It is a known fact of life that both wind and sun are a fluctuating source of energy. The current state of play in the scenario of sustainable energy supply is that there needs to be some way of storing the energy produced to be able to release it at times of high demand. Apart from the fact that the politicians are maneouvering to exclude domestic participants from the party which they have created, the only ways of storing electricity are pumped storage, electrolysis of water or rechargeable batteries. Pumped storage is in use for large scale energy storage, electrolysis of water has not yet been considered, and rechargeable batteries are being considered. The electrolysis of water produces a gas mixture known as HOH which can be burned to power vehicles as an alternative to petrol or diesel or hydrogen. It is relatively stable at atmospheric pressure provided it is not exposed to a source of ignition (as is hydrogen too). The spare electrical energy from domestic and utility scale generation is currently suppplied to the grid where it reduces the load on traditional power stations to supply the grid. Basically if you imagine the supply voltage as pressure from the grid to provide electrical energy, if you exceed that pressure in the reverse sense you export energy to the grid. This is done by sensing the supply voltage and using an inverter to transmit the generated power by exceeding the supply voltage.
The size of the battery banks which would be required to provide mass storage of electricity would be large indeed, and we know that old car batteries can be reconditioned to function adequately although not well enough to start an engine. Instead of immediately recycling the old batteries they could be attached to domestic generators, and by way of control electronics be used to supply electricity at times of high demand in your home when the solar cells are in darkness. Another domestic use for the excess energy is to divert it to heat water in an immersion heater tanlk. This is currently being marketed as an inner sun. The way the FIT(Feed In Tariff) is currently structured every kWhr generated gets subsidised by the other energy users @15p for 20 years. This is set by government.
You get paid this whether or not you (the generator) use the energy, so you might as well use as much as you can. This is economics at work! If you generate electricity sustainably you are avoiding the production of carbon dioxide which is deemed to be an environmentally good thing. On the other hand electricity costs on average 13or 14p a unit so you are getting slightly more than the going rate. It's not much but there is a feel-good-factor.
I propose to engineer a system to charge and discharge the batteries locally (in my home) using readily available building blocks, suitably modified and to report back and discuss with other contributors the design constraints and solutions of the proposed system.