1. Survey the roof before placing modules
Record membrane condition, insulation, drainage, equipment, shading and access. Check planned roof work and mounting compatibility with the materials. Preserve maintenance routes and service points. The maximum number of panels drawn on the gross roof area does not establish a feasible project.
2. Compare south-facing and east-west options consistently
Request capacity, footprint, tilt, spacing and monthly generation for each option. Compare row shading and hourly output with your consumption. Distinguish kWh per installed kW, total roof generation and on-site use. Denser layouts do not guarantee better returns, and steeper tilt may be unsuitable.
3. Have mounting and loads calculated
Have wind, snow, building geometry, edge zones and roof capacity assessed. Request a mounting and ballast plan for the chosen system. Mounting without penetrations may require ballast; anchored mounting needs weatherproofing and load transfer. Neither an average weight per panel nor a module rating replaces project calculations.
4. Plan approvals and future access
Confirm notification or permission requirements for the layout, visibility and building status. A flat roof does not create an automatic exemption. Include work safety and future maintenance access in the quote. Compare total cost including protection, ballast, handling, roof adaptations, connection and handover records; specify responsibility for leaks or later dismantling.
References for planning your project
- Swissolar — wind, terrain and building geometry
- Swissolar — flat-roof procedures
- Swissolar — installation and maintenance safety
Decision framework
A verifiable decision, not an isolated estimate
Before comparing solutions, clarify the project assumptions, their sources and dates, and the responsibilities involved. Use your bill, roof plan and written responses to check that each quote covers the same needs.
Start with a measurable question
Start your solar decision with building data. Record the address, building type, relevant area, energy use and desired result. When assessing the design of solar panels on a flat roof, distinguish readings, written confirmations and assumptions. Compare gross and net amounts for the same scope; separate installed capacity from annual generation. Check grant conditions before deducting support from the budget. Prepare open questions for the installer, municipality, grid operator and insurer, identifying the record or measurement needed to answer each one.
Turn your bills into scenarios
Gather twelve months of bills if possible. Separate energy, network use, metering, taxes, levies and optional services. Include heating, hot water, EV charging and absences. An annual average can hide demand concentrated in mornings, evenings or winter. Compare conservative, central and favourable scenarios for a homeowner or condominium association comparing quotation scope. Keep units, scope and tariff dates consistent so that differences reflect the options being compared.
Check the roof and surroundings
Orientation, slope, chimneys, dormers, trees, antennas, snow, access, ventilation and neighbouring buildings affect solar generation. Ask for an aerial image, a dimensioned roof plan and a seasonal shading assessment. Have the roof covering, possible asbestos, structural capacity and cable routes assessed before committing to system capacity. A simulation for the design of solar panels on a flat roof should explain losses, show monthly generation and account for roof renovation or expansion before installation.
Compare quotes for the same scope
Three quotes are comparable only when they cover the same scope. Ask for the brand and exact model of each module, inverter, battery, protective device and mounting system. List scaffolding, distribution-board upgrades, grid connection, metering, applications, monitoring, maintenance, VAT and options separately. A lower price may exclude a service; a higher price may include a structural assessment or broader service terms. Identify who coordinates with the DSO and provides commissioning documents.
Check warranties and responsibilities
Product, performance and installation warranties, and insurance, cover different matters. Check duration, exclusions, beneficiary, claims procedure, response times and service arrangements if a manufacturer changes distributor. Keep invoices, serial numbers, photos, certificates, diagrams and handover records. The owner should retain access to the file documenting the dimensioned plan, load-bearing capacity, membrane, ballast, drainage and warranties, even if the installer or project manager changes. Identify who addresses sizing errors, water ingress, communication faults or substantial differences between simulated and measured generation.
Compare the full cost
Include purchase, installation, applications, maintenance, remaining grid purchases, inverter replacement, possible roof work and surplus revenue. For a battery, consider usable capacity, losses, cycles, backup reserve, temperature, software and replacement. For a contract, check subscriptions, price changes, credit validity and exit terms. For a grant, consider eligibility and payment timing. Test whether the decision remains affordable if feed-in tariffs fall, consumption changes or the project is delayed.
Prepare for commissioning and handover
Before work starts, request a list of tests and documents to be provided. These may include insulation measurements, protective-device checks, grid settings, backup settings, connector checks, circuit labels, monitoring access and meter readings. An app displaying data does not replace a complete technical handover. Ask for safe shutdown instructions, a service contact and the circuit diagram. A dated handover record supports warranty claims and comparisons between expected and measured generation, bills and consumption.
Plan for future electricity use
A heat pump, water heater, EV, home working, extension, tenant change or renovation can alter a home’s electricity use. Include planned changes in the simulation. Check whether the inverter, distribution board, communications, available space and grid connection allow realistic expansion. An open system can be more useful than a larger system with limited compatibility. For a homeowner or condominium association comparing quotation scope, assess how to avoid a second costly installation when needs change.
Keep the evidence organised
Keep annotated bills, plans, simulations, compared quotes, grant conditions, official applications, before-and-after photos, certificates, warranties and generation records in one file. Date each item because tariffs and programmes change. An undated screenshot cannot establish a contractual condition. Record the amount stated, the condition that applied and the person responsible. These records support budget checks, a future sale and discussions with the DSO, insurer or authorities.
Check the quote before signing
Before signing, check the description, address, owner, capacity, models, generation estimate, exclusions, prices, VAT, grants, schedule, handover, warranties and termination. Gather the relevant records: the dimensioned plan, load-bearing capacity, membrane, ballast, drainage and warranties. Request written answers to unclear points and identify who will resolve them. Keep the final quote, data sheets and contract terms together. A promised saving or equipment brand cannot replace the scope of work, calculation assumptions and service arrangements.
Use this section with your invoice, roof plan and quotes. The final decision must remain linked to the official conditions, the actual connection and the written contract.