Photovoltaic equipment is also widely known as P.V. or solar electricity. P.V. is the high tech side of the solar industry. The photovoltaic industry is still in its relative infancy compared to the solar heating industry. If the efficiencies of P.V. panels ever reach the efficiency of today’s heating collectors, and the costs are kept down, the energy usage on earth will be dramatically changed.
The basic building block of a photovoltaic system is a solar cell. It is made of silicon semiconductor material and converts light into electricity. A matrix of solar cells are wired together to make a solar panel, which typically outputs 12, 24, or 48 volts direct current (Vdc). A single solar panel can be used individually for small charging chores such charging a 12 volt battery or charging electronic equipment such as cell phones. However, to supply electricity to a whole household, several or many solar panels must be wired together to form a solar array. This solar array is usually mounted on an equator facing roof top or a metal post. The electrical output of your solar array is totally dependent on the amount of direct sunlight that hits the panels. Any obstructions, such as trees or clouds, will severely reduce the amount of electricity produced.
Although the photovoltaic effect was discovered over a century and a half ago, due to low outputs and extremely high costs, applications for P.V.'s didn't get going until the space program. Satellites in earth orbits or deep space required a source of energy to power their transmitters and other equipment. Photovoltaics, regardless of cost was the only viable option available to NASA engineers. The fruits of the space pioneer's development are harvested today in applications such as remote communications, powering homes, pumping water, charging R.V. batteries and remote lighting. The effort in bringing down the cost of P.V.'s is opening new markets daily although payback cannot yet be realized without subsidies if low cost grid power (power lines) is available.
PV remote battery systems can be DC or AC systems. Many smaller systems are DC only. These systems are typically used in small cab- ins, remote homes, boats and outdoor lighting. A DC only battery system is more efficient than an AC battery system because the maximum inverter efficiency is only about 90%.
The most common batteries in use today are deep cycle sealed lead acid (SLA) batteries. These are very economical, sold in a competitive market, and are more durable than car batteries. You can also get Nickel and Lithium batteries for solar energy storage, but the costs are several times that of SLA for the same amount of capacity. However, you get what you pay for. Nickel and Lithium batteries last much longer, can be charged thousands of time, and are much lighter than SLA.
On hot summer days with clear skies your solar panels produce large amounts of electricity. This high output may damage your batteries. A charge controller is installed between your solar panels and batteries. The charge controller assures a safe voltage is fed to the batteries preventing overcharging.
Charge controllers can have some pretty sophisticated sensing circuitry that can control how your battery pack is charged. Some have temperature sensors that adjust the charge rate based on how hot or cold it is. Advanced techniques such as Pulse width modulation (PWM) and maximum power point tracker (MPPT) are offered in many of today's solar PV charge controllers. These algorithms maximize charge capacity of the battery pack.
For many decades alternating current (AC) has been used to move electricity long distances. It is the default method of delivery for all electric utilities. Solar panels produce direct current, meaning the electrons flow in one direction. To sell your power to the grid you need a DC to AC inverter. This device simply converts DC to an AC format that is compatible with your electric utility provider.
Most inverters accept 12, 24, or 48 volts DC input, but not all three at once. The most popular inverters for small to average systems accept 12v DC input. On the output side most solar PV inverters can produce 115VAC or 220VAC, but not both. The inverter and charge control functions can be provided in the same box.
Smaller inverters typically provide AC outlets called ground-fault circuit interrupter (GFCI). GFCI, basically means the oulet has a third jack that goes to earth ground. These inverters may also include a DC 12 volt outlet, usually in the form of a cigarette lighter plug in a car. In some of the more portable units the DC connection is bi-directional, meaning that it can provide power to DC appliances as well as being used as a charge port.
Higher powered inverters tie directly into a building's electrical system, typically at the fuse box. They will not have GFCI connectors. These more powerful units have capacities of several thousand watts continuous. They would definitely be installed by a qualified electrician.
The National Electric Code (NEC) governs and gives instructions on what types of cable and conduit to use for various solar PV systems being installed. DC systems require much heavier cable than AC runs. Conduit is simply a protective tubing used to protect the wire from outside weather and to protect people from electrical shock. It is important to follow the guidelines of NEC in order to have the installation approved by local authorities. In most cases a licensed electrician is required to make the wire connections.
Most home electrical systems have a breaker box, breaker panel, or fuse box even before a PV system is installed. Additional fuses and/or breakers may be needed to provide safely between the components in a PV set-up.
There are many other PV system components that can be placed in the chain to allow for a more intelligent system.
Tags: components of solar electric systems.