The starting point
A meaningful comparison puts the complete installed cost beside clearly defined savings. Keep example allowances, indicative budgets and an installer’s surveyed quotation distinct.
Compare matching scopes
Ask each installer to identify the panels, inverter, usable battery capacity, mounting, electrical works and commissioning included. Clarify any roof-access costs and exclusions.
Backup equipment, supply alterations and future expansion can materially change the scope. Include them consistently when comparing offers.
Separate a forecast from a quotation
A forecast depends on assumptions about demand, generation, tariffs, losses and operation. A quotation describes what will be supplied and installed at an agreed price.
Our recommendation is to keep the assumptions alongside the result. This makes it possible to revisit the decision when the tariff, equipment or household use changes.
Ask what could change the result
Review a lower-saving case as well as the central estimate. Check maintenance, replacement, financing and reserve assumptions rather than relying on one headline return.
- Which savings already include export income?
- What costs are omitted?
- What changes if demand or tariffs fall?