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#1 cj!

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Posted 18 June 2017 - 01:02 PM

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.

 

 

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#2 cj!

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Posted 18 June 2017 - 01:05 PM

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.

 

 

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#3 cj!

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Posted 18 June 2017 - 01:20 PM

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

 

 

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#4 eruptn

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Posted 19 June 2017 - 01:16 PM

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.


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#5 Knot Me... maybe

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Posted 19 June 2017 - 02:56 PM

I've set mine up so the panels can follow the sun even when sailing. As noted above that can make a huge difference to their output each day, very huge.

 

That will have to happen manually though, we couldn't work out a decent auto tracking system for when at sea in a small boat, they wobble too much for the trackers to handle.


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#6 idlerboat

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Posted 29 June 2017 - 05:02 PM

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..


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#7 cj!

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Posted 29 June 2017 - 08:14 PM

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.

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#8 island time

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Posted 29 June 2017 - 09:30 PM

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.


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#9 cj!

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Posted 29 June 2017 - 10:04 PM

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


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#10 island time

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Posted 30 June 2017 - 09:37 AM

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.sensorso...que-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.


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