The number of single-family homes installing rooftop photovoltaic systems is steadily rising; any extra electricity they generate has to be fed into power grids as required. However, these grids, built up over many years according to historical need, are not always able to absorb all the electricity produced. Especially in areas with a lot of distributed producers, this kind of overloading will only get more acute without outside help. This is where battery storage systems for buildings with solar arrays come in: they store electrical energy until it is either needed within the household or can be absorbed by the grid, smoothing out supply peaks and increasing grid capacity. If stationary storage systems with a capacity of up to ten kilowatt hours are to work cost-effectively and efficiently feed the electricity generated into the grid, what should they look like? The current PV Home Storage System (PV-HOST) research project explores precisely this question. The goal of the project is to optimize distributed battery storage from both technical and economic perspectives. To do this, three research partners are systematically comparing the solar storage technologies currently available from German manufacturers that are potential candidates for use in single-family homes over the next few years.
Better interaction between energy storage systems and the grid
At present, less than one percent of German single-family homes with photovoltaic systems have a solar energy storage system despite incentives by the government-owned KfW development bank to invest in this technology. Previous research projects in this area concentrated on further developing a specific storage technology and generally sought to increase the proportion of electricity households used that they themselves had generated with the goal of making them as self-sufficient as possible. In contrast, the PV-HOST project provides an overview of the different technologies. The researchers want to find out what operating strategy allows a household storage system to most effectively serve grid needs. In other words, the storage system should not just cover the households own needs, but also reduce supply peaks, ensuring that the grid can absorb more energy from solar installations on the whole.
Comparing different battery types
The project partners are evaluating four battery types: lithium-ion, lead-acid, high-temperature, and redox flow batteries. For each type, the researchers are working out the technical and economic potential. On top of this, they are investigating three further issues: the optimum configuration of the entire photovoltaic storage system effectively, the size and power of the various components the optimum operating strategy for the battery storage system, and the optimum means of integrating distributed storage systems into the power grid. In particular, the team wants to subject lithium-ion batteries to comprehensive lab and field tests. The goal of the research into high-temperature batteries is to minimize heat loss and thereby improve efficiency.
Optimised technology for lower costs
In order to increase renewables share of overall power supply, storage technology has to be further developed. PV-HOST is contributing to the success of Germanys move to alternative forms of energy, because solar energy storage systems have a big role to play here. They allow more photovoltaic systems to be usefully integrated into existing grids, meaning that less power is required from conventional power plants. Compared to central storage systems, battery storage systems have the advantage of presenting a lower investment hurdle. In addition, the self-generated electricity households feed into the grid is very lucrative for them. Another key issue is costs, and here the researchers are seeking to optimize battery storage systems to make them even more cost-effective.
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