Environmental Engineering Reference
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solar-thermal projects connect directly to the high-voltage transmission grid. These
generators are often directly integrated into wholesale electricity markets, with power
plants sold to utilities, or bid directly into the wholesale markets. Managing large-scale
renewable variability and integrating renewable resources into the system presents an
ongoing challenge. Improved prediction of wind and solar resources and developing new
control systems to manage large-scale renewables all depend on smart grid technologies.
By contrast, rooftop solar photovoltaic (PV) and small-scale wind turbines connect
directly to the low-voltage distribution grid, which is usually operated by the local utility.
Many argue that the addition of distributed generation diversifies supply, reduces risks
of outages, improves overall grid reliability, and reduces fossil fuel reliance and carbon
emissions, but integration into a distribution network that was not designed to directly
integrate production and allow bidirectional flow has proven challenging. The Pecan Street
Smart Grid pilot project in Austin, Texas, for example, has encouraged more than 200
homes to install rooftop solar PV. As more distributed generation is deployed, continued
development of communication protocols and control technology is needed to ensure
smooth integration. Each of these technologies could be considered a smart grid
technology.
3.3.3 Transmission Technologies for Smart Grid
One smart grid technology that is crucial for the integration of more distributed renewable
electricity into the grid is the grid-tie inverter (GTI) that converts DC electricity into
AC. Renewable generation from solar PV or wind turbines produces DC electricity, while
the grid transmits and distributes AC electricity for use by households and industrial
consumersofelectricity.EfficientconversionoftheDCpowertoACisnecessarytoenable
more renewable generation to contribute to the electricity system for both the high-voltage
transmission system and the low-voltage distribution network. With the grid-interactive
inverter, electricity generated from small-scale renewable technology, such as solar and
wind, which is not used on-site can be sold back to the utility's distribution network and
compensated either through net metering or feed-in tariffs. The grid-tie inverter includes an
oscillator that synchronizes the frequency of the renewably generated electricity to that of
the grid. Another function of the GTI is to disconnect from the grid if the electricity in the
grid is disrupted. This safety function prevents electricity from flowing in the downed grid
system while repairs are made, but it also means that households or businesses with solar
PV on their rooftops cannot use the generated power until the system is back online.
One of the most important smart grid technologies associated with improving the
transmission part of the electricity system is the synchrophasor or phasor measurement
unit, a technology that measures conditions on transmission lines through assessment of
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