You're confusing price per watt and price per kilowatt hour.
The quoted price is $0.30 / watt. That means that it would have to run for 3000 hours to have an average price of $0.10 / kilowatt hour. To get 3000 hours you need 250 12-hour days of sunlight. You might not get that the first year, but even if it has a two year payoff I would be covering my roof with them.
There will be some additional costs for energy storage so you can turn on a light bulb at night and use power at a higher surge rate than the sun is providing.
The sun has to be pretty high in the sky to approach the peak power a solar panel is rated at. The usual method of taking that into account is to figure 5 hours of sunlight per day as an average over the year.
Current PV panels require about one square foot to produce a peak 10w. So if you need 1000kwh per month, you need 1000kwh / 30days = 33kwh per day / 5 hours per day = 6.6kw capacity = 660 square feet of panels.
At 30 cents per watt, the panels would cost $2,000. Batteries, inverter, installation, etc., however, would make it $10,000 for a home system. A grid-tie system would be cheaper because it wouldn’t need batteries. That would save $3,000 and eliminate the recurring replacement expense. Deep cycle lead batteries only last about two years. Even at $10,000 initial cost plus $1,500/yr recurring cost, it would be cheaper than my current annual electric bill in southern California.
My roof is covered with snow about 4 months of the year. That's also that same time frame when I get minimum daylight. At 42 degrees north, the amount of solar energy available is limited anyway.
In warm climates the highest energy use is during the sunniest part of the day. Energy companies actually pump water from lower lakes to higher lakes at night and generate electricity during the day as the water flows back down through the turbines. Electricity consumers can also sign up for programs that charge less at night.
What this means is that photo-voltaic cells on individual homes and businesses would be connected to the power grid and would supplement the power supply during heavy load periods. If enough of them were used, then the coal-fired and natural gas plants could be throttled down.
If a home had enough cells and the occupants were not at home during the day using electricity, their meters would run backwards.
No storage system is needed.