Green power roundtable: Exploring green impacts of electrical distribution systems
Q: Integration of facilities’ varied electrical generation systems is becoming more prevalent. How is your company/product meeting this need? Provide a recent project example.
Loucks: When integrating varied electrical generation systems, it is important that the system is designed so that faults are localized and that one system cannot disrupt another. There are specific standards in place for interconnecting distributed generation sources. However, there are aspects of the standards that can be challenging, especially for biogas power generation providers, which generate electric power from methane gases extracted from a landfill or digester to fuel reciprocating gas engines. IEEE 1547: Standard for Interconnecting Distributed Resources with Electric Power Systems addresses how the control and protection logic within a distributed generation system is supposed to function. Yet, Section 220.127.116.11.5 of the IEEE 1547.2 standard states: “In some cases, reactive scheme protection can be fooled if the generator is able to carry the load of the island without a substantial change in voltage or frequency.” This means that proper operation of the distributed generation system can be compromised if the power output exactly equals the power consumed at the site, in other words, there is no net power flowing through the utility connection. In this case, utility power can disconnect and reconnect from the site without the protection logic detection, potentially causing resynchronization problems that result in damage to the distributed generation system. To address this problem, Eaton developed a unique solution (U.S. Patent Application 12/967,688) that deals with this problem by modifying the algorithms used to control the engine-generator, which helps enhance installation safety and reduce equipment risks and service interruptions. UL has witnessed and certified that this solution does solve the problem outlined in 18.104.22.168.5 of IEEE 1547.
Powell: Our control systems help to keep the overall energy costs low while keeping the network stable. We have several examples of this in Europe.
Smith: The combination of multiple electrical generation sources onto a single dc bus along with the use of independent, controlled power converters allows for seamless integration of multiple sources without the need for transfer switches or the possibility of an interruption. Appropriate prioritization of power sources minimizes the cost of operation without compromising reliability.
At a recent off-grid cell site installation, 39 solar panels provided the primary source of power to a 2,000 W radio system load. For this installation, three strings of valve-regulated lead-acid (VRLA) batteries provided backup and power storage capability for up to 100 hours. A propane generator is also available on-site to provide power in case of extended absence of solar energy.
Q: Which code/standard proves to be most challenging in electrical distribution systems?
Loucks: Some facilities have found it difficult to keep up-to-date with evolving electrical standards, especially safety standards. Yet, OSHA’s General Duty Clause prohibits ignorance of the law as an excuse. Examples include the 3-year code cycles for NFPA 70: National Electrical Code (NEC); 2011 is the latest version, and NPFA 70E: Standard for Electrical Safety in the Workplace; the 2012 version is the most current. These standards require that the employer certify that the workplace is safe and that personnel have been trained. This places a large burden on organizations to be educated on the latest requirements, even while the laws change.
Powell: Selective coordination within a distribution system has been a challenging topic over the past several years, as engineers have sought to balance these requirements with personnel safety, equipment protection, and cost. To complicate the discussion, different locales within the U.S. have varying levels of adoption of NEC requirements, resulting in a nonuniform approach across the country. Our approach is to help educate engineers on the requirements and the impact on equipment/system design, as well as work with the standards community as it further refines the requirements for power distribution systems.
Q: Which renewable energy system is the engineering community requesting the most information about? Describe any information or data you have on this trend.
Loucks: Biogas electric power generation is a growing trend from both landfill and wastewater treatment. Methane that normally leaks directly into the atmosphere is captured and used as free fuel for on-site electrical generation. This method of carbon capture is net-zero because no new carbon is put into the atmosphere as a result of the power plant.
Landfill gas has generated a lot of interest. Wastewater treatment plant digester-methane powered electrical generation has received a lot of interest. Beyond the free fuel aspect, wastewater treatment plants can use the waste heat to accelerate the digester process and reduce retention times. This can serve to reduce capacity (tank) sizing, which reduces the capital needed to build the tanks. In a 2011 study, the U.S. Environmental Protection Agency estimated that several hundred existing wastewater treatment plants across the U.S. are good candidates for digester methane capture.
Powell: As most of the micro grids are facility/campus based, solar PV is the most preferred form of renewable energy for these because they can be mounted on the rooftop and are already close to grid parity in price.
Smith: From my perspective or experience, the most popular renewable energy system is the solar panel. As costs decrease, I expect this trend to continue. As previously stated, the cost has not come down to a point where solar panels are an economical alternative to the $0.10/kWh grid power and do not provide the ROI that our customers expect. However, in cases where inexpensive grid power is not available or very unreliable, it is a very attractive alternative.
Walker: Highly distributed, small PV panels are generating a great deal of interest in order to avoid problems on distribution as penetration increases. CES is commonly included in the discussion as one possible means to address issues. The fact that CES is also highly distributed and can be co-located near the PV generation sources solves the problem and makes it a technically attractive solution.