Pearson Boats - Common Systems > Deck Mounted Hardware

Where to mount 15W solar panel?

(1/4) > >>

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 80o 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:

--- Quote from: selene on March 22, 2012, 12:18:19 PM ---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 80o 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.
--- End quote ---

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?

Navigation

[0] Message Index

[#] Next page