Solar Panel Sizing Calculator

Solar Panel Sizing Guide

Start With Load

Solar panel sizing starts with the daily load. Every appliance uses watts for a set time. Multiply both values. Then add each result. This gives daily watt hours. A strong calculator also includes losses. Real systems lose energy in wires, batteries, controllers, heat, dust, and inverter conversion. That is why the array must be larger than the raw load.

Use Peak Sun Hours

Peak sun hours are central. They describe useful solar energy per day. A site with five peak sun hours can use a smaller array than a site with three. Roof angle, shade, and seasons change this value. Use a conservative value for critical systems. Winter sizing often gives safer results.

Size Battery Storage

Battery sizing depends on autonomy. Autonomy means days of backup. A cabin may need two or three days. A grid tied home may need less. Depth of discharge also matters. Lithium batteries can usually use more capacity than lead acid batteries. The calculator converts the needed stored energy into amp hours at the selected system voltage.

Check Inverter and Controller

Inverter sizing should cover the running load and starting surge. Motors, pumps, refrigerators, and tools can start hard. Their surge can be much higher than normal use. A margin protects equipment. It also reduces nuisance shutdowns during short overloads.

Charge controller sizing uses array watts and system voltage. A safety factor is added. This helps handle cold weather and strong sun. Larger arrays may need an MPPT controller. Smaller simple systems may use PWM. Always compare the calculated current with the controller nameplate.

Review Wire Loss and Cost

Wire loss can reduce output. Long cable runs need larger conductors. The voltage drop check estimates whether the run is reasonable. Keep drops low on battery and array circuits. This improves charging and lowers heat.

Cost and savings are planning estimates. They do not replace a site survey. Still, they help compare options quickly. Use current equipment prices and local energy rates. The payback result is simple. It divides estimated system cost by yearly savings.

Final Design Notes

Use this tool as a design guide. Then confirm code rules, roof capacity, permits, grounding, disconnects, and protection devices with a qualified professional. Good inputs matter. Measure loads carefully. Review bills when available. Add future appliances early. A planned margin prevents costly changes later during installation work.