PHOENIX (AP) -- It's the question visitors to Arizona ask often when the subject is sustainability: With so much sunshine and so much empty land - and empty rooftops - where's all the solar power?

The quick answer is cost. Building solar-power plants is expensive and would spike electricity bills in a state where prices are comparatively low. Rooftop panels also have high upfront costs.

In a sustainable world, individuals and businesses would accept at least part of the added cost as the price of finding a lasting balance between the need for energy and the benefits to the environment of renewable resources.

Some people already have accepted the cost and converted to clean energy. But regulatory hurdles and practical obstacles remain. And even a clean energy source like solar power isn't sustainable if it disrupts the economy and excludes customers who can't afford it. That's why utilities are exploring a wider mix of sources, including wind, geothermal and biomass.

At the base of the White Mountains just outside Snowflake, a biomass power plant went online in June, cranking up toward an expected output of 24 megawatts, or enough for about 9,000 homes.

That's not much in a state with growing electricity demands, but on the day it went live, the plant became Arizona's largest single source of renewable energy other than hydroelectric dams.

On a scarred ridge above Heber, work crews gather the fuel for the plant: skeletons of trees charred by the 2002 Rodeo-Chediski fire.

Although too damaged for timber companies, the trees still hold biomass, material that can be burned to make steam to turn power turbines. That potential caught the interest of entrepreneur Robert Worsley, who wanted to build a renewable-energy operation on land he owned in the White Mountains.

"We're all about BTUs," said Scott Higginson, a vice president at Tempe-based Renegy Holdings, which built the plant. said Scott Higginson, a vice president at Tempe-based Renegy Holdings, which built the plant. bulk of its fuel will come from green forest areas being thinned under a Forest Service plan to protect communities from future fires.

The plant was built next to a recycled paper mill operated by the Canadian company Catalyst. The operation recycles paper products, mostly trucked up from Phoenix, and produces newsprint. Renegy will add waste from the process to its biomass fuel mix, making the plant that much more sustainable.

Without the plant, the Forest Service would burn much of the green waste cleared from the forests, releasing carbon and other pollutants, or allow the materials to decompose, releasing methane. Renegy says it will remove almost every trace of pollutant as the biomass burns.

Arizona Public Service Co. and Salt River Project have agreed to buy the plant's output.

In 2007, the Arizona Corporation Commission adopted one of the nation's most aggressive renewable energy standards, requiring regulated utilities to produce or buy 15 percent of their power needs from renewable sources by 2025.

The new rules also will push clean energy, mostly solar deeper into the private sector.

Of the 15 percent renewable power mandated by the commission, 30 percent must come from distributed solar, systems installed on rooftops. The commission estimates that the requirement will lead to 5,500 new rooftop arrays in 2009 and 9,125 new systems in 2010.

"That was very deliberate," said commissioner Kris Mayes, who helped develop the standards. "We wanted people throughout the state to benefit."

The rooftop rules are likely to help small companies that can help homeowners figure out how residential systems work and could spur ground-level efforts to cut costs.

Already, several upstart companies have landed in the state with offers to lease rooftop arrays to contain costs.

Businesses that can take advantage of incentives, scale and a long payoff period will likely lead the way, Mayes said.

"It makes good sense for them," she said. "This is a way to shield themselves against what's coming."

What's coming is government action to curb global warming, whether it's a direct carbon tax or a cap-and-trade program that would cap smokestack emissions then allow cleaner-burning companies to trade pollution credits with those that exceed limits.

Either option will likely push energy costs higher, turning expensive solar projects into more affordable alternatives.

Cost remains a high hurdle for people who seek sustainable alternatives. Solar energy comes with a steep upfront cost, from tens of thousands of dollars for homeowners to millions of dollars for businesses that want to install systems.

Lee Feliciano thinks he can help larger businesses take their first sustainable steps into solar power. A former solar-system installer, Feliciano started SolEquity as a way to finance solar projects and get big rooftops wired for the sun sooner.

He packages deals that let businesses go solar and then his company keeps the incentives and tax credits in return. Most of his customers will spend $1 million or more on the projects.

"With solar and with wind, as renewable energy, 90 percent of your costs or more is front-loaded," he said. "There are not a lot of people with that sort of long-term perspective. Financing is the key to unlocking it."

His deals work best in places where power costs already have risen. In California, with some of the most expensive electricity in the nation, it's relatively easy to finance a solar project that makes financial sense, one that probably wouldn't pencil out in Arizona.

"There's a two-word answer why that is," he said. "Cheap electricity. Generally speaking, I think it's fair to say the price of electricity in California is double what it is in Arizona. If you compare the incentives given, they're not that far off. The real kicker is their electricity costs twice as much."

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Information from: The Arizona Republic, http://www.azcentral.com

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