Listees:

I am thinking about adding two solar panels to the PH hardtop of our Marlow 70, using a controller to recharge my paralleled two house banks.  The house banks are two 8D batteries each and the system is 24VDC. The two service/house banks are put in parallel by a selection switch; but the boat does not use any combiners for charging automatically.  These house banks run all of the 24VDC, which is mostly black, grey and fresh water pumps, lights, and the stuff on the inverter (Subzero galley freezers and refrigerators, microwave, AV systems, and 110VAC plugs throughout). The amperage on this is usually showing as 3-5 total amps (at least until a hairdryer or something like that is plugged in).

So, I am wondering if a solar panel system like this will be the right size:

https://www.earthtechproducts.com/nature-power-330-watt-monocrystalline-solar-panel.html

Not sure how to size or select this sort of thing.  What we are seeking is a reasonable means to stay on the hook for a day or two without running the generator.  Assume that we are in some sort of tropical place with lots of sun and that we are not running the AC chillers or any other heavy duty loads.

Some forum discussions seem to point toward LG technology for higher temperature environments.

Do you have any idea?

Thanks.

Mike

Mike Curreri

M/V Bravo Zulu (Marlow 7018)
443.831.4138

Michael,

We installed a couple of panels 5 years ago and are very happy with them.  A
few thoughts:

1. The panels you linked to are massively overpriced!  Even with the latest
   import tariffs you should expect to pay around $1/watt, the linked panels
   should cost more like $350 each, not 4x of that.
2. Shipping can be a killer.  Almost as much as the panel cost.  If you are
   able to locate a local supplier at reasonable costs, that will help a lot.
   (We ended up using a local supplier - panel cost was about the same as
   mail-ordering panels + shipping, we picked the local suppler:  less risk of
   damage, and supporting a local company).

To your question of sizing.  It is great that you have framed the question
by defining the goal you are looking for: "What we are seeking is a
reasonable means to stay on the hook for a day or two without running the
generator."    --  allows for a bit more deterministic approach to sizing
then just 'All one can get'.  Two other key questions are:  How much is your
daily usage, and how much do you wish to rely on the batteries.

You mentioned 3-5 amps, this must be AC amps? Do you have an Amp-hour meter
installed that can tell you the typical DC daily usage?  Running from an
inverter I would think you could expect to see 60-70Ah/day (at 24v) for each
of the Sub-Zero devices, entertainment can really add up (We can use almost
as much energy via the computers in a day vs. refrigeration).  You may well
be drawing 200-300Ah in a day.

On the other side of things the Panels:  You might expect a typical
production from one panel of around 40-50Ah (24v) per panel per day.  (If
you want to get a more specific geo-data derived estimate, I have some guide
lines for how to use the NREL data website and 'convert' it for boat usage
here:
http://mvvikingstar.blogspot.com/2012/10/solar-panels-on-boat-modeling-and.h
tml    Scroll down to the part titled  "An easier way (the Shortcut)"

So, if you consume say 200Ah/day, and produce say 100Ah/day from two panels

• that leaves a deficit of 100Ah / day.  If I am reading correctly you have
  a total of 4x 8D's in your house banks, for around 500Ah -- translating into
  perhaps 200Ah usable capacity (assuming fully charged when you arrive at
  anchor, and only drawing out 40% of their capacity).

So - a quick back-of-the-napkin estimates says a couple of panels just might
allow you to be at anchor for a day or two w/o needing the generator and
using the reserves in your house battery bank.    Of course the ALL depends
on the actual usage, which if you can confirm actual usage would be best.
But worst case, you may have to do a short generator run on the 2nd day...

As to panel brand, myself I would not get too caught up in it.  One well
aimed seagull can easily take out any advantage offered by the 'best'
panels.  I would say:  If you can locate a good quality brand locally from a
retailer your feel comfortable with would be as, or more, important then
getting the 'Best of the Best' panels  - just IMHO.

