Making Waves Over Tidal Energy

Tidal energy (and wave energy) offer some very good alternatives that are environmentally benign...for very limited regions of the earth. It is very unlikely that the technology is going to have an impact on the energy equation in Topeka, Kansas. tidal energy (more so than wave energy) has demonstrated its economic feasibility in a number of isolated installations. This does not mean that it is feasible as a general solution to the world energy crisis.

Offshore wind needs to address the maintenance issue before it can prove its commercial viability. My understanding is that, although there has been some recent progress, there is a long way to go. A Mean Time Between Failure of 18 months is not going to cut it in the long term.

MTBF of 18 months just doesn't work for infrastructure. I wasn't aware it was that abysmal.

Harvesting energy with site dependent solutions is not that strange. You didn't mention hydro's unsuitability in the Simpson Desert as an example of a regional limitation.....

Wave or tidal energy harvesting will go ahead wherever it is worthwhile to pursue. With so few in commercial operation it's hard to predict how well they will perform, their impact on the environment and their reliability.

Its all good. Let's build them. Let's find out.

Actually, tidal energy has been tapped for many, many years- In England, Eling Mill still functions today. There are others dating to Roman times in France and England. Moving into the more recent past, the tidal plant (generating electricity) at Rance, France, has been operating since 1966. Guess what? That predates modern solar applications (well, if you consider that solar powers the food chain, humans have been using solar for our entire history).

A question everyone should ask, considering our dependence on solar energy is, "If solar was adequate to meet our demands, why would we ever have looked for alternatives?"

Another issue: since solar energy powers most of life on earth, and since there is only a finite amount of solar energy available on earth, what impact are you having on the biosphere when you divert significant amounts of this energy for producing electricity to power modern human toys?

If you try to grow a plant that normally thrives in full sunshine, under the shade of a solar collector then, in all likelihood, it will suffer.

Fossil fuel (if it is truly fossil and not geo-chemical or abiogenic) is stored solar energy, so we have been using solar energy albeit in a concentrated form for a very long time.

As living entities we are impacting the biosphere by our very existence. What's "wrong" with that?

You are absolutely right when you assert that as living entities, we are impacting the biosphere, and I have no issue with that. It is part of life.

My primary concern, actually, is fresh water. Living in the tropics in a place where rain is more than abundant, there is a problem of reliably delivering potable water to the populace. I could go through a whole long list of political and cultural reasons as to why this happens, but I am sure there would be nothing new.

A major contributor to the situation is uncontrolled urban development, which is infringing on the natural watershed that supports the potable water supply. Part of this development involves deforestation for the purpose of building hydro-electric facilities- locally, each megawatt of electricity capacity by hydroelectric costs on the order of 5 hectares of rain forest. I would much rather see tidal energy developed (on the Pacific coast of Panama, we enjoy diurnal tides normally in excess of 5 meters).

Locally, the environmentalists are pushing for hydro and wind. Wind is worse than hydro, demanding the cutting of 50 hectares of rain forest per megawatt. Solar is a bit easier on the rain forest than wind, coming in at only 20 hectares per megawatt.

Tidal energy does not require cutting any rain forest. Preserving the fresh water supply.

Of course, we are not talking about a significant reduction of fossil fuel usage in Panama as a result- most of the petroleum products imported into Panama go to the transportation sector, not the energy sector.

There are always trade-offs. Unfortunately, many alternative-energy advocates are not completely honest about the trade-offs...

Solar thermal is lot more land efficient.....

Shore based tidal systems would gobble up a lot of shore line. 5 metres is not much of a head. I have no idea how much ocean needs to be compromised/MW for a wave energy harvesting setup.

The Panama Canal has its own artificial "tide" thing going on. Is any of the pumping energy recovered in this system?

Unfortunately, the canal operation itself is not being used to generate electricity, something else I have been trying to draw attention to. The two large lakes supplying the canal (for many years after the formation of these lakes, they held the title of largest man made lakes in the world) are used to generate electricity (although during the dry season, such usage is curtailed to insure enough waterr is available for the canal operations) as well as supplying potable waterr to much of the Panama city urban region.

