We are often asked about the pay-back time of the energy saving improvements we've made and the gadgets we've bought. Our standard answer has been that it's too difficult to calculate and, anyway, not a factor in our decision to do it. But we've finally given in to pressure and have attempted to come up with some figures.
The exercise has convinced us that it is well nigh impossible to give a meaningful answer. Even estimates of annual savings brought about by any particular change are very crude and can't be used to predict savings from similar investment by others:
- Future fossil fuel prices are unpredictable. The columns on the right of the electricity and gas tables in the pdf document linked below illustrate the effect of changing unit prices for energy.
- The order of doing things changes the rate of energy saving, e.g. we have insulated some of our walls and also moved radiators away from outside walls. If a radiator is moved from a well insulated wall, then the saving will be less than if it is moved from a wall through which there is more heat loss.
- The payback time of replacing a gadget, e.g. fridge, with a more energy efficient model, should be longer if you did not need to replace the item.
But, if you are really keen on figures about the value of this kind of investment, take a look at the following:
Detailed calculations - spreadsheet
Simplifed version - pdf file