Integrating Renewables

Deck: 

Opportunity for advancement or exercise in futility?

Fortnightly Magazine - March 2010

With the U.N. Climate Change Conference in Copenhagen now over, the electric utility industry is under an ever-expanding microscope and is being confronted by a wide array of global energy concerns, a result of political and economic policies targeting climate change. While the Copenhagen Conference might not have been the success that some hoped, it has caused intensified scrutiny. Many of the concerns addressed at the conference have created the most significant impetus for change the industry ever has seen. The subsequent alignment of worries among many politicians, regulators, and customers has renewed concerns that ultimately should result in new legislation and regulations aimed at combating climate change.

An important concern that will need to be addressed by the industry as it tries to combat climate change is the incorporation of new sources of renewable energy (e.g., wind and solar) into the electric grid. Integrating these new sources of energy will result in a variety of positive outcomes, including the reduction of carbon emissions, the curbing of reliance on foreign sources of energy, and the creation of new green sector jobs that have become a constant topic of discussion in the current economic and political climate.

Renewable sources of energy also pose significant challenges, because they operate in a very different manner from the more common forms of energy generation. Renewables tend to be more expensive, while their energy production is neither constant nor predictable. For these reasons, the electric utility industry has been slow to embrace renewables as the answer to current and future energy production needs. In order to allow renewable energy sources to evolve into a possible solution, new tools need to be developed to forecast and control their production capabilities as they become increasingly prolific, while new forms of energy capture and storage also need to be devised or further improved.

Fortunately, recent scientific and technological advancements to assist with this process currently are being analyzed, and several of them are being piloted. Examples of these recent advancements include: wind energy forecasting, power system visualization and transparency in grid operations, and advanced concepts of power system automation and control through the use of phasor measurement units (PMUs). Ultimately, integrating renewable sources of energy into the electric grid will be viewed from one of two conflicting viewpoints. Will this process be viewed as an impediment to progress, or as the next great opportunity for the electric industry?

As the climate-change debate continues to rage, and regardless of one’s position, there are certain incontrovertible facts:

• The cost of gasoline and other petroleum-related fuels will continue to rise as global demand increases, while at the same time the availability of low-cost reserves will decrease, making production even more expensive;

• Auto makers are attempting to reposition themselves as friends to the environment, with the introduction of electric and electric-hybrid vehicles, leading to increased electrification of transportation; and

• Electric load is continuing to grow both in quantity and complexity, forcing utilities to think of new ways to deliver increased load without the added costs or difficulty associated with new generation.

The electric utility industry has accepted these facts and is attempting to increase its emphasis on developing and deploying new and alternative forms of energy generation and storage. In order to come to fruition, the challenge of renewable integration will need to be addressed as a key science and technology issue.

The U.S. Department of Energy (DOE) has recognized these needs as a priority for its National Labs and, in an attempt to hasten development, has tasked them with investigating renewable integration and energy storage options, in cooperation with the private energy industry.

As new energy sources become essential to overall energy production and availability, the associated technologies and the ability to integrate them into the electric transmission and distribution grid becomes critical.

Renewable Characteristics

An energy resource qualifies as renewable if it is replenished by natural processes at a rate comparable to, or faster than, its rate of consumption by humans. This definition highlights two major dimensions of renewable energy:

• Sustainability: From an energy perspective, sustainability refers to a resource’s ability to be replenished at a rate comparable to, or greater than, the level at which it is used. By this definition, energy derived from traditional sources like coal and oil can’t be considered sustainable because at some point in the future they no longer will be available.

• Reduced Environmental Footprint: Renewable energy resources should, ideally, significantly reduce the emission of greenhouse gases (GHG) into the atmosphere, reduce the need for limited resources such as water, and avoid the creation of other waste products (e.g., fly ash) that cannot be recycled easily. Reduction of waste and disposing of waste harmlessly also are areas of increased focus.

