Solar Thermal vs Solar PV: Which Is Right for Your UK Home?

ndent renewable-energy writer focused on practical UK home solar decisions, installation economics, and policy changes that affect payback.

Photo by Quang Nguyen Vinh on Pexels

If you're weighing up solar options for your UK home, you've likely encountered a confusing array of terminology, conflicting advice, and sales pitches that overstate savings whilst glossing over the fine print.

The fundamental choice between solar photovoltaic (PV) panels and solar thermal collectors isn't simply about which technology is "better" — it's about which system aligns with your household's energy consumption patterns, property characteristics, and financial expectations.

Both technologies harness sunlight, but they serve distinctly different purposes.

Solar PV generates electricity that can power your lights, appliances, and increasingly, your heating systems.

Solar thermal captures heat directly to warm your hot water cylinder.

In some homes, the answer is straightforward.

In others, particularly those with specific hot water demands or limited roof space, the calculus becomes considerably more nuanced.

This analysis examines both technologies through a UK-specific lens, accounting for our climate, regulatory framework, and current incentive structures — not generic advice that assumes Californian sunshine or Australian feed-in tariffs.

Understanding Solar PV: Electricity Generation for UK Homes

Solar photovoltaic panels convert sunlight directly into electricity using semiconductor materials.

When photons strike the panel's surface, they dislodge electrons, creating a flow of direct current (DC).

An inverter then converts this to alternating current (AC) suitable for household appliances.

The UK installed capacity has grown substantially over the past decade, with over 1.3 million British homes now sporting solar PV systems.

This uptake reflects both falling equipment costs and rising electricity prices — the economics have shifted dramatically even as our climate hasn't.

How UK Climate Affects PV Output

Let's address the elephant in the room: Britain isn't renowned for abundant sunshine.

A typical UK location receives roughly 1,000–1,200 kilowatt-hours per square metre (kWh/m²) of solar irradiation annually.

Compare this to southern Spain (1,800–2,000 kWh/m²) or Germany, which despite its similar latitude to the UK, benefits from a more continental climate with clearer summer skies.

However, this doesn't render solar PV uneconomic.

Panels respond to daylight, not just direct sunshine, and they actually perform better in cooler temperatures — a distinct advantage during bright spring and autumn days when panel efficiency can exceed rated specifications.

The key metric isn't peak output but annual yield, measured in kWh per kilowatt-peak (kWh/kWp) installed.

The Self-Consumption Challenge

Here's where many installations fall short of sales projections.

PV panels generate electricity during daylight hours, peaking around midday.

Most households consume the bulk of their electricity in mornings and evenings.

Without battery storage, excess generation flows to the grid — and under the current Smart Export Guarantee (SEG), you'll receive payment for this, but at rates significantly below what you pay for imported electricity.

The economics hinge on maximising self-consumption.

Every kWh you use directly saves you the full retail electricity price (currently around 24–28p per kWh for typical domestic tariffs).

Every kWh exported earns you 4–15p per kWh, depending on your SEG tariff.

This disparity — roughly 15–20p per kWh — makes self-consumption the primary economic driver, not export income.

Battery Storage: Transforming the Equation

Adding battery storage fundamentally changes PV economics by allowing you to store daytime generation for evening use.

A typical 5–10kWh home battery might cost £3,000–£6,000 installed, but can increase self-consumption rates from 25–30% to 60–80% depending on household patterns and system sizing.

The battery decision isn't straightforward.

Current electricity prices make the maths work, but battery warranties typically cover 10 years with a guaranteed remaining capacity (usually 60–80%).

Factor in degradation, and the long-term economics require careful modelling.

Some households opt for a "battery-ready" inverter initially, adding storage later when prices fall further or finances allow.

Solar Thermal: Hot Water From British Sunshine

Solar thermal systems use collectors — either flat plates or evacuated tubes — to absorb solar radiation and transfer heat to a fluid.

This heated fluid circulates through a coil in your hot water cylinder, raising the temperature of your domestic hot water supply.

Unlike PV, which can feed any electrical load, solar thermal serves a single purpose: water heating.

In the UK context, solar thermal has both distinct advantages and significant limitations.

Understanding these requires examining our climate patterns alongside typical household hot water consumption.

Flat Plate vs Evacuated Tube Collectors

Two main collector types dominate the UK market:

Flat plate collectors

resemble PV panels in appearance.

A dark absorber plate sits beneath a transparent cover, with copper pipes carrying the heat-transfer fluid.

