Green power roundtable: Exploring green impacts of electrical distribution systems
Energy efficiency is a buzzword for building owners and engineers' clients. Demand for distributed generation (DG) and renewable energy sources, such as wind and solar, is growing rapidly. Here, a group of experts discuss the impact that DG (10 MW or less) and renewable energy sources, which are connected to the utility at the distribution level, have on distribution system reliability.
Meet our green power roundtable participants
- David G. Loucks, PE, CEM, manager, Power Systems and Advanced Applications, Eaton, Pittsburgh
- Barry Powell, vice president, Low Voltage and Products business unit, Siemens Industry Inc., Norcross, Ga.
- Paul Smith, technical marketing manager, Critical Power business, GE, Plano, Texas
- Tom Walker, PE, senior engineer, Automation Systems, S&C Electric Co., Chicago
Q: How have the characteristics of electrical distribution systems changed in recent years, and what should engineers expect to see in the near future (1 to 2 years)?
Loucks: Today’s electrical distribution systems are smarter, more connected, and better able to provide the information needed to help operation and maintenance personnel identify and correct problems for more reliable and efficient operations. For example, predictive diagnostics now includes medium-voltage insulation monitoring that can detect and locate insulation degradation in real time, so that maintenance personnel can fix the problem and help to avoid downtime and equipment damage. Equipment environmental monitoring is helping to identify adverse conditions. Advanced centralized monitoring—both in-house and with contracted third parties—provides an overview of power and energy systems and delivers specific information to keep facilities operating efficiently and reliably. Sophisticated intelligence involves advanced protective relaying and automatic throw-over schemes to maintain service continuity. There is also more reliance on environmentally friendly vacuum switching technology that avoids the use of sulfur hexafluoride, which may contribute to the greenhouse gas effect. There is a commensurate increased need to perform transient voltage studies, especially for low BIL devices such as motors or dry-type transformers. Additionally, there is a higher percentage of power electronic loads, so there is more harmonic distortion. Harmonic, grounding, and voltage flicker analyses are helping sensitive circuits operate effectively.
Powell: The trend for increased arc flash protection of personnel has impacted low- and medium-voltage power distribution designs. Another trend is the need for increased energy efficiency, which has resulted in a need for increased transparency of energy usage within the power distribution system.
Walker: New and innovative approaches have increasingly been introduced by electric utilities over recent years to gain better and smarter utilization of distribution assets. At the heart of this revolution is the superposition of telecommunications on the power system. With this comes an abundance of opportunities to apply intelligent devices for the monitoring and control of the distribution system. Monitoring is a crucial component of the improved view of operating conditions enabling faster, more effective response to problems. Remote control by distribution operators enables response that may delay or eliminate dispatch of physical crews. Even better, fully automated systems bring the concepts of self-healing and asset optimization to reality.
Among the initial trials and pilot efforts, there have been successes that now provide a meaningful basis for utilities to establish plans moving forward on a larger scale. Over the next couple of years, many of these success stories will result in larger scale deployments of mature smart technologies that have met expectations.
Q: Describe the various green electrical generation sources, such as wind and solar, you’ve provided for nonresidential buildings, and their challenges and opportunities.
Loucks: With a robust services organization and a range of balance of system solutions for utility and commercial (and residential) installations, Eaton is improving costs and system performance, and reducing dependence on fossil fuels. Eaton has installed a number of solar PV systems on both our own and customer facilities, ranging in size from a 20 kW solar parking canopy to a 3 MW system on multiple buildings.
Solar PV systems typically do not supply a building’s total electrical requirements, but rather offset the electrical purchases from the local utility. Solar PV systems also generate solar renewable energy credits, or SRECs, that can be used to offset GHG emissions.
Powell: Siemens provides solar microinverters for commercial and light industrial markets. These solar microinverters have a slightly higher upfront cost. However, for financially savvy customers, microinverters provide a greatly reduced long-term cost of ownership for solar installations. According to a recent study, by providing 7% to 10% more energy, solar microinverters provide a faster payback due to greater energy cost offset. In addition, microinverters provide lower cost maintenance requirements because of the distributed nature of the system itself and a standard 25-year warranty.