While both traditional and renewable sources of energy require financial investments, the former creates a situation in which the commodity costs of the fuel required to produce the energy will continue to increase (i.e., as evidenced by the cost of gasoline last year), when at the same time, the potential of finding new sources of inexpensive fuels diminishes over time. A renewable resource, on the other hand, will continue delivering power over a much longer period of time at a consistent or reduced cost. Renewable resources will require a vastly different restriction on the generation of power. Fossil fuel-based generation (e.g., coal, natural gas and oil) also creates GHG as a byproduct. Newly conceived financial systems are being developed (e.g., carbon tax, cap and trade, etc.) to deal with the broader societal costs of these emissions, which also will result in increased costs for GHG-producing generation. The renewable sources of energy largely would be immune to these taxes because they don’t release GHG. As some of these programs are very aggressive, certain countries, as well as many U.S. states, have developed renewable portfolio standards (RPS) to promote development. Implementation of a national RPS standard currently is under debate in the United States.

Not all sources of renewables present significant problems involving integration into the market and operations. For example, small hydroelectric, biomass and geothermal generation are more predictable in terms of production levels. The major challenges will come from solar and wind energy.

Photovoltaic (PV)-based generation is an intermittent source of renewable energy, generally deployed in local situations. Thanks in part to limited use of PV up to this point, integration hasn’t posed major problems. While the amount of concentrated solar generation is expected to increase significantly over the next 15 to 20 years, its impact as a percentage of the overall generation mix will remain low in most locations. As a result, while integration standards for the local distribution grid are required, no serious system operating issues are expected with the expansion of market penetration by the current generation of solar power.

New wind generating facilities are the fastest renewable resource to install and interconnect to the power grid. Wind generation, however, also presents the most significant operational and planning challenges. The penetration of wind-generated power is anticipated even in largely urbanized regions of the United States during the next decade.

The challenges of wind integration at scale can be viewed as seven associated, but distinct, attributes that are characteristic of intermittent wind energy sources:

• Intermittency: Wind generation energy production is extremely variable. In many places, it often produces its highest energy output when the demand for power is at a low point. During periods of favorable wind conditions, it’s possible that all wind projects in an area will be at their full energy output. If that happens, the transmission line could become overloaded and wind generation on that line would need to be curtailed.

• Ability to dispatch: Unlike traditional forms of generation, renewable forms of energy (especially wind and solar) will generate only when the wind is blowing or the sun is shining. Controlling their output, in these instances, is an obvious challenge.

• Remote siting: Wind projects tend to cluster mainly in rural areas not supported by strong transmission systems, and remote from major load centers. Consequently, wind projects have tended to cluster along unfavorable locations, often on lower voltage transmission lines.

• Ability to Forecast: Wind generation is difficult to forecast because it doesn’t always follow a predictable production pattern and forecast technologies aren’t well developed. Solar has similar limitations as a localized cloud cover can suddenly reduce or eliminate the power output.

• Land Requirements: In general, both wind and solar need expansive land area to generate the equivalent power of one normal fossil-fired generating unit. Over time, this will be a limiting factor in how much overall generating capacity can be expected from wind and solar.

• Expensive: Cost is still a significant issue with most renewable forms of generation. They are at an order of magnitude of about 10 to 50 times the cost of free venting, fossil-fired generation. However with appropriate incentives, with innovation in their design and some form of carbon taxation, at least wind likely will be cost competitive within the next three to five years.

• Non-Utility Generation: Possibly for the first time, major generation will be built by companies and people who don’t have a utility mindset. Many of them are property owners or developers. Utilities will need to understand regulatory requirements for accommodating non-utility renewables—such as net-metering arrangements and interconnection standards—and implement them where they’re needed instead of trying to apply them across the entire service territory, at an unnecessarily high cost. In addition, non-utility projects tend to get implemented much faster than conventional generation, which means interconnection processes need to speed up.

Key Mechanisms

There are several factors that need to be considered when identifying mechanisms for managing and operating renewable resources: The first factor is siting constraints and characteristics. The location of wind or solar farms is a significant factor regarding management and operation. Important aspects of siting include the ability to: appropriately locate generation facilities in areas of high-energy resource availability; provide transmission corridors to deliver energy from generation to load; and effectively forecast power generation levels and schedules.

