Solar Export Limit Calculator

Calculator Inputs

Enter nameplate values and conservative loads.

PV array size (kWdc)

DC nameplate of installed PV modules.

Inverter AC rating (kWac)

Maximum continuous AC output capability.

Derate factor (0.50–1.05)

Accounts for temperature, wiring, soiling, and losses.

Inverter efficiency (%)

Use datasheet or tested commissioning values.

Minimum onsite load during peak (kW)

Conservative load helps prevent export exceedance.

Battery charge power at peak (kW)

Set to zero if no battery is charging.

Approved export limit (kW)

Export cap at the point of connection.

Peak sun hours (h/day)

Used for lost export energy estimates.

Days for estimate (1–31)

Planning window for monthly comparisons.

Planning note: Export control must match protection, metering, and approvals.

Example Data Table

Scenario	PV (kWdc)	Inverter (kWac)	Load (kW)	Export cap (kW)	Typical Interpretation
Small commercial retrofit	30	25	6	5	Set ceiling near load + cap; minor curtailment.
Warehouse with low daytime demand	120	100	12	0	Non-export requires strict controls and monitoring.
Site with battery charging window	80	60	10	15	Battery charging reduces export and curtailment risk.

Formula Used

PV AC Potential

P_AC,pv = P_DC · Derate · (η / 100)

Converts DC nameplate to expected AC output.

Available Inverter Output

P_avail = min(P_inv, P_AC,pv)

Limits output to inverter rating.

Net Export Without Cap

P_export = max(0, P_avail − P_load − P_batt)

Uses minimum load and battery charging as sinks.

Curtailment and Setpoint

P_curt = max(0, P_export − P_limit)
P_set = min(P_avail, P_load + P_batt + P_limit)

Keeps export at or below the approved cap.

Engineering note: This is simplified planning. Final settings must follow approved control logic, meter placement, and protection coordination.

How to Use This Calculator

Enter PV DC size and the inverter AC rating.
Set a derate factor and inverter efficiency from data.
Use a conservative minimum daytime load for compliance.
Add battery charging power if it absorbs PV energy.
Enter the approved export limit from the utility letter.
Optionally set peak sun hours for energy impact estimates.
Press Calculate to view results above the form.
Download CSV or PDF for project records and handover.

Export Limits and Grid Approvals

Export caps are often set by utility studies, transformer limits, or feeder constraints. This calculator helps translate an approved cap into a practical inverter output ceiling. It compares expected AC production against conservative minimum load and optional battery charging so commissioning teams can demonstrate compliance during witness testing. It supports non‑export modes and partial export agreements on shared services and generator interlocks.

Sizing Inputs for Construction Submittals

Use PV nameplate (kWdc), inverter rating (kWac), and a realistic derate factor that reflects temperature, wiring, and soiling. Enter inverter efficiency from the datasheet or site tests. The model then estimates PV AC potential and enforces the inverter limit, producing a defensible starting point for export control settings. Include a conservative minimum load from interval logs, not nameplate. Document assumptions in method statements.

Curtailment and Setpoint Interpretation

When net export exceeds the approved limit, the tool reports the required curtailment in kW and as a percentage of available output. The recommended setpoint equals load plus battery charging plus the export cap, capped by available inverter output. This value is useful for controller configuration and documentation. If load is uncertain, run scenarios for low and high demand periods during.

Energy Impact from Limiting Export

Peak sun hours allow a simple estimate of lost export energy. Daily and monthly lost kWh quantify the commercial impact of strict caps and can justify enabling battery charging windows, shifting loads, or resizing inverters. Treat these as planning values, then validate with measured interval data. A battery can absorb peaks, reducing curtailment hours significantly without changing grid approval.

Reporting for Handover and Compliance Records

The CSV download supports quick review in spreadsheets and inclusion in closeout packages. The PDF summary is suitable for site binders, inspectors, and client sign‑off. Save reports with revision dates, and re‑run after load changes, protection updates, or firmware adjustments to keep records aligned. Keep copies with as‑built drawings and commissioning checklists for audits later requests.

FAQs

What does “export limit” mean at the point of connection?

It is the maximum power allowed to flow from the site into the grid. The cap is typically stated in kW and enforced by inverter controls, metering, or a site controller.

How do I use minimum load in the calculation?

Enter the lowest realistic daytime load during peak solar hours. Using a conservative value reduces the risk of exceeding the approved export cap when occupants, processes, or HVAC cycles change.

Why include a derate factor and efficiency?

They convert DC nameplate to a realistic AC output estimate. Temperature, wiring, soiling, and conversion losses reduce deliverable power, which affects the net export and curtailment requirement.

What is the recommended output setpoint used for?

It suggests the maximum inverter output that keeps export within the cap after accounting for load and battery charging. Use it as a starting value for controller configuration and commissioning records.

How should I interpret the lost export kWh values?

They estimate energy that cannot be exported due to the cap, based on peak sun hours and days. Use them for planning and compare later against measured interval data for accuracy.

Can this replace formal utility studies or protection design?

No. It is a simplified planning tool. Final settings must match the approved interconnection agreement, protection coordination, metering layout, and site acceptance tests.

Meta and Tagline Checks

Meta description (25 words)

Calculate compliant solar export caps for site connections. Model inverter output, onsite demand, and curtailment settings. Generate reports to support commissioning, permits, and inspections today.

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Tagline (24 words)

Set export limits to meet utility approval quickly. Compare PV size, inverter rating, and loads. Download clear summaries and coordinate electrical work confidently onsite.