Compare the same useful service
Start with the loads and working hours the system must support. A cheaper system covering fewer loads is not directly comparable with a broader design. Record scope, equipment, protection, installation and support in each proposal.
Make the assumptions visible
- Initial equipment and installation costs.
- Fuel, grid and maintenance costs you actually incur.
- Expected replacement items and their assumptions.
- Usage patterns and any growth in demand.
There is no universal payback period. Changing fuel prices, tariffs, equipment condition and usage can change the result. Ask for a transparent comparison, without guaranteed savings or investment returns.