In wind turbine design, the Tip Speed Ratio (TSR) is a critical factor. TSR stands for the ratio of wind speed to the speed of the blade tips on a wind turbine.
What is a wind turbine’s average energy output?
The average American home uses 893 kilowatt-hours (kWh) of power each month, according to the US Energy Information Administration. The average capacity of wind turbines that began commercial operations in 2020 is 2.75 megawatts, according to the US Wind Turbine Database (MW). That average turbine would generate over 843,000 kWh per month, enough for more than 940 average U.S. homes, based on a 42 percent capacity factor (i.e., the average among recently built wind turbines in the United States, according to the 2021 edition of the US Department of Energy’s Land-Based Wind Market Report). To put it another way, the average wind turbine that went online in 2020 provides enough electricity to power a typical U.S. home for a month in just 46 minutes.
What is a wind turbine’s TSR? How is it put to use?
Wind turbine manufacturers employ the Tip Speed Ratio (TSR) to properly match and optimize a blade set to a certain generator (i.e. the permanent magnet alternator). This is necessary in order to respond to one of the most often asked questions: What blade size should I get to go with my generator?
We’ll try to answer this topic by focusing on the elementary physics that go into computing the Tip Speed Ratio!
Understanding Tip Speed Ratio
TSR is defined as the speed of the blade at its tip divided by the wind speed. The TSR is 5 (100 mph/20 mph) if the tip of a blade is traveling at 100 mph (161 kph) and the wind speed is 20 mph (32 kph or 9 m/s). Simply put, the blade’s tip is going five times faster than the wind speed.
You’re probably asking why this is significant. If the blade configuration for a given generator spins too slowly, the majority of the wind will pass through the rotor without being collected by the blades. The blades will always be traveling through used/turbulent wind if they spin too fast. This is due to the fact that the blades will always be passing through the same area that the blade in front of it recently passed through (and used up all the wind in that location). It is critical that adequate time passes between two blades passing through the same spot, allowing new/unused wind to enter. As a result, the following blade passing by this position will be able to capture new/unused wind. In other words, if the blades are spinning too quickly, they are capturing less wind than they could, and if they are spinning too slow, they are rotating through used/turbulent wind. As a result, TSRs are used in the design of wind turbines to ensure that the maximum amount of energy may be harvested from the wind using a specific generator.
Without getting into too much detail, physics and study have determined that the approximate ideal TSRs for a particular blade rotor are as follows:
Analyzing TSRs can lead to a number of useful findings. Let’s go over a few of the most basic and vital elements for the do-it-yourselfer who is putting up their own wind generator:
- Many bladed rotors (e.g., 11 blades) are generally not a good choice. The ideal TSR for an 11-bladed rotor would be relatively low. This means that an 11-bladed rotor will perform best at extremely low rpms. There is no benefit or need to utilize a rotor with multiple blades because practically all generators (permanent magnet alternators) are not suited for extremely low rpms. Remember that rotors with a large number of blades capture used/turbulent wind at high TSRs, making them inefficient when employed as a high-rpm blade set. This is a crucial topic since many people mistakenly believe that having more blades means having a faster and more efficient blade set. The principles of physics, however, state that this is not the case.
- A two or three blade rotor is your best bet if you already have a generator or motor that requires high rpms to reach charging voltage. At high rpms, these rotors are more efficient. Additionally, keep the blades as short as is practical, because shorter blades spin quicker than longer blades.
- Last but not least, keep the Tip to Speed Ratio in mind. If the TSR of your wind generator rotor is lower than the optimum value, the blades of your wind turbine will stall before reaching maximum power/efficiency. The blades of a wind turbine will be moving through turbulent wind if they are spinning faster than the recommended TSR. Not only is this inefficient, but the turbulent wind causes unnecessary stress and fatigue on your blades and wind turbine as a whole.
How to Measure TSR
It’s simple to calculate a blade set’s TSR. You’ll need two things to complete this measurement:
- A tachometer that is digital. These can be purchased for around $25 on the internet and are used to measure the rpms of a blade set.
- An anemometer is a device that measures the wind speed. A digital anemometer is used to measure wind speed and may be obtained online for around $20.
You can get the measurements you need to calculate TSRs with these two products. However, one question remains. If we just have the rpm at the tip of the blade from our tachometer measurement, how do we compute the speed at the tip of the blade? So, we’ll have to do some math. Let’s have a look at each stage of the calculation:
Circumference of a circle with radius r = (2)(?) = distance traveled by the blade tip to complete one revolution (r)
Sample Calculation
Let’s say we use our digital tachometer to get a reading of 450 rpm at the blade’s tip. In one hour, how far does the blade’s tip travel?
Because this is the first calculation we made, we know that the blade tip travels 6.28 meters in one rotation!
As a result, we now know that the blade’s tip moves 169,560 meters in one hour. Let’s convert meters to miles now:
All right, we’re almost done. The speed at the blade’s tip must now be calculated. We know the blade’s tip traveled 105 miles in an hour, so this is simple. As an example, consider the following calculation:
That concludes our discussion. This blade’s tip speed is 105 miles per hour at 450 revolutions per minute. So what if the wind was blowing at 20 miles per hour when we measured 450 revolutions per minute? What exactly is the TSR? It’s simple:
What is the greatest percentage of output from wind power?
