Tidal power at work

The project discussed in the article, and most tidal energy projects that I have read about, use turbines- as the article says, essentially underwater wind turbines. I did hear a talk last year about a proposed tidal energy project that would use a big flexible tube on the seafloor. The force of the tide on it compresses it, and the expelled air is used to generate electricity. If I can find a link to it, I will post it.

 

<div class='quotetop'>QUOTE(tripp @ Apr 16 2007, 11:28 AM) [snapback]424019[/snapback]</div>

Question. Is the ultimate source of tide energy the moon? Solar is obvious. Wind energy is also from the sun's affecting sea temperature/atmospheric temperature and thus weather and wind movement. But the tide is from the moon's gravitational pull, correct? RME=renewable moon energy. I like it.

 

<div class='quotetop'>QUOTE(burritos @ Apr 16 2007, 03:45 PM) [snapback]424166[/snapback]</div>

The moon contributes about twice as much to tides on earth as does the sun, The gravitational force between two bodies is given by:
F = g(m1*m2)/d^2

where g is the gravitational constant (9.8 m/sec^2), m1 and m2 are the masses of the two bodies, and d is the distance between them (which, note, is squared in the denominator). The sun has a much greater mass than the moon, but it is also much further. If you plug in the numbers, the gravitational force between the earth and moon is roughly twice that of the earth and sun.

 

<div class='quotetop'>QUOTE(larkinmj @ Apr 16 2007, 03:17 PM) [snapback]424198[/snapback]</div>

But then theoretically is this energy finite? or infinite? Assuming the sun doesn't blow up, can we expect to get free tidal energy due to the gravitational pull of the moon? I suspect this would violate some thermodynamic law.

 

Here's an article about a wave energy project in Rhode Island:

http://www.blockislandtimes.com/news/2007/...t_Page/003.html

Energy wave of the future
Program that could plummet power bills backed by state
By Pippa Jack

The state is looking to fund a $2.25- million pilot program that
would link a wave-powered turbine to the island's electrical grid,
feeding cheap, renewable power into the most expensive electrical
market in Rhode Island.

What's more, the project could become reality within as little as a
year, says Andrew C. Dzykewicz, commissioner of the Rhode Island
Office of Energy Resources.

The company that manufactures the wave-power plant is called
Oceanlinx (it changed its name in April from Energetech). In 2004,
the company announced that it would be installing a commercial plant
in the waters off Point Judith. It still plans to, but the project is
stalled awaiting permitting from the federal Energy Regulatory
Commission.

Federal permitting is quicker for smaller, pilot programs, says
Dzykewicz. Enter the idea of a small, non-commercial plant in the
wave-blown waters off Block Island, which could be permitted,
installed and generating power within a year.

"I've been working on this stuff now for about a year and a half,"
Dzykewicz says. "In the past three weeks, I've really become a
believer. This company is ready to absolutely pop, and it's something
Rhode Island can benefit from."

The wave plant could reduce power costs on the island by 15 to 18
cents per kilowatt hour, says Dzykewicz. "Block Island needs some
relief pretty badly" from high power rates, he adds. This power "only
costs about four cents to generate. It's clean, it's renewable, and
it's more than competitive, even with the electric market on the
mainland."

His mood mirrors the one upstate, where talk last week centered on a
windfarm proposal championed by the governor. This week, a Senate
bill proposing that the state create the Rhode Island Power Authority
was scheduled to go to committee late Thursday afternoon. The new,
quasi-governmental body would finance and oversee wind, wave and
hydroelectric projects, helping the state meet its goal of 15 percent
renewable power.

If created, says Dzykewicz, the power agency would be "the tool we
need to make these projects a reality, and move our state closer to
energy independence."

Earlier in the week, Dzykewicz joined representatives from Oceanlinx
on Block Island. The group traveled here Monday, April 30, for a
meeting with the island's electric utility task group.

The local group was formed several months ago to examine the energy
situation on Block Island, where electricity rates are high and the
isolated grid makes the island reliant on diesel-burning generators
and the boats that bring their fuel.

Block Island Power Company (BIPCo) is also looking at the situation.
In an agreement reached after the last increase in rates, the state
Public Utilities Commission asked the company to hire consultants to
analyze the island's present and future energy needs and find the
cheapest, most environmentally sensitive ways to meet them. The
consultants, a firm called HDR, have not yet publicly released any
findings.

When the town energy commission was formed, it was charged with
examining all the options, including a cable to the mainland and
municipal buyout of BIPCo.

This week, members had lots of questions after hearing from
Oceanlinx about their wave-power machine, which would generate enough
power for 1,000 to 1,500 homes.

Many questions remain, from where the plant would be located, to
what it would do to wave patterns around it, to how it would tie in
to the existing power infrastructure. The energy commission formed a
subcommittee to examine these issues and report back at the next
meeting, Tuesday, May 29. The commission will then forward a list of
questions to the state Office of Energy Resources.

One condition of a pilot program is that the energy be given away.
But the state may look for something in return, says Dzykewicz.
Perhaps the island could contribute into the state's renewable energy
fund, he suggests. That fund currently raises about $2.5 million a
year from a surcharge on power bills.

The Energetech machine, about 100 feet by 100 feet, focuses the
energy of waves to produce electricity. The plant's generator
resembles a funnel placed upside-down in the water. As a wave surges
into the chamber, the air is compressed and pushed upward through the
funnel, accelerating in force as the chamber narrows. A turbine
located at the top of the inverted funnel converts the rushing air's
energy into electricity, much like a turbine at a hydroelectric dam.

In a unique engineering feature, Energetech's turbine operates in
both directions. As the wave recedes, and air is sucked back into the
chamber, the turbine continues to spin and generate electricity.

The International Academy of Science recently named the Energetech
technology as one of the 10 most outstanding technologies in the
world for 2006. The company installed its first machine two years ago
at Port Kembla in Australia, and the test project has gone well.

The technology would not replace the generators BIPCo now has, says Dzykewicz.

The island "would need to have something in reserve. But this should
reduce fuel use substantially."

Wave technology, while not as proven as wind, is a more consistent
source of power because ocean swells occur year-round, Dzykewicz
says. That makes this plant a better fit for the pattern of
electricity use on Block Island than wind, which tends to be higher
in the winter and much less in the summer, when seasonal tourism
peaks.

Block Island has its own company that specializes in big wind
turbines, Lorax Energy Systems, run by Henry duPont. The company
installed a big wind turbine at Portsmouth Abbey School last summer,
the first in the state. Dzykewicz says the project has done well. But
aside from patterns of energy use, the island has another impediment
to a big wind turbine, he said; Federal Aviation Authority rules that
govern the permitting of tall structures like wind turbines near an
airport.

If the wave plant is built, says Dzykewicz, there may be unintended
consequences. Energy use now is relatively low on Block Island. "The
question becomes, when you have lower-cost power, will the draw
increase?" he asks. Many more homes and businesses could decide to
install air-conditioning, he suggests.

 

Hi All,

Tidal energy is coupled into the Earth's rotational inertia. Over time, and large exploitation of Tidal energy, the Earth will spin down until its rotational period matches the orbit period of the moon. Then there will be no Tidal energy left. That is, one month long days. Oooh, cold.....Ohh Hot..... This might take millions of years, however. Anybody know for sure ? What is the moment of inertia of a sphere, the mass of the Earth, etc....