Solar PV Terms & Conditions

Standard Assessment Procedure (SAP 2012) calculation for Solar PV

Photovoltaic (PV) technology harnesses the energy of the sun by converting it into electricity. The total amount of free electricity produced per year depends on the installed peak power of each PV panel. All panels are rated by manufacturers in terms of their peak power output under standard test conditions (i.e. radiation of 1,000 W/m2 at 25oC). For PV panels this will vary according to the type of cell technology used with some panels producing more electricity per square meter than others.

The design tool establishes what the total peak power output is by multiplying the manufacturers quoted peak output for a particular panel model by the total number of panels that are to be installed. The SAP 2012 calculator assumes that for the UK climate a 1kWp PV system will typically produce 900 kWh of electricity per year if positioned at an optimal orientation and inclination and when there is no shadowing by any nearby buildings, trees etc. From this the total electricity produced in a year by the PV array can be established.

Proposed Site Characteristics

The surface on which a PV array is mounted should receive as much light as possible as the more light received, the more electricity will be generated. The three issues that affect how much light a surface receives are:

• Orientation – a south facing surface is generally the best possible orientation however, a building facing in a south easterly or south westerly direction is acceptable in most instances.
• Inclination – a tilted array will receive more light than a vertical array. Tilts should be between 20 and 50 degrees of horizontal for maximum performance with the optimum angle being 30 – 45 degrees.
• Shadowing – a solar PV system performs best when there is no shadowing from objects nearby such as tall trees or buildings all of which can reduce system performance considerably.

Working Information

For a grid connected system electricity generated will always be used in your home first if there is anything switched on that requires power. Any surplus power will be exported back into the national grid. All installations above 3.68kW have to be approved by UK power network and an application is completed on your behalf by OHM energy. Subject to UK Power approval will depend on how much can be exported back to the grid. Knowing what the proportion that you expect to use on site is important as it will affect the potential revenue you might expect to receive. The proportion used will depend on the size of PV system installed and your expected daytime summer electricity demand. For example, most homes have some continuous or near continuous demand due to freezers fridges and standby electronics at a low level. This means that for a large proportion of the time all the output from a small PV system will be used on site, displacing the need to buy grid electricity. However, if you were to install a much larger PV system and used very little electricity during the day the proportion exported would be much higher.

Applications

There are a number of applications OHM will make on your behalf, such as local authority notifications and DNO (Distribution Network Operator) applications, amongst others.  Please note, if we have not received any of these approvals in time for when your final balance is due, we will still require the final balance to be paid on time upon completion of our works. Our works are deemed completed upon completion of the DC side, and in some cases where possible, we will install an export limitation device until the export has been agreed.

Design Tool Outputs

The design tool generates predicted annual outputs for energy, revenue and carbon. The calculator shows the expected revenue.

One is the money you will save from displacing electricity that you would otherwise buy in from the grid. The value of this will be determined by how much the solar PV system generates and how much of this generation you expect to use on site.

Any energy that isn’t used can be exported back into the grid. This is a further source of income and for this to happen you will need to apply to a Smart Export Guarantee (SEG) Licensee. Each provider will have details of their specific application process on their website. SEG Licenses do not need to be the same company as your current energy supplier. You can choose to use separate companies for your SEG payments.

This calculator assumes that the system is grid connected and will be for a retrofit installation.  Also that 75% of the energy produced by the Solar will be used on site and 25% will be exported at a rate of 5p per kWh for any export (current offered rate as of July 2021).  Please note a Smart meter must be fitted in line with your supplier’s guidelines to benefit from the Export tariff.

Disclaimer

The performance of solar PV systems is impossible to predict with certainty due to the variability in the amount of solar radiation (sunlight) from location to location and from year to year. This estimate is based upon the Government’s standard assessment procedure for energy rating of buildings (SAP) and is given as guidance only. It should not be considered as a guarantee of performance.  We have assumed that all electricity generated will be consumed on site, also that the average electricity price is 35p per kWh – these assumptions should not be used or interpreted as fact.