Solar Photo Voltaic Panels
Introduction
The use of Solar Energy has increased significantly in both the residential and commercial sectors in Ireland and the UK over the last decade. There are 2 main categories of solar panels which use completely different technologies to make the most of the energy from the sun:
- Photovoltaic or Solar Electric Panels: These transform solar radiation directly into electricity, which can then be used throughout the building.
- Solar Water Heating Collectors: These panels absorb the energy from the sun and transfer it to heat water.
In this is summary information that will inform the commercial customer about Carbon footprint measurement & reduction, the methodologies and basic calculation.
Photo Voltaic Technology
Photovoltaic (PV) cells are so called because they convert light directly into electricity. There are two types of cell, crystalline and thin film. While crystalline systems use the electronic properties of crystals to generate a current from light, thin film systems rely on semi-conductor technology for the current flow. Traditionally, crystalline systems are the more efficient, although more expensive as they require the development of crystals of suitable quality. Conversely, thin film systems can be manufactured more quickly and cheaply and their efficiencies are improving.
Thin film PV cells are semi-conductor devices, usually made of silicon, which contain no liquids, corrosive chemicals or moving parts. They produce electricity as long as light shines on them, they require little maintenance, do not pollute and they operate silently, making photovoltaic energy the cleanest and safest method of power generation.
Photo Voltaic Electricity Generation
Sunlight is converted to electricity using photovoltaic or solar cells. Photovoltaic (PV) cells are semiconductor devices, usually made of silicon, which contain no liquids, corrosive chemicals or moving parts. They produce electricity as long as light shines on them, they require little maintenance, do not pollute and they operate silently, making photovoltaic energy the cleanest and safest method of power generation.
Photo Voltaic cells come in many sizes, but most are 10 cm by 10 cm and generate about half a volt of electricity. PV cells are bundled together in modules or panels to produce higher voltages and increased power. A 12-volt module, for example, depending on its power output, could have 30 to 40 PV cells. A module producing 50 watts of power measures approximately 40cm by 100cm. Currently, PV panels are not highly efficient, converting only 12 to 15% of the sun's light into electricity, however laboratory prototypes are reported to be reaching 30% efficiency, which suggests that new models being launched onto the market in the coming months and years should reach or indeed exceed this level of efficiency.
To determine the amount of energy you need for a stand-alone PV system, multiply an electrical device’s power in watts by the number of hours a day the device will be used. For example, a 17-watt fluorescent light lit for 18 hours a day uses 306 watt-hours (or 0.306 kilowatt-hours) of electricity. To get total power use, do this calculation for each electric device and add the results. The PV system should supply at least as many kilowatt-hours (under a variety of lighting conditions) as your total electric needs. When sizing your PV system you should also consider the ability of your system to expand to meet any unexpected demands, such as the purchase of a new appliance, computer etc.
Sizing a PV system
PV modules produce electricity only when sunlight shines on them.The electricity produced by PV Panels will need to be either stored in batteries or exported to the grid (which requires grid synchronisation equipment). A low voltage circuit can be run directly off batteries, although mains voltage appliances in the house or property may require an inverter.
When sizing a stand-alone PV system, the energy output of the PV panels and the storage capacity of the batteries should be high enough to operate devices at night and on cloudy days when little sunlight is available. Grid-linked or grid-tied PV systems connect to the mains to feed excess capacity back to the local mains electrical grid. When insufficient electricity is generated, or the batteries are not fully charged, electricity drawn from the mains grid can make up the shortfall.
Grid-tied PV systems should be at least 8-10 M˛ in size, as larger systems are proportionately less expensive than smaller ones and the larger amount of electricity exported will mean a more rapid payback period (once domestic producers begin to be compensated for the electricity generated).
Roof Orientation and Panel Placement
To ensure maximum efficiency, solar PV panels should ideally be mounted on a south / south-east / south-west facing roof, away from any shadows from trees, surrounding buildings or chimneys. This enables the panels to receive as much direct solar radiation as possible. Solar panels will also work on east or west facing roofs; however, a larger area of solar panels may be required to compensate for the reduced level of sunlight.
With regard to the angle of installation, the Solar Collector / Panel will be most effective when the angle of the sun is at right angles with the plane of the collector. However, the solar angle changes throughout the day and the year. On average, the optimum inclination angle for solar panels in the United Kingdom and Ireland is around 30-40 degrees, which fortunately, is also the normal pitch of a roof in this part of Europe.
PV systems can power any electric device but they 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.
