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
- Transmission lines
- Power Purchase Agreements
- Operation & Maintenance
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.
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%
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.
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.
When operating at near capacity, a wind gust may increase input power by 8 times, which overloads the machine.
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
- 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
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
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
- Improve blade design
- Predict wind
- Match load
- Maintain optimum TSR
- Prevent overloading
- Reduce transmission losses
- Eliminate parasitic losses
- Eliminate reactive power
- 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
- Utilize laser anemometer
- Predict wind direction, speed, duration, onset
- 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
- 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%
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.