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.
Q: What electrical system reliability issues have you seen, and how are your technologies addressing these?
Loucks: Switching inductive loads can produce voltage transients, which are initiated whenever there is a sudden change of circuit conditions. We have seen situations where dry-type transformers have been damaged due to switching transients. These switching transients produce both steep-front wave and end-of-turn damage to transformers and motors, but they also excite resonances that occur within a core-and-coil assembly of a motor or transformer. A transient voltage study is highly effective at identifying the corrective measures that are required to avoid system downtime and equipment damage. Typical corrective measures include surge arrestors, damping resistor-capacitor combinations, and modified switching resistors.
Powell: Power outages are occurring more frequently than ever and lasting longer with devastating effects. Siemens standby generators protect homes and businesses from unpredictable weather and unforeseen outages. They are available from 8 kW to 150 kW and are powerful enough to back entire homes or businesses without the cost of an expensive configured system.
Smith: When powering equipment from dc with a direct connection to a backup battery, failures in the upstream ac generation and distribution network do not impact the critical load for a period of time dictated by the capacity of the battery system. Additional isolation from electronic failures is provided by provisioning redundant elements in the system architecture. Multiple redundant battery strings are employed to protect from battery element failures. The same redundant approach is taken in renewable energy systems, with multiple solar panel strings being used to feed the dc storage bus and battery elements through independent converters.
Walker: CES attacks reliability issues head-on and results in a new paradigm for level of service. The CES units are deployed near the customer and contain an energy reserve for reliability. If a facility outage occurs, the storage unit immediately isolates from the grid and continues to supply the local customers. The interruption can be avoided altogether as long as the grid is returned to service within a few hours. Even the momentary interruptions typically associated with a line sectionalizing event are avoided due to the immediate transfer of load from the utility system to the energy storage battery system.
Q: What impacts are green power sources having on system reliability, and how is your company addressing these issues?
Loucks: There is voltage imbalance due to variable single-phase distributed generation. But even 3-phase distributed generation is causing issues. The Texas Competitive Renewable Energy Zone project is adding 20 GW of wind from West Texas and the Panhandle to highly populated metropolitan areas of the state. Due to the variable nature of renewable energy and to reduce flicker, substantial additional power electronic hardware is being added.
As the percentage of renewable power increases, grid stability is reduced. A solution is to provide more transmission interconnects to distribute sources and loads over larger areas. However, there is a lot of resistance to building more towers where people live, work, and play (and rely on electrical power to do so). To address these issues, Eaton is working with energy storage solutions that mitigate fluctuations due to the variable nature of renewable energy. Integrated, grid-tied storage is helping to make renewable energy a dependable, on-demand power that is deliverable with controllable power ramp rates.
Powell: Renewable energy can be hard to control because it generates power intermittently. However, our control systems—together with storage—minimize the adverse impact arising out of these on the micro grid as well as the macro grid.
Smith: Many sources of green power, such as solar and wind, are inherently intermittent. The traditional architecture of a dc power system with battery backup provides protection from the intermittent absence of the green source by storing backup energy for use during these times. Proper understanding of the availability of the sources, combined with appropriate provisioning of the power generating elements, sizing of the storage battery, and provisioning alternative or backup sources, allows for maximum reliability and minimum cost to be achieved.
Walker: One of the concerns of highly distributed, small solar generators is their power output fluctuation, which results from rapidly varying sunlight. The power output variations of solar generators across a distribution feeder are tightly synchronized, causing voltage swings that are faster than traditional voltage regulation can compensate. CES units that are deployed in the same area will provide the necessary compensation to stabilize voltage. The CES units operate in four quadrants, which are defined as real and reactive power both in and out. They can be configured to perform power smoothing where real power is exchanged, stored, or released to compensate solar generator output variations. The CES units also consume or produce reactive power as required to directly control local voltage magnitude swings.
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 188.8.131.52.5 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 184.108.40.206.5 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.
Q: Have you seen the demand for electric vehicle charging stations increase?
Loucks: The demand for electric vehicle supply equipment has increased with grid-connected vehicle sales. With a range of innovative products and services, Eaton is helping to create the critical infrastructure for EV corridors, advance the aggressive early adoption of clean transportation, and reduce customers’ impact on the environment. Smart charging technology that manages the efficiency, availability, and reliability of power—especially during peak times and at popular charging locations—will provide more options to consumers and strengthen the charging infrastructure and the electrical grid.
Powell: Yes, we have seen the demand increase, driven by two market dynamics:
- Increase in deployment of e-vehicle sales: Sales have nearly quadrupled in calendar year 2012 and there is no sales slowdown in sight.
