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Popularity of Class III wind turbines

In 1999 more than 95% of the turbines installed in the US were Class I; in 2013, more than 65% of the turbines are Class III.  In the same period, the average specific power has dropped from more than 390 W/m2 to about 250 W/m2.  

Turbine manufacturers and independent engineers are approving Class III turbines for sites with Class II wind speeds & turbulence.  This is done after site-specific load analysis of the turbine.  The reasons are Class III turbines produce more energy because of larger rotor.

IEC 61400-1 specifies Class requirements for turbines in terms of a) Vref, which is onsite 50 year extreme wind speed computed based on 10-min average, and b) Iref, which is onsite turbulence intensity (TI) at wind speed of 7.5 to 8 m/s.  Part (a) determines Class I, II, III or IV, while part (b) determines A, B, C.  

Part (a).  Although the IEC standard specifies classification in terms of Vref, a more practical classification is in terms of annual average wind speed has evolved.  Vref is difficult to compute because unavailability of dataset of sufficient size, so for a quick classification average wind speed is used.  Note, the manufacturer or an independent engineer will still compute Vref before approving the turbine class.

Class I:  Wind speed up to 10 m/s

Class II:  Wind speed up to 8.5 m/s

Class III: Wind speed up to 7.5 m/s

Class IV:  Wind speed 6 m/s

Part (b).  Here X is I, II, III or IV.

Class X A:  TI less than 0.16

Class X B:  TI less than 0.14

Class X C:  TI less than 0.12

So a wind turbine classified as Class IIIA is designed for wind conditions: Average wind speed is less than 7.5 m/s, and TI is less than 0.16.

 

Source:  North American WindPower, January 2015.

YieldCo & MLPs: A new method to finance wind projects

About 8 YieldCos have been formed in 2014 as a way to tap the stock market for funds.  NextEra, SunEdison and others have created yieldCo companies, and sold a lot of their renewable assets to these new companies.  The new companies pay dividents to shareholders based on revenues from electricity generation.  Selling assets to YieldCos frees up a lot of capital for new RE investments.

According to Senator Chris Coons (D-DE) “By statute, MLPs have only been available to investors in energy portfolios for oil, natural gas, coal extraction, and pipeline projects. These projects get access to capital at a lower cost and are more liquid than traditional financing approaches to energy projects, making them highly effective at attracting private investment."  He continues, “Investors in renewable energy projects, however, have been explicitly prevented from forming MLPs, starving a growing portion of America's domestic energy sector of the capital it needs to build and grow.”

For more see http://www.altenergystocks.com/archives/2015/01/solwind_new_yieldco_with...

 

Wind generation in Denmark

 

Denmark generated a record amount of from wind in 2014, it amounted to 39% of electricity consumption in the country.  This twice the percentage 10 years ago.

Energinet.dk, the Danish national transmission operator reports that Denmark is on track to reach 50% of electricity from wind by 2020.  The key challenge is to better use wind energy for heating.

For more details see, http://cphpost.dk/news/denmark-nearing-2020-wind-energy-target.12139.html

 

Wind farm fined for bird deaths

PacificCorp Energy was fined $2.5m for bird deaths in Wyoming wind farms.  The US government alleged that "PacifiCorp Energy failed to make all reasonable efforts to build the projects in a way that would avoid the risk of avian deaths by collision with turbine blades, despite prior guidance from the U.S. Fish and Wildlife Service."

 

For more see, http://www.denverpost.com/news/ci_27269019/company-fined-2-5-million-aft...

 

Uncertain future of the first US offshore wind project

Two power companies terminated the PPA contract with Cape Wind, the wind project in Nantucket Sound which was projected to be the first offshore wind farm in the US.  The reason given: "failure to obtain financing and begin construction by Dec 31, 2014."

 

For details see, http://www.bostonglobe.com/metro/2015/01/06/major-setback-for-cape-wind-...

China lowers Feed-in Tariff for wind

For details see, http://www.windpowermonthly.com/article/1328437/china-confirms-cut-onsho...

FiT will be cut down by $0.02 for type 1, type 2 and type 3 wind regions, reducing electricity prices to CNY 0.49 ($0.078), CNY 0.52 and CNY 0.56 per kilowatt hour.

The CNY 0.61/kWh FIT will be unchanged in the type 4 region, which has low wind resources.

Applications of Wind Energy

Penetration level of Wind Energy and Impact on Grid

I am often asked, what is the "standard" or "safe-level" for penetration of wind energy into the grid.  This blog will attempt to provide answers and explains the issues related to variability of wind power.

