Calculator
Export Limitation and Curtailment Loss Calculator
Network operators increasingly grant connections on condition that export never exceeds a set limit. Owners assume that a 5 kW limit on a 10 kWp array halves their income. It rarely does: the array only exceeds the limit for a small number of hours in the middle of the brightest days.
This calculator estimates the clipped energy, its value, and how much of it a battery or a shifted load could recover.
Enter the connection constraint
Real peak after thermal and inverter losses.
Unconstrained annual generation
14,000 kWh
Realistic peak AC output
8.5 kW
Headroom before clipping
5.6 kW
5 kW export plus 0.6 kW of site load
Energy lost to the export limit
2,728 kWh/yr
19.5% of generation
Value of that loss
€218
At the export price entered
Recovered by the battery
No battery entered
Residual loss after storage
2,728 kWh/yr
How the calculation works
Clipping only occurs when instantaneous output exceeds the export limit plus whatever the site is consuming at that moment. Because a fixed array spends most of the year well below its peak, the clipped area under the curve is much smaller than the ratio of limit to capacity suggests.
Real peak output is typically 80 to 88% of nameplate after thermal losses, inverter conversion and the fact that 1,000 W/m² rarely occurs at the plane of the array outside a few hours. That alone absorbs part of the constraint.
Site load raises the effective ceiling. A 0.6 kW baseline consumption means a 5 kW export limit permits 5.6 kW of generation before anything is lost, which is why shifting loads into the middle of the day is the cheapest curtailment mitigation available.
A battery charging during the clipped hours converts lost export into avoided import, which is worth considerably more per kilowatt-hour than the export would have been.
The formula
P_peak = P_kWp × k_peak Headroom = P_limit + P_load r = Headroom / P_peak f_clip ≈ 0 for r ≥ 1, else 1.35 × (1 − r)^1.8 E_clip = E_annual × f_clip Recovery = min(E_clip, C_battery × cycles_effective)
Assumptions behind the numbers
- The clipping fraction is an empirical fit for fixed south-facing arrays in mid-latitudes. Tracking arrays and east-west layouts clip differently and need hourly simulation.
- Site load is treated as constant through daylight hours, which understates the benefit for sites with a genuine midday load.
- Battery recovery assumes about 250 effective charging days on clipped energy, which is optimistic in northern climates and conservative in southern ones.
- Dynamic export limitation with fast metering is assumed. Fixed inverter derating to the limit is cruder and clips more.
- No network curtailment instructions beyond the static limit are modelled.
How to read the result
A limit at 50% of array capacity typically costs 4 to 8% of annual generation, not 50%. That is why accepting a constrained connection is usually better than waiting years for a reinforcement.
Because clipped energy would only have earned the export price, its value is low. The same energy stored and self-consumed is worth the import price, so a battery converts a cheap loss into an expensive saving — which is the strongest economic argument for storage on a constrained site.
Before buying storage, shift controllable loads. Running the immersion heater, dishwasher, pool pump or EV charger at midday costs nothing and eliminates part of the clipping directly.
Worked example
A 10 kWp array yielding 1,400 kWh/kWp is granted a 5 kW export limit, with 0.6 kW of average daytime site load and a realistic peak of 85% of nameplate.
Peak output is 8.5 kW against 5.6 kW of headroom, a ratio of 0.66. The empirical fit gives a clipping fraction of about 1.35 × 0.34^1.8 = 0.19 — around 19%, or 2,660 kWh a year, worth €213 at €0.08/kWh export.
Adding a 10 kWh battery recovers up to 2,500 kWh of that, and because it displaces imports at €0.26/kWh rather than exports at €0.08/kWh, the recovered energy is worth about €450 a year rather than €200. The constraint turns a marginal battery case into a good one.
Mistakes that skew the answer
- Assuming the percentage loss equals the percentage by which the limit falls below array capacity.
- Using nameplate DC capacity as the peak output, which overstates clipping by 15 to 20%.
- Ignoring site load, which for a commercial building can be larger than the export limit itself.
- Valuing clipped energy at the retail tariff. It would have been exported, so the export price is the correct comparison.
- Installing a battery sized to the annual clipped energy rather than to the daily clipped energy, which leaves most of it unused.
Questions readers ask
- How much does an export limit cost me?
- For a typical residential array with a limit at half of capacity, 4 to 10% of annual generation. The loss grows steeply once the limit falls below about 40% of realistic peak output, and is close to zero above 85%.
- Should I install a smaller array to match the limit?
- Almost never. The extra capacity still produces fully in the morning, evening, winter and on cloudy days — precisely when the limit is not binding. Oversizing against an export limit is standard practice.
- How does export limitation work technically?
- A meter at the point of connection measures net export and signals the inverter to reduce output when the limit is approached. Static configuration simply caps the inverter, which clips more; dynamic control uses the real-time measurement and preserves the site-load headroom.
- Does a battery always fix curtailment?
- It fixes the part that occurs while the battery has capacity. On a bright summer day the battery fills by early afternoon and the array clips for the rest of the day. Sizing to the daily clipped energy, not the annual figure, is what determines how much is recovered.
- Can I ask the network operator for a higher limit?
- Yes, and it is worth doing. Limits are often set by a standard rule rather than a site study. Where a study shows the local network can accept more, operators frequently raise the limit, sometimes for a connection fee far below the cost of storage.