Capacity Factor and Nameplate Rating Explained

Rated output, also known as Nameplate rating, is determined by the wind turbine manufacturer, based on their chosen wind speed.  The rated output can be a high number or a low number, depending on the wind regime chosen for performance calculations. In its current state, there is no unified approach to wind turbine ratings, making the process capricious.

Actual net output is not affected by output rating, but capacity factor is, since capacity factor is a percent of the output rating.

If we say that a machine is rated at 50kW and it delivers 20kW on average, its capacity factor will be 40%. If we rate that same machine at 60kW, the average output remains the same but the capacity factor changes to 33%. 

You can start to see how nameplate rating (output rating) and capacity factor are arbitrary.

Most good performing machines average 25% of rated output, a very good machine will deliver 35%, but again, these percentages are based on the wind turbine maker's chosen power rating.

Imagine the scenario where a manufacturer wants to give the illusion of a high output machine; they could use performance figures from unusually high wind speeds, utilize a generator big enough to support these unrealistic wind conditions and presto, they've got virtually whatever size machine they want. Not only is this deceiving to the consumer but utilizing a generator that's too big for the application drives the cost up and hurts efficiency. 

So, since there's no industry standard for wind turbine power ratings, what's the best way to compare machines?

Cost per kilowatt hour.

Output per square foot of footprint or swept area is another way to compare apples-to-apples but the one we use most frequently at Uprise Energy is $/kWhr.

If you have another metric that you use or would like to continue the discussion, please use the comments section below. Thanks for reading!

Why The Uprise Energy Portable Wind Turbine Is Needed

There are many niches that could be served with an off-grid, portable, renewable power generator. This discussion will focus on those that do not have reliable power as a result of not being served by an electrical grid.

Most, if not all of the readers of this blog have never experienced life without electricity, yet over a third of the world's population is not so fortunate. This is primarily due to an absence of power "grids" in many parts of the world and it's unlikely this will ever change, given the cost to connect all the remote regions and islands with power transmission lines.

So, take a minute and imagine life without reliable electricity. No electrical sockets, no light switches, no refrigerators and certainly no power for the computer or smartphone you're reading this on. Kinda scary, isn't it?

I'm writing this post from San Diego, CA, where one year ago, we experienced a county wide power outage that lasted almost 2 days. Being in the business of portable, renewable power, I often imagined what life would be like without the electrical conveniences most of us take for granted. Well, I can tell you that no amount of daydreaming could equal the experience we had. Let's just say, the day after the outage, my phone has never rang so much. It was the veritable splash of cold water to the face, so to speak.

So without utility power, where do these people turn to serve their needs? Well, many rely on diesel generators, which are reliable and easy to use... if you have diesel fuel. That last part ends up being the bugaboo for a lot of these unconnected people.

Sure, petroleum has the clear advantage of superior energy density and ease of use, so it's no wonder this form of power is so ubiquitous but the knowledge we have today paints a much better picture of all factors involved.

Until recently, petroleum was abundant and affordable but not anymore. Petroleum prices have been rising faster than most commodities, largely due to it being a limited resource. At today’s cost of diesel, plus the difficulty of refueling in remote regions, a kilowatt of electrical power will cost anywhere from $1 to $40.  At these prices, economic viability of diesel generators gives way to alternative methods. Then there's the environmental issues associated with extracting and burning fossil fuels, putting an exclamation point on the need for renewable energy sources.

Modern sciences are proving many power needs can be accommodated and be economically viable thru use of renewable energy. And of course, there's environmental benefits of generating power thru renewable sources as well.

Uprise has assessed the entire spectrum of energy needs.  Who needs power, where they are, what can they afford and what their constraints are. This exercise has illuminated the need for a small power generator, that is easily delivered, requires no site improvements or machinery to set up, is renewable, makes meaningful power and is affordable. Serving this need was the inspiration behind the Uprise Energy 50kW Portable Power Center.

