Portland General Electric tackles a number of challenges in developing infrastructure to support significant solar energy.
The state of Oregon is a leader in driving for energy conservation and the development of renewable energy sources. Portland General Electric (PGE) is a homegrown utility that leads the way in helping the state fulfill its promise. Three years ago, PGE took on the challenge of supplying 25% of its customers' energy needs with renewable resources by the year 2025. Meeting this goal will require a concerted effort between PGE and a large number of suppliers and partners, and the need for collaboration is particularly important in the area of solar power production.
Frequent communications with solar system component vendors and installers are helping to resolve technical issues and are essential to meeting the utility's goals. In particular, two issues are receiving intense attention these days:
Driving down the levelized cost of solar energy (LCOE) and maximizing the return on solar investments
Solving technical problems and developing new technologies to interconnect numerous photovoltaic (PV) resources and maximizing their support for the PGE power system.
A Grid to Support a Shift in Power Sources
PGE is working through these issues and others relating to the nation's developing smart grid infrastructure. For example, some of the developments are necessary to support a fundamental shift in the nation's power infrastructure from a relatively small set of centralized generating resources to a highly distributed network of power sources of different types. The new topologies require grid support for capabilities such as low-voltage ride-through (which requires compensation for voltage changes on the grid), maintaining grid frequencies and economical island detection (the ability to diagnose grid outages when neighboring distributed generators may keep the power flowing).
Enabling utilities to manage and interact with a diverse array of power sources requires two-way communications and control support for interfacing inverter systems (in the case of solar) with utilities. This requires work to develop both the technologies involved and the standards that will enforce interoperability.
Unfortunately, many inverter manufacturers have either grown up from the residential market or not considered utility system communications when developing their grid-tied inverters. Generally, communications systems do not meet the demands of a utility or a large solar developer owner/operator. Many inverters are using proprietary communications systems for their own monitoring software or serial communications that reflect 1970s technology. Though their inverters may use advanced DC-AC conversion technology, current systems on the market do not reflect the direction of smart grid with interoperability and open system standards for communication.
In PGE's distributed resources department, IEC 61850-7-420 is the adopted standard for distributed resource equipment. And the utility expects vendors to consider adopting the same standard. It has been noticed that some new smart meter technology falls short of providing the reliable, fast two-way communication needed for an owner/operator of large distributed solar equipment. If there could be one requested enhancement for all inverters, it would be to install an Ethernet connection with access to a relevant set of common registers and alarms and allow for remote disconnect. Some future enhancements the Electric Power Research Institute is exploring could be deferred for a bit.
Many Technology Issues Compete for Attention
Beyond communications, other inverter issues are being worked as part of the Solar Energy Grid Integration Systems (SEGIS) project, commissioned by the U.S. Department of Energy under the Solar America Initiative (SAI) to encourage the development of new technology and products that will accelerate penetration of PV systems into the country's utility grids. SEGIS has been funding teams of component vendors and utilities to work on specific developments, first in the lab and then commercializing the technologies for deployment nationwide.
PGE is part of a team — led by PV Powered, an Advanced Energy company, and including industry experts Schweitzer Engineering Laboratories (SEL) and Northern Plains Power Technologies — that is working on a subset of these issues.
For example, some SEGIS development work is directed at mitigating the effects of islanding. When power on the grid is interrupted, numerous working solar power sources may become island producers. This situation is more likely to occur as utilities shift to a more distributed network of solar or other distributed power sources.
Traditionally, the response of the islanded solar inverter is to disconnect from the grid so as not to risk becoming damaged by attempting to bear the load of the grid by itself. On the other hand, if a solar inverter could differentiate between the cases of an unintentional island caused by grid failure and a grid situation such as a lower frequency event in which power production support from the PV system would be beneficial, then the solar source could assist in providing stability to the grid.
To capitalize on this opportunity, the Advanced Energy's PV Powered SEGIS team is developing a new method for island detection by leveraging synchrophasor measurements taken between the solar power plant and a utility reference point like the serving substation. Phasor measurement units (PMUs) are devices that take synchrophasor measurements at different locations in a power system using the same absolute time base that compensates for the time it takes readings to arrive at a common collection point, to provide an easy method of correlating power levels and phase angles at different places on the grid. This enables the inverter to differentiate between a true unintentional island case, when it should disconnect from the grid, and a case where grid support from the PV plant is required.
Synchrophasors have been used on utility transmission systems, but use on the distribution networks has been limited because of cost. The SEL team is looking forward to more common use as smart grid developments improve economics.
Smart Grid Demonstrations
The SEGIS team's synchrophasor work was tested on PGE's America's First Solar Highway project, a 104-kW system that contains about 8000 sq ft (743 sq m) of solar panels extending about the length of two football fields. In order to facilitate communications with PGE's command and control systems, the PV Powered solar inverter on the site has been connected to the utility's GenOnSys distributed generation and demand response control system. In this way, PGE is making solar power more dispatchable by treating all inverters and other generation sources, whether owned by PGE or its customers, virtual power plants possessing significant capacity.
