Compare Offers · Chapter 15
Comparing offers honestly: the scope-honesty method
Why solar offers are deliberately hard to compare — and how to bring them onto the same scope.
Collect several PV and heat-pump offers and you notice fast: you can't just lay them side by side. One vendor includes something the next lists as an option. The battery sits in a different chapter from the PV array. The meter cabinet shows up sometimes as a full rebuild, sometimes as a minor upgrade. That's not an accident — it makes comparison hard.
This piece shows the method for bringing offers fairly onto the same scope.
Why offers aren't comparable
Offers are often structured so a direct comparison is nearly impossible:
- Some bundle items others list as an option (roof integration/metal tiles, backup, extra battery modules).
- PV and battery sit in separate chapters — both must go into the total.
- The meter cabinet scope varies enormously (a full new cabinet vs. a mere §14a modernisation of the existing one).
The principle: normalise to the same scope
Before you compare, bring every offer onto the same scope. Treat optional add-ons (metal tiles, backup, extra battery modules) consistently — either in every total or in none, and state which you did.
The most common real errors
All of these actually happened in a real project:
- Battery not summed into the PV total (because it sat in its own chapter).
- Roof tiles/backup counted as "included" when they were optional line items — in one case a ~€2,400 swing.
- Meter cabinet: one vendor builds a complete new 2-field cabinet; another only §14a-modernises the existing one. With old cabinets (e.g. from 1972) that can be €1,350–4,200. It's a major hidden difference.
- Wallbox: device included vs. only the connection — about €1,200 difference.
And: verify OCR-extracted numbers visually against the source PDF — digits get misread.
The comparison system
- Keep one canonical spreadsheet: a tab per vendor plus a shortlist tab with identical criteria rows across all columns.
- Add new vendor columns rather than overwriting existing ones (preserve history) — except when an offer is explicitly superseded by a renewed one.
- Structure the shortlist tab in sections: PV prices → PV tech → HP prices → HP tech → total cost → service/risk → verdict. Use colour (green = good, amber = clarify, red = risk).
- Compute effective cost = gross − subsidy on the same scope. State every assumption.
Clarify and negotiate
- Have scope-critical points put in writing into the order confirmation — standard terms often say datasheet figures are "descriptive, not guaranteed."
- Watch contract wording that caps flat-rate positions at a smaller system size than actually planned (e.g. "up to 15 kWp" when the array is 17.6 kWp) — a surcharge loophole.
- Mind the signature sequence: e.g. don't give up the 14-day cancellation right before the scope-critical points are confirmed.
Bottom line
The lowest headline price is rarely the honest comparison. First bring every offer onto the same scope — options treated consistently, battery included, meter cabinet compared explicitly — then compute effective cost. The ranking often flips once the scope is right.
A separate article provides the comparison template (Excel) as a download.