They're robust, relatively affordable, and aesthetically unobtrusive.

However, they lose heat through convection, making them less efficient in cold or windy conditions — relevant for exposed UK rooftops.

Evacuated tube collectors

consist of parallel glass tubes containing absorber strips.

The vacuum inside each tube provides excellent insulation, dramatically reducing heat loss.

They're more efficient per unit area, particularly in low-light conditions and during winter months.

This efficiency comes at a cost premium of roughly 30–50% over flat plates.

For most UK installations, the choice depends on available roof area and budget.

If space is constrained, evacuated tubes deliver more heat from a smaller footprint.

If you have ample south-facing roof, flat plates often provide better value per kWh generated.

Seasonal Performance Patterns

Solar thermal output follows a pronounced seasonal curve.

During June and July, a well-designed UK system can provide nearly all domestic hot water needs for a typical family.

In December and January, contribution drops to 10–20% of requirements, with the boiler or immersion heater providing the remainder.

This seasonality matters more than with PV.

Electricity has year-round value — we don't switch off lights in summer.

Hot water demand remains relatively constant, but solar thermal's ability to meet that demand fluctuates dramatically.

Annual contribution typically ranges from 50–70% of hot water needs, with the higher figures achieved by households with larger collector areas and higher-efficiency tubes.

The Cylinder Requirement

Solar thermal requires a dedicated hot water cylinder with a solar coil.

If your home currently has a combi boiler with no cylinder, installation costs increase substantially — you'll need a new cylinder, pipework, and potentially a system boiler conversion.

This requirement alone rules out solar thermal for many UK homes, particularly flats and smaller properties where space is at a premium.

Even homes with existing cylinders may need upgrades.

Solar coils require specific surface areas to transfer heat effectively.

Many standard cylinders lack appropriately sized coils, necessitating replacement.

A solar-compatible cylinder typically costs £800–£1,500, with installation adding further expense.

Head-to-Head: Comparing the Technologies

Beyond the fundamental difference in output — electricity versus hot water — several practical factors influence which technology suits your circumstances.

Installation Considerations for UK Properties

Both technologies require MCS (Microgeneration Certification Scheme) installation to qualify for available incentives and ensure quality.

However, the installation processes differ significantly, as do the regulatory considerations.

Roof Suitability and Structural Assessment

A thorough site survey should assess roof orientation, pitch, shading, and structural capacity.

South-facing roofs are optimal for both technologies, but east-west splits can work — particularly for PV, where dual-array configurations can spread generation more evenly across the day.

Shading is more problematic for PV than solar thermal.

A shaded PV panel can disproportionately affect the entire string's output, depending on inverter configuration.

Modern optimisers and microinverters mitigate this, but add cost.

Solar thermal systems are less sensitive to partial shading, though output still reduces proportionally.

Structural assessment is critical.

PV panels add roughly 15–20kg per m² to roof loading.

Most UK roofs can accommodate this, but older properties or those with existing modifications (velux windows, dormers) may require structural reinforcement.

Your installer should provide a written structural assessment as part of the quotation process.

DNO Approval and Grid Connection

Solar PV requires notification to your local Distribution Network Operator (DNO) — the regional company responsible for electricity infrastructure.

For most domestic installations under 3.68kW per phase, this is a straightforward notification process (G98 application).

Installers handle this as standard practice.

Larger systems, or those where you already have significant generation capacity (perhaps from an existing installation), require formal DNO approval via a G99 application.

This process can take 6–10 weeks and may involve network reinforcement costs if local infrastructure cannot accommodate additional generation.

Solar thermal requires no DNO notification as it doesn't connect to the electrical grid.

VAT and Current Tax Treatment

Since April 2022, the UK has applied a 0% VAT rate on the supply and installation of both solar PV and solar thermal systems on residential properties.

This temporary measure (currently legislated until March 2027) significantly improves installation economics.

Previously, VAT was charged at 5% for professionally installed systems.

It's worth noting that this 0% rate applies to the complete installed system, including necessary ancillary works (scaffolding, electrical upgrades, cylinder replacement).

However, if you're undertaking broader renovation works, the VAT treatment may differ — seek professional advice for complex projects.

Financial Analysis: Beyond Simple Payback

Simple payback calculations provide a starting point but fail to capture the full picture.

Energy prices fluctuate, systems degrade over time, and opportunity costs matter.

