TODAY’S STUDY: A MATTER OF DEGREES (WIND WILL WORK ON THE GRID)

Habit, Mark Twain observed, is not something that should be “flung out of the window” but something that should be “coaxed downstairs a step at a time.”

This is certainly proving to be true for the nation’s utilities and grid operators. The old habits of relying on inefficient, polluting fossil fuels and potentially dangerous nuclear power are hard to break. The conscientious folks who keep the lights on and the air conditioning cooling are not comfortable with the variability of the sun and the wind. It demands from them a new perspective.

That new perspective will reveal not a threat but many opportunities. Multiple, rigorous studies, as typified by the report highlighted below, show that variable renewables can readily be integrated into the national grid supply, as it exists today, in significant proportions if utilities and grid operators will consider changing their perspective just a matter of degrees and changing their habits a step at a time.

With a subtly altered perspective, step-by-step changes in the management of the various energy sources available to them would make it possible for system operators to get as much as 35 percent of their power from the New Energies without any alteration to present infrastructure. Doing so would not threaten the security of the electricity supply, it would improve it.

With a slight few degrees change in their perspective on the way their transmission systems can be managed, grid operators could sustain the transition to a New Energy economy.

That would allow the nation to break its dependence on foreign oil by facilitating the growth of battery-powered personal transport.

It would allow the nation to break its dependence on coal and nuclear by facilitating the emergence of a grid powered by a natural gas-New Energy synergy.

Shifting the energy sector to domestic sources would restart domestic manufacturing, reignite the economy and restore job opportunities sector-wide.

It would also relieve the overburdened health care sector by reducing the cardiovascular harms done by the air pollution that follows the burning of coal and oil.

Finally, and perhaps most importantly, it would reduce the threat from global climate change by curtailing the atmospheric havoc done by the greenhouse gases that follow the burning of fossil fuels.

Changing old habits by even a slight few degrees is challenging. Not everybody welcomes challenges. But challenges are coming and they will provoke changes in the way the nation gets and uses energy, welcome or not. The logic of New Energy will not be denied.

If smart methods of integrating New Energy into the transmission system are not put to work one step at a time, dramatic results will sooner or later induce bigger, more challenging changes that will feel like being “flung out of the window.”

Impacts of Wind Generation Integration
May 2011 (Electric Power Research Institute)

Executive Summary

Worldwide, several power systems already are coping with large amounts of wind power – up to 20% of their annual energy consumption, and sometimes more than 50% of off-peak power production. Wind inherently is variable, difficult to accurately predict, and frequently anti-correlated with electricity load. The often remote location of wind resources relative to load centers requires cost-effective transmission. Thus, integrating significant amounts of wind generation presents a unique challenge to the power system, requiring additional flexibility while simultaneously imposing a decreased capacity factor on conven¬tional generating units.

The system impacts of wind power integration are highly variable, pri¬marily depending on wind penetration, existing transmission infrastruc¬ture, and system operating flexibility. High penetration of wind power is expected to produce power system impacts that can be reduced through smarter power plant interconnection, transmission and resource plan¬ning, and system and market operations.

click to enlarge

The need for additional system flexibility -- that is, the ability of the system to respond to variability and uncertainty -- principally is deter¬mined by wind-related features, with wind penetration being the single greatest factor. Studies and experience to date have shown that most power systems can, on an energy basis, reliably accommodate up to 10% wind penetration, with only minor cost and operating impacts…

The cost to provide this system flexibility (as opposed to the costs to actu¬ally connect wind to transmission and distribution networks) is best described as the additional costs induced by balancing the variability and uncertainty of wind, and is a function of the existing power system, plus any new investment required. A 2009 International Energy Agency (IEA) study, which compared the wind integration costs from studies across Europe and North America, cited a cost range of 0-4.0€ /MWh, or about 0-$5.63/MWh…

The definitive studies on this subject were done by NREL (click to enlarge)

With regard to moving wind energy to load, transmission issues are particularly challenging. From planning to permitting, from capital cost estimation to cost allocation, there is no clear indication how and whether sufficient transmission will be constructed to tap our vast, remote, domestic wind resources.

The definitive studies on this subject were done by NREL (click to enlarge)

System Flexibility: Needs, Availability, Costs

The superposition of wind power and existing load yields the crucial variable “net load,” which is defined as the load minus the wind. Research findings and actual operator experience agree that the variability of net load exceeds that of the system when wind was not present, thus confirming the need for greater system flexibility under conditions of high wind penetration. Further, the mostly diurnal pattern of onshore wind means wind resources tend to peak when load is at its minimum. Existing commitment constraints imposed by thermoelectric baseload units means that even without transmission bottlenecks, wind power sometimes would be spilled to prevent minimum load problems.
Thus, wind requires system flexibility in the form of ramping capability and lower minimum load; more flexible systems should see a lower balancing cost for wind. Many systems already have a large degree of flexibility which can be utilized to integrate wind.

