Solar Electricity
Solar electricity is used to power equipment in areas where there is no mains supply (in off-grid or stand-alone systems) or attached to buildings to feed directly into their AC electricity supply (in grid-connected systems). It is silent and non-polluting, with no moving parts to wear out. It needs no fuel and little or no maintenance.
At the heart of these solar electricity systems are solar cells which convert daylight directly into DC electricity. The technology is called photovoltaics or PV for short. Solar cells are assembled into robust units called solar modules (PV modules) which can be connected together to form systems of any required size.
Photovoltaics should not be confused with solar heating, where daylight is used to heat water. That is quite different technology.
Photovoltaic was first developed for use in spacecraft in the 1950s and is still used today to power satellites. In the 1970s and 1980s the industry grew to provide power for specialist use on the ground. In the past few years the growth and cost reduction have been dramatic – the average annual growth of the industry has exceeded 40% already more than ten years. Solar modules mounted on buildings and feeding electricity into the grid has become quite a common sight.
In a grid-connected system the collection of solar modules (the PV array) feeds DC electricity into an inverter which then supplies AC electricity into the mains. Any excess electric power not used within the building is exported.
In most off-grid systems the solar module or array feeds DC electricity into a battery via a charge controller. The equipment can draw DC electricity from the battery at any time, day or night. If AC electricity is required, an inverter can be used to step up the voltage and convert the DC to AC. In some off-grid systems there is no battery and a special water pump or fan is powered directly from the PV array.
Off-grid System
In 'off-the-grid' systems for remote areas, there is no mains power source. Such systems come almost always with the need for electricity storage, which is managed with battery banks.
In all the off-grid systems there are one or more solar modules mounted outside, facing the sun, and there are batteries to store the solar electricity and release it when it is needed. The number and size of the modules and batteries depends on how much daily energy is needed. The system can be quite large, or quite small, depending on the load. A charge controller is vital to prevent the PV panels overcharging the battery. Charge regulation is needed to prevent excessive water losses, overheating and reduction of battery life
During the day, the PV array produces enough During the night, the load continues to be powered,
energy to power the load and to charge the battery. drawing on energy stored in the battery.
1 Solar Modules 2 Controller 3 Fusebox 4 Battery Bank 5 Loads
Grid Connected System
In a grid-connected solar electricity system, DC electricity produced by the solar cells is converted to AC electricity with an inverter, and fed into the grid. Arrays of solar modules can be retrofitted over roofs or walls, integrated into the building fabric, or mounted on the ground. Solar arrays can be installed practically everywhere, in sizes ranging from small domestic house installations to large centralized power plants.
The peak electrical demands of commercial and public buildings normally coincide with the peak in production from a solar electricity system. This means that the electricity produced can largely be used within the building. If excess energy is generated, that can be exported to the electricity network. The solar electricity system thus reduces, or can even exceed, the building’s overall energy demand. In places where the grid electricity supply is unreliable, the solar electricity systems can be combined with battery banks to provide the back-up function when needed.
1 Solar modules
2 Array box
3 DC switch (optional)
4 Inverter
5 AC switch (optional)
6 Energy meters
7 House distribution box
8 Net connection
