Want to retrofit your existing property with PV?
Good for you. But before you put the first screw on the roof, a structured preparation is worthwhile. This checklist will help you not to forget anything – from planning to cable routing.
✅ Step 1: Check roof condition
- Is the roof structure suitable for the weight of the modules? (Rule of thumb: approx. 15–25 kg/m²)
- How old is the roofing? Modules last 25+ years – if the roof needs to be replaced in 10 years, better do it at the same time now.
- Are there already slate, trapezoidal sheet metal, or special tiles? Then fastening and penetration require particular care.
✅ Step 2: Analyze orientation and shading
- South, southwest, or southeast: optimal. East/west: possible with a slight loss of yield.
- Chimneys, trees, neighboring buildings: How much shade falls on the planned area? Even 10% shade on one module can significantly reduce the string.
- Tip: Tools like Google Project Sunroof or pvgis.ec.europa.eu provide an initial yield estimate.
✅ Step 3: Clarify inverter and meter
- Does your meter box have space for the inverter? (Wall mounting, proximity to the feed-in point)
- Does your meter need a reverse lock or a new bidirectional meter? → Ask the grid operator.
- Registration with the grid operator before commissioning – don't forget!
✅ Step 4: Plan cable route
The cable route from the module to the inverter is one of the most critical points in retrofitting:
- Where does the cable pass through the roof skin? This point must be absolutely sealed.
- Are there sharp edges (tile edges, roof battens, sheet metal edges) along which the cable runs? Mechanical protection is mandatory here.
- Is the cable route protected indoors (no UV, no frost) or does a part run along the outside of the building? Outdoor cables require UV-resistant cable protection.
- Plan for strain relief: the cable must be fixed immediately after the penetration.
✅ Step 5: Procure materials
- PV cable (H1Z2Z2-K) in the correct length – always plan for a buffer
- MC4 connectors or compatible connectors
- Cable gland with abrasion protection for the roof point
- Cable clamps and strain relief for the interior
- Roof hook set and mounting rails for module fastening
✅ Step 6: Who does what?
Cable laying and module installation: depending on your DIY skills, this can be done by a homeowner. Electrical connection, commissioning, registration with the grid operator, and feed-in contract: in Germany, this must be carried out by a licensed electrical company.
Conclusion
PV retrofitting is not rocket science – but it needs to be well planned. Anyone who works through the checklist point by point will save themselves later rework and ensure that the system runs safely and efficiently from day 1.
You can find the right cable glands with abrasion protection for your pitched roof in the NEXCAPE® shop.
For safe, abrasion-protected cable routing through the tiled roof: View NEXCAPE PV cable glands.
