Past Blogs

Risk management is critically important in a wind project. A systematic method is required to identify risk factors, quantify the risk factors, compute the impact of risk factors on project performance and mitigate the risk.

Download Wind Project Risk Assessment whitepaper for details. In it a framework is presented for: Categorizing risk, quantifying risk and assessing impact of risk on the project. In addition, strategies for mitigating risk are described.

Risk is categorized based on phases of a wind project:

• Planning/installation risk is related to factors during the pre-energy production stage that impact the cost of and timeframe for implementation of a project.
• Operational risk factors are those that lead to uncertainty in revenue and cost after the implementation, which is during the energy production phase of the project.
• Systemic risk factors are those that impact both implementation and operations.

In the framework risk is quantified along three parameters:

• What does this risk factor impact? Choose one or more.
  • Revenue
  • Cost
  • Time
• What is the amount of uncertainty?
• What is the impact of risk factor on Revenue, Cost and Time? And how does the impact change over time?

The impact of risk is estimated based on the P84, P90 and more generically Pn estimates, where n is any number greater than 50 and less than 100. In the whitepaper the concept is explained through examples.

Article written by Pramod Jain

Commercial applications of single or a few wind turbines with rated power capacity in the range of 50KW to 2,500KW are the focus of this blog. Such turbines can be cost effective for a wide range of applications: Factories; warehouses; office parks; housing communities; schools/colleges; hospitals; municipal facilities like jails; water treatment facilities; and others. These projects are referred to as "Behind the Meter" projects.

A white paper is available that briefly describes: How such projects can fit into your energy mix; how much energy can be produced; how is variability of wind energy managed; what are the incentives; what is the cost of wind energy; what is the ideal location of a wind project; and what to avoid.

It concludes that such projects can deliver electricity at stable costs (because raw material is free) and under the right wind conditions such projects may deliver electricity at a cost that is below retail.

Article written by Pramod Jain

Fact: The amount of wind energy that is produced and delivered to the grid depends on the wind speed.

Fact: Although wind speeds can be forecasted (uncertainty in forecast can be reduced), the variability in wind speed cannot be controlled. Meaning wind has its own schedule, we may be able to predict it, but we cannot match its schedule of the demand schedule.

Fact: The goal of a Utility is to provide reliable power, whenever the customer demands (of course within reason).

Question: What happens when wind is strong (high supply) and there is low demand on the grid?

Question: What happens when there is no wind (low supply) and demand is high on the grid?

Before answering these questions let me present the background. For simplicity there are three types of generators in a grid: Base load generators, spinning reserve and non-spinning reserves.

Base load generators are the large thermal and nuclear power plants that supply electricity. These generators operate 24x7, and produce almost constant amount of electrical power running close to rated power capacity.

Spinning reserves are generators that are spinning (or on) all the time and react of changes in electrical energy demand. Examples are natural gas fired and hydro generators. The amount of fuel is regulated by the demand. These generators are typically running at low output but can react to changes in demand quickly by increasing or decreasing output without sharp drop in efficiency.

Non-spinning reserves are generators that are turned on in case of large spike in demand or large decrease in supply. The startup time is 10 to 30 minutes. In case of unexpected events, these reserves relieve spinning reserves running at full throttle.

These reserves are pooled across utilities and grid operators manage uncertainties in demand and supply with reserves they own and moving energy from other utilities.

When wind energy is added the grid, it introduces variability to the supply side. The same mechanisms of spinning and non-spinning reserves which are used to manage variability in the grid are also used to manage wind energy variability. Meaning when wind energy is on, spinning reserves reduce output. According to Brady and Gramlich[1], when there is high penetration of wind energy, there may be a need to increase reserves, but the increase is modest. Studies have shown that integration of 10 to 20 percent wind can cost $0.005/kWh.

[1] D. Brady, R. Gramlich, “Getting Smart About Wind and Demand Response,” Wind Systems, pp. 28-33, July 2009.

Article written by Dr. Pramod Jain

A large fraction of small wind projects turn out to be subpar financial investments because of simple mistakes made in the initial phases of project development. This entry focuses on those common mistakes and provides simple steps that can be taken to ensure a more viable project from the performance and financial perspectives. For more details see the associated whitepaper.

Small turbines, with power ratings of less than 100KW, are being installed at a rapid pace. These wind projects are being used to power small businesses, buildings, malls, houses and a variety of other applications. Unlike the multi-million dollar large scale projects that undergo rigorous wind resource, siting, and financial assessments, small wind projects undergo significantly less analysis and preparation. The end result generally reflects the lack of preparation, as turbines produce less energy than advertised.

