Combining battery storage and solar panels merely enables homeowners to increase the proportion of self-generated electricity they consume themselves rather than feed into the grid, and cannot be used to contribute to grid stability. This is a widespread assumption which may no longer hold true. According to a study by market research firm Prognos, the use of solar batteries in southern Germany alone – the region with the most PV plants in the country – could reduce grid expansion costs by more than EUR 100 million per year. The reason: modern storage technology meets the technical requirements for automatic grid-optimised feed-in of solar power on the basis of weather and consumption data. This could help prevent feed-in peaks in the middle of the day, substantially reducing the need for grid expansion measures that would otherwise be necessary, the study claims.
This is good news for the industry, providing a solid counter-argument to the claim that vigorous expansion of PV will give rise to runaway grid expansion costs. What is more, smallscale solar storage offers a relatively simple way of flexibly adjusting PV to grid conditions: in the event of a surplus in the power supply, the batteries can simply retain the solar electricity until it is needed. This relieves some of the pressure on the solar industry to develop alternative, more complex storage solutions such as power-to-gas technology, which uses electrolysis to convert excess electricity into hydrogen. “Simulations show that even in the event of higher feed-in volumes of solar electricity in the future, the problem is not insurmountable. Home storage can play a key role in the solution,” says researcher Raphael Niepelt of the Institute for Solar Energy Research Hamelin (ISFH). Consequently, home storage providers are developing business models which go beyond simple domestic consumption and allow a wider range of applications for the technology. Anyone using solar electricity directly from their own rooftop without intermediate storage can achieve own consumption levels of around 30 percent. A home storage unit can increase own consumption to between 70 and 80 percent.
Leipzig-based company Senec now claims to have developed a concept which promises full autonomy from the grid. To achieve this, 500 household storage units are connected virtually. Any solar electricity not immediately consumed or stored in batteries is passed on to the “Senec Cloud”, which acts as a form of intermediate storage, saving the power for later use. Owners who consume less power from the cloud than they contributed over the course of the year are remunerated at a rate equivalent to the applicable feed-in tariff, currently around EUR 0.12 per kilowatt hour (kWh). Those who consume more than they contributed are charged EUR 0.29 per kWh – around the same as they would have paid for household mains electricity.
This is an abridged version of the article “Balancing act” – the full text is available in new energy issue 5/2016.