The solar electricity calculator considers an investment in a domestic solar PV system and estimates a) the average annual electricity bill savings, and b) the no. of years taken for these savings to accrue to the value of the initial investment (i.e. simple payback period)
The simple payback calculation carried out in the calculator considers all costs as an initial investment outlay, a figure for which is entered by the user under question 5.
In question 5 users are asked to enter the up-front capital cost only but there may be other costs associated with installing and operating a solar PV system which users may also wish to include in their response. For example, the costs of getting a Building Energy Rating, or any future repair and maintenance costs (including the cost of replacement components) are not requested here, but users may wish to ask their installer for an estimate of these figures so they can include them.
The monetary savings come about as a result of homeowners reducing the amount of electricity they need to purchase from their electricity supplier. By buying less electricity from their supplier a monetary saving is made. Homeowners with solar PV systems will still pay the same amount on their electricity bill for standing charges and for the Public Service Obligation, but they will reduce the ‘unit usage’ (the amount of electricity consumed).
Question 6 is used to estimate the proportion of the generated electricity that the homeowner can use themselves. In most cases homeowners will not be able to use 100% of the electricity they generate because it needs to be used at the point in time that it is generated and this is not always possible (for example if there is nobody in the home using electrical appliances at a particular time).
If the user is not sure which response to select in any of the questions they can leave them unanswered and default responses will be used. These default responses use typical or average figures.
All of the data and assumptions used in the calculator including the default responses can be examined by users by downloading the excel version of the tool. If you would like to provide feedback on any aspect of the calculator please send your comments to firstname.lastname@example.org
The calculator assesses the savings and payback for a simple domestic solar PV system only – at present it is not configured to assess the impact of including storage technologies such as an immersion diverter or a battery. Factoring in the costs and savings arising from these additional technologies will change the savings and payback period.