Estimate what it takes to keep essential equipment running during an outage. Enter the average load, hours of backup and the amount of useful sun available for recharging. The calculator returns a first estimate for your battery and panels. Use it to explain what you need when asking a Botswana installer for a quotation.
Solar backup estimate
Estimate energy, nominal battery capacity and an array size for daily recharge. The starting values are examples. Enter your own site assumptions and ask an installer to check surge loads, equipment compatibility and the final design.
Start with the appliances you need to keep running
List the lights, router, computers, refrigeration or other equipment you want to run on backup. Write down each device’s running watts and the time you expect it to run. A device that cycles, such as a refrigerator, uses energy differently from a light that stays on for the entire outage. Use a plug-in meter where appropriate, or ask your installer to measure the load. Keep heaters, kettles and other large appliances off your essential-load list unless you need them on backup and can account for their demand.
The tool uses one average wattage. For appliances with different operating times, multiply each device’s watts by its hours, add those watt-hours together, and divide by the backup period to obtain an equivalent average load. Record which appliances might start together. Inverter sizing needs a separate check of simultaneous running load and starting surge, especially for motors, pumps and compressors.
Read the battery and solar panel estimates
Energy in kilowatt-hours equals average watts multiplied by backup hours and divided by 1,000. The nominal battery estimate divides that energy by the usable battery fraction and by the assumed system efficiency. The solar estimate divides the energy to replace each day by the peak sun hours and system efficiency. The tool uses the same efficiency input as a rough allowance in both calculations. An installer can use separate conversion, charging and storage losses for a more detailed design.
For a 500 W average load running for four hours, the devices use 2 kWh. At 85% efficiency and an 80% usable battery fraction, the result is about 2.94 kWh of nominal battery capacity. With five peak sun hours, the estimated array for replacing the 2 kWh is about 471 W. These are example inputs. The array result covers replenishing the energy used in the backup period. Add any daytime consumption the array must serve while charging, and discuss how quickly the battery must recover after consecutive outages.
Use site-specific assumptions for Botswana installations
Peak sun hours express useful sunlight as an equivalent number of hours at a standard intensity. Use a figure appropriate to your location and the month you want the system to cover. Roof direction, tilt, tree or building shade, dust and equipment temperature can change output. Check the roof or ground mounting area, the proposed battery location and the cable route. Ask your installer what happens if cloudy weather or a shaded array reduces the expected recharge.
Keep the equipment budget separate from the design. If a supplier quotes approximate unit costs, the optional price inputs give you a subtotal based on those assumptions. Compare that figure with an itemised quote for actual equipment, installation, protection, mounting, commissioning and any applicable taxes or approvals. Ask what warranty applies, who handles faults and whether batteries can be expanded later.
Send suppliers the same brief
Give each provider your town and site type, load list, expected backup duration, preferred recharge window and any existing equipment. Ask which loads the proposal covers and what is excluded. If the design is connected to the utility, ask the installer to confirm the applicable requirements with the utility and relevant authorities. A measured site survey and an agreed design give you a better purchasing basis than a rounded calculator number alone.
Frequently asked questions
What is the difference between watts and kilowatt-hours?
Watts measure power at a given moment. Kilowatt-hours measure energy used over time. A 500-watt load running for four hours uses 2 kWh.
Does the battery estimate tell me the inverter size?
The battery estimate covers energy capacity. Ask your installer to check the inverter against simultaneous running power and the highest starting surge.
Should I always use five peak sun hours in Botswana?
Five is an example input. Use a site and season estimate that accounts for the panel orientation, local weather and shade.
Does the panel estimate include appliances running while the battery recharges?
The estimate replaces the energy entered for the backup period. Include other energy that must be supplied during recharge when discussing the actual system design.
Does the cost estimate include installation?
The subtotal uses only the prices and allowance you enter. Ask the installer for a quote showing equipment, labour, mounting, protection and any other charges.
