of blades in comparison with three-bladed large-scale wind turbines. Finally, none of them is built using 3D-printing. There are few scientific studies about the design of small-scale wind turbines. Fortunately, unlike documentation of commercially-sold wind turbines, scientific articles give much more useful information. Hirahara et al. [22] developed a 4-bladed 0.5 m diameter wind turbine called µF500. They used the NACA2404 airfoil and linearly tapered and twisted blades. They experimentally obtained a maximum power coefficient of 0.4 and a total efficiency of 0.28, which is higher than all the commercially available wind turbines presented. Finally, the optimal TSR of their wind turbine is 2.7, which is much lower than for usual large-scale wind turbines (see Vestas V80 in Table 1.1). Kishore, Coudron and Priya [24] developed a 0.394m diameter prototype of small-scale wind energy portable turbine (SWEPT). Their objective was a very low cut-in velocity in order to produce power even with very weak wind. They found a cut-in speed of 2.7 m/s, which is quite low, but at the expense of a very low maximal power coefficienct: only 0.14. As the µF500, the SWEPT has a low optimal TSR compared to large wind turbines. Kishore and Priya [25] then developed a second version of the SWEPT. It has the same number of blades and almost the same diameter as the older SWEPT. But they achieved a much better power coefficient of 0.32 with almost the same cut-in velocity: 3 m/s. Finally, the blades and the hub were 3D-printed and withstood rotational speeds of over 1600 rpm without problem. However, the rated power is still very limited: only 1W. Type
Wind bine
Commercial
Rutland 504 [40] Rutland 914i [41] Superwind 350 [48] Aeromax Lakota [3] Skystream 3.7 [45]
3D printed
Research
design
Large-scale wind turbine
tur- D [m]
B
Vc [m/s]
Vr [m/s]
Pr [W]
0,51
6
3
11
30
0.18
0,91
6
3
11
143
0.27
1.2
3
3.5
12,5
350
0,26
2,09
3
2.7
12.87
1000
0.22
3.72
3
3.2
11
2100
0.24
Reprap wind turbine [39]
0.84
3
2.8
4,15
5
0.2
SWEPT [24] SWEPT 2 [25] µF500 [22]
0.394 0.4
3 3
2.7 3
5 4
0.83 1
2.9 4.1
0.14 0.32
0.089 0.20
0.5
4
3.6
12
50
2.7
0.4
0.28
Vestas V80 [57]
80
3
4
16
2×
106
λopt
8
CP
ηmax
0.435
Table 1.1: Examples of existing small wind turbines Finally, there are also many small wind turbine models on DIY communities such as Thingiverse or Shapeways. Most of the time these designs are only concepts and the designers give no information about performance. However there is one interesting project: the Reprap wind turbine [39]. To build it, you must first purchase the construction manual, print the parts in your own 3D printer and then assemble it. It proves the possibility to create a small wind turbine 20