This detailed comparison table breaks down dimensions, wattage, efficiency, and costs to help you make informed decisions. Whether you're a homeowner, installer, or business buyer, discover how panel size impacts energy output and budget. 40 per watt, making a 400W panel cost $320-$560. Professional installation dramatically increases the per-panel cost due to labor, permits, and supporting equipment: This installed cost includes the panel, inverter portion, mounting. Curious about how much it will cost to install solar panels on your home or business? Our solar price estimator helps you calculate a personalized cost estimate based on your energy needs, location, and system size. Divide annual kWh by ~1,200 (typical kWh/year per kW of solar in much of California). What Is a Solar Panel Calculator? A solar calculator is an online tool designed to help homeowners and.