Where to mount 15W solar panel?

[Dave]

Any ideas, any places that have proven to be a serious no-no?

[selene]

I'd welcome some info when you are done - I was embarking on a similar project this year.  My thought was off the back rail. This article (from an excellent site which I have used extensively) at  http://www.pbase.com/mainecruising/solar_panel  inspired me.

(DISCLAIMER: I'm no expert, so just researching right now)

Are you sure 15W will be enough for top-up (I assume)? I have 2 G27 batteries: 2x115AH = 230AH

Per Trojan: “Trojan batteries self-discharge approximately 4% per week at 80^o F”
(http://www.trojanbattery.com/Tech-Support/FAQ/Charging.aspx)

4% of 230A =  ~1.5A per day discharge = 20W (minimum) to replace each day for maintenance. 

Then factor in hours of sunlight, etc.

[Dave]

I have shore power and when we are cruising I have a EU2000. I got this panel primarily for maintainibg the batteries if I am away from the boat without shore power so they do not discharge.

[Dolce_Vita]

Are you sure 15W will be enough for top-up (I assume)? I have 2 G27 batteries: 2x115AH = 230AH

Per Trojan: “Trojan batteries self-discharge approximately 4% per week at 80^o F”
(http://www.trojanbattery.com/Tech-Support/FAQ/Charging.aspx)

4% of 230A =  ~1.5A per day discharge = 20W (minimum) to replace each day for maintenance.

Sorry, but your numbers are off.

4% of 230 Amp-Hours is 9.2 Amp-Hours per week

9.2 Amp-hours x 12 Volts = 94.4 Watt-Hours per week
 
A week is 168 hours.

So , 94.4 Watt-hours divided by 168 Hours = 0.56 Watts of self discharge rate

A 20 Watt panel would only need full sun a little over a half hour a day to make this up.

[selene]

Ed, always good to learn from you!

Out maths take different paths, but I think reach the same destination.

You did make a small typo - 9.2 Amp-hours x 12 Volts = 110.4W-hours, not 94.4W-hours.  When corrected, your result was 0.66W per hour self-discharge; mine was 1.3A per day (which I rounded to 1.5A).  Take your result, convert to mine: (0.66w*24hrs)/12v = 1.3A  per day. It's the same!  Nothing funny there!

So I think we both agree that we need to replace 1.3A - or 15.7 watt-hours per day.

For sizing, you are right, a 15W panel should be big enough - but barely.  When you take into account the 12v solar panels puts out 15-16V (even with a good MPPT you lose some of that), hours of productive sunshine (typically people use 4.5), cloudy days, poor angle in relation to the sunshine over the day, etc...as Don Casey says "A good rule of thumb is 3.5 watts per 100 amp-hours of battery capacity. But throw in an occasional sunless day, put blocking diodes in the circuit, and let the bilge pump run once in a while, and five watts will be about right. " (http://www.boatus.com/boattech/casey/30.htm).  Of course, the output also depends where the boat is kept (how much sunshine). And the P323 doesn't need a bilge pump  to run regularly

Now back to the OP - where to put the panel?

[Dolce_Vita]

For me, the back rail isn't a good mounting choice.  It's already too cluttered with the swim ladder, dinghy outboard, and grill.  I also have a tower on the aft-port corner for a wind generator.

I have a bimini, so my prime location would be on top of that.

[Dave]

I have been thinking of making some brackets that mount to the bimini frame so that it is easy to remove when I am not using the panel. It seems like the best place to get the most sunlight without anything on the boat obstructing the sun. I also fish from my boat and often have trolling lines out, so the back rail would interfere with that.

[Libations Too]

This is both an interesting and timely thread since I am planning the addition of a 15 to 30 watt panel this summer. Dave and Selene, I hope that you will continue to post status updates here...especially your decisions regarding controllers, panels, and mounting locations.

I have no Bimini so the aft rail is the most likely location for me, perhaps on the port side based on my slip orientation to the sun. I want some type of adjustable mount so that I can reposition as sailing conditions and sun angles change. I like the pbase website that Selene shared....thank you!

[selene]

Preliminary findings from various sites/discussions online...
- Most of the mounting fittings needed can be purchased from Sailrite
- Sunwize seem to be a popular panel manufacturer; about $179 for a 40W panel.
- Genesun GV-4 MPPT seems to be the most popular low-end controller ($105 for a lead/acid battery)

Preliminary estimate/budget:
- $179 for 40W panel (Wholesale Solar)
- $105 for GV-4 (Genesun)
- $126 brackets etc. (Sailrite)
- $40 misc wiring, fuses, etc
(plus shipping)

Boy, adds up fast...

[Libations Too]

Thanks for sharing!

Yes, it does add up quickly. An observation: the cost of the controller and mounting hardware seem great places to look for cost savings....or to review cost/benefit balance. Is the MPPT controller worth the premium cost? Can a lower cost mounting system be devised?