As to controller:  Lee noted he directly connected his panels to his 24v
system.  It is a consideration.  A typical 60-cell (common large panel) has
optimal voltage of around 30v, so one will lose some efficiency by using a
direct connection to a 24v lead-acid battery bank vs. using a MPPT
controller, but not as much as one thinks. (please do not even think of
connecting a 60 cell panel directly to a 12v bank).  One disadvantage of the
direct connection is you will want to make sure not to leave it connected if
you have the boat in moorage / shore power  (Lee is a full time live-aboard,
and has consistent energy demands).  If you can 'remember' to do this
manually, great.  But it might be safer to look for a good reliable
controller.  And here you can make some tradeoffs:  Wire the panels in
parallel and use a good PWM controller - more cost on the wiring (Need
heaver wires) / more susceptible to shading losses, or wire them in series
and use a higher cost MPPT controller.  ++ and -- to each approach, much
depends on the exact install.  But again IMHO, I would caution most boaters
against installs w/o some type of automatic controller, unless your usage
pattern is closer to Lee's -- in which case the approach he took make a lot
of sense.  (Namely:  Take the cost of that controller and purchase another
panel or two!  You will be far ahead of the game)

As you might be able to tell, I am not satisfied with antidotal approached
to things - but with that will pass on:  Our 2x  245w panels support the
vast majority of our DC power usage from May through August, perhaps half on
the shoulder months.  (More details in the blog, under the Solar tab).  We
support a refrigerator and a separate freezer.  You units are larger than
ours, but maybe not excessively so - in the end I would say a couple of
solar panels likely would allow you to be at anchor for one day, maybe 2,
without the generator given the usage you described.

Oh, another things:  I do believe the US Fed tax credit for Solar installs
is still active.  It was written to specifically INCLUDE marine installs, so
worth checking out.

I hope this has helped - good luck, let us know what you end up doing!

-al-

Viking Star
45' Monk Sr. / McQueen
mvVikingStar.blogspot.com

Al,

Thanks for the kind words. Each of my six panels is connected to a common
distribution box whig is connected thru it out manual isolation switch in
the ER by the DC panel via 2.3 meters of "0000" battery cable that had to
be installed thru two steel bulkheads, each hole needing to be sealed to
allow the ER to be re-certified to its Lloyd's air tightness rating.

When I go away for days at a time, I disconnect shore power, and solar
keeps my batteries charged enough. Last year, went to USA for 34 days in
February and left the refrigerator, freezer, and bilge pumps on. Cam back
and battery was at 85-86% of full charge.

Lastly,I ordered my panels with diodes in the power cables. By directly
connecting each to the battery, it appears that when one panel is shaded,
it does not appear to degrade the performance of the other panels by more
than the one panel shaded.

Lastly, a 1500 watt+ controller costs A LOT of $$$$ here. I have paid for
the costs of the panels in electricity I did not have to buy from the
marinas, plus the fuel saved by not running the generator. If I did buy a
controller, I would still be behind on the investment for a few years to
com.

YMMV. Not worth the paper this is printed on……… etc etc etc

https://www.facebook.com/leezeforsale/

http://leezeforsale.com

https://whereisleeze.blogspot.com/

leezerphtrawlerforsale@gmail.com

---------- Forwarded message ----------
From: Al Thomason
Date: Wed, Apr 11, 2018 at 8:29 PM
Subject: Re: T&T: Sizing a solar panel array

…As to controller:  Lee noted he directly connected his panels to his 24v
system.  It is a consideration.  A typical 60-cell (common large panel) has
optimal voltage of around 30v, so one will lose some efficiency by using a
direct connection to a 24v lead-acid battery bank vs. using a MPPT
controller, but not as much as one thinks. (please do not even think of
connecting a 60 cell panel directly to a 12v bank).  One disadvantage of the
direct connection is you will want to make sure not to leave it connected if
you have the boat in moorage / shore power  (Lee is a full time live-aboard,
and has consistent energy demands).  If you can 'remember' to do this
manually, great.  But it might be safer to look for a good reliable
controller.  And here you can make some tradeoffs:  Wire the panels in
parallel and use a good PWM controller - more cost on the wiring (Need
heaver wires) / more susceptible to shading losses, or wire them in series
and use a higher cost MPPT controller.  ++ and -- to each approach, much
depends on the exact install.  But again IMHO, I would caution most boaters
against installs w/o some type of automatic controller, unless your usage
pattern is closer to Lee's -- in which case the approach he took make a lot
of sense.  (Namely:  Take the cost of that controller and purchase another
panel or two!  You will be far ahead of the game)