[Editors] MIT studies impact of solar energy on emissions reductions

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MIT studies impact of solar energy on emissions reductions
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For Immediate Release
THURSDAY, APR. 8, 2004
Contact: Nancy Stauffer
Phone: 617-253-3405
Email: stauffer at mit.edu

CAMBRIDGE, Mass.--State regulators are required to develop formal plans 
describing the monitoring programs, emissions standards and other 
measures they will undertake to ensure that their regions meet federal 
clean air laws. Now an MIT study can help them obtain reasonable 
estimates of the emissions reductions they could achieve by including 
solar-generated electricity in their plans.

Researchers at MIT’s Laboratory for Energy and the Environment’s 
Analysis Group for Regional Electricity Alternatives (AGREA) used 
information from numerous databases, including that of the U.S. 
Environmental Protection Agency, to look at how emissions reductions 
from solar photovoltaic systems vary across the contiguous 48 states.

The researchers examined hourly electricity generation from 
photovoltaic systems and matched it with the per-kilowatt-hour 
emissions from fossil-fuel-fired units in the same power grid, in the 
same hour. To make their “avoided emissions” estimates more accurate, 
they used EPA’s generation and emissions data from 1998 to 2002 to 
calculate emissions rates from those fossil units that respond to 
changes in electricity demand, including changes due to the operation 
of small sources of generation such as photovoltaic systems and small 
and moderately sized wind farms.

Their results confirm that emissions reductions from “nondispatchable” 
resources such as solar and wind generation and electricity 
conservation are highly dependent on exactly where they are used and 
the relation between the solar resource and electric system demand.

For example, in Texas, photovoltaic systems displace more pollutant 
emissions in winter than they do in summer, even though the 
photovoltaic systems generate more electricity in summer. The 
explanation: in summer, Texas must bring on more expensive, yet cleaner 
natural-gas-fired methods of generating electricity to meet 
air-conditioning needs, so the first units to respond to the 
solar-generated electricity are the cleaner ones.

Another comparison shows that a photovoltaic system used in the 
Southwest will produce 30 percent more kilowatt-hours than similar 
systems in the Ohio Valley will. However, the resulting reduction in 
annual sulfur dioxide emissions will be greater in the Ohio Valley 
because coal-fired power plants in that region use coal with higher 
sulfur levels. Both observations demonstrate the importance of putting 
future renewable systems such as solar and wind not only where it’s 
sunny or windy, but also where electricity production is dirty. It also 
points toward incorporating the environmental benefits in evaluating 
the economics of solar power.

The study was conducted by graduate students Michael Adams and 
Katherine Martin of MIT’s Engineering Systems Division, assisted by 
AGREA director Stephen Connors and LFEE research engineer Edward Kern.

The MIT group is looking to extend this work to emissions reductions 
from wind power and electricity conservation. With estimates of where 
and when wind power is being generated or where energy savings from 
conservation programs occur, the researchers can easily calculate the 
emissions savings there.

Other AGREA activities include continuing to help the Mexico City 
Program design integrated emissions-reduction strategies, and a new 
project with universities in Norway and Sweden to identify viable ways 
of moving to a sustainable energy future.