Large scale wind power integration in China: Analysis from a policy perspective

Between 2006 and 2010 the installed capacity of wind power in China has doubled and by 2010 China's cumulative installed capacity of wind power ranked the first in the world, surpassing the United States. However, the rapid expansion of installed capacity has not been matched by grid connection, and this deficiency has aroused the concern of both policy makers and scholars. Unlike most of the current studies which focus on technical strategies in China's wind power industry, this paper analyzes the problem from a policy perspective. The paper analyzes the four challenges that large scale wind power integration in China faces: the uncoordinated development between wind power capacity and power grids; the lack of suitable technical codes for wind power integration; the unclear nature of the grid companies’ responsibility for grid connection; and the inadequate economic incentives for grid enterprises. To address these problems, the paper recommends that the government: formulates policies to better coordinate the development of wind power and the planning and construction of power grids; establishes grid codes that reflect in particular the requirements to be met by users of power transmission and distribution networks; and integrates administrative intervention and economic incentive policies to stimulate the grid enterprises’ enthusiasm to absorb wind power generation.     

The interaction of wind power generation with electricity demand in the context of a small grid

An investigation into the integration of the intermittent electricity output of a hypothetical wind farm in Malta with the actual electricity demand for one particular year is reported. Available hourly wind data from three sites for 2001 were analysed. The probability density of the load resulting from the reduction of the renewable output from the electricity demand on an hourly basis was determined by a convolution method. The calculated shift in the load duration extends over the whole spectrum of power demand. The equivalent power at the most favourable site was considerably higher than the nominal value commonly in use. In view of the limited availability of sites for wind farms in Malta rotor designs better suited to the lower wind speed régime inland should be considered.     

The role of demand-side management in the grid integration of wind power

In a scenario of large scale penetration of renewable production from wind and other intermittent resources, it is fundamental that the electric system has appropriate means to compensate the effects of the variability and randomness of the wind power availability. This concern was traditionally addressed by the promotion of wind resource studies and acting in the supply side of energy and using energy storage technologies. However, in electric system planning, other options deserve to be evaluated, namely the options related with the energy demand.     

The variability of interconnected wind plants

We present the first frequency-dependent analyses of the geographic smoothing of wind power’s variability, analyzing the interconnected measured output of 20 wind plants in Texas. Reductions in variability occur at frequencies corresponding to times shorter than ∼24 h and are quantified by measuring the departure from a Kolmogorov spectrum. At a frequency of 2.8×10⁻⁴ Hz (corresponding to 1 h), an 87% reduction of the variability of a single wind plant is obtained by interconnecting 4 wind plants. Interconnecting the remaining 16 wind plants produces only an additional 8% reduction. We use step change analyses and correlation coefficients to compare our results with previous studies, finding that wind power ramps up faster than it ramps down for each of the step change intervals analyzed and that correlation between the power output of wind plants 200 km away is half that of co-located wind plants. To examine variability at very low frequencies, we estimate yearly wind energy production in the Great Plains region of the United States from automated wind observations at airports covering 36 years. The estimated wind power has significant inter-annual variability and the severity of wind drought years is estimated to be about half that observed nationally for hydroelectric power.     

Combining wave energy with wind and solar: Short-term forecasting

While wind and solar have been the leading sources of renewable energy up to now, waves are increasingly being recognized as a viable source of power for coastal regions. This study analyzes integrating wave energy into the grid, in conjunction with wind and solar. The Pacific Northwest in the United States has a favorable mix of all three sources. Load and wind power series are obtained from government databases. Solar power is calculated from 12 sites over five states. Wave energy is calculated using buoy data, simulations of the ECMWF model, and power matrices for three types of wave energy converters. At the short horizons required for planning, the properties of the load and renewable energy are dissimilar. The load exhibits cycles at 24 h and seven days, seasonality and long-term trending. Solar power is dominated by the diurnal cycle and by seasonality, but also exhibits nonlinear variability due to cloud cover, atmospheric turbidity and precipitation. Wind power is dominated by large ramp events–irregular transitions between states of high and low power. Wave energy exhibits seasonal cycles and is generally smoother, although there are still some large transitions, particularly during winter months. Forecasting experiments are run over horizons of 1–4 h for the load and all three types of renewable energy. Waves are found to be more predictable than wind and solar. The forecast error at 1 h for the simulated wave farms is in the range of 5–7 percent, while the forecast errors for solar and wind are 17 and 22 percent. Geographic dispersal increases forecast accuracy. At the 1 h horizon, the forecast error for large-scale wave farms is 39–49 percent lower than at individual buoys. Grid integration costs are quantified by calculating balancing reserves. Waves show the lowest reserve costs, less than half wind and solar.     

