How much electricity does a solar panel produce?

In the simplest terms, solar panels convert energy from sunlight into electrical power using photovoltaic (PV) cells. But how much electricity can a solar panel produce?

According to our calculator, a 4.5 kilowatt (kW) system with 12 panels would produce on average 4,100 kilowatt hours (kWh) in a year, enough for a 3 bedroom house. 

However, there are a range of factors that can affect how much electricity your solar panels produce, from the efficiency of your system to the angle of your roof. Our guide below takes you through everything you need to know.

In the simplest terms, solar panels convert energy from sunlight into electrical power using photovoltaic (PV) cells.

A PV cell is constructed using semiconductor materials, usually silicon. Sunlight is composed of particles called photons, which strike these cells and displace electrons in the semiconductor material.

The cells’ internal electric field captures and channels the displaced electrons and produces an electric current. 

The electric current flows into a solar system component known as an inverter, which turns the direct current (DC) from the solar panel into alternating current (AC) that can power household appliances.

Specific types of measurements are used to gauge solar panels’ output and performance.

Understanding power in watts

Assessments of wattage are at the heart of any discussion about solar panels.

• A solar panel’s wattage rating indicates the panel’s maximum power output under ideal conditions. The rating is determined during standardised testing in which the panel is exposed to an irradiance of 1kW/m^2, and the cell temperature is 25C.
• A solar panel’s efficiency is defined as the ratio of the electrical power output to the incident solar power. A 20% efficient 1m^2 solar panel under 1kW/m^2 of sunlight would have a wattage rating of 200W because it can convert 20% of the incident 1kW to electricity.

The concept of kilowatt hours

In addition to wattage ratings, we also need a broader metric that measures energy usage over time.

This is where kWh comes into play.

• A kWh represents the energy a 1kW device would use if it ran for an entire hour.
• Under optimum conditions, a 300W solar panel operating at maximum capacity for five hours would generate 1.5kWh of energy (300W x 5h = 1,500Wh, or 1.5kWh).

Real-world performance

The actual performance of solar panels can vary because of real-world conditions.

• Solar panels’ listed wattage is measured under ideal conditions, including a specific light intensity and temperature. These conditions might occur only rarely in everyday scenarios.
• Factors such as unpredictable weather, the angle of sunlight (especially during winter months) and occasional obstructions from clouds, debris or bird droppings can affect a panel’s output. It’s essential to understand that although the “300W” label offers a benchmark, the panel’s performance can fluctuate based on these variables.

Examples of solar power effectiveness

To contextualise the potential of solar panels:

• The average UK household, with 2.4 people living in it, uses about 2,799kWh of electricity every year according to Ofgem
• A household that installed enough solar panels to produce an average of 10kWh a day would generate around 3,650kWh annually. That would be enough power to cover the average household’s yearly electricity consumption. Factors such as location, panel orientation and local weather conditions would have a significant impact.

Here are 3 examples of how solar power generation differs across the UK for various types and scales of solar systems:

1. 3-bedroom Victorian townhouse in London

• Size and number of solar panels: Given the average insolation, a 4.5kW system requires around 12 panels (each with an approximate capacity of 375W). This setup could potentially generate around 4,383kWh a year

2. 2-bedroom countryside cottage in the Scottish Highlands

• Size and number of solar panels: Given the insolation and solar panel efficiency, a 3kW system requires around 8 panels (each with an approximate capacity of 375W). This system’s potential output could be around 2,220kWh annually.

3. 4-bedroom modern detached house in Brighton

• Size and number of solar panels: A 6kW system requires about 16 panels (each with an approximate capacity of 375W). The system could potentially produce about 5,844kWh annually. This is a large array that needs a substantial amount of space.

Before we dive into solar panels’ power output and functionality, it’s important to understand the key factors influencing how panels harness the sun’s energy. 

You can think of solar irradiance as the sunlight’s brightness or intensity at a specific time and place. Solar irradiance is measured in terms of how much solar energy is received per unit of area, which is usually expressed as W/m^2.