The machine that Uprise has developed applies a number of modern technologies to produce a small wind machine that is portable and excels in low wind speed environments (where most of this market lives). The Uprise machine is truly like none other and stands to revolutionize the wind and renewable power industries.

Thanks for reading and please use the comments section below to keep this conversation going.

Methods To Improve Wind Turbine Performance

Renewable energy is imperative.  While no renewable source is the answer for all of our energy needs, wind energy has its attributes.  Unlike the sun, wind is everywhere all the time.  Wind power has become reasonably cost effective compared to other renewable forms.  However, wind is not as cost effective as it should be.  The variability of wind causes severe constraints on the design of wind machines, which reduces its effective capture of available wind energy.

The goal of Uprise Energy is to improve wind gust energy capture thru the use and application of four innovations.

  1. Wind prediction
  2. Variable speed transmission
  3. Constant speed generator
  4. Sophisticated programming of loads and RPM

It is important to understand the reasons for the above mentioned  constraints in order to appreciate the solutions.

The variability of wind is manifested in two manners.  Wind velocity and wind direction. 

Wind velocity creates benefits and problems.  The power in wind increases dramatically as wind velocities increase.  For example, 20 MPH wind has 8 times the power of 10 MPH wind, and 30 MPH wind has 27 times the power of 10 MPH wind.  This example illustrates the importance of capturing the energy of higher velocity wind.  The problem is that wind is not steady. 

There is universal agreement that a wind turbine blade will perform optimally at a given relationship to the wind speed.  Therefore, as wind velocities vary from 10 MPH to 30 MPH, such as in a gust, the blades and rotor RPM must vary (triple) in direct relationship to the wind speed, or suffer inefficiencies.

Unfortunately, conventional wind turbines do not react quickly to the variability of wind velocities, and therefore do not capture much of the gust energy.

Wind does not always blow in the same direction.  The efficiency of a wind machine depends on the rotor to face the wind squarely, not on an angle.  Again, turning the rotor to face the wind takes time, and the power of a wind gust may be lost.

The blade RPM response problem is further exacerbated by another constraint in the industry, generator RPM.

The grid is the problem.  The world’s power grid is either 50 or 60 HZ alternating current (AC).  In order to generate electricity and deliver power into the AC grid, exact frequency must be adhered to. 

A typical conventional large wind machine must deliver AC power to the grid at a steady voltage and frequency.  With variable wind velocities, the rotor rpm will vary, and the voltage and frequencies will fluctuate, which requires use of expensive and inefficient transformers and inverters to purify the power to be grid acceptable.  In order to eliminate expensive, heavy, and failure prone gearboxes, generators are custom purpose built at great costs.  Even so, the industry uses permanent magnet induction generators as a poor substitute for a superior AC synchronous generator, simply because they cannot maintain constant RPM and frequency.

The negative consequences for the use of the gearbox, transformer, inverter, and custom induction generator are higher costs, weight, parasitic losses, and poor power factor for which the power company discounts the value of the supplied power.

Power factor of less than 1.0 (unity) is a result of an imbalance of capacitive vs inductive loads.  When a generator is running slower than or faster than grid frequency, a leading or lagging power factor occurs. The power company will discount KW production for power factors less than 1.0.

All of these negative consequences are mitigated with the Uprise Energy system.

In order to prevent severe voltage and frequency fluctuations, wind turbine designers constrain rotor RPM.  This is accomplished thru the use of brakes and pitch stall. Essentially, they purposefully avoid wind gust energy thru dumping wind energy to prevent overspeeding.

All of these constraints and limitations can be mitigated. 

Uprise Energy, thru years of experience, has developed an understanding of these constraints, and has developed an innovative and sophisticated system to exploit wind gust variability.

While Uprise Energy has developed a number of additional features to improve wind turbine output, the scope of this project is to focus on a system that can be applied to any machine, small, medium, or large, new or retrofit.

