Thursday, March 26, 2020

Solar, And Temperature

These cool, partly cloudy spring days provided me an opportunity to see the temperature dependence of solar panel energy generation right up close and personally.

In one particular instance, it had been cloudy for at least an hour.  There was a gentle breeze blowing and the temperature was in the high 40s.  Because of the breeze and the shade, my solar panels were cool.

Then the clouds parted and the sun came out, pretty much all at once.

551.6 watts

I know it's a little hard to read, but the blue system monitor at the lower right is showing 551.6 watts.

A few minutes later, the solar panels were still in full sun - that is, no change in energy falling on the panels.  Yet, here is the output:

Later, 532.4 watts

Yup, output has dropped to 532.4 watts as the panels heated up...  that's a drop of 3%.  That is a pretty significant drop.  You folks in the tropics should be able to get a pretty substantial increase in solar output if you can figure out some way too cool your panels...

(FWIW, the biggest reading I saw came later in the day when the sun was higher, and again just after a cloud has passed:  571 watts.  I love seeing that current meter needle buried!)


Friday, March 20, 2020

New Hatch Covers, Again

When we assumed responsibility for Eolian way back in 1997, she had covers for the hatches, but they were solid canvas, making it very dark down below - not an ideal situation for a liveaboard.  So we put some clear vinyl into the covers, first stitching it around the perimeter, and then cutting away the canvas that covered the vinyl.  In this way, the shape of the original cover was preserved.  When cutting away the opening, we left a 1/2" allowance which we folded under and stitched down with a second row of stitches.

But the best vinyl we had available to us in Seattle was not the good stuff, and it clouded over in 7 or 8 years, necessitating a replacement.  Which we did.  Again.  With the same crummy vinyl.

Now here we are again.  But this time the problem is bigger.  In addition to the failed vinyl, now the stitching is rotten and the Sunbrella has shrunken up.  But, in the intervening years, I have learned a few things.

Always 100% cloudy down below

Stitching is rotten too...
So now it is time for a full fresh start.  And this time, I am using Strataglass, the top of the line vinyl ($216 for a 54"x110" sheet, and worth every single penny of that.).  It is a three-part lamination, with fluoropolymer outer layers that prevent migration and loss of the plasticizers which make vinyl pliable (without the plasticizers, vinyl is hard...  records are made from unplasticized vinyl).  The fluoropolymer layers also greatly reduce UV degradation.

Some design work was needed...
  • What is the size of the hatch?
  • How big should the vinyl cutout be?
  • How long should the skirt be?
  • How big should the bottom hem be (it should be wide enough so the snaps pass thru at least a double layer of fabric)?
  • How big should the fold back hem at the vinyl be?
  • And finally, where should the seams be located?  This is important to limit the fabric thicknesses to be sewn thru.
I didn't want to make the cover from a big piece of fabric and then cut out the center (following the process that got us here via the original covers), because that would be a huge waste of Sunbrella.  So I cut 4 strips of fabric that satisfied the design criteria above, hemmed them, and stitched them together, making an open square.  (Note that I am using Tenara teflon thread - no polyester thread is suitable for outdoor service.  Polyester thread will last about 5 years outside in the sun; Tenara has a lifetime guarantee.)

It was a little tricky attaching the floppy open square to the vinyl - judicious use of basting tape saved the day.  As a secondary benefit, the basting tape sealed the vinyl to the fabric, making a water-resistant (waterproof?) joint between vinyl and fabric.

Now we need corners
Now to make the corners...  I used the procedure outlined in Jim Grant's book below.  Wrong side up, you place the square over the hatch and crease the corners.  Mark the end points of the creases, which should be the actual outside corners of the hatch, plus a little wiggle room.  Stitch up the corners at a 45° angle from the crease.  In the illustration below, Jim suggested cutting off the triangles; I just stitched them to the sides.

At this point I should make yet another recommendation for Sailrite.  All my canvas work supplies come from them (including my sewing machine!), and they are constantly giving back to the community with hundreds of how-to videos and tutorials.  In fact, this book was written by Jim Grant, who I assume to be part of the Sailrite operation which was created by the Grant family way back in 1969.

