# Micro-Wind Turbine Review & Performance Guide

If you're thinking about buying a wind turbine, one of the most important questions you might ask is,

"How much energy can I get out of this thing?"

In fact, this could be the most important question in selecting a wind generator, yet answering this question is made incredibly difficult by the industry.

We conducted a piece of research into the performance of popular micro-wind turbines to help answer this question. As part of this research, we:

- collected all the popular micro-wind turbine power charts
- digitised them from images to data
- interpolated data to fill any gaps
- standardised reporting
- consolidated the power curves onto a single chart

Then, after looking at instantaneous power metrics, we really wanted to compare energy output estimates in terms of kWh per day. However not all turbines provide energy output charts and when they do, comparing those charts at face-value overlooks the varied range of assumptions that manufacturers could adopt when converting power (for a given wind speed) to energy yield (for a location with varying weather over time).

To overcome this issue, we:

- developed a simulation model of the wind
- applied that same model to all the power curves
- calculated the implied daily energy outputs in kWh per day
- performed a like-for-like comparison on the results

As far as we know, this is the only such resource available on the internet. And it's free!!!

#### What is a "micro-wind turbine"?

We define micro-wind turbines as those with a diameter of up to 1.3m. You could also think of them as the size range used in marine applications, including boats, yachts, barges, pontoons, etc.

#### Causes of confusion

What makes evaluation so difficult?

For one thing, just getting used to the terminology and concepts in renewable energy can be tricky for the average person. To many people, power and energy are pretty much the same thing, but in the industry, the difference is stark. Energy is the product of power and time. We measure power in Watts and energy in Watt hours. Throw volts and amps into the mix and we have a recipe for confusion.

Then there is the way information is presented. When turbine manufacturers release the specifications of their wind turbines, they include a power curve chart. It shows how much power the turbine can produce at different wind speeds. Here is an example:

So now we know that this turbine at a wind speed of 8 m/s (metres per second) produces 100W of power (in perfect conditions). What we still don't know is:

- What wind speed should we be looking at?
- How much power is that over the course of a day?
- Or more importantly, will this run my appliances?

Also, we need to be careful because these charts make some 'perfect-world' assumptions about what type of wind is blowing. They assume your 8 m/s is laminar wind flow which means the wind flows perfectly smoothly without any imperfections or disruptions.

Here is another example from a different manufacturer. This time the wind speed is given in Knots so comparing the two requires some arithmetic.

Some manufacturers like to express the Y-axis in Amps for a given voltage of turbine, further complicating the comparison process.

Others still like to use bar graphs, sometimes even 3D bar graphs.

#### Comparing Power Curves

Power curves can tell you part of the story and it helps to see them on the same chart, using the same scales.

Firstly, worth noting the size differences:

- Most turbines in the chart are 1.2m in diameter.
- Smallest is the Rutland 914i at 0.9m.
- The Eclectic D400 is 1.1m
- Largest is the WindiStar at 1.26m diameter, propelling it to the top.