The global capacity of solar PV is growing at a record pace, driven by supportive government policies such as subsidies and feed-in tariffs and decreasing costs due to advancements in technology. Between 2010 and 2020 solar module prices fell by up to 93%, making them the cheapest form of electricity and nearly a third cheaper than electricity generated from fossil fuels.

According to the Energy Institute’s Statistical Review of World Energy 2024 there was a 32.4% increase worldwide in installed solar PV and a 24.3% increase in solar PV generation worldwide from 2022–2023. Over half of installed solar PV was in China (609 GW), followed by the US (138 GW), India (73 GW), Japan (87 GW) and Germany (82 GW).

According to the International Energy Agency (IEA) solar PV is predicted to account for 80% of growth in global renewable capacity between 2024 and 2030.

What is solar capacity factor?
At installation, a solar panel, or an array of panels, will have a rated power generation capacity. For example, a 1 kWp (peak) capacity panel will generate 1 kWh in ideal circumstances. Unfortunately, since ideal conditions only rarely exist in the real world, solar plant performance can be measured in solar capacity factor. This is calculated as the actual generation divided by the theoretical continuous maximum possible output in a given period of time and is expressed as a percentage.

For the purpose of this article, solar capacity factors have been calculated on a whole country-level basis, based on 2023 solar PV generation and installed PV power figures (the calculation being: annual solar PV generation/(solar PV capacity x 365 days x 24 hours/day). This provides a high-level overview for a general sense of how well that country’s solar performs against others; the figure is certainly not intended as a criticism of any particular plants or operators.

The countries with the top three solar capacity factors (out of the 20 top solar generating countries) are Mexico (28.4%), United Arab Emirates (26.4%) and Chile (24.6%). The countries ranked lowest are the UK with a solar capacity factor of 10.1%, Germany with 8.5% and Poland with 8.4%.

The solar capacity factor is heavily influenced by climatology and the technologies used. It does not necessarily correlate with generation and installation figures. For example, although China had the highest solar PV generation and capacity in 2023 of all countries, with the country responsible for around a quarter of the growth of solar capacity, its solar capacity (10.9%) factor ranks 16th out of the top 20 countries.

In fact, the countries with the highest solar capacity factors are situated near the Equator and are characterised by having abundant sunshine and higher average daily solar irradiance levels. By contrast, the countries ranking lowest are all situated at higher latitudes in the northern hemisphere and are characterised by shorter daylight hours in winter and lower average daily solar irradiance levels.

According to ESMAP’s Global Photovoltaic Power Potential by Country data, Mexico’s average theoretical daily solar irradiance level is 5.73 kWh/m²; United Arab Emirates’ is 6.05 kWh/m² and Chile’s is 5.76 kWh/m², compared to the UK which has an average daily solar irradiance level of 2.59 kWh/m², or Germany and Poland, both of which have 2.98 kWh/m².

Other countries benefitting from high average theoretical solar daily irradiance levels include Saudi Arabia with an irradiance level of 6.21 kWh/m² and Morocco with an irradiance level of 5.56 kWh/m². Both these countries’ solar markets are on the rise; the former increasing its solar PV installed capacity by a mega 473% from 2022–2023 (Statistical Review of World Energy 2024). Morocco has five major solar parks, with a target of generating 52% of its electricity from renewable sources by 2030 and a hope to answer European electricity demand by exporting a lot of it back to Europe via undersea cables.

Different technologies also play a key role. PV systems that have solar tracking perform to much higher standards than those that are fixed. One study on PV system performance in Chile found that PV systems with solar tracking had annual capacity factors of up to 25.89%, whilst some of the fixed systems only reached 18.56%. Bifacial (two-sided) panels also perform better than monofacial panels, depending on the surface albedo (a measure of how reflective a surface is).

A study in Palestine published in 2023 showed that on average bifacial PV modules produced 6.81% more electricity per year than monofacial panels, with the highest generation for the bifacial PV achieved when it was situated over white paint.

However, developers have to take into consideration cost versus generation when implementing these systems as these technologies are more expensive.

