Page 289 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

276 Fundamentals of Ocean Renewable Energy

20 s(i.e.itissaidtobe dispatchable). This is a valuable asset for any renewable
energy resource, especially when a resource is also predictable. One ocean
energy resource that could meet both of these conditions is tidal range energy. As
discussed in Section 3.14, tidal range power plants make use of an impoundment
to store potential energy. Although there will be many constraints, release of this
potential energy for conversion into electricity could be controlled. For example,
if the timing of tides on a particular day is such that electricity can only be
generated via a tidal range power plant between 03:00–06:00 (when demand
is low), this may not be as useful for the electrical grid system as electricity
that can be generated between 06:00–09:00 when a peak in demand occurs (see
Fig. 1.12). However, if the potential energy could be temporarily stored in the
impoundment and then released some time later, this would inject some much
needed flexibility into the grid, from a predictable/renewable resource that has
significant capacity potential. Another option is to pump water into the lagoon
during periods of low power demand (preferably using other renewable energy
resources) to optimize generation [4]. Tidal range power plants, therefore,
almost uniquely amongst ocean renewable energy resources, offer some degree
of flexibility/dispatchability.
An effective method that could resolve the short-timescale variability of
renewable energy sources, when supply and demand are not in phase, is energy
storage. Conventional fossil fuel-based energy systems have a major advantage
over renewables, because the power output from fossil fuel-based power plants
can be varied to meet demand, that is, they are controllable (but not necessarily
dispatchable). Therefore, energy storage technologies have not evolved at
the same pace as conventional energy technologies in the past. However, as
renewable energy systems gradually displace fossil fuel-based systems, many
energy storage solutions are emerging to help balance supply and demand.
Some of these methods include mechanical (pumped-storage, compressed air),
electrochemical (rechargeable batteries), and chemical (hydrogen storage).

10.1.2 Long Timescale Changes to the Resource
It is now accepted that global warming will lead to a future change in the
statistical distribution of weather patterns. Global warming will, therefore,
influence the future marine renewable energy resource, and this can manifest
in several ways. First, globally coordinated efforts to reduce carbon emissions,
in addition to dwindling fossil fuel reserves, will increase the proportion of
renewables in the future energy mix (e.g. see Section 1.2). Second, climate
change will, by its very definition, lead to a change in weather patterns
that will directly influence wave and offshore wind resources. Further, global
warming leads to sea-level rise, and this will alter the tidal range and tidal
stream resources; for example, by increasing mean water depth, the resonance
characteristics of ocean basins will be affected (e.g. see Section 3.5), leading
to a change in the magnitude and distribution of regions of high tidal range.