April 23, 2021
◼ Grid feed-in hinders the energy revolution
Heating from photovoltaic is a keystone for a sustainable energy future.
"Feed-in doesn't interest me. Feed-in hinders the energy revolution because the power grid can't store it. The energy revolution cannot be continued with feed-in.1" Quoted by Dr. Andreas Piepenbrink, CEO of battery storage manufacturer E3/DC, it signifies how important is the self-usage of self-generated photovoltaic power is for our energy future. Even with the batteries alone, our home storage options are far from exhausted: there is another way to maximize the degree of self-use, in particular through heat generation.
Recent adaptation to the German Renewable Energy Sources Act (EEG) has brought about two major changes. First, the limit for the levy exemption has been raised from 10 kWp to 30 kWp. Thus, the motto for the construction of new photovoltaic systems in Germany from now is: "Fill up the roof first, please! A clever trick by some of the planners to automatically generate a relatively high share of self-consumption through the smallest possible system would be a thing of the past. And secondly, lucrative compensation is over anyway. Selling the kilowatt-hours fed into the grid at the market price is financially unattractive.
But where to put the excess energy?
To solve this problem, the first choice is usually to install a battery storage system. There is no doubt that batteries, whether stationary or in electric cars, are an essential part of the energy revolution. However, the storage capacities are usually still quite small. Typical batteries in single-family homes have a capacity in the order of 5 to 10 kWh. Considering the generation capacities on the roofs, this is quite an inconsiderable capacity, which unfortunately means an insignificant investment step for the operators to date.
A cheaper alternative to this is heat generation. Power controllers that divert solar energy for heat generation modulate the heat output precisely adapted to the respective excess PV energy situation. They have been entrenched in the market for several years now and are available at a low cost. Additionally, hot water boilers, buffer tanks or any heating system energy storage capacity in the building can absorb incomparably more energy than the batteries.
Batteries are often already fully charged in the course of the morning
However, to reduce the load on the power grids and prevent the power limitation or even the shutdown of PV systems, it is important to use as many forms of storage as possible. Above all, the worst for energy revolution is to not utilize the free & clean energy from one’s rooftop PV. Consequently, a combination of battery and heat storage is now also available as a combined system solution.
Especially this combination creates maximum self-usage, as on days with good solar irradiation it can be often observed during noon that the batteries are fully charged as illustrated in the figure. From this moment onwards, there is a lot of excess energy available, which can be consumed in the house. For example, water heating, termed as "PV power-to-heat" and "integrated energy" are indications that the concept is now in the process of becoming entrenched in-home automation.
1 https://youtu.be/11bpNgfg7GU, Minute 25, accessed 3/24/2021