Calculating your solar PV savings in Ireland before you buy is essential — not just for knowing whether solar makes financial sense, but for evaluating installer quotes and avoiding inflated projections. This guide walks you through the complete calculation methodology, with worked examples for different Irish household scenarios.
Step 1: Estimate Your Annual Solar Output
Your system’s annual electricity generation depends on:
- System size (kWp)
- Location (county — affects annual irradiance)
- Roof orientation (south, SE/SW, east, west)
- Tilt angle (typically 30–40° for Irish pitches)
Use this table to estimate kWh output per kWp for your location and orientation:
Tipperary, Kilkenny, Carlow
Roscommon, Sligo, Leitrim
Formula: Annual Output (kWh) = System Size (kWp) × Specific Yield (kWh/kWp)
Example: 4 kWp system, south-facing, Dublin → 4 × 950 = 3,800 kWh/year
Step 2: Estimate Your Self-Consumption Rate
Self-consumption is the proportion of your generated solar electricity that you use yourself (rather than exporting). This is the most important variable in your savings calculation.
Self-Consumption Rate (Without Battery)
Retired couple (home most of day)
Family with children (home after school)
Two adults with EV charging from solar
Single person, home in evenings
Formula: Self-Consumed kWh = Annual Output × Self-Consumption Rate
Example: 3,800 kWh × 45% = 1,710 kWh self-consumed
Step 3: Calculate Bill Savings from Self-Consumption
Your self-consumed solar electricity replaces grid electricity at the current blended import rate.
Ireland’s 2026 blended household electricity rate (including all taxes, levies, and standing charges, averaged to per-kWh equivalent): approximately €0.28–€0.33/kWh depending on supplier and plan. Use €0.30/kWh as a reasonable mid-point.
Formula: Annual Bill Saving = Self-Consumed kWh × €0.30
Example: 1,710 kWh × €0.30 = €513/year
Step 4: Calculate MSS Export Income
Your exported electricity (output not self-consumed) earns the MSS Clean Export Guarantee rate.
Formula:
- Exported kWh = Annual Output × (1 – Self-Consumption Rate)
- Export Income = Exported kWh × MSS Rate (€0.20/kWh typical in 2026)
Example:
- Exported: 3,800 × 55% = 2,090 kWh
- Export income: 2,090 × €0.20 = €418/year
Step 5: Total Annual Financial Benefit
Total Annual Benefit = Bill Savings + Export Income
Example: €513 + €418 = €931/year
Step 6: Calculate Net Investment and Payback
Net Investment = System Cost – SEAI Grant
Simple Payback (years) = Net Investment ÷ Total Annual Benefit
Example: €8,200 ÷ €931 = 8.8 years simple payback
Step 7: Account for Electricity Price Escalation
Electricity prices in Ireland have historically risen faster than general inflation. If you assume 3% annual electricity price escalation, your annual savings grow each year. This significantly improves the true payback period.
Cumulative benefit with 3% annual escalation (4 kWp, Dublin example):
Net 25-year return (after €8,200 net investment): €26,238 — a very strong return on a 25-year asset.
Complete Worked Examples for Three Household Types
Example A: Retired Couple, Wexford, 3 kWp
- Annual output: 3 kWp × 1,000 kWh/kWp = 3,000 kWh
- Self-consumption: 65% (home most of day) → 1,950 kWh
- Exported: 35% → 1,050 kWh
- Bill savings: 1,950 × €0.30 = €585
- Export income: 1,050 × €0.20 = €210
- Total annual benefit: €795
- Net investment: €5,700 (€7,500 cost – €1,800 grant)
- Simple payback: 5,700 ÷ 795 = 7.2 years
Example B: Family of 4 with EV, Dublin, 6 kWp
- Annual output: 6 kWp × 950 kWh/kWp = 5,700 kWh
- Self-consumption: 60% (EV charging + diverter) → 3,420 kWh
- Exported: 40% → 2,280 kWh
- Bill savings: 3,420 × €0.30 = €1,026
- Export income: 2,280 × €0.20 = €456
- Total annual benefit: €1,482
- Net investment: €12,200 (€14,000 – €1,800)
- Simple payback: 12,200 ÷ 1,482 = 8.2 years
Example C: Two Adults, 9-to-5 Jobs, 4 kWp + Battery, Cork
- Annual output: 4 kWp × 1,020 kWh/kWp = 4,080 kWh
- Self-consumption with battery: 75% → 3,060 kWh
- Exported: 25% → 1,020 kWh
- Bill savings: 3,060 × €0.30 = €918
- Export income: 1,020 × €0.20 = €204
- Total annual benefit: €1,122
- Net investment: €13,700 (€15,500 solar+battery – €1,800 grant)
- Simple payback: 13,700 ÷ 1,122 = 12.2 years
The battery adds roughly 4 years to payback but significantly improves self-sufficiency and is particularly valuable as electricity prices rise.
Using PVGIS for Precise Output Estimates
For a precise output estimate using meteorological data for your exact location:
- Go to re.jrc.ec.europa.eu/pvg_tools/en/
- Enter your location (GPS or address)
- Set mounted technology: crystalline silicon
- Set system loss: 14% (typical for Irish systems)
- Set installed capacity: your kWp
- Set slope: your roof pitch in degrees
- Set azimuth: your roof orientation (0° = south)
- Run calculation → get monthly and annual production data
PVGIS data is calibrated to satellite-measured irradiance — it’s far more accurate than a sales-generated estimate.
Red Flags in Installer Savings Estimates
When reviewing installer-provided savings projections, watch for:
- Self-consumption rate above 60% without a battery and 9-to-5 household — unrealistic
- Electricity price assumed above €0.35/kWh today — inflated baseline
- Export rate not clearly stated — should specify MSS CEG rate, not a hypothetical future rate
- No weather adjustment for your specific location — a Dublin estimate using Cork irradiance overstates output by 5–10%
- No system losses included — professional models use 14–18% total system losses
Always ask for the annual kWh output figure that the projection is based on. Then compare it to PVGIS output for the same system specifications. If the installer’s figure is more than 10% above PVGIS, question it.