The system allows any wind machine:

  1. To allow the blades to spin at their optimum RPM to maintain a correct ratio to the wind speed
  2. To drive an AC synchronous generator at grid voltage and frequency without the need for transformers and inverters
  3. To predict wind direction, speed, and duration thru the use of laser anemometers
  4. To adjust the system load thru programmable excitation of the AC generator.

The benefits of this system are interesting.

  1. An existing machine can increase its annual output
  2. A smaller machine can replace a larger machine at a lower cost
  3. Shipping costs, erection costs will be less
  4. Total elimination of transformers, static inverters, gearboxes, and weight
  5. Lower operation and maintenance costs
  6. Lower parasitic losses
  7. Technically simpler machine
  8. Programmable to optimize each machine and its behavior in each wind environment
  9. Programmable for seasonal conditions
  10. Power down features
  11. Lower mast loads
  12. Off the shelf components
  13. Lower cost generator

The Uprise system blends an intelligent mixture of conventional equipment with state of the art programming to prepare any wind machine for the wind conditions, optimizing wind energy capture.

Problem In The Wind Industry and The Uprise Solution

The problems encountered in generating electricity from the wind and delivering the electricity to a user are numerous.  This post will address the essential element of this industry, converting the kinetic energy in wind into electricity.

Other essential elements of conventional wind energy, which cannot be excluded, include:

  • Land / Site acquisition
  • Wind & Environmental studies
  • Permits 
  • Infrastructure
  • Transmission lines
  • Power Purchase Agreements
  • Operation & Maintenance

Premise/Problem calculated

We start with the premise that converting wind strength into electricity is our number one objective. 

The formula to calculate the kinetic energy in steady wind is:

1/2AV3rho/1000 = kW

Once the Kinetic Energy (KE) of a steady wind has been calculated, there are various factors that reduce the captured energy to a NET OUTPUT.

Betz' Law says that you can only convert less than 16/27 (or 59.3%) of the kinetic energy in the wind to mechanical energy using a wind turbine.

Betz' Law says that you can only convert less than 16/27 (or 59.3%) of the kinetic energy in the wind to mechanical energy using a wind turbine.

KE at 100% of steady wind = 100%
Betz limit = 59.3%
Modern Rotor efficiency = 50%
Transmission losses = -5%
Transformer losses = -4%
Inverter losses = -3%
Reactive power losses = -15%
NET POWER = 23%

Net Energy

The net energy from a Conventional Wind Machine (CWM) in a steady wind delivered to the user is approx 23% of the kinetic energy of the steady wind.

In most cases wind is not steady.  Calculating the kinetic energy in a variable wind (wind gusts and lulls) is a function of amplitude and duration. 

The calculation of the KE in a variable wind is not a function of the average wind speed due to the cube root power factor. KE above the average wind speed is greater than KE below the average wind speed.


Efficiency Revealed

A Conventional Wind Machine captures 23% of steady wind and none of the gust wind energy above the steady wind average.  As a result, the real efficiency is 23/270, or 8.5%.

A Conventional Wind Machine does not seek nor capture gust energy.

The principle reasons why a Conventional Wind Machine does not seek or capture gust energy are EXCESS WIND LOAD and RPM CONTROL.

LOAD

When operating at near capacity, a wind gust may increase input power by 8 times, which overloads the machine. 

The consequences of excess wind speed and power include:

  • Blade strike
  • Tower loads
  • Gearbox failures
  • RPM: A CWM drives the generator directly, either with or without a step-up gearbox.  In either case the rotor rpm must be constant or the generator rpm will vary unacceptably, causing fluctuations in voltage and cycles.

A Conventional Wind Machine incorporates a variety of design elements to offset the excess power and wind speed.

