# Testing wind/water turbine performance

• van4
In summary, to measure the voltage produced by the generator while it's driving the turbine, you will need resistors rated at 25W or 10W.
van4
I'm required to test a harizontal axis turbine's performance and plot a RPM vs Power curve. The turbine is driving a small DC generator that produces 5V at the turbine's maximum RPM with no other load on the generator.

I am planning on installing different sized resistors in parallel with the generator and then measuring the voltage out. This will effectively act as a load which will decrease the RPM, and in turn decrease the voltage produced by the generator, which can then give me a plot. My question is - what size resistors do I need?

Through my study of wind/water turbines, I've calculated that the maximum power that this turbine can extract from it's environment is ~20W ideally. My attempt at answering my question was that I use P=V^2/R to rearrange for R=V^2/P=5^2/20=1.25Ω. So would I need resistors from 0Ω to 1.25Ω?

Well, a 0Ω load will be a short circuit, which means you will have zero voltage across it; tough to get any power without any voltage .

The 1.25Ω load will be around the maximum power point so you will need resistors above and below that value. In addition to a 1.25Ω load, three values below and three values above should give you a decent curve. The lowest and highest values values could be a factor of four or five from the 1.25Ω, or about 0.25Ω to 6.25Ω.

Since you are working with rather low resistances here, be sure to account for any significant resistance in the wiring. That means you should measure both the resistance and the voltage at the point they connect to the generator terminals.

Have fun!... and let us know your results.

Tom.G said:
Well, a 0Ω load will be a short circuit, which means you will have zero voltage across it; tough to get any power without any voltage .

The 1.25Ω load will be around the maximum power point so you will need resistors above and below that value. In addition to a 1.25Ω load, three values below and three values above should give you a decent curve. The lowest and highest values values could be a factor of four or five from the 1.25Ω, or about 0.25Ω to 6.25Ω.

Since you are working with rather low resistances here, be sure to account for any significant resistance in the wiring. That means you should measure both the resistance and the voltage at the point they connect to the generator terminals.

Have fun!... and let us know your results.

Great, thanks a lot.

I mentioned 0Ω, but what I meant was a very very small Ω :)

I was worried that resistors below the 1.25Ω value would cause some sort of problem because if you put the resistance into P=V^2/R, you get a higher power out than you have available. But your comment does make sense. Also, I assume I'll need resistors which are rated to ~20W? (My knowledge of electronics is very basic)

Thanks

van4 said:
Also, I assume I'll need resistors which are rated to ~20W?
Fortunately one of the standard power ratings for resistors is 25W. We normally use a safety factor of two for power ratings which means a 50W resistor would be specified; that's another standard power rating but a bit hard to find from the usual electronic suppliers. The reason for the 2X safety factor is to keep the temperature down, prolonging the life, and so you don't get burned when you touch them!

In your specific case only for low voltage and brief laboratory use, you could use 25W or even 10W resistors if they are immersed in a water bath to keep them cool.

Actually since the peak power will be with the 1.25Ω resistor, the other values will dissipate less power. For instance both the 0.25Ω and the 6.25Ω load will dissipate somewhere between 4W and 16W, depending on the characteristics of the generator.

To cut down on the costs, remember that resistance adds for series connected resistors. And for the lower values you can parallel several resistors. For instance four 5Ω resistors in parallel equals 1.25Ω. If the resistors in a series or a parallel combination are all the same value then the power dissipation is evenly distributed among them. Thus four 5W resistors would be rated at 20W provided there is air/coolant flow around and between them... that means don't mount them into a tight bundle.

## What is the purpose of testing wind/water turbine performance?

The purpose of testing wind/water turbine performance is to evaluate the efficiency and effectiveness of the turbine in converting wind or water energy into mechanical or electrical energy. This helps to identify any potential issues or areas for improvement in the design or operation of the turbine.

## What factors affect wind/water turbine performance?

There are several factors that can affect wind/water turbine performance, including wind/water speed, direction and turbulence, blade design, rotor size, and environmental conditions such as temperature and humidity. These factors can impact the amount of energy that can be harnessed by the turbine and its overall efficiency.

## How is the performance of a wind/water turbine measured?

The performance of a wind/water turbine is typically measured by the amount of energy it produces over a given period of time. This can be measured in terms of power output (in watts or kilowatts) or energy output (in watt-hours or kilowatt-hours). Other factors such as rotational speed and torque may also be measured to assess the performance of the turbine.

## What are the different types of tests used to evaluate wind/water turbine performance?

There are several types of tests that can be used to evaluate wind/water turbine performance, including power performance testing, load testing, and endurance testing. Power performance testing involves measuring the power output of the turbine under various wind/water conditions. Load testing involves subjecting the turbine to different loads and measuring its response. Endurance testing involves running the turbine for an extended period of time to assess its durability and reliability.

## Why is it important to test wind/water turbine performance?

Testing wind/water turbine performance is important for several reasons. It helps to ensure that the turbine is functioning properly and producing the expected amount of energy. It also helps to identify any potential issues or areas for improvement in the design or operation of the turbine. Additionally, testing can provide valuable data for future research and development of more efficient and effective wind/water turbine technologies.

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