A more sophisticated analysis considers these factors alongside your specific circumstances.

Energy Price Projections and Sensitivity

Current high electricity prices have dramatically improved PV economics compared to the low-price environment of the late 2010s.

However, assuming prices remain permanently elevated is unwise.

The Energy Price Cap mechanism, government intervention, and market evolution all create uncertainty.

A prudent approach models multiple scenarios.

Consider how your investment performs if electricity prices average 20p/kWh, 25p/kWh, and 30p/kWh over the next decade.

Similarly, model gas prices at 5p/kWh, 7p/kWh, and 10p/kWh for solar thermal calculations.

If an investment only makes sense under the most optimistic price assumptions, it may not be the right choice.

The Boiler Upgrade Scheme and Future Heating

If you're considering a heat pump under the Boiler Upgrade Scheme (BUS), which provides £7,500 grants towards air source heat pump installation, solar PV becomes considerably more attractive.

Heat pumps typically achieve 300–400% efficiency (delivering 3–4kWh of heat per kWh of electricity consumed).

Running a heat pump from solar generation — either directly during daylight hours or via battery storage — can dramatically reduce running costs.

Solar thermal can complement a heat pump, pre-heating water before the heat pump raises it to target temperature.

However, the economics are marginal.

The heat pump's high efficiency means the value of each kWh of solar thermal heat is relatively low compared to direct electricity savings from PV.

Legacy Feed-in Tariff Considerations

Some homeowners still receive payments under the Feed-in Tariff (FIT) scheme, which closed to new applicants in March 2019.

If you have an existing FIT-registered installation, adding panels or a second system requires careful consideration.

FIT payments are typically calculated on a deemed export basis (50% of generation) for older installations.

Adding capacity may affect this arrangement, potentially requiring transition to SEG for the new system whilst maintaining FIT for the original.

Grant and Incentive Landscape

The current UK incentive landscape differs markedly from the generous FIT era.

Understanding what's available — and what isn't — is essential for realistic financial planning.

Smart Export Guarantee (SEG)

The SEG requires licensed electricity suppliers to offer tariffs for exported renewable electricity.

Rates vary significantly between suppliers, from around 4p/kWh to over 15p/kWh for some specialist tariffs.

Unlike FIT, SEG is a market-driven arrangement, and rates can change with reasonable notice.

To qualify for SEG, your installation must be MCS-certified.

Some suppliers also require specific metering arrangements — increasingly, smart export meters that separately record outgoing electricity.

Your installer should advise on metering requirements for your chosen SEG tariff.

ECO4 and Energy Efficiency First

The Energy Company Obligation (ECO4) scheme, running until March 2026, requires energy suppliers to fund energy efficiency improvements for eligible households.

Whilst primarily focused on insulation and heating upgrades, solar PV can be funded in some circumstances — typically for households in fuel poverty or those meeting specific vulnerability criteria.

Eligibility is complex and depends on benefits received, property characteristics, and your energy supplier's ECO delivery approach.

If you think you might qualify, contact your energy supplier or an ECO-approved installer for assessment.

Don't assume you'll be offered solar — ECO prioritises insulation and heating system upgrades, with solar as a secondary measure in some cases.

No Direct Grants for Most Households

For the majority of UK homeowners who don't qualify for ECO4 support, there are currently no direct government grants for solar PV or solar thermal installation.

The 0% VAT rate is the primary support mechanism.

Various local authority schemes exist patchily across the country, but these change frequently and have limited budgets.

Which Technology Suits Your Home?

Neither technology is universally superior.

The right choice depends on your specific circumstances, and for some households, the answer may be "both" or "neither."

Solar PV Makes Most Sense When:

• You have high daytime electricity consumption, or can shift loads (washing machines, dishwashers, EV charging) to daylight hours

• You're considering battery storage now or in the future

• You heat your home with electricity (heat pump, storage heaters, or electric radiators)

• You have an electric vehicle or plan to purchase one

• Your property has a suitable south, east, or west-facing roof with minimal shading

• You want maximum flexibility — electricity can power any load, be stored, or be exported

• You have a combi boiler with no hot water cylinder

Solar Thermal Makes Most Sense When:

• You have an existing hot water cylinder with a compatible solar coil, or space to install one

• Your hot water demand is significant (four or more occupants, or high usage)

• You heat water with electricity (immersion heater) or oil, making each kWh of solar heat valuable

• Your roof space is limited — solar thermal requires less area than equivalent-value PV

• You already have PV installed and want to maximise renewable contribution

• You're not planning a heat pump installation in the near future

• You have a system or regular boiler that's compatible with solar thermal integration

When Neither May Be Appropriate:

Not every home benefits from solar.

