Build the project around your property and electricity use. Treat funding, connection and installation as separate items to confirm.
Prepare one brief for every installer
Gather your annual electricity use, roof information and any plans for an electric vehicle or heat pump. Ask for a site visit and a clearly stated generation estimate. Separate current consumption from future purchases so the proposed system is not justified only by equipment you may never install.
Compare the full installation
Ask each company to identify its responsibilities for scaffolding, the meter cabinet, electrical work, grid coordination and handover. Use the Verbraucherzentrale planning guide as a reference when preparing questions. Do not assume all enabling work is included in a headline price.
Keep finance visible
KfW publishes information on photovoltaic financing. Check the current product and application conditions before relying on it, and distinguish a loan from a grant. Local offers can differ; make a written list of confirmed support rather than subtracting assumed funding from your budget.
Choose a realistic consumption scenario
Prepare one scenario for the household today and another for changes already planned. State when an electric car would be at home and how heating demand varies through the year. More annual consumption does not necessarily mean more direct solar use. Ask for monthly production and grid purchases for each scenario so an attractive annual total does not hide a mismatch between summer generation and winter demand.
Treat the meter cabinet as part of the project
Ask the installer to inspect the existing electrical installation and identify any work associated with metering or connection. Request a clear price or an explicit provisional allowance, with responsibility for confirming it. Also agree the positions of the inverter and any storage, maintenance access and cable routes. Putting these details on the site-visit record reduces the scope for a low initial quote to grow after work starts.
Use a project timeline, not just a fitting date
Map the roof survey, design approval, any prerequisite works, equipment delivery, installation, commissioning and administrative handover. Add financing steps where relevant. Mark which dates depend on another organisation. Ask what you will receive at each stage and what makes the system ready for normal operation. Keep an allowance for unresolved items separate from the equipment price rather than treating every provisional figure as a fixed commitment.
Your planning checklist
- Current use and confirmed future changes kept separate.
- Roof-specific monthly output and household-use estimates.
- Electrical enabling work and connection responsibilities priced.
- Project stages, dependencies and handover documents listed.
Common questions
Is a KfW loan the same as a discount on the installation?
No. Borrowing changes how the project is paid for; it does not remove the need to repay it. Compare the installed price and the financing schedule separately, including interest and any relevant charges.
Should a planned heat pump justify a larger solar array?
It can change the design brief, but use a seasonal demand estimate. Much of a heat pump’s heating demand occurs when solar output is lower. Ask to see the combined monthly model.