So today I was wondering just what would be required to become completely independent of the energy companies. Most of us are familiar with solar energy by now but anyone who has looked into it has come to the realisation that it wont be enough. What if they turn on an electric oven, what if they have an electric shower, and so on. Important note for anyone reading. This is a discussion piece from someone interested in this sort of project. This is not expert advice.

The average person would never even consider coming off the grid, I am not the average person. At this point the only thing stopping me is that its a big initial outlay, as any solar setup has some significant setup cost. But what do we need to cut the cable (please don't actually cut the cable that wouldn't be safe).

  • A solar kit big enough for my uses
  • A battery large enough for my uses
  • A backup generator

Working out how much power you use is not easy, it takes some maths to calculate your usage over the year. If we simplify things and take the average you could look at your units used and divide by the billing period, take at least a year, and you have a guide to how much you use. Then there are questions of when are your peaks, this is harder to tell by the energy companies because for most of us the peaks simply represent when they read the meter.  A peak could be when you made Xmas dinner for the family, you have 2 electric ovens running, a 5 ring hob and a microwave (this scenario is important later) and the family probably has a stereo on and a load of Xmas lights. All of us have peak usage times that don't happen in our day to day, then there are daily or weekly peaks, like taking a shower if its electric, or putting the dishwasher on, or running an electric heater if you are cold. That one is an important one. If your heating is electric you are going to be using more energy on a daily basis when your solar output is at its lowest. This can be mitigated somewhat by adding a wind turbine to your system but wind is not reliable. It can also be mitigated by having a larger solar system, but you wont necessarily have room on the roof for that. It is also worth considering the energy rating of all the appliances in your home as well as how many people are there. In my case I easily average under 2kw, and I have an electric oven and hob. My central heating and hot water are gas.

When it comes to batteries there are two considerations. You need enough capacity to make sure you make it over any peak usage or low generation times and you need a high enough output to handle your peak usage when theres little or no generation. If you have any large continuous output devices like a rapid electric car charger that will merit a larger higher output battery. Ovens and electric showers have a high peak too, but since they are short term use don't need anywhere near the capacity you would need to supply a car charger. One of the benefits of many of these systems is they can be expanded in an add-on fashion to increase capacity and output. So if you get an electric car in 5 years and want to add a rapid charger you can do that. Battery type can be a consideration too, lead-acid will last up to 5 years, litium-ion 11+

Despite all of this we do need to consider what if we do run out of power. For that we have a generator as backup. The generator does use fuel, but we intend to never use it, its a backup just incase. How much you need it to use it will depend on your usage, in my case it would be unlikely except big event like Xmas dinner, in the summer I tend to use a charcoal BBQ for most of the cooking so summer events use very little power. The generator can be set to auto start when it sense the power is low. The mode I looked at will produce 2.4kwh for 1 litre of fuel, current cost £1.80. Even on Xmas day I cant imagine using it for more than a couple hours, I would be surprised if I ever need it given my usage.

So lets look at cost.

4kwh solar system £3800

4.8kwh battery pack £1800

2.4kwh Generator with auto start £1000

20L Jerry can + Fuel as backup £60

Total cost £6,660, lets call it £6700 after getting a good stock of tea and biscuits for the installers.

Given that energy prices for a 3 bed house are currently above £3500 annually, This would pay itself back in two years. Time to start looking down the back of the sofa for that £6,700 I guess.