Jennifer Runyon, Chief Editor, RenewableEnergyWorld.com
April 28, 2014 | 10 Comments
The Electrical Structure of Carros — A “Smart City” by the Sea
The city of Carros, population 11,000, is located just outside Nice, France, which lies on the Mediterranean ocean. There are 5,900 residential electricity customers and 136 industrial electricity customers and total installed capacity for the city is 2.5 MW. In France baseload power is supplied by hydro (30 percent) and nuclear (70 percent). Peak demand for the residential customers is 30 GWh and for the industrial customers it is 20 GWh.
The city was selected to be part of the pilot program due to its location on the periphery of France’s transmission grid, its abundant sunshine and its broad consumption needs: there are apartment dwellers, residential homes and industrial facilities all within the small city limits.
As part of the test project, the consortium is seeking 550 residential customers and 11 industrial customers to participate in voluntary load shedding. A portion of those will also be equipped with solar PV.
Three Levels of Energy Storage
Interestingly, in the Nice Grid grid, energy storage capacity in the form of batteries will be installed in three different levels on the network offering the grid operator maximum flexibility according to Alstom. “Flexibility through energy storage is no longer a concept,” said Davy Theophile, Conversion Solution Director with Alstom in a presentation about about the Nice Grid energy storage system.
The centralized 1-MW battery (already in place) stores 560 kWh of energy and is located at the point between the high-voltage transmission line that transmits power to the region and the distribution network that sends power to the customers. This battery, which can provide 30 minutes of energy storage is is used for peak shaving, explained Theophile. The battery plus voluntary load shedding or demand response reduces the need for ERDF to purchase additional power when demand spikes occur.
The second level of storage is at the residential homes. ERDF is currently recruiting residential customers to be equipped with 3-kW PV systems and 4-kW/4-kWh batteries. They anticipate that about 50 residents will participate. These residential batteries will absorb excess energy in order to manage overvoltage situations that may occur. “So this may happen on a summer afternoon on a sunny day when people are at work or at the beach. Then you may have more production than consumption in some parts of the low-voltage grid,” explained Marc Delprat, Smart Grid Pilot Program Director for Alstom. One way to control for that will be to encourage consumers to use more energy during those times — perhaps run their appliances in the afternoon instead of the evening. (In France, residential consumers are subject to peak rates and off-peak rates. Off-peak rates begin at midnight and grid operators see a spike in demand at that time as residents turn on their electric water heaters at midnight.) One of the aims of the Nice Grid is to see if consumers will shift their behavior at the request of the grid operator. If there is still an over-voltage situation, the batteries will absorb the excess energy.
The third level of energy storage is located at three industrial buildings, which will be equipped with PV systems and 33-kW/100-kWh batteries. There will be a larger 250-kW/600-kWh battery also part of this system, and together the batteries will be used for islanding and load shedding. These batteries will balance the micro-grid in the event that Nice Grid is detached from the main high-voltage transmission line. “To our knowledge this is a world premier — to experiment with such islanding scenario without any kind of rotating device,” said Delprat. “We are doing that only with solar production and battery storage so this is completely carbon free energy,” he added. Overall the storage system should allow for 4 hours of grid independence. See the sketch this page for a breakdown of the energy storage system.
Who is In Charge?
Controlling all of this is the Network Energy Manager (NEM), provided by Alstom, otherwise known as the “brain behind the grid,” according to executives with the company. The NEM collects the solar production and load forecast, imports regional load reduction requests and then calculates local grid constraints and grid constraints and identifies the risks of overvoltage. With this information, it publishes power adjustment needs to the suppliers and computes an optimal schedule of “flexibilities” according to Alstom. (Flexibilities include both demand response and energy storage.) Finally the NEM communicates the activation schedules for the flexibilities and the cycle begins again.
The total cost of the project is €30 million. The EU provided €7 million and the French Agency ADEME provided €4 million as part of its Future Investments Program. The rest of the cost was born by the project partners. The total cost of the energy storage system is about €1.3 million. In total the system will provide about 1,660 kWh of energy storage at a cost of €800 per kWh.
Why Go Through all of This?
In speaking with executives about the Nice Grid there is a sense that a great experiment is underway, driven by an urgency to get in front of the transformation of the electricity grid. Alstom is currently involved in more than 30 smart grid demonstration projects all over the world. The company says that it uses these projects to test functionality and different combinations of innovative technological solutions. Of the Nice Grid, ERDF’s Arnoult explained that his company is concerned about the “dramatic increase of solar generation connected to the DSO grid,” and the potential harm it could do. “We are studying a potential solution to turn this constraint into an opportunity,” he said.
Overall, it seems that rather than recoil from the grid of the future, or fight it tooth and nail, these European energy companies are stepping into the great unknown and testing all sorts of different potential solutions to address all foreseeable challenges. And for that, they should be applauded.
[Editor's note: Want to hear more on this topic? Sign up for our upcoming webcast: Solar and Energy Storage: The Power Behind the Microgrid by clicking on this link.]
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