Solar Thermal vs Solar PV

Solar Thermal vs Solar PV – What's the Difference?

If you've been researching solar energy, you've likely encountered both solar thermal and solar PV systems. The terminology can be confusing, and many homeowners aren't sure which technology would work best for their situation. This comprehensive guide explains how each system works, compares their benefits, and helps you understand why solar PV has become the dominant choice for UK properties in recent years.

Whether you're looking to reduce energy bills, lower your carbon footprint, or increase your property's energy independence, understanding the practical differences between these technologies is the first step toward making an informed decision. Let's examine what each system offers and which might be right for your home or business.

What Is Solar Thermal?

Solar thermal technology uses sunlight to heat water directly. The system consists of solar collectors (panels) mounted on your roof that absorb heat from the sun, which is then transferred to water stored in a specially designed hot water cylinder inside your home.

How Solar Thermal Systems Work

Solar thermal collectors contain tubes or channels filled with a heat-transfer fluid, typically a water and antifreeze mixture. When sunlight hits the collectors, this fluid heats up and circulates through a coil in your hot water cylinder, transferring heat to your domestic water supply. A pump and controller manage the circulation to maximise efficiency.

There are two main types of solar thermal collectors used in UK installations:

• Flat plate collectors: These resemble traditional solar panels with a flat, dark surface beneath protective glass. They're generally more affordable and suitable for most domestic applications.
• Evacuated tube collectors: These consist of glass tubes containing copper pipes in a vacuum, which provides excellent insulation and better performance in cold weather. They're typically more efficient but cost more.

What Solar Thermal Is Best For

Solar thermal systems are specifically designed to provide hot water. They work well for properties with high hot water demand, such as larger families, properties with multiple bathrooms, or buildings like care homes and hotels where hot water usage is consistently high.

Limitations of Solar Thermal

Whilst solar thermal can be highly efficient at its specific task, it has notable limitations that have contributed to its declining popularity in the UK market:

• Single-purpose output: The system only produces hot water—it cannot power appliances, lighting, or other electrical needs
• Seasonal performance variation: Output drops significantly during winter months when hot water demand is typically highest
• System compatibility: Requires specific plumbing and a compatible hot water cylinder
• No export option: Unlike electricity, you cannot sell excess heat to the grid
• Higher maintenance: More mechanical components mean more potential points of failure

What Is Solar PV?

Solar PV (photovoltaic) technology converts sunlight directly into electricity. The panels contain semiconductor cells—typically silicon—that generate an electrical current when exposed to light. This electricity can then power anything in your home or business that runs on electricity.

How Solar PV Systems Work

Solar PV panels generate direct current (DC) electricity when photons from sunlight knock electrons free from atoms in the semiconductor material. An inverter then converts this DC electricity into alternating current (AC), which is the standard form used by household appliances and the national grid.

Modern solar PV systems typically include monitoring equipment that tracks energy generation in real-time, allowing you to see exactly how much electricity your system produces and how it's being used. Many systems also connect to smart home energy management systems for optimised consumption.

The Versatility of Solar PV

Unlike solar thermal, which serves a single purpose, solar PV offers remarkable flexibility in how you use the energy generated:

• Power all electrical appliances: From lighting and cooking to entertainment systems and home offices
• Heat water: Using an immersion heater with a solar diverter, or by powering a heat pump
• Charge electric vehicles: Home EV charging with solar dramatically reduces transport costs
• Store energy: Battery storage systems let you save surplus electricity for evening use
• Export to the grid: Earn money through the Smart Export Guarantee (SEG) for surplus electricity
• Power heating systems: Run electric radiators, underfloor heating, or heat pumps

This versatility explains why solar PV has become the dominant solar technology in UK homes and businesses. The ability to use generated electricity however you choose—including for water heating—makes it a far more practical investment for most properties.

Key Differences Between Solar Thermal and Solar PV

Understanding the fundamental differences between these technologies helps clarify why solar PV has become the preferred choice for most UK installations. The following comparison covers all the critical factors affecting performance and long-term value.

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Which System Performs Better in the UK Climate?

The UK's climate presents specific challenges for solar energy systems. Our relatively high latitude, frequent cloud cover, and significant seasonal variation in daylight hours all affect performance. Understanding how each technology responds to these conditions is crucial for setting realistic expectations.

Year-Round Performance Comparison

Solar thermal systems experience dramatic performance drops during winter months—precisely when hot water demand peaks. A typical UK solar thermal installation might provide 60-70% of hot water needs in summer but only 10-20% in winter. This seasonal mismatch limits the practical savings achievable.

Solar PV also generates less electricity in winter due to shorter days and lower sun angles, but the output remains useful year-round. Modern monocrystalline panels perform well even in diffuse light conditions, continuing to generate meaningful electricity on overcast days. A well-designed system in the East Midlands typically produces 850-1,000 kWh per kWp annually, with roughly 40% generated during winter months.

Cloudy Weather Performance

Both technologies see reduced output in cloudy conditions, but the impact differs significantly:

• Solar thermal: Requires direct sunlight to heat the transfer fluid effectively. Heavy cloud cover dramatically reduces heat generation, often to near-zero on overcast days.
• Solar PV: Continues generating electricity from diffuse light, typically producing 10-25% of peak output even under heavy cloud. Understanding solar panel efficiency helps set realistic expectations for UK conditions.

