Comparing solar quotes in the UK is less about finding the lowest headline price and more about checking whether each proposal is based on the same system size, performance assumptions, equipment, installation scope and financial model. This guide provides a repeatable checklist for homes and businesses, with practical calculations for comparing commercial solar PV proposals and deciding which questions to ask before signing.
Overview
A solar quote should make it possible to understand what you are buying, how the system is expected to operate and which assumptions affect the payback period. A professional proposal will normally describe the solar array, inverter, mounting system, monitoring, electrical work, warranties and expected output. For a business, it should also address roof condition, working arrangements, grid connection requirements and how the installation will fit around trading or production.
Do not compare quotes using price per panel alone. Two proposals may contain different panel capacities, roof layouts, inverter sizes or levels of scaffolding and electrical work. Instead, compare the complete installed system and its expected annual value.
For commercial solar panels in the UK, the most important financial question is often how much generation can be used on site. A business that operates during daylight hours may use a larger share of its solar electricity directly than a business with low daytime demand. Export payments can form part of the model, but they should not be treated as a substitute for understanding your actual load profile and electricity contract.
For homes, the same principle applies. A quote that includes home battery storage UK customers may need should be assessed against evening demand, battery usable capacity, charge and discharge limits, warranty terms and the likely value of stored electricity. A battery is not automatically the best choice for every property or business.
How to estimate and compare solar quotes
Start by putting every quote into a common comparison table. Record the following for each supplier:
- Total installed price, with the tax treatment clearly stated.
- Solar array size in kilowatts peak (kWp), number of panels and panel wattage.
- Panel manufacturer, model, product warranty and performance warranty.
- Inverter manufacturer, model, rated output, warranty and monitoring arrangements.
- Battery capacity, if included, separating usable capacity from nominal capacity.
- Estimated annual generation and the method used to calculate it.
- Estimated on-site consumption, exported electricity and annual bill reduction.
- Mounting system, access equipment, cabling, protection equipment and commissioning.
- Expected programme, payment schedule and exclusions.
A useful first calculation is:
Estimated annual generation = system size in kWp × expected generation per kWp
The second calculation separates the value of electricity used by the site from the value of exported electricity:
Annual energy value = (generation used on site × avoided import rate) + (generation exported × export rate)
Use the rates from your electricity and export arrangements rather than generic figures. If a supplier uses an optimistic rate, ask them to rerun the estimate with your actual tariff, a lower export assumption and a less favourable generation scenario.
For a simple payback estimate:
Simple payback = total project cost ÷ estimated annual financial benefit
This is only a screening calculation. It does not fully account for maintenance, inverter replacement, battery degradation, financing costs, insurance, tax treatment, changing tariffs or the time value of money. For a business investment decision, request a cash-flow model showing these items separately.
Inputs and assumptions to check
System size and roof design
Check that the proposed kWp fits the usable roof area and takes account of shading, orientation, roof pitch, access routes, rooflights, plant and fire-safety requirements. A larger system is not necessarily better if much of its output is exported at a lower value. Ask the installer to show the proposed panel layout and identify any areas excluded from the calculation.
For warehouses, farms and other commercial buildings, roof structure and condition deserve particular attention. Ask whether a structural survey is included, who will arrange it and what happens if remedial work is required. Flat roofs may require a ballasted or fixed mounting approach, each with different implications for loading, waterproofing and maintenance. See our guide to flat-roof solar panels for further context.
Generation estimates
Ask which modelling tool, location data, shading assumptions and system losses have been used. The quote should distinguish between estimated generation and guaranteed performance. It is reasonable to request a monthly generation profile, particularly where your electricity demand changes seasonally. Our guide to solar panel output in the UK by month can help you assess whether the profile looks plausible.
Equipment and warranties
Record the exact panel and inverter models rather than accepting descriptions such as “premium” or “high efficiency”. Check whether warranties cover parts, labour, removal and reinstallation, and whether claims must be made through the installer or manufacturer. For batteries, compare usable capacity, maximum power, round-trip efficiency, operating temperature, cycle or throughput conditions and backup capability.
If backup during a power cut matters, ask whether the proposed system can operate when the grid is down. Many standard grid-connected systems do not provide whole-property backup without suitable control equipment, isolation and an appropriately designed critical-load circuit. Read our battery backup guide before treating backup as an included feature.
