Solar panel jargon buster: A simple guide to green terms

If you’re seriously considering 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.

“An informed consumer is always the best consumer,” says Martin Desmond, Managing Director of Wizer Energy, “and being able to understand the more technical jargon of the solar panel industry will demonstrate to companies that you are a serious consumer and willing to do your own research to be fully informed on the process.” 

Understanding the data sheets from different suppliers and the language utilised could see maximised potential from solar panels from the get-go. Desmond adds: “This could help ensure that you receive the best possible service. Installing solar panels is no small feat and they are a long-term commitment so, taking the time to understand how they actually work and how to get the most from them is important for ensuring that they are worth the investment.”

Similarly, Alan Duncan, Director of Solar Panels Network, advises: “Understanding these terms will help you communicate more effectively with solar panel installers and enable you to ask the right questions.” He also highlights how understanding these elements, as well as the Government’s Smart Energy Guarantee (SEG), an alternative to the Feed-in Tariff (FiT) scheme, which is now closed to applications, can help you determine whether you’ll receive payment for any excess energy your solar panels generate.

A solar panel system uses multiple components to supply a home with electricity. It will be a major advantage to understand what they do and how they work together. (Image credit: Adobe)

Solar panels convert the light from the sun into energy. The most popular type of solar panels are photovoltaic, which provide electricity, while solar thermal panels can be used to create hot water:

• Photovoltaic: 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’. 
• Solar thermal panels: 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. 
• Solar hybrid panels: Hybrid solar panels use both PV and thermal panels in order to generate both electricity and heat, giving them the name solar PVT. 

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 types of solar cell include: 

• Monocrystalline: These solar cells are made up of a single crystalline silicon. They are common in homes and have been around the longest; they tend to be more expensive due to a more complicated manufacturing process and their high efficiency. 
• Polycrystalline: 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.
• Thin-film: 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.

This simply refers to the number of solar panels on your roof or on a commercial building. How big your solar array is depends on your home’s position and location, the roof space you have available, and your energy needs.

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.  

Installers and suppliers will be able to advise on the best mounting system for your solar panels. (Image credit: Adobe)

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 the most cost-effective solution. Flat roofs, on the other hand, generally use console bins (a triangular-shaped box) to create the angle required. Newer technologies, such as in-line panels or solar 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.

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.

Solar panel production is measured in kWh. It means one kilowatt of electricity is used per hour.

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.

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.

These stop the battery from overcharging by regulating the voltage current coming through from the solar panel: 

• Maximum Power Point Tracking (MPPT) solar charge controller: MPPT controllers are typically more expensive than the alternative. It acts as a DC to DC converter and is designed to maximise the amount of current from a solar panel feeding into the battery, allowing it to charge it at a more efficient level. MPPT itself is an algorithm which compares the output to the battery voltage before adjusting it. 

• Pulse Width Modulation (PWM) solar charge controller: This works by slowing down and reducing the amount of power going into a battery. When it reaches capacity it still continues to charge, but with a smaller charging current to avoid overheating or gassing the battery.

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 SEG scheme, so that you can receive the right payment for energy you export.

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.

Homes without solar panels are known as being ‘on-grid’ while homes that are not connected to the National Grid are ‘off-grid’. Most homes with solar panels use a hybrid set-up. (Image credit: Adobe)

If you are 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.

The efficiency of a solar panel refers to power output, in other words, the amount of sunlight it can convert into electricity. 

The SEG is a government scheme which allows homeowners with solar panels to export excess energy generated back to the grid in return for payment.

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.

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.

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. 

This is expressed in watt peak (wP) and is the maximum output measurement of solar PV panels. Although brands calculate this using Standard Test Conditions (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 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, etc.

This is measured and given in amps. The number represents the power input at its maximum when connected to a MPPT controller under STC. Note that a PWM controller may receive slightly higher results under STC.

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.

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.

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.

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:

• Light induced degradation (LID): This could be considered wear-and-tear for solar panels. It is caused by the initial stages of exposure to sunlight at the start of the day reducing photovoltaic efficiency.
• Light and elevated temperature-induced degradation (LeTID): Similarly, this is a reduction in efficiency as a result of being over-exposed to light and temperature.
• Potential induced degradation (PID): This is caused by voltage leaks or damaged or cracked cells.
• Hot spot: This occurs when there is one shaded cell in a series of high short-circuit current solar cells, leading to energy being dispersed into the one cell, essentially wasted energy. You’ll see some brands markup that their solar panels have lower risk of hot spot.

Direction insolation is unobstructed sunlight. Clouds and dust in the atmosphere scatter sunlight and result in diffuse insolation.