I can't really explain why turbines are prices are so varied. My gut feeling is that it is a combination of several factors.
- Like any business some products have the brand name/reputation priced into the product.
- The components and the quality of build i.e. the heavier and more rugged the turbine the bigger the price.
- Research and Development costs have to be recouped.
- Warranties on blades and components etc e.g. I paid a slight bit more for solar panels that had a 10 yr warranty
I would try and be objective in the comparison. I would use the following features to guide me.
1- Diameter of blades. Bigger the diameter, the larger the wind swept area.
2 - Weight of turbine
3 - Design of turbine does it cut out at high speeds or does it continue operation.
4 - At what speed m/s was it rated at 2.5 kw.A turbine rated at 12 m/s is different to a turbine rated at 9 or 10 m/s. If turbine A is rated at 13 m/s and turbine B is rated at 9 m/s, turbine A will generate less power at 6 m/s than turbine B.
5 - A what speed does the inverter kick in and generate power i.e. does it generate power at low wind speeds?
6 - Estimated output at 3,4,5,6,7,8,9 m/s. The majority of wind at my house would fall in the 3 - 6 m/s range.
7 - Price of turbine, tower, inverter, installation and grid tie cost
8 - Warranties on blades, tower etc. Remember your turbine needs to be operational for at least 15 - 20 years.
9 - Type of tower tied or monopole
10 - How do you raise lower the tower, hydruallic/crane etc
11 - Service cost per year (approx)
12 - Customer support, is there some one who can get to your site next day to address an issue.
13 - Do you need to oil/grease the turbine on an annual basis.
14 - Do they have any data on noise
Before you buy you should go and see them in operation, and talk to the owners.
The true acid test for any turbine is to record your wind speeds for 1 year and use wind swept area calculations (which uses the diameter) to calculate the number of kw hrs the turbine would generate in 1 year. This will give you a good idea on estimated pay back period.
At the moment I would sooner buy an affordable 2.5 kw turbine than an expensive 6 kw turbine as I feel they blend better in urban/rural areas and offer a realistic pay back period. Smaller blades also mean that the bottom of the blade has a better probabilty of being taller than the nearest obstacle.