Measuring solar irradiance enables you to understand how much energy a solar panel can capture. In the UK, the average solar irradiance is around 101W/m^2. It ranges from 128.4W/m^2 in the south of England to 71.8 W/m^2 in the northwest of Scotland. 

However, this value can spike on particularly sunny days, especially in the summer, when it often ranges between 600 and 800W/m^2.

Solar insolation refers to the total amount of solar energy received at a particular location over a specific period, which is typically expressed as kWh/m^2.

While measuring solar irradiance gives a snapshot of energy output, measuring solar insolation shows the big picture. Annually, insolation in the UK ranges between 750 and 1,100kWh/m^2. This is an average of roughly 2.53kWh/m^2 per day (using the midpoint value of 925kWh/m^2 per year).

Efficiency is the fraction of the incident solar energy (radiant solar energy that hits the Earth) that a solar panel can convert into usable electricity. A solar panel typically has 15 to 22% efficiency.

For instance:

1. High-efficiency panel: A solar panel with an efficiency of 20% converts 20 of every 100W of sunlight that strike it into usable electricity.
2. Moderate-efficiency panel: A solar panel with an efficiency of 15% converts 15 of every 100W of sunlight it receives into usable power.

Panel size is a significant determinant of solar energy production. 

• Physical dimensions: A residential solar panel is typically about 1.6m x 1m in size. The bigger the panel, the more PV cells it contains, and the more sunlight it can convert into electricity.
• Wattage variance: Panels of the same size might produce different amounts of electricity if their manufacturers or models are different. Common wattages range between 250W and 350W.
• Array potential: Under ideal sunlight, a setup of nine panels producing an average of 300W per panel could generate around 2.7kW of electricity. Ideal sunlight isn’t consistent because of factors including daily and seasonal weather variations.
• Roofing factors: Not every roof can accommodate a large number of solar panels. And space isn’t the only concern. Obstructions such as chimneys and shadows from trees can diminish a panel’s efficiency.

Geographic location plays a major role in solar energy production. Solar insolation, which is the amount of energy harnessed annually per square metre, greatly varies worldwide. 

Latitude and sunlight intensity

Latitude is a measure of how far north or south a place is from the Earth’s equator and it plays a significant role in solar intensity.

Near the equator, sunlight beams down almost directly, providing a higher concentration of solar energy. Closer to the North and South Poles, sunlight hits the Earth more obliquely, spreading over a larger area and losing its intensity.

This is why solar panels in tropical regions can produce more energy than those in higher latitudes.

Insolation in London reaches 1,100 kWh/m^2, in New York, it’s 1,300 kWh/m^2, and in the Sahara, it’s a considerably higher 2,800 kWh/m^2. This figure varies widely, even in the UK. 

Seasonal shifts and day length

The tilt of the Earth’s axis causes daytime lengths to vary as the Earth orbits the sun. Longer summer days offer more sunlight hours, maximising solar energy potential. 

Shorter winter days in high-latitude regions offer drastically reduced sunlight hours and less potential energy. It’s not just about the total hours of daylight, though.

Peak sunlight hours are especially crucial. A summer day might be long but nevertheless have a relatively short period in which solar generation conditions are ideal. For example, London receives 0.52kWh/m2 of solar energy per day in December and 4.74kWh/m2 of solar energy per day in July.

Climate

The amount and intensity of sunlight are just one part of the solar energy equation. Local weather conditions and climate are another. They can either boost or hinder solar panel efficiency.

Clouds, fog and precipitation can obstruct sunlight, decreasing solar output. Solar panels still function on cloudy days but have a lower efficiency than they do when the weather is clear and sunny.

Temperature

We associate solar panels with bright, sunny conditions, but temperature also affects the panels’ efficiency. Extreme heat can reduce a solar panel’s performance. So, in regions such as the Sahara, the impact of impressive solar intensity is partly diminished by the effects of extreme heat. Cooler, sunny days in other parts of the world can offer better conditions for solar panels.

Solar panels’ performance largely depends on their orientation and tilt angle. 

