# Solar Power and Scale Factor

Discussion in 'Boat Design' started by alan craig, Jan 25, 2017.

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### SkyakSenior Member

I love sails but in some places wind is impractical -doldrums around the equator -in the same way that solar is in other locations. A hybrid sail/solar has the best chance of practicality. Your statement that solar is useless for propulsion is flat wrong unless you assume location and configuration limits.

I don't see any big increase coming in solar density/efficiency, but storage efficiency is still improving at an impressive speed. Solar cost is already low enough that everyone needs to consider it.

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### StumbleSenior Member

Solar for house loads is a no brainer but for propulsion it is still, and will remain for the forseable future ridiculous if not physically impossible.

If you run the numbers and stop talking in generalities about what would be nice to have happen it is pretty clear. Solar radiation isn't energy dense enough, and battery storage isn't energy dense enough and likely never will be.

Just as an example, my 38' sailboat uses about 12kwh at cruising speed. A 50lb deep cycle battery with an allowable rod of 50% holds about 1.4kwh or power. So I need 12/1.4*2=17.14 batteries for an hour. To motor 24 hours, which I consider a bare minimum for a cruising boat would take 411 batteries, or 20,570lbs. Or more than my entire boat weighs.

A rectangle the size of my boat has 42m^2 of surface area, so we can approximate that as 42kwh of solar production a day.

So to recharge my batteries assuming my entire boat is covered in solar panels (and including the excess bits handing off the edge), it would take 6.86 days to recharge those batteries.

But what if I plug into shore power instead of using solar? Well 12kwh*24h=288kwh. To recharge that much usage with a standard 30amp shore power cord would take 30amp*110v=3.3kw. So 288/3.3=87 hours, or 3.6 days.

All of this assumes no effiency losses, and running at maximum capacity.

Battery technology doesn't just need to get a little better (like switching to lifepo) it needs to get an order of magnitude better. Solar doesn't need to get more efficient, it needs to get almost impossibly more efficient (say an increase to 80% from its current 20%) before it is practical.

Liquid fuels of some sort will be powering boats for a long time to come, because nothing else has the energy density to take over the job.

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### Scot McPhersonSenior Member

Stumble,
I said almost exactly this in the other solar thread...SolarMax...I forgot to mention about energy density of fuels, but I was thinking about that last night.

Fossil Fuels by density whether liquid or solid carry more energy density than any other combustion fuel. Nuclear is a denser option, it is used for producing propulsion energy for vastly large vessels like air craft carriers, but it's not likely to be released for public use anytime soon if ever. The consequences of mistakes and taking shortcuts are far too disastrous and not something I want to think about.

Gaseous fuel is an option but the energy density is so low, and the storage requirements are really tough to consider on such a grand scale as powering a large ship. Even 80 cubic foot tanks need to hold 10000psi to hold an appreciable amount of gas. I can't imagine what kind of pressure would be needed for tanks that would fuel cargo ships. You couldn't do it with a series of 80 cubic foot tanks, because they wouldn't even be able to release the gas fast enough to power the giant engines that would be needed to get the horse power out of gas.

That means we are stuck with bunker-c or sail...I just don't see any other alternatives.

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### RurudyneSenior Member

One need only look at how far LNG carriers have to go for repair when one gets damaged to realize that "large" gas under pressure is a no go.

That said, hydrogen stored in metal hydrides is indeed viable and safe. Not terribly expensive either. There are sometimes, from what I understand, legal hurdles to selling metal hydrides but owning them is perfectly legal.

Here solar power certainly can play a role in (mainly) non-commercial craft that aren't in motion for extended periods of time: you can use electricity or heat from solar to crack water to recharge your hydride tanks. This is a somewhat slow process but it would likely be an actually workable source of hydrogen as a co-combustible with liquid fuels than pie in the sky efforts to generate hydrogen from power from the alternator.

I would point out the obvious special case of your solar hydrogen plant is not being on board: you could fuel up a lake boat or day cruiser just as you might a converted car. Solar power without having a "solar boat".

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### Scot McPhersonSenior Member

Skyak,
This is what I mean by changing expectations. The age of steam changed out expectations, we could now go in a straight line (great circle straight line that is) across the ocean. If you went to sail, it would make no sense to try and sail through the doldrums and horses. You would sail closer to land to take advantage of the seabreazes and land breazes. Yes it's the longer way around, but 14kts around a circumference of a circle, it a lot faster than 1kts across the diameter.

You are assuming here that we would still have to go through the middle of the doldrums. You would simply just not do so.

