The tool does not include the following:
- Fuel price increases over time
- Inflation (though FITs are index linked)
- Net present value
It uses a current average electricity price of 12.95p/kWh.
Tax is not included in the calculations. FIT income is not taxable for domestic installations.
Annual energy generation for solar electricity assumes optimal orientation and tilt, out put will be affected if the panel is not facing due south, or has over shading.
The solar map indicates the differing levels of solar irradiation across the country and has been designed to provide a basic guide only.
The calculation for solar PV does not include any maintenance costs. Well installed systems should last many years maintenance free though inverters are the most likely part to require maintenance though many come with 3-5 year warranties. Customers should check these details with their installer. Solar PV modules typically come with 20-25 year warranties ensuring at least 80% of rated performance at end of period. Calculations in calculator assume 100% performance over lifetime of tariffs i.e. 25 years.
Income is generated using the FIT rates published by Government available here: http://www.decc.gov.uk/en/content/cms/consultations/elec_financial/elec_financial.aspx
Fuel bill savings have been limited to £500 a year.
For assumptions around the wind speed data base please see here: http://www.energysavingtrust.org.uk/Generate-your-own-energy/Can-I-generate-electricity-from-the-wind-at-my-home
Tariff levels, for technologies installed between 15th July 2009 and 31st March 2012 of most significance to householders:
| Technology
|
Scale
|
Tariff (p/kWh)
|
Tariff lifetime (years)
|
| Solar electricity (PV)
|
=4 kW (existing build)
|
41.3
|
25
|
| Solar electricity (PV)
|
=4 kW (new build)
|
36.1
|
25
|
| Wind
|
=1.5 kW
|
34.5
|
20
|
| Wind
|
>1.5 – 15 kW
|
26.7
|
20
|
Last updated: June 2010