With every ship transit (upwards of 30 times a day) about 55,000,000 gallons of fresh water is dumped into the ocean, dropping 80 feet to sea level. That's a whole bunch of both water and energy wasted. The canal was built back in the days when electrical generation was just getting started, so probably no one thought of adding turbines to the 20 foot diameter discharge pipes. The canal also is on of the biggest single users of electricity in the region. It would be rather easy to retro-fit some of the newer tidal turbine designs to the discharge pipes.

The problem is that the flow is not continuous. It takes something like 15 minutes to empty a chamber. Pause while the vessel passes to the next chamber. Repeat one more time. Then wait while the next ship enters the locks. I am convinced this could be overcome by using the turbines to drive hydraulic pumps feeding receivers. It is a hard sell, since most of the revenues generated by the canal are dedicated to supporting the populist government policies that are bankrupting most countries. Plus, I am pretty much invisible to the powers that be...

Has any body ever suggested the idea of an Energy Recovery System for the Panama Canal in the past or at present?

The duty cycle is something that would need to be engineered around and would make it harder to amortize the capital investment through energy re-use savings, but hey, if you don't squeak you won't get any oil...

For a lock system fed entirely from above (i.e., no pumps necessary), "energy recovery" might not be the best term. However, "energy utilization" could be worthwhile, by draining each lock compartment through a turbine. The head from compartment to compartment is not large, and the process is intermittent. It might be interesting to see how it "pencils out," though.

Your right there.

Think abut it though, that's 55,000,000 gallons a day through 20' dia pipes that must manifest as a nett cumulative quasi-constant flow somewhere in the works.

We need the as-builts.....

I bet that's peanuts for a serious hydroelectric installation, but I haven't done the arithmetic yet.

If they need that energy they'll build something to catch it. The Panama canal was a result of need after all.

On very preliminary calculations, I come up with ~1215 kw of power generation available from the Panama Canal flow (55,000,000 gpd) and head (85 ft ≈ 39.8 psid). This is equivalent to a medium-sized genset.

If they need this amount of power, building a genset system will be much cheaper than a set of low/medium head hydro turbines.

What have practical considerations got to do with these threads?

For some folks they matter; for others they don't....

Although both may be enjoyed, science fiction ≠ engineering.

That is not 55,000,000 gallons per day. That is 55,000,000 gallons per every ship that passes through the canal- on a good day, upwards of 30 ships per day. There is enough power to meet at least the demands of the canal operation itself. The issue is that the 55,000,000 gallons are dumped quickly, with a lot of dead time in between ships. Somewhere I had some preliminary calculations based on published data from the Canal Authority, but it's back in the city and I am out in the Jungle this week. If there is enough interest, I will dig the information out and post it when I get back to civilization...

Remember that the 85 feet is the total drop from the Gatun Lake to the ocean. There are a number of locks on each side of the lake and the actual drop each time is from an upper lock to the next lower lower and so on till it reaches the ocean, so if there are 5 or 6 locks on each side each drop is only 14 to 17 feet between each lock. i forget how many are on each each side.

There are three sets locks on each side. On the north side (The Caribbean side) the three sets are all together. On the South side (Pacific side) two of the sets are together, one is a bit further up. Each set consists of two locks. The ideal situation is when one ship is transiting north while another is transiting south. It doesn't always happen that way.

I think the best way to capture some of the energy (one could not capture it all, because that would slow the water transfer rate, and thus slow down transit time too much). I believe the best approach would be to drive hydraulic pumps with in-stream turbines. The pumps would charge receivers, from which one would drive hydraulic motors which drive the generators. This would tend to smooth out the power availability a bit...

