What is it Solar PV and how does it work?

‘Photovoltaic’ is a combination of two words; ‘photo’, Greek for light, and ‘voltaic’, from ‘volt’, meaning electrical power.

The solar cell is the main component of Photovoltaic technology and Solar PV systems use these cells to convert solar radiation into electricity. These solar cells consist of one or two layers of a semi-conductor and the most common material used in these cells is silicon, an abundant element most commonly found in sand. Solar cells can be wired together to form a module (a solar panel) and these can then be connected together to form an array.

How do solar cells produce electricity from light?

Essentially, when light shines on the cell it creates an electric field across the layers causing electricity to flow. The more intense the light is, the greater the flow of electricity. However, PV cells produce electricity in the form of direct current (DC). An inverter is needed to covert this electricity to Alternating Current (AC) which can then be used in your house and exported to the national grid.

Click here for the science section on NASA’s website for a more technical explanation of how PV cells work.

A large number of homes in the UK have recently been installing PV systems, and the number is increasing exponentially since the introduction of the Feed in Tariff (FiT) – the financial incentive scheme introduced by Government on 1st April 2010. The aim of the FiT is to increase the uptake of on-site electricity generating technologies including PV.

Types of Solar Panel

There are 3 basic construction types of Photovoltaic solar panels:

Monocrystalline cells are cut from a single crystal of silicon and are the most efficient type, but also the most expensive to produce. They are completely rigid and must be mounted in a rigid frame for protection.

• Polycrystalline

Polycrystalline cells are made from a slice cut from a block of silicon that consists of many crystals. Solar PV panels made from these types of cell are slightly less efficient but also cheaper than monocrystalline cells. They also need to be mounted in a rigid frame.

• Thin Film – Amorphous

Amorphous cells are manufactured by placing a thin film of non crystalline silicon onto a wide range of surfaces. This creates the least efficient type of PV panels but also the cheapest and if manufactured on a flexible surface, the whole PV panel can be flexible. One problem with amorphous cells, however, is that their power output reduces over time, particularly during the first few months, after which they become stable.

Benefits of Solar PV

Lower carbon emissions

Solar PV electricity is renewable once the installation offsets the carbon emitted during its construction. A typical 2.5 kWp system could provide up to 50% of a household’s annual electricity, saving around 1200 kg of CO₂ per year and around 30 tonnes over its lifetime.

Lower energy bills

By producing up to 50% of the annual electricity consumed in a typical house, electricity bills could be reduced significantly, thus providing protection against rising energy bills.

Generate additional income

Under the Governments clean energy cash back scheme (known as the Feed in Tariff), owners of Solar PV systems are paid for producing electricity regardless of whether it is used within the property, in addition, a lesser payment is also made for exporting unused electricity to the national grid.

Energy storage options

If a home is not connected to the national grid, Solar PV systems can provide alternative energy that may be far more flexible as excess electricity can be stored in special batteries.

Potential of Solar PV in the UK

Optimal location for Solar PV panels on buildings

The diagram above outlines the optimal orientation for solar PV panels in the UK (red dot) and percentage of maximum performance if installed at a different orientation.

How much power can a Solar PV system generate?

PV systems are typically rated in kWp (kilowatt peak) which indicates the combined potential capacity of all the PV modules installed under prime conditions.

Roughly speaking, if a solar PV system faces due south and is installed at an angle of 30⁰ and is unshaded, each installed kWp can be expected to produce around 850kWh (units) of electricity per year in the UK. A 2kWp system would thus produce approximately 1,700kWh / year, around half of the annual electricity consumption.

Components of a PV system

What does a typical PV system require?

The following components are essential to any PV system. 

Solar cells and modules

These are used to capture the suns energy, initially supplying Direct Current to the system

Power Inverters

An inverter converts the Direct Current electricity provided by the solar PV system into Alternating Current for use in the building and for export via the national grid.

Solar PV mounting system

A mounting system will be needed to accommodate the PV system.

Isolators

Isolators enable separation from and within the PV system for safety when carrying out installations, upgrades and maintenance work.

Cables & Connectors

Used to connect the various components of a PV system and are selected based on the size and characteristics of each PV system.

System Monitoring

Monitoring will be needed so you can you track the amount of electricity the system is producing, how much is used within the property and how much is being exported back to the grid. This can be carried out by most commercially available inverters and can be integrated into PC and web applications

Junction box

These are used to allow the parallel connection of several strings of PV modules