Calculating Your Return From Solar Panels

There are several free tools available on the internet that will help you calculate your return. Some of them will offer you a quick, rough estimate based on your answers to a few basic questions about your home's location, size of installation and household needs. Others require specific details for a more accurate calculation. You can also ask an installer to help you work out your return and we will discuss choosing an installer in a later chapter.

Online calculators use varied combinations of information to calculate your return and at the end of this section you'll find a list of possible information required to help you get the most accurate calculation. Although you may not need answers to all the questions for every calculator, the information about your property is worth having.

Knowing the factors taken into consideration during a survey of your home and why they make such a difference to the outcome, will help you choose the most powerful and cost-effective system and maximise your return. The installer you finally choose to do the work will also need access to much of this information.

How Your Return Will Be Calculated

Small systems installed on existing roofs are referred to as ‘retrofit' and at the moment the generation tariff for this type of installation stands at 43.3p per kWh. At the time of installation the installer will provide a generation meter which will measure the amount of energy being generated.

Tariffs vary with the size and type of installation, as follows:

Next you assess what percentage of the energy you generate will be used on running your household. This will depend on what extent the electricity is being used during the day. You will also need to know how much you are being charged per unit of electricity which is usually shown on your electricity bill, but if in doubt, 13p is considered a reasonable average.

Now you can gauge how much free energy you can expect by taking the percentage of the units generated and multiply them by the unit cost of the electricity, giving you your Free Energy for the year.

The remaining percentage of units will be exported to the grid, so if you multiply them by the export tariff earning that will give you the total Export Tariff earnings for the year. All you have to do then is to add the three figures together to get the Total Yearly Income and Savings which usually falls between £300 and £1,500 per year.

You will find a 4-Step Calculation Example in the Feed In Tariff Chapter and a lot more detail about how the tariff works, but this chapter is dedicated to showing what things will affect your calculation and final income and savings. Some things, like your location for example, cannot be changed, but there are choices that you will need to make that will affect results. You need to be aware of them so you can get the most from being part of the Feed In Tariff scheme.

Calculating Your Return From Solar Panels

There are several free tools available on the internet that will help you calculate your return. Some of them will offer you a quick, rough estimate based on your answers to a few basic questions about your home's location, size of installation and household needs. Others require specific details for a more accurate calculation. You can also ask an installer to help you work out your return and we will discuss choosing an installer in a later chapter.

Online calculators use varied combinations of information to calculate your return and at the end of this section you'll find a list of possible information required to help you get the most accurate calculation. Although you may not need answers to all the questions for every calculator, the information about your property is worth having.

Knowing the factors taken into consideration during a survey of your home and why they make such a difference to the outcome, will help you choose the most powerful and cost-effective system and maximise your return. The installer you finally choose to do the work will also need access to much of this information.

Questions That Will Help You Get The Most Accurate Calculation

Postcode? Your postcode shows your exact location and can be used to view your roof top on Google Maps. You can see how close you are to having an ideal south-facing area for your panels which is all helpful in calculating your roof's solar potential

How much roof space do you have on your most southern facing roof?

To answer this question you will need to know the size of your roof space in square metres minus any obstructions like dormer windows or skylights.

What is your maximum budget? By knowing the answers to available roof space and budget you will be able to determine the size of the system you could install.

What is or will be the size category of your installation?

- 4 kW Existing Build or Retrofit (refers to attaching a PV system to an existing building as an added accessory)
- 4 kW New Build (refers to where a PV system was installed at time of build and prior to anyone moving in)
- 4 - 10 kW
- 10 - 100 kW
- 100 kW – 5MW
- Stand Alone System (refers to a system that is neither attached to a building nor wired to electricity to an occupied building)

When did you/do you plan to install the technology?

- Installed BEFORE 15 July 2009
- BETWEEN 15 July 2009 and 31 March 2012
- BETWEEN 1 April 2012 and 31 March 2013
- BETWEEN 1 April 2013 and 31 March 2014
- BETWEEN 1 April 2014 and 31 March 2015

What is the estimated export?

- 100% (Export ALL electricity generated)
- 50% (Out of the house most of the time)
- 25% (In the house most of the time)
- 0% (Use ALL the electricity generated)

What way does your roof face?

- South
- South South West
- South South East
- South West
- South East
- West South West
- East South East

-West
-East
-North West
-North East
-North
-Upwards (flat roof)

What is the angle or pitch of your roof, in degrees?

(The average UK roof is around 35 degree pitch).

To what extent is your roof overshadowed?

How much electricity do you pay per unit?

(You should be able to find this information on your electricity bill but if in doubt choose 13p).

SAP 2009 Calculation

Standard Assessment Procedure (SAP) is the government's official guidelines to calculating your return. This calculator takes into consideration such things as:

- System size in Kilowatt peak (kWp)
- Tilt of the installation area in degrees
- Installations orientation, north to south and all its variations
- Level of overshadowing
- Whether the panels will be fitted to an existing or new building (not applicable to systems over 4kWp)
- Your Electricity tariff (pence). If in doubt you are advised to select 13p
- Whether you are at home during the day

This will give you the expected performance of your system as:
- Annual Output
- Applicable Feed In Tariff
- FIT per Annum
- Savings on Electricity Bill
- Export Tariff
- Total Annual Tariffs/Savings

The main problem with the SAP method of calculation is that it isn't taking into consideration the latitude or location of the property which makes it inaccurate to the point that it can underestimate the performance in coastal areas and many parts of southern England by between 2-14%.

