Looking to retrofit your existing property with PV?
Great! But before you send the first installer onto the roof, structured preparation is worthwhile. This checklist will help you not to forget anything – from planning to cable routing.
✅ Step 1: Check the 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 replacing in 10 years, it's better to do it at the same time now.
- Are there already slate, trapezoidal sheets or special tiles? Then the attachment 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's output.
- Tip: Tools like Google Project Sunroof or pvgis.ec.europa.eu provide an initial yield estimate.
✅ Step 3: Clarify inverters and meters
- Does your meter cabinet 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 your grid operator.
- Registration with the grid operator before commissioning – don't forget!
✅ Step 4: Plan the cable route
The cable route from the module to the inverter is one of the most critical points when 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 strain relief: immediately after the penetration, the cable must be fixed.
✅ 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 penetration
- Cable clamps and strain relief for the interior
- Roof hook set and mounting rails for module attachment
✅ Step 6: Who does what?
Cable laying and module installation: depending on your DIY skills, possible as a do-it-yourselfer. Electrical connection, commissioning, registration with the grid operator and feed-in contract: in Germany, this must be carried out by an approved electrical specialist.
Conclusion
A PV retrofit is not rocket science – but it needs to be well planned. If you go through the checklist point by point, you will save yourself rework later 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.
