A single solar panel is made up of a series of photovoltaic cells joined together in strings. Photovoltaic simply means that these cells allow sunlight (photons) to create an electrical field (measured in volts). Solar panels can be joined together to form a solar PV system, with the aim of generating a specified electrical output. The photovoltaic cells are made of semiconducting material, usually silicon, and they work by allowing light particles, also known as photons, to separate electrons from atoms and thereby generate a flow of electricity.
The PV cells can only do their job if an electric field has been established. An electric field is an environment in which opposite charges are separated, and can be induced by “doping” the silicon with different materials to cause a positive or negative electrical charge. In other words, adding phosphorus to the top layer of silicon adds more negatively charged electrons to that layer. The bottom layer of silicon has boron added to it to create a positive charge.
This combination creates an electric field in the space between the layers of silicon so that when a photon displaces an electron, the electric field pushes the electron away. These electrons are then turned into electrical power!
Solar panels operate at relatively low-efficiency levels due to the number of different things which can happen to photons when they encounter the surface of the panel. Whilst the aim is for as many as possible to displace electrons to generate electricity, there can be other outcomes too. Some of the photons will be reflected off the panel, some will pass right through the panel without knocking into any electrons, and others will be absorbed but their energy will be converted into heat instead.
One of the main concerns people may have when thinking about getting solar panels is how well they will function when not in beaming sunlight. While it’s true that solar panels can produce much more electricity in direct sunlight, they can still function surprisingly well even in some less well-lit scenarios.
Most solar panels are capable of producing some electricity when it is cloudy, albeit a smaller amount than in direct sunlight. You should expect roughly 25% of the same performance from your panels when it is cloudy, or around 10% if the sky is heavily obscured.
If solar panels are located in an area that often falls into shade due to nearby trees or buildings, the ability of the panels to collect solar energy is limited. While it won’t necessarily mean that the panels aren’t able to function as the sun moves throughout the day, you should always aim to place solar panels in the area which will get the most consistent direct sunlight.
Believe it or not, a bit of rain can actually help your solar panels to perform at their best! The rainfall helps to keep the surface of the panels clean and free of impurities, helping to maximise their efficiency. As with cloudy weather though, if the sky is obscured during periods of rain then you can expect to see a decrease in output.
The question of whether solar panels can work at night is an interesting one. For all intents and purposes, the answer is no. However, sometimes you may see a very negligible reading if your solar panel has been catching any moonlight. Although the moon itself does not emit light, it is capable of reflecting light from the sun which is why you may see very tiny readings overnight.
Solar cells can function in artificial light on a smaller scale, for instance, to charge a solar-powered calculator or watch. This is because incandescent or fluorescent sources of artificial light mimic the wavelength of the sun’s rays. For instance, incandescent lights are defined as falling within a spectrum of 300-830nm, and if a solar panel can generate power from wavelengths of 300nm-1,200nm then they should be able to extract some energy from this light. However, direct sunlight is always best.
The number of hours that a solar panel can function for really depends on the number of direct sunlight hours it receives. This varies throughout the seasons and in the UK it’s estimated that the number of sunlight hours ranges from 1.6 in December through to 6.4 in July. This, in turn, affects the number of solar panels a property needs in order to meet its electricity consumption needs, but qualified solar experts like the team at Tonik will be happy to calculate this for you.
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