How does solar heating work? (Is it effective in the UK?)

Solar thermal water heating works with roof-mounted panels that harness the sun’s energy to provide free, eco-friendly hot water for your home.

What could be better than harnessing the powerful free energy of the sun to heat your home? How about saving money! Well, that's the promise of Solar heating, but does it live up to the hype, especially in the UK? In this article, I explain how solar heating works, how it can save you money, and ultimately, whether it's effective in the UK, where we only get 62.2 days of sunshine each year.

Understanding Solar Thermal Energy

What is Solar Thermal Energy?

Solar thermal energy is simply the energy from the sun that we capture and use for heating. Unlike PV solar panels that generate electricity, Solar Thermal systems directly convert solar radiation into heat. Active Solar heating uses the sun's rays to heat a fluid, usually a mixture of water and antifreeze, which is then used to heat water in a tank. If the solar system cannot provide all the heating needs, an auxiliary or backup system kicks in to provide additional heat, so you're not left in the cold.

How Solar Thermal Panels Work

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Solar thermal panels work by capturing solar energy and transferring that heat to water, which then heats your home. There are five key steps:

1. The process begins with solar collectors, commonly referred to as solar panels, installed on your roof. Inside these solar thermal panels, a heat transfer fluid, usually a mixture of water and antifreeze, circulates through small pipes.
2. As the sun shines on the panels, this fluid absorbs the amount of solar energy available and gets hot.
3. The heated liquid is then pumped from the thermal panels on your roof, flowing through pipes into your hot water cylinder. 
4. Inside the tank, these pipes coil around, warming the water. The coiled pipes are known as a heat exchanger.
5. The cycle continues as the cooled fluid is pumped back to the panels to be reheated by the energy from the sun. This efficient heat transfer ensures a constant supply of hot water.

Types of Solar Thermal Panels

When considering a solar thermal system, it's essential to understand the different types of solar thermal panels available. Two common types of solar panels are evacuated tubes and flat plate collectors.

Flat-plate collectors are generally the most common type of solar panel; they can be fixed to roof tiles or even integrated directly into the roof structure. Evacuated tubes, on the other hand, use a bank of glass tubes mounted on roof tiles. Both types effectively capture solar energy, but their efficiency and cost can vary.

Choosing the right type of thermal panel depends on your specific heating needs and budget, so you should seek the advice of a qualified solar heating installer.

Benefits of Solar Water Heating

Cost Savings on Energy Bills

Perhaps the most compelling advantage of installing a solar water heating system is the potential for significant cost savings on your energy bill. The beauty of solar thermal systems lies in the fact that sunlight is a free and renewable energy source, meaning you're harnessing the energy from the sun to heat water rather than relying solely on gas or electricity. Solar water heating systems are generally capable of providing, on average, roughly half of your hot water heating needs. This, in turn, drastically reduces your reliance on conventional water systems and central heating, leading to lower monthly expenses. The initial investment in solar panels may seem daunting, but the long-term energy savings can be substantial, making it a worthwhile investment. The Energy Saving Trust can offer advice on the specific savings possible.

Environmental Impact of Solar Heating Systems

By utilising solar energy, you're directly reducing your dependence on fossil fuels for heating your home, which reduces your carbon footprint and helps combat climate change. Solar thermal energy is a clean, renewable energy source, meaning it replenishes naturally and doesn't contribute to the depletion of finite resources. By choosing a solar hot water system, you are actively contributing to a more sustainable future for the environment.

Increased Property Value

Investing in solar thermal panels and other renewable energy improvements can significantly increase your property value. Potential buyers are increasingly aware of the benefits of renewable energy, including lower energy bills and a reduced environmental impact. A home equipped with a solar heating system is therefore more attractive in the market and may command a higher selling price.

Effectiveness of Solar Heating in the UK

Climate Considerations for Solar Energy

Considering the UK's climate, where we only get 62.2 days of sunshine each year, the effectiveness of solar thermal systems is a natural concern. The energy from the sun varies depending on the season. In summer, it might cover approximately 90% of hot water requirements, whereas in winter, this may drop to around 25%. For this reason, solar heating is integrated with conventional heating systems, such as a boiler or heat pump, where both heat sources share a hot water tank.

Much like PV solar panels, solar hot water collectors perform optimally on a south-facing roof, ideally between east to west. A space of around five square meters is needed, ensuring direct sunlight exposure for most of the day. Despite seasonal variations, the solar thermal system functions year-round.

On average, homes using solar water heating systems can reduce their reliance on traditional energy sources by up to 50% for hot water heating. However, the actual energy saving depends on factors like panel size, orientation, and daily water usage.

Installing a Solar Water Heating System

Choosing the Right Solar Thermal System

Choosing the right solar thermal system for your home depends largely on your existing heating system. If you currently have a conventional boiler with a hot water cylinder, it's often compatible with solar water heating. However, you might need to replace your existing hot water cylinder with one specifically designed for solar hot water or install a dedicated solar water cylinder. If you have a combi boiler, adding a solar hot water cylinder and possibly replacing the boiler with a conventional boiler or a heat pump may be necessary.

Installation Process Overview

The installation process for a solar heating system should begin with a professional assessment of your property to determine the optimal placement for solar thermal panels. Your installer can advise on the best routing for the pipes that will connect your roof panels to the cylinder during their visit. Installation involves mounting the solar panels on your roof, connecting them to the solar hot water cylinder, and integrating the system with your existing water systems. A qualified installer will ensure that all components are properly connected and that the system operates efficiently and safely.

Maintenance Tips for Solar Thermal Panels 

Proper maintenance is needed to ensure the longevity and efficiency of your solar panels. To help keep your system running smoothly, consider these actions:

1. Your installer should provide written details of any maintenance checks to carry out.
2. Regularly inspect the system control panel for warnings, and contact your installer if any issues arise.

A thorough system check every five years is recommended to flush the system and replace the heat transfer fluid mix. For peace of mind, consider a shorter annual service check. It's advisable to leave the system running while on holiday, utilising any 'holiday' functions; a smart thermostat can help with this. Simple steps can help prevent heat loss, maximise energy saving, and prolong the lifespan of your solar water heating system, ensuring it continues to meet your heating needs. The solar system and solar thermal system should be well looked after.