Fact: Wind energy (or solar energy) is variable; it is produced only when wind is blowing (or sun is shining), and the amount of energy produced depends on the wind speed (or amount of radiation).

Fact:  Electricity demand is variable; consumers turn on appliances at will.  And in most grids, electricity is provided by the grid reliably to meet this variable demand.

Fact: In general, there is no correlation between demand and renewable energy supply; if you are lucky, when the consumer loads are high, renewable energy production is also high.

Fact:  At any given point of time, the amount of electrical energy supply must be equal to the amount of energy consumption, if the grid has no electrical storage.

Fact: Modern wind plants are grid friendly.  It provides both real and reactive power, and have low voltage ride-through (LVRT) capability.  Electrical energy is provided at desired voltage and frequency.  Forecasts of wind plant output is reasonably accurate for when the wind is hour-ahead to 6 hours ahead.  Accuracy of day-ahead forecasts is being improved continuously.

So the question is, how is this real-time balance achieved?  The answer is, flexible generation units; there are different names like peaking generation units or reserve units (spinning and non-spinning).  Spinning reserves are online and spinning, these units sense the changes in load and produce appropriate amount of energy to deliver to the grid--examples of such units are gas-fired generators and hydro-electric plants.  Non-spinning reserves are generators that are turned on and start producing energy in a few minutes; for example dispatch center may turn on a diesel generator at 9AM every weekday because the demand starts rising at 9AM.  Both spinning and non-spinning reserves provide the ability to balance the energy supply and demand.  Then there are the base-load generation units that provide almost constant electrical energy through out the day.  Examples are coal-fire or nuclear power plants that are run at 90%+ of rated capacity.

Consider an illustrative example: Grid has demand with the following profile (over a period of one year), minimum demand of 900MW, maximum demand of 2,200MW, and average demand of 1,600MW.  In this situation, it would make sense (with out going into lot of detailed demand analysis) to have a base load generation of 900MW and reserves of at least 1,300MW.  The reason for saying at least is because generator failures need to be accounted; reserves not only provide energy during peak demand times, but also serve as backup then base-load and/or other reserve generators fail.  So, reserves determine reliability of a grid to meet demand.

Base-load generation plants have some flexibility (depending on specs)--they may be run between say 80% and 100% capacity.  So these plants also follow the load within limits.  Below the minimum level of rated capacity, the plant become too inefficient or unworkable.

As a rule, base-load generation is the cheapest, non-spinning reserve is next, and spinning reserve is the most expensive.  It turns out this is not always the case: Non-spinning reserves like Diesel or Heavy Oil plants produce electricity at a higher cost than gas-based plants.  So the grid operator dispatches plants (turns them on or off) based on cost, contracts, response rate, operating range, and few other factors.

In this back drop, wind energy generators provides variable source of energy into the grid.  For illustration, lets consider the following simplistic cases (real life is much more complicated):

  1. Case 1: Penetration level of wind is small (less than 5% in annual energy terms):
    1. When grid is at minimum demand and supply is from base-load generation plants, then the grid is able to absorb wind energy by adjusting output of base-load plants--remember base-load plants have a range in which output may be adjusted. Note if wind plants are providing 5% energy annually and the wind plants have a capacity factor of 33%, then at time of peak wind, the wind plants will provide 15%-plus of energy into the grid when demand is low
    2. When grid is at maximum demand, and supply is from base-load and reserves (spinning and non-spinning), then wind energy displaces reserves (grid operator decides how to distribute the reduction among the reserves)
    3. When grid demand is at some intermediate level, then again grid operator decides how to distribute the reduction
  2. Case 2: Penetration level of wind is higher (between 5% to 20%):
    1. When grid is at minimum demand and supply is from base-load generation plants, then the grid is able to absorb wind energy by adjusting output of base-load plants--remember base-load plants have a range in which output may be adjusted. Note if wind plants are providing 20% energy annually and the wind plants have a capacity factor of 33%, then at time of peak wind, the wind plants will provide 60%-plus of energy into the grid when demand is low
    2. When grid is at maximum demand, and supply is from base-load and reserves (spinning and non-spinning), then wind energy displaces reserves (grid operator decides how to distribute the reduction among the reserves)
    3. When grid demand is at some intermediate level, then again grid operator decides how to distribute the reduction

It is clear that the problem is at times of minimum demand and when the base-load generation cannot be reduced below the minimum acceptable level. In these cases, there are unfortunately no options other than curtail wind energy production.

To be continued ...