Sponsored by the German Federal Ministry for Economic Affairs and Energy: Paving the way for solar energy in the power grid Research into storage technology for rooftop photovoltaic systems on single-family homes

  • “PV Home Storage System” (PV-HOST) research project
  • Optimizing battery systems in 10 kWh size class
  • Energy storage systems make important contribution to Germany’s move to alternative forms of energy
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  • May 02, 2014
  • Research
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press release

Stuttgart – 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 household’s 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.

Optimized 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 Germany’s 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.

Research collaboration
Led by Robert Bosch GmbH, the research project has two other partners – the Institute for Power Electronics and Electrical Drives (ISEA) at RWTH Aachen University and münsterNETZ GmbH, the grid operator for the Münster municipal works. PV-HOST began in July 2013 and will run for four years. The project is part of the German government’s Energy Storage Funding Initiative and has received a grant of three million euros from the German Federal Ministry for Economic Affairs and Energy.

Background information online:
Energy Storage Funding Initiative
KfW support for solar energy storage systems

Organizations involved in the project:
German Federal Ministry for Economic Affairs and Energy
Robert Bosch GmbH
ISEA Institute for Power Electronics and Electrical Drives, RWTH Aachen University
münsterNETZ GmbH

The Bosch Group is a leading global supplier of technology and services. It employs roughly 375,000 associates worldwide (as of December 31, 2015). The company generated sales of 70.6 billion euros in 2015. Its operations are divided into four business sectors: Mobility Solutions, Industrial Technology, Consumer Goods, and Energy and Building Technology. The Bosch Group comprises Robert Bosch GmbH and its roughly 440 subsidiaries and regional companies in some 60 countries. Including sales and service partners, Bosch’s global manufacturing and sales network covers some 150 countries. The basis for the company’s future growth is its innovative strength. Bosch employs 55,800 associates in research and development at 118 locations across the globe. The Bosch Group’s strategic objective is to deliver innovations for a connected life. Bosch improves quality of life worldwide with products and services that are innovative and spark enthusiasm. In short, Bosch creates technology that is “Invented for life.”

The company was set up in Stuttgart in 1886 by Robert Bosch (1861-1942) as “Workshop for Precision Mechanics and Electrical Engineering.” The special ownership structure of Robert Bosch GmbH guarantees the entrepreneurial freedom of the Bosch Group, making it possible for the company to plan over the long term and to undertake significant up-front investments in the safeguarding of its future. Ninety-two percent of the share capital of Robert Bosch GmbH is held by Robert Bosch Stiftung GmbH, a charitable foundation. The majority of voting rights are held by Robert Bosch Industrietreuhand KG, an industrial trust. The entrepreneurial ownership functions are carried out by the trust. The remaining shares are held by the Bosch family and by Robert Bosch GmbH.

Additional information is available online at and,

PI8565 - May 02, 2014

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