How to Evaluate a Solar Installer's Savings-Guarantee Claim

A solar savings guarantee is only as good as what it actually promises and what happens if it is not met. Scrutinising the specifics before signing, not just the headline number, is the only way to tell a genuine, enforceable commitment from a sales claim.

What should a real guarantee actually specify?

Three things, at minimum: exactly what is guaranteed, either a generation figure in kWh or a savings figure in dollars, not a vague claim of big savings; the specific assumptions the guarantee is calculated from, ideally your actual electricity consumption data and current verified tariff rate, not generic averages; and a concrete, written remedy if actual results fall short, whether that is a partial refund, a system adjustment, or another specific action.

What are the clearest red flags?

A guarantee made verbally or in marketing material but not written into the actual contract carries no real weight. A guarantee calculated from assumed or generic consumption figures rather than your actual usage data is built on a foundation that may not reflect your real situation. And vague language about remedy, phrases like we'll make it right without a specific action defined, means there is effectively nothing to hold the installer to if the guarantee is missed.

What actually makes a written guarantee legally enforceable in Singapore?

The same thing that makes any consumer contract term enforceable: it has to actually be a term of the written contract, not a verbal promise or a claim in marketing material sitting outside the signed agreement. Singapore's Consumer Protection (Fair Trading) Act gives homeowners recourse against unfair practices, including false or misleading claims made to induce a purchase, and CASE, the Consumers Association of Singapore, is the body homeowners can approach for a dispute over a contract term an installer fails to honour.

None of this replaces reading the actual contract before signing. A guarantee mentioned in a sales conversation or a glossy brochure but absent from the signed document is not a term either CASE or a small claims tribunal can enforce, since there is no contractual language to point to. Confirming the guarantee, its assumptions, and its remedy are all written into the contract itself, not just discussed verbally, is the step that actually determines whether it means anything.

How does a savings guarantee relate to the P50/P90 estimate an installer should already be giving you?

Directly, and understanding the connection helps you spot a guarantee built on shaky ground. A credible generation estimate is expressed as a P50 figure, the level of output with a 50% probability of being met or exceeded, alongside a more conservative P90 figure, covered fully in the P50/P90 estimates guide. A savings guarantee pegged to an optimistic P50 number, without acknowledging the real statistical spread around it, is guaranteeing a figure that has, by definition, roughly a 50% chance of falling short in any given year.

A more genuinely defensible guarantee is pegged closer to the conservative P90 figure, or explicitly averaged across multiple years rather than judged against any single year's weather variation. Asking which of the two an installer's guarantee is actually based on is a specific, revealing question, since a guarantee built on the optimistic number is quietly setting itself up to be missed.

What does a shortfall remedy actually look like worked through with numbers?

Take a hypothetical 10 kWp system guaranteed to generate at least 12,000 kWh annually. If actual generation comes in at 10,800 kWh, a 10% shortfall, a genuine written remedy specifies exactly what happens next: a cash refund calculated against the shortfall at a stated rate, a system adjustment such as additional panels or a cleaning and inspection at no cost, or another concrete, pre-agreed action. A guarantee without this worked-through mechanism specified in writing is not something you can actually invoke if the shortfall happens, no matter how confident the original sales conversation sounded.

Does a missing guarantee mean an installer is untrustworthy?

Not necessarily. What matters more than the presence of a formal guarantee is whether the underlying savings estimate is transparently calculated from your actual consumption data and current, verifiable tariff figures. A detailed, well-documented estimate without a formal guarantee attached can be more trustworthy than a headline guarantee number built on generic assumptions that may not apply to your specific home.

What should you actually ask before signing?

Ask the installer to walk through exactly how their savings or generation figure was calculated, using your own consumption data, and to put both the guarantee and its remedy in writing if one is offered. A confident, specific, written answer is a far stronger signal than the size of the headline number itself.

Further reading: see the P50/P90 estimates guide for how a realistic generation figure should actually be calculated, and the solar buyer's checklist for the full pre-signing checklist. See red flags in a solar quote, annotated for what an unsupported savings claim looks like alongside the rest of a genuinely weak quote. Run the Sunnify solar estimate for a transparent, data-based estimate of your own.