Page 320 - Alternative Energy Systems in Building Design

294 OCEAN ENERGY TECHNOLOGIES

will never be generated in a year. A value called the capacity factor C is used to
f
estimate the percentage of the maximum that actually will be generated in a year.
A capacity factor of approximately 40 percent is assumed for Scottish waters. Thus

Electricity generated per annum in kWh = 2,102,400,000 × 0.40
= 840,960,000 kWh

To calculate the number of homes this quantity of electricity will provide for in a
year, average annual household consumption is used. Average annual household con-
sumption is assumed to be 4377 kWh/year. Thus

Number of homes supplied = 840,960,000/4377 = 192,131 homes

Economics The capital required to start the construction of a barrage is quite signifi-
cant and has been the main obstacle in the deployment of the technology because it is
associated with long payback periods. In general, the advancement of the technology
always has been subsidized by government funding or by large organizations getting
involved with tidal power. However, once the construction of the barrage is complete,
there are few associated maintenance and operational costs. On average, the turbines need
replacing only once every 30 years.
The key to the economic success of tidal barrages is an optimal design that can
produce the most power with the smallest barrage possible.

Environmental concerns When constructing tidal barrages, it is important to
take into consideration environmental and ecologic effects on the local area, which
may be different for each location. The change in water level and possible flooding
could affect the vegetation around the coast, having an impact on the aquatic and
shoreline ecosystems. The quality of the water in the basin or estuary also could be
affected, and the sediment levels could change, affecting the turbidity of the water and
thus the animals that live in and depend on it, such as fish and birds. Fish undoubtedly
would be affected, unless provisions were made for them to pass through the barrages.
Not all these changes adversely affect the environment, though, because some may
result in the growth of different species of plants and animals, which may flourish in
the area where they are not normally found.
Concerns over the environmental effects of barrage tidal plants present at the
La Rance Tidal Power Station have been overcome recently by the development
of technologies that have resulted in newly designed tidal turbines (known as
tidal mills).

Social implications The building of a tidal barrage can have many social conse-
quences on the surrounding area. An example is seen at the world’s largest tidal bar-
rage, La Rance in France, which took over 5 years to construct. The barrage can be
used as a road or rail link, providing a time-saving method of crossing the bay or estuary.
The bays also could be used as recreation facilities or tourist attractions.