The Solar Thermal Storage Duration Estimator calculates how long usable stored heat can meet a steady thermal load after storage and delivery losses. It uses the storage system's thermal-energy capacity directly, so it works for water tanks, phase-change systems, and other media when capacity is known in thermal kilowatt-hours.
Designers and facility operators can use the estimate to screen overnight coverage, demand shifting, or short interruptions in solar collection. Actual duration depends on changing load, temperature limits, standby loss, and heat-exchanger performance.
Use capacity over the actual operating temperature range.
Exclude temperature reserve or inaccessible stored energy.
Account for heat exchanger, piping, and discharge losses.
Use the mean thermal power required during the storage-only period.
The result assumes that thermal demand stays at the entered level.
Usable stored heat = Storage capacity × Usable fraction
Delivered heat = Usable stored heat × Delivery efficiency
Storage duration (h) = Delivered heat (kWhₜₕ) ÷ Heat load (kWₜₕ)
The store begins fully charged, load and efficiencies remain constant, and time-dependent standby loss is represented only if included in the delivery-efficiency input.
The duration is a constant-load equivalent. Falling tank temperature or rising heat demand can shorten useful service before nominal energy is exhausted.
For final sizing, model temperature stratification, minimum delivery temperature, standby loss, charge/discharge power, and the hourly load profile.
Usable heat = 1,200 × 0.85 = 1,020 kWhₜₕ
Delivered heat = 1,020 × 0.90 = 918 kWhₜₕ
Duration = 918 ÷ 180 = 5.10 hours
Estimated coverage: 5.10 hours
The modeled storage can serve a constant 180 kW thermal load for about 5 hours and 6 minutes.
The duration is a constant-load equivalent. Falling tank temperature or rising heat demand can shorten useful service before nominal energy is exhausted.
Use a site- and system-specific value for the resource, efficiency, production, price, or load input that drives this calculation. Keep its time period and unit consistent with the other entries.
For final sizing, model temperature stratification, minimum delivery temperature, standby loss, charge/discharge power, and the hourly load profile.
A required denominator or physical quantity must be greater than zero, while percentage inputs must stay within their displayed limits. Reset restores the worked-example values.
Confirm site data, equipment specifications, system boundaries, applicable codes, and the time basis of every input. Use a detailed model and qualified professional review for final engineering or investment approval.