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M. Majidi Nezhad et al. Sustainable Energy Technologies and Assessments 30 (2018) 68–76
model, whose power matrix was found in literature, and the scaled Table 2
device with rated powers of 500 kW and 1 MW. It follows a brief ex- WECs power performance indicators obtained.
planation of the devices studied and the baseline model used for each
Model Rated Mean Capacity Rated Hours of
case. power output factor [%] capacity operation [h/
[kW] [kW] [%] y]
Wave Star
Wave star 600 141.92 23.65 2.11 5864
The Wave Star is an attenuator device that exploit the wave energy
1000 166.02 16.6 0.0 6111
through partially submerged floats that rise and fall with the motion of
Oyster 290 56.79 19.58 0.83 5219
the waves. The floats are connected to their own hydraulic cylinder that
500 94.55 18.91 0.0 5563
power up the hydraulic motor and the generator. The system is attached 1000 109.92 10.99 0.0 5273
to a platform that stands on legs secured to the sea floor that raises the
Wave Dragon 500 220.84 44.17 21.35 8696
floats in case of excessively strong weather conditions. This converter
1000 335.82 33.58 9.73 8732
can be installed at depths of 10–20 m [51]. 5900 773.61 13.11 0.0 8188
The baseline power matrix referred to a 600 kW device [51],it
AWS 500 105.5 21.1 0.0 5500
presents its best efficiency for value of H m between 3 and 4 m and a T e 1000 79.06 7.91 0.0 5794
of 5–9 s. In this case, it has not been considered a 500 kW device, since 2400 50.25 2.1 0.0 4416
the power difference with the original device was not significant and a
more accurate analysis has been preferred. Furthermore as power ma-
trix for the 1 MW scaled device the one obtained in [50] with the same
method has been used. each considered device and thus the best matching size was found. The
scaling process significantly changed the best efficiency range of H m
Oyster and T e and consequentially varied the final performances. The device
The Oyster technology is an Oscillating Wave Surge Converter. This with the higher number of hours of operation is the Wave Dragon,
device is composed by two main components, an oscillating flap hinged precisely the 1 MW scaled device is the one with the greatest value
to the bottom of the sea and an onshore hydraulic turbine that serves as all the other converters have similar amount of operation hours.
power take-off system. The mechanical energy of the waves is used to Concerning the rated capacity, just four options have a value higher
pump water to the turbine and thus to generate electricity. It is speci- than zero and also in this case the highest value is the one of the Wave
fically designed to operate nearshore (0.5 km from the coast) at ap- Dragon. In particular, the 500 kW model reach a value of 21.35%,
proximately 10–15 m water depth [52,53]. meaning that the device output is equal or higher than 90% of the rated
The power matrix used as baseline model has a rated power of power for 1870 h/y. The scaling process changed the highest conver-
290 kW and has its best performance for waves of H m of 4–6 m and T e of sion efficiency ranges to 6.5–8.5 s for T e and for wave significant
7–10 s [4]. heights greater than 2 m, creating the best matching for the Favignana
HS. The relation between rated capacity and capacity factor is strong, in
Wave Dragon fact the devices with the best rated capacity are the ones with the
The Wave Dragon according the classification is a floating over- highest capacity factor. The best capacity factor is 44.17% for 500 kW
topping wave energy device. It consists of two reflector arms that focus Wave Dragon, while the 1 MW Wave Dragon has the second highest
the wave to a central hull behind which there is a reservoir above the value (33.58%). The third best capacity factor is 23.65% related to the
mean sea level. When the reservoir is filled over a minimum level it 600 kW Wave star.
releases the water that goes through low-head water turbine. The Wave Since the 500 kW Wave Dragon version is the best device for the
Dragon is mainly a large size device, it can be considered both as a Favignan HS, its impact on the grid was analysed.
nearshore (working at depth higher than 6 m) or as an offshore device
(depth higher than 25 m) [54,55]. The original power matrix con- WEC integration in the grid
sidered as baseline was about a 5.9 MW device.
A Wave Dragon has a very stable output and, according with its In order to analyse the impact of a WEC into the grid the current
power matrix, the maximum power output is obtained between a wide system has been simulated and used as baseline. The current system
range of H m and T e , respectively of 4.5–8 m and 4–13 s. Such a wide simulated produces 14,084.79 MWh/y versus an annual load of
range is due to the Wave Dragon operation strategy that allows to ex- 13,915.21 MWh/y. There is a small amount of excess electricity pro-
ploit energy from waves significant height and energy periods higher duced equal to 156.38 MWh/y, the 1.1% of the energy produced, it is
than the one it was designed for [56]. completely due to diesel plants management. The mean output of the
PV is 30.16 kW with a capacity factor of 17.74%. The PV penetration in
Archimedes Wave Swing (AWS) the system is equal to 1.9% with a total production of 264.19 MWh/y.
The AWS is a point absorber technology designed for different lo- The renewable fraction is very low, a value of 0.7% has been obtained.
cations, offshore and nearshore. It consists of a fully-submerged, Favignana uses 3,638,047 l/y of diesel that leads to a value of emissions
bottom-fixed structure composed by two interconnected chambers that of Carbon dioxide of 9539.78 ton/y.
are the silo and the floater that heaves due to the wave motion changes The integration of the best device in the system has been performed
of pressure [56,57]. by means of HOMER. Table 3 shows the main outcomes of the analysis.
The base analysis was performed on the power matrix provided by Compared to the baseline case, the system with the WEC produced a
the literature with a rated power of 2.4 [56] MW, the best performance higher amount of excess electricity that is equal to 360,9 MWh/y, 2.5%
for this device is registered for value of H m of 5.5–6.5 m and T e from of the overall energy production. The renewable fraction grows to a
12 s to 15 s. value of 13.1% even if the WEC penetration is equal to 13.9% of the
total, generating a high annual saving of diesel equal to 3,192,872 l/y,
Results and discussion 445,175 l/y less than the baseline case. An important carbon avoidance
of 12% is registered, for a total annual value of 8372.4 tonCO 2 /y.
WEC analysis Thus, the integration of an optimal sized battery storage has been
analysed. In order to do so, the sizes of WEC, PV and diesel generators
As shown in Table 2, the evaluation gave different responses for have been fixed, and then the storage size has been evaluated by means

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