Project Inputs
Use the form to estimate how much solar energy is used on-site versus exported.
Formula Used
PV generation: PV_gen = system_size × specific_yield.
Direct self-use: PV_direct = min(PV_gen, annual_load × daytime_share).
Surplus: Surplus = max(0, PV_gen − PV_direct).
Battery PV into storage (annual approximation): PV_batt_in = min(Surplus, battery_kWh × 365 × cycles/day × usable_fraction).
Battery delivered to loads: Batt_to_load = min(remaining_load, PV_batt_in × round_trip_eff × inverter_eff).
Export: PV_export = max(0, PV_gen − PV_direct − PV_batt_in).
Self-consumption rate: SCR = (PV_direct + PV_batt_in) / PV_gen.
Self-sufficiency rate: SSR = (PV_direct + Batt_to_load) / annual_load.
How to Use This Calculator
- Enter the PV size and a realistic annual yield for your location.
- Add the site’s annual electricity use and daytime share.
- If you have storage, enter battery capacity and efficiencies.
- Set tariffs and O&M to estimate annual savings and revenue.
- Press Calculate to view self-consumption, export, and benefits.
- Use CSV or PDF to attach results to project documentation.
Professional Notes
Self-consumption and export drivers
Self-consumption is the share of photovoltaic generation used on-site rather than exported. It depends on the overlap between production hours and demand. Construction sites often show strong daytime activity from offices, tools, and ventilation, which increases direct use. When generation exceeds instantaneous demand, the surplus becomes export unless storage or flexible loads are available.
Load profiling for site planning
Accurate inputs start with a simple load profile. Use meter data where available, or estimate annual energy from equipment schedules and duty cycles. The daytime load share is a practical proxy when hourly data is missing. If temporary loads vary by phase, run scenarios for excavation, structure, and finishing to see how self-sufficiency changes with staffing and machinery.
Storage impact and realistic limits
Batteries raise self-consumption by shifting midday surplus into evening demand. The usable fraction reflects depth-of-discharge limits, while round-trip efficiency captures charge and discharge losses. Cycles per day represent how frequently the battery can be filled and emptied. Oversizing storage can reduce export, but may underutilize capacity if the site lacks consistent surplus or night load.
Tariffs, savings, and project economics
Financial benefit combines avoided imports and export revenue, minus annual operating costs. Import tariff drives savings because each self-used kilowatt-hour offsets grid purchases. Feed-in rates matter when export is high or tariffs are low. Keep units consistent and use conservative prices during early budgeting. For full feasibility, add capital cost, incentives, and financing to compute payback or net present value.
Documentation for construction stakeholders
Owners and contractors typically need transparent assumptions and repeatable outputs. Report PV generation, retained energy, export, and remaining imports, then explain which inputs are estimates versus measured values. Use the download files to attach results to tender documents, sustainability reports, or site energy plans. If emissions factors are required, confirm the chosen factor matches your grid accounting method. Consider adding a contingency range and note seasonal effects; winter production and site heating loads can shift these ratios significantly.
FAQs
1) What does self-consumption rate mean?
It is the portion of solar generation kept on-site, including energy routed into a battery. Higher values generally indicate less export and better alignment between production and demand.
2) What does self-sufficiency rate mean?
It is the portion of your annual electricity demand supplied by solar directly and by battery discharge. It indicates how much grid import remains after solar and storage.
3) Why is daytime load share important?
Without detailed hourly data, daytime share approximates how much demand occurs during solar hours. A higher share increases direct solar use and typically reduces exports.
4) Can I use this for temporary construction sites?
Yes. Enter expected annual energy and daytime share for the site phase. Run multiple scenarios if loads change across phases or if generator use reduces grid imports.
5) How should I set battery cycles per day?
Use 0.3–0.8 for light cycling and 0.8–1.2 for frequent cycling, depending on load shape and surplus. Overstating cycles can overestimate battery contribution.
6) Are the results suitable for final design?
They are best for budgeting and concept evaluation. Final design should use hourly simulation with real irradiance and load data, plus detailed inverter and battery constraints.
Example Data Table
| Scenario | PV size (kW) | Yield (kWh/kW/yr) | Load (kWh/yr) | Daytime share | Battery (kWh) | Self-consumption rate | Export (kWh/yr) |
|---|---|---|---|---|---|---|---|
| Office cabin, no battery | 5 | 1400 | 6000 | 45% | 0 | ~64% | ~2,500 |
| Same site, with storage | 5 | 1400 | 6000 | 45% | 7 | ~86% | ~1,000 |
| Higher daytime activity | 8 | 1300 | 12000 | 60% | 10 | ~78% | ~2,000 |
Values are illustrative. Your results will depend on load shape, climate, and system design.