HomeBackup & Solar
Plan your backup power

Free backup & solar calculators

Work out inverter size, battery backup time and solar capacity using your appliance load and clear loss settings.

9free calculators100%formulas shown
Recommended starting point

Home Electrical Load Calculator

Start with the appliances that must run during a power cut.

Start here
A simple decision path

From appliance load to backup time

  1. Choose the question that matches your decision.
  2. Replace every example with a label, bill, drawing, product sheet or record value.
  3. Open the formula and check all hidden assumptions.
  4. Save or print the result, then verify the final decision.
Which tool should I use?

Match your question to a calculator

Add running and starting loadHome load Choose inverter capacityInverter size Estimate battery runtimeBackup time Find required battery AhBattery capacity Plan solar array sizeSolar panel size
Know before you calculate

Three things to check first

Learn the terms, follow the method, then avoid the most common mistakes.

01
Common terminology

Words you will see

W
real power used by appliances.
VA
inverter capacity after power factor and margin.
Ah
battery charge capacity at a stated voltage.
02
Worked example

How the logic flows

A runtime estimate first finds nominal Wh, then applies usable depth of discharge and inverter efficiency before dividing by the connected watts.

03
Beginner mistakes

Check these first

  • Adding battery Ah without checking voltage.

  • Ignoring motor or compressor starting surge.

  • Treating theoretical runtime as a guarantee for an aged battery.

Detailed guides

Learn the method

Read the inverter and battery guide Understand 150 Ah backup time Compare watts, VA and Ah Explain lower real backup Browse every guide
Official verification links

Backup power and rooftop solar

These independent government and standards resources help you verify the inputs or decision. Inclusion is not an endorsement.

National Power PortalMinistry of Power, Government of IndiaUse the national portal for official power-sector data and reporting context.Open official resource PM Surya Ghar rooftop-solar portalGovernment of IndiaCheck the official residential rooftop-solar process, eligibility and portal services.Open official resource Grid-connected rooftop solar programmeMinistry of New and Renewable Energy, Government of IndiaRead official rooftop-solar programme context before making a project decision.Open official resource Approved solar PV models and manufacturersMinistry of New and Renewable Energy, Government of IndiaCheck the current ALMM information where it applies to the planned solar project.Open official resource Renewable-energy schemes and guidelinesMinistry of New and Renewable Energy, Government of IndiaVerify current scheme documents instead of relying on old subsidy summaries.Open official resource National Institute of Solar EnergyMinistry of New and Renewable Energy, Government of IndiaFind official solar research, training and resource information.Open official resource
Browse all 72 verified links
All tools

Choose a calculator

Working shownBackup & SolarHome Electrical Load Calculator

running and starting load for backup appliances

Open calculator Working shownBackup & SolarInverter Size Calculator

an inverter VA range from watts, surge, power factor and margin

Open calculator Working shownBackup & SolarBattery Backup Time Calculator

battery runtime with depth-of-discharge and inverter losses

Open calculator Working shownBackup & SolarRequired Battery Capacity Calculator

required Ah for a desired backup time

Open calculator Working shownBackup & SolarUPS Runtime Calculator

UPS runtime from its battery bank and actual load

Open calculator Working shownBackup & SolarInverter and Battery Combined Planner

inverter capacity and battery Ah in one joined workflow

Open calculator Working shownBackup & SolarSolar Panel Size Calculator

an array and panel count from daily energy and local peak sun hours

Open calculator Working shownBackup & SolarSolar Battery Size Calculator

a battery bank for daily solar-supported energy and autonomy

Open calculator Working shownBackup & SolarSolar Savings Estimator

first-year savings, simple payback and a ten-year scenario

Open calculator
Two-minute explanation

Inverter size and battery time are different

The inverter VA rating must handle the running load and starting surge. Battery Wh or Ah helps estimate how long that load can run after losses.

Common questions

Before you calculate

Why are watts and VA different?

Watts measure real power used by the load. VA is the inverter’s apparent-power rating and also depends on power factor, so the required VA can be higher than the running watts.

How does battery depth of discharge matter?

Depth of discharge is the share of stored battery energy you plan to use before recharging. A smaller usable share reduces estimated runtime but keeps the unused reserve visible.

Why is solar yield location-specific?

Sunlight, season, roof direction, tilt, shade, temperature and system losses vary by location. Enter a local peak-sun-hour or generation assumption instead of using one India-wide yield.