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General information

Photovoltaic: (PV) solar technology - What it is and how it works

Photovoltaic: (PV) solar technology turns light into electricity. It doesn´t require direct sunlight, so it works even in cloudy Britain. The "clean" energy produced does not contribute to climate change: it produces no pollution, and is completely silent. There are no moving parts, so it is reliable and low-maintenance. There are no running costs, so once your system is installed the electricity is free.

How does PV solar work?

PV solar operates on the principle that electricity will flow between two semiconductors (typically crystalline silicon) when they are put in contact with each other and exposed to light. By linking a number of these 'cells' into a panel (also called a panel), a useful flow of electricity can be generated. Any number of panels may be used in a system, providing a very flexible approach to power generation

Does PV solar heat water?

PV solar differs from the more familiar 'thermal' solar power, which uses the sun's energy to directly heat air or water. PV panels do not heat water; instead, they produce electricity directly from the light that falls on them. The electricity produced can of course be used to heat water, if you wish.

Is the power produced by PV solar free?

Once you have bought and installed your equipment, yes, it is free. The system should not require any maintenance and uses no consumables; there are no ongoing fees.

What can I use PV solar for?

PV solar produces electricity, and as such can provide power to any device that uses electricity. The electricity generated when light hits a PV material is direct current (DC), which is the same as that produced by a battery. This means that PV solar systems can run battery-operated equipment or charge batteries. Some typical examples of solar powered devices using DC power are: fluorescent lights, boat or caravan battery charging, phone charging, PDA charging, portable fridge, pumps. Using an inverter, the DC current produced by PV can be converted into alternating current (AC) to power mains-operated devices, like a portable television or radio/CD player.

What about clouds and cold weather?

PV solar panels actually operate better at colder temperatures (some of the best efficiencies ever recorded were at the South Pole!). They also continue to work even in cloudy conditions, although they do produce less electricity. Under a light overcast, the panels might produce about half as much as under full sun level, ranging down to as little as 5-10% under a dark overcast day. However, we provide UNI-SOLAR panels that use unique Triple Junction technology. In temperate and northerly latitudes, this technology produces more power, more efficiently, than crystalline panel technology. This is because cells are composed of three semi-conductor layers, each absorbing a different part (colour) of the light spectrum, so the panel will deliver more power in overcast conditions than other technologies. Additional cell diodes mean that these panels continue to function well even in partially shaded conditions. If 10% is covered by shadow, you will only lose 10% of the panel's maximum power output.

How do I use PV power at night or in bad weather?

When combined with a battery, PV solar can be a reliable source of power day and night, rain or shine. PV systems with battery storage are being used all over the world to power lights, sensors, recording equipment, switches, appliances, telephones, televisions, and even power tools.

What do I need?

We have especially tried to 'make solar simple' and have therefore developed some kits for specific applications. These kits have been designed so that they include everything that you will need, and in some cases we have connected some of the components together. We provide simple instructions, which have been tested. If the kit does not provide a battery, you will usually need to know the voltage and capacity in Ampere Hours (Ah) of the battery that the system will be connected to. Naturally, if you have an application for which we do not yet have a kit, contact us and we will endeavour to help. We also sell a range of individual panels and accessories for those of you who are technologically confident!

How difficult is it to install and use?

This depends on what you buy! We provide kits to take the guesswork out of what components are required in a system, and with these, we provide easy, tried and tested instructions. Simple kits, particularly the mobile power kit and the small boat or caravan kits require little or no installation as they can be connected to a battery via a cigarette-lighter cable. Other kits require very simple wiring. The lighting kit is perhaps the most complex, but remains simple enough to be suitable for school projects. Individual flexible panels have built-in blocking diodes and fuses, but in the framed panels you will need to wire these yourself. If you are not familiar with electrical equipment you may need the services of an electrician - or consider one of our kits. Once installed correctly, PV is very simple to use - simply plug in your appliance. Some customers use their panels for multiple applications, and in some of these cases they need to unplug one connector and replace it with another.

How I can work out what size panel I need?

The type of panel you choose will depend on two things: how much power your panel will produce and what you want to use the panel for.

How much power will it produce?
The power (watt hours) produced from your panel can be estimated by multiplying the power (watts peak) rating by the number of hours peak sunshine. As a very rough guide, the UK, northern Europe and Canada average 1 hour of peak sunshine per day in winter and 3 hours in summer. Thus, a 30 watt peak panel will produce 90 watt hours of power on an average British summers day.

Will this be enough?
That depends on what you want to use the panel for. The amount of power you need can be calculated by multiplying the power of your appliance by the length of time you expect to use it each day. For example, if you expect to use a 30 watt CD player for two hours a day you will require 60 watt hours of power. The power (watts) used by an appliance should be written somewhere on the appliance. If you cannot find it, look for Amps (A) and volts (V) and multiply them together to estimate watts (AxV=W).

How do I choose a battery?

Battery size (Amp hours, or Ahrs) will depend on the amount of power you need each day (see the previous question 'Will this be enough?'), and the number of days you want to be autonomous for (that is, how many days you want the battery to supply power without being recharged by the PV panel). The daily power (watt hours) required, multiplied by the number of days autonomy, gives you the amount of available power that the battery needs to be able to supply. Thus if you require 60 watt hours every day, and 5 days autonomy, you need 300 watt hours available. However, as most batteries cannot be drained more than half empty, total battery storage needs to be at least twice the available power. In our example the battery would thus need to hold at least 600 watt hours. Battery size in Ahrs is then obtained by dividing the battery storage by the battery voltage (usually 12 or 24 volts). Thus, 600/12 gives 50Ahrs. In this case, the battery would need to be at least 50Ahrs.

What type of battery should I use?
It is possible to use any 12V flooded or sealed lead-acid battery with our panels, though it is better to use a "deep cycle" battery. Deep cycle batteries are designed to endure sustained discharge whereas some batteries, e.g. car battery, are designed for short bursts of energy only. We recommend a 75Ahr flooded lead acid battery.

Is PV solar environmentally friendly?

Yes. PV solar is a renewable energy that does not rely on burning fossil fuels (technically, the sun will stop burning in 4.5 billion years but for all practical purposes, it provides an endless source of energy!). More energy reaches the earth from the sun in one day than would be consumed by the world's population in 27 years. Even better, PV solar generates no CO2 so does not contribute to global climate change. While operating, it is silent and emits no pollutants or waste, and it requires no fuel.

Is PV solar a new technology?

Although PV was first described in 1839 (by French physicist Edmond Becquerel, when he was just 19), its commercial development began only in the 1940s. By 1954 Bell Laboratories had produced a 4% efficient crystalline silicon cell. Since then, development of sophisticated semi-conductors has increased operating efficiencies to more than 14% (and even more in the laboratory) and brought down prices. In the 1950s and 1960s PV cells were used in space, for example, powering radio transmitters on satellites, and solar-powered satellites continue to be launched every year. Today, however, PV is used around the world for applications ranging from large-scale power generation to building power to battery charging, and the PV industry is rapidly expanding.

What is Watts peak?

This is a measure of how much power the panels produce under standardised laboratory test conditions. To obtain this measure, panels are irradiated with 1000 watts of light energy per square metre at 25°C. In fact operating conditions are more likely to be say, 500 watts from the sun at 40°C. Panels with the same watts peak rating may therefore have different actual outputs.