Generation from solar, wind, geothermal, etc., each have specific output characteristics. Even within solar, for example, the output characteristics of different types of solar cells operate differently under different conditions. When combined in large output modes (i.e., as in a wind farm) behaviors will drive their impact to the grid under different conditions. This specific characteristic actually can be a benefit, in that it can smooth out the rapid fluctuations of wind-energy output to a certain extent. Mechanisms exist to model this information into the forecasting approach so that the variability in the source can be converted into variability in the delivery of power into the grid.

But a key sticking point in the integration of renewables is the availability and ability to build transmission lines and corridors to bring the power from renewable sources into the load centers. This problem has more of a policy aspect than a technical aspect to it. Policy mechanisms are being considered toward finding a solution.

Also, wind and solar energy forecasting has been the focus of much research at DOE laboratories and universities for several years now. The current focus is on forecast error and determining how these sources of generation will fit into the market models and support the balancing authority.

A key aspect of forecast error involves a concept called the “tail event.” A tail event happens when forecast errors for load and wind result in divergence of power demand and supply. Large wind power ramps in a power system (see Figure 1) can create significant imbalances between generation and load, resulting in grid instabilities. Such events occur infrequently but are much more substantial as the market penetration of wind increases.

A second major factor is the use of technology and automation. Two key areas of technology and automation under serious consideration for renewables integration include hardware and software systems.

Examples of hardware systems include synchro-phasor monitoring units (SPMUs), static VAR compensators (SVCs) and flexible AC transmission systems (FACTS). SVCs and FACTS devices represent the fast-acting switching controls for both real and reactive power flow across the grid. They provide operators with a near real-time ability to implement controlling actions in response to system challenges. However, to be effective, they will require greater visibility and transparency of grid status, also in near real-time.

Synchro-phasor technology provides time-synchronized, sub-second data applicable for wide area monitoring and allows the system operator to operate the power system closer to operating margin. SPMUs take the sampling window from six seconds to 60 times per second and provide a GPS time stamp for all measurements. Phasor data will drive a new generation of monitoring, operator decision support and, ultimately, fast real-time controls to improve grid performance.

Software systems also are advancing in ways that will help integrate renewable resources. Control centers will see a new slate of applications focused primarily on wide-area monitoring and power system visualization. Such visualization tools can allow operators to enhance system status knowledge and highlight interconnection status and priorities.

A third major factor involves operational changes. Increased integration of wind and other similar renewables-based generation also will result in the need for newer and more advanced operational methods and processes. Some techniques that merit consideration in large interconnected systems as found in Europe, United States and China include wind-only balancing areas, ACE diversity interchange and second-tier control centers.

Wind-only balancing areas create a virtual balancing authority across multiple control areas, allowing each control area to reduce its overall reserve requirements needed to support the appropriate amount of wind integration. This mechanism leverages geographic diversity both from the generation from renewables as well as load.

ACE diversity interchange (ADI) involves pooling individual area control errors (ACE) to take advantage of control error diversity—i.e., sign differences associated with the momentary generation and load imbalances of each control area. By pooling ACE, participants likely will be able to reduce control burden on individual control areas, unnecessary generator control movement, and sensitivity to resources with potentially volatile output such as wind, and allow reserve sharing across control areas.

Second tier control centers represent a further step in system operations. The continued evolution of operational methods and processes might result in a need to provide increased operator supervision to these activities. This stems from increased importance in understanding probabilistic elements of the grid, such as wind and load forecasts, and the availability of distributed smart resources. The system operator will need to collect the data and formulate an optimal dispatch method that coordinates with transmission dispatch. The attention deserved by such a task implies the need for additional control room support. Whether an additional desk is added to existing transmission control rooms or a second tier control center is established to support a group of transmission control centers is unknown. However, such coordination of assets likely will be necessary.

A fourth factor involves the role of demand management, which offers near-term potential for smart-grid implementations, with substantial benefits for managing peak loads and generation requirements. Demand management could supply valuable ancillary services to accommodate ramping rates for renewable resources, and to reduce the need for spinning and non-spinning reserves, as was demonstrated in the Olympic Peninsula pilot (see Figure 2).

