Wind Power Generation - Renewable Energy: Technology, Economics and Environment - page 337

with this system, when compared to the wind parks of large grids, is its in-
appropriateness as a buffer. Under the described conditions, grid penetration with
wind energy, or the ratio of electric power generated by wind energy to the total
energy demand within a given period, are either very low or suitable measures
need to be taken to compensate for wind energy fluctuations or to store wind
power. Furthermore, the existing power grids are often very weak when combined
with such wind-diesel systems, particularly if the wind energy converter or wind
park is to be connected to the power grid. Besides power generation regulation
difficulties (adaptation of diesel and wind turbine operation), further problems are
encountered with regard to adequate power distribution. Thus, increased wind
portions in wind-diesel systems often require grid extension or reinforcement
measures.
The described wind-diesel systems are mainly applied in developing or emerg-
ing countries. However, they can also be sensibly applied on the islands of
industrialised countries.
Wind-sea water desalination. Distillation and reverse osmosis are the two dif-
ferent processes available for sea water desalination.
For distillation, sea water is first evaporated by heat and subsequently re-
condensed in order to obtain a desalinated distillate. The remaining condensed
seawater is discarded. Most processes use the available condensation heat to pre-
heat seawater or for evaporation at a low pressure level. Thermal energy con-
sumption per m 3 of distillate amounts to between 60 and 80 kWh. Additionally,
about 3 kWh/m 3 are required for pumping.
For reverse osmosis seawater is pressed through a semi-permeable membrane
at high pressure (between 50 and 80 bar). Most of the ions dissolved in water stay
back so that a low-salt permeate of potable water quality is obtained. Also for this
process the remaining and highly condensed seawater is discarded. The energy of
the highly pressurised concentrate may be recovered by pelton turbines or pres-
sure exchangers. The energy consumption of reverse osmosis amounts to between
6 and 8 kWh/m 3 excluding energy recuperation, and to between 3 and 4 kWh/m 3
including energy recuperation. Since reverse osmosis plants have considerably
lower energy consumption when compared to distillation plants they are more
suitable for wind energy converters.
Fig. 7.25 shows the main system components of a seawater desalination plant
based on the reverse osmosis principle. First, particulate matter is removed from
sea water to protect the sensitive membranes. Subsequently, the required pressure
is built up by a high-pressure pump. Part of the seawater is pressed through the
reverse osmosis membrane (approximately 30 to 50 %), while the remainder of
the water stays back in the form of concentrate. The pressure energy contained in
the concentrate flow may subsequently be recuperated by turbines or pressure ex-
changers. Prior to distribution to customers permeate is usually chlorinated if nec-
essary pH value and water hardness are manipulated.