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### Scot McPhersonSenior Member

rurudyne,
right? I think the pressure increase square to the diameter of the cylinder or something like that. So 10000 portable 80 cubic foot tank (roughly a 6 inch cylinder), is already under a lot of pressure. Increase that cylinder to 12 inches, and 10000 psi puts a square more pressure against the walls.

My math and formula may be way off, but the principle is right...

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### RurudyneSenior Member

This is why metal hydride is important: it is a low pressure storage system. It can achieve adequate storage densities as well, though there is a limit on how much hydrogen a given size tank will produce when the spigot is turned on so that multiple tanks plumbed together are frequently used.

As I understand it, metal hydride was pioneered when there was a need to safely store large quantities of hydrogen for the Manhattan Project and also for use in storing hydrogen in the bombs themselves once hydrogen bombs were being made ... and it is from this that lingering legal problems selling metal hydride emerge.

As for a fully charged metal hydride tank, they will neither explode nor burn vigorously ... and in that they are safer than gasoline. I dream of building a boat for the great loop and this technology is in my view, not as the principal fuel source but as a supplemental burning agent. As for the fuel, the United States is littered with deep fryers and given hydrogen co-combustion strained cooking grease not only makes an excellent diesel fuel it is darn cheap and also one that liberally lubricates engines running them (they run smoother, quieter and cooler on average). Adequate hydrogen also addresses emmissions issues. At the same time ordinary diesel can still be burned in a pinch.

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### Scot McPhersonSenior Member

Run,
I am glad you brought up biodiesel (fryer grease). Unfortunately that's not suitable for shipping either (though recreational boating, perhaps) the issue is that the nations restautants if they supplied all their waste grease each day and supplied that to a biodiesel equipped ship (not a whole lot to do really) could supply 1 mega ship with an hour, may 2 worth of fuel. That's how much those suckers burn.

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### StumbleSenior Member

I have zero experience with hydrides, but don't they require very high tempratures to release the hydrogen?

I could see something like this, or I was reading the other day about a catalized reaction that can create ethanol from eletricity and atmospheric CO2 relatively efficiently. Which would also have the energy density to move a ship, though at lower mpg (well for ships, higher GPM).

Heck hydrogen stored in hydrocarbons got us into this mess in the first place, finding a way to reverse the process and store energy as liquid hydrocarbons may be the answer eventually, and we already have a massive knowledge base about how to deal with them.

I really can envision a future where excess renewable energy is stored as hydrocarbons, then burned in a few high demand applications directly (shipping and flying) with the excess used to power the grid when renewables fall short.

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### RurudyneSenior Member

My own interest are for recreational: for a shallow draft, relatively narrow cruiser to be specific.

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### DennisRBSenior Member

https://www.av8n.com/physics/scaling.htm#sec-volume-length

You will see surface area (for panels) does not go up at the same rate as volume / displacement. Powering requirements are roughly based on displacement. That means as the vessel gets larger, each square meter of panels needs to account for more displacement. So as the ship gets twice as big, it will have exponentially less area for panels for each ton of displacement.

Therefore a feasible solar boat design will have the largest area of panels possible with the lowest possible weight. So the best performing solar boat will be something like a smallish racing sailing cat for light weight, and the wide nature of this vessel will also have the most available space for panels compared to its displacement.

Think a tornado with an awning as big as its footprint covered in solar panels. A tornado has about a 19m2 footprint. That should give about 2.8kw of power which would move a tornado at a decent pace. I guess maybe 7 knots in full sunshine including the weight of the panels and one passenger? Decent fun for sure.

Heres is something a bit bigger which appears to be a feasible energy proposition unlike many other scam solar boats.

http://soelyachts.com/soelcat12-solar-electric-catamaran/

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### Emerson WhiteJunior Member

Employing more people costs more money, not less.

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### Scot McPhersonSenior Member

Try comparing the costs of building and running a mega ship with running 10 sailing ships that can carry the same amount of cargo combined, along with teh costs of fuel and human resources, etc etc....

the lifecycle cost of the 10 sailing ships is much less.

The only reason we keep building larger and large ships is scaling of economy, which when you talk about engine powered ships makes sense (which are run for the reasons I explained that ocurred at the beginning of the age of steam). but when comparing engine powered ships to sailing ships, it's comparing apples to oranges...The costs of sailing ships are much less, but we need to change out expectations when we switch back to sail because we can't always go around a great circle anymore, and we can't push the ship faster than cruising speed by shoving a huge bow wave infront of the ship anymore by burning extra fuel to push the boat faster than we should.