GenOnSys allows the utility to aggregate a diverse set of resources located throughout its distribution network and make those resources available to its balancing authority and control area operations.
As part of the Pacific Northwest Smart Grid Demonstraton Project led by Battelle, PGE is implementing smart grid technologies in Salem, Oregon. PGE will be installing fast switching, a 5-MW battery system and various demand-response technologies on a 13-kV feeder serving commercial and residential customers.
The objectives of this project will be to demonstrate a smart self-healing feeder capable of automatically isolating faulted distribution segments from the grid and self-healing after outages. The project also will demonstrate an advanced battery storage system that serves three purposes: to allow ride-through of feeder loads until distributed generation can be started for micro-grid operations, to reduce peak demand and to demonstrate wind and solar balancing of the system. The battery system also can be recharged if abundant wind energy is available during off-peak hours.
How Can Component Vendors Decrease the LCOE of Solar?
A major factor that influences solar power economics is the reliability and uptime of system components. In this regard, a key reliability link is the solar inverter. Industry studies have shown that even though the cost of the inverter is typically less than 10% of the solar power plant, inverters have resulted in up to 70% of system failures. Hence, major improvements in LCOE may be obtained by improving inverter reliability, and the risks to utilities can be mitigated if inverter manufacturers can offer longer warranty periods for their products. PV Powered is one inverter company focused on these issues.
Inverter manufacturers also can provide efficient use of new array technologies and allow for commingling of different panel types, such as thin film and crystalline on the same inverter. The advantages of this capability is evident in PGE's solar highway work. The utility likes the durability of thin film closer to the roadways, where rock and other debris may be kicked into the panels and the higher kilowatt capacities of crystalline in rows farther away from the roadway.
In addition, it is critical that vendors of balance of system (BOS) elements — inverters, trackers, junction boxes, combiners and transformers — collaborate on monitoring technologies and interoperability standards that maximize energy output, minimize system downtime and provide proper alarming of system problems, such as the loss of an inverter or an entire string of solar panels. Again, this capability is important to large distributed solar array systems where the utility or developer manages and protects its investment against downtime in unmanned solar plants, like solar highway development projects.
Is Solar Technology Ready for Prime Time?
In a word: yes. New large-scale commercial systems are proving that solar technologies are mature (enough) to justify the investment by utilities in planning for larger-scale solar deployments. For example, PGE recently participated in the development of a new 3.5-MW project in Portland, Oregon, the largest rooftop solar project in the Pacific Northwest. The project, managed by PGE and co-funded by U.S. Bank, covers 10 ProLogis distribution warehouses in the Portland area with thin-film solar panels.
The first phase of the project comprised three buildings in the industrial zone along the Columbia River near Portland International Airport. The combined solar footprint of this installation is more than 464,000 sq ft (43,107 sq m), with a generation capacity of 1.1 MW.
Completed in December 2008, the installation took only three months from agreement to production ready. The PV panels use thin-film amorphous silicon technology and are integrated into the building roofs. Such panels are lighter than crystalline solar panels, do not require separate racking for support and allow for rapid installation.
The second phase of the project included seven more buildings in three different ProLogis parks. All told, the second-phase installation covered more than 906,000 sq ft (84,170 sq m) and added another 2.4 MW of generation capacity. Phase two began construction in March 2010 and came on-line in July 2010, using the same thin-film technology as the previous phase.
In October 2009, the Solar Electric Power Association (SEPA) selected the first phase of this project as the winner of the SEPA Solar Business Achievement Award in the category “Partnering for Success.”
Making It All Pencil Out
Special financing arrangements (for example, collecting tax incentives and grants, and entering into power purchase agreement programs and U.S. feed-in-tariffs) are helping to get project justifications over the hump from a business perspective. With the current advances in solar system technology and the formation of creative business relationships, such as the solar triad — solar host, utility, tax equity investor — solar's bright future is being realized.
Mark Osborn (email@example.com) is the smart grid manager at Portland General Electric (PGE). He oversees the utility's solar power development, automated demand response, and storage research & development projects. Osborn also leads PGE's efforts in the Pacific Northwest smart grid demonstration project in Salem, Oregon. Under Osborn's management, PGE has installed three major solar installations in Oregon, including the U.S.'s first solar highway project (104 kW) and two of the Northwest's largest rooftop installations totaling 3.5 MW in northeast Portland.
Advanced Energy www.advanced-energy.com
Department of Energy www.energy.gov
Electric Power Research Institute www.epri.com
Northern Plains Power Technologies
Portland General Electric www.portlandgeneral.com
PV Powered www.pvpowered.com
Schweitzer Engineering Laboratories www.selinc.com
Solar Electric Power Association