We’re out of time, which is a good thing since it forces a decision on the solar array, hence this post. What you see in these images is what we’ll be looking at from the dinghy, the view with which we are most concerned.
As you will know by now, the array is aft.
There are three issues driving the layout. First, we want it all inboard when docking or anchored in traffic. Second, headroom is required coming up the steps from the swim platform. Third, minimized shading on the panels is important for output.
When the outer panels are folded down they are inboard of the rub rail, so we have good protection. And the headroom is fine.
This is a worst case scenario for shading. The boat is aligned with the sun off the bow. By a couple of hours after sunrise or before sunset there are no shadows.
If the hull is off the sun’s axis by 25 degrees there are essentially no shadows. This is a much simpler arrangement than what we have worked through previously, with minimal aesthetic impact at anchor.
Theoretical output is roughly as follows. There are four panels with a rating of 320 watts each, so 1280 watts per hour potential output. We are assuming we can harvest 90% of this after allowing for shading and the fact these are flat rather than angled. This gives us 1150 watts net per hour. Then the question is one of how many “solar hours” we’ll be getting. This will vary from seven in the Bahamas in late spring to early summer, to maybe five in the summer in New England. So, something between 8000 and 5750 watts. To convert this to amp hours divide by your rate of charge, in our case 27.8 volts. This leaves us with between 206 amp hours and 287 amp hours (at 24 volts). We are reducing these figures by a further ten percent in our own calculations.
With our previous mode of cruising, where we were on the move a lot, the genset was rarely needed. The last two years we have been sitting more, with shorter engine runs between anchorages, and the charge cycle requires a bit of genset time. This by itself is not enough to warrant the solar array. But we are now more dependent on the genset/inverter-charger system. We have the option of charging with the engine(s) at anchor, but this is not an appealing backup. With the output of this array we can double our time sitting before a charge is needed, and could easily drop our consumption to match the solar output if required.
The second consideration is when the boat is in storage mode. We think in many cases there will be close to sufficient output to run a freezer and the dehumidifier, so that if shore power is lost for a period of time it is not a major problem.
The third, and final issue is that we think having this much power available from the sun is cool, and in many cases will eliminate the need for the genset, except for the clothes drying cycle.
Now we just need to the panels in a timely manner (they are in high demand on huge projects).
Posted by Steve Dashew (December 3, 2011)
December 3rd, 2011 at 3:32 am
Hi
Maybe I am just missing something here, but why not just mount the solar panels out of the way on the roof over the flying bridge. You might check out the Sanyo HIT Double Bifacial Photovoltaic Module panels that have crystalline cells on the front and thin-film technology on the back of the panel. Sanyo claims up to 19.1 watts/sqft and compare them to the Sunpower’s panels. The Sunpower panels required a positive ground so your MPPT controller most be able to be connected with a positive ground. Also the efficiency curve of the MPPT must be optimized to the panel’s power or a 5% or more loss can occur.
Stephen
December 4th, 2011 at 6:15 am
Thanks for the heads up Stephen:
We’ll check these comments. Re the roof, this is covered in earlier posts.
December 3rd, 2011 at 10:45 am
Just curious, why not on top of the deck roof? It seems less windage and more stability and no shadows?
I am sure you thought of this but was curious as to your reasons why not?
Thanks
December 4th, 2011 at 6:23 am
Hi Stuart:
We looked at this in detail (see earlier posts). There are shadowing problems, maintenance issues, and center of gravity concerns with the array over the flying bridge.
December 3rd, 2011 at 12:01 pm
On a new build do you see any reasonable way to put the radar ant. someplace else so a hard top over the fly bridge would make more sense? Can the radar be put to the side of the mast without confusing the issue? On your boat the down rigger / hoist booms would be an issue but if that weren’t the case? How would it work putting the radar ant. forward? How far would the ant. need to be from people if it were to sweep humans?
December 4th, 2011 at 6:26 am
Morning Daryl:
The radar does not impact the roof material as it is above it. A hard top would be significantly heavier (and more costly).
December 4th, 2011 at 11:01 am
Is it just a “transatlantic” thing, but I see you referring to ‘amp hours’ when you mean ‘amps’?
Amp hours is a perfectly good term but it does not mean watts divided by voltage, as here.
I have seen this usage before, and have wondered where it has come from.
Mike
December 4th, 2011 at 8:00 pm
Hi Mike:
There are lots of views on the amp/amp hours/ watts nomenclature. In a battery capacity context, which is our concern, amp hours at a certain voltage is a common method of expressing capacity. In other words, on the FPB 64 there is a 24V house bank with a capacity of giving you 1200 amp at a discharge rate of 10% of capacity, 0r 120 amps per hour for ten hours. Of course the batteries would then be flat. In our case we are interested in the charging potential of the solars, so we are diving the solar array output by our charging voltage (27.8VDC).
December 5th, 2011 at 12:05 pm
Ok, yes, that is how I am accustomed to using the term too. A 110 A/Hr battery could, in theory, either provide 1 amp for 110 hours or 110 amps for 1 hour, or all the permutations in between. It could not of course do this, as you say, it would be flat and ruined!
My query arose because I often see articles where people say that a bit of equipment needs 12 A/Hr or something. Even the phrase Amps per Hour is meaningless too, but common. Why they don’t just say ‘amps’ I never know.
Anyway, thanks for the clarification.
Mike
December 5th, 2011 at 12:12 pm
An irrelevant question, sorry, but why are there two holes in your swim platform? Or am I misunderstanding the illustrations above?
Mike
December 5th, 2011 at 11:40 pm
Hi Mike:
Those are hatch openings from t he construction drawings, which we didn’t bother to fill.
December 18th, 2011 at 4:21 am
Steve,
I’m planning very similar configuration 4X300Watt panels, but decided agains mounting the panels low on the aft deck, as I was concerned of the salt water spray destroying the panels over time. I decided to build an A-frame structure over my aft deck and place the panels there. I understand the downside that the weight will be about 6-7 feet higher, but on upside they will provide shade on y aft-deck. It is definitely way better to work on boat design from scratch as you do, but I have my old boat that I think will have to do on getting me around the world over the next 4-5 years. I will appreciate if you can have a look at my boat http://www.seawitch.ca and give me some recommendations with regard to my trip preparation.
Jordan
December 19th, 2011 at 10:24 pm
Hello Jordan:
We have not found salt water a problem in the past with quality panels.
December 30th, 2011 at 11:46 am
Steve, have you ever considered or evaluated gyro stabilization?
January 6th, 2012 at 12:11 am
Use the search function and you will find several comments about gyro stabilization.