R-Squared Energy Blog

Pure Energy

Interview with The Reef Tank

A couple of weeks ago, I was contacted by a website called The Reef Tank about doing an interview with them on Energy and The Marine World. At first I said that this was a bit outside my expertise, but they said that was OK; I could just try to answer the questions to the best of my ability. We discussed my background and my interest in energy, this blog, climate change, and energy from the oceans.

They have asked me if I would mind linking to the interview so they might reach a scientifically-minded audience that is of a somewhat different cross-section than what they might normally reach. The interview is available at the link above. Below are excerpts:

Tell me about your interest in the potential of wave and tidal power.

I became interested in the topic several years ago. I was watching a story on the Panama Canal, and watched the level of a ship fall as the water in one of the locks was pumped down. I started thinking about the energy that could be extracted as that massive ship moved to a lower level. That led me to investigate wave power, which is similar in principle to the water rising and falling in a lock. Little did I know when I started investigating that a large body of work had already taken place in this area. Looking into waves naturally caused me to happen upon tidal power as well, and the enormous potential of the flow of the Gulf Stream. [RR: See this story that I did in early 2008: Infinite Underwater Energy.]

Tell me about your interest in ocean thermal energy conversion. How does it work?

I didn’t know too much about ocean thermal energy conversion (OTEC) until I was contacted last year by Bob Cohen, who is a friend of a friend and an advocate of OTEC. [RR: See Bob’s guest post here on OTEC: Ocean Thermal Energy Conversion.] The principle is pretty straightforward. Anywhere you have temperature differentials – such as a warm ocean surface and much colder layers deep down – you can use those differentials to extract work via a heat engine. You are essentially capturing some of the heat flow from the higher temperature reservoir to the lower.

I am sitting in Amsterdam’s Schiphol Airport right now, about to fly back to the U.S. When I get home, I am going to take my first real vacation with the family in a long time. I don’t expect to post anything or answer e-mails for the next week. Please keep the discussions civil, and if trolls show up just ignore them and I will deal with them when I can. Let me also take this opportunity to thank the readers and regular posters who make this effort worthwhile.

Aloha. 🙂

May 7, 2009 Posted by | ocean currents, ocean thermal energy conversion, tidal energy, wave power | 100 Comments

Infinite Underwater Energy

I am always on the lookout for novel energy sources that don’t have obvious knockout factors. I have kept vaguely abreast of developments around tidal energy, and it always seemed like this should be a very attractive option for the energy needs of coastal communities. I was present at an alternative energy presentation last year where I heard that the primary problem is that the tides tend to tear the equipment up. It has to be able to withstand the worst conditions it could possibly see, and in the ocean that can be pretty bad.

While this is a serious problem for tidal energy, this morning I spotted a different variation of this concept. I have heard this mentioned before, but this story really goes into detail. I will provide a few excerpts, but the entire article is worth a read:

Oceans Eyed As New Energy Source

DANIA BEACH, Fla. – Just 15 miles off Florida’s coast, the world’s most powerful sustained ocean current – the mighty Gulf Stream – rushes by at nearly 8.5 billion gallons per second. And it never stops.

To scientists, it represents a tantalizing possibility: a new, plentiful and uninterrupted source of clean energy.

Florida Atlantic University researchers say the current could someday be used to drive thousands of underwater turbines, produce as much energy as perhaps 10 nuclear plants and supply one-third of Florida’s electricity. A small test turbine is expected to be installed within months.

From Oregon to Maine, Europe to Australia and beyond, researchers are looking to the sea – currents, tides and waves – for its infinite energy. So far, there are no commercial-scale projects in the U.S. delivering electricity to the grid.

Because the technology is still taking shape, it is too soon to say how much it might cost. But researchers hope to make it as cost-effective as fossil fuels. While the initial investment may be higher, the currents that drive the machinery are free.

Of course there is always an element of hype in these sorts of stories (I can be quite nit picky about the word “infinite”), and until they actually start to install these turbines, it is unclear whether there are serious knockout factors.

There are still many unknowns and risks. One fear is the “Cuisinart effect”: The spinning underwater blades could chop up fish and other creatures.

I would think that could be solved with a grid at the entrance to the turbines. That would increase pressure drop a little, but should be able to keep out the fish.

The field is growing, but there have been growing pains:

The Federal Energy Regulatory Commission has issued 47 preliminary permits for ocean, wave and tidal energy projects, said spokeswoman Celeste Miller. Most such permits grant rights just to study an area’s energy-producing potential, not to build anything.

