency

frequency containment reserve-1Our smart EV charging platform enables aggregators to use EVs as reserves for demand response. These reserves can be controlled with any energy system signal, and also with the frequency of the electrical grid.

Let's say that an aggregator has a pool of 1 000 EVs, all charging with 22 kW power (3x32 A, 220 V). The charging power of these cars can be throttled down to as low as 4 kW (3x6 A, 220 V) without the charging event breaking. This creates a reserve of 18 MW for grid stabilization ([22 kW - 4 kW] * 1 000).

The same calculation can be done with bidirectional charging: 1 000 EVs that can push electricity to the grid with 10 kW power create a reserve of 10 MW.

When the grid overloads and the frequency drops, EV charging power is brought down automatically as our charging points are controlled from the cloud. The need to adjust these disturbance frequency containment reserves typically occurs a few times a day and lasts a minute or two, so it has no practical effect on the charging experience. 

 

Building a business from Frequency Containment Reserves

As a first step, the reserve pools described earlier could be sold to a Transmission System Operator (TSO) as Frequency Containment Reserves (FCR). Virta has developed a Proof of Concept together with the Finnish TSO Fingrid that already enables the business model.

A second step would be to get EV drivers on board. Part of the value extracted from the TSO contract should be mediated to the end user, for example as free charging events.

Currently EVs can be used as frequency containment reserves for short-time, temporary disturbances (FCR-D). However, various different kind of reserves will be needed increasingly in the future, as more periodic renewables, such as wind and solar power, are being exploited.

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