During the winter of 1998 through the spring of 1999, I installed equipment to measure the power curve of first mini and then eventually micro wind turbines. The description of this effort and the reason for the hardware choices made is found in my year 2000 article Testing the Power Curves of Small Wind Turbines.
I elaborate below on the equipment used and the changes made recently as a result of my failed attempt to measure the performance of the Selsam Super Twin.
The equipment was chosen to meet in a simple a manner as possible international standards for testing of small wind turbines which were then being developed. Since then, testing standards for small wind turbines have become far more sophisticated and complex.
Though I have upgraded my hardware, my test apparatus won’t meet international standards in all regards.
Test Stands (Towers)
There are two test stands or towers.
Tower A is a 4.5-inch diameter 19.5 m NRG tilt-up tower. It’s dubbed “tall” tower and is suitable for mini wind turbines up to 3 m in diameter.
Tower B is a 3.5-inch 13 m NRG tilt-up tower. It is dubbed the “short tower and is suitable for micro turbines up to 1.5 m in diameter.
Both anemometers are calibrated Maximum #40.
The anemometer on Tower A was calibrated by Second Wind.
The anemometer on Tower B was calibrated by NRG.
Tower A: 17.7 m
Tower B: 9.2 m
Tower A: Originally 45.7 m of #8 AWG (3.26 mm) stranded copper (BWC 850). Subsequently this was replaced with 45.7 m of #6 AWG (4.1 mm) stranded copper.
Tower B: 60m of #4 AWG (5.2 mm) stranded copper.
The system is nominally 24 VDC. This voltage is adequate for small cabins using micro wind turbines up to mini wind turbines ~3 m in diameter. All the components worked well together with both a micro turbine (Air series) and a mini wind turbine (Whisper H40) operating at the same time. However, for larger turbines, such as Selsam’s Super Twin, it would be better to move to 48 VDC and size the components accordingly.
Four six-volt, 200 amp hour “golf cart” batteries.
Trace 175 A power panel with 60-amp DC circuit breakers.
Pulse TC 60 with internal 60-amp circuit breaker. Diversion voltage set manually at 26.6-26.7 VDC for both charge and float voltage. This conformed to the then developing international standard. The Pulse reliably held voltage constant between these values when sufficient wind was present.
In December, 2009 the Pulse TC 60 was replaced with a Tristar C60. Charge voltage was set at 27.4 VDC and float was 27.2 VDC. The voltage of the Tristar C60 can be set electronically. This has yet to be done.
The developing American testing standard for small wind turbines calls for voltage to held at 25.2 VDC with an accuracy of 5%. This would require that the voltage be held to no more than 26.5 VDC. The settings for neither the Pulse TC 60 nor the Tristar C60 would meet this requirement.
Three transducers have been used to measure DC amps, AC amps, and Watts. Each transducer uses a Hall-effect sensor that passes around the conductor in question.
DC Amps transducer: Ohio Semitronics CTA 101.
AC Amps transducer: Ohio Semitronics CTA A2135 X
Watt transducer: Ohio Semitronics PC8-002-01B with LRB 5000 Ohm resistor
From 1998 to late 2009, air pressure was determined from site elevation and station barometric pressure adjustments. I considered this adequate for my purposes as all expenses incurred were pro bono.
In late 2009, a Setra 276 barometric pressure sensor from Second Wind was installed with the Nomad 2.
Interestingly the air pressure measured by the Setra 276 during the first tests in December, 2009 nearly matched those calculated from the site’s elevation.
Temperature was derived from the internal temperature of the Nomad 1 logger and preliminary tests in late 2009 also relied on the internal temperature of the Nomad 2 logger. The internal sensor is accurate to +/- 2°C.
Through 2008, a single air heater was sufficient to act as a load for the Pulse TC 60. However in 2009 the single air heater was replaced by two 40 amp air heaters in parallel that I bought from Sierra Solar Systems (HL-75).
From 1998 to late 2009 a Second Wind Nomad 1 with RAM card and 115 VAC power supply was used. This unit was third hand by the time I received it and it worked more or less reliably until 2009. This unit used Second Wind’s Insite and Winsite software. The software is not compatible with Windows Vista 64-bit and I chose to replace it with modern hardware and software.
In December, 2009 I installed Second Wind’s Nomad 2 with Windows Vista 64-bit compatible software. This too is a used unit. The Nomad 2 is a far more sophisticated instrument designed for the commercial wind assessment industry.
Inverter (for AC instruments)
To power the signal conditioners (transducers) and the data logger a Trace DR 1524 was used.
Tri-Metric Battery System Monitor is used to visually monitor battery voltage and charging current.