The dirty little secret about power generation is that most states, including Arizona, rely heavily on coal. Sure, Arizona has mandated 15% renewable energy by 2025 but for now, King Coal reigns.
Even California, which has a much more ambitious plan of 33% renewable by 2020, relies heavily on coal. However, and somewhat hypocritically, California has banned coal plants within its borders while importing a vast amount of coal power from neighboring states, including Nevada, Arizona, and New Mexico. Southern California Edison (SCE) and the Los Angeles Department of Water and Power (LADWP) in particular import prodigious amounts of coal power from out of state.
Further complicating this is the glaring fact that many of these coal plants are on Indian land, leading some to call this environmental racism, building polluting facilities on impoverished, usually non-White areas. But these same plants also provide jobs for probably thousands of Indians. The pollution may be bad but the job loss could be worse. That could be what's coming too.
The EPA is mandating new rules that may drastically impact these coal plants, perhaps curtailing production. This in turn will affect how much power Arizona gets. The Four Corners coal plant on Navajo land in New Mexico may be one of the dirtiest coal plants in the country. The California push for clean energy means that Southern California Edison will no longer be able to buy that dirty power. Plus, the cost to upgrade the five Four Corners units to current EPA standards is expensive, perhaps prohibitively so. So, Arizona Public Service (APS) wants to buy SCE's shares of units 4 and 5, bring them up to code, and simultaneously shutdown units 1-3, which they own. This plan is complicated (as you might imagine) as units 4 and 5 are also co-owned by El Paso Electric, Salt River Project, and Tucson Electric, they are on Navajo Nation land, and the deal is subject to approval by numerous authorities including the EPA. And it's a given that environmentalists will try to shut down the plants completely.
Four Corners outputs 1298 MW of power in total. If units 1-3 are closed, 560 MW will be lost. If units 4-5 have to be closed, then another 738 MW is gone. The same type of process is happening with the Navajo Generating Station (2,250 MW) near Page AZ and the San Juan Generating Station (1800 MW) in New Mexico. New EPA regulations may force expensive upgrades or perhaps even shutdowns. The Page facility is partly owned by LADWP while San Juan is a primary source of power for PNM in New Mexico, so the ramifications of this will spread throughout several states.
By contrast, the total amount of installed solar power as of December 2010 in Arizona was about 100 MW. The three coal plants mentioned generate 5,348 MW. You can see the problem. It would appear that everyone knows coal is dirty and needs to either be cleaned up (at great expense) or replaced. But how do we do that? Renewable energy is nowhere close to filling the gap now.