Ta Da!
Now to get the full advantage of the new, clear vinyl, I have to clean the plexiglass on the hatch itself - it is dirty and water stained from the rain, etc. that the failed cover let in.

Monday, February 10, 2020

Carbon Foam Batteries 

Recently a friend of mine asked me to opine on carbon foam batteries.  This is what I told him:
First, how a conventional lead acid battery works. There are two chemical reactions going on in the battery as it discharges... at the positive plates, PbO2 > PbSO4, and at the negative plate, Pb > PbSO4. (that's a very simplified version). But here's the rub... PbO2 and PbSO4 are both non-metallic powdery solids. How to keep them in contact with the plates (which, BTW are also made of Pb)? The solution which has evolved over the century or so that lead acid batteries have existed is to form the Pb plate into a kind of grid of fine Pb 'wires' supported by a Pb framework, one which will hopefully provide pockets where the solids can be kept in contact with the plate metal.

The carbon foam battery is a departure from this. In this battery, the 'plate' is actually a sheet of carbon foam. Carbon, because it is a (pretty good) conductor - perhaps even better than the Pb of conventional plates - and because (unlike the Pb plates) it is completely inert in sulphuric acid. But the primary benefit is that each of those millions of little tiny pockets in the foam serves to trap and contain the PbO2 and/or PbSO4 powders, keeping them in intimate contact with the plate.

How is this an advantage?
  • First, imagine a standard car battery - it is subjected to vibration all the time the car is moving. Vibration loosens the powders, allowing them to fall out of the Pb grid, to the bottom of the battery, where they are lost forever from participating in the charge/discharge chemistry, thereby reducing the battery's capacity. In fact, if enough falls to the bottom of the battery, it will create a shorted cell. Consequently, batteries are taller than they strictly need to be in order to give a little room at the bottom for lost reactants. Because the powder reactants in a carbon foam battery are more intimately contained and therefore less likely to be shaken loose, I would think therefore that its plates could be taller while still fitting inside the standard battery form factors, creating a slightly greater amp-hour capacity in the same form factor.
  •  Charge and discharge rates are determined by surface area of the plates. Not the gross size of the plates, but the micro surface area. Carbon foam has orders of magnitude more surface area per unit volume than even the best lead screen design of a conventional plate. Therefore, the discharge rates achievable by carbon foam batteries should be much higher (perhaps only temperature limited? I don't know).
  •  Battery capacity (amp-hours) is determined by the quantity of reactants available. The more reactants, the more capacity. I don't know how the reactant storage capacity of carbon foam compares to the capacity of the lead screen plates.  
  • Never forget that the sulphuric acid is also one of the reactants (not shown above). The acid needs to get to and circulate around the plates for the energy producing reactions to happen.  The carbon foam battery needs to make provision for sulphuric acid circulation in depth in the plates. I don't know how they address this issue. If acid flow channels have to be made in the foam, this will reduce the potential storage capacity of the plate.

So, carbon foam batteries should *potentially* have higher capacity and greater discharge rates, but whether this can be realized in practice will be dependent on the specific mechanical design of the carbon foam plates. This is an interesting technology to watch as it develops...  
Maybe someone out there with knowledge in the industry could comment?


Friday, February 7, 2020

Otter Exclusion Technology, Mk II

Well, so far, so good. I hope I'm not jinxing things by reporting this...

The Mark II version of the otter exclusion technology seems to be working.

First, one or two mothballs tucked under the lines where they are wrapped on a cleat seems to be working to discourage the otters from viewing these as their personal toilets.  This is a HUGE gain!

Our lines - see the moth balls?

The boat we share the finger pier with needs them too
...All the cleats on our finger need to be provided with moth balls if we are to discourage the otters from enjoying this finger pier.

But this seems to be the piece d' resistance... 

The first time we checked after installing these, the two big rat traps had been tripped.  No otters were apparently harmed, since there was no blood.  But those traps make plenty of noise when they go off - perhaps that was enough.

Now, a couple of weeks later, the traps and the boat are unmolested!

As I said...  So far, so good...

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