This pilot project, led by Battelle and Pacific Northwest National Laboratory (PNNL), showed that with proper value signals and automated controls, customer loads could be effectively and rapidly engaged to stabilize the aggregate load of a feeder. This virtually eliminated the need for regulation for periods lasting many hours, all without inconvenience to the consumers.

The demonstration utilized an automated premise dispatch agent that acted in accordance to previously defined customer preferences, in response to five-minute interval market signals. The trial also included very fast-acting (~1 sec), autonomous, short-term load shedding for clothes dryers and water heaters to provide a stabilizing force when the grid gets into trouble or needs to support renewables.

The Olympic Peninsula pilot led to three major conclusions:

• Demand-management resources are capable of responding to ancillary service signals on short (minutes) to very short (seconds) time scales. Peak demand reductions of 16 percent and average demand reductions of 9 percent to 10 percent were realized over extended periods;

• The ability to measure and confirm response of resources was evidenced, at least for groups of customers if not individually;

• A structure for incentives can be offered to customers for short-term response; and

• While providing ancillary services wasn’t a direct objective of the experiment, the observations provided an important foundation for launching a directed effort to engage demand response in providing these benefits.

A fifth factor is the expanding role of storage. Energy storage forms a key part of the portfolio that will be required to support the integration of renewables. Storage is needed to manage or regulate the variable nature of wind, allowing it to be relied on as a semi-firm energy resource.

Much work is being done to target operational principles, algorithms, market integration rules, functional design and technical specification for energy storage that mitigates the intermittency and fast ramps that occur at higher penetration of renewable generation. Some of the technologies that are being studied and deployed include:

• Field experiment design and monitoring of the flywheel energy storage for existing and future renewable penetration;

• Addressing the characteristics and the role of battery storage facility and the regulatory issues to create feasible, economic applications for the battery storage devices; and

• Deploying virtual storage applications, such as Ice Energy’s system for freezing water to shift air conditioning load to off-peak hours (see “Cold Storage in Cali”).

A sixth factor involves the need for active demonstrations. While several options have been presented that can serve as mechanisms for managing and operating renewable resources, it’s important to note that both the applicability to specific locations, as well as the acceptability to different operating conditions, will vary. This only can be mitigated through performing continued active demonstrations of the available mechanisms. Active demonstrations in real-life will allow the different stakeholders to understand and validate the costs and benefits of each solution.

Critical Mass

While many people see the pursuit of renewables integration as a noble cause, they simultaneously view it with a great deal of skepticism. Timing of the change is important. While the renewable integration challenge remains at a manageable level today, it will reach a point of critical mass in the next three to five years, based on the best available data. The fact that renewable sources of energy already are entering various transmission and distribution networks also must be considered. A difficulty presented by this is that solutions available in one region might not be available in others.

For example, the hydro dams in the Northwest that can be used to regulate electric generation to match the ramping of wind power aren’t available in the Midwest. This regional availability—or the lack thereof—of renewable resources makes a one-size-fits-all solution impossible. Every solution also will be saddled with its own downside, either economic or environmental. Solutions will need to be judged individually by region and merit.

The ultimate choice between pursuing renewables integration or not has both pros and cons, but nature and necessity are leading in one direction. Thus, while specific solutions are important, a framework of customizable and tailor-made solutions will need to be developed for each region and resource as they struggle with these problems.

As countries and individual states ponder RPS standards, as well as the implications of carbon regulation, economic considerations raise important concerns, particularly during a period of global recession. Due to the recent turmoil in the world’s financial markets, U.S. states are looking toward the influx of American Recovery and Reinvestment Act funding. The possibility of receiving a handout from the ARRA for the purpose of investing in technologies that will assist in renewables integration is becoming increasingly attractive. This funding is temporary, but in general government entities are much more likely to pursue the energy produced by wind and solar-powered sources if they are perceived as bringing money into their regions, while at the same time generating new jobs.

RPS standards and the entry of large amounts of wind power into the grid eventually will be implemented; the main concern is how it will impact the renewables integration big picture and its subsequent impact on grid stability. This isn’t a simple problem. By nature, however, it is fundamentally an engineering problem, and therefore it can be solved.