Open Letter to the US DOE

Scott Van Pelt

Urban Green Energy

330 W. 38th Street, Suite 1103

New York, NY 10018 USA

March 18, 2014

Mark Higgins

U.S. Department of Energy

1000 Independence Avenue SW.

Washington DC 20585


Mr. Higgins,

I am writing to you in regards to the upcoming External Merit Review Meeting to urge the US Department of Energy, Office of Energy Efficiency and Renewable Energy to continue funding research into distributed wind systems and, in particular, vertical axis wind turbines.  The staff at Urban Green Energy and our global network of over 150 distributors & partners applaud your recent work in this area.

Distributed wind turbines, including vertical axis wind turbines (VAWTs), can play a vital role in the mix of energy sources that are required to offset climate change and global warming.  This is particularly true when working to reduce or eliminate the greenhouse gas emissions of generators that are used to power onsite energy needs.  Local power generation is required for off-grid sites, locations with unstable utility grids, and micro-grids, including those that are being designed as part of urban resiliency efforts.  The generators that are used for these applications are relatively small, are often run below maximum capacity, and frequently cycle on and off.  As a result, these generators are less efficient, requiring more fossil based fuel to generate a given amount of power than their utility sized counterparts.

The existence of sites requiring local power generation is expected to grow in the future.  As mentioned above, this is partially due to efforts by New York City and multiple other municipalities to set up micro-grids to increase the resiliency of the power grid.  However, the bigger opportunity exists internationally.  Developing countries around the world, particularly in Africa and South America, are looking to local electricity generation as a primary means to electrify remote villages.  In locations such as India, where there is already a grid but an unstable one, onsite electricity generation is quickly becoming a necessity for hospitals, banks, and other locations that require 100% uptime of their power systems.

Traditionally, local power generation was provided by a either fossil fuel powered generator or a PV solar array.  The negative impact on the environment by small generators has already been discussed above and although solar panel arrays can at times produce adequate energy to power sites, they require energy storage for night time power use and for power use during cloudy days.  Energy storage is often the most expensive part of these local renewable power generating systems.  In many cases the amount of energy storage makes powering the location using solely solar financially infeasible, forcing the hand of the organization installing the electricity generator to rely on fossil fuels.

The key to bringing down the cost of the renewable energy system is to reduce the amount of energy storage that is required through the use of wind power.  There is a natural inverse relationship between wind and solar.  When the sun shines the wind is typically calm, and vice versa.  The classic example of this relationship is a stormy day but there are more subtle cases as well, including the natural seasonal and diurnal cycles, as the wind as it increases speed when the sun rises and sets, times when solar power is low. Therefore, by installing hybrid wind and solar systems, the renewable energy sources provide a more consistent flow of energy which reduces the need for energy storage.

By taking advantage of this relationship and accounting for it in the design of a local energy generating system, the designer can dramatically reduce the required amount of energy storage. This reduces the overall cost of the renewable energy system to the point that the levelized cost of energy for the renewable system is equal to or cheaper than the conventional generator.

Within the market for wind turbines that can be used for the purpose of local power generation, there are a variety of designs.  The two predominant categories are horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs).  VAWTs present certain advantages over their more conventional, horizontal axis counterparts.  VAWTs typically operate at lower revolutions per minutes (RPM) than a HAWT to produce the same amount of power.  Lower RPM results in lower noise, lower vibrations and fewer cyclical fatigue loads on bearings and other structural components which increases the operable life of the turbine.  VAWTs, in particular darrieus style turbines, are often perceived as more aesthetically pleasing.  Their simple symmetric design and performance reduces several contentious issues.  

Despite these advantages, the academic and wind turbine communities have been slow to accept the vertical axis platform.  Issues with self starting, start-up speed, overall efficiency, and others have plagued past VAWT manufacturers.  However, it has recently been shown that vertical axis wind turbines are a reliable and efficient way to produce clean energy.

On March 5th, 2014 Intertek released a test report verifying the power curve for the "VisionAIR" wind turbine manufactured by Urban Green Energy.  This testing was performed per the IEC 61400-12 test standard at the regional test center in Otisco, NY.  The test report confirms that the VisionAIR was able to self start, had a cut-in wind speed of only 3.5m/s [7mph] and an exponential power curve. Although this is a major accomplishment for the small wind community, and VAWT manufacturers in particular, more research is required to maximize efficiency of the vertical axis platform.

A major barrier to entry for VAWT manufacturers has been the current edition of the IEC 61400-2 standard.  Although the standard is essential to creating a level playing field for the various small wind manufacturers and preventing structurally unsound designs from being installed, there is a significant disparity in the cost to complete testing per this standard for HAWTs and VAWTs.  While simplified load calculations exist to confirm that the structural strength of HAWTs meet the required safety factors, no such equations exist for VAWTs.  As a result, in order to show compliance with the -2 standard, vertical axis turbines must undergo a full scale testing campaign per the IEC 61400-13 test standard.  This is at a cost of over $100,000 USD to the VAWT manufacturer, in addition to the 6-figure cost of the other necessary IEC 61400 standards.  By funding research to create simplified load calculations for common VAWT designs, a greater number of qualified wind turbines can be brought to market.  This will increase competition, drive innovation, and will ultimately boost turbine efficiency while decreasing price.

Thank you for your consideration.  Please feel free to contact me if you have any questions on any of the material presented above or would like to discuss this matter further.



Scott Van Pelt, P.E., LEED AP BD+C                                                                      

Vice President, Engineering

Urban Green Energy