Solar PV Q & A

How does Solar PV work?
Photovoltaic (PV) cells are made from layers of semi-conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced. Groups of cells are mounted together in panels or modules. The power of a PV cell is measured in kilowatts peak (kWp), the rate at which the cell generates energy at peak performance in full direct sunlight.  

How much space does a Solar PV system need?
The required array size is dependent upon the electricity consumption of the property. A typical Solar panel is 1640mm x 990mm and 250watt. 16 panels to provide a 4Kwp system requires slightly over 32m2 including clearances. Array layouts can be installed to suit roofs of all shapes and sizes. The most common layout for a tradition roof is 2 rows of 8 Panels in Portrait (3.8 High x 8.6 Wide).
What happens to the Electricity I don’t use from the Solar PV system?
The electricity produced by your system will be fed from the Panels to your Distribution Board. If the power being produced from the Solar PV System is greater than what is needed within the property the surplus will be fed back into the Grid through your mains connection.
Export controls are available which can automatically divert surplus power into an Immersion or other Electric Element. Maximising the usage of power produced and reducing the heating bills for hot water.
 
What is the Solar PV Feed-in-Tariff? 
Solar PV is a renewable technology supported by the governments Feed in Tariff. A financial incentive to support the growth of renewable energy and meet targets of carbon reduction. The tariff is slowly reduced at quarterly intervals as the uptake of the scheme is increased. The current tariff is available from the Ofgem website. The payment are made quarterly over a 20 year period. The FiT Scheme pays the owner a generation rate for the renewable power produced, and an export payment. It is deemed that a domestic dwelling will not use all of the power produced from a Solar PV system. Any surplus power that is not used is fed back into the National Grid. The export payment is for supplying power back into the network at the current rate it costs the electricity Suppliers to generate electricity. The export payment for systems up to 30Kwp will be deemed as 50% of the generated power. The export payment is not monitored and will not change if you use all the produced power from your Solar PV system.

What is the payback period of Solar PV?
The payback period is dependent on the electricity consumption of the property. A typical 4Kwp Solar PV system will produce 3300Kwhr each year. At a Feed in Tariff of 4p/Kwhr, and an Export rate of 4.85p/Kwhr. The annual combined Generation and Export payments would be £212.00 each year. The savings are dependent on how much imported power you pay for can be replaced by Solar PV generated power. A guide of 50% is usually used for calculation although when using timed devices for appliances and export controls a higher saving is achievable. 50% of generated power is 1650Kwhr each year. If you pay 13p/Kkwhr to your Electric Supplier the savings would equate to £214.50 each year. Based on the system above the payback total would total £426.00 each year.
Based on the above, 4kwp system costing £4,000 will take 9.5 years to payback the initial investment.
The Feed-in-Tariff is fixed for a 20 year period. During the 20 years the system example above would return £8,520. A 213% return from the initial investment.
Note: For a simple example the figures above do not include inflation

How long will a Solar PV system last?
All MCS accredited Solar panels have a minimum of a 10 Year Product Warranty, and 20 Year Performance Warranty. The Solar PV inverter warranties vary from each manufacturer from 5-20 years with extended warranty options. The Solar PV components can be warranted for 20 years, a well maintain system would expect to last 25 years.

What is the best orientation and pitch for Solar PV in the UK?
Using a 4kwp Solar PV system installed at a 30° optimum tilt the variation in output is as follows.
West 80% of Achievable Power
South-West 95% of Achievable Power
South 100% of Achievable Power
South-East 95% of Achievable Power
East 80% of Achievable Power
If a split system between East and West is installed the annual production would be 80% of a single South facing Array. The benefit would be larger production in the early hours of the morning, and later hours of the evening. Which in some circumstances can achieve greater savings for consumption of produced power before and after a working day.

What is a Solar PV Inverter?
The Solar Photovoltaic Cells which are joined together to make a Solar Panel produce Direct Current (DC) Electricity. The UK National Grid supplies our homes and businesses with Alternating Current (AC) Electricity. The Solar PV Inverter changes the power produced from the Solar System from DC to AC current to match our main network and appliances. An Inverter loses approximately 10% of the DC Input during the conversion to AC Output. This is why a typical 4Kwp Solar PV System is usually connected to a 3.6Kw Inverter.

Can Solar Panels be Tiled or Slated into a roof?
Yes, especially on a new build project or a damaged roof, in-roof systems provide a more cost effective fixing method. The cost of roofing materials and labour for the array can be offset against the Solar PV system cost which reduces the payback.
Can Solar Panels be mounted on the Ground?
Yes, various mounting frames are available for almost all installations. Ground Mounted Solar PV will almost certainly require planning permission.

Do I need Planning Permission to Install a Solar PV system?
A Solar PV system will come under permitted development unless:
• Installed on any part of the external walls of the building if the building contains a flat
• Panels when installed on a flat roof are situated within 1 metre of the edge of the roof or protrude more than 1 metre above the plane of the roof
• Panels when installed project higher than the highest point of the roof (excluding the chimney)
• The building is within a Conservation Area or World Heritage Site and the Solar PV equipment is installed on a roof which forms the front of the building and is visible from the road.
The Solar PV equipment, must as far as reasonably practical, minimise its effect on the amenity of the area and be removed when it is no longer needed or used for domestic micro generation.




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