Capacity factors: solar versus wind
Solar capacity factors trail behind wind capacity factors. In fact, they have one of the lowest capacity factors compared to other forms of power generation. While the solar capacity factors of countries in Table 1 range from 28.4% in Mexico to 8.4% in Poland, wind capacity factors in the same period ranged from 45.1% in South Korea to 20.3% in Brazil.

For that reason, 1 GW of wind generates twice as much electricity as 1 GW of solar, according to an Ember report. Although the installed capacity of solar will be double that of wind in the 11,000 GW of renewables capacity expected in 2030, because of the gap in capacity factor, they will generate similar amounts of electricity to the grid, 31% and 36% respectively, according to Ember.

On the other hand, wind and solar complement each other in meeting daily and seasonal electricity demands. Wind energy typically peaks during the morning and evening, while solar energy reaches its maximum at midday. Seasonally, wind energy is most abundant during winter, whereas solar energy peaks during the summer months.

Table 1: Statistics showing top 20 solar PV generating countries ranked by solar capacity factor
Source: Energy Institute Statistical Review of World Energy 2024 and ESMAP Global Photovoltaic Power Potential by Country

 

What technologies could improve solar capacity factors in the future?
According to the IEA, crystalline polysilicon is the dominant technology for PV modules and has a market share of more than 98%. Its popularity is down to a long lifespan of more than 25 years, whilst maintaining over 80% of their original power production after this time, high efficiency and low cost. Manufacturing is well-established, and the technology is reliable. They can convert on average around 22% of the sunlight they absorb into power but are reaching their economic power conversion limit. It is believed that with experimenting with new solar technologies this figure could exceed 45%.

Unlike single junction cells that typically use silicon as a semiconductor, multi-junction solar cells consist of multiple layers of different semiconductor materials. Semiconductors that are commonly used include gallium indium phosphide, indium gallium arsenide and germanium. The material in each layer has a different bandgap and absorbs a different wavelength of sunlight from the next layer. This allows the solar cell to absorb a wider range of wavelengths than a single junction cell, which makes them more efficient at converting sunlight into electricity.

Multi junction solar cells are very costly to produce and are currently reserved for use in niche applications such as space exploration, drones and in the military.

Oxford PV, former winner of the most innovative technology at the Energy Institute Awards in 2022, is a pioneer in the field of perovskite (a type of thin film cell) solar photovoltaics. Perovskite is better at absorbing light across a larger range of wavelengths and converting it into electricity than silicon. Perovskite can be stacked upon silicon, creating a perovskite-on-silicon tandem cell, which is a type of multi junction solar cell. The silicon can absorb colours of the spectrum that perovskite can’t, which results in a solar cell that has a theoretical efficiency limit of 43% versus 29% for silicon cells.

Currently Oxford PV has achieved efficiency of 26.8% for a commercial-sized perovskite-on-silicon tandem solar cell; it is developing the technology to exceed 30% efficiency. Berlin, Germany, houses the company’s production line, which is ramping up manufacturing to produce high volumes of perovskite-on-silicon cells.

In 2023, the US National Renewable Energy Laboratory developed a bifacial perovskite cell that could generate 10–20% more power than a monofacial perovskite cell, by absorbing reflected light on the rear of the panel. This type of technology requires further scientific study, but in time could be deemed as better investments than their monofacial counterparts due to the increase in power generation.  

Advancements in solar PV technology are paving the way for higher efficiency and, in turn, higher solar capacity factors. As we move towards 2030, ongoing development and innovation in these technologies will be vital in maximising their potential in our pursuit of sustainable energy goals.

• Further reading: ‘Desert is served: The Middle East countries turning a profit from overground solar and wind resources’. Find out how some of the wealthiest Gulf states, particularly the United Arab Emirates and Saudi Arabia, are scaling up their renewable energy capacity, aiming to position themselves as global leaders in the clean energy transition.
• In these days of rapid growth of renewable energy technologies, the geography of the global energy industry is itself also changing, writes New Energy World’s Editor-at-Large Steve Hodgson.