By Bill Dawson
Texas Climate News
“Grid reliability” – the ability of a region’s electricity grid to meet users’ demand with enough resilience to survive sudden disturbances – is one or many points of debate over the Obama administration’s proposed Clean Power Plan, which aims to reduce climate-changing pollution from power plants.
Under the proposal, states would be required to come up with plans, tailored to their particular situations, to cut emissions of carbon dioxide, the major human-produced greenhouse gas. For instance, Texas might choose to use more Texas-produced natural gas, step up the state’s wind generation and encourage energy conservation to substitute for some of its current use of imported coal, the dirtiest of the fossil fuels.
Texas officials have unleashed a multifaceted barrage of criticism at the Clean Power Plan, however. One reliability-related line of attack is from the Electricity Reliability Council of Texas (ERCOT), the agency that manages the electric grid in most of the state. Supporters of the federal proposal, meanwhile, have offered spirited rebuttals of the ERCOT argument.
Now, a new study by researchers at Arizona State University raises a different, though relevant, issue with regard to grid reliability and climate change. After a series of calculations involving the Western Interconnection, an electric grid that serves 11 states – including New Mexico, adjoining Texas’ Panhandle and Trans-Pecos regions – they concluded that “climate change may constrain future electricity generation capacity [in the 11 states] by increasing the incidence of extreme heat and drought events.”
The estimated reductions in generating capacity are “based on long-term changes in streamflow, air temperature, water temperature, humidity and air density,” the researchers wrote in a study published in May in the journal Nature Climate Change.
For vulnerable power stations (46 percent of existing capacity), climate change may reduce average summertime generating capacity by 1.1 to 3.0 percent with reductions of up to 7.2 to 8.8 percent under a ten-year drought. At present, power providers do not account for climate impacts in their development plans, meaning that they could be overestimating their ability to meet future electricity needs.
TCN asked Matthew Bartos, one of the study authors, if Texas’ grid, though not included in their analysis, might be similarly vulnerable.
Some important background information for understanding his reply: ERCOT announced in January that the 2014 power-generation mix in its grid included natural gas at 41.1 percent of the electricity produced, coal at 36 percent, nuclear at 11.6 percent, wind at 10.6 percent, water (hydroelectric) at 0.1 percent and other sources at 0.4 percent. One of the state’s nuclear plants is on the Gulf coast, one is located inland.
Bartos’ emailed comments:
[Texas] is not directly connected to the Western power grid, meaning that the results of our study do not predict any direct impacts for the state of Texas.
However, our findings do suggest some general factors that may result in reduced power supply.
The most vulnerable facilities are large base-load thermoelectric facilities (i.e. coal and nuclear power plants) and combustion turbine facilities. Hydroelectric generating facilities may also be vulnerable if they are located in an area of the country that is expected to receive significantly less precipitation. “Base-load” fossil-fuel plants [those intended to consistently meet minimum demand] may suffer capacity losses for a variety of reasons: (a) they may lack sufficient water to reject heat from the plant’s generator, (b) environmental regulations may prevent the power plant from discharging water if the discharge temperature is too high, and (c) changes in ambient temperature and humidity may cause incremental decreases in thermal efficiency. Combustion turbine facilities generally use natural gas for fuel, and are mainly used to satisfy “peaking” electricity load. These facilities suffer capacity losses under high ambient air temperatures – mostly due to decreased air density (and thus a lower mass flow rate through the turbine).
That said, Texas may experience similar impacts if it is overly reliant on the following technologies:
(a) Large base-load coal and nuclear facilities that use fresh surface water for cooling – especially those utilizing open-loop cooling systems. (Note that power stations relying on ocean water for cooling are not usually considered to be vulnerable–at least not for the reasons that we analyzed).
(b) Combustion turbine generators, deployed either in isolation or in a combined-cycle configuration [working in tandem].
(c) Hydropower deployed in regions expected to receive significant drying.
Most of the climate models seem to predict less precipitation and higher temperatures for Texas, meaning that impacts to all of these technologies are likely.
Climate Central, a nonprofit reporting and research organization, noted in its account of the study that the researchers did not say renewable power sources are risk-free in a warming climate:
Renewables take a hit, too, but are much less vulnerable to climate change.
Solar photovoltaic panels generate less power as air temperatures rise, leading to a power generation capacity loss of up to 1.7 percent. And, just like airplanes have difficulty getting airborne in Phoenix on hot summer days because the air isn’t dense enough to create sufficient lift from the wings and power from the jet engines, wind turbines operate less efficiently when the air is hot and less dense. The study says climate change’s effect on wind turbines is too uncertain to estimate a possible loss in power generation capacity, however.
The Arizona State study recommends Western states invest in wind, solar and other “resilient” renewable energy sources while upgrading the power grid and encouraging conservation as ways to overcome some of the challenges climate change poses to the region’s power supply.
ERCOT said in a report last November that its “primary concern with the Clean Power Plan is that, given the ERCOT region’s market design and existing transmission infrastructure, the timing and scale of the expected changes needed to reach the CO2 emission goals could have a harmful impact on reliability.”
- The anticipated retirement of up to half of the existing coal capacity in the ERCOT region will pose challenges to reliable operation of the grid in replacing the dispatchable generation capacity and reliability services provided by these resources.
- Integrating new wind and solar resources will increase the challenges of reliably operating all resources, and pose costs to procure additional regulating services, improve forecast accuracy, and address system inertia issues.
- Accelerated resource mix changes will require major improvements to ERCOT’s transmission system, posing significant costs not considered in EPA’s Regulatory Impact Analysis.
In a countering blog post, Jim Marston, Austin-based U.S. vice president for climate and energy of the Environmental Defense Fund, said ERCOT had overestimated Texas’ challenges in complying with the Clean Power Plan (CPP) and failed to include “key tools” the state can use to comply:
- ERCOT appears to have looked at growing existing energy efficiency programs, rather than the full scale of what Texas could achieve under the CPP.…
- [ERCOT’s] analysis forecasts a boom in solar generation, but it doesn’t take into account the full potential of residential and distributed solar energy, which will not only help Texas meet the CPP, but also help lower prices for homeowners and businesses.
- ERCOT fails to include energy storage technologies that help integrate more West Texas wind energy and solar power by providing backup power when the sun isn’t shining or the wind isn’t blowing.…
- The report does not recognize the real opportunity available to enhance system reliability through demand response, which rewards people for using less electricity, rather than turning on coal-fired power plants to meet electricity demand.…
The Bloomberg news service reported in April that the head of the California Public Utilities Commission was confident that currently drought-stricken state can maintain a reliable power supply completely derived from renewable sources, meaning it can easily achieve Gov. Jerry Brown’s target of 50 percent renewable generation by 2030.
Michael Picker, the agency president, said the California grid had “comfortably” handled solar and wind power up to 40 percent for a few days in 2014, and “can add the flexibility needed to manage power that flows only when the wind blows or the sun shines,” Bloomberg reported.
[Picker’s statement] adds to evidence that grid managers can work with the variable flows of power that come from renewables, undercutting the argument from coal producers and some utilities that clean energy will damage energy security.
Germany got about 28 percent of its electricity from renewables last year, making it the biggest economy to rely on wind and solar.
Picker said that by placing renewable energy resources where they’re needed most to support the grid and shipping excess supplies to neighboring states, California can absorb more variable power flows than it is now.