ROI Calculator — a payback estimate you can quote in the first call

The ROI Calculator gives a homeowner a 20-year payback picture from three numbers: monthly bill, roof orientation, and postcode. Useful the moment the conversation turns to “is this worth it?” — quote payback years and lifetime savings before you’ve measured a thing.

When to use it

On a first phone call, a walk-in enquiry, or a follow-up on a website lead — any time you have the customer’s rough monthly bill and a postcode. Answerable in under a minute, and the numbers hold up well enough to set realistic expectations.

Not a substitute for a real quote — this is a sizing-and-framing tool; the Quote Generator is where a customer-ready price lives.

How to run it

1. From your sidebar, open Pre-Sales Tools → ROI Calculator.
2. Fill in average monthly electricity bill (€), roof orientation (South ★ best / South-East / South-West / East / West / North), and optionally your postcode.
3. Click Calculate My Solar ROI — results appear immediately below.

What the result tells you

• Payback years — how long before cumulative savings equal system cost. Sunny orientations on a bright postcode pay back faster.
• Annual savings — a first-year figure combining self-consumption savings (~70% of generation, no battery) and export credit under Greek net billing (Law 4685/2020).
• 20-year lifetime savings — first-year savings extrapolated with 0.5%/year panel degradation.
• Recommended system size — sized to cover about 80% of annual consumption, capped at 10.8 kWp for single-phase connections (Greek regulatory limit).

How the estimate is built

The tariff is genuinely live and per-country — it fetches your country’s current electricity rate from a Eurostat-backed feed, falling back to a stored default (€0.20/kWh for Greece) if the feed is temporarily unreachable.

The postcode, orientation, sizing cap, and install cost figures are Greek-calibrated today, applied regardless of your country. A Greek irradiance table is keyed by the first digit of the postcode — Attica around 1,620 kWh/kWp/yr, Central Greece around 1,650, Crete up to 1,750, the North closer to 1,550. Leave the postcode blank and it falls back to a nationwide average (1,580), fine for a first-pass conversation but off by roughly -8% to +11% depending on the actual zone. Outside Greece, treat these figures as a rough analogue, not a locally-calibrated number.

Orientation applies a multiplier to that irradiance figure: South = 1.00, South-East / South-West = 0.95, East / West = 0.85, North = 0.65. That range alone can shift payback by two or three years.

Install cost is all-in — components, labour, permits, grid connection. The tool uses €1,300/kWp installed, intentionally higher than the Cost Estimator’s Standard-tier total because it includes the permit + connection fees the other tool doesn’t.

Difference from Bill Savings and Solar Potential

• solar-potential answers “will the roof work?” from just the address.
• ROI Calculator answers “how long before it pays back?” from a bill + roof + location.
• bill-savings answers “what does the annual bill drop to?” with editable, live tariffs.

Reach for whichever question the customer is actually asking.

Where to go from here

• The full pre-sales toolkit: pre-sales-tools-overview
• If you have the address before the bill: solar-potential
• If the customer wants a savings-per-year framing instead: bill-savings