A Feasibility Study - Aaltodoc - Aalto-yliopisto

at 0,15 m³/s the load factor is still a very good 0,92, but it starts rapidly decreasing after
that. The permeate production also decreases after the nominal pump capacity of 0,15
m³/s due to the fact that a large portion of the wave resource has become too small for
the RO membranes to utilize and that power is therefore lost. The permeate production
of Site 1 is presented in Figure 42.
Permeate (m³/day)
2500
2000
1500
1000
500
0
Permeate (m³/day)
Load factor (%)
0
0 0,05 0,1 0,15 0,2 0,25 0,3
WaveRoller nominal pump capacity (m³/s)
Figure 42. Permeate production (m³/day) and load factor on Site 1.
The RO facility consists of many pressure vessels, each having seven elements. For
instance at 0,15 m³/s, there are 39 pressure vessels and in total 273 RO membranes. The
nominal output for this configuration is 6825 m³/day. Due to the variable nature of wave
power and to the fact that not all wave power states are acceptable, the nominal output
is far greater than the actual 1996 m³/day. However, the nominal output has been
determined at laboratory conditions with a pressure level of 55 bar by the Dow
Chemical Company, and therefore the results are not directly comparable.
The cost of water is presented in Figure 43. The minimum cost of water is 0,76 €/m³ and
it is reached with a nominal pump capacity of 0,12 m³/s when the load factor is 0,95.
With pump capacities smaller than this, too large portion of the wave resource is left
unutilized and thus the cost increases. When the pump capacities are greater than 0,12
m³/s, the costs of the entire system begin to increase faster than the permeate
production. Combined with the knowledge of Figure 42, that the permeate production
begins to drop after 0,15 m³/s, it is no surprise that the cost of water begins a steep rise
after the nominal pump capacity of 0,12 m³/s.
60
1,2
1
0,8
0,6
0,4
0,2
Load factor