How do you become independent of the power grid?

Photovoltaic systems for private households have become increasingly popular in recent years. Not only are they environmentally friendly, but they also provide relatively cheap electricity. But only when the sun is shining. At night and in the winter months, solar panels do not provide enough energy, so it still has to be obtained from the grid. On sunny days, on the other hand, more electricity is generated than a single household needs. So it seems sensible to store this energy for bad times. But that’s not quite as easy and it’s not always profitable.

Every owner of a photovoltaic system can feed excess electricity into the grid and is paid a so-called feed-in tariff for this. How high this is also depends on the age of the system. For systems that have been in operation for some time, a fixed rate is paid that does not change for 20 years. It can be over 30 cents per kilowatt hour: That is more than it costs to generate the solar power, so it promises profits.

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In the case of newer systems, on the other hand, the Renewable Energy Sources Act (EEG) stipulates that the feed-in tariff decreases over time. It is currently between 6.2 and 13.4 cents, depending on the size of a system and the proportion of electricity that is fed into the grid. According to Stiftung Warentest, this is often less than it costs to generate solar power. Operating a system primarily to sell electricity is then no longer worthwhile. Newer photovoltaic systems are only profitable if you use as much solar power as possible yourself an expert from Stiftung Warentest.

Batteries don’t always pay off

If you want to use more of the self-generated solar power in your own household, you can also buy a battery storage system with lithium batteries. About every second new solar system is equipped with such systems today. Excess electricity that is generated during the day is then no longer completely fed into the grid. Instead, it is used to charge the batteries. The energy stored in this way can then be used during the night.

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The self-used share of the electricity produced can According to the Federal Association of Consumers (VZBV) can thus be increased from around 25 to up to 70 percent for a single-family house. Battery storage also ensures greater independence from the grid. However, the storage systems are relatively expensive: a kilowatt hour of storage capacity costs between 750 and 1200 euros, with government subsidies varying in amount depending on the system and the federal state. Of the VZBV recommends a storage capacity of one kilowatt hour for every 1000 kilowatt hours of annual consumption. This means that for a household that consumes 6000 kilowatt hours of electricity per year, the batteries should be able to store six kilowatt hours. According to an industry analysis, consumers invested an average of 11,000 euros in batteries for their solar power systems in 2020.

Such a system can pay off in the long term, since more self-produced electricity is used, which is cheaper. However, according to an assessment by the VZBV, it is not always certain whether the expenses for the battery can be offset: “The question of the profitability of a battery system depends heavily on the expectations for the development of the electricity price in the coming years. It is currently very difficult to make a prognosis on this, ”says a publication by the association.

Hydrogen storage still too expensive

Some battery storage systems can also be used as an emergency power generator. For example, some have an emergency power socket that can be used in the event of short-term power failures, but only for a limited time. In any case, a battery system does not make households with solar systems completely independent of the power grid, as they only store small amounts of electricity. In the winter months, a photovoltaic system always supplies so little electricity that additional electricity has to be drawn from the grid. Battery storage with its relatively low storage capacity does not change that.

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Storing solar power for weeks or even months, on the other hand, is only possible with a different technology: solar power generated in summer is used to produce hydrogen from water. This can be stored in liquid form in gas cylinders or pressed into metal pellets. In winter, the hydrogen can then be used to generate electricity with the help of a fuel cell. With such systems, a completely self-sufficient supply would be possible all year round. However, to date they have hardly been used in private households.

There is a risk of explosion if hydrogen is handled incorrectly, which is why storage tanks have to be set up outside the house. The technology could also be more mature and is extremely expensive to purchase. The company HPS, which offers such hydrogen storage systems, estimates the costs at 85,000 to 120,000 euros. The expenses therefore far exceed what consumers would have to pay for electricity without a solar system. However, it is to be expected that the technology will continue to develop in the coming years and will probably also become cheaper and perhaps even safer.

Correction: In a previous version, we accidentally specified the product name Picea as the company name of HPS.

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