Solar Power, what is it and how Solar Power works
Solar Power refers to the process of harvesting the Sun's energy (transmitted via light as solar energy
) into an energy source, such as electricity. Solar power
can be converted into other energy forms, like steam, but often in the residential setting direct conversion into electrical energy is used.
Solar powered systems, the key parts
Whether bought and installed at home or at the office, most solar powered
systems consist of up to three main parts: a solar collector (i.e. the solar panels
), an inverter
and optionally a charge controller and battery set if you are operating 'off the grid'; i.e. without mains power supply. The diagrammatic form of this is shown below.
The solar collector, usually photo voltaic (PV), otherwise known as solar panels, convert the solar energy from the Sun into electricity. The solar panels are rated by peak power output measured in Watts.
Solar Panels come in many different forms, often varying in efficiency in relation to the initial cost outlay. The three main types of solar panel are described below:
1) Amorphous solar panels
Amorphous based solar cells are often used for small solar panels, such as in calculators. The individual cells are not distinctly visible as they form part of a thin film on another material. Amorphous cells are less power efficient (up to 6.5%) then mono- and polycrystalline cells but their quality is constantly improving, so at the moment their big advantage is lower cost.
2) Mono-crystalline solar panels
Mono-crystalline solar panels are based on individual 'cells' each a slice of a silicon crystal processed to act as a solar collector. These individual cells are wired together as a set to make the overall rated wattage for the whole panel. You can often tell a mono-crystal by the circular nature of the individual cells, leading to gaps between them at the corners.
The recorded highest power efficiency for mono-crystalline solar panels was set in February 2009 by Mitsubishi Electric Corporation at 18.9%. This type of panel is also the most reliable and often the solar panel used for homes.
3) Poly-crystalline solar panels
Poly-crystalline solar panels are made from cast square ingots, so the gaps in the corners of the mono type do not exist. Poly-crystalline solar panels are cheaper to produce than mono panels but are also less power efficient (up to 12.5%)
Solar Panel Ouput voltage
Solar panels most often produce a 'nominal' 12v DC output or multiples there of (i.e. 12 volt solar panels, 24 volt solar panels, etc) - the actual stated peak voltage will be about 40% higher than this at peak watt power output - assuming ideal solar conditions. Such a varying voltage depending on the solar conditions is not that useful for today's devices that often require a precise AC supply at much high voltages, usually either 240 volt or 120 volt.. Now you can put solar panels together in series to get to around this voltage, but it would be in DC and highly unstable as to the exact voltage at any given time...
So, this is where the inverter comes in. Its job is to take a 'nominal' 12 volt (or maybe 24 volt) from the solar panels (with a high Current level) and converts and 'smooths' it into a regular AC voltage output for mains devices.. What basically happens inside it is that the voltage is stepped up in return for reducing the current (Power equals voltage times current, or P=IV); usually with a small loss of power efficiency along the way. If you are connected to the mains grid, the other function the inverter can do is to synchronize the AC produced from the inverter with the AC of the mains supply.
Off the grid installations
When you are solely using solar power to operate your electrical devices, when the Sun goes down you have no power! So to get round this an off the grid installation is so scaled so that enough power is harvested during the day to provide power to your mains devices and enough is spare to charge up a rack of batteries to provide power at night.
Although this is not as simple as it sounds. Typically lead acid batteries are used to provide the storage, these as well as being expensive & heavy need to be charged in a very precise way. If overcharged they tend to 'gas off' and corrode internally, which shortens their lifespan and capacity. If undercharged or overdrawn, they tend to loose capacity also.. So often a dedicated battery charger unit (often known as a controller) is required to 'manage' the batteries for you and provide safeguards against such bad charging.
You can also get solar controllers which will deal with managing the power from the solar panels and where to route it depending on demand. These can also often deal with battery charging, and possibly be configured to 'fire up' a back-up generator if the solar panels or batteries prove unable to meet the demand.
In most residential situations a grid connected
system would be most suitable, for several reasons:
- Financial return. Solar often provides power when the grid power is expensive. Usually power supply companies will operate different tariffs during the day, with the most expensive usually being during afternoon office hours to the evening - this is exactly the time that you have highest chance of it being Sunny!
- Feed in tariffs. Quite often it is possible for your 'excess' solar power to be fed back into the grid for a premium of the normal tariff (i.e. you are being paid to produce electricity). Now given it is likely that you will not be home when its sunny, this is a great way for the solar panels to pay for themselves by offsetting your electricity costs. Although do be very careful in doing your maths and remember your power consumption over time will tend to increase, so the amount you sell back will keep getting less.
- Gross feed in tariffs. This is like the feed in tariff above but you get paid for all the solar power you generate and not just the excess. For instance the NSW government is putting in place in Jan 2010 a 60c a KwH gross feed in tariff..
- Low maintenance. Once the system is installed it requires no real maintenance as such. The electronics is all automatic.
Sometimes people operate grid connected systems with batteries, on the basis that the excess power is first used to charge the batteries, then is fed into the grid. The only real benefit with this is if you suffer a power grid outage at night, you will still have power. Although do be careful to make sure the batteries are rated for such work (i.e. being left fully charged the majority of the time).