Use this estimate to discuss system size. A site survey is needed for a quotation and installation design. Use a bill from before solar installation. Sites with an existing solar system need a separate assessment. The model uses daily averages. Hourly demand and sunlight will affect energy coverage, bills and whole-home backup capability.
Electricity use The calculator divides your bill by the average unit rate, or uses the actual kWh entered. It divides the result by the billing days and applies your day/night split. The default 4.50 THB/kWh is a modelling assumption. Use billed kWh for time-of-use tariffs or commercial bills with demand charges.
Solar panels For on-grid, divide the daytime energy target by the net daily yield per kWp. For hybrid, first add nighttime energy divided by 90% round-trip storage efficiency. Round the panel count up to the next whole panel. The default net yield of 4.0 kWh/kWp/day already includes PV losses.
Battery Rated capacity (kWh) is the nighttime energy target divided by depth of discharge and by 95% discharge efficiency, rounded up to the next kWh. This is total capacity. Check the battery model, unit count, state-of-charge range, warranty and allowances for ageing or multi-day outages separately.
Inverter Divide array capacity by the DC/AC ratio and round up to an example inverter rating. For backup loads, use the higher of this result and the backup load plus 20%. Confirm available models, approved grid connection, phases, MPPT limits, PV voltage and current, battery charge/discharge power, starting currents and utility requirements before installation.
A standard on-grid system shuts down during a power cut. A hybrid system needs a compatible backup circuit and equipment to keep loads running during an outage. This calculation estimates how much solar energy can be shifted to nighttime use.
Further reading Battery capacity and power — energy.gov.au · PV array and inverter sizing — SAM / PVWatts · Energy estimates and their limitations — EGAT
This calculator uses a simplified in-house model. It does not call the PVWatts API, and the organisations listed above have not certified its results.