- Energy-efficient/LEED certified/energy-conscious facilities: Building owners and operators are conscious about energy consumption and encourage employees and visitors to act in the same manner.
Q: What tax incentives, rebates, or other incentives should engineers know about (to then pass on to their building owner clients)?
Loucks: The energy-efficient commercial buildings deduction in 26 USC § 179D is expiring this year. However, legislation is being proposed to extend and expand the deduction. This law provides tax incentives for those buildings that use less energy than key ASHRAE industry standards.
Powell: The DOE-sponsored DSIRE website provides information on incentives and policies that support renewables and energy efficiency in the U.S. by zip code and state.
Smith: Many federal, state, and utility company programs can offset some of the cost of renewable energy systems through efficiency improvement incentives. Replacing older, less efficient energy conversion systems with modern, high efficiency systems can reduce utility power consumption and may qualify for rebates and incentives. These programs vary by state and utility provider and should be investigated accordingly.
Q: How will the Smart Grid challenge electrical engineering design/specification now and in the future?
Loucks: As more devices are interconnected, cyber security becomes increasingly important. Traditionally, electrical devices have not encrypted data entering or leaving their communication ports. Solutions include specialized firewalls that perform deep packet inspection of the industrial protocols and help detect unusual activity. However, the fact remains that it will be an arms race between those trying to attack your system and those trying to block that attack.
Powell: The Smart Grid will require power distribution products with smart communication capabilities. Smart devices, such as circuit breakers, relays, and meters, have existed for more than 30 years. These smart devices are self monitoring, configurable, and have communication capabilities, but individually they are only islands of intelligence. Historically, integrated remote monitoring, configuration, and control have been available only with the inclusion of upstream PMCS, PCS, DCS, or SCADA systems.
Q: Describe how your company’s electrical products are Smart Grid compatible.
Loucks: Eaton Smart Grid solutions help to distribute electrical power more intelligently.
With a comprehensive range of services and products, Eaton is helping to reliably, efficiently, and safely manage power across utility, commercial, industrial, and residential markets. Products are now available that include industry standard protocols and methods for connecting to the utility infrastructure, using common protocols such as IEC 61850, DNP3, Modbus (RTU and TCP), and others. Eaton also includes built-in routing and gateway functions that allow devices with other protocols, such as SNMP (a common data center protocol) or BACnet/IP (a building automation protocol), to interconnect with utility protocols.
Eaton has a long list of hardware including one or more of these protocols that spans traditional electrical distribution equipment, control and automation solutions, power quality solutions, and the equipment used in renewable installations and electric vehicle charging. Specific equipment includes:
- Electric vehicle service equipment
- Solar inverters (including integrated solar/EV canopy controllers)
- Utility underground network protectors
- Protective relays for switchgear, transformers, generators, or bus
- Reclosers and sectionalizers
- Rectifiers, such as dc power systems for telecom
- Power and power quality meters
- Power factor and harmonic correction units
- Automatic transfer switches
- Generator switchgear (diesel, natural gas, propane, and biogas)
- Programmable controllers
- Human/machine and operator interfaces
- Intelligent power strips
- Low- (1,000 V and less) and medium-voltage (40 kV and less) circuit breakers
- Plasma power supplies for dc welding, plasma torches
- Smart motor control centers—both low voltage and medium voltage
- Building lighting control and automation systems
- Grid tie inverters and battery storage systems
- Power conditioning products, such as sag ride-through and electronic voltage regulation
- Predictive diagnostic solutions.
Powell: With the advent of smart gear—such as Siemens’ smart low-voltage switchgear—remote monitoring, configuration, and control become standard features that are integral to the electrical apparatus product.
Smith: GE’s focus on power conversion efficiency and its use of alternative energy sources, such as solar, are very consistent with the goals of the Smart Grid and the use of distributed generation sources. Building intelligent controls and communications into all of our products enables easy integration into a Smart Grid capable of managing both sources and consumers. In addition, telecom users using intelligent dc power systems are currently able to respond to requests to go off grid during times of peak demand and use their backup sources or battery reserves during these high-demand periods.
Walker: Our Smart Grid offerings necessarily comply with utility technical requirements including communications protocols, interoperability, and security. Beyond that, they must also be compatible with the environment within which they operate. The metamorphosis of the distribution dispatch center into an operations center with a broad range of responsibilities requires an astute understanding by the supplier.
Smart Grid solutions must fit into the operating environment without burdening the operator or introducing new complexities. This is accomplished by having systems that are fully autonomous and permit quick and easy understanding of system performance at a high level along with underlying details if and when desired. It is not sufficient to address only technical compatibility. Compatibility with operational philosophies must also be taken under consideration.