It has been about 45 years since my last transit through the Canal but I do remember the parallel locks for transit in each direction. I thought that when you exited the upper of any two locks the water was released to the lower lock to raise the next vessel up. If those are 20' diameter pipes allowing the flow I would think that a tidal flow turbine like the attached link describes could be made to fit inside.

http://www.reuk.co.uk/Lunar-Energy-Tidal-Power.htm

The biggest problem would be any downtime required for the installation since it is a very busy canal. If there is any redundancy in the system like extra parallel piping then it may be feasible.

Since your local is Panama I'm assuming that you would have some access to that information. Even though each transitional head isn't much tidal turbines are designed to move and generate with only tidal action so even 15 to 20 feet of head might be sufficient. The main question again would be "Is the cost worth amount of power generated. With all the sunshine in Panama and the available real estate within the Canal Zone solar might be more practical.

The problem with solar is the fact that you have to destroy a lot of rain forest to build a sizable solar farm. Also, I just spent several days in the Jungle in a downpour. That's right- several DAYS (and nights) of downpour- constant rain, falling at about 2 inches per hour. Ther is one region of Panama (the Azuero Peninsula) where solar might be more practical, but that has been declared a World Heritage Site (although why anyone would declare a man-made desert a World Heritage Site is beyond me). It was created by clearing land for sugar cane fields, which ultimately gave way to cattle farming, which ultimately gave way to desert- even in this climate. Cutting down trees is not a good idea...

Electricity in Panama is about 60% hydro electric, with most of the rest coming from thermo-electric (using imported petroleum products). Since, for the primary urban center (Panama city-Colon), most of the hydro electric is developed from the same reservoir as the canal, there are times where the hydro electric has to be curtailed (i.e., the dry season, 3-5 months) to insure enough water is available for the canal (the city also gets most of its drinking water from the same reservoir). Meanwhile, uncontrolled urban development (if it has been more than 10 years since you have been to Panama, you would not recognize the city- the skyline resembles Miami, these days) not only results in increased demand (for both electricity and for water), it also encroaches on the water shed, meaning there is less available as time goes on. Plus, the new set of locks under construction are going to use a LOT more water than the existing canals (publicity says they are going to recover some of that water, but when one runs the numbers, it turns out to be a vanishingly small amount). NOT sustainable.

Most new energy production focuses on hydro, but they are running out of viable sites, and there is a lot of popular resistance to destroying habitat (including gun battles and forced evictions).

Something like the tidal turbine you reference is what I have been trying to push here in Panama. While the head is limited between locks, the velocity is quite high. Flow is intermittent, which creates problems. Enough energy could most likely be generated to operate the canal without impacting the infrastructure or operation of the canal that much. Mostly, the problem is political...

The key to useful harvesting of this energy source is storage. That's where the magic will be.

Unfortunately, I don't have access to the applicable historical records to determine if or what sort of energy recovery systems have been suggested for the Canal. I would be very surprised if there hadn't been a variety of proposals in the past. The major issue is that, up until about the past 10 years, it most likely wasn't economically feasible due to the fact that demand was pretty much met be existing facilities, and it is pretty hard to compete with existing hydro-electric facilities (those for which land acquisition has already been amortized).

There is growing interest in alternatives these days in Panama- unfortunately, there seems to be a lot of focus on wind, without full disclosure of the total impact. Seems there are a lot of used/refurbished wind turbines (apparently originating in the North Sea region) that are being offered at significant discount (compared to new equipment). We have to work through the "dream meets reality" cycle to get over this infatuation with wind...

I also favor the tidal and ocean wave technologies--There have been several experiments with multijointed "arms", acting on lobes , much like a cam shaft, turning geared drive shafts etc., using wave power. Since a large portion of the world's population resides within 3-40 miles of oceans (Think the US, Australia, Europe etc, ), transmission losses would be overcome using current technologies. Another Ocean based concept that was being bandied about was the Ocean Currents potential (Think Gulf Stream), using "fixed- in- place Turbines", on tether systems, like the off shore oil rigs, placed at safe depths to avoid surface interaction with shipping etc. So many POTENTIAL ways to go.