Photovoltaic or solar cell/panel converts sunlight directly into electricity which can be used to power light bulbs, household electrical appliances or recharge a battery. PV cells come in various sizes ranging from 10mm by 10mm to 100mm by 100mm, the most common size being 100mm by 100mm cells. A single PV cell produces about 1 to 2 watts of electricity; an amount that is quite insignificant compared to what is required by most electrical equipment.

Two or more PV Cells are built to produce a PV Module to provide higher wattages as required. For instance, a PV module producing 50 watts may comprise of at least 25 of 2 Watts output PV cells.

To meet the the electrical need of a home or an industrial setting, PV Modules are assembled together to form a PV Array that meets the total energy requirement.

A PVC system design begins with determining the total energy requirement for a facility to be powered. Next the number of solar panel units required and other components of the PVC (description below) are determined.

A basic Solar PV system comprises of the components shown in the drawing below and further explained in the notes that follow the drawing.

 PVC System

• Solar panels:  Collect visible light from Sun and converts it to electricity. The type of electricity current solar panels is Direct Current (DC).
• Charge Controller (CC): Controls the amount of electricity deposited in the battery bank at any time. In other words, it f eeds electricity from the solar panel to the batteries in a manner that prevents the solar panel from overcharging the batteries. Solar PV system can operate without a CC but the solar panels may overcharge the battery.
• Batteries (rechargeable) Store solar energy up to provide electricity for sun-down periods (nights and cloudy days). They must be able to discharge and recharge. Rechargeable batteries are a little more expensive than the disposable batteries. Without batteries a PVC system can only provide electricity when it is sunny.
• Power Inverter converts the low-voltage direct currents (DC) from the battery to high-voltage alternating current (AC) required by most household appliances.

Solar panels generate low voltage Direct Current (DC) electricity. Some appliances (e.g. incandescent lights) may be powered directly by the energy from the panels as these appliances are DC compliant. However, most electrical appliances require Alternating Current (AC) electricity and usually at high voltages (110V in North America and 230V in most of Europe and developing world (e.g. Africa)) to function. Inverters are used to convert the low voltage DC to AC at required voltages.

In summary, the solar cells collect direct sunlight, converts sunlight into low-voltage DC. Where energy storage in a battery for future use is required, the DC is stored directly in batteries. A charge controller is installed between the Solar panels and the batteries to ensure he batteries are not overcharged. A Power Inverter is used to convert the DC from battery to AC to power the AC appliances.

Other PVC system components that may be required are: wires and cables (for connection of the components) and meters and monitors (for monitoring the voltage and reading the currents of the system.

PV system is a preferred approach for electricity supply because of its modular features, its ability to generate electricity at the actual point of use, its low maintenance requirements and its non-polluting technologies. It is an attractive option for electricity supply in developing countries where there is abundant sunlight and large rural population without the proper infrastructure to develop an electrical grid. In such countries, PV system can be used to provide electricity to homes, rural clinics and government/corporate offices.

PV systems are also useful in remote and isolated locations in developed Worlds (e.g. northern Canadian territories - Nunavut, Yukon and NWT, arctic Greenland and Iceland and various World Islands).

PV systems are not suitable for water heating or other heat related appliances. A solar heater can heat water more quickly and efficiently than an electric water heater powered by PV panels. Solar heaters convert up to 60 per cent of the sun's energy into heat whereas PV cells are far less efficient and convert only 12 to 15 per cent of the sun's energy into electricity.

The Size of a PV System

To size a PV system, follow these process:

1. Determine the amount of electricity required:

• Determine the number of devices to be supported,
• Multiply the power (in watts or KW) on each device by the number of hours in a day the device will be used to obtain the electrical energy required in KWh,
• Add all the KWhs together to get the current total energy requirement for the PV system;
• Allow for expansions to your system. Depending on your resources, you may want to consider a factor of safety of 1.3 (i.e. 30% above your current requirement) or 1.5 (i.e. 50% above your current requirement).

2. Size your PV Module and your battery capacities:

Keep in mind that a PV cell of say 100mm by 100mm cell produces about 1 to 2 watts of electricity. The battery should be sufficient to store electricity for use during sun-down hours (nights and cloudy days).

The Cost of PV System

Sample costs:

A portable PV unit with a 50-watt solar panel, low-power inverter and battery, are about $700 and can operate three high-efficiency lights, a small TV and a water pump.

A more powerful PV system that produces 600 watts and operates several lights, a TV, stereo, microwave oven and water pump - but not at the same time - costs about $8,000.

New production techniques and applications combined with lowering prices for photovoltaic should increase the acceptance of this environmentally friendly technology.

What do you do with excess solar electricity

If you generate more electricity than you require to power your home, you can store the excess electricity in batteries or sell the excess electricity to the utility provider in your area under a feed-in-tariff scheme. To do the later, your home solar power electricity has to be connected to the regional or national grid in your area. You will need to find about the possibility of tying your grid to the regional/national grid in your area. Tying a solar (or other energy type) power to a national or regional grid is governed by some laws or regulations of the country in which you are. You will need to contact the responsible authority. obtain the permit to do grid tie and collect the specialized equipment that links your power source to the national grid. The equipment has to be installed by certified individuals. When you are under using power, the unused electricity is sent to the grid and used to provide power for other people, and you get a refund or credit from the regional or national body supplying you with electricity. The reverse is the case when your electricity usage is more that the electricity you are generating. Your excess electricity requirement is met from the regional or national grid in which case to pay the cost of the additional electricity you are getting from the grid to the national or regional authority supplying the electricity.

Related Information on EB:

Solar Energy

Solar Heating

Solar Electricity

Daylighting

Information from other sources:

• Solar Energy - Energy from the Sun
• EIA Energy Kids - Solar