Solar thermal propulsion.

Since the "Solar heat boat" thread disappeared I allow myself to start a new one.
The thread is dedicated to the discussion of the practical use of solar heat as propulsion.
Inspiration is important for a good start:

 

Ok, I'll make some renders with some concepts to illustrate it

 

There are working examples of solar thermal powerplants out there so concept definately works, but I think there would be a ton of practical difficulties like keeping everything properly aligned on a boat that moves all over the place. I suppose you would have big curved mirror concentrating sunlight on small steam boiler to run mini steam turbine. The whole mirror assembly would have to be on some sort of gimbal to keep it towards the sun no matter what the boat does. I could see it quickly going mechanically complex and expensive.
Solar electric is much simpler. Panels are fit and forget.

 

Solar propulsion is necessary where there's no sail power like in total calm or islands downwind shore so in these conditions CSP solar propulsion is not a big issue just using a gimbal lense with some poles overhanging from the stern, once the course is taken the lense will keep the same angle and can be easily corrected by hand from the stern seat

No battery, no panels, no converters, no electric engine just some boiled water closed loop and a pneumatic drill thats it

 

Your approach to the problem is feasible, today I thought similarly. Except for the mirror and gimbal.

 

That's a good idea but a bit complex, he is referring to a solar heliostat and heliostat are more complex systems, a single reflective fresnel lense will do like this one



Solar heliostat could be used in more elaborated propulsion systems

And a small circular fresnel lense can be used with funnel mirrors at the sides, just like he is referring so the lense can be pretty small

 

I tried to search the internet and couldn't find any working examples of solar thermal boat. While a proof of concept model definitely would work I suppose there would be a ton of practical difficulties like for example how to integrate this huge and fragile mirror and lens contraption into a practical boat so it doesn't mess with sailing rig, doesn't create huge windage in a storm, doesn't accidentally start fire or blind someone. Small thermal engines have low efficiency so the whole mirror and lens system would have to be fairly big, much bigger than in picture above to work as an auxiliary engine for average cruising sailboat. Besides it would work only in direct sunlight. If no sun and no wind then no propulsion.

 

Yes solar thermal engines are inefficient, however Ripasso stirling engine has the record of 34% compared to 20-40% of ICE internal combustion engines which are also sort of thermal and phase change compressed air engines.

In the case of solar steam the efficiency to create steam seems going to 100% because more efficient creation of solar steam just like recent solar stills that include evaporation enhancement with sponges or carbonised fungi .

Otherwise aluminium vapor deposition panel has reflectance of 80-90% and steam engines can have an efficiency of 30% compared to solar panels 10-15% efficiency ( not to mention panel reflection and heating losses, power voltage or dc-ac conversion losses, electric engine losses, battery charging losses while a PV panel hooked directly to a trolling motor would be more efficient) so you will get more output from the same surface with solar Stirling and solar steam, just using some funneling aluminium coated panels thats all

Only a square meter usually has 1000w of solar energy which is enough for a trolling motor engine to create 2-3 knots and store when there's wind to use sails instead

And without wind or sun there are rowing poles, the same masts can be used as oars

 

Solar steam propulsion consists of:

+A CSP surface as fresnel lense and funnel reflectors

+A water heating device , just a pressure cooking pan painted in black and with some evaporation enhancer as carbonised fungi and with thermal insulation like oven furnace fabric and aluminium foil to contain infrared and thermal dissipation.

+A closed loop system well insulated to bring back exhaust steam to the heating device

+An air motor or workshop pneumatic tool as engine to move the propeller with hot compressed air

 

I still wonder how practical it would be. I looked few Stirling engine powered boat videos and they look like quite low power, maybe reaching similar speed a trolling motor would give. They used propane to heat the hot side and whole contraption was fairly big. If you added lens and mirror array to equal heating power of propane burner they used it would be several meters in size, too big for small boats used. A small catamaran like Tornado may be able to mount that because of better stability, but it would be basically propulsion system that at best rivals a trolling motor, but takes up whole boat and would massively interfere with sailing gear.

 

The thread is about converting solar heat to power at propeller.In other words how much of 1000w/m2 solar radiation can be converted into power at the propeller. It has to be a special boat, not a sailboat.

 

Yes, but irrespective of the type of boat surely one should be looking for an efficient power source? Even on our little 7' timber dinghy or the 10' poly Walker Bay, a 40lb thrust trolling motor gets the same speed as that Stirling engine which is on a much longer boat that should have much lower resistance at 3 knots than our smaller dinghies which have reached hull speed.

The trolling motor battery charges easily with the power from 200W of solar. Some people claim to have good success with just having solar panels in the dinghy to charge the battery. Solar panels are much more easily handled than large mirrors - ours just hang off the pushpit where they don't interfere with deck space or rigging at all.

 

Found on Youtube pretty cool video about 25 kw solar Stirling system from 40 years ago.


Claimed efficiency 24% which is similar to good PV panels. It seems that in an era before cheap PV panels those systems were considered for industrial scale solar power generation.

However putting that thing on boat would not be very practical. A boat big enough to carry it safely would be severely underpowered with only 25 kw. It would work fine as a tech demonstrator boat that can slowly cruise around calm lake on sunny day. Completely impractical as auxiliary propulsion for average cruising sailboat even if you could get away with only 5 - 6 m diameter system. PV panels are just so much better in boat application.

 

0:26 I thought I clicked on some other vintage video.
You are right but each example can cause some solutions. Some information can be useful. Thx for the movie.

 

Again bringing bias and fallacies, thats one stirling design between plenty of them and they haven't been researched much

Do you know a small parabolic concentrator can melt glass, metal, rock, etc? What information have you checked to claim to put a "many" meters CSP device??

And what do you want? A 500hp? A trolling motor is enough to power 3 knots even a 28 sailboat on calm water and if there's wind, the sail