Photovoltaic (PV) Array Sizing Calculator

Dimensiona il tuo impianto fotovoltaico: potenza kWp, numero di moduli, superficie occupata, produzione annua stimata, autoconsumo, immissione in rete e risparmio economico. Formula standard EN 15316. Gratis, in 5 lingue.

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What a PV system is and how it works

A photovoltaic (PV) system directly converts solar radiation into electricity via the photovoltaic effect in silicon cells. It is the fastest-growing renewable technology worldwide: in 2024 installed global capacity exceeded 1500 GW, with Italy reaching 30 GW installed (2030 target: 80 GW). A residential 3-6 kWp system covers 3000-7000 kWh/year, the typical consumption of a 3-5 person family. With incentives (50% tax rebate, Superbonus 90% until 2025, Reddito Energetico 2024-2027), payback dropped to 5-8 years vs 25-30 years module lifetime (manufacturer 25-year warranty at 80% initial P_kWp). Calculating required kWp, modules and yearly production is the first project step: this calculator uses the EN 15316-4-6 standard method.

The base formula: E_year = P_kWp · H_year · PR

Yearly PV production is estimated by:

E_year = P_kWp · H_year · PR

where P_kWp is peak power (kW at STC: 1000 W/m², 25 °C, AM 1.5), H_year is yearly irradiation on the module plane (kWh/m²·year, typically 1300-2000 in Italy), and PR is the Performance Ratio (0.75-0.85 for well-designed systems). PR includes system losses reducing production vs theoretical:

  • Cell temperature: STC cells at 25 °C but in summer reach 50-70 °C; every +1 °C above 25 reduces power by 0.4-0.5% (−6-15% loss in summer).
  • Soiling: dust, dirty rain, leaves → −2-5% average.
  • DC cabling: voltage drop in DC cables → −1-3%.
  • Inverter: typical European efficiency 96-98% → −2-4%.
  • Mismatch: differences between series modules limit string to weakest → −1-3%.
  • Partial shading (chimney, tree, other buildings) → variable 0-30%.
  • AC cabling and transformer: −0.5-1%.

Example: 3 kWp system in Rome (H=1600 kWh/m²·year), PR=0.80 → E_year = 3·1600·0.80 = 3840 kWh/year.

Reverse sizing method

To size the system from consumption, invert the formula:

P_kWp = E_target / (H_year · PR)

Example: family of 4 with 3500 kWh/year consumption, central Italy site (H=1500 kWh/m²·year), PR=0.80 → P_kWp = 3500/(1500·0.80) = 2.92 kWp. Then compute number of modules: standard 425 W monocrystalline modules (2024): N = ceil(2920/425) = 7 modules, effective installed 7·0.425 = 2.975 kWp. Occupied area depends on module efficiency (kWp/m²): standard 200 W/m² module (η=20%) on 2.975 kWp needs 14.9 m². Premium 220 W/m² module: 13.5 m². Optimal orientation: south, tilt = latitude − 10° (Italy 30-35°). Deviations ±30° from optimal lose only 3-5%; pure east/west lose 15-20%.

Solar irradiation in Italy and worldwide

Geography is critical. Typical horizontal irradiation (kWh/m²·year):

  • Northern Italy (Milan, Turin, Bologna): 1200-1400.
  • Central Italy (Florence, Rome, Ancona): 1500-1700.
  • Southern Italy (Naples, Bari, Palermo): 1700-1900.
  • South Sicily/Sardinia: 1900-2000.
  • Alps: 1000-1300 (winter fog).

Optimally tilted plane (30-35° south) increases irradiation by 10-15%. From north to south of Italy production varies 30-40%: 3 kWp in Milan produces ~3300 kWh/year, Rome 4000, Palermo 4600. Data sources: PVGIS (Photovoltaic Geographical Information System, JRC), Meteonorm/NASA-SSE databases. For serious projects use PVGIS with precise GPS coordinates.

Technologies: mono-Si, poly-Si, thin film, TOPCon, HJT

  • Monocrystalline silicon (mono-Si): 2024 market standard, 20-23% efficiency (200-230 W/m²), uniform black colour, ~150-250 €/kWp supply price.
  • Polycrystalline silicon (poly-Si): obsolete, 90s-2010s tech, 15-17% efficiency, mottled blue. Practically extinct in 2024.
  • Thin film (CIGS, CdTe): 12-15% efficiency, low production cost, large surfaces (industrial). First Solar dominant US brand.
  • TOPCon (Tunnel Oxide Passivated Contact): 2022-2024 evolution of mono-Si, 22-24% efficiency. Replacing PERC.
  • HJT (Heterojunction): 23-24.5% efficiency, better temperature coefficient, cost +10-20%. Premium installations.
  • Bifacial modules: capture light also from back (ground albedo, white roof), +5-15% production.
  • Perovskite tandem: lab 30%+ efficiency, industrial production 2025-2027. Expected revolution.

Self-consumption, batteries and Energy Communities

Self-consumption factor (production share used directly at home) is crucial for profitability:

  • No batteries: typical self-consumption 25-35% (peak production at noon vs peak consumption morning/evening).
  • Appliance timers (washer/dishwasher programmed at noon): rises to 35-45%.
  • With battery storage (5-10 kWh): rises to 60-80%.
  • With EV daytime charging: rises to 70-90%.

