It depends on the sort of person you are. Did you dig up the garden to install a fall out bunker during the cold war, now probably an underground pond or the centre of your mushroom business or did you consider, post apocalypse, the last people you would want to share a scorched earth with would be exactly those paying out huge sums for such hole in the back yard. But the energy crisis is a little more guaranteed and less costly to prepare for. Essentially it is like the the Boy Scout analogy. “Be Prepared”. Apologies to any Girl Guides. An auxiliary generator is not rocket science and installation is neither expensive or difficult.
There are two simple avenues: manually switched transfer(MST) or Automatically Switched Transfer (AST, sometimes referred to as AMF[automatic mains failure]). There is ONE MAJOR CAVEAT though. This is playing with the mains supply to the house between the electricity meter and the consumer unit. Legally, and practically, this is beyond the DIY enthusiast and should be done by a qualified electrician. It should take little more than an hour and the certificate provided will be useful for the insurers in the event of a future conflagration.
First you need to ascertain your minimum power requirement. The fridge, freezer, central heating, lights and possibly water pump if you are on a private supply. A minimum requirement for a house is probably about 3kw. The cost of a manual transfer switch and
3.5kw manual start generator is around £800 incl vat but plus installation. Hardly going to break the bank. The generator will run for about 10 hours and can be refilled, due care
being taken. Hot generators and petrol need to be treated with caution. As in the diagram the generator should be sited outside and consider that generators are heavy so wheels (about £70 extra) may be appropriate depending on your circumstances. Also consider the noise if you are close to neighbours. As they shiver in the cold they may take exception to a noisy generator next door! If you have a generator already a manual switch is around £250 plus installation.
The alternative is an automatic switched system which requires an electric start generator with remote sensing input. The switch will recognise the power outage and send a signal to the generator which will start up and in a few seconds take over the load. When the power comes back it will simply switch back to the main supply and in about thirty seconds the generator will turn off. The cost of this luxury is about £1800 plus installation. There may be an added cost of an exhaust pipe for the generator if it is sited in an outbuilding or garage. The added advantage is that this model is 5.3kw so will cook the Christmas Turkey! This system also comes with AVR(automatic voltage regulation) which removes spikes in the power supply which could damage sensitive electronic equipment such as computers. However you can get surge protection extension cables for computers reasonably cheaply if you prefer the more economical option. Another alternative is to go for a larger 4.95kv Manual switch system with AVR for £1154 incl vat. Good automatic systems include a trickle charger for the generator battery which protects against the possibility of the embarrassment of a failure of the system. The neighbours will notice quicker than even you!!
A useful web site is http://generators.co.uk or http://mainsfailure.com. I have no contact with either site and many more are available through Google.
Go on, splash out and really upset your neighbours as they freeze in front of one candle on the coldest night of the year.
THIS IS NOT A DIY JOB. THIS DOES REQUIRE A QUALIFIED ELECTRICIAN!