
Salters Duck - atilev
http://en.wikipedia.org/wiki/Salter%27s_duck
======
dredmorbius
Total available wave energy relative to present human energy consumption is
minuscule.

Realize: wave energy is solar power twice removed. First solar heating
converted to wind energy, then wind to waves. If you can capture the initial
solar flux, you're better off. Wind is your second-best option, and where
that's locally high, the EROEI (energy returned on energy invested) is quite
high.

Marine installations are notoriously high maintenance. Water, salt, corrosion,
marine life, snagging, navigations hazards, and other factors, all play a
role. Few man-made (or natural) materials survive well, and those which do
tend not to play a big role in power generation.

Even tidal energy, with both more available power and greater concentration
than wave energy, has at best limited potential. As an example that may be
relateable to HN, the energy avaiable from daily fluctuations in the San
Francisco Bay, at the Golden Gate. In 2006, EPRI (the Electric Power Research
Institute) established that the Golden Gate has a tidal energy potential of
35.5 megawatts of total extractable average energy power (852 MWh/day, 310
GWh/year), of which 15 to 17 GWh might be practically exploitable at costs
comparable with current wind and natural gas projects.

The total tidal energy represented at the gate is 237 MW (average). Capturing
the entire amount would require blocking the Bay to any and all shipping
traffic, or installing locks or other means to allow shipping in and out of
the Bay. The total daily energy (5,688 MWh) _is still well below the 18,000
MWh consumed by San Francisco daily),_ though it is a healthy fraction at 32%.

Note that that's the power draw _of San Francisco alone_. Not the greater Bay
Area.

Yes, all that water flowing in and out of the bay daily and the "immeasurable
energy" it represents? About 1/3 of the City of San Francisco's electricity
usage.

 _Human beings use a LOT of energy._

[http://www.sfenvironment.org/article/hydro/tidal-
energy](http://www.sfenvironment.org/article/hydro/tidal-energy)
[http://oceanenergy.epri.com/attachments/streamenergy/reports...](http://oceanenergy.epri.com/attachments/streamenergy/reports/006_CA_06-10_-06.pdf)

~~~
msandford
What waves and tidal energy represent, though, is something which might be a
lot more capital efficient.

Yes you're much closer to the power source using photovoltaics but they're
only 20% or so efficient right now commercially. Further, the sun only shines
on where I live between 8 and 16 hours a day, depending on the season. The
useful average power I can expect to extract on average is about 3-4 hours per
day.

Waves, on the other hand, are an excellent store of energy and they persist
for a long time. Easily overnight and actually over many days. So if you can
reliably produce power from waves for the same capital cost per watt
installed, you might get 3x-5x the energy production from the wave plant
versus the solar plant. And that's before you take into account the storage
necessary for solar!

In other words you might be able to spend 10x on a wave power plant as a solar
plant and break even. If it only costs 2-3x as much per watt, well, you're
saving money. And the batteries (the ocean) are free.

~~~
darkmighty
Solar: purchase panel and leave it in an incline for 15 years. If you have net
metering you don't need to even think about storage.

Wave: develop massive steel structures in the ocean and transmit power to land
with low power density.

It's telling that, given the possibility to pick anywhere to develop wave
power (even at the most convenient locations) the tech has barely any
projects.

~~~
dredmorbius
At some point _someone_ has to consider storage (or alternative provisioning,
or dispatchable load) for solar-backed grid. Even if it's not the homeowner
with panels on their own roof.

~~~
alexvoda
Theoretically with solar panels you could have a round-the-clock, round-the-
globe balanced network requiring no storage. It would be a network with the
same capacity of panels on each meridian. Of course this is not very
practical.

~~~
msandford
Not only not very practical but it would require entirely new transmission
technologies: the maximum practical length of a 60Hz transmission line is only
a few thousand miles. To go from the bright side to the dark side of the earth
is worst-case 12,000 miles so new tech would be needed, or you'd just have to
suffer 30% (or more) transmission line loss.

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rndn
I like this concept in particular, because it has no mechanical parts in
contact with the water:
[https://www.youtube.com/watch?v=gcStpg3i5V8](https://www.youtube.com/watch?v=gcStpg3i5V8)

Edit: It seems however that tidal power is a more interesting research area
[1]. I still find it's a neat idea, it also makes awesome noises:
[https://www.youtube.com/watch?v=IK65S0sPtsg](https://www.youtube.com/watch?v=IK65S0sPtsg)
(loud)

[1]
[https://en.wikipedia.org/wiki/Wavegen](https://en.wikipedia.org/wiki/Wavegen)

------
wxm
A friend of mine worked with Prof. Salter. He's an incredibly brilliant, smart
and kind scientist. Unfortunately, much of his research was 'blocked' due to
someone miscalculating the cost by twice the amount, starving the research
field of funding until recently. There are quite a few related spin-outs (e.g.
Pelamis Wave, website currently down). Edinburgh also just got a huge wave
tank for more experiments ([http://www.bbc.co.uk/news/science-
environment-27702506](http://www.bbc.co.uk/news/science-
environment-27702506)).

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guelo
That's the problem with cheap oil, like we have now with fracking, it kills
all market incentive to develop clean energy. If we're ever going to get
serious about climate change we need a dynamic carbon tax that keeps the price
of fossil fuels stable and high.

If we had such a carbon tax right now, that kept gas price at the previous
price of $4/gallon, it would be a huge windfall that could be used to spend on
clean energy incentives as well as low-income energy subsidies.

