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Calculate what you could earn from PV
Fill in the tabbed screens below to find out what you could earn from PV.
Start with the one marked Roof size.
The total benefit after 25 years,
allowing for inflation and electricity price rises.
The first year return expressed as
a percentage of the capital cost.
The sum of the two tariffs
and the saving above.
For domestic installations this is all tax-free.
As well as receiving the two above
tariffs, you will of course save on your
electricity bill, for the electricity you would
have bought before but now have generated yourself.
An additional tariff, paid on
every unit of power you export to the
Grid. Until smart meters come in, electricity
companies assume you will export half
of what you generate.
This is paid on every unit
your PV system produced, irrespective of whether
you use or export the unit. It increases
each year with RPI. Figures used are for 2011-2012.
An approx estimate from Soltrac
assuming installation is straightforward.
Our exact price, following a site visit, may
be more or less depending on circumstances.
The power of the PV system is measured
in kilowatts-peak (kWp), the DC power of
the array under 1000 watts/sq m of sunlight.
- Roof size
- Roof angles
- Refine 1
- Refine 2
Enter information on the roof size and press Calculate
1. Location
We are obliged to use the Government's SAP method for calculating the energy generated (kWh). This uses the same formula for the whole of the UK. It is about 10% too low for the south of England. Soltrac's existing installations are generating 120.7% more than their SAP predictions so far, but some of this is due to the exceptionally sunny March and April.
The EU offer another predictor that takes acccount of location, as measured by postcode. Try it from here; first take a note of the kWp we have assessed for you.
2. Orientation and pitch (ie slope) of roof
Again, the SAP system used fixed variables as used here. The EU predictor allows you to enter exact figures for pitch (ie slope of roof from the horizontal) and orientation (as measured in degrees from south, ie south = 0, southeast = -45, southwest = +45).
3. Shading
Our calculator assumes your roof is unshaded. Even a small amount of shading (eg from a power cable) can degrade performance. We can get round this using specially adapted panels and/or microinverters (one inverter per panel). It is not practical to offer calculations for such systems on-line; we can do a careful on-site assessment for you. If shading is severe, don't even consider solar PV; if it is mild, the additional cost and/or drop in benefit is likely to be around 10%.
4. Type of solar panels
Our figures are based on high quality polycrystalline and monocrystalline modules. If the energy generated is too low, try instead using the Sanyo HIT panels which are more expensive per kWp but give more power per unit area.
(Button). Recalculate using Sanyo HIT/Revert (not yet available on this system).
The best return is usually obtained from systems rated at 3-4 kWp. Higher levels receive lower tariffs, so as not advised for most homes. Systems below 1.4 kWp are unlikely to be cost-effective though may be worth doing for environmental reasons.
Financial variables.
The total benefit received depends on assumptions on inflation and electricity prices in future.
We have used the following values which are conservative. Change them here if you wish and press Recalculate.