Why Two Solar Quotes Can Differ by £3,000 — And What You Are Really Paying For

Author: Steve Fairless
Originally Published: 2nd March 2026 · Updated: 28th August 2026

Two solar quotes can differ by £3,000 or more because the quotes may not describe the same engineered system, installation scope or long-term support. Panel count is only the visible part. Inverter capability, battery size, roof access, scaffolding, mounting hardware, electrical upgrades, DNO process, monitoring, warranties, consumer protection, design time and aftercare can all change the price.

At Sustainable Energy Engineering, we think a solar quote should be readable as a technical proposal, not a mystery total at the bottom of a page. If two prices differ, a homeowner should be able to identify why.

Updated: 28th August 2026 to reflect the current MCS solar PV standard, RECC consumer rules, network-connection requirements and the VAT position.

Start by Comparing the Quote, Not the Headline Price

RECC's consumer guidance recommends obtaining at least three quotations. That only helps if the proposals are compared on the same basis. A £9,000 quote is not automatically cheaper than an £11,000 quote if the first excludes scaffolding, uses a smaller battery, omits backup hardware or assumes electrical work that later becomes chargeable.

MCS Issue 6.0 Makes Technical Information Part of the Buying Decision

The current MCS MIS 3002 Solar PV Systems standard (Issue 6.0, March 2026) requires minimum technical information to be communicated in writing at or before contract award.

If one quote provides this level of information and another simply says “12 panels + battery”, you are not comparing equivalent proposals.

Panel Count Is a Poor Way to Compare System Size

Twelve 400 W modules equal 4.8 kWp. Twelve 455 W modules equal 5.46 kWp — nearly 14% more nominal DC capacity from the same panel count. Physical dimensions and electrical characteristics can differ too.

When comparing quotes, look at array kWp, module model, efficiency, dimensions, warranty and roof layout — not just “number of panels”.

The Inverter Can Change Both Price and Capability

A basic grid-tied inverter, a hybrid inverter and an AC-coupled battery inverter solve different problems. They can have different maximum PV input power, MPPT counts, battery voltages, backup capability, monitoring and export-control options.

A cheaper inverter is not automatically poor, and a more expensive inverter is not automatically better. The question is whether it matches the array, grid connection, battery and future loads.

Battery Quotes Can Look Similar While Being Fundamentally Different

Battery capacity in kWh is only one dimension. We compare usable capacity, continuous power, charge power, backup capability, warranty terms, operating temperature, expansion rules and the inverter architecture.

A 10 kWh battery that can only discharge at 3 kW behaves differently from one that can sustain a higher household load. A quote with whole-home backup hardware is not like-for-like with one that only provides normal grid-connected storage.

For customers considering storage, we design solar PV with battery storage around actual demand rather than selecting battery kWh in isolation.

DNO Requirements Can Affect Cost and Timescale

Electricity network connection rules are often invisible in a headline quote. Under ENA Engineering Recommendation G98, the microgenerator threshold is 16 A per phase, corresponding to 3.68 kW on a single-phase 230 V connection. Larger or more complex arrangements can fall under G99 procedures and may require approval before connection.

This does not mean every array above 3.68 kWp needs a smaller inverter. DC array size, inverter AC rating, export limitation and storage arrangements all interact. It means the network connection needs to be designed and processed correctly.

Roof Access and Scaffolding Can Move a Quote by Hundreds or Thousands

A simple two-storey tiled roof with clear access is very different from a three-storey property with conservatories, extensions, fragile slate, multiple roof faces or restricted scaffold positions.

A transparent quote should make clear what access is included and what could trigger an additional charge. If scaffolding is omitted from a cheap headline price and added later, the original comparison was meaningless.

Mounting Systems Are Not All the Same

The mounting system transfers wind and snow loads into the building structure while maintaining weather-tightness. Rail, hooks, roof anchors, flashings, clamps and fixings must suit the roof type and module configuration.

Quality mounting hardware costs more than improvised fixings, but this is not an area where we believe saving a small amount upfront makes sense on an installation expected to remain in place for decades.

Electrical Upgrades Can Be Legitimate Extras — But They Should Be Identified Early

Some properties need consumer-unit work, earthing improvements, surge protection, cable routes, meter changes or additional isolation. A good survey identifies these before contract wherever reasonably possible.

RECC's “no surprises” approach is important here: foreseeable work should not be hidden until installation day.

Performance Modelling Is Part of What You Are Buying

A solar system is valuable because of the energy it will generate and the grid energy it will replace. MCS therefore requires a documented performance estimate. RECC also requires financial estimates to be based on the consumer's actual energy use and pattern of use.

This is one reason we ask for annual kWh and, where available, half-hourly smart-meter data. A generic savings figure can look attractive while being poorly matched to the household.

Worked Example: Same Roof, Different Proposal

Illustrative comparison only. It is designed to show why headline prices can diverge; it is not a price list.

Zero-Rated VAT Should Not Be Used to Disguise a Price Difference

Qualifying installations of solar panels and certain other energy-saving materials in UK residential accommodation are currently subject to a temporary 0% VAT rate until 31 March 2027, after which the reduced 5% rate is scheduled to apply under current rules.

If two qualifying residential quotes are being compared in August 2026, both should apply the relevant VAT treatment correctly. A salesperson presenting 0% VAT as a unique company discount is not describing the tax position accurately.

SEG Eligibility and Documentation Matter

The Smart Export Guarantee requires participating electricity suppliers to offer payment for eligible exported low-carbon electricity. Solar PV installations up to 5 MW can qualify subject to the scheme criteria.

Different suppliers set their own rates and terms. The installation documentation matters because export-tariff providers may require evidence that the generating system meets the relevant technical and certification requirements.

Cheap Quotes Can Be Good — Expensive Quotes Can Be Bad

Price is not a quality certificate. A well-run installer can sometimes offer excellent value because of efficient procurement, low overheads and good supplier relationships. Equally, a high price can simply be a high price.

The purpose of this guide is not to tell customers to choose the most expensive quote. It is to help you establish whether the scope, equipment, protection and forecast are genuinely comparable.

Questions We Would Ask Before Accepting Any Solar Quote

Why Our Quote May Not Be the Same as Another Installer's

We build around the site and the customer's electricity use. That can mean a different module count, inverter rating, battery size, roof layout or grid strategy from another company. We are comfortable with customers comparing quotes — RECC actively recommends it — provided the comparison is technical as well as financial.

For a domestic system, you can see the type of work we design through our solar PV for home service. For business projects, the same principle applies at larger scale through our commercial solar installations.

The Question to Ask Is Not “Why Are You £3,000 More?”

A better question is: “Show me exactly what is different.” If the equipment, design, access, electrical work, warranties and service are genuinely identical, then price becomes the main differentiator. If they are not, the gap may be buying additional capability or simply exposing items another quote has left out.