The field has been dealt some setbacks. An ocean test last year ended in disaster when its $2 million buoy off Oregon’s coast sank to the sea floor. Similarly, a small test project using turbines powered by tidal currents in New York City’s East River ran into trouble last year after turbine blades broke.

One analysis showed that the overall potential is less than 10% of current electricity usage, but different areas are going to want to apply different solutions. Maybe ocean currents in Florida, but perhaps solar in Nevada and Arizona, and wind in Oklahoma.

Roger Bedard of the Electric Power Research Institute said an analysis by his organization found that wave- and tide-generated energy could supply only about 6.5 percent of today’s electricity needs.

I asked a colleague who has expertise in this area what he thought, and he replied:

Had not seen, but have seen similar before.


– Power density goes with v^3, may need very big kit if velocities low (the ever reliable web says 1-2 m/s for Gulf Stream whereas tidal can be somewhat higher (2.5m/s) at peaks BUT is not constant, while Gulf Stream is, hence better load factor, no need for off design point operation)

– Power is force x velocity, need lots of mooring force to restrain if velocities low – obviously you would go for high velocity areas

– Conversion of big forces going slowly to little forces going fast is pricey (x100 gearboxes are expensive) but there are good solutions around, including hydraulics and lower speed up combined with non synchronous generation (Multibrid are doing this for wind).

– Near surface, you cannot do more than about 1MW per unit without getting into blade tip cavitation, likely not a problem in Gulf Stream (just go deeper)

– None of this is impossible, just needs smart people, good engineering and time – energy payback is likely to be good (wind turbines pay back in less than one year) since electric power is the other side of the Carnot efficiency – every kWh is displacing at least 2kWh of gas, more like 3 of coal (but you knew that).

There are lots of tidal devices around – speeds tend to be a bit higher and resource is near coasts. The Gulf Stream near US seems to be the highest speed ocean current, likely a good place to start development.

It will be interesting to watch this technology develop.

February 15, 2008 Posted by | electricity, ocean currents, tidal energy, wave power | 462 Comments

Harnessing the Tides

I saw an interesting story from the Miami Herald a few days ago:

Keys man’s dream: Harnessing the tides

KEY WEST — Douglas Bedgood recently stood on a defunct Henry Flagler railroad bridge, watching as the tide forcefully moved water from the Gulf of Mexico through a channel to the Atlantic Ocean.

What he saw was untapped energy. Enough tidal power, he believes, to light and cool every residence and business in the Lower Keys.

To capture that power and convert it to electricity, Bedgood founded Florida Keys Hydro Power Research Corp. in July. The nonprofit is working to put underwater tidal turbine farms in the Keys’ channels.

“People have been talking about this for a long time: Why not use the tides?” said Bedgood, 65. “But everybody was waiting for government or somebody else to do it. So it never got done.”

I have wondered about this for a long time as well. It seems to make perfect sense, and I didn’t understand why we aren’t exploiting this to the fullest extent. Then, I recently went to a presentation on the status of tidal energy, and found that those tides and the salt water play havoc with the equipment. The generators have to be built to withstand the most powerful tide they will ever encounter, and that drives up the cost. And on top of that, the tides still tear them up.

No offense, but I did find a bit of humor in this paragraph:

Bedgood, a massage therapist who has developed aquatic therapy devices and tried to build a wind farm in California in the 1970s, said his motive is green — but not for the color of money: “I want to do my part to save the planet.”

Finally, a few of the details:

The goal: To clump enough turbines — at least 300 — to create 160 megawatts of electricity while doing virtually no damage to the channel site or its marine life, part of Florida Keys National Marine Sanctuary.

At peak usage, the Lower Keys use 140 megawatts.

The first major step is getting the test turbine, dubbed “the football” because of its shape, into Bahia Honda Channel near mile marker 36. The turbine has four 4 ½-foot long paddles on each end to capture the tides going in and out. It will be anchored on hard sea bottom where there’s scattered small corals and no sea grass, and where the water is as much as 30 feet deep so it would not interrupt navigation, Bedgood says.

“We know it will work to get power,” said project manager Steve French of Stuart-based Applied Concepts Unleashed. “The question is how much can we get and how efficiently can we get it?”

Finally, a word about costs:

While the tides are free, producing energy from them is not.

Each turbine is expected to cost about $100,000. Bedgood said it will cost millions for the cable system and substation. To date, he has provided all the financing for his end of the project, which he expects will cost about $15 million to get the first 10 turbines up and running. He’s searching for private charitable contributors.

I hope they are successful. Tidal always seemed like a great idea to me. The devil, though, usually is buried in the details.

November 16, 2007 Posted by | tidal energy | 11 Comments