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The terms you ought to know if you’re switching to solar power, according to specialists
If you’re seriously considering the best solar panels, you will probably be familiar with their many advantages. But to truly understand and make the most of solar energy to reduce your carbon footprint, lower household bills and even increase your home’s resale value, knowing how solar panels work is essential. However, you don’t have to research all that far to realise there are some industry-specific terms worth familiarising yourself with.
This is the angle of the sun’s rays compared with the panel’s surface. For solar PV, the smaller the angle for the rays to hit the panel, the better. In the UK, the best orientation for solar panels is between 30 degrees and 45 degrees.
Bifacial solar panels are exposed to the sun on the back and front, increasing energy production by up to 30 per cent when compared to traditional panels that only capture sunlight on one side.
Direction insolation is unobstructed sunlight. Clouds and dust in the atmosphere scatter sunlight and result in diffuse insolation.
The efficiency of a solar panel refers to power output, in other words, the amount of sunlight it can convert into electricity.
This is known as the National Grid in the UK. It generates and distributes electricity to power homes and businesses across the country. Even with solar panels installed you will still be connected to and therefore have some reliance on the grid, unless your solar array is above average and you have suitable battery storage.
A metre will show how much energy your solar panels have generated and how much will be exported to the grid, or conserved in your own solar batteries. This is especially important if you’re on the FiT or Smart Export Guarantee scheme, so that you can receive the right payment for energy you export.
This represents any excess solar energy produced which, unless you have a battery store, will be exported back into the grid. If you signed up for the FiT scheme before 2019 or qualify for the SEG, you should have an agreed rate at which the grid will buy energy back.
An immersion diverter measures the amount of excess energy that is exported to the grid and instead redirects it to an immersion heater. The immersion diverter regulates the levels given for water heating so that only the equivalent amount of extra energy is consumed that would have been sent to the grid.
If you run out of solar energy, you will import electricity from the National Grid via cables called interconnectors; these form the UK’s electricity network, allowing power to be shared to households and businesses.
Solar panel production is measured in kWh. It means 1 kilowatt of electricity is used per hour.
This is measured and given in amps. The number represents the power input at its maximum under Standard Testing Conditions (STC).
This is the voltage measured when the power output is at its highest. What you’ll find on a data sheet will be measured against STC but in practice the figure will vary depending on the time of day, shade, and so on.
These solar cells are made up of a single crystalline silicon. They are the most popular type of domestic solar panel cell; they tend to be more expensive due to a more complicated manufacturing process and their high efficiency.
The type of roof you have will determine the mounting system used. Pitched roofs generally use an on-roof fixing system as the panels are directly secured to the roof; this is tan effective solution, when it comes to solar panel costs. Flat roofs, on the other hand, generally use console bins (a triangular-shaped box) to create the angle required. Newer technologies, such as integrated panels or solar roof tiles will be some of the most expensive, but arguably the less intrusive visually. Solar panels can also be ground-mounted, if you have the land available.
If you are living off-grid, you will solely rely on your solar system and other renewable energy types, as you will not be connected to a backup power source like the National Grid. It is unlikely that in the UK homeowners will be able to live entirely off-grid without the assistance of a back-up generator in winter. Most homes with solar panels live partially off-grid, using a hybrid system of batteries to provide power for the majority of the year, and use the National Grid when running low.
OCV is the maximum voltage available from a solar cell at zero current. It is essentially the max voltage a solar panel can safely produce. A higher reading means the solar panel can begin charging earlier in the day and continue to charge for longer. This is always higher than the operating voltage as it’s measured without a load. You can measure the OCV yourself with a digital multimeter or voltmeter with leads. However, bear in mind that it will differ from the measurement marked up on the spec sheet. As of 2022, a good OCV is around 30-58V. Panels with any less than 30V are likely to be smaller and, with smaller power output, it is a good indicator of power output and longevity.
Solar photovoltaic (PV) panels convert sunlight into direct current (DC) electricity via semiconducting materials; photo means light, voltaic means electricity. These are the most common type of solar technology and are what most people refer to when they use the generic term ‘solar panel’.
Pitch is very important when assessing a home for solar panels. In the UK, a south-facing pitched roof at 30 – 35 degrees is ideal. However, if you have a flat roof or a different pitch, different mounting systems can angle the panels to the optimal degree.
These cells consist of multiple crystalline silicons melted together. They are sealed under aluminium or glass and are cheaper and slightly less efficient than monocrystalline.
This is expressed in watt peak (wP) and is the maximum output measurement of solar PV panels. Although brands calculate this using STC, the results typically aren’t true to most real-life scenarios and it’s unlikely that the solar panel array will actually produce this much power on your roof. In reality, determining factors include size of array and location. For a more accurate Pmax, use the Nominal Operating Cell Temperature (NOCT).
This reading determines the largest current that can be taken from a solar cell when it’s short circuited and when the voltage is zero. It depends on a number of factors including the solar cell area, number of photons and the incident light spectrum.
The SEG is a government solar panel scheme that allows homeowners with solar panels to export excess energy generated back to the grid in return for payment.
This simply refers to the number of solar panels on your roof or on a commercial building. How big your solar array need to be depends on the roof space you have available and your energy usage.
A solar battery can be bought along with your solar array or added after installation to store excess electricity produced. This means you are less reliant on using power from the grid at night or during the winter.
Cells are usually made from a semiconducting material, most commonly silicon. When the cells are exposed to light, they absorb the energy which is extracted using conductive metal contacts. The three main types of solar cells are monocrystalline, polycrystalline and thin-film.
These stop the battery from overcharging by regulating the voltage current coming through from the solar panel:
Hybrid solar panels use both PV and thermal panels in order to generate both electricity and heat, giving them the name solar PVT.
A key element of your solar power system, inverters convert DC power generated by the PV cells of your solar panels into alternating current (AC) electricity which can be used for conventional household power. DC flows in one direction at a constant voltage and AC goes in both directions.
Brands may mark up a percentage of degradation over a number of years in their data sheets. This will consider a decrease in energy output over time thanks to damage, UV exposure, temperature changes and other factors. The most common types of degradation with solar panels are:
An older technology to PV panels, solar thermal panels use glass to refract the sun’s light to heat a fluid (usually water and glycol) in mounted tubes. This fluid then warms water in a hot water cylinder and can provide domestic hot water.
The temperature coefficient is a figure that indicates the rate of change expected in the efficiency of a solar panel with a rise in temperature. For solar panels, which are made primarily using silicon, the resistance decreases as temperature increases. The closer the number is to zero, the less affected the panels are by the rise in temperature. This is different across suppliers and you’ll see that many include temperature coefficients of OCV and Isc also.
These are formed by layering films of photovoltaic material onto a surface such as glass, plastic or metal to form the solar module. There are a few different types, depending on the material used, which can include amorphous silicon and cadmium telluride. Thin-film solar panels are typically used in commercial buildings as they are thinner and more flexible, allowing them to even be laminated onto windows or surfaced on the roofs of solar plants and large-scale farms.