Smith: GE’s Critical Power business provides telecom service providers with products, engineered solutions, and services designed to operate from a nominal -48-V dc power supply. Traditional telephony specifications call for 99.999% availability, so battery backup on the dc bus is standard operating procedure. Cell sites in remote locations require the same level of power availability, and solar energy is a favored renewable source for these locations. Conversion of the dc energy obtained from the solar panel directly to the -48 V required by the battery and load eliminates conversion steps and maximizes efficient use of this energy. The battery maintains availability of load supply and stores energy during daylight or sunshine hours for use when the sun is not shining. In cases where the solar energy is insufficient to power the load, a standby generator is used to supplement this energy. The combination of the energy from the standby generator on the dc bus with battery storage forms a simple and reliable system.
Q: What trends are you seeing in distributed generation sources?
Loucks: According to the Solar Energy Industry Association, the average installed price for a nonresidential commercial solar photovoltaic system in the U.S. fell from $4.31/W in Q2 of 2012 to $4.18/W in Q3 of 2012. For projects above 100 kW, the final project prices were consistently in the $2.25/W to $2.75/W range. Also, the Federal Investment Tax Credit is helping to offset project costs in the U.S. with a 30% tax credit for residential and commercial solar systems. This tax credit is available through 2016. Further, many states provide various financial incentives. These can be accessed through www.dsireusa.org, a U.S. Dept. of Energy sponsored site.
Powell: The number of distributed generation and renewable energy installations is growing rapidly globally. Solar PV and wind are the most widely used forms of renewable energy in facilities/campuses as well as eco districts.
Walker: Stepping beyond automation of the classic components of the distribution system, this better, smarter grid also incorporates distributed resources that can be controlled independently or collectively to have a dramatic impact on the balance of supply and demand with regard to both power and energy. Initial efforts tended to focus on a small number of larger installations. The trend, however, is toward incorporation of more, smaller installations. This trend crosses the spectrum of distributed resource offerings: demand response alternatives; renewable generation, such as photovoltaics, Volt/VAR management as a means of reducing consumption, and energy storage. The trend is toward highly distributed deployments. A crucial aspect of this is the aggregation of these many small distributed resources in the manner that benefits the power system as a whole; at the generation, transmission, and distribution levels.
Community Energy Storage (CES) is an interesting example of this. It aggregates many, small storage facilities that provide benefits at a higher level while meeting local needs. The small units are installed near customer service points on the low-voltage side of distribution transformers. Here, they can address local needs and can also be controlled as a fleet to respond to feeder and substation level concerns. They may even be called to service for major system events that require capacity curtailment, which could be accomplished by shifting customers to local storage rather than dropping loads.
Q: What payback period are engineers and building owners requesting for renewable electrical generation projects?
Loucks: The payback for a solar PV system varies widely based on the local electric utility rates. In addition, many states offer various financial incentives, which are summarized at a DOE-sponsored website (www.dsireusa.org). In some states, such as Hawaii and California, paybacks can be less than 2 to 3 years. Eaton looked at several solar projects in Ohio and Pennsylvania that were in the 8-year payback range. However, most nonresidential solar projects in the U.S. are now financed through Power Purchase Agreements (PPAs), where the building owner typically puts little or no money into the project upfront. Instead, the building owner agrees to purchase the power produced by the solar PV system for a period of time (typically 20 years). With a PPA, there are various energy procurement scenarios possible, including either fixed costs or indexed rates adjusted to the local utility rates.
Powell: It varies. Most private customers want grid parity in energy cost and would prefer a PPA that guarantees this.
Smith: In the telecom service-provider market, there is considerable pressure to maximize the return on investment (ROI), especially in power equipment, which is not considered revenue generating. Typically, ROI periods are expected to be less than 3 years and preferably less than 2 years. Current costs of solar panels do not lend themselves to achieving these short payback periods, especially when compared to the fairly typical $0.10/kWh available from the utility grid. When the alternative is the investment of installing grid power to inaccessible sites or generators with the associated fuel and transportation costs, solar energy begins to be a more attractive source.