Free energy from the Sun
Micro Generation of electricity with PV Panels is a popular technique and according to some the most environmentally friendly. If you exclude the initial cost of equipment the cheapest electrical energy generating system is solar power because the fuel (that is solar energy) is totally free for any one to use.
As you are now aware to qualify as a micro generation system your equipments power rating should be less than 25A (5.75 kw) single phase or 16 A (11kw) if 3 phase.
Solar cells convert suns radiant energy falling on it to electrical energy. The conversion has not exceeded 20% efficiency even in the best of laboratory conditions as yet except in highly experimental designs with split light. The installed efficiency of an array is therefore in the region of 12% to 15% which decreases further with age.
A Photo Voltaic module (Panel) is an assembly of electrically interconnected solar cells or PV cells generally made today out of Crystalline Silicon, Cadmium Telluride or Silicon. Most of the module types are rigid but the type made out of thin film substrate is physically more flexible.
The overheating of solar cells reduce the efficiency of the PV modules drastically but except for incorporating diodes in the electrical circuit no other design features are found in PV panels for this purpose. Any such arrangement therefore is incorporated in the installation. A group of solar modules connected in a single circuit electrically and mechanically is called a Photo voltaic array.
The working of PV cells
Photons in the suns rays’ incident on the PV panels are absorbed by the semiconductor material such as Silicon in the solar cells. Electrons are dislodged from the atoms making an electric current flow through in one direction while positive charges move in the opposite direction when the circuit is closed. The current is DC and an inverter is used to convert it to AC usable in a common domestic electrical distribution system or export to the utility grid (in a grid tied system).
Types of PV Panels
The commercially available PV modules come in two different distinct designs based on the manufacturing technique and therefore the structure and material used in the solar cells. These are;
• Wafer –based Crystalline Silicon cells and,
• Thin Film cell based on cadmium telluride or silicon
The solar cells are easily susceptible to mechanical and electrical damage due to external sources such as hail and rain. Dust and other particulate block the incidence of solar energy on the PV cells reducing the power out put. Therefore normally an additional glass panel with a rigid metal frame is provided over the solar cells for protection.
The rating of PV Panels
The power out put of solar cell arrays is measured in watts or kilowatts. The generated power is in DC.
The connection of modules may be in series (to obtain a higher voltage) or parallel (in order to obtain a higher current) or a combination of the two according to the desired out put.
A typical large capacity solar panel may be sized 2m x 1 m x 50mm thick producing electrical power up to 250w. The maximum Power voltage in this case would be 34.4 V and the maximum power current 7.26 A.
Capital and operating costs
While the operating costs are not high as the devices are static with no moving parts the
initial investment is high compared to even Wind turbines.
The freely available crystalline silicon solar panels mass produced in
China cost approximately US$ 4.00 per watt ex factory.
New houses can incorporate solar panels as part of the architectural design while old houses too can be retrofitted with relatively minor modifications to the roof, the most popular location for PV panels.
In a remote panel installation this may not be necessary but the high losses in transmission have to be considered.