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In a previous article we explored the use of solar energy in the development of an off-grid electrical system for a sustainable campervan project. This time around, we will be exploring the use of wind power in the interest of building combined renewables to support our fast growing off-grid objectives.
This article will cover the process of assembling the Marlec Rutland Furlmatic 910-4 Windcharger and evaluate the charging potential of miniature wind turbines in the interest of generating useable power for off-grid environments. Our eventual goal will then turn to utilise wind power as part of a larger hybrid solar and wind based renewable energy system mounted to a campervan.
- Marlec Rutland FM910-4 Windcharger (790-3971)
- Marlec HRDi Charge Controller
- Deep Cycle Leisure Battery
Assembly and Test
The Rutland 910-4 Windcharger kit comes with everything we need to build our turbine but does require some assembly before we can begin to take advantage of any untapped wind power. This particular model features a three-phase generator with a low-friction slip ring that allows for efficient yield even in low wind speeds, changing wind directions and even turbulent airflow.
The Windcharger kit comes packaged with the main generator head-unit alongside six rotor blades and a nose cone. The turbine also features a mechanically furling tail fin that protects the generator by automatically turning it out of strong winds during adverse weather conditions.
For this experiment, a two-core cable has also been attached to the turbine for testing purposes and to later connect the charge regulator that will be responsible for converting any energy for storage in the leisure batteries.
The Rutland 910-4 Windcharger kit
The kit includes all the fixings required to build the turbine so assembly is simply a matter of following the instruction manual. The first step is to attach the blades to the head-unit using the self-tapping screws provided and a firm hand. Each blade is fitted using four screws, two on each side, and an interference fitting, which means the rotor is incredibly secure and safe, even at high wind speeds. The rotor hub is designed in such a way that it is impossible to insert a blade in the wrong direction thanks to small notches in each blade. The recess in the generator plastic moulding also makes it easy to tighten the screws using a long screwdriver.
Attaching the blades
The furling tail fin is designed to freely pivot between two end stops using a pair of plastic bushes attached to the end of the metal tail assembly. The fin is pitched at fifteen degrees off vertical which stops it from flapping around in lower wind speeds but is designed to push the turbine away once the wind speed rises above an aerodynamic threshold. The tail fin can be easily attached with two nyloc nuts.
Attaching the furling tail fin
The final stage of the turbine assembly is to attach the nose cone, in this case by using a short piece of scaffolding pole to mount the generator at an accessible height, while making sure to limit the movement of the blades. Additionally, we can then test the free movement of both the rotor and slip-ring to ensure there are very few friction losses that may impede our overall energy yield.
Attaching the nose cone
With the turbine now fully assembled we can use a longer piece of metal tube to mount the turbine overhead in an area of clean air-flow ready for testing. For this experiment, we will again be using an old piece of scaffolding as a temporary mount while we conduct testing, as it conveniently meets the requirements for inner and outer tube diameter as specified by Marlec. Feeding the extended power cable through the old scaffolding pole will allow us to take measurements from the wind turbine while observing it from the ground.
Full assembly mounted on a steel pole
We can observe the raw voltage output from the turbine using an oscilloscope. The trace allows us to see the rectified three-phase output from the generator, its rotational frequency and the mean voltage which is proportional to the respective wind speed. Once we have confirmed the voltage output from the turbine, we need to start converting this power into a useable format in order to charge our off-grid batteries. To do this, we will be using the Marlec HRDi charge regulator which is designed for the Furlmatic 910-4 turbine.
Marlec HRDi charge regulator
The HRDi charge regulator can accept two separate battery banks that need to be connected first in order for the device to detect the target battery voltage. Additionally, the battery sensor probe can be placed nearby to provide temperature compensation while charging. With the turbine temporarily restrained, we can then connect the output cable using the screw terminals provided, before letting it spin freely and observing the charging characteristics of the generator.
The claimed yield of the turbine
The charge regulator features an LCD screen that displays some key metrics which include the current generated from the turbine and the charge status of each battery in real-time. However, during testing, I discovered that the turbine output voltage needed to be higher than the battery voltage before any charging could occur. This meant that despite the useable voltages generated from the turbine at moderate wind speeds, the yield from the charge regulator was actually zero!
The claimed power curve of the turbine
This behaviour suggests a significant compromise in the efficiency and yield of the system, especially where the turbine is designed to start generating power at a very low cut-in windspeed. The power curve graph illustrates this further, where the turbine can be seen to start generating as soon as the windspeed rises above three meters a second, which is accurate, but the regulator may not cut in until around eight!
Moderate to higher wind speeds generate 11v with no yield from the regulator
Comparing the performance of the turbine against an equivalent photovoltaic system, a solar panel will generate small currents at a high nominal voltage even during cloudy weather, which by contrast suggests an inefficiency in the way wind power is converted to electrical potential in this case. Testing revealed that the turbine would actually start spinning even when there was no perceivable wind and would generate tens of watts confidently during a moderate breeze. It was therefore very frustrating to observe the lack of power converted into charge for the batteries, despite the otherwise excellent performance of the regulator when the turbine was exposed to strong winds.
Stronger winds cut in to produce around 20 watts
In conclusion, the Furlmatic 910-4 wind turbine is simple to use, easily assembled and has a lot of potential as an off-grid energy solution but is hindered by the need for optimal environmental and aerodynamic conditions. Ironically, the turbine itself performs exceptionally well in low-wind speeds and turbulent air, as evidenced by my testing setup. However, if the performance of the charge regulator can be used as an accurate benchmark for all miniature wind turbine applications, this inefficiency may affect their widespread feasibility as a sustainable solution for existing and future infrastructure projects.
With this in mind, I am keen to continue testing the Furlmatic Windcharger in more optimal conditions and compare its performance against any equivalent models in the interest of developing a feasible solution for my off-grid campervan project. I am particularly keen to demonstrate an intelligent blend of wind and solar power as part of a more rounded renewable system that is reactive to changing environmental conditions such as day and night running modes.
Visit the Kickstart Kamper landing page on DesignSpark