~~~
mangecoeur
well no, because most renewable energy sources aim to produce electricity.
Very little electricity is generated using oil, so the oil price should have
little impact on most renewable energy production. The culprits are cheap gas
and coal - especially coal, which really should be heavily taxed because of
the huge health and environmental impacts from mining and burning coal.

~~~
dredmorbius
A few corrections.

 _Within_ the US, little electrical generation comes from oil (about TK%), but
_outside_ the US that level's rather higher -- something I only learned
recently myself when trying to rebut the statement that oil _was_ significant
in electricity generation elsewhere.

Hrm. Still not _all_ that big. 256 Mtoe per the IEA in 2012, of 6,497 MTOE,
about 4% - 6% depending on how you read net global imports / exports. (How
does the world import/export to itself?)

[http://www.iea.org/Sankey/index.html](http://www.iea.org/Sankey/index.html)

Though in many parts of the world, electricity comes from gasoline or diesel
generators on small scale rather than central generation plants.

There's also the fact that renewable energy _can_ produce liquid or gas fuels
via the Sabatier process (resulting in natural gas) or Fischer-Tropsch fuel
synthesis (liquids). These aren't used in bulk now, but could be, and
represent a possible carbon-neutral gas and liquid hydrocarbon fuel source in
future.

------
pavel_lishin
"DUCK EFFICIENCY on COMPLIANT AXIS" is a great title for a graph. It would
make for a pretty amusing piece of art.

[http://i.imgur.com/NR34IOt.jpg](http://i.imgur.com/NR34IOt.jpg)

~~~
joezydeco
Wasn't it the title of an ELP album from the 1970s?

------
jacquesm
Wave energy is one of those ideas that 100's of clever people have had
independently over the years and not a single one has been able to make it
work reliably and cost effectively.

We've seen a wide variety of prototypes, some even made it to net power out
but absolutely _nothing_ came close to winning the prize. (Though that didn't
stop the government from pumping large amounts of subsidy into some of these.)

When you compare 'wind' to 'waves' (or tides, for that matter) the environment
is even more hostile, the power transportation problem more acute and the
engineering challenges incredibly more formidable and the maintenance
headaches harder still.

Having mostly stationary waterborne structures is hard enough and commands
skills that are rare and very expensive (think oilrigs). Now change that to
dynamic structures which drive generators, add in storms, salt water and
interference with shipping and you're looking at a very expensive and complex
mixture. It will take extremely deep pockets to pull this off successfully,
with the inbuilt assumption of a number of false starts and resulting re-
engineering.

Elon Musk will likely walk on Mars (or die on impact) before we will see
widespread adoption of tidal energy for electricity generation on Earth. Which
is a pity, because it seems such a good idea.

~~~
wgx
This one is in use in Scotland:
[http://en.m.wikipedia.org/wiki/Islay_LIMPET](http://en.m.wikipedia.org/wiki/Islay_LIMPET)

~~~
jacquesm
500 KW (now derated to 250KW), it's neat but that's piddly little bits of
power for an installation that size. A single present day wind turbine will
produce up to 3 MW continuously rather than pulsed.

Pity I didn't know about it when I toured Scotland a couple of years ago
looking at their renewable energy installations.

This one was by far the most impressive:

[http://pics.camarades.com/v/jacques/trips/scotland08/dscf158...](http://pics.camarades.com/v/jacques/trips/scotland08/dscf1585.jpg.html)

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mangecoeur
[http://en.wikipedia.org/wiki/Pelamis_Wave_Energy_Converter](http://en.wikipedia.org/wiki/Pelamis_Wave_Energy_Converter)

The Pelamis, based on technology evolved from the Salters Duck at the
Edinburgh labs, was installed in pilot installations for a few years through
the company has sadly since gone bankrupt

------
deegles
I couldn't find any pictures or videos of how this works.

~~~
forgotpasswd3x
[http://www.technologystudent.com/energy1/tidal7.htm](http://www.technologystudent.com/energy1/tidal7.htm)

------
chadpaulson
Interesting overview of Edinburgh duck R&D.
[https://www.youtube.com/watch?v=_bdeNuRF-
yE](https://www.youtube.com/watch?v=_bdeNuRF-yE)

------
wiml
A lot of wave and tidal motors were built along the California coast in the
late 1800s and early 1900s. It's an interesting history. Cheap fossil power
made them uneconomical, though.

[http://bldgblog.blogspot.com/2009/05/wave-motors-of-
californ...](http://bldgblog.blogspot.com/2009/05/wave-motors-of-
california.html)

[http://www.outsidelands.org/wave-tidal.php](http://www.outsidelands.org/wave-
tidal.php)

------
Shivetya
Still never understood why they don't concentrate on using areas where
currents are well known, for Europe that would be the Straight of Gibraltar.
There is energy in the outflow from the Med into the Atlantic at the bottom
layers, surely capturing energy like that is not as difficult as surviving the
forces waves put out.

------
jfroma
I've read another article about a similar device in Brasil:

[http://m.youtube.com/watch?v=GA_UgVm9bvU](http://m.youtube.com/watch?v=GA_UgVm9bvU)

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tootie
Tidal generators are in production. There's a pilot program installing them in
NY harbor. They're fully submerged and I don't think they're ducks.

~~~
knodi123
this is not about tidal power

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platz
Does it generate DC or AC? I think there are losses if you want to transport
and connect the power generated up to the grid

~~~
jacquesm
It generates pulses of AC power, but that can be overcome by feeding those
pulses into a flywheel or superconductor based short-term storage system.

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atilev
What's more interesting is that Salter was Studying AI at the university of
Edinburgh

------
krylon
It sounds like a brilliant idea, how come these things aren't all over the
North sea?

~~~
sethrin
Because waves don't transfer that much energy. There's a reason why ships had
sails, even though winds were highly variable and waves somewhat less so.
Also, maintenance on anything you put in the ocean tends to be high.

