Thomas Edison 1931
Photovoltaic FAQs
Which panels do you supply and why?
Which inverter and why?
If we export it, how can we use it, surely we can’t do both?
What is a kW and kWh?
How long does the install take?
Is there much disruption?
What about loading on the roof?
Inverter location?
Which panels do you supply and why?
We do not have any ties with any particular supplier. Our approach is to specify the correct panels for each job individually. However we do feel as the panels and FIT lasts 25 years and the UK market is still in its infancy it is best to use panels from names that have been around a while. We therefore predominately use Sharp. We also use Romag, as they are a UK company, and CP-solar who have been prevalent in the European market.
Which inverter and why?
We almost always use Aurora, SMA or Fronius – all trusted inverter manufacturers that have stood the test of time in the American and European markets.
If we export it, how can we use it, surely we can’t do both?
On the majority of domestic installs the electric will not be exported as it will get used. The electricity provider will assume half of the units generated will be fed into the grid and pay you 3p for this whether or not in reality this happens. On larger and commercial arrays an export meter will be fitted and any exported electric measured.
What is a kW and kWh?
A kiloWatt is a 1000 Watts. This is an instantaneous figure. In order to translate this into a measureable figure kW is translated in kWh.
A kWh is 1000 watts over 1 hour. This can be difficult to understand so the best way is via an example.
A 4kWp system will produce 3373kWh over a year. This is calculated by taking the kWp, in this case 4, and multiplying it by the annual radiation figure for the area. For purposes of this example we have used the 2009 SAP figure for London on 1054.
So 4 x 1054 = 4216kWh.
For prudence we then take 20% off, as per the SAP calculation, thus giving 4216 x 0.8 = 3373kWh. This figure now corresponds with the energy provider measurement and in essence means that you can generate 3373kW for a period of one hour.
So what does this mean? Well let us take a 40w light bulb. 40 watts is 0.04kW.
If we divide this figure by 1kW we will be given the number of light bulbs per kW.
1/0.04 = 25
So from 1kWh we can run 25 light bulbs for 1 hour. In the example above we could run 84,325 light bulbs for 1 hour. (25 x 3373 = 84325)
This equates to 9 light bulbs 24 hours a day all year round. This is for example purposes only and obviously you cannot run the light bulbs all day and night as the system will only work when the sun is out.
How long does the install take?
A PV installation up to 4kW will take no more than 2 days – typically the installation team will be in and out in a day.
Is there much disruption?
There is little disruption. The circuit is completely separate and therefore your existing electrics will remain the same.
What about loading on the roof?
It is important that your roof can take the panels – but as long as the roof has not had any major supports removed the chances are the roof will have sufficient strength. The panels only weigh around 17-20kg with is the equivalent of 20 bags of sugar – therefore not heavy at all. The panels will be fitted to bars that spread across different rafters therefore also spreading the weight of the panels. It is therefore no different to a man walking around on the roof.
Inverter location?
PV cells and Inverters work better the cooler they are, it is therefore wise if possible not to locate the inverter in the loft as in the summer they tend to get very warm. The garage is an ideal location.
