Balcony power plants are only for support and allow a part of the electricity consumption to be covered with self-generated electricity. However, only a part of the generated electricity can actually be used by oneself; a significant part is given away free of charge to the grid operator due to a lack of simultaneous consumption. This can be changed with batteries for the plug-in solar power plant. Thanks to low acquisition costs, it's even worth it.
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Such systems have been available for a long time – but usually at high prices. And that was the problem: the storage systems simply did not pay for themselves over an assumed lifespan of 10 years or even up to 15 years.
Practical example of cost-effectiveness
A balcony power plant that is not optimally set up with two solar modules with a total peak output of over 800 watts connected to a micro inverter with an 800-watt output delivers roughly around 500 kWh of electricity per year in Northern Germany. Without time-controlled consumers switched on specifically during sunny periods, more than 200 kWh often end up as a donation to the struggling grid operator. The self-consumption rate is therefore roughly 60 percent, a truly practical and common value.
Even with a cheap electricity tariff of around 24 cents per kilowatt-hour, this is an annual gift of around 50 euros. A storage system cannot bring the self-consumption rate up to 100 percent, but 85 percent should be realistically achievable. Rounded up, this means saving 40 euros per year. If the batteries last for 10 years, as manufacturers promise with 10-year warranties, they must cost less than 400 euros to be worthwhile in any case. And since last December, prices for affordable storage systems with more than 2 kWh capacity have only been just over 300 euros.
Meanwhile, storage systems like the Marstek B2500-D are available for around 320 euros; the Growatt NOAH 2000 is in a similar price range; with 1.6 kWh, the Anker Solix battery with slightly less capacity is now available cheaply. Some offers also include a smart meter for a small surcharge, which measures consumption in the fuse box and thus enables demand-based power output from the 2-kWh storage (usually scalable with multiple devices up to 6 or 8 kWh) and thus achieves an optimal self-consumption rate.
Installing such storage systems is simple. Connect the solar modules from the micro inverter to the storage system and the battery outputs to the micro inverter inputs, and the setup is complete. The storage systems are thus inserted between the solar panels and the inverter. An IP65 or even IP66 certification allows outdoor installation in wind and weather.
In this configuration, manual feed-in rules can be set for these storage systems. For example, the feed-in into the home network can be limited to 200 W during the day, and then 400 W can be output in the evening during typical television viewing times.
However, with the installation of a networked intermediate meter, such as the CT-002 included with many Marstek offers or a Shelly Pro 3EM known from smart homes, in the control cabinet, things become really flexible and optimal. These meters tap into the individual phases from the circuit breakers to measure the voltage, while inductive current clamps are clipped onto the phase supply lines. Such installations require professional hands of a trained electrician according to the rules in Germany. Therefore, a small additional charge usually has to be factored in for this – depending on the electricity price; this then again approaches the amortization limit to the battery lifespan.
In the apps for the storage systems, the smart meters can be integrated, and then the feed-in can be automatically adjusted to the current demand up to a maximum of 800 watts. Demand-based feed-in helps optimize self-consumption as much as possible. Due to the longer amortization periods, this may be a zero-sum game, but due to the persistently high electricity prices, amortization is now possible even with this. This then brings more than just the good feeling of generating and using as much renewable energy as possible yourself.
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