Why Two Solar Panel Quotes Can Have Very Different Prices

The most common mistake is comparing panel count and final price. Panel wattage differs, batteries with the same headline capacity can have different usable capacity and power, and one installer may include work another excludes.

First compare system capacity, not panel count

System size is stated in kilowatt-peak (kWp):

Ten 450 W panels form a 4.5 kWp array. Twelve 400 W panels form a 4.8 kWp array. The second quote has more panels, but only 0.3 kWp more capacity. Panel efficiency also affects how much roof area is needed for a given kWp.

Record the exact module model, wattage, product warranty and performance warranty.

Compare the annual generation estimate

Annual generation in kWh is what creates bill savings and export income. It depends on location, orientation, pitch, shading and losses. The MCS solar PV standard requires a performance estimate and warns that output cannot be predicted with certainty because sunlight varies by location and year.

If two installers propose similar kWp but materially different annual generation, ask both to show:

• roof orientation and pitch;
• shading factor and how it was assessed;
• system losses;
• inverter clipping or export limits;
• whether all roof faces were modelled separately.

Do not average the two forecasts. Understand why they differ.

Inverter architecture can change the price

A quote may use a central string inverter, multiple strings, module optimisers or microinverters. The best choice depends on roof complexity, shading, monitoring needs, design and warranty preferences.

Compare:

• inverter model and rated AC output;
• number of trackers or strings;
• module-level equipment;
• monitoring features;
• warranty length and extension cost;
• labour and access cover if a component fails.

A more expensive architecture is not automatically better, and a cheaper string-inverter design is not automatically inferior.

Battery quotes often look similar when they are not

Compare more than headline kWh:

Energy Saving Trust says battery storage tends to cost around £5,000 to £8,000, so differences in battery scope can explain a substantial quote gap.

Roof access, structure and electrical work

One installer may have included full scaffolding, roof reinforcement and consumer-unit work after a detailed survey. Another may have left these subject to survey.

Compare whether each quote includes:

• scaffolding, permits and unusual access;
• tile replacement and weatherproof making-good;
• structural assessment or engineering;
• consumer-unit, earthing and cabling upgrades;
• meter or communications work;
• DNO notification or application;
• monitoring and commissioning.

A quote is not genuinely fixed if important items remain unpriced.

Warranties and consumer protection have value

Separate panel product, panel performance, inverter, battery, mounting and workmanship warranties. Ask who provides each one and what happens if the installer stops trading.

MCS explains that certification includes consumer protections and an independent complaints route. The RECC Consumer Code covers marketing, pre-contract information, quotations, deposits, contracts, guarantees and after-sales service for member companies.

A higher quote may include longer workmanship cover, insurance-backed protection or stronger after-sales service. Confirm the documents rather than paying for vague reassurance.

Cash price and financed price are not comparable

One quote may advertise a cash price while another headline shows a monthly finance payment. Put both into the same format:

• cash price;
• deposit;
• interest rate and APR;
• fees;
• term;
• total amount repayable;
• early repayment conditions.

Calculate payback using the total cost relevant to how you will buy.

Savings forecasts can create an artificial price advantage

An expensive quote can appear “better value” if its forecast assumes:

• higher annual generation;
• higher self-consumption;
• a more generous export tariff;
• rapid electricity-price inflation;
• no degradation or maintenance;
• no finance cost.

Use the same assumptions for every quote. From 1 July to 30 September 2026, the Ofgem price cap average electricity unit rate is 26.11p/kWh for standard variable tariffs paid by Direct Debit in England, Scotland and Wales. The Smart Export Guarantee has no single national export rate because suppliers set their own terms.

An illustrative quote comparison

Normalise each quote in five steps

1. Match capacity. Calculate price per kWp only after checking equipment and scope. It is a screening metric, not a verdict.
2. Remove optional extras. Compare solar-only, battery, backup, EV charger and bird protection separately.
3. Use one financial model. Apply the same import rate, export rate, self-consumption and tariff-growth assumptions.
4. Add exclusions. Include likely scaffolding, electrical, roof and finance costs.
5. Score warranties and service. Record documents, providers, exclusions and installer responsibilities.

Questions to send both installers

• What is the exact array size in kWp?
• What annual generation and shading factor are assumed?
• What equipment model numbers are included?
• Which items remain subject to survey?
• Is scaffolding fixed and included?
• What electrical and DNO work is included?
• What are the usable battery capacity and continuous power?
• Is backup included or only battery storage?
• Which import, export and inflation assumptions drive the savings forecast?
• What is the all-inclusive cash price and total financed price?

When a lower quote may be the better quote

The lower price may be better value when the system is appropriately sized, the equipment is suitable, the scope is genuinely complete, assumptions are conservative and the installer provides clear certification, warranties and after-sales arrangements.

When a higher quote may be justified

A higher price may be justified by a larger useful array, difficult access, necessary roof or electrical work, a battery, backup equipment, more suitable inverter design, longer documented protection or a more complete fixed scope.

Red flags regardless of price

• No written property-specific performance estimate.
• No exact model numbers.
• Savings shown without the underlying tariff and self-consumption assumptions.
• Pressure to sign immediately.
• Large unexplained discount or “free” equipment.
• No clear installer certification or consumer-code membership.
• No list of exclusions.
• Finance sold without total amount repayable.

RECC recommends at least three quotes. A third proposal often reveals whether one of the first two is unusually cheap, unusually expensive or simply different in scope.

Frequently asked questions

Sources

• MCS — Solar PV Installation Standard
• MCS — certification and consumer protection
• RECC — Consumer Code
• RECC — consumer top tips
• Energy Saving Trust — current solar and battery costs
• Ofgem — current electricity price cap
• Ofgem — Smart Export Guarantee

Updated 6 August 2026. The comparison table is fictional and is included only to demonstrate a method. Obtain written, property-specific quotes before making a purchase.