On our old farmhouse we had ‚solar hot water‘; enough to provide all of our heating and hot water needs for more than half of the year, backed up, as required, with a wood burning stove with a back boiler and large storage tanks for the winter.
Now that we are down in Spain, where there is much more sun, we want to try solar electricity, as all kinds of 'fire' is more than a bit dodgy in this dry land.
Of course sun power is only there when the sun actually shines, so you need batteries to provide a back up for overnight. This means that your solar panels need, in theory, to provide twice as much energy as you need during the day. In reality you need three times as much capacity, because of energy lost during transmission and storage and all of that on the worst day in winter ! But what if the sun does not shine for a couple of days

In reality, both your panels and batteries need to be many times more capable than would at first appear to be the case. This all boils down to you paying out a lot more than simple calculations would suggest. The bottom line is you pay for your electricity for about 10 years in advance. I always knew this, that's why I have so far avoided investing in photovoltaic power !
Your batteries can be 12, 24 or 48 Volts. In practice this means half of that number of 2 Volt cells. Having more 2 Volt cells, ie: 24 for 48 Volts allows you not only to draw more power more quickly but also to store more power more quickly, because of the charge / discharge rates (speed). This means that the inverter which changes DC into AC at 240 Volts can have a higher output. Very roughly: 12 Volts can provide about 1,2 kW, 24 Volts about 2,4 kW and 48 Volts about 4,8 kW. Exceeding these levels will damage your batteries and shorten their lifespan. This is important to understand as most electric motors pull a lot more power, in their start up phase, than their stated maximum rating. So, if for instance your fridge, washing machine and oven were all to kick in at the same time, the higher your inverter rating, the less chance there is of your fuzes blowing and or you damaging your batteries on a regular basis.
Bearing in mind a normal house will have a main fuze rating of more than 50 amps, many modern houses often have 100 amp main fuzes. With a battery bank of 48 Volts and a suitable inverter you only have about 4800 Watts -:- 240 Volts = 20 amps, so you will always still need to be aware of what you are demanding of your system.
There are various sorts of Batteries, the most tried and tested are unquestionably the OPZS lead acid batteries. They are cheaper than the more modern ion Lithium batteries who’s advantages of size and weight are uninteresting at a static object. Other supposed advantages like a longer lifespan are purely theoretical, as no battery is as old as their 30 year calculated - anticipated life.
OPZS batteries on the other hand are, if you do not overload them and stay within the DOD (depth of discharge) limits, proven to last 10 to 15 years. There are also a lot of misstated ‚facts‘ about ion Lithium. It often gets quoted that they have a DOD of 90% but their longevity is calculated on an 80% DOD rate being observed basis. Also, new combinations of the metals used in the + and - poles and the liquids used to activate them (create a current) are constantly changing; so you don’t really know what you will get or how long it ‚might last', it’s a gamble. In fact the whole issue of solar electricity is a gamble, because nobody really knows just how often the sun will shine for (hours a day and daily or not).
So my tip is to stick with the tried and tested OPSZ batteries and reduce the risk factor by half.
Paying your electricity bill 10 years up front, the cost of installing a good system, might seem nuts, but, the future is very uncertain and we would all find things very difficult without electricity !
Our leaders have now jumped on the environmental bandwagon, MY BANDWAGON, but they clearly can’t see past the end of their noses: As mentioned above, a normal house will perhaps have a 50 amp fuze rating, a modern house perhaps 100 amp rating; clearly the demand for electricity is going up, but the ‚grid‘ was installed decades ago when nobody could have foreseen this modern demand !
THEY now also want us all to buy electric cars, which we should charge up … at home. To do this at speed everyone will need a much higher fuze rating. If three houses on your street draw that much more electricity at that speed, the fuze for your street will blow and YOU CAN’T RESET IT YOURSELF ! If three streets draw that much more electricity at the same time (every evening when they get home from work) your zone’s fuzes will blow, if three zones fuzes blow at the same time your town’s fuzes could blow. If this happens the whole network will get a surge and power stations will fail. Were this to happen there could easily be long periods of (nation wide ?) blackouts. If you have your own ‚independent solar electricity supply‘ you will not suffer as badly as those relying entirely on the grid ! And you will be helping to avoid such a 'crash'

So it’s not just a question of ‚what it costs‘, if you can afford it, it’s a question of personal security and comfort. In Spain I want to be able to switch on my air-conditioning or heating, without worrying about the cost at the end of the month or … am I contributing towards an impending blackout.
This also proves, without a doubt, that I am as mad as ever and still an active environmentalist as opposed to an environmental activist.
Just for the record, I completed the engineer grade ‚Energy Consultant‘, having satisfied the german examining board of my status as a ‚Master Craftsman‘ in the trades of Hydraulics, Pneumatics, Gas and Water, so my information is not just scaremongering.