The definitive studies on this subject were done by NREL (click to enlarge)

Flexibility requirements for accommodating wind hinge upon:

1) Wind penetration

2) Variability of wind output for the system

3) Location of wind resource, especially relative to load – only 7 percent of the U.S. population inhabits the top 10 states for wind potential…

The definitive studies on this subject were done by NREL (click to enlarge)

4) Strength of transmission network (increased connection be¬tween regions reduces variability and uncertainty and increases the available flexible resources needed to balance wind)

5) Accuracy and integration of wind forecast

6) System stability requirements pertaining to additional need for voltage, frequency control, reactive power, and more

7) The monitor and control system capabilities of the individual wind plants. This system commonly is referred to as the supervisory control and data acquisition (SCADA) system.

The definitive studies on this subject were done by NREL (click to enlarge)

Power system flexibility is a function of:

1) Grid infrastructure

2) The existing generation and resource mix, including access to flexible resources such energy storage, gas turbines and demand side management

3) Operating procedures, market operations and pricing mecha¬nisms

The definitive studies on this subject were done by NREL (click to enlarge)

Increasing system flexibility primarily entails two cost categories:

1) Balancing resources: In response to the increased frequency and magnitude of ramping events, the bulk power system may need to commit proportionately more dispatchable resources, even if perfect wind forecasting would be achievable. The increased demand for flexible dispatchable plant will mostly be in the 10-minutes-to-6-hour time frame, though at a threshold depth of penetration, additional resources also will be required at the larger time scales, as the system may go from high wind/night¬time periods to low wind/peak hour in a matter of one to two days…

2) Transmission: Wind resources tend to be located far from the load, requiring additional, potentially massive, investments in transmission infrastructure. However, due to low wind capacity factor, the new transmission lines either will be under-utilized – if built to wind power nameplate capacity – or else large curtail¬ments sometimes will occur.

The definitive studies on this subject were done by NREL (click to enlarge)

Importantly, an increase in reserve requirements would not neces¬sarily require new investments. The amount of wind-caused reserves is highest when wind power is at a high production level. In these situations, other power stations can be operated on a low level, which means that they can potentially act as reserves and increase the generation if wind power decreases. An IEA study estimated that at 20% penetration, the expected increase in system operating costs was about 1.4€/MWh ($2/MWh), which is on the order of 10% of the wholesale value of the wind energy…

Minimum load considerations present a technical limit on the amount of wind that a power system can accommodate. Proposed federal environmental regulations directed at thermoelectric power plants inadvertently will decrease operational flexibility, especially for baseload and mid- duty units, by increasing higher minimum loads and slowing ramp rates. At periods of low net load -- for ex¬ample, overnight or a weekend -- thermoelectric power plants may be shut down to accommodate wind. Many combined cycle natural gas-fired units and some coal units already operate in this two-shift mode, meaning they shut down overnight. This type of operation may be needed for more units, which will be particularly difficult for those which were designed and have operated as baseloaded units for most of their lifetime.

The definitive studies on this subject were done by NREL (click to enlarge)

There are several options for increasing flexibility of the power system: flexible conventional plant (such as open-cycle gas turbines, though less-flexible conventional plants also can contribute to meeting changes in net load), demand response, and storage and increased transmission between regions, which allows greater sharing of flexibility and reduces the need for balancing due to geographic diversity. Unless additional energy storage capacity proves cost- ef-fective or alternative resources, such as demand response, flexible conventional plant or increased transmission and coordination between regions, can be scaled up, wind occasionally may have to be spilled.

Research indicates that even at wind penetration levels of 10-20% of gross demand, the building of new electricity storage is not cost-effective…Beyond 20% penetration, the value of storage hinges on system characteristics, such as load shape, characteristics of exist¬ing generation mix, and congestion patterns, as well as capital costs and efficiency of storage. Research on wind and energy storage con¬sistently has shown no economic benefit to a dedicated back-up for wind…instead, economic benefit is optimized when the energy storage operation decisions are based on the aggregated balancing needs of the entire bulk power system for that region.

The definitive studies on this subject were done by NREL (click to enlarge)

Most existing power system planning and operating techniques were not developed with variable generation in mind. Accommodating high wind penetration most likely will involve modifications to system configuration and operation practices. This consideration is complex, involving regional power markets or closer coordination between areas, system operators, plant operators and more. Optimi¬zation of many system processes may defy a prescriptive approach; additionally, the best answer for each system will vary – for example, parts of the Northwest U.S. may be able to utilize large amounts of flexible hydropower not present in some other areas…

The definitive studies on this subject were done by NREL (click to enlarge)

Conclusion

When the penetration of variable generation reaches relatively high levels, the characteristics and operation of the bulk power system will be significantly altered. The greater overall system variability, on time scales from seconds to days, will provoke an increased need for flexibility, prompting changes in the resource adequacy and trans¬mission planning processes as well as market design and operations. Many issues remain to be addressed, not least of which is how to calculate and allocate the costs and benefits. It seems likely the costs will vary depending on the flexibility and infrastructure inherent in the region. Some regions will see relatively small wind integration costs due to existing flexibility and transmission infrastructure; others may see very large costs, and benefits also will vary by region. By taking a system-specific approach, the overall costs can be assessed while also ensuring infrastructure build-out can be done in an economical, sustainable manner.