Photovoltaic System Benefits and Components
Photovoltaic System-How They Work
A PV system can generate electricity for your home or business, either as part of a stand-alone power system, or for buildings already connected to the local electricity network. The term “photovoltaic” means "light-electricity." A photovoltaic system (often just called a PV or solar electric system) converts radiant energy from the sun directly into electricity. The benefits of solar electric systems
Photovoltaic systems A PV system can be installed in stages: it can start small and be expanded as energy use or financial resources grow. It also requires very little maintenance over its lifespan.
Where are PVs used?
PV systems are used to power a range of equipment such as communications equipment, water pumps, lights on navigational buoys, electric fences on farms, and some of the calculators and wrist watches that we use every day. Larger systems have been used for some time on homes, farms, public buildings, petrol stations and lighthouses in remote areas.
Innovative applications for PV are being developed all the time. For example, ferry vessels can now be powered by PV, and a PV powered plane set an altitude record of 29,524 meters in 2001. In Australia, there is a popular race for cars powered by nothing but the sun’s energy.
Pv systems are often part of a stand alone power system (SAPS) that is not connected to the electrical distribution network. In these systems, the electricity generated by the PV system is stored in batteries where it can be used when the PV cells are not producing electricity.
A stand-alone PV system avoids the cost of connecting a property to the local lines network, which can be between $18,000 and $24,000 per kilometer. Given this investment, it becomes cost effective to consider SAPS solutions using PV panels for homes, communications stations, and farms or lodges in remote areas.
Network-connected systems:
On a property that already has a main power connection, additional equipment can be used to link a PV system to the local lines network. This allows electricity to be drawn from the lines network if there is a shortfall, or electricity to be supplied to the network if the PV system is generating excess power. Effectively, the network acts as the back-up system, instead of a generator and batteries.
When your PV system generates excess electricity you may be paid for electricity exported to the network. As a consumer you pay for electricity imported from the network. No changes in the household wiring are necessary, but the system must meet the technical and safety requirements of the local network company, and the Electricity Regulations 2000. You will also need an agreement with your retailer if you are to sell electricity. The requirements vary between network companies and electricity retailers. Your retailer will be able to advise you of their requirements and which network company you need to contact.
PV system components:
PV panels:The panels are the collector of the system and are made up of individual PV cells wired together. Each panel has a rating specifying its maximum (or “peak”) electrical output under standard conditions. For example, a panel with a 75W peak rating (75Wp) will have a power output of 75W at a sun intensity of 1000W per square meter (about what you would get at noon on a fine summer day) and an outside temperature of 78 degree’s.
The main advantage of solar panels is that they are robust, virtually maintenance free, and fairly unobtrusive. They are designed to withstand arctic cold, desert heat, tropical humidity, winds in excess of 200kph, and 25mm diameter hail stones. The panels require sturdy mounting hardware to protect them from wind and snow loads.
Batteries:PV panels do not generate power continuously, so in a stand-alone system the output can be stored using batteries. If you have a network-connected installation you will not require batteries. At present, banks of 12v to 48v lead-acid batteries are commonly used. Sealed batteries cost more and require less maintenance, but a well maintained lead-acid battery will usually last longer than a sealed battery. For optimum life, deep-cycle batteries should be used. Electronic devices called “charge controllers” are used to control the battery charging and extend their life. The batteries will typically need replacing in 4 to 10 years, depending on quality, sizing and how they are used.
Inverter: PV panels generate direct current (DC). Since most household appliances run on alternating current (AC), an inverter is usually required. In a network-connected installation the inverter will convert DC to 230v AC before it gets exported or used in the house. In a stand-alone system the inverter converts power stored in the batteries to 230v AC. A range of DC household appliances does exist, but the choice of products is limited at present.
Protective devices such as diodes, DC fuses or circuit breakers, safety switches, grounds and properly gauged wiring are required to meet electrical code safety standards.
How do photovoltaic systems turn sunlight into electricity?
PV cells convert sunlight into electricity by a simple energy conversion process. When sunlight (in the form of photons) hits the PV cells, the photons excite electrons in the atoms of a semi-conducting material used to make the cells. The energized electrons result in an electrical voltage being generated, and when an electrical circuit is closed, electrons flow producing an electric current (see diagram).
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