In order to attain on par financial performance of small wind projects the following due diligence must be performed:

• Ensure that the energy production used in the calculation is based on your local wind conditions and based on independently tested or certified power curve.
  
• Ensure that the wind speeds used in the calculations have been verified through onsite measurement or some other means.
  
• A location has been chosen that will receive unobstructed wind and minimum turbulence from obstacles and local vegetation.
  
• Ensure that the turbine is well built and is suitable for your environment and,
  
• Check if the turbine is certified; if it is not, obtain test results
  

If the proper due diligence is not performed you are likely to be negatively surprised by the results.

There are several air exhaust applications where large volume of air is pumped externally continuously. Examples are: Coal mines; covered parking lots; and, industrial air handling systems. The first two applications extract contaminated air necessary to maintain satisfactory air quality, and the third application is to use air to transport materials, remove moisture, etc.

Using the above examples, a natural assumption is that the exhaust emissions can be captured and converted into useable energy. Let us consider a few scenarios:

1. Attach a wind turbine directly to the exhaust. In this scenario the exhaust air (speed = V_a, Kinetic energy = K_a) is directly fed to the turbine; the turbine extracts (K_b), a fraction of the kinetic energy in the wind; the remaining kinetic energy is expelled (K_c) with wind speed = V_c. In this scenario, the turbine is able to extract K_b, which will be less than (K_a – K_c); losses will reduce the amount of electrical energy generated.

   Assume that the original exhaust system used K₀ amount of energy, which produced an exhaust with kinetic energy of K_a.

   At this point let us ask the question, what if the exhaust system reduced the amount of energy used from K₀ to K₀ – K_b? This would lower the exhaust kinetic energy from K_a to K_c, assuming no losses. So placing an exhaust turbine is equivalent to reducing the input energy of the system.

   Therefore, when losses are taken into account, it is more energy efficient to reduce the input energy rather than install an exhaust turbine. Of course reducing the input energy does not cost anything, whereas installing a turbine incurs a cost.

   To recap, it is much more efficient to reduce the overall energy consumption of the system from K₀ to K₀-K_b, rather than place a turbine to extract K_b energy. Both lead to expulsion of K_c amount of energy.

   So in this scenario an exhaust turbine does not make sense.

2. Place a wind turbine at some distance from and in relation to the exhaust duct. In this situation significant energy will be lost to the outside and the other energy that hits the turbine can be conceptually viewed as a tube of air that is subject to exactly the same analysis as was conducted in item 1. So for this tube of air it is better to reduce the amount of input energy as opposed to recovering it using a wind turbine.

In conclusion, although the exhaust wind turbine idea seems promising conceptually, it is not.

The International Electrotechnical Commission (IEC) creates and publishes standards for wind turbines among other electrical and electronics equipments. The IEC 61400 deals with wind turbine generators (WTG). This blog entry will explain turbine classes. Turbine classes are determined by three parameters the average wind speed, extreme 50-year gust, and turbulence. The following table explains the classifications.

For standards purposes, wind speeds are measured every 3 seconds, and every 10 minutes wind speed and standard deviation are recorded. For design load calculations purposes the wind speed over 10 minutes is assumed to be a Rayleigh distribution.

All wind speeds in the above table are at hub height. The extreme wind speed are based on the 3 second average wind speed. I₁₅Turbulence is the standard deviation of wind speed measured at 15 m/s wind speed.

As an illustration consider GE 1.5sle, a Class IIA WTG and GE 1.5xle a Class IIIB WTG. The Class IIA WTG has a rotor diameter of 77m and hub heights of 65m and 80m. It is designed for average wind speed at hub height of 8.5 m/s with turbulence of 18%.

The Class IIIB WTG has a rotor diameter of 82.5m and hub height of 80m. Because the Class IIIB WTG is designed for lower wind speed (7.5 m/s at hub height) and lower turbulence (16%), the design loads are going to be smaller, therefore its blades are larger and hub height is taller. Bigger rotors of Class IIIB WTGs therefore capture more wind energy and yield higher capacity factors compared to Class I or II WTG.

In conclusion, a wind resource assessment that is based on onsite wind measurements can provide not only the annual average wind speed, but also provide turbulence and extreme wind conditions. This data is necessary to select the class of a turbine. Wind data that is typically used for prospecting like reanalysis data and 10m airport wind data do not provide information about turbulence.

There is immense interest in capturing wind energy with turbines installed on rooftops. This blog entry and the associated whitepaper will answer the questions: Does it make sense to place a wind turbine generator on a roof?

Examples of prominent rooftop installs include: Twenty 1KW Aerovironment turbines at Boston's Logan Airport, the Brooklyn Naval Shipyard, and on top of comedian Jay Leno's garage.

