Understanding the Difference Between Solar Thermal Systems and Solar Panels (PV)

If you’re a UK homeowner or a small business owner looking to harness solar energy, it's essential to understand the difference between solar thermal systems and solar photovoltaic (PV) panels, as these serve different purposes and work in distinct ways.

What is a Solar Thermal System?

A solar thermal system uses solar energy to heat water. It captures the sun’s heat through specially designed panels (collectors) that circulate a fluid, which absorbs the heat and transfers it to your hot water storage tank. This heated water can then be used for domestic hot water needs, such as showers, washing, and heating radiators.

What are Solar Panels (Photovoltaic or PV)?

Solar PV panels convert sunlight directly into electricity. They contain photovoltaic cells that generate electrical power when exposed to solar radiation. This electricity can be used to power your home or business appliances, lighting, and can also be fed back into the electricity grid.

Key Differences Between Solar Thermal and Solar PV

Aspect	Solar Thermal	Solar PV
Primary Output	Hot water (thermal energy)	Electricity
Efficiency	Up to ~70% efficient at collecting heat	Around 15-20% efficient at converting sunlight to electricity
Roof Space Required	Less, due to higher efficiency	More, due to lower efficiency
Installation Cost	Typically £3,000 to £6,000	Typically £4,000 to £7,000 for a 4kW system
Return on Investment	Often quicker payback by reducing heating bills	Savings mainly from reduced electricity bills and possible export income
Weather Suitability	Works well even in cooler or cloudy UK weather	Electricity generation reduces on cloudy days
Government Incentives	No direct income from exporting heat	Can earn from Smart Export Guarantee (SEG) by exporting excess electricity
Typical Use	Water heating, space heating	Powering electrical appliances

Types and Variations of Solar Thermal Systems

• Flat Plate Collectors: Large, flat panels mounted on roofs that absorb sunlight.
• Evacuated Tube Collectors: Cylindrical tubes that are more efficient in colder climates, making them suitable for the UK.
• Thermodynamic Systems: Hybrid heat pumps that work around the clock using ambient heat and solar energy to heat water efficiently throughout the year.

Real-World Applications in the UK

• Domestic Hot Water: Solar thermal can cover a significant portion of hot water needs in homes during UK summers and reduce reliance on gas boilers in colder months.
• Larger Properties: Solar thermal is effective for larger homes or small businesses with higher hot water and heating demands.
• Combined Systems: Some UK homes install both solar thermal and solar PV systems to cover electricity and heating needs, maximizing energy savings.
• Thermodynamic Systems: Gaining popularity for UK climates as they provide more consistent year-round hot water.

Recent UK-Specific Facts and Policies (2024-2025)

• Solar thermal systems are more space-efficient and cost-effective in the UK climate than PV alone.
• Installation costs for solar thermal range between £3,000 and £6,000, generally cheaper than comparable PV systems.
• Solar PV installation costs for an average 4kW system are roughly £4,000 to £7,000.
• The Smart Export Guarantee (SEG) allows solar PV owners to export unused electricity to the grid; however, returns have decreased recently and are less lucrative than in past years.
• Solar thermal panels can save approximately £1,350 over their lifespan by reducing heating costs.
• Solar PV systems can reduce electricity bills by up to 70%, or even 90% with battery storage during summer months.

Practical Advice and Common Mistakes

Pros of Solar Thermal

• High efficiency for water heating (up to 70%).
• Reduces gas or electric heating bills.
• Works well in UK’s cooler, cloudy climate.
• Can pay for itself relatively quickly.

Cons of Solar Thermal

• May not meet 100% of hot water needs in winter.
• Requires space for hot water storage tanks.
• Installation may require a qualified plumber and compliance with building regulations.

Pros of Solar PV

• Reduces electricity bills significantly.
• Generates clean electricity for multiple uses.
• Eligible for SEG payments for excess electricity exported.
• Can be combined with battery storage for energy independence.

Cons of Solar PV

• Lower efficiency than solar thermal.
• Requires more roof space.
• Investment payback can be longer, especially with reduced export tariffs.

Common Mistakes to Avoid

• Expecting solar thermal to cover all heating and hot water needs year-round.
• Underestimating roof space or orientation for solar panels.
• Overlooking the benefits of combining solar PV with battery storage for greater savings.
• Ignoring maintenance and system checks necessary for optimal performance.

Summary

For UK homeowners and small businesses aiming to reduce their carbon footprint and energy bills:

• Choose solar thermal if your main goal is to heat water efficiently and save on gas or electric heating bills.
• Choose solar PV if you want to generate your own electricity, reduce electric bills, and possibly earn from exporting surplus power.
• Combining both or opting for thermodynamic systems can provide a more comprehensive solution but involves higher upfront costs.

Understanding these differences will help ensure you invest in the right solar technology tailored to your specific energy needs and UK conditions.