Assessment of imbalance settlement exemptions for offshore wind power generation in Belgium

This article deals with a specific support mechanism exempting offshore wind power generators partially from their balancing responsibilities by means of a tolerance margin. This specific support mechanism was enforced in Belgium as from 2009 and is defended by its proponents in view of the lower power output predictability at offshore locations. Although policies accommodating offshore developments may be seen as important to tap better wind resources, this contribution stresses the importance of full balancing responsibility for variable renewables. After a detailed evaluation of the support mechanism and its impact on the balancing costs for wind power generators, the use of current applied production support mechanisms is recommended. These can be used to acquire the same financial effect without increasing market complexity and harming the operation of the balancing market. The first part of the study deals with the specific implementation of the tolerance margin in the Belgian context. Secondly, its underlying motivation is quantitatively assessed, namely the relatively higher offshore prediction errors. Finally, the total offshore subsidy resulting from the measure is determined. Expressed in €/MWh, this subsidy is currently determined at €1.4–1.7/MWh, which represents the required increase of production support in order to replace the regulation.     

Contribution of wind power and CHP to exports from Western Denmark during 2000–2004

The experience of Denmark is used by the United Kingdom's anti-wind lobby to demonstrate that intermittency and inaccuracies in wind forecasting make wind power ineffective and expensive. A further assertion is that most of the power is ‘unwanted’ since up to 80% of it is exported. Here, available data for Danish energy production for 2000–2004 is used to assess the link between wind generation and exports and test the validity of these claims.Net exports in Western Denmark showed good correlation with wind production. However, they were more significantly correlated with the production from local combined heat and power (CHP) plants. In order to test the 80% export claim, a simple technique was devised to correlate and rank hourly net exports and generation from wind and local CHP. In the case where net exports were primarily attributed to (or blamed on) wind, 44–84% of annual wind production was deemed to be exported, with wind ‘causing’ 57–79% of net annual exports. For this extreme scenario, the percentage values are in line with those of critics. However, under the opposite extreme scenario in which exports are attributed to local CHP, 77–94% of exports were caused by CHP and only 4–32% of wind production was exported.Overall, this study shows that there is some degree of correlation between net exports and wind power, but that the claim that 80% is exported is unwarranted since it ignores the demonstrably stronger influence of local CHP.     

Investigation on wind power potential on Hong Kong islands—an analysis of wind power and wind turbine characteristics

This paper discusses the potential for electricity generation on Hong Kong islands through an analysis of the local weather data and typical wind turbine characteristics. An optimum wind speed, u_op, is proposed to choose an optimal type of wind turbine for different weather conditions. A simulation model has been established to describe the characteristics of a particular wind turbine. A case study investigation allows wind speed and wind power density to be obtained using different hub heights, and the annual power generated by the wind turbine to be simulated. The wind turbine's capacity factor, being the ratio of actual annual power generation to the rated annual power generation, is shown to be 0.353, with the capacity factor in October as high as 0.50. The simulation shows the potential for wind power generation on the islands surrounding Hong Kong.     

Well-functioning balancing markets: A prerequisite for wind power integration

This article focuses on the design of balancing markets in Europe taking into account an increasing wind power penetration. In several European countries, wind generation is so far not burdened with full balancing responsibility. However, the more wind power penetration, the less bearable for the system not to allocate balancing costs to the responsible parties. Given the variability and limited predictability of wind generation, full balancing exposure is however only feasible conditionally to well-functioning balancing markets. On that account, recommendations ensuring an optimal balancing market design are formulated and their impact on wind generation is assessed. Taking market-based or cost-reflective imbalance prices as the main objective, it is advised that: (1) the imbalance settlement should not contain penalties or power exchange prices, (2) capacity payments should be allocated to imbalanced BRPs via an additive component in the imbalance price and (3) a cap should be imposed on the amount of reserves. Efficient implementation of the proposed market design may require balancing markets being integrated across borders.     