The results of rooftop installs are not encouraging. The Massachusetts Technology Collaborative (MTC) sampled 19 small wind turbines installed using MTC grants. The data revealed that the actual average power output is only 27 percent of that estimated, with the high being 59 percent and the low an abysmal 2 percent. As a result of poor performance, in the fall of 2008 MTC cancelled the small wind initiative.

What is not to like about rooftop turbines? These are some of the positive considerations: Wind speeds increase with height; the wind tends to accelerate as it rises over the eaves of the building; there is nothing on the roof anyway; and, energy is produced very close to where it will be used.

Some of the negatives are: Due to the eaves and building contour, there tends to be a sharp increase in turbulence that causes excessive and unbalanced loads on the turbine that lead to premature component failure; residential and most commercial roofs are not suitable as they were not designed to carry the additional weight, dynamic load and vibration of the wind turbine generator; commercial metal roofs are not suitable because of vibration induced noise; turbulence causes energy output to reduce significantly; turbulence causes the life of turbine to be significantly shorter; the orientation of the building significantly impacts the airflow; rooftops produce the rated amount of energy only when the wind direction is in a small 30 degree sector, and in all other wind directions there is a sharp drop in energy production.

At the recent 2009 American Wind Energy Association annual convention, Brad Cochran of CPP presented a paper on "Optimizing the Placement of Building Integrated Wind Turbines." The authors contend that:

• Proper placement of turbines on the roof is essential. The wind speeds can range from 0.1 to 1.5 times that wind speed at eave height. A location closest to the eave that is perpendicular to the predominant direction of wind is the best.
• Building orientation with respect to predominant direction of wind is important. The widest part of the building should be perpendicular to the predominant direction of wind. Rooftop installs makes sense only in situations where the most favorable wind conditions are in a 30 degree sector.
• Height of building and height of turbine above roof are important. A 400 ft building will experience significantly higher wind speeds at roof level compared to a 40 ft building. 30 to 50 feet above the rooftop will experience normal turbulence levels; any turbines below this height will encounter high turbulence intensities.

In conclusion, a rooftop turbine install makes sense in the following situations:

• Building is in a high wind area and the building is tall. The average wind speed at hub height should be at least 6 m/s, preferably higher.
• The predominant energy from wind is in a 30 degree sector. The orientation of the building must be such that the broad side of the building is perpendicular to the predominant wind direction.
• Turbine should be at least 30 ft (preferably 40 to 50 ft) above the rooftop and any other taller structure in the vicinity. For shorter buildings (20 ft or lower), consider other alternatives like installing turbine on a 70 to 100 ft pole. Any hub height less than this will not see sufficient wind resource.
• Rooftop must be able to withstand the moments due to forces on a 30 ft cantilever. Roof must also be able to withstand the weight of the turbine. Roof must be of thick concrete so it does not vibrate.
• The turbine should be located as close to the eave as possible.
• The selected turbine must be tested in high shear and high turbulence environment because a roof will experience such conditions.

Failure to follow these guidelines will lead to significant reduction in wind turbine output.

In the recent years there has been a big push toward attaining LEED certification of buildings. In this entry I will describe the connection between renewable energy and LEED points, and describe ways to finance a renewable energy project that does not impact the cost.

When a "Design and Build" company proposes a LEED design to a developer, it chooses the most cost effective components of the design such that the points add up to the desired LEED level. For instance, if a designer wants to achieve a Gold level of LEED certification, then it needs 39 to 51 points. Inserting renewable energy generation into a project is a very expensive way to achieve this Gold target. There are several other significantly less expensive design options to accomplish the same goal.

My whitepaper argues that such a simplistic way of evaluating a renewable energy project is seriously flawed. A more sophisticated look reveals that on a variety of financial measures, a LEED design with renewable energy can be a very attractive investment in the long run. A wind project in a Class 3 wind area can yield substantial positive cash flow.

The whitepaper also describes financing mechanisms like performance contracting or other similar methods to pay for wind projects with no upfront costs.

Sonic Detection and Ranging (SODAR) is a ground based remote sensing technique for measuring wind speed in the three directions. It is based on Doppler shift in the frequency of the sound waves that are backscattered by temperature fluctuations in the atmosphere.

As the hub heights and blade lengths of turbines have increased, met-tower based measurements at 40, 50 and 60 meters, or sometimes 80 meters height are inadequate to provide an accurate estimate for wind speed at the hub height, let alone over the entire turbine rotor. With both hub heights and rotor diameter above 85m, met-towers of height 150m or more would be required to measure the wind speed over the entire turbine rotor. This would be cost prohibitive. SODAR provides an economical method to measure wind speed in this range of heights.

