Is there a best, cost effective deep-water offshore foundation?

Editor’s note: This article is a version of the poster presented by Andy Zalay at the 2015 AWEA Offshore Wind conference in Baltimore.

Andy Zalay, P.E., PNE Wind USA Inc

Because 60% of U.S. offshore sites are located in waters over 40-m deep, including some of the highest offshore wind resource areas, the development of practical, cost-effective deep-water foundations and wind turbines installation methods are critical to the success of the emerging U.S. offshore industry.

Success of the industry will also depend on finding the lowest cost and lowest impact design. Cost effective and practical deep-water foundations require an integrated wind turbine erection and assembly system that includes:

1) Use of existing infrastructure — no new graving docks,

2) Minimum environmental footprint –least disturbance,

3) Safety and technical merit, such as minimum, open-water construction time, and

4) Lowest levelized cost of electricity — minimum capex + O&M costs.

The challenge is to match technologies against success criteria. That is, evaluate deep water foundation solutions including high water plane floaters, spar buoys, and stee and concrete Tension Leg Platforms or TLPs.

The path forward involves comparing these several deep-water offshore foundations. One suggests TLPs are best able to meet the success factors because barge-mounted construction uses the existing infrastructure. For example, no new graving docks are required. A gravity anchor creates the least disturbance and minimal environmental footprint. A submersible barge with wing walls replaces expensive marine cranes and minimizes the time in open-water construction. Lastly, a result is the lowest levelized cost of electricity because most of the construction is done in a safe-harbor port using shore based equipment and slip formed concrete (lowest capex). A floating concrete TLP has no steel and requires minimum maintenance. Furthermore, a wind turbine can be towed back to port for major O&M (lowest O&M cost).

The contenders