Solar Panel Oversizing Calculator
Simulate the annual energy generation for solar panel systems that have a DC power rating far higher than the inverter AC capacity. Based on Met Éireann climate data from Gurteen, Co Tipperary for the full year of 2023. [Companion article]
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System Sizing & Return Breakdown
Detailed comparison of system sizes on your inverter setup. Active system highlighted in blue.
| Array Size | Delivered / Year | Inverter Utilisation | Annual Value | Marginal kWh / kWp | Marginal Payback |
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See How Much Your Roof Could Generate
Find out if your roof is suitable for solar panels and get tailored quotes for your home.
Calculate Your Quotes ➜Why DC Oversizing Works in Ireland
Ireland has an oceanic climate with frequent cloud cover and high levels of diffuse sunlight. Solar panels rarely operate under peak Standard Test Conditions (1,000 W/m² at 25°C). Most of our daylight arrives at modest irradiance levels between 100 and 500 W/m².
Under these conditions, a standard 5.5 kWp solar array produces only 0.6 kW to 2.2 kW, leaving plenty of hearoom from additional panels to contribute more useful power output. By installing 10 kWp of panels or more, your system generates substantially more usable electricity during overcast days, early mornings, late evenings, and the dark winter months, without reaching the inverter limit.
Understanding Inverter Utilisation & Capacity Factor
A solar inverter represents fixed capacity. If you connect a standard 5.5 kW array to a 5.5 kW inverter in Ireland, the inverter operates at a capacity factor of only around 10% to 11% across the year, sitting idle or lightly loaded for most hours.
Connecting over 12 kWp of panels boosts inverter capacity factor to 20%+, generating far more value from the sunlight falling on your roof. [Full discussion]
Calculation Details & Data Export
Half-Hour by Half-Hour Simulation
This calculator runs an electrical simulation across 17,520 half-hourly intervals using Met Éireann pyranometer and meteorological data recorded at the Gurteen Weather Station (County Tipperary, Central Ireland).
You can export the full 17,520-row simulation table for your chosen configuration as a CSV file:
Physical Modeling Methodology
1. Solar Geometry: Solar elevation and azimuth are calculated for each interval using standard NOAA solar equations for Gurteen (53.04°N, 8.01°W).
2. Plane-of-Array Irradiance: Met Éireann Global Horizontal Irradiance (GHI) is transposed to tilted roof surfaces using the Erbs diffuse decomposition model combined with isotropic sky and ground-reflection components.
3. Optical & Thermal Derating: The model applies ASHRAE incidence-angle modifiers (b₀ = 0.05) to account for reflection losses at oblique sun angles, dynamic NOCT cell temperature derating (-0.35%/°C above 25°C), and low-light efficiency fall-off (relative module efficiency η/η_STC = 1 + 0.045 log₁₀(G/1000)).
4. Inverter & Battery Simulation: Instantaneous AC power is evaluated against the specified inverter limit. When surplus DC power is generated and a DC-coupled battery is present, excess energy is absorbed up to the daily battery capacity limit before any remaining power is constrained.