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Over the past decade, states across the nation including Arizona have responded to public demand to increase renewable energy from sources like solar and wind power.听

As a result, renewable sources surpassed coal in generating electricity for the first time in the United States this year, according to the Federal Energy Regulatory Commission (FERC).

As more states ratchet up requirements – some calling for 100 percent renewable energy – that poses significant challenges for states, municipalities and utilities.听

Political will vs. scientific reality听听

Renewable sources of energy are unable to provide constant, reliable energy after the sun sets and the wind does not blow.听

Energy storage is the most promising solution. But current technology is not reliable or affordable enough to provide enough storage to produce 80 to 100 percent renewable energy,听 research shows.听听

鈥淭here鈥檚 definitely a customer driven demand for cleaner sources of energy,鈥� said Brad Albert,听 vice president of resource management for Arizona Public Service Company (APS), the largest and oldest utility in Arizona. 鈥淥ur key challenge here is that we don鈥檛 compromise reliability or affordability.鈥澨�

In today鈥檚 world, the cost to install huge battery storage fields to meet today鈥檚 demand would be staggering, according to a study published in the Journal of Energy & Environmental Science.听

An analysis of 36 years of global, hourly weather data revealed that utilizing wind-heavy or solar-heavy U.S.-scale power generation could eventually provide about 80 percent of total annual U.S. electricity demand, the study states.听听

鈥淛ust getting to 80 percent of demand reliably with only wind and solar would require either a U.S.-wide high-speed transmission system or 12 hours of electricity storage. A storage system of that size across the U.S. would cost more than $2.5 trillion for a battery system,鈥� states a review of the in MIT Technology Review.

Another study released last month by global energy consulting and research group, Wood Mackenzie, estimates the cost of a 100 percent renewable energy transition by 2030 within the U.S. could cost $4.5 trillion, or about $35,000 per U.S. household.

Cookie-cutter approach wrong path for energy听听

As the call for renewable energy moves onward, cookie-cutter mandates are unrealistic because every state has its own unique challenges Albert said. Solar is a good fit in Arizona. But it does little good when demand is at its highest in the summer months.听

鈥淚n Arizona, customers by necessity have to use a lot of electricity. That鈥檚 the climate where we live. We love it. But it鈥檚 a lot different from living in a coastal area of California where people don鈥檛 need air conditioning like we do,鈥� Albert said. 鈥淪olar鈥檚 peak production here is around noon but by the time our customer demand peaks from 6 to 7 pm., those solar plants are going to sleep.鈥澨�听

The right balance of 鈥減ower鈥�

As scientists and researchers search for new solutions and better storage technology, clean energy sources like nuclear and natural gas offer an important balance to renewable energy,听 providing a constant source of power with no fluctuations.听

As corporations and utilities press forward to seek new answers to meet public demand for clean energy, breakthroughs are coming quickly.听

Last week, ExxonMobil and Global Thermostat announced a joint development agreement to advance breakthrough technology that can capture and concentrate carbon dioxide emissions from industrial sources, including power plants.听

The signed June 27, states that the two companies are moving to evaluate potential scalability of the technology. Applications could extend across multiple industrial sectors.听

Arizona investing in renewable storage technology听

Meanwhile, the state鈥檚 two largest utilities, APS and Tucson Electric Power (TEP), have been gradually moving away from coal and investing hundreds of millions of dollars in solar plants, wind power and battery storage technology.听

In addition to its growing solar and wind installations, Arizona is home to the Palo Verde Generating Station, the largest producer of clean, emission-free energy in the country.听

For now, battery storage is the hope for the future of renewable energy, Albert said. Last year, APS announced the largest purchase of battery technology in the country to be installed over the next several years.听

But for now, it鈥檚 just a drop in the proverbial bucket. Nationally, there鈥檚 only 1,000 to 2,000 megawatt hours of battery storage deployed in utility service across the country right now, he said.听

During one summer day in Arizona, APS customers alone will consume about 100,000 megawatt hours of energy.