The French grid goes virtual
RTE's world-first project combines energy storage and digital control to transmit power virtually.
French grid operator RTE is using a Saft energy storage system (ESS) in its €80 million RINGO project, a world-first trial project that will evaluate the technique of virtual power transmission. RTE will use different energy storage technologies at three locations on the grid. Saft and its partner Schneider Electric will deploy a lithium-ion (Li-ion) ESS with power conversion and control systems.
One or two of these sites can inject power into the grid while the other site releases it simultaneously. ln effect, this acts as a virtual power line, transmitting power to where it is needed and overcoming congestion on the grid at peak time.
Like many utilities, RTE is not permitted to influence the price or availability of energy. That rules out using batteries to store energy at times of peak production when the price of energy is low and releasing it later to meet peak demand when the price is high. Therefore, by using multiple ESS sites working together, RTE can deliver power to customers without affecting the energy market or building new power lines.
Providing flexibility for the power grid
RTE estimates that the electricity network will need significantly more flexibility from 2030 to support the energy transition. Electricity is often consumed far from the point where it is generated as we shift from traditional power stations to naturally variable wind and solar generators. Additionally, electric mobility and smart buildings will change the traditional patterns of demand.
The conventional approach to providing new capacity would be to make large investments to upgrade substations to handle growing peak power demand. However, these peaks may only last for a few hours per year. Therefore, RTE prefers 'light' solutions with greater flexibility.
Energy storage has a vital role in delivering this flexibility - for example by riding through sudden changes in supply and demand, storing excess solar energy until it is needed in the evening or supporting virtual power transmission.
How virtual power lines work
ln a typical city, renewable energy could supply a peak demand of 130 MW. However, the existing power lines can only carry 100 MW.
By placing an ESS at either end of a grid bottleneck, RTE can create a virtual power line. This will store 30 MW upstream of the bottleneck at the same time as releasing 30 MW close to the city. As a result, customers in the city can draw the full 130 MW of renewable energy, even du ring peak periods.
Once peak demand is over, the system will discharge the battery system near the generation plant at the same time as recharging the system near the city. Once complete, this will ensure that the virtual transmission line is ready for the next period of peak demand.
This principle can be multiplied with energy storage at many strategic locations across the grid. An operator like RTE could use these to transfer energy in bulk to where it is needed.
12 Saft ESS containers
Under the RINGO project, Saft and Schneider Electric are working together to deliver an installation at Bellac, central France, where there is high solar photovoltaic production. The site is planned to power up in May 2021 and enter service in October 2021.
Saft is supplying a Li-ion ESS capable of storing up to 30 MWh, and with a power rating of 10 MW. This is equivalent to the power production from five wind turbines or the electricity need of 10,000 homes annually.
The system will be based on Saft's lntensium Max 20 High Energy system, which is designed to sustain long charge and discharge cycles of up to four hours. This makes this type of system ideal to caver the typical peak demand experienced on the power grid.
RTE will also build systems with the same energy storage and power capacity at Ventavon in the southeast and Vingeanne in the northeast of France. These locations were selected due to their high renewable energy production.
Three-year trial period
The RINGO project is due to enter operation in 2021 for a three-year trial of the virtual power lines. After that, the energy storage capacity will be available to support other services, such as frequency regulation, grid balancing and energy arbitrage.