Technology
Viryd utilizes NuVinci® continuously variable planetary (CVP) technology to provide benefits that reduce the cost of energy (COE) for wind turbines. Developed by Fallbrook Technologies Inc. (www.fallbrooktech.com), NuVinci CVP technology is suitable for use in a wide variety of applications from automobiles to bicycles to wind turbines of all sizes. Viryd has an exclusive license from Fallbrook for the use of NuVinci technology in wind energy applications.
NuVinci technology for wind improves energy capture and can reduce both capital costs, and ongoing operations and maintenance. By increasing energy capture, reducing cost, and providing greater reliability, the Viryd system has the lowest (COE) of any competitive system.
Energy Capture
- The NuVinci CVP provides automatic and continuously variable ratio change that changes rotor speed as wind speed changes. This enables the rotor to maintain high efficiency at all wind speeds. If a rotor spins too fast or slow its efficiency drops. Traditional small wind turbines suffer from varying rotor speeds at each wind speed, and all of these rotor speeds except for one produces losses in efficiency. A few small wind turbines, called constant speed wind turbines, have only one rotor speed no matter what the wind speed. These turbines suffer losses in efficiency at all wind speeds except for one (design speed or design condition).
The NuVinci CVP is the only technology that can produce and maintain the ideal rotor speed for every wind speed. The result is that wind turbines equipped with the NuVinci CVP capture more energy than traditional systems.
- High winds produce too much power and can damage wind turbine drivetrains. All wind turbines face the problem of how to handle excess power destroying the generator and other components in high winds.
- Most small wind turbines employ a crude method called passive furling, which turns the rotor out of the wind when wind speeds are too high. Passive furl is unreliable because wind direction can suddenly change, hitting the rotor straight on during high winds. Small wind turbines compensate for this problem and inherently inaccurate furling by including a safety margin in their passive furl systems. The result is that small wind turbines that use passive furl actually see power production decrease in high winds.
- Another method used to control excess power in high winds is called passive stall. With this method, the rotor blades transition to stall in high winds and become inefficient. The result is that wind turbines employing passive stall also produce less power in high winds.
The NuVinci CVP can precisely slow the rotor in high winds, shedding the exact amount of power necessary to maintain peak energy production, and capture more energy from the wind.
- The unique ability of the NuVinci CVP to control rotor speed allows the use of a larger rotor than competing systems. Larger rotors exacerbate the problem of too much power entering the drivetrain from gusts and high winds. Because the NuVinci CVP can precisely control rotor speed, it can use a rotor with approximately 20% more area, resulting in nearly 20% more energy capture.
- Variable speed small wind turbines use an inefficient device called an inverter to produce grid acceptable electricity. Good inverters, which advertise efficiencies up to 96%, are actually about 86% efficient when the time spent shut down or not producing power is considered. A gust in high winds can cause an inverter to shut down to prevent damage, and typically the inverter will remain off for a programmed period of time (~ 5 minutes). A gust at low winds will cause an inverter to turn on, when the low wind speed can’t produce power. An inverter will draw power during this standby time.
The NuVinci CVP doesn’t need an inverter because it can shift with wind speed changes, allowing it to eliminate the ~ 14% losses from the inverter and capture more energy from the wind than competing systems.
Lower Capital Costs:
- Inverters are expensive. A good inverter comprises about 15% of the cost of a small wind turbine. The NuVinci CVP eliminates the need for an inverter, resulting in an approximately 15% reduction in the cost of the system.
- Most small wind turbines use expensive permanent magnet generators. These custom low speed generators can have as many as 38 poles and cost over twice as much as the induction generator that the Viryd system uses.
Maintenance & Reliability
- Viryd systems eliminate the inverter which is prone to failure from the variable and harsh conditions produced by the wind. Downtime from inverter failures is expensive, and troubleshooting the source can be difficult. Often a professional must be hired or the entire inverter needs to be replaced. If the source of failure is found, replacement parts can often have long lead times.
- Gusts produce torque spikes which can damage wind turbine drivetrains. The NuVinci CVP is a compliant device that spreads the torque spike over time. It can also accelerate the rotor to reduce the torque spike. This ability to absorb torque spikes smooths the variable effects of the wind and helps keep the Viryd system operating longer and without interruption.