Solar Energy Calculator

The Solar Energy Calculator estimates the fuel bill savings you could make from installing a PV system in your home.

The calculator provides estimates based on the information you provide and makes a number of assumptions to indicate what benefit could be made; this is to help you decide whether a PV system is for you.

Use of the tool and its outputs is not a guarantee that you will see the exact same fuel bill savings from the installation of your planned system

In January 2019, the Department for Business, Energy & Industrial Strategy (BEIS) published a consultation on a ‘Smart Export Guarantee’. Under this, the government would legislate for suppliers to remunerate small-scale low-carbon generators for electricity they export to the grid.

You can find out more here: The future for small-scale low-carbon generation – the Smart Export Guarantee : Call for Evidence

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Property energy efficiency rating

Your property’s energy rating can be found on your home’s Energy Performance Certificate (EPC). You can search if your home has an EPC here: https://www.scottishepcregister.org.uk/


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Property details

Every roof is exposed to different amounts of sun. This depends on your location, the slope of your roof, shading and the direction your roof faces. The map below will help you determine which direction the sunniest side of your roof faces. The typical roof slope for the average UK home is about 40 degrees.

You can also choose the size of your solar power system. Use the slider or type in a specific value and enter a quote if you have one. If you need help, see our sizing guide.

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Roof slope

30°

0° is a flat roof and 90° means that you want to install PV panels on a vertical surface such as a wall.

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Shading

Description

Use the slider to indicate how much shading you expect to have on your roof where the solar PV system will be installed.

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Roof direction

Adjust the map to find the property and then adjust the compass to align it with the desired orientation.

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Installation size

Please choose the size of the system you’re interested in installing. View sizing guide for more help.


What is the peak generation of your system in kilowatts:

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Your current monthly electricity bills

Please enter your monthly electricity bill

Installation quote

Have you received an installation quote? (optional)

When you are at home

Please tell us when you are typically at home during the week to help us estimate how much of the electricity you will use

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Assumptions

Your results

For more information, please read the calculator assumptions.


kWp
kWh
 tonnes of CO2

For more information, please read the calculator assumptions.


kWp
kWh
 tonnes of CO2
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Next steps

For free, independent and local energy saving advice (including further information on installing solar panels on your home) and for information on local installers, call Home Energy Scotland on 0808 808 2282

In January 2019, the Department for Business, Energy & Industrial Strategy (BEIS) published a consultation on a ‘Smart Export Guarantee’. Under this, the government would legislate for suppliers to remunerate small-scale low-carbon generators for electricity they export to the grid. The response has yet to be published. 

In the interim some energy suppliers are offering similar deals, paying customers set tariffs for electricity they export to the grid. Deals are specific to each household and could involve generation and supply being metered. Deals may also be time limited and have other conditions which you should consider carefully in order to make the best choice for you.

The Solar Trade Association website lists the current deals available. 

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Solar Energy Calculator - Property details

Every roof is exposed to different amounts of sun. This depends on your location, the slope of your roof, shading and the direction your roof faces. The map below will help you determine which direction the sunniest side of your roof faces. The typical roof slope for the average UK home is about 40 degrees.

You can also choose the size of your solar power system. Use the slider or type in a specific value and enter a quote if you have one. If you need help, see our sizing guide.

Solar Energy Calculator - Property details

Every roof is exposed to different amounts of sun. This depends on your location, the slope of your roof, shading and the direction your roof faces. The map below will help you determine which direction the sunniest side of your roof faces. The typical roof slope for the average UK home is about 40 degrees.

You can also choose the size of your solar power system. Use the slider or type in a specific value and enter a quote if you have one. If you need help, see our sizing guide.

Solar Energy Calculator - Property details

Every roof is exposed to different amounts of sun. This depends on your location, the slope of your roof, shading and the direction your roof faces. The map below will help you determine which direction the sunniest side of your roof faces. The typical roof slope for the average UK home is about 40 degrees.

You can also choose the size of your solar power system. Use the slider or type in a specific value and enter a quote if you have one. If you need help, see our sizing guide.

Solar Energy Calculator - Roof slope

If you have a flat roof, panels can be angled when installed. The optimum angle for solar power collection in the UK is 35°.

One way of determining the slope of your roof is to look at the rafters on your attic. Use the default of 40° if you are unsure as this is the typical for a UK roof.

Solar Energy Calculator - Overshading

Shading from nearby obstacles, such as trees and buildings, will reduce the solar energy that reaches your PV panels, and therefore reduce the electricity generated. 

Ideally you would only install panels on roofs with no nearby obstructions, but that isn’t always possible.

Solar Energy Calculator - Roof direction

You can use the map to see which way the best side of your roof is facing. The closer you can be the better but it doesn't have to be exact. The best direction for solar power collection in the UK is south facing.
If you have a flat roof your panels can face any direction.

Solar Energy Calculator - Installation size

Solar electricity systems are given a rating in kilowatts peak (kWp). This is the rate at which they generate electricity at peak performance, for examples at noon on a sunny day. The capacity (kWp) of a domestic system will vary depending on how much a customer wants to spend and the roof area available to accommodate the panels. Typically system sizes are between 1-4 kWp

Solar Energy Calculator - Monthly electricity bills

An average 3-bedroom gas-heated home in the UK uses about £50/month of electricity (this is around 3,950 kWh each year). You don’t have to be too accurate with the figure as it is only used to give you a guide to what percentage of your home’s electricity will be delivered by your solar panels.

Solar Energy Calculator - Assumptions

This calculator estimates the performance of domestic solar photovoltaic (PV) systems. Its calculations account for the local effects of incident solar radiation (sunlight), ambient air temperature, wind speeds, roof direction and roof slope.
The performance of solar PV systems is impossible to predict with certainty due to the variability in sunlight from location to location, and from year to year. Whilst the estimates from the Solar Energy Calculator are based on the best information available, they should not be considered as a guarantee of performance.

This calculator is designed to give estimates for those who have not yet installed a PV system.

Your actual fuel bill savings will depend on a number of factors including the size, efficiency and location of your PV system and how much electricity you use when the system is generating.

For the avoidance of doubt, the results in this calculator are not exactly the same as those estimated by the Standard Estimation Method which is used by MCS certified installers in solar PV quotations. The methodology used in this calculator is based on the Government's Standard Assessment Procedure (SAP) 2012 which uses different assumptions for the average level of solar radiation in an area.

This calculator is regularly reviewed and updated to reflect changes in electricity prices, and any new statistics relating to equipment performance and electricity use in the home.

Calculation assumptions

This calculator presents financial performance in ‘real’ accounting terms (i.e. in today’s money).

No maintenance costs have been included in our calculations (e.g. replacing the inverter or inverter components). Typically an inverter will need to be replaced once during the lifetime of the system, costing around £800; however this will vary depending on the type of inverter installed.

The electricity price used is 14.33p/kWh (based on domestic use in 2017-2018)

Savings are based on a well oriented unshaded 4kWp system. Scottish savings are based on a system in Stirling, generating 3,370 kWh of energy per year. The rate of the electricity generated that is used directly in the home (‘self-consumption’) is estimated based on Loughborough’s self-consumption model which accounts for different occupancy archetypes. The energy that is not used directly in the home is exported to the grid. Householders will get export payments only for 50 per cent of the energy generated regardless of their actual self-consumption (export payments are assumed to be deemed, not metered).

The amount of electricity generated by PV panels is assumed to decline steadily over time, with the performance in year 25 assumed to be 80% of the performance in year 1.

For estimates of the carbon emissions impact, national grid electricity is assumed to have a carbon intensity of 0.447 kgCO2 /kWh.