Friday, March 16, 2018

A Sunny Trend for Solar Energy in the Bluegrass State

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Kentucky Utilities Use EPRI Research to Design and Build 10-Megawatt Solar Power Plant

In Kentucky, one of the nation’s largest coal-producing states, coal-fired power plants have long served as a primary source of electricity generation. While the Bluegrass State is one of only 21 states without a renewable energy standard or goal, deployment of renewables is growing here. With technical support from EPRI, Louisville Gas & Electric Company and Kentucky Utilities Company (LG&E and KU) recently designed, developed, and commissioned a 10-megawatt solar facility at the E.W. Brown Generating Station in Harrodsburg, Kentucky.

According to Dr. Nicholas Jewell, an R&D electrical engineer and scientist with LG&E and KU, changing environmental regulations and growing customer interest in renewables could increase solar’s market share. These factors are driving the energy company to assess the technology through projects such as the Harrodsburg solar facility.

“While solar has been on our technology radar, we had very little practical experience with it,” said Jewell. “As regulated utilities, LG&E and KU are required to provide reliable, safe energy at a reasonable cost to our customers. But solar energy generation in our service territory poses a challenge to that model.”

Jewell adds that in Kentucky the levelized cost of electricity of a new solar facility is nearly double that of an existing coal-fired power plant, primarily as a result of differences in capacity factor and energy availability. (The cost of solar varies widely by location; there are areas in the United States where it is one of the lowest cost energy options.) The energy company relies on coal- and natural-gas-fired plants to provide backup capacity when the solar plant is not available, including times of intermittent generation as a result of passing clouds.


The 10-megawatt solar facility at the E.W. Brown Generating Station. Photo courtesy of Louisville Gas & Electric Company and Kentucky Utilities Company.

According to Jewell, approval of large solar projects in Kentucky can be time-intensive because requirements and processes for renewables are still emerging. For example, state law requires electricity utilities to charge “fair, just and reasonable rates for services rendered,” and the Kentucky Public Service Commission (KPSC) only recently began expanding this requirement to consider higher cost renewable energy.

Jewell says that EPRI reports and technical guidance on solar technology options helped LG&E and KU inform its internal decisions and also inform the KPSC as it considered approval of the project.

“LG&E and KU’s Research and Development team relied on EPRI research products and staff expertise to get up to speed on various solar project design and development considerations, as well as best practices for plant operations and maintenance,” said EPRI Senior Technical Leader Cara Libby. “They participated in EPRI field testing projects, attended in-person meetings and webcasts, reached out to EPRI staff with technical questions, and incorporated relevant knowledge and insights into their project.”

While seeking approval from the KPSC, LG&E and KU drew supporting information on technology options, solar irradiance in Kentucky, and power production profiles for different system configurations from EPRI’s Solar Power Fact Book. The same resource helped inform their system design, including capacity and sizing, mounting structures, weather monitoring, and cables and conduits. LG&E and KU staff also gathered design information during EPRI meetings hosted at the Solar Technology Acceleration Center (SolarTAC), an outdoor test facility near Denver, Colorado.

From a design perspective, solar arrays with trackers produce more energy than fixed-tilt arrays, but typically have higher capital, operations, and maintenance costs. In most scenarios, EPRI research has shown trackers to be the most cost-effective option. However, LG&E and KU opted for a fixed-tilt array, concluding that maintenance of motors, linkages, and other tracker components would make their overall project less cost-effective.

To compensate for the lower output of fixed-tilt arrays, the utilities are applying a clever adaptation detailed in the Solar Power Fact Book. Developers often “overbuild” solar fields, installing extra direct current (DC) production capacity relative to the alternating current (AC) plant output. This makes up for conversion losses at the inverter, increasing energy production at minimal additional capital cost. Based on an internal analysis, the energy company found that aggressively overbuilding the plant with fixed-tilt arrays would sufficiently increase the plant’s capacity factor and reduce operations and maintenance costs, yielding a lower levelized cost of electricity relative to a tracking system.

Practices for mounting panels onto racking systems were based on research results from EPRI solar performance testing at SolarTAC. LG&E and KU also adopted solar forecasting and performance monitoring tools, panel cleaning, detection of defective panels, and other aspects of operations and maintenance described in EPRI research results from SolarTAC.

Collaborative EPRI research at the Southeastern Solar Research Center helped to inform the utilities’ decision to monitor solar energy production at the combiner boxes in addition to the inverters. According to Libby, combiner box–level monitoring can provide more granular production data and better insight into performance and maintenance needs.

LG&E and KU adopted EPRI best practices for monitoring weather and system conditions such as solar irradiation, back-of-module temperatures, and ambient temperature, pressure, and humidity.

“Production data from the combiners every second—along with data from on-site weather stations—help us to see how well this plant is operating,” said Jewell.

The plant has attracted plenty of attention from customers, utilities, and other organizations requesting site visits to learn more about deploying solar. As a result of this interest, LG&E and KU have expanded their solar program offerings. Options for residential and business customers now include net metering for installations, a program allowing customers to buy renewable energy credits, and a community solar program called Solar Share.

The experience with the E.W. Brown solar facility informed a new business solar program, in which the utilities build and maintain solar facilities on customers’ properties. Participants pay a fixed monthly fee and receive credits for renewable production.

Key EPRI Technical Experts:

Cara Libby

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