The SAP calculation is based on 1 kilowatt peak (1 kWp) producing 858 kilowatt hours (858 kWh) but this is only true for the inland strip from Coventry up to the Scottish border. In Devon and Cornwall a 1 kWp can be expected to generate up to 975 kWh per year which is 14% more than the SAP calculation. Installers will have more accurate systems for predicting your return by taking other factors into account. For this reason we recommend getting a couple of surveys done by different companies in order to compare and make sure that everything has been taken into account.

Factors That Will Affect Your Return

Location

We have seen from the information on the governments SAP calculator how location is an important factor in what you can expect from your solar panel installation. Although the UK may not seem a large area in the scheme of things, we have seen variations of up to 30% in the power generation capacity of solar panels in the South West of England compared to the North of Scotland.

Size And Type Of Installation

The total energy produced is dependent on the size of the system, along with the other factors. Size of installation can be limited by roof space and budget. There are systems available that generate more power per panel or smaller panel. They are more expensive but if you have to have less panels because of area restrictions they can work out cost-effective. Solar panel technology does seem to be a case where you get what you pay for. More expensive usually means more effective and when you think what a long term investment they are and what can be achieved, it's worth getting it right from the outset.

Whether Or Not You Use An MCS Accredited Installer And Product

MCS stands for the Microgenerational Certification Scheme. It is an internationally recognised, industry led and funded scheme focused onensuring the quality of renewable technology installations and products that's been developed over a number of years. As far as the Feed In Tariff scheme is concerned, you must use an MCS accredited product and installer to qualify for the full payment available.

How You Choose To Finance The Installation

Naturally, how much you can earn from the FIT scheme will be influenced by how you choose to finance the installation. You may go to a traditional finance company like a bank, and mortgage lenders have also developed a range of products to help their customers fund solar power systems.

Some installers finance the product and installation themselves and you can pay them or a third party they use back over a specific term. There are companies offering free panels which you may qualify for or you may have money you wish to invest yourself and would find it difficult to get a better return on your investment. Whatever you choose you will find some benefits and savings possible.

Hidden Costs

PV modules do not require a lot of care and rain usually ensures they are kept clean and free of most debris. However the modules can be cleaned with a cloth, perhaps when other outside maintenance is being done like gutter clearing. Tough weather conditions have been taken into consideration at design and manufacturing stages and strong winds, snow load and harsh frost shouldn't be a problem.

For areas prone to extreme weather conditions, insurance is an option but data from the insurance industry indicates that claims are very rare. A small amount should be budgeted for maintenance repairs and insurance so that your system is working at its maximum capability and bringing you the best returns on your investment.

The Date When Your Panels Were Or Will Be Installed

If you've already had your solar panel system installed there are time sensitive stipulations you need to be aware of in order to ensure you qualify for the FIT scheme in the first place and to what extent you can benefit. Similarly, if you are just thinking about installation, you do need to take a look at the information relating to timings in order to ensure you get the maximum financial benefits from the scheme. These details can be found in the Feed In Tariff Explained chapter of this book.

When You Will Be Using The Electricity The Most

If you're rarely at home during the day and the house is unoccupied, your savings and income will not be as big as if there were electrical appliances in use. But with many household appliances having timers now it may be possible to have things charging or operating like washing machines while you're out. It's certainly something that's worth thinking about.

Orientation And Pitch Or Angle Of Roof

Ideally your roof should be facing south but it's possible to compensate for most other directions and you need to remember panels can be attached to the front or the back of the roof. Even if solar modules are installed on a roof which is 40O from south, only small losses are incurred.

The pitch or angle of the roof can affect the number of hours of sunlight your panels will receive during the course of a year. The question of the pitch of the roof is asked when planning and particularly for an online calculation but when it comes to the actual installation, solar modules can be manoeuvred into an appropriate position by means of a support structure even if the actual pitch of the roof itself isn't favourable. The optimum angle of inclination and orientation must correspond to the latitude of the location.

Shade

Solar panels are designed to deal with cloudy and overcast conditions but shade caused by overshadowing trees and neighbouring buildings can be a problem. Shade on one panel can shut down operations on the others so it's a very important factor to get right. Installers have a gadget that can reveal any shady areas on the roof whatever the time of year.Once this is known the panel layout can be designed around any such areas and problems avoided.

Size of Areas And Amount Of Panel Space

High efficiency means taking up less space on your roof for the solar array. Efficiency isn't usually a big concern unless the roof area to be used is unusually small, in which case a little more spent for less panels of a higher efficiency will work out the most cost effective.

Frequently Asked Questions About Calculating Your Return

Q: Won't my installer be able to work out my return for me or do I have to try to do it myself?

A: Your installer will survey your site and work out the best solution to optimise your return. However, the installer will still need answers about your household that only you can supply. So whether you calculate your return yourself, try an online calculator or ask an installer, you need to be aware of the information required and the choices available to get the best return.

Q: Once my solar system is operating how can I be sure what electricity I'm producing?

A: There are two types of meters that you'll need, a generation meter that will come with your system and will let you know the total amount of electricity it's generating. The other is an export meter and can only be fitted by your electricity provider.