When people think of solar power, they tend to think of panels on rooftops.

In other words, utilities are beginning to voluntarily opt for big solar. Why is that? Utility solar is being boosted by three strengths — and it’s making progress against its one weakness Strength #1: Price The total installed cost of big solar, per watt of capacity, is rapidly getting cheaper:     As you can see, most of the cost drop has been due to the falling cost of solar modules — and panels are only expected to get cheaper. According to this 2015 Lawrence Berkeley National Laboratory report (the latest comprehensive data I could find), the installed cost of big solar has fallen 50 percent since 2009, from $6.30/W to around $3.10/W at the end of 2014. Some projects were down as low as $2/W when LBNL released its report. And these days, solar projects in North Carolina and Georgia regularly report costs as low as $1.15/W. The stretch goal of the Department of Energy’s 2011 Sunshot Initiative is to drive installation costs down to $1/W, which it says “would make solar without additional subsidies competitive with the wholesale rate of electricity, nearly everywhere in the US.” The CEO of First Solar recently said that “by 2017, we’ll be under $1.00 per watt fully installed on a tracker in the western United States.” (More on trackers later.) It appears costs are falling faster than almost anyone predicted....