Bog'liq wave power surveillance study of the development elforskrapporter
Device development - an overview Developers
There are probably some 50 to 100 con-
cepts being actively developed, i.e. there
is company formed around the concept
and active development is taking place.
With one or two exceptions the compa-
nies sole activity is wave power develop-
ment and are small (from a few employ-
ees to the 60 or so of Pelamis and Ocean
Power Technologies).
Also with one or two exceptions the de-
velopers are struggling financially. The
main hurdle is going from basic develop-
ment and scale tests to full-scale proto-
type. This stage typically involves costs
in the SEK 50-100 million bracket with
limited possibilities of positive financial
return. Belatedly authorities have re-
cognized this and funding for prototype
development and deployment is increa-
singly available although by necessity for
a small number of devices.
Device rating and production
One reoccurring question is what kind of
rated power we can expect for full scale,
commercial wave power plants. The
answer is complex as it is dependent and
limited by a number of factors such as
wave climate vs. optimum performance,
water depth, ease of handling and eco-
nomy of scale. As a rule of the thumb
the optimum size for Atlantic open oce-
an waves will be around 1-2 MW for
most free floating devices while moving
to a less energetic wave climate, e.g. the
North Sea will result in smaller devices.
This also means that wave power con-
verters will primarily be developed for
a specific wave climate and not directly
deployable in a different wave climate.
With regard to the production of the
wave power converter the cost of pro-
duced electricity is in the end the deter-
mining factor rather than “efficiency”
or similar. However, a capacity factor
of 30-40 % (average in relation to ra-
ted power) has been generally quoted
as both necessary and feasible to make
wave power cost effective. Most wave
power devices incorporate active control
or tuning where somewhat simplified
the device adapts to height and wavel-
ength of the incoming waves in order
to maximize wave energy absorption.
This active control can mean 50 % or
more absorption and is thus crucial for
economy. However this part is probably
the least developed part of wave energy
converters and underlines the need for
full-scale prototypes.
Cost
The cost of electricity from wave power
today cannot be stated with any degree
of accuracy as life length, O&M costs
etc are not verified. Furthermore few
full-scale devices have been tested at all
and then only for shorter periods. Ho-
wever the long-term goal stated by most
developers is to be competitive with off-
shore wind power.
There are very few publicly available fi-
gures of what a wave power device costs
today. ReNews names a rumored cost of
£5 million for the Pelamis 750 kW P2
machine recently ordered from by Scot-
tish Power. However, this figure by cer-
tainty includes costs of the development
work.
Survivability
Survivability is a critical and fundamen-
tal issue. The strategies for survivability
varies from concept to concept but in
general devices will go into a protective
mode terminating generation and pas-
sively follow the waves. If possible cri-
tical components will be sheltered, e.g.
the legs of Wavestar will be lifted out
of the water or the swinging section of
Aquamarine Power’s concept Oyster bal-
lasted down to the seafloor. However, in
most cases structures have to be built to
withstand the extreme forces.
Survivability has not been proved yet to a
great extent in practice. Typically small-
scale models have been tested in tanks
successfully but mainly for single extre-
me waves, “the hundred-year wave”. But
how they withstand the pounding at full
scale in real sea and successive storms is
probably the most outstanding issue for
wave power to be tested. However, there
is obviously a reluctance to risk expen-
sive prototypes in the worst conditions
so it will be gradual process where tests
are carried out at sites with challenging
but still not the worst wave climate e.g.
EMEC before moving out to the really
rough sites.
Operation & maintenance
O&M strategies vary from concept to
concept. Pelamis for example plans to
do all maintenance in harbor and has
developed a mechanical and electric con-
nection that can be released (or recon-
nected) in short time even in fairly high
seas. Other developers plan to do main-
tenance at sea and/or to have as little
need for maintenance as possible. Lack
of real demonstrations makes it difficult
to estimate costs today. However, to get
acceptable O&M costs there will be ne-
cessary to have large farms in order to
distribute costs for workboats and per-
sonnel.