Regardless of the design of a wind turbine in open flow, Betz’s law specifies the maximum power that may be extracted from the wind. Albert Betz, a German scientist, published it in 1919. The law is based on the concepts of mass and momentum conservation in an air stream moving through a hypothetical “actuator disk” that takes energy from the wind. No turbine can catch more than 16/27 (59.3%) of the kinetic energy in wind, according to Betz’s law. Betz’s coefficient is defined as the factor 16/27 (0.593). At their peak, utility-scale wind turbines reach 7580 percent of the Betz limit.
An open-disk actuator is used to set the Betz limit. More energy can be recovered if a diffuser is employed to gather more wind flow and route it through the turbine, but the restriction still applies to the cross-section of the overall construction.
What exactly is the TSR ratio?
Overall shareholder return (TSR) is a financial performance indicator that indicates the total amount an investor earns from a particular investment, such as stocks or equities. TSR considers capital gains and dividends from a stock, as well as special distributions, stock splits, and warrants, to get at its total, which is commonly stated as a percentage. TSR is the whole total of what a stock has returned to individuals who have invested in it, regardless of how it is computed.
What factors influence the tip speed ratio (TSR)?
The ideal tip speed ratio, which is defined as the ratio of the rotor tip speed to the free stream wind speed, is another significant term in wind turbine power. If a rotor rotates too slowly, too much wind is allowed to flow through undisturbed, and so the rotor does not extract as much energy as it could (within the Betz Criterion, of course).
If the rotor turns too quickly, however, it looks to the wind as a giant flat disc, which causes a lot of drag. The rotor Tip Speed Ratio, or TSR, is determined by the blade airfoil profile, number of blades, and wind turbine type. Three-bladed wind turbines typically have a TSR of 6 to 8, with 7 being the most commonly reported number.
Other concerns dictate the TSR to which a wind turbine is designed, in addition to the factors described above. A high TSR is desirable in general because it results in a high shaft rotational speed, which allows an electrical generator to operate efficiently. However, there are certain drawbacks to having a high TSR:
Blade tips traveling at speeds more than 80 m/s are vulnerable to leading edge erosion from dust and sand particles, necessitating particular leading edge treatments similar to those used on helicopter blades.
Higher-speed rotors necessitate considerably larger braking systems to prevent the rotor from reaching a runaway state, which could cause the turbine rotor blades to disintegrate.
How many kWh does a wind turbine generate on a daily basis?
The majority of turbines are rated in kilowatts (kW). The figure is similar to that of a car’s horsepower. It indicates which engine or turbine is larger, but it is not a true representation of the machine’s total energy output. Without vehicle weight, driving circumstances, and other data, the number of “horses under the hood” does not represent fuel efficiency or top speed. Most automobile purchasers, at the very least, have driven a car before, so they have a rough concept of how to convert horsepower figures. Homeowners, on the other hand, are often purchasing their first turbine and thus have no comparative data.
Utility bills are calculated in kilowatt-hours (kWh), which is the product of power consumption multiplied by time. One kWh is used by a 100-watt light bulb that is left on for 10 hours. Although many firms and industry associations claim that a 10 kW system will generate 10,000 kWh per year (equivalent to the average electricity demand in a US home), the actual output will be either higher or significantly lower. Under ideal conditions, the turbine can create a maximum of 10 kW, which means it could theoretically generate 10 kW for 24 hours a day, 365 days a year, or 87,600 kW per year. It will barely generate a few watts with only light gusts.
Multiplying the mechanical efficiency by the wind speed, air density, and rotor blade length yields the real power output of a wind turbine in watts.
How much energy is produced by a 1.5 MW wind turbine?
Installing a tiny wind turbine in a community that wants to create their own green power could be an alternative. Small wind turbines are electric generators that utilise the wind’s energy to provide clean, emission-free electricity for individual homes, farms, and small enterprises.
However, because wind power is intermittent and unpredictable, a wind turbine will only produce power at or above its annual average rate 40% of the time. That is, for the most part.
What is a megawatt or a megawatt-hour?
The maximum, or rated, capacity of wind turbines to generate electric power is measured in megawatts by manufacturers (MW). One million watts equals one megawatt.
Megawatt-hours (MWh) or kilowatt-hours (kWh) of energy are used to measure the amount of electricity produced over time. One thousand watts equals a kilowatt. 1 MWh of energy is produced when 1 MW of power is produced for 1 hour.
What is the power capacity of wind turbines?
A 1.5-megawatt type made by General Electric (GE) was previously commonly utilized. Its rated, or maximum, capacity is 1.5 MW, which means it can create power at that rate when the wind speed is between 27 and 56 mph, which is optimal for that model. Turbines currently typically range from 2 to 3 megawatts.
What determines how much power a wind turbine can produce?
Because electricity is generated by capturing wind energy and converting it to rotational torque inside a generator, the power of a turbine is determined by its ability to push electrons into the grid. Larger blades capture more wind energy, while a taller tower allows access to more consistent winds. Larger blades and/or stronger winds are required for a larger generator.
How much energy do wind turbines produce?
Every wind turbine has a different range of wind speeds in which it will produce at its rated, or maximum capacity, which is normally about 30 to 55 mph. The production drops considerably at lower wind speeds. When the wind speed is cut in half, the amount of energy produced drops by a factor of eight. Wind turbines, on average, do not generate near their full capacity. Annual outputs of 30-40% are projected by industry estimates, however real-world experience reveals that annual outputs of 15-30% of capacity are more common.
A 1.5-MW turbine with a 25% capacity factor would produce:
A wind turbine generates how many watts per day?
The output of a wind turbine is determined by the size of the turbine and the speed of the wind through the rotor. Today’s wind turbines have power ratings ranging from 250 watts to 7 megawatts.