Solar Panel & Battery Storage Calculator

To work out the true impact on your energy consumption of owning solar PV panels or battery storage use our calculator. The calculator will help you evaluate the financial benefit of your investment in both solar panels and battery storage.

The calculator takes your annual electricity use (kWh) and the annual output of your solar system and works out how much of your solar generated electricity will be used in the home or exported to the grid. Add the price you pay for electricity together with the export tariff rate (now known as Solar Export Guarantee or SEG payments) to calculate the annual benefit of:

• Savings on electricity bills
• Export payments under your SEG tariff

If you are also considering adding battery storage then by entering the storage capacity you can see the impact this has on your solar electricity use. If the purchase cost of the solar panels and/or the battery storage are available, then the calculator also works out the payback on the investment.

For more information see the Frequently Asked Questions section at the bottom of this page.

How are the results calculated?

The calculator uses typical profiles of annual domestic energy usage and solar output to project a likely energy export profile for each 30 minute minute period over the year. It then works out your export payments under the SEG scheme, based on your tariff, to project indicative SEG payments under these conditions. For wholesale price based SEG tariffs these can not be guaranteed, as market based pricing changes every 30 minutes. However, they are a good indication of likely payments.

The Calculator’s default settings are:

• Home energy use – 3,500 kWh per year (typical UK home)
• Electricity price of 18p per kWh (excluding standing charge)
• Solar electricity generation – 3,400 kWh per year (typical 4kWh solar PV system with average output of 850 kWh per year per kW of panel).
• No battery storage system connected
• Any battery storage is assumed to be uncharged to start
• A fixed rate SEG payment of 5.38p per kWh
• Solar panel and battery storage costs based on typical prices available if both are installed together.

We would be delighted to get suggestions for improving this calculator via the comments section below.

Frequently Asked Questions

What are Solar Export Guarantee (SEG) payments?

Solar Export Guarantee (SEG) payments are paid by energy companies when you supply your excess electricity to the electricity grid. They will be available from all large energy suppliers by January 2020 and are a replacement for Feed in Tariff (FIT) payments which were stopped for new solar installations from April 2019.

Details are starting to emerge from suppliers. There are likely to be at least three different approaches by energy suppliers:

• A flat rate for each kWh exported ( we are assuming that an export rate of 5.38p per kWh will be available, the same as the export rate under the old FIT scheme).
• A rate which varies every half hour, based on 30-minute wholesale prices. This means that the rate will only be available as the electricity is exported
• A rate which varies every half hour, based on day ahead auction prices for each 30-minute time period. The auction takes place once a day and allows the energy supplier offering the SEG to pre-sell the electricity likely to be exported. As a result, prices for each 30-minute period of the next day are known a “day ahead”.

Some SEG tariffs from energy suppliers will also vary by electricity distribution network. This is because the electricity distribution costs of each network do vary. There are fourteen different distribution networks in Great Britain which between them are owned by six different suppliers. You can find out more about this on the Ofgem website (See ofgem.gov.uk/key-term-explained/map-who-operates-electricity-distribution-network).

Where can I find my annual electricity usage and solar generation figures

Annual electricity usage information is available on your electricity bill.
Annual Solar generation figures should be available from your old Feed in Tariff (FIT) payments if you were part of the old scheme.

For new installations an annual figure can be estimated based on typical generation of 850kWh of electricity per year for each kW Peak of solar panels. A 4kW Peak solar array should generate around 3,400kWh per year. In an unshaded south facing location with good climate then panels can generate, on an annual basis, upto 1,000kWh per kW of solar panel fitted.

What are the “30 minute prices” shown on the calculator?

Selecting this takes historic 30 minute prices from Octopus Energy. As homes switch to Smart Meters, more suppliers will offer pricing which varies every 30 minutes based on potential energy demand. The Octopus Energy pricing varies every 30 minutes. Pricing for each 30 minute period is available 5-30 hours before it is applied, allowing different battery strategies to be applied.

What do “Solar used via battery” & “Solar in battery” mean?

Solar used via battery: Measures the solar electricity stored in the battery and then reused in the home at a later time/date.

Solar in battery: Measures the increase in energy stored in the battery during the year which has not yet been used in the home or exported.

What does the battery utilisation figure mean?

This measures how charged the battery is on average throughout the year. A figure of 50% means that the battery is typically half charged. In reality the figure will be lower in winter months when output is lower and much higher in summer months.

What data do I enter

• Enter the annual amount of electricity your home uses in kWh and the price you pay in pence including VAT.
• Choose your electricity usage profile. Decide whether occupants are usually home during the daytime (eg older retired people and those who work from home) or whether occupants are out at work (eg those working elsewhere or with children at school). The default is the average profile for all types of home.
• Does the home have a solar pv array? How much energy does it produce each year?
• Is a storage battery connected in the home. If so what is the storage capacity
• Choose a fixed rate SEG or one linked to wholesale electricity prices. If fixed enter the price paid per kWh exported.
• How much do the solar PV panel and battery storage systems cost?

How do I change figures in the greyed out areas?

To access the battery storage areas select yes to battery available input area.

Where does the data come from?

The solar data is from a 2013 study by UK Power Networks and the usage profile is from DECC Household Electricity Study. The 30 min wholesale data covers the year upto 9 June 2019. The day ahead figures are from historic “Outgoing Agile” calculations from Octopus Energy.