HOW SOLAR WORKS

Energy from the sun

Solar photo voltaic systems are a great way to generate clean electricity for homes and businesses all year round.
The sun provides a plentiful and free source of clean energy in the form of natural light and heat. It is possible to capture some of this free sunlight and convert it into electricity using solar photovoltaic (PV) panels. Because solar PV panels react on light from the sun they work in the winter and also on overcast days however, output will depend on the hours of daylight and the angle of the sun in the sky.

Solar  PV Technology

A solar pv system is made up of photovoltaic cells, devices that are capable of converting light into electrical power by using a thin layer of semi conducting material usually silicon.  The cells are encased between a sheet of glass and a polymer resin to form a module or panel which can be interconnected to form what is known as an array. The panels are manufactured in a variety of ways to give monocrystalline, polycrystalline or hybrid modules.

Monocrystaline and Polycrystaline Modules

Practical Differences – what is the impact on cell performance?
Since polycrystalline cells contain many crystals, they have a less perfect surface than monocrystalline cells.  This means that they absorb slightly less solar energy and produce slightly less electricity per square metre. On the plus side, the process of creating the silicon for a polycrystalline cell is much simpler, so these cells are generally cheaper per square metre.
On balance, the cost of monocrystalline vs polycrystalline based panels per Watt of power output works out about the same, but the polycrystalline panels will be slightly larger than equivalent monocrystalline panels.  This is generally not a problem unless you have a very limited area available for the installation, in which case you will want to maximise the power output per square metre.
Hybrid modules can produce a higher rate of efficiency per square metre compared to all other pv panels and are ideal for installations where space it ata premium. The combination of amorphous silicon and monocrystalline silicon means they perform better in low light levels and will produce around 15% more power.

Cell type             Efficiencies*         Approximate area per kW(m2)

Monocrystalline         13-17%                 6-8
Polycrystalline           11-15%                 7-9
Hybrid                        17%+                   5-6

* The efficiency of a solar cell gives an indication of how much of the sun’s energy is actually used by the system per unit area. The higher the efficiency, the better the cell is at converting the sun’s energy

Generating Electricity

When the pv panels are exposed to daylight  the electrons in the semi conducting material become energised and are able to generate an electrical direct current (DC).
The direct current (DC)  then needs to be converted into a 240V alternative current (AC) so it can be connected to the main electricity supply. This means an additional device called an inverter is used which constantly monitors the electricity imported from the national grid, modifies the DC electricity produced by the solar panels and converts it into AC to match the usable electricity.
Once converted into AC electricity by the inverter the electricity generated by the Solar PV system is automatically used to power the lights and electrical appliances.

What does kWp and kWh mean?

Solar electricity systems are given arating in kilowatts peak (kWp). This is essentially the rate at which it generates energy at peak performance for example at noon on a sunny day. The kWp of a domestic system will vary depending on how much a customer wants to spend and the roof area available to accommodate the panels.
The total amount of electricity the system actually generates in a year is measured in kilowatt hours (kWh). This will depend on the system’s orientation, shading and how sunny your site is, as well as the size of the system (in kWp) that you have installed.
A typical domestic system is between 1.5 to 3kWp. Each kWp should generate around 800 to 850kWh per year if unshaded and perfectly south facing with a tilt of around 30-50°. A solar roof array would typically generate 1200 to 2400kWh per year depending on size.

By contrast an average home uses 4000kWh of electricity per year on lights and appliances. However, an energy efficient home using A rated appliances and lighting could conceivably use half this value.

Power from Solar PV

The maximum power a module is likely to produce in optimal conditions with clear skies, strong sunlight and no shading is described as its peak power (KWp). KWp is also referred to as peak wattage and is defined as the electrical output in watts achieved under standard test conditions – 1000W/m2 solar insolation, 25°C