The optimum mix of electricity from wind- and solar-sources in conventional power systems: Evaluating the case for New York State

Several countries and states have set targets for substantially increasing renewable energy (RE) contributions in their electricity grids. As the potential for additional hydro-electricity is limited in the US most future RE penetration is envisioned to be in the form of wind and solar. Our simulations, based on hourly resource and load data, demonstrate the maximum penetration achievable in the grid managed by the New York Independent System Operator (NYISO), by wind- and solar-power independently, and when they are combined. By optimizing the synergy between these two intermittent resources, a maximum penetration of renewable-energy in the grid can be accomplished; this is shown for different scenarios of grid flexibility. For example, for an 80% flexible grid, a total penetration of 30% of wind and solar energy can be achieved in the NY state without adding storage and without having to dump more than 3% energy, whereas if this was to be met by wind alone, 12% of energy would have to be dumped. Considering that several US states and countries have high targets for renewable energy penetration, optimizing the mixture of RE to accomplish such goals is valuable for energy managing and planning.     

Attitudes towards on-land and offshore wind power development in Denmark; choice of development strategy

Wind power generation is expected to increase significantly in the near future. Owing to the increasingly limited possibilities for using on-land turbines, offshore wind generation is a potential alternative. However, wind turbines located offshore are still associated with visual disamenities potentially making offshore location a less attractive alternative to on-land wind power generation. The present paper analyses attitudes towards both on-land and offshore wind power development using a probit model. It also discusses the elicited determinants of attitude in relation to developing wind power on-land or offshore. Compared to other papers on attitude, the paper is unique in the sense that the Danish population has considerable experience with the different impacts associated with wind turbines compared to most of the other countries investing in wind power generation. This is particularly evident with regards to offshore development. The paper establishes that whilst offshore wind farms are preferred to on-land development, the results also imply that on-land development is still a feasible alternative. In that relation, differences in wind power generation costs and the substitution of smaller on-land turbines with fewer but larger turbines might make on-land development even more attractive. On a more detailed level, younger respondents are more positive towards wind power than older respondents. Interestingly, respondents living close to either on-land or offshore wind turbines did not display a more negative attitude towards wind power generation when compared to respondents who were not living close to wind turbines.     

Geographic aggregation of wind power—an optimization methodology for avoiding low outputs

This work investigates macro‐geographic allocation as a means to improve the performance of aggregated wind power output. The focus is on the spatial smoothing effect so as to avoid periods of low output. The work applies multi‐objective optimization, in which two measures of aggregated wind power output variation are minimized, whereas the average output is maximized. The results show that it is possible to allocate wind power so that the frequency of low outputs is substantially reduced, while maintaining the average output at around 30% of nameplate capacity, as compared with the corresponding output of 20% for the present allocation system. We conclude that in a future, fully electrically integrated Europe, geographic allocation can substantially reduce instances of low aggregate output, while impairing little on capacity factor and at the same time providing reduction in of short‐term jumps in output. Copyright © 2016 John Wiley & Sons, Ltd.     

Understanding the variability of wind power costs

Wind power has a significant contribution to make in efforts to abate CO₂ emissions from global energy systems. Currently, wind power generation costs are approaching parity with costs attributed to conventional, carbon-based sources of energy but the economic advantage still rests decidedly with conventional sources. Therefore, there is an imperative to ensure that wind power projects are developed in the most economically optimal fashion. For wind power project developers, shaving a few tenths of a cent off of the kilowatts per hour cost of wind power can mean the difference between a commercially viable project and a non-starter. For civic authorities who are responsible for managing municipally supported wind power projects, optimizing the economics of such projects can attenuate stakeholder opposition. This paper attempts to contribute to a better understanding of how to economically optimise wind power projects by conflating research from the fields of energy economics, wind power engineering, aerodynamics, geography and climate science to identify critical factors that influence the economic optimization of wind power projects.     

The impact of wind power on electricity prices

This paper investigates the impact of wind power on electricity prices using a production cost model of the Independent System Operator – New England power system. Different scenarios in terms of wind penetration, wind forecasts, and wind curtailment are modeled in order to analyze the impact of wind power on electricity prices for different wind penetration levels and for different levels of wind power visibility and controllability. The analysis concludes that electricity price volatility increases even as electricity prices decrease with increasing wind penetration levels. The impact of wind power on price volatility is larger in the shorter term (5-min compared to hour-to-hour). The results presented show that over-forecasting wind power increases electricity prices while under-forecasting wind power reduces them. The modeling results also show that controlling wind power by allowing curtailment increases electricity prices, and for higher wind penetrations it also reduces their volatility.     

