This has an impact on how much solar irradiation your new panels will receive. In Cornwall for example there are approximately 1100 usable daylight hours per year, whereas in the North West of the country that figure is around 900 hours. This has a direct impact on the amount of electricity produced by the solar panels.
Anything above 5° and below 70° from horizontal are acceptable roof pitches for solar PV. If your roof has less than a 30° pitch, a roof survey is required to determine its weight load capabilities. Our experienced, expert surveyors always conduct an internal roof survey, but when a pitch is below 30° there are extra calculations that need to be made. These calculations are based on the Trada tables that are used by structural engineers in the UK. If our calculations show that there are not sufficient weight load capabilities, then strengthening is needed to the existing rafters. We can offer this as part of our installation.
This is possibly the most important factor when considering where to put your solar PV. Optimal orientation on the compass point is East 90° to South 180° to West 270°. Anything outside of this facing towards North reduces the amount of sunlight on your panels.
We will survey your property fully to ensure we specify the right system for your roof. There will be many installation companies that tell you they can measure from the inside of the roof, but we have found the only fool-proof way of measuring a roof is from a set of ladders. We take into consideration any chimneys, soffits, vertical vents and any existing damage that may need repairing. It is also important to identify the roof slate or tile so should there be an existing broken one on the roof, it can be replaced rather than just glued before it is covered by the solar panels.
Once accurate measurements have been taken by using a set of ladders, we then draw it out to on 3D software to scale. This enables us to try various different layout options for the solar panels (landscape or portrait) and we can look at the best size panels to maximize the available space.
The highest available tariff for domestic properties at the moment is for systems equal to or below 4kW, which is usually made up of 16 panels that have a 250W output (16 x 250W = 4kW). You can purchase less panels with higher output if you do not have the space.
If your roof does not have enough space for 16 solar panels then you can get as close to 4kW as possible by using a more powerful panel i.e 13 panels of 300W = 3.9kW although less than 4kW it is closer than 13 panels x 250W panels = 3.25kW.
Above 4kW the tariff drops (please see commercial solar PV)
The shading analysis is a very important part the survey because it calculates any losses that shading may have on your generation that will affect your payback and how to best avoid them when installing your system. The shading analysis is carried out in accordance with the MCS. A sun chart is used to take into consideration both near (within 10 meters) and far objects (horizon lines). An equation is then used to calculate how this will affect the overall system payback.
In many cases a solar array will need to be split over 2 locations on the same roof because of lack of space. Often these 2 locations face in different directions e.g South/West or East/West. It is important that the inverter specified copes with the split load efficiently. The type of inverter required in this scenario is known as a dual tracker, because it deals with uneven inputs of power independently. Many dual tracking inverters cope with even loads, for example, 8 panels on one part of the roof and 8 on another, however, problems occur when installers do not specify the inverter correctly for uneven loads, e.g. 10 panels on one roof and 6 on another. The inverter specified for even loads will cope with the unbalanced load but not efficiently, which means instead of running 95% efficient it might only be running at 70%, so it is important that this is specified correctly. If there are unbalanced loads the best way to specify the correct inverter is to use the manufacturers software. The manufacturers are obliged to give accurate figures on inverter efficiency with different loads. It is equally important that the installer programs the inverter to deal with the split load as inverters have different settings.
If you think your solar panels are not performing, give Harvest Cornwall a call as our team of electrical engineers are trained in programming both commercial and domestic inverters.
When considering the mounting system it is important to specify robust fixings that will resist high wind loads over very long periods of time. We use Wind Load Charts to show areas that are most affected.
Roof hooks and rails are the basis of the mounting system and there are different types on the market. At Harvest Cornwall we specify roof mounting kits that take into consideration high wind loads, and even in areas that are not as exposed. We err on the side of caution by specifying the most robust roof hooks and rail available. The mounting kit can never be over engineered and the difference in cost for high quality kit is approximately £100, a relatively small price to pay for the peace of mind considering something that is to stay on your roof for 20+ years.
In order to qualify for the higher tariff, a property needs to have a valid EPC certificate of grade 'D' or above AFTER the solar panels have been installed. This has caught buyers out in the past where installers have installed the solar panels and the client has had an EPC and still not managed a grade 'D'. An independent EPC assessor will visit your property and carry out a draft assessment, highlighting what grade your house is now and guaranteeing what the final grade will be when solar panels are fitted.
All the pertinent factors are then summarised in a report so that we can offer the best system for your property and we can give you a good estimate of the returns over 20 years, the lifespan of the Feed in Tariff.