Solar Load Calculator

How to Use the Solar Load Calculator

Start by listing the appliances or electrical loads you want to include. Enter the quantity, rated power in watts and average hours of operation per day. Then set peak sun hours, system losses and the backup load/time if you need battery sizing. The results estimate connected load, daily energy consumption, PV capacity, inverter capacity and equivalent battery capacity.

Solar Load Calculation Formula

The basic energy calculation is applied to each appliance and then summed:

Daily energy (Wh) = Quantity × Power (W) × Operating time (h/day)

The calculator also derives monthly consumption from 30 days and annual consumption from 365 days. These are planning conversions rather than calendar-billing statements.

How Solar Panel Capacity Is Calculated

ToolVault converts daily energy into a PV power estimate using your peak-sun-hours and system-loss assumptions:

PV power (W) = Daily energy (Wh/day) ÷ [Peak sun hours × (1 − losses/100)]

The result is rounded upward to the nearest 10 W in the interface. This method treats peak sun hours as an equivalent daily solar-resource input; actual PV production also depends on orientation, temperature, shading, soiling and equipment performance.

How Inverter Size Is Estimated

The connected appliance load is multiplied by a 25% planning headroom factor, then rounded upward in 0.1 kW steps:

Inverter estimate (kW) = ceil[(Connected load × 1.25) / 100] ÷ 10

This is a simple connected-load estimate. Motor starting current, surge power, inverter efficiency and the inverter manufacturer's continuous/peak ratings can require a different final selection.

How Battery Capacity Is Calculated

The battery section starts with the backup load and required backup time:

Backup energy (Wh) = Backup load (W) × Backup time (h)

ToolVault then divides by the 80% usable-energy assumption and converts the resulting nominal watt-hours into amp-hours for 12 V, 24 V and 48 V systems:

Nominal battery energy = Backup energy ÷ 0.80
Battery capacity (Ah) = Nominal battery energy (Wh) ÷ System voltage (V)

The displayed capacity is then rounded upward to the next practical module value available in the calculator. Battery chemistry, inverter efficiency, temperature, ageing and manufacturer limits are not included in this simplified estimate.

Worked Example: Solar Load to PV and Battery

Suppose a small system has 5 LED bulbs at 10 W for 6 hours, 3 fans at 70 W for 8 hours and one 100 W TV for 5 hours.

Daily energy: (5 × 10 × 6) + (3 × 70 × 8) + (1 × 100 × 5) = 2,480 Wh/day = 2.48 kWh/day.

With 5 peak sun hours and 20% system losses, PV power = 2,480 ÷ [5 × 0.80] = 620 W. If the connected load is 360 W, the 25% headroom calculation gives 450 W, which rounds to a 0.5 kW inverter estimate.

For a 500 W backup load for 4 hours, backup energy = 2,000 Wh. With 80% usable energy, nominal battery energy = 2,500 Wh; at 48 V this is about 52.1 Ah, after which the calculator selects the next practical 48 V module value.

What Does the Solar Load Calculator Include?

The calculator covers appliance load estimation, daily/monthly/annual energy use, PV sizing from peak sun hours, a simple inverter headroom estimate and 12 V / 24 V / 48 V battery-capacity planning. It is intended for preliminary solar system sizing, not final electrical design.

Frequently Asked Questions

How do I calculate solar load?

Multiply each appliance's quantity, wattage and average daily operating hours to find its daily watt-hours, then add all appliances together.

How many solar panels do I need?

This calculator deliberately reports the required PV capacity rather than forcing one panel wattage. After choosing the panel wattage you plan to use, divide the required PV watts by that panel wattage and round up to a practical number of panels.

What are peak sun hours?

Peak sun hours are an equivalent daily solar-resource measure. They are not simply the number of daylight hours and should be selected from a reasonable site or location estimate.

Is the battery result a complete battery design?

No. It is an energy-based planning estimate. Final battery selection should also consider chemistry, depth-of-discharge limits, temperature, ageing, efficiency and the manufacturer's specifications.

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