  • Blade area is minimized to prevent overloading in high wind speeds. The consequence is poor performance at low wind speeds.
  • Blade shape is compromised to enable quick rotation of the blade to dump gust energy
  • Brakes are used to prevent excess RPM
  • The machine will turn (Yaw) out of wind to prevent overloading
  • Generator output is directed into capacitors to provide instant load braking
Conventional Wind Machine nacelle fire caused by overloading

Conventional Wind Machine nacelle fire caused by overloading

Negative Consequences

There are negative consequences resulting from the load and RPM constraints listed above.
The rotor rpm of a CWM is constrained and remains relatively constant, regardless of the wind speed.  As a result, Tip-Speed-Ratios (TSR) and blade efficiency are compromised.
Energy is dumped to prevent overload and over revving.
A fixed ratio step-up gearbox is used, which has inefficiencies, and is easily overloaded in wind gusts, which is the #1 industry failure.
A transformer is required to stabilize the voltage
An inverter is used to stabilize the hertz
An induction generator is used which causes a lagging power factor and need for reactive power from the grid
In the event of a direct drive generator without the use of a gearbox, the low RPM of the generator causes cogging and flicker.
Torque on the system is amplified when load is high and RPM is constrained
Noise from the blades is amplified when blade loading is high
Teetering is amplified at high loads

Uprise responds

In response to these constraints, Uprise has designed the PPC and the ECS to operate in a variable wind speed.

Ideally, a wind machine would optimize energy capture and deliver power as a ratio to the winds energy.

The Uprise machine has been designed to:

  • Operate at a higher efficiency than a CWM, especially in low wind speeds
  • Eliminate the parasitic losses caused by the gearbox, the transformer, and the inverter
  • Eliminate the reactive power losses of the induction generator
  • Capture a reasonable amount of the KE of gust wind
Uprise ECS driving the PPC

Uprise ECS driving the PPC

Uprise methodology

  • Improve blade design
  • Predict wind
  • Match load
  • Maintain optimum TSR
  • Prevent overloading
  • Reduce transmission losses
  • Eliminate parasitic losses
  • Eliminate reactive power

Blade design

  • Incorporate sweep and twist
  • Add winglet
  • Reduce inertia
  • Add blade area
  • 2 forms of pitch control
  • Eliminate pitch stall shape
  • Carry foil shape to root
  • Maintain TSR

Predict wind

  • Utilize laser anemometer
  • Predict wind direction, speed, duration, onset

Match load

  • Programming to manage system components thru sensors 
  • Compute kinetic energy of oncoming wind
  • Instruct rotor to change pitch and rpm to optimize TSR

Maintain optimum Tip-Speed-Ratio (TSR)

  • Adjust pitch and load to allow rotor to spin at optimum rpm

Prevent overloading

  • Torque and blade loading are minimized by allowing rotor to increase in RPM as load increases
  • Machine shuts down and lays down when wind load approaches overload

Reduce transmission losses

  • Utilize proprietary hydrostatic drive

Eliminate parasitic losses

  • The fixed ratio gearbox, transformer, and inverter found in a CWM are parasites that rob power. All three are eliminated in the Uprise Energy Conversion System (ECS)

Eliminate reactive power losses

  • Use of off-the-shelf synchronous generator eliminates the power factor problem and produces quality sine wave power.
  • Induction generators are used in CWM because they cannot regulate RPM accurately to maintain 60 HZ in a variable wind condition. Consequences of using an induction generator are severe. Lagging power factors result, and reactive power is needed from the grid to compensate.  Net power is reduced by an average of 15% 

Summary

The above abstract summarizes the constraints of conventional wind machines, the additional Kinetic Energy in variable wind, and the methods that enable the Uprise machine to capture higher levels of energy.

In addition, due to its portability it solves two of the greatest constraints, transmission lines and/or reliance on fossil fuels.

Modern wind farms are located where wind currents are strong and steady to minimize the problems caused by wind variability.  As a result, the power must be delivered to the user thru a transmission system, which is the #1 reason why 30% of the world’s population is not served with electricity.

The Uprise portable power center solves this problem.