Therefore, the upfront cost of the solar panels per watt are Costpanels = $600/75 watts = $8/watt Or, by multiplying numerator and denominator by 1000, Costpanels = $600/75 watts = $8000/kilo-watt. As determined from a survey of current market prices, it costs about $600 to purchase and install a 75 watt panel.o, for example, if you use 10 kilowatt-hours a day, and the cost of power is about 10 cents per kilowatt-hour, then you electrical costs would be about $1 per day (ten times 10 cents), or $30 per month. Also, we need to know how long the sun shines each day on average. Let this be denoted by Tsun,