Solar energy has long played a subordinate role in France, but now the country wants to catch up. In addition to financial incentives, pilot projects are also promoting the use of solar power - one of which is the Solenbat project in Alsace. Here, procedures are being developed to increase self-consumption of solar production in buildings. Seven partners from industry, science and society are involved; the region and the French equivalent of the Kreditanstalt für Wiederaufbau (KfW) 'Bpi-france' provided 4 million euros for the energy technology equipment and the development of a simulation tool by the University of Strasbourg. Two small residential buildings, an existing building and a new building, as well as two office buildings, also an old and a new building, serve as demonstration objects.

One of the demonstration properties is Socomec's new office building at the company's site in Benfeld near Strasbourg. The property was planned with just under 2300 m² for around 180 employees and designed as a low-energy building in accordance with the French RT 2012 standard. Among other things, it was equipped with thermal insulation and a shading system that is controlled by a weather station. Inside, an LED lighting system, which is based on presence sensors and takes daylight into account to regulate brightness, ensures low energy consumption. Heating and cooling are provided by a revertible groundwater heat pump; in addition, the windows are automatically opened at night in summer to cool the rooms.

Once the building is completed in mid-2014, the energy requirements should be determined and optimizations implemented so that a photovoltaic system can be suitably dimensioned, the optimal orientation determined and the capacity for energy storage determined.

Optimize energy use

The 'Diris Digiware' measuring system with its separable and flexible sensors is suitable for retrofitting existing systems.

© Socomec

The optimization process therefore began with the installation of an energy measurement system. Socomec uses its own products for this: the 'Diris Digiware' measuring system for recording energy consumption and the 'Vertelis' energy management software for evaluation.

Surprisingly, even in a new low-energy building, energy use can be further optimized. Savings of around 30% were expected from the metrological analysis - but within the first four months of analyzing the energy consumption, energy use was reduced by 40%. A significant proportion of the savings were made on the heat pump, which does not have to run at full power at weekends when the building is empty, for example. Further savings were made in the ventilation of the building and in hot water preparation.

Power generation and storage system

A photovoltaic system was to supply the electricity for the operation of the office building. The one-year observation of the load profile created the basis for the dimensioning of the photovoltaic system and storage unit.

The storage system consists of the Sunsys PCS² inverter with 66 kW and 95.2 kWh storage capacity in lithium-ion batteries.

© Socomec

The consumption profile - with work starting in the morning and finishing in the late afternoon - initially suggested an east-west orientation for the panels. However, as the use of energy storage systems was planned, the decision was made in favor of the south-facing orientation. Although it does not match the load profile perfectly, it produces more electricity for storage and therefore enables higher self-consumption.
Simulations helped to determine the capacity of the photovoltaic system. Assuming the highest possible self-consumption in spring and fall, the calculations resulted in a power requirement of 50 kWp. With the system alone, self-consumption amounted to 68% of the energy generated in the autumn and 77% in the spring. In winter, the rate was 87 % and in summer 60 %.
The storage system was also dimensioned for the highest possible self-consumption in spring and fall. Socomec's 'Sunsys PCS²' with 66 kW and 95.2 kWh storage capacity in lithium-ion batteries serves as the inverter and energy storage system. This solution significantly increased the proportion of self-consumption: to 99% in winter and 75% in summer, 87% in spring and 93% in fall. This resulted in cost reductions of 68% in summer and 41% in winter - a significant proportion of which was achieved by capping consumption peaks.

Island operation

In France, there are always problems with the grid supply, for example during a heatwave when air conditioning systems and fans are running at full speed across the country without interruption. Or when unfavorable factors come together, such as in the winter of 2016/2017 when several nuclear power plants were shut down during a cold spell - in France, a third of households use electric heating.

The storage system is also intended to step in during such events and ensure the power supply in the event of a grid failure. The 'Nice Grid' project, the French contribution to the 'Grid-4EU' smart grid project, has demonstrated that the technology used is suitable for island operation of the building with the energy generated during the outage and stored in the batteries. The storage system takes on all the regulatory tasks that are otherwise mainly the responsibility of the grid operator and keeps energy generation and energy demand in balance, stabilizes voltage and frequency and compensates for disturbances such as harmonics or voltage fluctuations. It is also capable of black starts and manages the two critical phases in the event of a grid failure - the start of the decentralized supply and reconnection to the grid - without interruption to consumers.

Playing with the electricity price

Overall, the building's energy consumption was reduced beyond expectations and self-consumption from solar power production was significantly increased thanks to the energy storage system. The system can also cap peak loads and supply the building in the event of a power failure.

Another effect has arisen almost incidentally: The use of energy management software and electricity storage systems opens up the possibility of playing with the electricity price and taking profits from electricity price differences. Particularly in winter, the price in France fluctuates considerably depending on availability. Electricity is then stored from the grid when it is cheap and sold when the price has peaked.

The plan for the future is to identify and implement further optimization potential. The focus here is on further increasing the company's own use. In addition, simulations will be carried out under different electricity price conditions in different countries to ensure the transferability of the project results.

Author: Steffen Breiter is Marketing Manager Germany at Socomec in Mannheim.