I have written a whitepaper that describes how SODAR may be cost effectively used for prospecting. With SODAR based measurements a developer is able to evaluate multiple sites in a short amount of time. For instance, over a period of 6 months, a developer may be able to evaluate 6 to 7 potential sites with real measurements at heights of 50 to 200 meters in increments of 10 meters. In most cases, short-term (4 weeks) SODAR measurements are sufficient for this task; it requires that the correlations with longer-term reference wind data be within acceptable range.

Among the challenges in piecing together a wind project is the selection of a wind turbine. Several factors are used to determine the appropriate wind turbine for each project. Primary among these is using the manufacturer's rated capacity to estimate energy production.

Some turbine manufacturers claim higher turbine name-plate capacity and therefore higher energy production than what a customer will realize. We have observed this most frequently in smaller vertical axis wind turbines (VAWT) and less frequently in horizontal axis wind turbines (HAWT). This is a particular problem if power ratings and power curves are not certified by an independent agency. I have written a whitepaper that will describe a quick method to verify, at a theoretical level, if a turbine's actual production will ever measure up to the claim. The analysis in the whitepaper and rules of thumb can be easily applied to assist you in evaluating a wind turbine for your project. A 'back-of-the-envelope' check, of both the rated capacity as stated by the manufacturer and the power curve supplied by the manufacturer, can prevent you from choosing a turbine that will not perform as advertised because, after all, the energy production cannot defy the laws of physics.

In this entry I will talk about the cost of energy for small wind projects. The previous blog addressed how the cost of energy is computed and presented the cost of energy generation for utility scale turbines. The focus of this blog entry will be on turbines that are rated 10KW or less.

To recap, the cost of energy production depends on average annual energy production (AEP), total cost of installation, recurring cost for operations and maintenance, and the discount rate.

Three turbines will be compared in this analysis: Bergey 10KW with 7m rotor diameter and 30.5m hub height; SkyStream 2.4KW with 3.7m rotor diameter and 13.7m hub height; and MariahPower 1.2KW with 1.2m width and 6.1m height. The first two are horizontal axis wind turbines (HAWT) and the third is a vertical axis wind turbine (VAWT).

The following parameters will be used for comparison purposes:

• Wind conditions: 7m/s at 50m, which is Class 3 wind regime
  
• Operations and maintenance costs: 1c per kWh of energy produced
  
• Annual sinking fund for repairs: 0.75% of total installed cost
  
• 3% inflation in costs
  
• Wind shear of 0.15; this is used to compute wind speed at hub height while assuming wind speed of 7m/s at 50m
  
• Life of wind project: 20 years
  
• Annual Energy Production (AEP) is computed based on power curves provided by the manufacturer
  

The following table contains average AEP, the installed cost and cost of energy.

Note the cost of energy does not include incentives or tax credits.

Since VAWT do have a hub-height, for computation purposes the hub height was assumed to be the height of pole plus half the height of the turbine, which is equal to 6m for the Mariah Power VAWT. If the VAWT is installed on a roof, then the hub-height would have to be appropriately adjusted, although the impact of turbulence due to air flow along the edge of the building would reduce energy production.

Next, let us examine the impact of the investment tax credit (ITC) grant of 30% that is part of the current stimulus package. In cases where the investment per KW is large, the ITC is preferable over the production tax credit (PTC). For a more detailed description, see WECC whitepaper on the stimulus package.

Note that as a result of the ITC grant the reduction in cost of energy is a little less than 30%.

Next, let us look at depreciation, the other major tax benefit. The stimulus package allows a bonus depreciation of 50%, in addition to the accelerated depreciation already allowed for renewable energy items, if the project is put in place before the end of 2009. When a project utilizes the 30% ITC grant, the depreciable basis of the project must be reduced by 50% of the grant amount. The following are costs per kWh when bonus depreciation is coupled with 5-year MACRS depreciation.

Note, bonus depreciation in addition to accelerated depreciation leads to a further reduction of about 33% of the cost of energy than with the 30% ITC grant.

On the benefits front one other item requires mention: Renewable Energy Credits (RECs). RECs are a tradable certificate of proof that 1 kWh of electricity was produced using a renewable source. They are typically sold to businesses seeking to reduce their carbon footprint or to government agencies trying to meet renewable portfolio standards set by state or national mandate. Their pricing depends on market conditions related to the current supply and demand of RECs. The price of a REC is typically in the range of 0.5c to 2c.

In conclusion, if a small wind project is able to use all of the tax benefits of ITC and depreciation, then the cost of electricity is reduced by more than 50% of the original installed cost without incentives.