Answers to common Solar questions
How is Photovoltaic power produced?
Photovoltaics are solid-state semiconductor devices that convert light directly into electricity. A photovoltaic solar cell consists of layers of semiconductor materials with different electronic properties. In a typical crystalline silicon cell the bulk of the material is silicon doped with a small quantity of boron to give it a positive or p-type character. A thin layer on the front of the cell is doped with phosphorus to give it a negative or n-type character. The interface between these two layers contains an electric field and is called a junction. Light consists of particles called photons and when light hits a solar cell some of the photons are absorbed in the silicon. If the photons have enough energy they will be able to free electrons and the electric field at the junction will cause the electrons to move through the silicon atoms in the cell and into an external circuit as electrical current. The photovoltaic process is completely solid-state and self-contained and no materials are consumed or emissions made. Although making solar cells requires advanced technology, they are simple to use when connected together into a solar module or large solar array.
What is a kilowatt peak?
A kilowatt peak is the standard measure for output of a PV system. Essentially it is the output of a PV system when tested under 1,000 watts per m2 of solar irradiance. Kilowatt peak is meaningful in drawing comparisons between different manufacturers’ products but does not reflect the true output of a system in the UK. Typically in our region a well sited 4kwp system will produce in excess of 3500kWh of electricity per year.
What is a kilowatt hour?
A kilowatt hour (kWh) is the equivalent of 1000 watts of energy for 1 hour. Domestic electricity bills are detailed in terms of kWh of consumption and electricity generated from solar PV systems is measured in kWh of production.
How does a PV system work?
When sunlight, from either sunny conditions or during cloudy conditions, falls on the surface of a PV cell a DC electric current is generated. PV cells are manufactured into panels which can be easily handled as they are robust and durable. Solar PV arrays are made up of multiple panels to create a system to suit the customer’s requirements and budget. Larger arrays have greater electrical output and higher income potential. The DC current builds as it flows through the panels that make up the array, before it is channeled away via the cabling to an inverter. The inverter converts this DC current into AC current, which is then seamlessly fed into the existing building electricity system for use or storage on-site or for export to the grid.
Do I need Planning Permission?
Fixing solar panels to your property is considered ‘permitted development’ under planning law with no need to apply for planning permission (except for Listed Buildings and any other buildings within their grounds, and Scheduled Monuments). Please visit the government run planning website for more information: www.planningportal.gov.uk.
Does PV work in winter?
Yes. Even in cloudy conditions where the light intensity is low the panels will produce electricity. As long as there is sufficient light the panels will work.
What happens in a power cut?
Grid connected PV systems in the UK automatically shut down when there is a power cut. This is a safety measure to prevent any electricity reaching the grid and causing damage or injury to those working to restore power.
What regular maintenance is required?
There is no maintenance required as Solar PV panels are solid-state technology and so have no moving parts. The surface of the panel is self-cleaning, meaning that rainfall and wind will do all the cleaning necessary. For panels mounted at less than about 15 degrees of pitch some dust may build up and this can easily be removed by hosing down the panels.
Does PV efficiency degrade?
The performance of all PV cells does drop over time, but only by a tiny amount. The performance of top quality panels drops by about 0.5% a year, so in 20 years they would still be working at 90% of their original output.
How durable are PV panels?
Panels are extremely durable and are used in many extreme conditions such as on weather stations in exposed wind-swept locations, in the icy conditions of the Antarctic and the sweltering heat of deserts, even in space. Most manufacturers offer 25 year warranties on panel performance and realistic life expectancies of high quality Solar PV panels are between 30 – 40+ years.
What is involved in the installation?
PV arrays are ideal for most roofs. A typical domestic installation would take between 1 – 2 days to complete and depending on safe access to the specified location may require the use of temporary scaffolding. For roof mounted systems rigid brackets are fixed into place under the roof tiles directly onto the rafters, then aluminium rails are secured to these brackets on which the panels are securely clamped. The inverter and other electrical components are wired into place and connected to the panels. The electrical supply to the property will only need to be interrupted once, briefly, when all the components are in place in order to make the final connection.
How does the exporting of power work?
If at any time you are using less power than you are generating, your excess power automatically goes back into the grid. Ideally, you want to use as much of your PV generated power as possible and this can be achieved through the use of an immersion control unit if you have an existing hot water cylinder with an immersion element, or a battery storage system.
I only have a small roof?
There are some very high efficiency panels available so even on small roofs it is possible to install a sizeable and effective Solar PV system.
My roof has some shading?
Limited shading and/or winter shading will have some small impact on the power production of a PV system, we will always design systems to minimize this impact and we will detail this fully for you in our Quotation. Significant shading of the roof is to be avoided if possible or technical solutions to reduce the impact of shading should be incorporated into the system design.
Is my property suitable?
Most properties are suitable for Solar PV as power production is good for South, East and West facing roofs, and even North facing roofs can be viable in certain circumstances – we can detail accurate production figures after we have conducted a free site survey. Generally, roof pitches in the UK are ideal for Solar PV too. Some customers have Solar PV installed on their outbuildings or garages rather than their main house roof.