Tag Archives: Solar


Ice on the Dodger

Ice on the Dodger, Nov 2011, 37 miles S of Norfolk Va

In the Ch-ch-ch-Changes post I noted that the solar aspects of changes in latitude were moot. That is only because of our solar system design. So, with one caveat, I’ll explain.

We wouldn’t intentionally live on a solar boat through a Chesapeake winter, even as far south as Mile “0”. That said, here’s what our 2011-12 changes in latitude meant in solar terms — as I sit barefoot barely in South Carolina eating clam dip listening to boat-tailed grackles and Christmas music waiting for the next cold front to have done with us so we can move on.

HoursFirst, the hours of sunlight along our route were 2675.8  compared to 2666.3 had we stayed at Hospital Point in Norfolk the same period (~0.36% more). Clearly, the temps would have been different!

ElevationSecond, the sun’s elevation was higher as we went south, and it’s trajectory was also longer, and thus, radiance was higher on average. This delivered  the improvement shown (for solar panels, if not skin).



These latitude driven changes combine to provide about 20% additional solar energy to the panels. This doesn’t count, that over the period charted, average cloudiness along the Eastern Seaboard was 45% while in the Bahamas it was 37% (and much of the undersides of those clouds were turquoise).

So what? Well, since the solar panels are sized to exceed demand by at least a third, they recharge the batteries pretty much in three hours no matter where we are, but we really enjoy those three hours a great deal more looking at turquiose bottomed clouds rather than ice crystals on the dodger.

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La Vida Solar

Well, we’ve just completed our first three days of evaluating how solar panels have and will change our cruising life. Chose one or all of the following — delightfully, dramatically, significantly. Basically, no fossil fuel consumption was required other than the gallon or so of diesel required to get us out where the wind was. I think we are going to like this. The supply-demand picture looks Continue reading

Ice and Electrons

Yesterday, a local contractor, MTS, showed up 10 minutes early to remove our injured batteries and replace them with new ones of a better pedigree. We got a very good price by being part of a truckload order, something folks should consider around boat show time.  We found several vendors were doing this with commodity type items.

The guys were professional, polite, friendly, and competent. Together there were more than 400# of batteries going off and a bit more coming on. Generally, I like to do just about everything on the boat — not this time.  When they left, I pulled the blanket (the switch) from the solar array, changed the AH capacity setting, and the sun did its work. A lovely feeling this.

And what about the ice? It was two-three inches thick at the shore line and around a half-inch at the boat. Even though the day warmed to 43°, the toastiest high this December, when the wind blew across all that ice it was a stern reminder we need to be somewhere else.  I don’t know which is worse, snow, ice floes, or Starling and Crow poop with no spot farther than three inches from the next.

Today we have 40 knot gusts.

The Birds

Our marina is under attack! The Atlantic Flyway crosses over us.  The Starlings (an imported species) and the Crows pass through daily. What has gone through their beaks in the last few minutes/hours ends up on our deck in an altered state — a seriously unpleasant one. That’s what we find when we go to the boat this time of year. Happily, the solar panels are keeping the batteries topped, bird-graced or no. Unplugged is a good thing. [The picture is Brilliant Star as captured by the Google Maps imagery supplier on 30 Aug 2010. I went aboard at 1630, about 4 hours after the picture was made.]

A Reason to Tilt, this season at least

Fortunately, this winter is being characterized by NOAA as having a 50-50 chance of being normal. The statisticians among you will chuckle, I’m sure.

However, that only offers partial comfort.  Plenty of 50-50 winters over the last 30 have required snow removal from the boat. Now, there are three square meters of solar panels lying flat and with a job to do. So I have gone ahead and fabricated, in prototype, the tilting arms I had intended and have elevated the starboard (north) side of the panels about 12 inches.

This should provide for snow melt and drainage [read: icicles].

Insolation; Lower Latitudes

Yesterday, I closed with comments about lower latitudes.  Today, I thought I would point out the solar advantages of cruising there.

On the Winter Solstice for each degree of latitude south from here to Panama, one receives about 5% more insolation.

But aside from gross insolation increases there are some subtleties that bear consideration while thinking about adding a solar power capability to a boat.

First, we don’t cruise on the Chesapeake on the Winter Solstice. We winterize around the first week of December, but for solar purposes consider 1 November the shoulder of our season.  So, the insolation for that date becomes our baseline. Why not the equivalent insolation day in the spring?  In the spring the water is cold and our refrigeration is at its most efficient and its current draw the least. It can be a significant difference.

The graphic (hover or click) shows the Sun’s trajectory for Deale on 1 Nov and that becomes our reference.  One can see that even in Titusville on the Winter Solstice we have more insolation than the Deale reference…but the water there is a bit warmer.

