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Battery storage for solar systems

Why battery storage? Storage is useful for the energy transition!

"In order to achieve a better adjustment between energy production and consumption, in addition to measures such as load management, stationary storage for electrical energy can also be considered." Quote from the VDI seminar
Why first a large solar system?
If only little solar energy is generated, only little excess energy can be stored. Only when the roof is fully occupied or a size of 15-40kWp has been reached for a private household does it make sense to think about battery storage. Larger solar systems also have lower specific production costs. 40kWp sounds like a lot, but one or two electric cars directly increase consumption by around 10,000 kWh per year. In the months of March to October, it is relatively easy to be almost self-sufficient with battery storage. In the remaining months, a large-scale solar system is important for a still acceptable solar self-sufficiency. Below is a table with the average annual consumption of different household types, the minimum recommended performance of the PV system and the achievable degree of self-sufficiency with and without battery storage. Assumption: Average power consumption per year and recommended solar system size with at least 40% self-sufficiency:
people power consumption Ø Solar system - south roof With battery storage With battery storage
10kWh 20kWh
1 Person 2.000 kWh 5.4kWp / 41.2% Autarkie 81.6% Autarkie 92.7% Autarkies
2 persons 3.300 kWh 7.8kWp / 42.3% Autarkie 82.1% Autarkie 89.2% Autarkies
3 persons 4.300 kWh 7.8kWp / 40.2% Autarkie 76.4% Autar trucks 88.0% Autarkies
4 people 5.000 kWh 10.8kWp / 41.1% Autarkie 77.5% Autarkies 90.1% Autarkies
5 people 6.200 kWh 13.8kWp / 40.3% Autarkie 78.3% Autarkies 89.3% Autarkie
The results look completely different when large consumers such as a heat pump for central heating with hot water generation and/or an electric car increase electricity consumption considerably:
case of need power consumption Ø Solar system south roof With storage 10kWh With storage 20kWh With storage 30kWh
With heat pump
4 people 8.451 kWh 24.5kWp / 39.1% Autarkie 68.4% Autar trucks 73.8% Autarkies 80.1% Autarkie
With WP and EV
4 people 13.542 kWh 44.2kWp / 28.0% Autarkie 50.6% Autarkies 64.9% Autarkie 81.5% Autarkies

*All figures were determined with SMA-SunnyDesignWeb. Assumption: South orientation, Li-ion storage with 90% usable capacity. No energy transition without energy storage The driver of the development is the energy transition, specifically: the expansion of renewable energies. Their share in the German energy mix was over 35 percent in 2019. According to estimates, they will account for 55 to 60 percent by 2035. What a sustainable improvement for the climate and environment entails is a major challenge for the power grid: Because the wind doesn't always blow and the sun doesn't shine at night, the increasing proportion of renewables also leads to greater fluctuations in the grid. These can partially compensate for smaller battery storage systems in the private sphere and large battery storage systems in commercial use.

Lithium Ion Batteries Are the Most Efficient Today's energy storage devices are typically Lithium Ion (Li-Ion) and Lithium Ferrite (LiFePo) batteries. The Li-ion cells have the clear advantage of the significantly higher energy density. Their share of the commercially available energy storage is around 95 percent. Earlier models were often still based on lead-gel or lead-acid technology, but today they only account for around six percent of energy storage devices. There are also isolated PV battery storage systems for private households based on salt water as an electrolyte, as well as vanadium redox flow battery storage systems. However, their share in Germany is less than 0.05 percent. This is the conclusion of a study by the Federal Ministry of Education and Research, the Institute for Applied Ecology (Öko-Institut) and FONA, the social-ecological research department of the BMBF. Modern lithium batteries are not only ahead of other technologies in terms of market penetration, they are also cheaper to manufacture, last longer and, above all, are more powerful. “Today's best Li-NCM cells achieve an energy density of almost 700 watt hours per liter of volume. That would be enough to run a 100-watt bulb for seven hours,” say the experts from the Fraunhofer Institute.

Lithium-ion battery cells - here:Tesla-18650 Li-ion battery modules from Tesla Model S and Model X vehicles Trademark notice: TESLA® is a trademark of Tesla, Inc, 45500 Fremont Boulevard, Fremont, CA 94538