Smart Export Guarantee (SEG) – PV Exclusive Benefit

One significant advantage of solar PV is eligibility for the Smart Export Guarantee. This government-backed scheme requires energy suppliers to pay for electricity you export to the grid. Rates vary considerably between suppliers—the best flat-rate tariffs currently offer 15-16p per kWh, whilst time-of-use tariffs can reach 25-30p during peak periods. This provides an income stream that solar thermal simply cannot match.

Solar thermal produces heat, which cannot be exported—any excess hot water generated on sunny summer days is essentially wasted if you don't use it. Solar PV surplus, by contrast, either earns export payments or can be stored in a battery system for later use.

Maintenance Requirements

The maintenance burden differs significantly between these technologies, affecting system reliability over time.

Solar Thermal Maintenance

Solar thermal systems contain more mechanical components, which require regular attention:

• Annual system check: Pump operation, pressure levels, controller function
• Antifreeze replacement: Heat transfer fluid degrades over time (typically every 3-5 years)
• Valve and pump inspection: Moving parts wear and may need replacement
• Cylinder anode check: Sacrificial anodes protect against corrosion
• Glycol testing: Ensuring antifreeze mixture remains effective

Annual maintenance is required for solar thermal systems, with occasional component replacements needed. Finding qualified solar thermal technicians is becoming increasingly difficult as the technology declines in popularity.

Solar PV Maintenance

Solar PV systems are remarkably low-maintenance due to their solid-state design with no moving parts:

• Occasional cleaning: Solar panel cleaning every 1-2 years, or more frequently near trees or busy roads
• Visual inspection: Checking for damage, debris, or shading changes
• Monitoring review: Checking generation data for anomalies
• Inverter replacement: Typically needed once after 10-15 years

Many PV systems operate for years with minimal intervention. Our solar panel maintenance and support services help ensure your system performs optimally throughout its lifespan, with regular system health checks identifying any issues early.

Pros and Cons Summary

This quick-reference comparison highlights the key advantages and disadvantages of each technology for UK installations.

Solar Thermal

Solar PV

Which System Should You Choose?

Choosing between solar thermal and solar PV ultimately depends on your specific circumstances, energy usage patterns, and goals. However, for the vast majority of UK properties, solar PV offers superior value and flexibility.

For most homeowners researching solar panel options, PV represents the smarter investment. The technology has matured significantly, costs have fallen dramatically, and the versatility of electrical generation provides benefits that solar thermal simply cannot match.

Can You Use Solar PV for Water Heating?

Yes—and this is a key reason why solar PV often makes more sense than dedicated solar thermal. Several options exist for using PV-generated electricity to heat water:

• Solar diverter (immersion controller): Devices like the iBoost or Eddi automatically divert surplus PV generation to your immersion heater, heating water for free rather than exporting at lower SEG rates.
• Heat pump systems: Smart home energy management can power air or ground source heat pumps using solar electricity for highly efficient water and space heating.
• Direct electric heating: Simply power your existing electric water heating system during peak solar generation periods.

These approaches provide the hot water benefits of solar thermal whilst retaining all the additional advantages of PV—including powering other appliances, battery storage compatibility, and SEG export income.

Frequently Asked Questions

Why Choose Spectrum Energy Systems for Solar PV?

At Spectrum Energy Systems, we've been designing and installing solar PV systems across the East Midlands since 2011. Our focus on PV technology reflects our belief that it offers the best value for UK homes and businesses—providing flexibility, strong returns, and genuine energy independence.

Our experienced team brings MCS accreditation and NICEIC certification to every project, ensuring your installation meets the highest standards. From initial assessment through design, installation, commissioning, and ongoing support, we manage the entire process—including DNO applications and grid connection paperwork.

What We Offer

• Expert design: Systems tailored to your property, usage patterns, and goals
• Quality components: Tier-one panels, reliable inverters, manufacturer-backed warranties
• Full project management: From survey to commissioning with minimal disruption
• Battery integration: Storage solutions to maximise self-consumption
• EV charging: Home charger installation to complement your solar system
• Ongoing support: Maintenance packages and monitoring assistance

Whether you're a homeowner looking to cut electricity bills or a business seeking to reduce operational costs and carbon footprint, we provide honest advice and professional installation you can trust. View our case studies to see real examples of our work across Nottingham, Derby, Leicester, Lincoln, and the wider East Midlands.

Conclusion: Solar PV Is the Clear Choice for Most UK Properties

Whilst both solar thermal and solar PV harness the sun's energy, they serve fundamentally different purposes—and for most UK homes and businesses, solar PV delivers substantially better value. The ability to power all electrical appliances, earn export income, integrate with battery storage and EV charging, and benefit from lower maintenance requirements makes PV the smarter long-term investment.

Solar thermal may still suit specific high-hot-water-demand scenarios, but the technology's declining market presence, lack of government support, and single-purpose output limit its appeal for most applications. With solar PV, you can heat water too—using diverters or heat pumps—whilst retaining all the additional benefits that electricity generation provides.

If you're considering solar energy for your property, focus your research on choosing the right solar panels, understanding efficiency factors, and working with experienced, accredited installers who can design a system optimised for your specific circumstances.

Ready to take the next step? Request a free quote or contact our team to discuss your solar options with specialists who've been helping East Midlands properties generate clean energy since 2011.

About Spectrum Energy Systems: Established in 2011, we're MCS-accredited solar PV installers serving Nottingham, Derby, Leicester, Lincoln, and the wider East Midlands. From initial design through installation to ongoing maintenance, we deliver complete solar solutions for homes and businesses. Learn more about our expertise or explore our homeowner resources for comprehensive solar guidance.