Consider delaying or avoiding installation if:

• Your roof is heavily shaded or faces due north

• Your roof requires imminent replacement (install after re-roofing)

• You're planning to move within 5–7 years (payback may not complete before sale)

• Your electricity and gas consumption are already very low

• You're in a conservation area or listed building where planning permission is unlikely

• Your property's EPC rating is very low — insulation and draught-proofing offer better returns

"The best solar installation is one that's sized to your actual consumption, not your installer's sales target.

Oversized systems export more and save less.

A smaller, well-matched system almost always offers better returns than an oversized array that dumps electricity to the grid at rock-bottom SEG rates."

Planning Permission and Permitted Development

Most domestic solar installations in England, Scotland, and Wales fall under permitted development rights, meaning planning permission isn't required.

However, conditions apply, and exceptions exist.

When Planning Permission Is Required:

You'll need to apply for planning permission if:

• Your property is a listed building

• Your property is in a designated conservation area (panels on principal elevation facing a highway)

• The installation would protrude more than 200mm from the roof surface

• You're in a World Heritage Site and panels would be visible from a highway

• You've already exceeded permitted development limits for outbuildings and extensions (rarely affects solar)

In Northern Ireland, planning rules differ slightly — always check with your local planning authority.

Additionally, if you're in a conservation area but not a listed building, permitted development may still apply for roof surfaces not visible from public highways.

Even when permitted development applies, it's worth notifying your local planning authority informally.

Some installers provide a "lawful development certificate" application service, which provides formal confirmation that planning permission isn't required — useful when selling your property.

Building Regulations and Structural Sign-off

Regardless of planning permission, installations must comply with building regulations.

Your MCS-certified installer should handle this, ensuring:

• Roof structure can support panel loading

• Electrical work meets BS 7671 requirements

• Fire safety provisions are adequate (particularly important with inverters in lofts)

• Any penetrations through weatherproof membranes are properly sealed

Upon completion, you should receive an MCS certificate and electrical installation certificate.

Keep these documents safe — they're required for SEG registration and may be requested by your mortgage provider or building insurer.

Installation Checklist: What to Ask Your Installer

Before committing to any installation, ensure you've covered these essentials:

• Site survey:

  Has a physical survey been conducted, not just a satellite assessment?

• Shading analysis:

  Have seasonal shading patterns been modelled?

• Structural assessment:

  Is written confirmation of roof adequacy provided?

• System design:

  Does the proposed system match your consumption patterns?

• Component specifications:

  Are panel and inverter (or collector and pump station) makes and models specified?

• MCS certification:

  Is the installer MCS-certified for the specific technology being installed?

• Insurance-backed guarantees:

  Is there a workmanship warranty with insurance backing?

• DNO notification:

  Will the installer handle G98/G99 applications?

• SEG support:

  Will the installer assist with SEG registration?

• Aftercare:

  What monitoring and maintenance support is provided?

• Payment schedule:

  Are payments staged, with significant retention until completion?

Making Your Decision

For most UK homeowners, solar PV represents the more versatile investment.

It generates a valuable commodity — electricity — that can power any household load, charge a vehicle, run a heat pump, or be stored for later use.

The market infrastructure (SEG tariffs, battery systems, smart energy management) is more developed, and the technology continues to improve incrementally.

Solar thermal remains relevant for specific situations: households with high hot water demand, electric or oil water heating, existing suitable cylinders, and limited roof space.

Its simpler technology can mean lower long-term maintenance, but the lack of flexibility — you can't run a dishwasher from hot water — limits its appeal.

Some households benefit from both technologies.

A modest PV system for electricity, combined with a solar thermal collector for hot water, can maximise renewable contribution from limited roof space.

However, this hybrid approach requires careful design to ensure both systems work optimally, and the combined cost may push payback periods beyond attractive timeframes.

The decision ultimately rests on honest assessment of your energy consumption, property characteristics, and financial objectives.

Be wary of sales presentations that overstate savings, understate shading effects, or push oversized systems.

Seek multiple quotations from MCS-certified installers, and don't feel pressured to proceed until you're confident in the numbers.

Solar technology, whether PV or thermal, is a long-term investment.

Getting it right matters more than getting it quickly.