Smart meters aren’t just for electricity anymore. In Santa Clara, the city is now using the technology to bring free citywide outdoor Wi-Fi to the entire community. The Washington Post recently covered the story New smart meters, now being installed on homes, are primarily for electricity and water metering. The meters send usage reports via… Continue reading
Viewing the water tag archive
Karen Piper, Professor of English at the University of Missouri in Columbia informs us of a factor behind the spring uprising in Egypt the mass media missed: the privatization of water. The American media focused mainly on internal corruption and oppression. They did not report on the role of the international superpowers in influencing the… Continue reading
Montana, home to some of the world’s best fly fishing, is also home to the country’s most far reaching law protecting their stream and river commons. The catalyst was a 1984 ruling by the Montana Supreme Court that any river or stream capable of being used for recreation purposes such as fishing and floating, can… Continue reading
In the 19th century, small private companies in U.S. and European cities supplied water only to those who could pay a premium. Then came epidemics of cholera and other waterborne illnesses, which vividly illustrated the widespread stakes for public health and human life and invigorated the political will needed to make a shared commitment to… Continue reading
Concentrating solar thermal power has promised big additions to renewable energy production with the additional benefit of energy storage. But with significant water consumption in desert locations, is the energy storage benefit of concentrating solar enough to compete with the dramatically falling cost of solar PV?
In May, I compared the water consumption of fossil fuel power plants to various solar technologies, noting that wet-cooled concentrating solar thermal power (think big mirrors) uses more water per megawatt-hour (MWh) than any other technology. The following chart, from the earlier post, illustrates the amount of water used to produce power from various technologies.
Water consumption can be cut dramatically by using “dry-cooling,” but this change increases the cost per kilowatt-hour (kWh) of power generated from concentrating solar power (CSP). In the 2009 report Juice from Concentrate, the World Resources Institute reports that the reduction in water consumption adds 2-10 percent to levelized costs and reduces the power plant’s efficiency by up to 5 percent.
Let’s see how that changes our original levelized cost comparison between CSP and solar PV. First, here’s the original chart comparing PV projects to CSP projects, with no discussion of water use or energy storage.
To make the comparison tighter, we’ll hypothetically transform the CSP plants from wet-cooled to dry-cooled, adjusting the levelized cost of power.
Using the midpoint of each estimate from Juice from Concentrate (6 percent increase to levelized costs and 2.5 percent efficiency reduction), the change in the cost per kWh for dry-cooling instead of wet-cooling is small but significant. For example, all three concentrating solar power projects listed in the chart are wet-cooled power plants. With a 6% increase in costs from dry cooling and a 2.5% reduction in efficiency, the delivered cost of electricity would rise by approximately 1.7 cents per kWh.
The following chart, modified from our earlier post, illustrates the comparison.
With the increased costs to reduce water consumption, CSP’s price is much less competitive with PV. In our May post, we noted that a distributed solar PV program by Southern California Edison has projected levelized costs of 17 cents per kWh for 1-2 MW solar arrays, and that a group purchase program for residential solar in Los Angeles has a levelized cost of just 20 cents per kWh.
In other words, while wet-cooled CSP already struggles to compete with low-cost, distributed PV, using dry cooling technology makes residential-scale PV competitive with CSP.
But there’s one more piece: storage.
While Nevada Solar One was built without storage, the PS10 and PS20 solar towers were built with 1 hour of thermal energy storage. Let’s see how that changes the economics.
To make the comparison comparable, we’ll add the cost of 1 hour of storage to our two PV projects, a cost of approximately $0.50 per Watt, or 2.4 cents per kWh. The following chart illustrates a comparison of PV to CSP, with all projects having 1 hour of storage (Nevada Solar One has been removed as it does not have storage).
When comparing CSP with storage (and lower water use) to PV with battery storage, we have a comparison that is remarkably similar to our first chart. Distributed PV at a commercial scale (1-2 MW) is still cheaper than CSP, but residential PV is more expensive.
Even though dry-cooled CSP competes favorably on price, it still uses much more water than PV. That issue is probably why many solar project developers are switching from CSP to PV technology for their large-scale desert projects.
Without a significant cost advantage, the water use of CSP may mean an increasing shift to PV technology.
Power plants use a stunning amount of water. In 2005, thermoelectric power (e.g. coal, natural gas) accounted for half of all water use in the United States. Across the country and particularly in the arid West, the water savings from renewable energy are as important as the pollution-free energy.
That makes the distinction in water use between centralized solar and decentralized solar a big deal, especially since centralized solar is only planned for the dry Southwest.
The following graphic illustrates water consumption for common types of power generation per MWh of electricity produced (additional reference here):
Traditional power generators are water hogs. For example, a nuclear power plant consumes 720 gallons of water for each megawatt-hour of electricity produced. Powering a single 75-watt incandescent light bulb for an two hours on nuclear-generated electricity would consume 14 ounces of water (more than a can of pop).
While most of that water is returned to the environment, this report by the Alliance for Water Efficiency and ACEEE notes that it’s not undamaged:
Water is returned to its original source, even though its qualities have changed, especially temperature and pollutant levels.
Nuclear and coal may be big offenders, but wet-cooled concentrating solar power uses even more water per MWh of electricity generated. Dry-cooled CSP cuts water consumption significantly, but it’s still far more than solar power from photovoltaics (or wind power).
If it were solely a question of cost, CSP and PV come out relatively close (see updated chart below) despite the former’s frequent need for transmission access.
But if the tradeoff is significant water consumption versus none, then decentralized PV may make more sense everywhere, including the sunny Southwest.
Photo credit: Flickr user Shovelling Son