Installer credentials and scope
When searching for solar installers near me, check the company’s relevant certifications, insurance, experience with similar roofs and evidence of completed commercial projects. If a scheme, warranty or export arrangement requires a particular certification, confirm the installer’s current status directly with the relevant body. MCS certification may be important for some customers and finance or incentive routes, but it should be checked rather than assumed from marketing language.
Ask for a written scope covering scaffolding, access, roof repairs, isolation, distribution-board work, cable routes, internet connectivity, commissioning, building-control matters, grid notifications and removal of packaging. Exclusions can make a low quote more expensive after work begins.
VAT, export and finance
Ask the supplier to state the VAT treatment and the reason for it, rather than relying on a headline “0 VAT” reference. Eligibility can depend on the customer, property and products included, and rules can change. Treat solar panel grants UK searches with similar caution: ask which programme is being referenced, who is eligible and whether funding is confirmed before using it in your financial model.
For exported electricity, confirm whether the proposal assumes a Smart Export Guarantee arrangement or another contract, who applies for it and what meter or documentation is required. Export rates and electricity tariffs can change, so model them as editable inputs. For solar panel finance, compare the total amount repayable, fees, deposit, interest, early settlement terms and ownership of the equipment—not only the monthly payment.
Worked examples
Example 1: small business rooftop system
Imagine a business receives a quote for a 20 kWp rooftop array. For illustration only, assume the system is modelled to generate 17,000 kWh annually. The business expects to use 70% on site and export 30%. Its spreadsheet should therefore show 11,900 kWh as on-site generation and 5,100 kWh as export.
Enter the business’s actual avoided import rate and export rate in separate cells. If the import rate is represented by I and the export rate by E, the annual energy value is:
(11,900 × I) + (5,100 × E)
Now divide the installed quote price by that result to produce a simple payback estimate. Recalculate it using a lower generation estimate, a lower export rate and a different daytime consumption percentage. If the result changes substantially, the proposal should be assessed as a range rather than a single promised payback figure.
Example 2: battery added to a commercial quote
Suppose a business is offered the same solar array with a battery. The battery may shift some solar generation from midday to late-afternoon or evening use, but its value depends on the site’s load profile, charge limits, losses, warranty and control strategy. Ask the installer to provide two models: solar-only and solar-plus-storage.
Compare the additional battery cost with the additional annual benefit attributed to the battery. That benefit should be shown separately from the solar array’s benefit. If the proposal combines both figures, request a transparent breakdown before assessing battery storage payback.
Example 3: a quote comparison checklist
Before choosing between suppliers, mark each item as confirmed, unclear or excluded:
- Array size and panel layout.
- Annual generation with monthly profile.
- On-site use and export assumptions.
- Exact panel, inverter and battery models.
- Roof survey and structural responsibility.
- Electrical, access and grid-connection works.
- Warranties, monitoring and aftercare.
- VAT treatment and payment schedule.
- Export registration responsibility.
- Evidence of relevant installer certification and insurance.
- Completion date, commissioning and handover documents.
Do not score an unclear item as zero or assume it is included. Ask for a revised written quote so every supplier is responding to the same specification.
When to recalculate and what to do next
Revisit your solar quote comparison whenever a material input changes. This includes an electricity contract renewal, a new export rate, a change in operating hours, a roof repair, a revised panel layout, a battery addition or a change in financing terms. Businesses should also recalculate after installing high-load equipment, changing shifts or moving from an office-led schedule to a more energy-intensive operation.
Before requesting final proposals, collect at least twelve months of half-hourly or interval electricity data if available, recent bills, roof plans, photographs of access routes and details of planned electrical loads. Give the same information to each installer. Ask each one to provide a design, generation estimate, consumption model and itemised scope on a consistent basis.
Finally, take time to check the contract, warranties, certification, insurance and cancellation terms. A clear quote should leave you able to explain the system size, expected use, export assumptions, total cost and main risks without relying on verbal promises. For related site-specific decisions, see the guides to warehouse solar installation, farm solar panels and commercial solar costs and ROI. Rechecking the inputs before accepting a quote is usually more valuable than comparing headline prices alone.