Non-self-consumed energy goes to the grid. Compensation mechanisms (2024 Italy):

  • Scambio sul Posto (SSP) — abolished 2024 for new systems.
  • Ritiro Dedicato (RID): GSE buys injected kWh at market PUN + bonus, typically 0.08-0.15 €/kWh.
  • Renewable Energy Communities (CER): shared incentives up to 120 €/MWh (D.M. 414 07/12/2023).
  • Superbonus 90-70-65%: finances integrated system with boiler/insulation up to 48,000 €/unit.

Production curve: hourly, seasonal, degradation

  • Hourly: starts 6-7 AM (east), peak at solar noon (13:00 CEST summer), ends 19-20. Symmetric bell curve with peak = P_kWp · 0.7-0.9.
  • Seasonal: max May-July, min Dec-Jan. Summer/winter ratio in Italy: 3-4:1.
  • Temperature effect: −0.4%/°C coefficient, at 50 °C −10% vs STC. Summer high theoretical but 10-15% real reduction from heat.
  • Module degradation: −0.5-0.7%/year for silicon (25-year warranty at 80% initial P_kWp). Total 15-20% loss after 25-30 years.
  • Maintenance: module cleaning 1-2×/year (deionised water + soft brush). Connection check every 3-5 years. Inverter replacement after 10-15 years.

How to use the calculator

Enter yearly electricity consumption in kWh/year to cover (from bills: 2500-4000 residential, 5000-10000 with heat pump + EV, 20000+ commercial). Enter yearly module-plane irradiation in kWh/m²·year (use PVGIS: 1300-1400 north, 1500-1700 central, 1800-2000 south Italy). Choose Performance Ratio (0.80 default new standard system; 0.75 partial shading; 0.85 premium well-oriented). Choose module efficiency in kWp/m² (0.20 standard 200 W/m²; 0.22 premium HJT) and single module nominal power (425 W 2024 standard; 500 W large roof). Set self-consumption factor (0.35 no battery; 0.70 with storage). Enter grid energy price (0.25-0.35 €/kWh Italy 2024 residential) and export price (0.08-0.15 €/kWh RID). Calculator returns theoretical required power, number of modules, effective installed power, yearly production estimate, occupied area, yearly self-consumption, economic savings and assessment with system size classification.

Frequently Asked Questions

How much does a PV system cost and what is the payback?

Turnkey residential system 2024-2025 in Italy: 1300-1800 €/kWp for 3-6 kWp without batteries. With 50% tax rebate net cost 650-900 €/kWp. A 3 kWp costs ~4500 € (net 2250 €), produces ~3600 kWh/year, savings 500-700 €/year. Payback 4-8 years with rebate, 10-14 without. With battery (~500-700 €/kWh installed) self-consumption rises to 70% and profitability improves. System life 25-30 years.

What is Performance Ratio and how to estimate it?

Performance Ratio (PR) is the ratio between actual produced energy and theoretical (STC nominal applied to real irradiation). Standardised by IEC 61724-1. PR = 1 would mean no losses (impossible). Typical values: 0.85-0.90 utility-scale; 0.80-0.85 good residential on well-oriented roof; 0.75-0.80 standard residential; 0.70-0.75 suboptimal; < 0.70 problem system.

Mono or poly modules?

In 2024 it's essentially only monocrystalline. Polycrystalline modules (mottled blue cells, 90s-2010s tech) have practically disappeared: lower efficiency (15-17% vs 20-23%), no longer cheaper. Monocrystalline dominates with uniform black cells, 20-23% for standard PERC and 22-24% for TOPCon/HJT (new 2023+ technologies).

Do I need battery storage? How much does it cost?

Depends on usage/goals. With SSP abolished in 2024, injected energy is less remunerated (0.08-0.15 €/kWh vs 0.25-0.35 €/kWh saved with self-consumption). Storage raises self-consumption from 30-35% to 60-80%. LiFePO4 lithium battery 5-10 kWh usable: 500-700 €/kWh installed, so 3000-6000 € for 6 kWh. Life 5000-8000 cycles = 15-20 years. Battery-specific payback: 8-12 years. Worth it if: (1) > 4000 kWh/year; (2) evening consumption peaks; (3) incentives cover storage too.

Do I need authorisation to install?

In Italy 2024: PV on existing buildings up to 200 kW needs only Simplified Single Communication (GSE model, notice to Municipality and grid operator). No DIA/SCIA for flat-roof residential. Ground-mounted or > 200 kW: PAS or Autorizzazione Unica. Historic centres and landscape constraints may need landscape authorisation: 2023 D.L. 13/2023 simplified many cases.

How to size the inverter vs modules?

Rule: P_inverter = 0.85-1.10 · P_modules. If P_inv < P_mod (10-15% undersize, e.g. 3 kWp modules with 2.5 kW inverter): inverter clips at noon, losing 1-3% yearly energy but saving cost. If P_inv ≈ P_mod: neutral standard sizing. European inverter efficiency: 96-98%. Inverter life 10-15 years vs 25-30 modules: must be replaced at least once.

Does calculator work for ground/industrial PV?

Yes, same formula. Changes only: (1) Higher PR (0.85-0.90) thanks to free optimal orientation, no shading; (2) Very low self-consumption (5-20%) as daytime consumption rarely matches production; (3) Trackers (single-axis increases production 20-30%); (4) Longer authorisation (PAS 90 days, VIA/VAS in constrained zones). Industrial > 20 kW: different energy compensation (direct PUN or PPAs). Renewable Energy Communities allow sharing energy with nearby consumers with incentives up to 120 €/MWh on shared energy.

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