For instance today we have 62º water in Deale. Titusville, 1 January ’09, had 72º water. In the BVI it was 79º and in Colon, Panama, 81º.  The air temps to match are/were 60º, 77º, 84º & 90º. So we can reasonably expect our amp-hour consumption to be higher. But how much?

With each 10º of water temperature increase from 60º our refrigeration load seems to go up by about 25% which means it would double at 90º water temps. (not that I would want to be where those are).  So we might see an additional 15 amp-hours a day in warmer cruising waters. This would require an additional hour of payback from panels producing ~7-22 amps in the bulk charge phase which typically occurs before 1200 on a clear day.

In the Mid-Chesapeake area, we are generally around -25 amp-hours in the morning and “net=zero” by 1400 on brilliant October days [our only data sample so far]. So, perhaps, we are talking abut adding an hour to reach net=zero. Doubling that for margin of error would seem reasonable. That would still put the batteries into float phase well before the sunlight tapers off.

So, are the panels going to lie flat or be tilted?

The insolation map posted yesterday noted the reference panel was tilted.  The rule of thumb for this tilt is often stated as “tilt the panel to numerically match the latitude.” But as you will notice from the graphic, the Sun’s trajectory across the sky changes shape as one moves south.  So, the rule of thumb and forefinger is:

For the winter, use 90% of latitude, and add 29º
For Deale this would mean a tilt of 65º

and for the BVI 45º.

For summer, use 90% of latitude, and subtract 23.5º
For Deale this would mean a tilt of 17º

and for the BVI -7º [which proves rules of thumb sometimes have their limits]

There are other formula for other times of year — this site is a good source. From an engineering and installation perspective and from an aesthetic one as well, 17º is not too hard to do and not too hard on the eyes. 65º is another matter.

For Titusville, I expected we would want a bit of tilt but perhaps not.  In the BVI, I have a hard time imagining 38% greater electrical consumption (The AC uses the genset or shore power.)  Having been to Colon Panama, I wouldn’t go there again, but I can easily imagine going to Grenada (-2ºN of there) where the air temps are cooler and the crime rate lower. I really can’t imagine 75% greater electrical consumption.

For one reason, we have invested  in converting the boat’s lighting, used when not under power, to LEDs (yes, “invested” — these little marvels, even from our friends in Fiji, cost mucho dinero* ).  Today, the total of our reading lights consume less than a single one did when we bought the boat. Our main loads of consequence are radar, autopilot, stereo (when playing CD’s — so I am ripping the CDs to MP3s we can play from a memory device) and refrigeration (per above).  Radar consumption will go up with the heat.  The autopilot is something of an unknown.

So, if our 405 Watt array meets our needs in Deale without tilting, it should do fine down south oriented the same way.

So why did I build the array to be tiltable?

Cloudy days and marinas.

While cloudiness reduces the impact of the Sun’s elevation by diffusing the light, there is still a brighter side of the sky.  When looking at percent cloudy days for Deale, Titusville, Key West, Tortola and St Georges, Grenada, they are 37, 13, 20, 14, “0”.  So,  (sorry, Judy C. and Joni M. ) I’ve looked at clouds from both sides now, from up and down, and still somehow, I don’t think we are likely to have to tilt the panels very often to overcome the impact of cumulus humulus.

Marinas, We all got ’em, we all want ’em. What do we do with [the solar panels while we are in] ’em? (Jimmy Buffett, Fruitcakes, 1994) Our slip in Deale faces very close to due west. This means we could tilt the panels up to port and improve output, and we well may when we move aboard.  But since I can’t sell power to the grid that tilt will be enough to meet needs only. As we move south, based on our 2008-2009 experience , we will face mostly north or south.  Here, tilting east for the three hours before solar noon or west for the three hours after could improve output.  Since the insolance is greater than Deale this may (hopefully) be unnecessary — it just is too much like dragging a sprinkler around a lawn.

Did I make the panels tiltable for no good reason?  Given I sized the array for the most I could possibly get from the real estate, time will tell.  But I am glad I have them installed the way I do and probably would have done the same had I given tilt no consideration at all. One can buy a lot of panel watts for the cost of sun-tracking panel-mounting equipment that leaves the boat looking like a TV News van.

So, Here comes the sun, here comes the sun, and I say it’s all right… (thanks George Harrison)

*Recent LED purchases from Cruising Solutions have been pleasing as well. While the Sensi-bulbs from SailorsSolutions have performed well, they aren’t all that aesthetic and they need an occasional tap-in to keep them seated in the G-4 socket. The Dr LED masthead anchor light is doing fine, but when we inspect the rig next year we will replace it and the Aqua-Signal incandescent with brighter LED products -from whom we shall see.