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windWhat is PV?
The photovoltaic (PV) process converts sunlight, the most abundant energy source on the planet directly into electricity. The equipment required for this process has no moving parts and as a result requires minimal maintenance. In addition, the electricity is generated with no emissions and no noise.
A PV cell consists of two or more thin layers of semiconducting material, most commonly silicon. When the cell is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC). The electrical output from a single cell is small, therefore multiple cells are connected together to provide a more useful output. Cells connected in this way are encapsulated (usually behind glass) to form a weatherproof module or panel.
Multiple modules can likewise be connected together in order to provide sufficient power for common electrical appliances.
What is the difference between PV solar panels and Solar Hot Water panels?
The panels in a PV system contain semi-conducting materials that generate electricity when exposed to sunlight. This electricity can be used to power household appliances or, if the property is mains connected, surplus electricity can be sold back to the National Grid.
The panels in a Solar Hot Water (SHW) system have pipes running through them and the sun's energy heats water as it flows along these pipes. The hot water is then stored in a cylinder until it is needed.
How long has Solar PV technology been around?
The photoelectric effect was discovered in the 1830s, but it was not until the mid 2oth century that it began to be used.
Initially, PV was used in the Space industry, but from the 1960s onwards, better technology was developed with lower prices. Solar PV began to be used for man more applications, particularly I n providing power in remote parts of the world.
Grid-connected Solar PV has had a massive growth since 1990's in the more developed countries of the world.
Are photovoltaic panels expensive?
Over the last 20 years the price of PV modules have fallen dramatically, from around £15 per Wp in 1980 to current prices of around £3.50 per Watt. That means that a single module, typically generating 60W of power under standard test conditions, now costs around £200 Solar PV is still a more expensive technology than most other forms of renewable energy, but it has many advantages over other systems.
Doesn't PV technology need bright sunshine to work properly?
The electrical output of a PV cell is dependent upon the intensity of the light to which it is exposed. So PV cells will tend to generate more electricity on bright days than when skies are overcast. However, photovoltaics do not need to be in direct sunlight to work, so even on overcast days a PV cell will be generating some electricity.
Is the British climate suitable for PV?
The amount of electricity generated by a PV cell depends on the intensity of the sunlight to which it is exposed. A solar cell will generate more electricity on bright summer days when the sun is stronger than on sunny winter days. In the south of Britain the sun's power, or irradiation, available at the surface of the earth averages around 950 watts per square meter. With typical solar cell efficiencies of around 14-16%, this will generate about 140-160W per square meter of panel, providing they are placed south facing into the sun and inclined between 30'º to 50'º from horizontal.
What happens when little or no electricity is being generated for example during the night?
During the times when your PV system is not generating sufficient, if any, electricity your energy requirements will be supplemented by your local electricity network, also known as the National Grid. This temporary switching of electricity supply is done automatically and does not require you to turn anything on or off on your PV system.
How do I know if my property is suitable for PV?
The following is a checklist of usual aspects to consider:
* Roof size - Each 1kWp of modules requires approximately 7.5m'² of roof space.
* Roof orientation - panels should face S, or between SE and SW and be tilted between 30-50 degrees to horizontal.
* Is the roof shaded? - Shading throughout the day should be minimized - although electricity will still be generated, it is best to install where there is unobstructed sun all day.
* Roof ownership and Planning permission - does the roof belong exclusively to the property owner or are there shared rights/access? Planning permission may be harder to obtain if the property is in a Conservation area or is Listed.
How much will I need to power my home?
A typical domestic system of 1.5 kW in the UK would produce around a third of the annual demand of an average family household (taking the average demand to be around 10 kWh per day). However, calculating the system size depends on many factors, for example whether the system is grid connected, energy demand of the household etc.
How much Power can I expect to get from my PVs?
Typically a 1kWp array will produce 750kWh/year. 1 kWh is known as a unit of electricity on your electricity bill.
Why are PVs rated in Wp rather than watts, kWp rather than kW?
Wp means peak Watts. KWp stands for kilowatt peak rather than kilowatt. In other words, a 100Wp panel will produce a maximum of 100W in peak conditions (1kW/m2 solar irradiation) - this is equivalent to a bright sunny midsummer day in the UK.
What does 'grid-connected' mean?
Most PV systems in the UK will be grid-connected, which means that the systems are connected to the local electricity network. During the day, the electricity generated by the PV system can either be used immediately to power electrical appliances in the home or workplace, or can be sold to one of the electricity utility companies. During the night when the solar system is unable to generate electricity, power can be bought back from the network. In effect, the grid is acting as an energy storage system, which means the PV system does not need to include battery storage.
Connecting a PV system to the distribution network will require permission from the Distribution Network Operator (DNO). The DNOs in the UK have different policies when it comes to connecting PV systems to their networks, and so different rates will be paid for exported electricity.
Technically, you will also need to use a grid-tie inverter. If you wish to get paid for the electricity you produce, you will need to ensure a G83-certified inverter is used. As more beneficial export contracts become available, more and more installations will include G83-certified inverters and export meters.
Is it true that I can get my electricity meter to spin backwards?
Net metering of this sort is not usual. Typically all systems will have a Total Generation meter installed. Your normal household meter measures the import electricity. And if you wish to take up a contract that is based on excess electricity exported to the grid, an export meter is required as well.
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How much will I get paid for the electricity I feed into the grid?
Typical contracts today offer 4-6p per kWh for the total electricity produced and the ROCs. Some trial contracts will pay a similar price to that paid for the normal imported units - maybe up to 8p per kWh - just for the exported electricity.
Are there any planning issues?
One of the conditions of the grant scheme is that you have received planning consent from your local council - please note, this is different from planning permission. For the majority of homeowners the addition of solar PV panels fall within 'permitted development rights', which means that the panels will be more or less flush with the roof.
If your property is in a conservation area, Area of Outstanding Natural Beauty or is a listed building you may need to apply for full planning permission. Initial enquiries should always be made with your local authority.
What maintenance does a PV system require?
One of the key advantages of PV systems over other renewable energy systems is the minimal maintenance required. There are no mechanical moving parts within the system that will get worn and need to be replaced. Any bird droppings or dust that settle on the modules will be washed off by rainfall, however, we do recommend a periodic thorough cleaning of the modules with an environmentally friendly cleaning agent. We also strongly recommend a periodic inspection/testing of the PV electrical system as would be required for any other electrical installation within the home. We can provide both of these services using our trained personnel and roof access platforms, if required.
How long will a PV system last?
PV modules made from crystalline silicon have an average life span of 25-30 years and can continue for longer. Some of the earliest solar electric panels, made about 35 years ago, are still producing energy today! Such is the reliability of some PV modules that manufacturers have begun to offer operation and power output guarantees for the lifetime of the equipment.
A PV Solar System has no moving parts that will get worn and need replacing. Periodic inspections by a qualified technician will help to alleviate any electrical faults.
