Can solar energy meet the hot water demands of residents of always-cloudy Britain? 

Solar water heating, also called solar thermal, makes use of sunlight to heat the water that can be used in the bathroom or kitchen.

Can solar energy meet the hot water demands of residents of always-cloudy Britain?

The answer is a reassuring yes!

Solar water heating and solar photovoltaic (PV) technology are distinct technologies with different purposes. Solar Water Heating technology is designed specifically to heat water.

How does solar water heating (or solar thermal) work?

Solar water heating captures the sun's energy to warm the water in solar collectors. Solar water heating is highly efficient and takes up less roof space compared to PV panels for the same energy output. Solar water heating is ideal for a home with larger hot water demand. It will not be as cost-effective for a small family with low hot water use. Solar Photovoltaic or PV panels, on the other hand, generate electricity from sunlight. They convert sunlight directly into electrical energy using photovoltaic cells. Some of the electricity generated by the PV panels is diverted to heat water using an immersion heater. This system is less efficient than using dedicated solar water heating systems.

However, these technologies can complement each other. Homes can install solar thermal (water heating) and solar PV systems on their roofs to maximise renewable energy generation. This approach allows homeowners to efficiently harness the sun's energy for electricity and hot water production.

A solar water heating system (also known as solar thermal) generally has three main parts:

• Solar collectors comprising tubes or panels that are mounted on the roof
• A pump managed by a controller unit
• A hot water cylinder with two heating coils

When the fluid in the collector is hotter than the water in the cylinder, the controller turns on the pump to circulate fluid to the coil and heat the cylinder. In winter or when the weather is bad, the cylinder needs more than one coil or input to allow top-up heating.

What type of solar equipment is best for the UK Climate?

In the UK's climate, solar thermal (water heating) and solar photovoltaic (PV) panels can be effective and offer good value for money.

So, do solar thermal panels for water heating work on cold days?

Due to their design, evacuated tube solar thermal panels may perform slightly better on cold, sunny days. They can capture more sunlight even in less-than-ideal weather conditions. The UK often experiences overcast or cloudy weather, which can limit the availability of direct sunlight. In such conditions, the performance difference between evacuated tubes and flat panels may not be significant as if there is no sun, neither solar thermal nor solar photovoltaic (PV) systems can generate energy. Both technologies rely on sunlight as their primary source of power.

Solar thermal systems use sunlight to heat a fluid, typically water or oil, which then produces steam to drive turbines and generate electricity. Without sunlight, solar thermal systems cannot produce heat and generate electricity. Solar PV systems convert sunlight directly into electricity using the photovoltaic effect. Solar panels made of semiconductor materials absorb photons from sunlight, creating an electric current. In the absence of sunlight, solar PV systems cannot generate electricity.

How many days does the UK have conditions suitable for solar panels (solar PV) and solar thermal water heating to work?

The efficiency and performance of solar thermal and solar PV systems in the UK depend on various factors, including the weather, geographical location, and time of year. The UK's weather is known for being relatively cloudy and receiving less sunlight compared to sunnier regions.
On average, the UK receives around 1,000 to 1,200 hours of sunshine per year. However, it is important to note that this figure represents the total annual hours of sunlight and not consecutive days of sufficient sunlight for solar systems to operate optimally.

This 1,000 to 1,200 hours of sunshine is about 1/8th of the total hours there being 24 hours/day * 365 days/year = 8,760 hours/year. In terms of the average UK daylight hours, there are around 12 to 14 hours of daylight per day during the year when considering the seasonal variations. Or say 13 hours/day * 365 days/year = 4,745 hours/year (approximately). So, this is just under 1/5th of the daylight hours that are fruitful for solar electricity generation or solar water heating.

Which works better in the UK, solar PV or solar thermal?

Solar thermal systems can work even on cloudy days, as they can still capture and utilise diffuse sunlight. However, their efficiency may be reduced compared to clear, sunny days. Solar PV systems, on the other hand, are more dependent on direct sunlight and can experience a significant drop in output on cloudy or overcast days.
To determine the number of days with sufficient sunlight for these systems to work effectively, a detailed analysis considering factors such as location, local weather patterns, and system design would be required. Additionally, it is worth noting that both solar thermal and solar PV systems can still produce some energy even on relatively cloudy days, although their output may be lower than under ideal conditions.

Solar PV Panels

Solar PV panels generate electricity, which can be used for various household needs, including heating water with an immersion heater or other electrical appliances. PV panels are generally more compact than solar thermal systems for the same energy output. They can be the best option for homes with limited roof space. Flat panels may blend in better visually with the roofs of houses, which could be a significant factor for homeowners concerned about the aesthetics of their solar installations.

How do you choose between solar thermal and solar PV panels?

The choice between solar thermal and solar PV panels in the UK depends on various factors, including the specific energy needs of the household, available roof space, aesthetic considerations, and budget. While both technologies can contribute to reducing energy costs and environmental impact, the decision should align with the users' priorities and circumstances.