Quote comparison
Solar panel cost per watt
Cost per watt is a common way to compare solar quotes. It divides the total installed system price by the system capacity in watts. The metric is useful, but only when the quotes include similar equipment, labour, warranties and scope.
How cost per watt is calculated
The basic calculation is installed cost divided by system watts. A 5 kW system is 5,000 watts. If the installed cost is 8,500, the cost per watt is 8,500 divided by 5,000, or 1.70 per watt. This single figure makes it easier to compare different system sizes, but it can hide important differences in quality and included work.
What should be included
A fair cost-per-watt comparison should include the solar panels, inverter, mounting system, electrical protection, cabling, monitoring, design, permits, inspection, grid connection work and normal installation labour. If one quote excludes scaffolding, tax, roof repairs or electrical upgrades, its cost per watt may look artificially low. Optional batteries should normally be compared separately because they can distort the solar-only cost per watt.
Why smaller systems can look expensive
Small systems often have a higher cost per watt because fixed costs are spread over fewer watts. Design, travel, permits, inspection and basic electrical work do not fall in perfect proportion to system size. A 3 kW system may therefore have a higher cost per watt than a 7 kW system even if the equipment quality is similar.
Do not compare only on price
A low cost per watt is not automatically the best deal. Check panel efficiency, inverter type, monitoring features, warranty terms, installer reputation, shading design and after-sales support. A slightly higher price can be justified if it includes better equipment, cleaner installation, stronger warranties or more realistic production modelling.
Worked example
Quote A is a 4 kW system for 7,200, which equals 1.80 per watt. Quote B is a 6 kW system for 9,900, which equals 1.65 per watt. Quote B is cheaper per watt, but it may still be the wrong choice if the home cannot use or export the extra generation effectively. Cost per watt should be reviewed together with annual production, self-consumption, export tariff and payback period.
Related pages
Normalize the quote before comparing price per watt
Cost per watt is only comparable when the numerator and denominator are defined the same way. Use the installed DC array capacity for the watt figure and decide whether both quotes are being compared before or after incentives. Do not compare a gross-cost quote with a net-cost quote. Similarly, remove optional batteries from both proposals if the goal is to compare the solar array itself.
Then compare scope. If one installer includes scaffolding, monitoring, optimisers, extended workmanship cover and grid paperwork while another does not, the cheaper price per watt may not represent the cheaper completed project. Ask for exclusions in writing and compare the total amount you would actually pay to reach an operational, approved system.
What cost per watt does not tell you
The metric does not measure expected kWh production, shading performance, warranty service, installer quality or how well the system size matches your electricity use. A well-designed smaller system can cost more per watt but produce a better financial result if it avoids low-value exports. Pair cost per watt with annual production, expected self-consumption and payback rather than treating it as a score by itself.