The short answer
Compare the complete proposed systems on the same scope. A lower headline price can reflect different equipment, usable storage, electrical work, backup coverage or aftercare.
Put the specifications side by side
Record panel model and quantity, inverter model, battery model and usable capacity. Ask the installer to identify the ratings and limitations for the complete combination.
Request a marked roof layout and a written description of mounting, access, cable routes and any alterations to the electrical installation.
Make the exclusions visible
Check scaffolding or other access, roof repairs, supply alterations, backup equipment and commissioning. Ask whether applicable taxes are included and how unforeseen work will be agreed.
If future expansion matters, request the supported expansion route in writing. Do not assume another battery or different inverter can be added simply because there is physical space.
Compare forecasts consistently
Ask each proposal to show generation, household demand, self-consumption, export and tariff assumptions. Note whether the load profile is measured or modelled.
For an illustrative comparison, Quote A with 5 kWh usable storage and Quote B with 10 kWh do not describe the same storage scope. Request the additional cost and expected benefit rather than ranking by total price alone.
Ask about the life after installation
Identify who handles commissioning, monitoring access, faults, equipment warranty claims and workmanship issues. Keep handover documents and the agreed settings with the installation record.
SolarIQ can help prepare the initial questions. For homes in Surrey and South West London, electricalworks can discuss the survey and a project-specific proposal. The two brands are operated by GThink Ltd.
Before your assessment
Bring these questions with you.
- Matching equipment and usable-capacity information.
- Included works and written exclusions.
- Transparent generation, demand and tariff assumptions.
- Named responsibility for handover and aftercare.