Only a part of the puzzle

People listening to policymakers debate the nation's energy future might think: Just erect a lot of wind turbines, and problem solved. Or install a bunch of solar panels, and let the sun do the work.

But renewable energy alternatives present costs and challenges just like traditional energy sources - coal, natural gas, nuclear and hydropower.

Even the American Wind Energy Association doesn't believe wind can produce 100 percent of the nation's electricity. Its goal is to produce 20 percent by 2030, not as quickly as next year or even the year after.

Many sources of energy, in fact, are likely to play decades-long roles in generating the power needed to bring reliable, cost-effective electricity to homes and businesses, according to utility executives in Nebraska and Iowa.

"We need multiple energy resources," said Marc Nichols, head of Omaha Public Power District's sustainable energy and environmental stewardship efforts. "If we have free fuel, like wind and solar, then we need to take advantage."

MidAmerican Energy Co. of Des Moines ranks first in the country among regulated utilities in ownership of wind-powered electric generation. Nearly 20 percent of its generation capacity comes from wind turbines. But even MidAmerican officials see numerous challenges ahead for wind and other types of renewable energy, said Tom Budler, general manager of the utility's wind projects.

"It really is a long-term view," Budler said.

David Rich, renewable energy development manager at Nebraska Public Power District, said his utility is committed to deriving 10 percent of its generation capacity from newly developed renewable sources by 2020. That would be on top of the 7 percent generation capacity it already has from hydropower, Rich said.

Technological breakthroughs could change the picture dramatically, but there are challenges to providing cost-effective generation and storage of renewable energy, Rich said.

"Customers want a low-cost, reliable product," Rich said. "It really gets down to economics."

How our energy sources stack up:

Solar

Pros: Free, renewable and no carbon emissions. A good complement for industry heavyweights like coal, natural gas and nuclear power.

Cons: Expensive. Clouds, dust and darkness make sun power available only about 16 percent of the time, limiting the ability of photovoltaic systems to generate electricity. Solar farms occupy large tracts of land that could produce food or have other uses. No cost-effective way to store solar electricity.

Wind

Pros: Free, renewable and no carbon emissions. A good complement for traditional energy generation sources.

Cons: Wildlife activists say wind turbine blades can kill birds. Expensive transmission lines are necessary to carry electricity from windy states like Nebraska and Iowa to population centers. Wind blows only about 40 percent of the time. No way to efficiently store energy when turbines stop spinning.

Biomass

Pros: Captures methane produced by manure, wastewater sludge and landfills that contributes to global warming. Produces energy from a waste stream, thus lessening global warming.

Cons: Requires large concentrations of biodegradable organic matter, which limits its feasibility to generate large amounts of electricity.

Coal

Pros: Relatively inexpensive, abundant and reliable. Burning coal produces about half the electricity generated in the U.S.

Cons: Major source of carbon dioxide emissions, which contribute to global warming. Currently no cost-effective process available to reduce emissions, such as capturing the carbon and storing it underground.

Natural Gas

Pros: Abundant, reliable and emits less carbon than coal. Gas heats quickly, reducing startup times, making it a good source to handle peaks in electricity demand.

Cons: More expensive than coal. As a fossil fuel it emits some carbon dioxide, though less than coal or oil. The process of removing natural gas from underground can harm the environment.

Nuclear

Pros: Reliable, no carbon emissions.

Cons: Building nuclear plants is expensive, and storage of spent fuel is problematic. Safety concerns include the potential for radiation leaks and becoming a source of materials for nuclear weapons.

Hydropower

Pros: Renewable, reliable, no carbon emissions. Reservoirs created for hydropower dams support water recreation such as boating and fishing, and provide water for irrigation.

Cons: Limited by geography because a water source is needed. Reservoirs require thousands of acres that could be forests, farms or housing. Reservoirs can disrupt fish migrations.

Geothermal

Pros: Reliable, no carbon emissions. Drawing heated fluids and gases from the earth to power electrical generators is renewable if properly managed by reinjecting the water into underground reservoirs.

Cons: Expensive, and historically limited to areas of high temperature sources relatively near the earth's surface. Improvements in technology could allow a wider geographic range for geothermal plants.