You have two solar quotes, and one is cheaper. But is it also the better choice for your home?
To answer that, you need to look at exactly what you’re buying: equipment, design, installation work, support, and a specific estimate of savings. Two quotes with similar total capacity may describe quite different projects.
At Solar Home, we believe the right decision starts with clear information. This guide will help you compare the quotes on an equal basis and identify anything that needs clarification before you proceed.
1. Ask to compare the same project
Start with a simple question: have both companies assessed the same needs?
Give everyone the same information: bills covering a full year, the hours the home is occupied, photos of the site, and any planned heat pump or electric car. Also clarify whether you want a system with a battery, without a battery, or one that can have a battery added in the future.
Next, check whether each quote specifies:
- Total panel capacity in kWp and inverter capacity in kW.
- Number of panels and proposed layout.
- Battery, if included.
- Installation work and processes handled by the company.
- Final price, VAT, and specific exclusions.
Panel capacity and inverter capacity are different figures. Ask for them to be listed separately, so you’re not comparing two vague descriptions such as “5 kW system.”
2. Check the exact equipment models
Descriptions such as “premium panels” and “branded inverter” aren’t enough for a meaningful comparison. Ask for the manufacturer, full model number, and technical datasheet for each key component.
For the panels, check the power rating per panel, dimensions, and warranty terms. For the inverter, ask why it was selected for the specific layout and which features it includes.
If you’d like more information about its role, read our guide to inverters in solar PV systems.
If there’s a battery, compare its usable storage capacity in kWh and its charging and discharging capabilities. Ask for confirmation that it’s compatible with the specific inverter. Technical datasheets, such as this one for the BYD Battery-Box, distinguish usable capacity and point out that how the system performs depends on the inverter.
Finally, clarify what happens if a model is unavailable: what replacement is proposed, and how you’ll be informed before you approve it.
3. See what the installation includes
The price of the main equipment is only part of the project. Ask for an itemized description of mounting structures, wiring, electrical protection, panels, equipment delivery, and labor.
Useful questions include:
- Are the necessary modifications to the existing electrical panel included?
- Have cable routes and roof access been assessed?
- Will additional lifting equipment or repair work be needed?
- Who handles the applications, and which related costs are included?
- What will be handed over once the work is complete, and who will show you how the system works?
Ask them to document whether any preliminary work is needed on the roof or terrace, and who is responsible for it. The condition of the roof and a clear description of the work are also key considerations in the U.S. Department of Energy’s guide to choosing an installer.
4. Compare generation using the same assumptions
If two quotes predict different annual generation, ask them to explain the difference.
Check which property location, tilt, orientation, shading, and losses were used. Also ask for a monthly breakdown: an annual figure doesn’t show when the energy will be available.
Tools such as the European Commission’s PVGIS calculate average monthly and annual generation using data from many years and specific installation parameters. Such a forecast is an estimate, not a guarantee of generation in any given year.
Ask them to show the calculation method and explain its assumptions. This lets you assess the supporting evidence, rather than simply choosing the larger figure.
5. Ask for an explanation of savings and payback
Annual generation doesn’t automatically translate into the same financial benefit for every home.
The comparison should show how much energy is estimated to be used in your home, how much will be fed into the grid, and which prices have been factored in. The importance of consumption, generation, and compensation for surplus energy is also explained in the Department of Energy’s guide to residential solar panels.
Ask both companies to use the same financial assumptions. Clarify whether the calculation includes financing, maintenance, or possible equipment replacement.
If a subsidy or tax benefit is shown, ask for it to be presented separately from the initial price and for confirmation that it applies to your situation. It is also worth asking for a scenario without this benefit.
To learn about our approach, you can read how we design solar PV systems at Solar Home.
6. Separate warranties from support
A reference to a “multi-year warranty” needs further explanation.
The product warranty and the panels’ performance warranty are different types of coverage. The latter concerns power retention under the manufacturer’s terms; it does not guarantee a specific amount of savings. This distinction is shown, for example, in Trinasolar’s documentation on the two warranties.
Ask for the terms for the panels, inverter, battery and installation labor separately. Ask who handles a fault claim and whether labor, transport and reinstallation are covered.
Also keep clear contact details for support after handover.
7. Calculate the final cost, including exclusions
Here is a hypothetical example, solely to help you understand the comparison:
- Offer A lists 8.000 €, but excludes electrical panel work 900 € and additional labor 700 €. The comparable total comes to 9.600 €.
- Offer B lists 9.500 € and includes the same work.
If the equipment, VAT and remaining scope are equivalent, the offer that was initially cheaper ends up costing more. The amounts are illustrative and do not represent market prices.
Before deciding, ask for written confirmation of the total amount, payment schedule, offer validity and the process for approving additional work. Also distinguish installation time from the time needed for connection and activation.
Frequently asked questions
Is the cheapest offer a bad choice?
Not necessarily. It may be competitive, as long as it covers the same scope and provides details about the equipment, work and support.
Is comparing the price per kWp enough?
It is an initial indicator, but it does not reflect the battery, the property’s specific circumstances or differences in the work involved. Use it only alongside the detailed description.
What should you do if an offer does not specify models?
Ask for a revised written offer with exact model codes and technical datasheets before proceeding with an agreement.
Why does the payback period differ between two offers?
Check whether the initial cost, production, estimated self-consumption or financial assumptions differ. Ask for a recalculation using the same basis.
Choose with a clear understanding of the project
A good offer lets you understand what is included, why it is recommended and what you can expect. Take time to ask for clarification before making a decision.
At Solar Home, we start with your property and needs so that the proposal makes practical and financial sense. Contact us to discuss the design of your system.