The assessment of actual wind power availability in ireland

Data on actual wind energy availability in Ireland are sparse. This is because (a) relatively little data on wind speeds have been collected in Ireland at sites of interest for wind exploitation, and (b) such data need in any case to be integrated with the characteristics of actual windmills which respond more efficiently to certain wind speed than to others. This paper describes a methodology for performing such an integration, and offers tables of specific output for windmills of different characteristics located at different sites in Ireland. the variations in this specific output are discussed.     

Profiling the regional wind power fluctuation in China

As China starts to build 6 10-GW wind zones in 5 provinces by 2020, accommodating the wind electricity generated from these large wind zones will be a great challenge for the regional grids. Inadequate wind observing data hinders profiling the wind power fluctuations at the regional grid level. This paper proposed a method to assess the seasonal and diurnal wind power patterns based on the wind speed data from the NASA GEOS-5 DAS system, which provides data to the study of climate processes including the long-term estimates of meteorological quantities. The wind power fluctuations for the 6 largest wind zones in China are presented with both the capacity factor and the megawatt wind power output. The measured hourly wind output in a regional grid is compared to the calculating result to test the analyzing model. To investigate the offsetting effect of dispersed wind farms over large regions, the regional correlations of hourly wind power fluctuations are calculated. The result illustrates the different offsetting effects of minute and hourly fluctuations.     

The influence of generation mix on the wind integrating capability of North China power grids: A modeling interpretation and potential solutions

The large-scale wind power development in China has reached a bottleneck of grid integrating capability. As a result, excess wind electricity has to be rejected in the nighttime low demand hours, when the wind power is ramping up. To compensate for the fluctuation of wind power, new coal-fired power plants are being constructed along with the big wind projects in the North China grids. This study analyzed why adding coal-fired generation cannot remove the bottleneck of wind integration by modeling the operating problem of the wind integration. The peak-load adjusting factor of the regional grid is defined. Building more coal-fired power plants will not increase the adjusting factor of the current grid. Although it does help to increase the total integrated wind power in the short term, it will add difficulties to the long-term wind integration. Alternatively, the coordinated resource utilization is then suggested with the discussion of both the effective pumped hydro storage and the potential electric vehicle storage.     

Low wind speed turbines and wind power potential in Minnesota, USA

Wind power development in Minnesota largely has been focused in the “windy” southwestern part of the state. This research evaluates the additional power that potentially could be generated via low wind speed turbines, particularly for areas of the state where there has been comparatively little wind energy investment. Data consist of 3 years (2002–2004) of wind speed measurements at 70–75 m above ground level, at four sites representing the range of wind speed regimes (Classes 2–5) found in Minnesota. Power estimates use three configurations of the General Electric 1.5-MW series turbine that vary in rotor diameter and in cut-in, cut-out, and rated speeds. Results show that lower cut-in, cut-out, and rated speeds, and especially the larger rotor diameters, yield increases of 15–30% in wind power potential at these sites. Gains are largest at low wind speed (Class 2) sites and during the summer months at all four sites. Total annual wind power at each site shows some year-to-year variability, with peaks at some sites partially compensating for lulls at others. Such compensation does not occur equally in all years: when large-scale atmospheric circulation patterns are strong (e.g., 2002), the four sites show similar patterns of above- and below-average wind power, somewhat reducing the ability of geographic dispersion to mitigate the effects of wind speed variability.     

Identification of vulnerable lines in power grids with wind power integration based on a weighted entropy analysis method

Vulnerable overhead electricity lines are a cause of serious risk to power distribution grids as damage can be the cause of large scale blackouts and cascading failures. With the integration of large scale wind power into generating capacity, both the topology structure and the distribution characteristics of power flow in distribution grid have undergone various changes that have increased line vulnerability. A novel approach to identify vulnerable lines based on the weighted entropy analysis method is proposed in this paper. In this approach, an assessment index, named the incremental power flow entropy, is first developed, which is used to describe influences caused by variation of the lines' capability of carrying power flow transfers on the vulnerability of the lines themselves at the same aggregation level. A second assessment index, named structural importance, describes the structural changes of a power grid that are caused by the integration of wind-generated electric power. The two assessment indices then are merged into one index by using the entropy weight analysis method, which can assess the vulnerability of the lines from the two aspects of power flow transmission and structural links. Vulnerability analysis under different situations, such as with and without the integration of the wind farm, and sharp fluctuations in wind speed at the wind farm, were carried out on an IEEE 39-bus system integrated with a 75 MW wind farm. Simulation results verified that the proposed assessment index not only can identify the vulnerable lines in a power grid with wind farm integration but also accurately reflected the vulnerability of the internal lines of the wind farm itself.