The short answer
Review solar generation month by month against demand. An annual surplus does not demonstrate that the house can meet its needs on a winter evening.
Ask for the monthly picture
Request a twelve-month generation estimate and the basis used to produce it. Climate-based modelling is a useful comparison; it is not a forecast of the weather on a particular day.
Compare each month with the household’s expected consumption. If electric heating is involved, an even division of annual demand may hide the period that matters most.
Read this simple energy balance
Suppose a modelled winter day has 5 kWh of solar generation and 15 kWh of household use. Even before conversion losses, at least 10 kWh must come from another source or previously stored energy.
A battery can move energy between times, but it does not create the missing energy. Grid charging is a separate purchase and needs to be included in the cost calculation.
Distinguish a seasonal estimate from backup
An ordinary monthly grid-connected estimate does not establish power-cut operation. A backup design must separately confirm compatible equipment, the available reserve and the supported loads.
When discussing a long winter outage, compare a conservative no-recharge scenario with an additional scenario that includes possible solar recharge.
Use the comparison to ask better questions
In SolarIQ, review the seasonal example and monthly costs rather than choosing solely from the annual savings figure. Keep the same usage and tariff when comparing systems.
For a proposed heating or EV change, prepare a second demand scenario. Record what changed so that the effect is visible.
Before your assessment
Bring these questions with you.
- Monthly generation and demand side by side.
- A separate winter-evening demand estimate.
- Grid-charging costs included where relevant.
- Backup treated as a separate design requirement.