Independent autarkic energy-supply with natural energy (without gazoline and Uranium) requires necessarily an adequate energy storage.
Doing an unbiased search via a simple quick Google standard search "energy storage" , we automatically end up with electrical energy storage devices and there especially with lithium-ion accumulators. These belong to the fashionable trends, are considered "high-performance" and "high-tech", but are absolutely unfavourable from a financial point of view. The prices are in the range of €450 ... €1200 per kWh, which makes manufacturers happy, but not consumers (as of June 1, 2021).
This is not what really helps us. What we (as energy consumers) need are inexpensive, robust, long-lasting solutions to enable cost-efficient supply everywhere.
If we then look to individual offers in a little more detail, the prices become somewhat more favourable, but not really significantly lower. One of these offers, the cheapest I found (as of June 1, 2021), comes to €354 per kWh, for example:
Sometimes the calculation of energy storage prices is also given in cents per kWh. See for example: https://www.energieheld.de/solaranlage/photovoltaik/stromspeicher/kosten
This price calculation there follows a very simple formula that satisfies our elementary intuition:
Storage price [in cents per kilowatt hour] = purchase price of the device [in euros] / storage capacity [in kWh] / lifetime of the device [in number of charge-discharge cycles].
Typical values can be found on the Internet in the range of 12 cents per kWh. The cheapest special offer quoted above, comes to 9 cents per kWh. Much higher prices can be found easily. I feel, that this is much too expensive for real applications.
By the way, most suppliers do not mention the finite efficiency (COP) of the different energy storage systems, which is a real disadvantage in many cases.
Such high storage prices are in a region, which large corporations pay for energy purchase. We don't really want that. So we have to research basically, which possibilities of the energy storage exist at all, in order to get a REAL alternative. An overview of the known technologies can be found at "Statista":
These are the following:
Coils, Superconducting Magnetic Energy Storage (SMES)
Capacitors / Super-Caps
Flywheel mass storage
Compressed air storage
Lead - sulfuric acid batteries
Since we are looking for low-cost robust long-life solutions for broad mass use, we do not need to consider all of these variants, for instance not such as coils and superconducting magnetic storage, capacitors and super-caps, redox-flow batteries.
Our declared goal is an improvement of the storage price by at least minimum one power of magnitude (which is a factor of ten), compared to what the accumulator suppliers (see above) present on the Internet. Thus, our aim is a purchase price in the two-digit price range, clearly less than 100 € per kWh, and a price per kWh below a single cent per kWh, in numbers: less than 1 cent per kWh. This brings us to the following systems to be considered:
=> Which system should we reccomend ? Well, it depends on the circumstances.