Direction

Solar panels operate at peak efficiency when they directly face the sun. In the Northern Hemisphere, this translates to a southern orientation. The sun’s journey from the east at dawn to the west at sunset means that panels pointing due south maximise their exposure to sunlight throughout the day. However, even if a roof doesn’t point directly south, the panels on it are far from useless. 

Solar panels with southwestern or southeastern orientations achieve around 85 to 90% of the potential energy output of panels with southern orientations. 

Tilt

The tilt or pitch of the solar panels also plays a pivotal role in their energy generation capacity. 

An ideal pitch allows the panel to absorb the maximum amount of sunlight, especially during peak hours. 

In the UK, a 35-to-40-degree tilt angle is deemed optimal for fixed installations.

Tracking systems

Solar tracking systems follow the sun’s movement. They reduce the tilt in summer and increase it in winter to enhance sunlight capture throughout the changing seasons. In London, the optimal summer angle is around 34 degrees, and the optimal winter angle is around 66 degrees.

Solar trackers are advanced systems that automatically adjust the panels’ orientation and tilt throughout the day, ensuring that they always face the sun in the most optimal manner possible.

Diffused light

It’s a common misconception that direct sunlight is the sole contributor to a solar panel’s output. Around half of the UK’s light energy is diffused by clouds or reflected off buildings and the ground. Because the light is diffused, even panels that aren’t perfectly oriented can generate substantial energy.

Solar panel costs, efficiency and lifespan are all factors that affect the overall output.

Here are the most common types of solar panels:

Monocrystalline panels

Monocrystalline panels are the most commonly used type of panel for domestic and commercial solar arrays. They are built from a single crystal structure and are considered the benchmark panel technology.

These panels have a sleek appearance and are a uniform shade of black. Their efficiency rates range from 15 to 22 per cent and are generally the more expensive panels to buy.

Polycrystalline panels

Polycrystalline panels have multiple crystal structures in each of their cells. The panels are made of silicon fragments that have been melted and poured into moulds. Their efficiency rates typically range from 13 to 18 per cent, so are not generally as efficient as monocrystalline panels.

However, the price point of polycrystalline panels is generally lower, making them an attractive option for property owners who have ample installation space on their roofs or are on tight budgets.

Thin-film panels

While monocrystalline and polycrystalline panels’ structures are rigid, thin-film panels’ structures are slim and flexible. Thin-film panels can be applied to a broad range of surfaces, including some that are unsuitable for traditional panels.

Thin-film panels’ efficiency rates generally range from 10 to 12 per cent. These panels are a viable alternative when there aren’t space constraints for solar systems or when traditional solar panels can’t be used.

The solar industry has experienced rapid advancements in recent years, which have pushed the boundaries of panel performance.  Advanced solar technologies include bifacial solar panels, which capture sunlight on both sides, and solar skins, which blend seamlessly with buildings. 

Manufacturers are also developing materials such as perovskite, which offers advantages over silicon. 

How new technologies are increasing the electricity production capacity of solar panels

Recent developments in panel technology that substantially boost electricity production include tandem solar cell designs, which layer different materials to capture a broad spectrum of sunlight. 

Advanced manufacturing techniques reduce the space between the cells in a panel, which results in higher power outputs. 

Also, innovations in inverter technology and solar tracking systems are optimising the conversion and capture of solar energy and further boosting overall system efficiency.

Upcoming technologies

Upcoming technologies include transparent solar cells, which show promise. They have the potential to transform windows and other surfaces into power generators without obstructing light or views. 

Perovskite cells are another upcoming technology. They can absorb light across a broader spectrum than silicon cells. And perovskite cells can be engineered at the molecular level to optimise their light absorption performance. 

Solar power is one of the most important forms of renewable energy we can access. Understanding the electricity production capacity of solar panels is crucial for anyone who is considering switching to solar energy.

Irradiance and insolation are fundamental keys to understanding solar energy production. Panel efficiency, size and output ratings govern how much solar energy can actually be captured. 

It’s crucial to understand that solar systems involve more than just panels. You must also factor in inverters, batteries and other components.