Austin is poised to dramatically expand its solar footprint.

In an 8-2 vote on Thursday, the City Council directed Austin’s utility to line up contracts adding 600 megawatts of solar power to the city's energy mix by the end of 2019.

Environmentalists heralded the plan as another sign that the no-carbon energy source is fast gaining a foothold on the Texas grid. 

"This is an incredibly good deal for Austin," Luke Metzger, director of Environment Texas, said in a statement. "The contracts come with record low prices, helping us save money while helping save the planet.”

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On average, a megawatt-hour of energy can power as many as 100 Texas homes for an hour on the hottest summer day. During average temperatures, it can power many times more.

The council’s latest vote means Austin will secure contracts for 450 megawatts of solar power this year and 150 megawatts more by 2019. Together, those additions would be far larger than the roughly 330 megawatts installed statewide in 2014, according to data provided by the Solar Energy Industries Association.

Under the plans, Austin could tap solar for 13 percent of its energy by 2017. 

Texas leads the nation in solar energy potential, but the industry long struggled to emerge as policymakers provided fewer incentives than other states. Solar energy makes up a tiny percentage of the state’s energy portfolio.

But that’s beginning to change as improving technology drives down the cost of harnessing the sun’s energy.

The plan approved Thursday was something of a compromise. Environmentalists had called for Austin to secure all 600 megawatts this year. Others, including Austin Energy, the city utility, expressed concerns about rate increases and called for a less ambitious plan. 

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An addition of 450 megawatts of solar power would add as much as $11 each year to the average Austin resident’s bill in 2017, the utility estimated. But it would cost energy-guzzling tech firms thousands of dollars more.

Austin has looked to West Texas to fuel much of its solar surge, signing long-term contracts with major solar generators to lock in the lowest rates. 

Earlier this month, for instance, the city approved a 15-year, $13 million deal with East Pecos Solar for 118 megawatts of energy. Last year, the city signed a 25-year deal for 150 megawatts of West Texas solar power.

Knowing when to pull the trigger on such deals can prove tricky since solar costs continue to drop. At the same time, however, a generous federal investment credit is set to expire at the end of 2016, motivating developers to finish projects sooner than later.

Disclosure: Environment Texas was a corporate sponsor of The Texas Tribune in 2013. A complete list of Tribune donors and sponsors can be viewed here.