Electrical work

The image above shows all of the electrical work involved in a solar installation. Often the inverter would be in a different place to the consumer unit – but here everything is next to each other.

Solar PV panels generate DC power – a DC cable goes from the panels to a DC isolator. This gives the ability to isolate the panels from the inverter.

A DC cable connects the DC isolator to the inverter. The inverter converters the power from DC to AC.

An AC cable goes from the inverter to an AC isolator to isolate the inverter from the consumer unit, and into a total generation meter. An AC cable runs to the consumer unit where the solar system is connected to the power supply.

Our electrical work is carried out by Andy Cope - our qualified PV electrciain.

Is my house suitable for solar panels?

How much sun?

The amount of power that solar panels produce is proportional to the amount of sunlight they get. If placed on a south-facing roof, they will therefore generate more electricity than an east- or west-facing roof. Shading will also make a difference, and significant shading will considerably reduce the output from your array.

The difference from orientation and tilt isn't as large as you might imagine. An east- or west-facing roof, if at a fairly shallow pitch, will generate only about 20% less electricity than an array at the optimum angle; between south-west and south-east you only lose about 5%.

Even vertical walls can be used to mount solar panels. The return from south-facing vertical panels is about 72% of their output at the optimum angle; the return from east or west facing vertical panels is about 54% of the potential maximum.

So although south is certainly the best option, it may well still be economically worthwhile even if you don't have a south-facing roof.

Not everyone has a perfect roof - but if yours has a potential return of at least 70% of the potential maximum after the effects of shading and orientation are taken into account, then it's quite likely to be economically sensible to install solar panels.

Even if nowhere is suitable for an array on the building itself, it may well be possible to mount an array on a mast in the grounds instead. Note however that the subsidies given by the government are higher for building-integrated systems.

Roof type

Solar panels can be fastened to most roof types. Conventional framed panels are the most cost-effective solutions for tiled or slate roofs. For 'standing-seam' roofs, the Unisolar peel-and-stick panels are a great alternative. For flat roofs, it's generally best to use mounting frames to fix the panels at an angle so that they catch more sun, and so that rain will wash dirt off more effectively.

Planning permission

Planning permission is not generally required for solar arrays. However, it may be needed if your building is listed, or if you are in a conservation area. If that is the case, you should contact your local planning department to ask if you would need to apply for permission.

Size of array

The bigger the area available, the more power you will get. You can calculate the approximate peak power of the largest solar array you can fit on your roof by multiplying the area available (in m2) by 130. If you have a space 5m x 4m available for example, you have 20m2, so the maximum array size is around 2600W. Because modules only come in particular sizes however, you may not be able to use the whole space.

Systems Larger than 4kW

The information on this page is now out of date - from 15 January 2016 some of the rules have changed

It is possible to install a system larger than 4kW on a domestic house. However, if you exceed the 4kW mark you get paid a slightly lower rate for every unit generated. In practice, it is probably only worth going over 4kW if 6kW or more can be installed on your roof. This would require a roof of approximately 4m x 12m.

However, the 4kW mark is slightly daft anyway - and has caused confusion throughout the industry. When connecting a Small Scale Electricity Generator (ie - solar panels or a wind turbine) to the national grid, the installation is required to met legislation set our by the District Network Operator. Through out the UK, most domestic installations under 4kW are installed under G83 rules - G83 rules state that a system must not exceed 16A per phase. On most houses this will be 3.68kW (230V x 16A) - which is less than 4kW! To get around this, inverters limit the AC output of the system to 16A - in practice a 4kW system would rarely exceed 16A per phase as conditions are rarely ideal! Current limiting is most likely to happen on a cool sunny spring day - click HERE to find out why.  If you wanted to exceed 16A, the inverter needs to comply with G59 rules. If you have a three phase supply, it is possible to install just over 11kW - so probably best to make use of the 10kW FiT.

If this is giving you a headache there is no need to worry - we deal with this on a regular basis and handle everything for you.

How solar panels work

Solar cells are made of silicon semiconductors, very similar to those used in transistors and electronic chips. A solar cell has two layers of silicon. The lower layer is silicon doped with boron atoms: boron atoms have one less electron than silicon, and so there is a shortage of electrons in this layer. The upper layer is doped with phosphorus atoms, which have one more electron than silicon.

Layers of silicon doped in this way exhibit what is called the photovoltaic effect. A photon of light hitting the top layer can knock one of the spare phosphorus electrons across the junction into the lower layer. The lower layer has therefore become negatively charged with respect to the upper layer, and so there is a potential difference (or voltage) across the two layers. Attach a couple of wires, and, say, a light bulb, between the two layers, and bingo! The electron can flow through the wires back to the top layer where it came from, and light the light bulb in the process.

The more light hitting the cell, the more electrons get knocked across, and the more power the cell can produce - although in practice even the best cells are barely 20% efficient, so only one in five of the photons is actually doing any work.

A single cell can only create a small voltage difference, and so to get a useful voltage from the panel it is usual to connect a number of cells in series.