Home storage

Home storage systems have enormous, still largely untapped potential for the energy transition. They can not only contribute to increasing self-consumption of self-generated electricity, but also serve as a household buffer. Households thus become a realistic and quantitatively significant starting point for grid-serving load management.


Relevance of this field of application

For some years now, the promotion of decentralised electricity generation from renewable energies has been aimed at strengthening self-consumption compared to feeding into the distribution grid. Home storage systems make it possible to significantly increase self-consumption by acting as a buffer between electricity generation and consumption. In this way, they can increase not only energy efficiency but also economic efficiency in photovoltaic (PV) systems as well as, for example, in heat-controlled combined heat and power plants (CHP).

References

However, the potential of home storage is much greater, both from a societal perspective (energy transition) and from the perspective of private households. This is because home storage could prove to be a key element in leveraging the immense load shifting potential of private households: in 2018, they consumed 129 TWh of electricity in Germany, which corresponds to more than 25 % of total electricity consumption.1

Home storage units can be used here as buffers that mediate between the household as a whole and the electricity distribution grid - independent of any electricity generation of their own. This means that the load management potential of households is not limited to individual "smart" household appliances. Instead, it includes a storage capacity that is oriented towards the electricity consumption of the entire household. Household buffers could thus become a central starting point for grid-serving load management on the consumer side (demand side management).

1 Umweltbundesamt (UBA) (2020): Entwicklung des Stromverbrauchs nach Sektoren.
Link ↗ (Zugriff am 15.01.2021).


Use of battery storage

The battery is located in a home storage system between the house connection (to the distribution grid) and the sub-distribution (to the house grid). It can be used to "store" electrical energy from the surplus of one's own generation or to relieve the distribution grid.

If a home storage system is used to increase self-consumption of self-generated electricity, the dimensioning of the battery primarily depends on the size of the installed PV system (or CHP) and the consumption behaviour of the household. Capacities between 5 and 10 kWh are common. If, on the other hand, home storage is used as a household buffer, the household consumption including any consumers with high loads (e.g. electric mobility, sauna, etc.) is decisive.


Performance requirements

Because of their location in residential buildings, high demands are placed on the operational safety of home storage batteries. In the early days of home storage use, cases of battery fires made headlines. More advanced technologies make it possible to virtually eliminate this risk.

For homeowners, investment security is also of decisive importance: the purchase of a PV system or a CHP unit, as well as the integration of a battery storage system into the household's electricity supply, are projects that are planned for decades. The performance of the battery used must therefore be guaranteed over a long period of time - comparable to investing in a new roof truss, for example. This is especially true when home storage batteries are not used as mere solar storage units, but as household buffers. In this function, they are confronted with higher demands on their cycle stability: It is precisely the intensive use of the storage unit for load shifting that is sought in this utilisation concept.

Home storage systems are socially relevant above all for achieving the goals of an environmentally compatible and geopolitically secure energy supply that the energy transition is striving for. This means that the resource efficiency of the batteries used also plays a central role: these can only make a credible contribution to the energy transition if their production itself meets high environmental and resource standards.


Market outlook

The addition of PV systems in Germany has increased again in recent years after a phase of low growth.2 The installed capacity at the end of 2019 was around 49 GW from 1.8 million systems. A total of 46.5 TWh of electricity was produced; this corresponded to 8.2 % of gross electricity consumption. Homeowners generally purchase systems in the output class below 10 kWp and thus have a share of just under 15 % of the total installed output.3

The home storage market is growing rapidly. After a sharp increase of 37,500 to around 96,000 in 2017, the number of installed home storage units doubled to 206,000 by the end of 2019.4 Although most home storage systems are connected to a PV system, only a fraction of PV systems are equipped with storage.5

The potential for using home storage as a household buffer is incomparably greater. In Germany, there are over 19 million residential buildings6 with over 41 million homes7. With a usual storage dimensioning of 5-10 KWh per system, this results in a calculated potential of 94 to 187 GWh for home storage at the national level alone.

 

2 Strom-Report (2020): Photovoltaik in Deutschland.
Link ↗ (Zugriff am 15.01.2021).

3 Wirth, Harry (2020): Aktuelle Fakten zur Photovoltaik in Deutschland. Fraunhofer ISE.
Link ↗ (Zugriff am 15.01.2021).

4 EUPD Research (2020): Ende 2019 sind gut 200.000 Heimspeicher in Deutschland installiert: sonnen und BYD als führende Anbieter.
Link ↗ (Zugriff am 18.01.2021).

5 Figgener, Jan; Stenzel, Peter et al. (2020): The development of stationary battery storage systems in Germany – A market review. Journal of Energy Storage, Vol. 29.
Link ↗ (Zugriff am 18.01.2021).

6 Destatis (2020a): Gebäude und Wohnungen.
Link ↗ (Zugriff am 15.01.2021).

7 Destatis (2020b): Bevölkerung – Haushalte und Familien.
Link ↗ (Zugriff am 15.01.2021).