Components Used in a Stand-alone PV System
The components used in a typical PV system are shown below along with a brief description of their operation.
The panels are made up from PV modules that have been assembled from individual PV cells. The panels are grouped together to form arrays of 12, 24, 36 or 48 volts. The normal building requires between 12 and 20 panels.
The types of materials used in the plate’s construction affect the efficiency of PV panels as noted below;
- Ø Amorphous Silicon – 5% efficient
- Ø Cadmium telluride – 7%
- Ø Copper Indium Diselenide – 9%
The type of materials also effects the costs of the panels, the most efficient being the most costly to purchase. It is therefore advisable to weigh up the pros and cons of the different materials, which are changing rapidly as the technology advances, choose the industries recommended or award-winning PV panels such as:
Award winning PV panels in USA are manufactured by Sunpower USA selling at $4/W, with Revolution.uk also manufacturing panels in the UK, gaining awards, and selling PV panels for £3.50 ($6/W).
Inverters are available from 100W to 10,000W, and play a very important role in the off-grid PV system. The inverters convert the array Direct Current (DC) output power from the PV array into Alternating Current (AC) at 120 or 240Volts.
AC is the most practical current to supply the building, but DC power from the array can be used (but most household equipment such as kitchen appliances, TV, and computers run on AC).
- Control and Safety Components
Integral to the inverter, or attached to it, there can be a Power Optimizer (a DC/DC converter) or a Maximum Power Point Tracking (MPPT) unit which control the system.
These components continually monitor PV output and ensure that in the event of a module failure or sudden changes in irradiance or temperature (all three detrimental to output), the best current and voltage is maintained.
Other controllers guard against overcharging the batteries, and gauges such as LED ammeters and voltmeters show the condition of the current being generated.
Electric fuses are located in each major component as a safety measure.
Reference Web: Windandsun - efficient multi-function off-grid PV array inverters and controllers
A bank of batteries should supply the house with power for at least a day, depending on the amount of power being used, and the output of the batteries.
Modern batteries are mostly deep-cycle batteries; these are becoming more efficient, of higher capacity, and lasting longer. This is mostly due to developments of the electric or hybrid car industry that is continually researching new battery technology.
Unfortunately, the prices of the batteries are still high, as I recently discovered when I replaced my Bruno electric disabled scooter batteries; $150 each! But the original batteries had lasted 10 years, so you get what you pay for.
Remember batteries give of fumes, so store them off the floor in a dry, well-ventilated area and check them regularly. Although the majority needs little maintenance, look for heat spots or the appearance of cracks, but do not touch them and, to keep the kids away from them, provide a locked access.
A diesel or petrol genny will be required as an extra back-up to the battery bank in the winter months when days are shorter and more clouds reduce the PV system's output.
The PV system installer will estimate the capacity required by the generator at peak loads and work back from there.
Try to get a generator with a decent sized fuel tank as you don’t want to be wandering about in the outback in your pajamas in the middle of a snow storm to top up a fuel tank!
Reference Web: smps.us - batteries and standby generators information.