1. Define hot-water and heating needs
Record hot-water and space-heating demand, temperatures and timing. Identify the existing equipment and planned work. Regular hot-water use and high winter heating demand need different assessments. Specify what each option replaces and what supplies heat when available solar energy is insufficient.
2. Describe complete systems
For solar thermal, itemise collectors, circuit, tank, pump, controls and auxiliary heat. For PV with a heat pump, specify modules, inverter, connection, heat pump, heat distribution and controls. Distinguish heat storage from an electrical battery. Comparing only collectors or panels omits components and work needed for a usable system.
3. Compare useful energy and seasons
Request useful heat, electricity generation and remaining purchases month by month. Collector efficiency cannot be directly compared with PV-cell efficiency to establish the final bill. Heat-pump performance depends on temperatures and operation. Have actual useful energy, storage losses and periods of output exceeding demand explained.
4. Define maintenance and operation
Request manufacturer instructions, inspections, access and service costs for each device. Specify controls and protection during high output and low demand. A PV option does not remove every heating-system maintenance need. Compare warranties, parts and replacement arrangements without assuming fault-free operation.
5. Compare quotations and operating costs
Include installation, roof work, plumbing, electrical work, storage, adaptations, maintenance and replacement. Value surplus electricity using the actual contract; it does not automatically finance all heating. Check grants and timing separately for each item. Compare an option retaining some existing equipment using the same demand and price assumptions.