As a reference point, here is a web retailer that offers a 40 watt panel and PWM controller for $165-170 plus shipping. http://store.sundancesolar.com/40wasopa.html. Lower cost options are available if one uses flexible panels, but the warranties also suggest lower quality and/or less expected useful life.

For my application I think I might be able to live with the PWM controller...and maybe even a smaller panel. For mounting hardware I have been thinking of a couple of pieces of webbing (same UV resistant kind as used on sails) to make simple loops that wrap around my upper pushpit rail and serve as hinges. Then add some type of adjustable support bar or bracket to hold the panel at the desired angle. With these modifications I think it possible to lop off $150-200 from the cost and still get most of what I want.

[Dave]

I bought my 15w solar panel from Harbor Frieght for $70. They sell the mounting bracket that tilts for another $30 and a controller for $20. All of it is made in China. From what I have read it is all decent stuff. There is rumor that the US may put a tariff on solar panels coming from China because how inexpensive thay are producing them.

I think that would really set back the movement to use solar technology.

[selene]

Dave - I'll be interesting to see how your project goes.  Harbor Freight is always a bit of a crapshoot - sometimes you get an unbelievable bargain, sometimes not so much. I hope in your case it is the former!

Richard - good point.  I had the same question when I was thinking it through a few weeks ago, and posted it on SailNet.  Here is a useful answer I received:
For a 15 or 20 watt panel, "overkill" with a small MPPT controller might very much be the way to go. They can provide a 20% boost in effective charging power, and while $120? for the Genasun might be as much or more than your panel, how else can you get 20% more power without buying a more expensive panel? Then there are the batteries themselves, the cheap controllers tend to be "all or none" affairs that turn on or off, period. That's not optimum for the batteries. The Genasun is a 3-stage controller, assuming your batteries can be topped off by it, it will keep them nicely formed with a 100% charge.

Of course, if you're just working with one WalMart Group24 battery...warranty replacement is the most effective way to go.

Unless your solar panel is a small percent of your battery capacity, in which no controller or regulation may be needed at all. (Except a blocking diode to prevent backcurrent at night. Not all panels are built with one.)

Like you, I am not looking to recharge a long-term cruising bank, and so am torn...the Morningstar range looks good, and could save some money; I have emailed them, and will let you know what products they recommend (as a datapoint).

[Libations Too]

Thanks Selene!

I did look a bit more closely at the panel options themselves. The Sundance Solar option that I referenced appears to NOT have the simple j-box option. The result is that one ends up needing the proprietary MC4 cable connectors. In retrospect I think the SunWize panel that you initially selected may be the better of the two. I also measured my likely mounting location (port or starboard pushpit rail) and it appears that the 40 watt panel may be too large; I am now leaning toward a 30 watt panel.

I also did a little research on how to wire downstream of the controller, which adds more questions for me. Whether to wire directly through my master battery switch or directly to one of my two batteries is the question. Has anyone here researched this aspect of the installation? I think the simplest installation would go through the master switch...thus allowing me to charge either or both batteries without adding more devices. Another (more costly) option would be a panel and charge controller wired to each of my two batteries. This would double the cost, but would also double the total output. Or perhaps two 20W panels through one controller to my master switch (this option has the possible advantage of smaller, easier to mount panels with one panel on each side of the boat...but can one run two panels through the low-cost Morningstar controller?). And yet another possibility is perhaps one 20W panel, no controller, and through my master switch to both batteries...could this work?

Any thoughts or comments would be appreciated.

[selene]

Response from Morningstar.  I asked for a suggested PWM controller for my boat - hopefully representative of others too (2 G27 lead/acid, 230AH total, single bank, possible 15-40W solar panel).  Their reply:

"I would suggest either the SunSaver-6 (3rd Generation), or the ProStar-15.  These are both PWM charge controllers, and are equipped with Three-Stage Charging.  (Bulk, Absorb, Float)    The Float stage is extremely important regarding battery life. Without Float, the charge controller will continually charge the battery at the absorption voltage.  There is the potential to "cook" the batteries.  During the Float stage, 12V batteries will be held at only 13.6 volts with minimal current.  This helps to preserve battery life."

The comments about the float stage reflects other research I have seen; not all controllers have it, and as our batteries tend to be expensive, it is an important feature. The SS-6 is around $45, the PS-15 around $85.

I would also welcome input on the wiring...AFAIK, you can run two panels though the controller in series (if it is a 24V controller) or parallel (if under max ampage).

[selene]

Yeah, I'm still kicking this around.

So I came across a company called "Solbian" who make flexible solar panels (local boatyard had some flyers).  For example, they can be fitted to the top of the bimini/dodger (boom shade risk) using zippers or velcro.

It is relatively expensive - $400 for a 23"x21" 40W 8v panel - but could be mounted with less cost.  I *think* (still researching) that a Genasun MPPT controller GV5 will boost the voltage for a 12V battery ($75). Right now I have no idea as to the longevity or feasibility, but I thought I would throw it out there in case any of you have any experience or observations. (I also need to measure my dodger before I get too excited!)