Why solar?

• Fossil fuel resources are depleting rapidly
• World energy demand is set to triple over the next 50 years
• Energy demand is growing faster than world population
• Supplies are plentiful: 6000x more sunlight than the world needs
• At 170W/m2 it has the highest power density of all renewables
• Little maintenance required
• Pollution free in use and minimal pollution in production/recycling Economically favourable in remote locations without grid access
• Generates most power during hours of peak demand when conventional power generation is most costly Grid connection enables local use, reducing energy distribution costs
• Low operating costs after the initial outlay

How do photovoltaic systems work?

• Light from the sun can be converted to electricity using a process known as photovoltaics (PV).
• Most PV cells are produced from silicon, one of the most abundant elements on earth.
• Ultra-thin wafers are cut from a large single crystal of silicon and then joined together to enable electrons to travel between the two layers.

A RAY OF SUNLIGHT SENDS A STREAM OF PHOTONS MOVING AT A SPEED OF 300,000 KMS OER SECOND, GENERATING POWER IN THE PROCESS

Single solar cells can be used to produce small amounts of electricity to power devices such as watches or calculators, but when linked together to form solar arrays or modules, these cells can produce enough electricity to power an entire building.

Cells that have been linked together to form a solar module are usually encapsulated in glass to protect them from the elements. Some will also have a frame to give additional mechanical strength and greater aesthetic appeal.

Most PV systems also require an inverter. This is a piece of equipment that transforms the direct current of the solar generator into alternating current with voltage compatible with that of your household appliances.

Solar panels are capable of generating electricity, even on cloudy days in winter. The amount of energy produced varies according to the intensity of the sunlight. No power is generated at night-time so any electricity required after sundown must be stored in a re-chargeable battery.

THE DEMAND FOR ELECTRICITY USUALLY PEAKS WHEN THE SUN IS AT ITS MOST INTENSE – IN THE MIDDLE OF THE WORKING DAY

Most solar installations run in parallel with the commercial electricity grid.

In such systems, all the energy produced is fed into the grid, regardless of the need for local consumption. Consumers often prefer this type of system as there is no need to store the electricity produced and there is often a premium paid by the utility companies for the supply of clean, solar energy.

Other installations take the form of island systems whereby energy is stored in a battery and supplied to an individual house, remote building, appliance or mobile unit which has no connection to the grid.

Which technology?
MONOCRYSTALLINE
Wafers thinly sliced from a large, single crystal ingot of high purity silicon, grown at very high temperature. Expensive process but produces a near perfect crystal structure. Dark blue black in colour.

POLYCRYSTALLINE
Molten silicon is moulded before being sliced into wafers. Considerably cheaper than mono-crystalline but the cells are less efficient because of the imperfections in the crystal structure arising from the casting process.

THIN FILM
Amorphous silicon, CIGS, CdTe
Less efficient than crystalline technologies but production costs are considerably lower as the manufacturing process is considerably simpler.

CRYSTALLINE

• 90% of today’s solar modules are produced using mono- or polycrystalline technologyVery efficient – well suited to installations where space is limited
• Tend to lose some power as temperatures rise or when shadows fall across the array

AMORPHOUS SILICON

• Less efficient than crystalline – better suited to installations where there are no space constraints
• Very efficient manufacturing process – lower cost per W of electricity
• Produce around 10% more power p.a. for each W installed
• Perform better in high temperatures or in low/diffuse light (STC data does not take this into account)
• Heat coefficient of 60% gives greater stability when temperatures rise
• Single junction a-Si layers are more than 500 thinner than those of crystalline silicon – use much less expensive raw material and are less susceptible to fluctuating raw material prices and shortages
• Production process is more energy efficient and therefore has a shorter energy payback time (1.6 years rather than 2.2 years)