13 Grid stability {Storing energy for a stable supply}

Self-sufficient or connected to the large power grid?
At a first glance, it might seem tempting to be completely autonomous from the power grid. One’s own solar system and battery storage appear to make this possible. However, unless we are talking about remote mountain huts or islands without electricity, this is rarely a good idea. The problem: The capacity of the battery storage would have to be very large to provide electricity even during weeks of little sunshine during winter. This would be very expensive and consume a lot of resources, especially if lithium-ion batteries were used. Even with more environmentally friendly saltwater batteries, there is no point in storing enough energy to prepare for winters with little sunshine.

Island networks or supergrid?
If an entire village links their power supplies and uses different renewable energy sources, e.g. solar power, wind, biogas from waste biomass, and hydropower, the situation is different already. Usually, more wind energy and water power are available in winter months, so that less energy storage per household is required. But even then, a lot of storage capacity is required to ensure that longer periods of combined low light and calm wind can be bridged.
The bigger the electricity network, the better a power shortage in one location is compensated by a simultaneous power excess in other places. If national power grids are interconnected to a European supergrid with high-performance DC (direct current) power lines, supra-regional macro weather conditions play hardly any role any more: while a high pressure area (anticyclone) brings lots of sun to one region, a low pressure area (depression) provides wind elsewhere. In addition, large and well-priced reservoirs in Scandinavia and the Alps can help to compensate seasonal fluctuations.
In such a large network it makes sense to use power-to-gas and power-to-liquid in places where a particularly large excess of electricity can be generated cheaply from wind, sun or geothermal energy, e.g. in North Africa or by offshore wind power. Gas pipelines and already existing huge gas storage facilities allow for seasonal storage. If synthetic methane from renewable power-to-gas plants is converted back into electricity, cogeneration (combined heat and power) is a good idea to make efficient use of the energy. The heat could be fed into local heat supply or, if only little heat is required at the time, even into a heat storage system.
 

Conclusion: storage integrated into a super grid
Networking provides the opportunity to carry out both power generation as well as power storage in places with lowest costs and least environmental impact.
In this case, the battery in the basement does not necessarily provide complete independence from the power grid, but compensates for the daily fluctuations in solar energy. For the individual, this is profitable if the feed-in tariffs are low and purchased electricity comparatively expensive. Which combination of decentralized and large-scale storage technologies will be the cheapest, safest and most environmentally friendly in the long term cannot be said today, yet.
 
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