Efficient systems

[cj! 19]

I've been giving some thought to systems for a boat with electric propulsion and recharging it. Obviously using solar panels is a pretty common solution for charging the battery bank but as most panels seem to mounted in a fixed position they are very rarely at the optimum position for maximum output. One option would be to mount the panels that would normally be fixed to an arch on tiltable and rotatable poles instead. It may mean less total panel area but would the efficiency gains of adjusting throughout the day be worth it? Here's a couple of examples and some anecdotal evidence from the panel on Kapowai that indicates the potential.

 

 

[cj! 19]

I also came across this adjustable solar panel that has a heat exchanger behind to provide hot water while also cooling the panel thereby increasing its efficiency which is useful as a replacement for the hot water generated by IC engines.

 

 

[cj! 19]

They seem to think that by using the heat exchanger to take some heat out of the panel increases the panel output by 10%.

 

 

[eruptn 95]

I'm involved in numerous remote data collection sites (seismic, GPS etc) and we design for a min 7:1 ratio. That is if the site draws 1A, we have solar that is rated for at least 7A of output. If its a poor site (hill that is often in cloud etc we up it to 10:1).

 

Our panels are fixed and we are looking at the system going all year (we Tx continuously).

 

Only a boat in a marina with the panels orientated similar would meet the same efficiency we achieve; anything under way, at anchor etc would be less efficient. More efficiency would be gained if the boat in a marina tracked the sun.

 

Another way to look at this is a well set up system (fixed orientated set of panels) will deliver over/about 15% of its rated out put over a year (often in winter the battery voltages can get low; lots of amber lights show on the monitoring software after 7-10 days of rain).

 

Solar is a great aid, just so long as you understand its capability. I've spoken to many panel owners and they often perceive its producing the 'rated output' (or close to) while the sun shines.

[idlerboat 116]

For extended cruisers..

 

Trackers are great when on anchor....

but when sailing the sails blanket the panels.....about half the time anyway.

Other sticky uppy bits....like wind generators or even GPS can throw enough shade to effect some panels efficiency.

If you do make one, make it strong and light. 

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I agree with eruptn...a lot of people vastly over estimate the REAL output of their system. 

To get an honest appraisal you need to  try it for an extended period of time while drawing off a proper load (under a variety of conditions including being on the move)...

Dont expect it to perform the same as sitting in the marina or on a mooring compared to extended cruising.

You will probably draw more power and receive less in ...when cruising.

Dont sit there and play with the numbers to try and justify a small  system..you will just end up running the motor.

Fit the largest size of panels that you can . 

Having your fridge shut down due to low power after a few grey days is the pits..

[cj! 19]

I agree that the more panel capacity that can be fitted the better is always going to be a good starting point then it's how can it's output be maximised and how can power usage be minimised. Shadowing of the panels is an unavoidable issue but some items could be masthead mounted to reduce the effect.

[Island Time 1,220]

Like everything on a boat, thats a compromise.

Putting a 10KG  wind gen on your 15m masthead, is like putting 150kg on your deck - without allowing for wind loading. It will effect your righting moment, quite a bit, as well as AVS etc. The designer wont have allowed for this.

[cj! 19]

Yes, there is an increased load that needs consideration but your calculations in your example might need a revisit.

[Island Time 1,220]

Yes, the numbers a a bit simplified, but allowing that the deck is 1m above the centre of rotation, and the masthead is 14m above that, 15 m total. The calculations are correct, for when the mast is horizontal.

 

 

Formula is 

τ = F x r

Symbols

• τ = Torque
• F = Force
• r = Lever Arm Length

If you'd like to check, you can do it on line - see https://www.sensorsone.com/force-and-length-to-torque-calculator/  for example.

 

Not only that, but it will also effect the roll moment, and the pitching of the vessel. Designers go to considerable lengths to keep weight central for these reasons.

[Sail Rock 28]

Cj

The solar panels shown in several of the photos you provided are just supported on single unbraced poles. I doubt they would survive in high winds or seas. For offshore, I would think fixing to the deck or a robust stainless steel frame would be required. That might make a sun tracking set up a bit more complicated.

[cj! 19]

I used those as examples to illustrate the idea but there's definitely a need for proper mounting which shouldn't be insurmountable. 

[cj! 19]

IT, I think it was your wording of putting a 10kg load on top of the mast being equal to 150kg on the deck, as an additional 10kg load bearing down is still only 10kg, rather than referring to it as the increased leverage as the boat heels that caused my reply. I wonder how much of a buffer designers allow for considering all of the additional things cruisers add all over their boats? 

[Island Time 1,220]

ok, but its ALWAYS on a long lever, unless the boat is completely still - which of course it isn't.

The answer to you question is "very little"

Hence the difference between an "as designed" stability curve, and an actual or "as built" curve....

[wheels 543]

I am just adding weight to IT's comments. He is exactly right with the comments. NEVER underestimate the difference a little extra weight can do up a Mast. the higher the object, the more influence it has. And even a small increase can have a huge negative affect. And that affect is transferred right on down to the Keel. As It said, the centre point to Boat rotates around is critical. That centre point is created by the Weight in the Keel and the Mast. Changing the weight of one influences the other and also changes the centre point. But interestingly, it can have an affect either direction of a central point in inertia. ummm, let me rephrase. You can make a Boat roll more, or roll less by increasing mass. If the Mast and Keel has been designed perfectly, the roll momentum should be perfectly dampened. If not, it will roll terribly. Heel is affected by weight up the mast as well. Some racers go to great lengths to reduce that weight aloft by even removing the covers off their Halyards.
      Then there is the concern of drilling holes in the mast to fit a bracket to mount a Radome. It happens most of the time, that Radomes get fitted at a point in the mast that tends to experience the largest amount of bending stress. Drilling holes creates the " tear across dotted line" effect.