The ONLY disadvantage to sail is that we have to change our expectations scheduling. That the ONLY disadvantage.

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### Emerson WhiteJunior Member

What studies have you done to determine that that is the ONLY additional cost?

The largest sail cargo ships were the windjammers. About 1/40th of the capacity of today's largest cargo ships but with a crew about 5 times as large. Assuming that modern technology lets you squeeze more labor out of each man let's say that you've got 4x the size but the same crew on the windjammers. That means you are looking at 50x the crew cost per day, but you have to keep in mind that the average cargo run will take more than way more than twice as long, so if we are generous and say twice as long you are paying 100x for crew.

So the biggest cargo ships run around 60 MW installed power, which means they run on 110 barrels of bunker oil an hour (at \$350 a barrel, a little less than \$40000 an hour) with your 12 member crew. So, the absolute best case imaginable for each hour of a current cargo vessel you have to pay \$40k/(12*99) \$33.70 per head per hour in crew costs all totalled. Does that seem like a realistic figure to you? Are you just thinking about Salary or are you thinking about benefits and compliance and HR and room and board and medical care and insurance etc?

On top of that you have to replace the rigging about once every 15 years, the sails need constant repair and frequently to be replaced. The myriad of winches and furlers and lines are going to need to be repaired and replaced. You will not be able to steer around or outrun most heavy weather so your ship is going to take a real beating. And the generator needed for the hotel load and navigational gear is going to be reproduced 20x so you'll have more maintenance costs for that than you will save by not having one large prime mover in a big cargo ship. You are also looking at spending more time in port since they have to work the cranes around the rigging. The ships are going to cost more because the decks have to handle the rig loads. High air draft means you can't go under bridges (no panama canal for you) and deep draft means that you'll lose out on some ports that are just too shallow.

The folks who run shipping companies tend to be pretty hard nosed number crunchers. The fact that even sail assist isn't being utilized while ships are burning \$40k an hour on a 12 day journey from Shenzhen to LA should suggest that there are costs there that you aren't taking into account.

Edit: It has been pointed out to me that the ships engines are not used at full tilt on a cruising speed run, so my fuel figures should be considerably lower.

Last edited: Jan 29, 2017

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### StumbleSenior Member

Not even close. The reason that ships keep getting bigger and bigger is driven entirely by economies of scale. Large ships are by far the most efficient and cheapest way to move goods around. Evengiven that they burn bunker fuel which is notoriously polluting they still generate less pollution per ton per mile than any other option.

As for moving cargo by sail... first just because sailingships don't use fuel doesn't mean they don't pollute. The energy cost of building them is immense compared to the lifetime cargo they can move, the ecological cost of making the sails is actually pretty high, and the cost would be immense.

Again using Emma Maersk, she has a Gross tonnage of 170,794 GT, compared to say Flying Cloud (a famous clipper ship) with a NRT (net registered tonnage) of 1,098. While these numbers aren't directly comparable because they measure slightly different things, they are both measures of cargo capacity and are close enough for estimates.

So you would need 156 Flying Clouds to just hold the same tonnage as EM. butthe Cliper ships were appreciably slower, meaning to move the same volume of cargo per year you will need still more. I couldn't find crossing speeds for the two, but let's assume the EM is twice as fast on average as FC. So you would need 312 clippers to equate to just one EM.

EM carries 13 crew, the average for a clipper ship FC's size was 80-100 depending on the route, but let's just use 80 to give the benefit of the doubt. So one EM carries 13 crew, and the clipper ships necessary to replace her need a crew compliment of 24,960. Labor costs just jumped 1,920 times what EM pays.

Of course we haven't discussed the port facilities or longshore requirements to unload this many vessels. And if you think traffic is bad coming out of your favorite busy port now, imagine what it will be with three hundred times more ships.

I guess we could redesign our modern cargo ships to operate with a dyna rig, but it has proven incredibly costly to sail the MF. So much so that the cost of fuel is actually far less than the cost of sailing. Bythe time you take into account sails, broken gear, and wear onthe vessel MF actually passages under power and just puts up the sails for fun.

Finally there is the issue of using cranes to unload cargo ships with massive masts in the way. No way do I want to trust a crane operator to pluck a container off my ship from a crane suspended hundreds of feet above the deck, when even a small miscalculation could see him pulling down a mast hundreds of feet tall.

If you want to make shipping more fuel efficient then the simple answer is we need bigger ships moving slower, deeper ports, and maybe something like the skysail as ancillary power. But a move back to sailing vessels isn't an answer.

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