Free checklist · solar, battery and hybrid quotes
12 questions to ask before you sign a solar quote
Use these with any installer's proposal for solar, batteries or a hybrid system with a generator. A good installer will answer every one in writing. Vague answers tell you something too.
Sizing
What load data was the system sized on?
Ask for the meter data or at least 12 months of bills behind the design. A system sized on one month's bill, or on the total of everything connected, is a guess.
How much of the solar energy will we actually use?
Ask for the share used on site. Energy produced while your site is closed is wasted unless it is stored or exported, and the savings in the proposal should only count what you use.
What yield is assumed, and with what losses?
Ask for the energy per kWp per year and the loss assumptions, including heat. Compare it with an independent source such as the Global Solar Atlas for your site; a much higher figure needs explaining.
Equipment
Can the inverters start our largest motor?
Motors draw several times their running current when they start. Ask how your largest motor starts on inverter power, and whether it needs a drive or soft starter.
How much battery energy reaches our loads?
Ask for usable energy at the inverter output, after depth of discharge and losses, not the battery's nameplate kWh. The difference is often 15–25%.
How fast will the battery lose capacity?
Ask what capacity the warranty guarantees at year 5 and year 10, and the cycle limit. Check that it matches how often you will charge and discharge.
Are the brands and models fixed in the contract?
Every major item should be named, with no substitution without your written approval. Otherwise the equipment you were quoted may not be the equipment you receive.
Contract
What exactly is guaranteed?
A useful performance guarantee names a measurable figure, such as energy per year or performance ratio, says how it is measured, and says what you get if it is missed.
When do the warranties start?
Warranties that start at shipment shrink before the system is even running. Ask for cover that starts at commissioning.
How will the system be tested before final payment?
Agree an acceptance test in the contract, and hold back part of the payment until the system passes it.
Money
What will maintenance cost over ten years?
Include cleaning, monitoring, spares and an inverter replacement around year 10 to 12 when you compare quotes. A low price with no maintenance plan is not a low price.
Can we see a priced breakdown?
Ask for modules, inverters, batteries, mounting, cabling, labour and margin as separate lines. A single lump sum cannot be compared between quotes.