Steam rises at power plant cooling towerAsk an expert on clean tech what the largest barriers to a low carbon energy future are, and chances are they will list higher technology costs, policy barriers, or the need for new infrastructure to accommodate novel energy sources.

But according to a set of expert panelists speaking at the MIT Energy Conference in Boston this Saturday, we're forgetting a big one: water.

Not convinced? Here's a few factoids to wet your appetite (pun intended):

  • The US power sector withdrew as much water from America's rivers, lakes, and oceans for cooling needs as the country uses to irrigate all agricultural lands, according to MIT Professor Ahmed Ghoniem.
  • Worldwide, baseload power plants use the same amount of water for cooling as 545 megacities the size of New York City, according to Peter Evans, Director of Global Planning and Strategy for GE. By 2025 as global power demand grows, water needs will rise to 660 New York City's worth.

Big numbers indeed, and a potentially substantial challenge to a low-carbon energy transition, particularly for new "baseload" or reliable sources of emissions-free power.

Excepting wind and solar photovoltaics, both intermittent energy sources, all other low-carbon power sources need water -- LOTS of it -- either for cooling needs (as in the case of geothermal, nuclear, solar thermal, or fossil plants with carbon capture) or as their motive force (in the case of hydroelectric and tidal power). 

To be clear, most of the water "used" by power plants for cooling needs isn't actually consumed. Except for whatever evaporates, most of the water ends up back in waterways--albeit a bit hotter. 

Still, when it comes to baseload low-carbon power needs, finding a source of cooling water can be a key constraint, cautioned the MIT conference panelists, who spanned industry, academia, and environmental backgrounds. 

As an example, the Palo Verde nuclear power station near Phoenix, Arizona, utilizes the city's wastewater to meet its cooling needs, pumping 73 million gallons of water to the plant every day, said Jerry Alexander, Global Director of Process Water for Siemens Water Technologies Division. 

As it turns out, Palo Verde, where construction began in 1976, was ahead of its time. Essentially all new power plants in America today are unable to secure permits to use freshwater sources for cooling needs, Alexander noted. New regulations coming down the pipe from the US Environmental Protection Agency could also force older, existing plants to switch to recycled water or "dry" cooling techniques that minimize water use.

That's a key opportunity for entrepreneurs. New technological innovations, thoughtful design and siting, and better recycling and management of power sector water needs are all key to overcoming this potential barrier, the panelists noted.

Consider the case of a new solar thermal electric power station, like the Ivanpah plant under construction now by BrightSource Energy in California. 

Out in the desert, freshwater isn't an option, and it's probably a long way to the nearest large municipal wastewater treatment plant. 

Dry evaporative cooling, or "air cooling," is the only real option, then, said Colleen Layman, a water treatment engineer with Bechtel Corporation, which helps build power plants all over the world, including the Ivanpah solar plant

Yet cooling needs at a solar thermal plant are highest during the heat of the day, when power output is greatest. That's also precisely when air cooling is least efficient, according to John Maulbetsch, a consultant specializing in water management. 

This isn't a challenge for solar thermal alone. Only two nuclear power plants in the world today are air cooled, said Siemens's Alexander. That's going to have to change, as new reactors come online in an increasingly water constrained world. 

Layman agreed, noting that Becthel is partnering with Babcock and Wilcox on new small, modular nuclear reactor designs. The consortia is focused on air cooled designs, she said.

Improving the efficiency of air cooled power plants is just one place where new innovation is needed. Maulbetsch also pointed to improvements in steam turbine designs that can optimize water usage or better facilitate air cooling, while Layman called for better membrane technologies to help treat water discharges from power plants.

All the panelists agreed: water shouldn't be a barrier to a low-carbon future.

"Where there's a will, there's a way," fisheries biologist Timothy Hogan optimistically concluded. 

New innovations in technology, siting, and practice will be the key.