Preparing for renewable marine energy
Science Centres: Energy
Preparing for renewable marine energy
Technology for New Zealand conditions
Development effort worldwide is moving wave and tidal energy from wishful thinking into a valuable contribution to energy supply.
Computer modelling and remote sensing are both vital, but they must be underpinned by in situ measurements. Bathymetric, current, and wave data are all needed to help define where it might be economic to install wave and tidal energy devices, and how to minimise environmental effects. An immediate challenge is to begin wave data collection programmes early enough so that the numbers are there in time for investment and design decisions.
NIWA is working with regional councils and others to get a wave buoy network in place to provide appropriate coverage. Such a network would have wide uses over and above supporting the development of renewable marine energy. These include safe recreational boating, understanding natural coastal processes (e.g., erosion), port operations, and planning and design of other off-shore facilities including aquaculture ventures, exploration platforms, and outfalls.
When investigating power generation using tidal current turbines, good current data is vital.
The gravitational effects of the moon and sun, which drive tides, are readily predictable. However the speed of tidal currents is sensitive to local influences such as the shape of the seafloor, water depth, and weather conditions, and is more difficult to predict.
NIWA regularly undertakes current measurements from boats or from fixed moorings (sometimes as deep as 3km). Often measuring currents at a single depth does not give the full picture. In estuaries, for example, we can have fresh river water flowing out of the estuary over the top of incoming salty (and therefore heavier) sea water. So in some situations it is important to get a profile of currents from surface to seafloor. This can be done with an acoustic Doppler current profiler (ADCP).
Recently, we used measurements to create detailed maps of currents at each phase of the tide in French Pass and Tory Channel. In this project, for Land Information New Zealand, we spent 14 hours at a stretch in a launch equipped with an ADCP traversing each area so we could measure the water flows across the entire tidal cycle. In addition, we used drifting floats equipped with GPS, microwave radar, and a fixed current meter to get as complete a picture as possible of the complex pattern of currents, whirlpools, and eddies. These are precisely the techniques that are required to assess tidal energy.