Turbine efficiency: What do you need to know?
The point of owning and operating a domestic sized wind turbine system is to generate electricity for whatever reason, be that domestic use, profit or generation for industrial purposes. Overall electricity generation of a wind turbine system depends on many different factors, many of which can be influenced by internal and external factors of the system itself or where the system is placed. This is to say, it matters not only what power rating your turbine has, but how efficient that turbine is at extracting the energy from the wind and converting it to electrical energy at the point of consumption. As an example, a 5kW generator in a turbine could, due to inefficiencies in the system, only generate 500W of power due to energy losses in the system if managed improperly. It is therefore important to characterise and understand the different causes of inefficiency and how they might be combatted.
How to get the most from the wind
We will start from the perspective of the wind and work our way through each of the inefficiencies until we get to the electricity used to charge the batteries in your home. Unfortunately you can't control what the wind is doing at all times so we unfortunately can't do much about its condition. It is worth noting, however, that, generally, the more laminar the flow of the wind is (a scientific name for a smooth flow of air) the higher the efficiency of the conversion of the wind's kinetic energy to the rotational kinetic energy of the wind turbine blades.
Turbulent flow is the opposite. This is when the air is chaotic and swirls around unpredictability. Local points within the flow of the wind can be pushing the wind backwards or sideways causing inconsistent forces applied to the turbine blades. The limited control that you do have over the wind that interacts with your turbine is how the environment around the turbine affects the flow conditions. Obstructions to the flow such as trees, buildings or other wind turbines will cause an increase in turbulent flow reaching the turbine. Hence when installing your turbine you should try to put it in a nice open area with minimal obstructions nearby.
It is also worth looking at the wind speed that your turbine will be subjected to in different installation positions as this can vary. The main point you should consider is the height of your turbine. The higher up the turbine is installed, generally the higher the wind speeds are. This is because as the wind interacts with the ground it slows down, slowing down the air just above it, then that air slows the air above it etc… till you get back to the unrestricted flow where the wind is flowing at full speed. This phenomenon is named the boundary layer in fluid dynamics: a layer of flow close to a boundary (air to ground) which has a speed gradient across its height.
Lift or drag
The second and quite important inefficiency when it comes to wind turbine systems is the theoretical limit on the amount of power that can be extracted from the wind by a given turbine blade. This depends predominantly on the shape of the blade used to harvest the wind energy. There are several popular designs of turbine blades, TESUP in particular employs lift type and drag type blades in their designs.
An example of a lift type blade can be seen on the Magnum 5 turbine. The blade is shaped in a manner known as an aerofoil. This is the shape of a plane wing if you were to look at its cross section. This shape produces lift when wind is passed over its surface in exactly the same manner as a plane wing. A good example of a drag type turbine is a TESUP AtlasX turbine. This type of turbine has a 'C' shaped blade and relies on the wind to directly 'push' on the turbine blades to spin them.
The theoretical maximum for lift type turbines sits around 40% and I know that might seem low at first glance, but the maximum efficiency of any turbine is only 45%! So really it's not bad at all! Drag type turbines tend to have lower efficiency in general. This is mainly due to the construction of the turbine. As two blades (one either side of the turbine) are being pushed by the wind at any one moment, one of the blades is working against the rotation of the turbine (how rude!) the C shape of the blade ensures more blade surface area is exposed to the wind and therefore one of the blades catches more wind and is pushed harder, generating rotation.
You may be thinking oh, that's rubbish, low efficiency? I will barely get any power from my TESUP turbine! But not to worry, there is a trade-off, and a great one at that! Drag type turbines have a lower startup speed and therefore spin more often than lift type turbines, very much like the tortoise and the hare of energy generation! TESUP works hard to make their turbines have higher efficiencies by carefully designing their blades. Just look at the redesigned blades of the AtlasX! Not only have they improved the efficiency of the turbine, and increased the wind catchment area, they also look great!
The necessity of good components in your operational system
The final hurdle between the wind and your electricity generation is electrical inefficiencies. These can and will occur in all electrical components be it the electrical generator in the turbine or the smallest wire in the system. Unfortunately electrical components have a tendency to waste electricity through the generation of thermal energy (think of when you have touched a phone charger and it was warm after charging a phone). Every step necessary in a wind turbine system for generating, transmitting and storing electrical energy will inherently