The impacts of the large-scale deployment of intermittent renewables—wind and solar—on conventional generation technologies, as well as on the power grid, was the topic of a report released by the MIT Energy Initiative (MITEI) at a panel discussion and press briefing on March 12.
The report, Managing the Large-Scale Penetration of Intermittent Renewables, summarizes the discussion and findings of a group of subject-matter experts who participated in a MITEI symposium on the topic held on campus last year. Highlights from the symposium and report were discussed at the March event by a panel of MIT experts that included MITEI Director Professor Ernest Moniz, who moderated the panel; MIT Institute Professor John Deutch; Howard Herzog, MITEI senior research engineer and director of the MIT Carbon Capture and Sequestration Technologies Program; Visiting Professor Ignacio Perez-Arriaga, Engineering Systems Division and Center for Energy and Environmental Policy Research; MITEI Executive Director Melanie Kenderdine; and John Michael Hagerty, graduate student in MIT’s Engineering Systems Division.
Symposium/report focus, findings
Twenty-nine US states, the European Union, and a number of other countries have adopted policy mandates and incentives to promote wind and solar power generation, both of which are intermittent. Absent large-scale storage options, these sources must be accommodated by the power delivery system as well as by the traditional thermal (coal, oil, natural gas, nuclear) generation units. The intermittent nature of wind and solar complicates the balancing of supply and demand while preserving reliability and economically efficient dispatch from the range of generation units within a service area or system. The proper allocation of costs requires an understanding of the system impacts of intermittent sources, including the need for backup capacity. The premise of the symposium was that implementation of appropriate cost allocation and operational protocols is a key enabler for future large-scale deployment of intermittent renewables.
The symposium examined several key areas of concern related to such mandates, including their emissions impacts, unintended consequences for system planners and market participants, impacts on the future generation mix and electricity markets, and the adequacy of existing regulatory frameworks and requirements. The following are some of the key findings in the symposium report:
Generation units
- Coal: Coal units are mostly not designed for flexible operation and will have efficiency reductions, increased emissions, and operational issues when pushed to operate flexibly. It is technically possible to design and retrofit coal units for flexible operation, but the required changes would be significant for existing plants.
- Nuclear: Relatively new nuclear reactors ramp “asymmetrically,” meaning plants can ramp down relatively quickly but take much longer to ramp back up to full load. Some nuclear plants in France were designed specifically to follow load. Also, nuclear plant ramping is not fully automated, increasing the potential for human error.
- Natural gas: Natural gas power plants provide the greatest generation flexibility to help manage intermittent renewable generation. New natural gas combined cycle (NGCC) plants continue to improve this capability, including rapid changes in power levels.
Economic impacts
- Absent the availability of utility-scale storage, incentives will likely be necessary to encourage investment in flexible generation.
- Flexible operation of nuclear plants dramatically impacts their profitability. Very high capital costs mean that nuclear plants need to run at high capacities to recoup investment costs.
- For economic reasons, plant owners will likely operate existing coal plants with minimal flexibility upgrades.
- The higher fuel cost for NGCC units generally places them last in the dispatch order; policies that mandate the dispatch of renewable generation, combined with the relatively low capacity factors for NGCC units, makes cost recovery more difficult because capital is amortized over fewer hours.
Transmission grid and system operations
- Intermittent renewables present integration challenges at all timescales for the power system. As renewable penetration increases, system stability on the timescales of a fraction of a second will increasingly matter, much like backup capacity currently matters at timescales of minutes and hours.
- Current algorithms to manage intermittent renewables do not accommodate the uncertainties involved in forecasting wind, load, and other variables. New algorithms and tools need to be developed to conduct geographic and temporal analyses and simulations that are of sufficient scale for power systems. Acquiring useful data from industry for such work is difficult.
Policies and regulation
- Policy challenges for integrating intermittent renewables exist in both short-term operations and long-term planning in order to maintain a reliable, economically efficient power system.
- The major areas being considered for policy/regulatory changes are reliability criteria, capacity markets, and cost allocation. New incentives that promote flexibility are needed.
- Too much generation from intermittent renewables is as much of a problem as too little; many renewables mandates require the dispatch of wind energy regardless of demand.
- Policy solutions need to be regionally focused because of vast geographic differences in resources, demand, and markets. Regions will need research to produce careful regulation that meets the needs of stakeholders and ensures overall system reliability and efficiency.
MITEI Symposium Series
This symposium is part of a series at MITEI designed to provide policymakers with technically grounded information and findings on topical energy issues. The series also provides graduate fellowships to support the symposium; graduate students Michael Hagerty and Tommy Leung served as rapporteurs for this symposium and are completing their master’s theses on related topics. MITEI Associate Members Cummins, Entergy, Exelon, and Hess provide support for the series. Earlier reports in the series include Retrofitting of Coal-Fired Power Plants for CO2 Emission Reductions and The Electrification of the Transportation System. The next symposium will address the prospects for alternative fueled light-duty vehicles. The symposium report on intermittent renewables includes seven white papers commissioned by MITEI from various experts to inform the discussion and the findings.
This article appears in the Spring 2012 issue of Energy Futures.