Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 14-04-2013, 14:37   #1
Registered User

Join Date: May 2009
Boat: Kirié Feeling 446
Posts: 130
How much solar panel power is enough?

I plan to use solar only.

The battery bank 6 x Trojan 105 or about 660 amp.hour.

For 24 hours I use around 125 amp.hour

Planning to install 750 watts of solar panels and the boat is in the southern Caribbean with just about 12 hours a day of light year round.

On a grey day would this be enough solar?
__________________

__________________
SaltyTanned is offline   Reply With Quote
Old 14-04-2013, 14:55   #2
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: How much solar panel power is enough?

The Caribbean has an average insolation of about 5.
750 w will be more than enough.
__________________

__________________
noelex 77 is offline   Reply With Quote
Old 14-04-2013, 15:32   #3
Registered User

Join Date: Dec 2008
Location: Oriental, NC
Boat: Mainship Pilot 34
Posts: 1,429
Re: How much solar panel power is enough?

750 watts will produce 250-300 amhours on a sunny day. So your batteries should be full after one sunny day. Your house bank can easily produce 330 amphours (50% discharged) and in a pinch you can go below 50%. So you are good for 3-4 really cloudy days, which doesn't happen often in the southern Caribbean.

David
__________________
djmarchand is offline   Reply With Quote
Old 14-04-2013, 15:52   #4
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: How much solar panel power is enough?

Quote:
Originally Posted by djmarchand View Post
750 watts will produce 250-300 amhours on a sunny day. So your batteries should be full after one sunny day. Your house bank can easily produce 330 amphours (50% discharged) and in a pinch you can go below 50%. So you are good for 3-4 really cloudy days, which doesn't happen often in the southern Caribbean.

David
I have not crused the caribbean, but given the isolation values I would expect even on a cloudy day that the production from 750w would be a significant contribution to the 125AHrs (I presume at 12v) required.
It is common, and erroneous, assumption to assume the batteries are required to provide all the power on cloudy days. The reality is solar will still produce some power even on very bad days. With a large solar array and modest demands (like the OP has) the number of cloudy days before the batteries reach 50% is much longer than a simple calculation, assuming zero production, would indicate.

The OP shoud manage much longer than 3-4 really cloudy days before reaching 50%.
__________________
noelex 77 is offline   Reply With Quote
Old 14-04-2013, 16:25   #5
Registered User

Join Date: May 2009
Boat: Kirié Feeling 446
Posts: 130
Re: How much solar panel power is enough?

Thanks for the quick and complete replies. I am reassured and promise to give the results by next winter.
__________________
SaltyTanned is offline   Reply With Quote
Old 14-04-2013, 16:32   #6
Registered User

Join Date: Oct 2011
Location: Winter Bahamas - Summer BC
Boat: Lagoon 450, Bavaria Vision 40
Posts: 615
Re: How much solar panel power is enough?

You would need a really dark cloudy day to not get 100Ahs. I would say you still get at least 150Ah on an overcast day.
__________________
roetter is offline   Reply With Quote
Old 14-04-2013, 20:57   #7
Registered User
 
S/V Alchemy's Avatar

Join Date: May 2008
Location: Toronto
Boat: Custom 41' Steel Pilothouse Cutter
Posts: 4,575
Re: How much solar panel power is enough?

Quote:
Originally Posted by SaltyTanned View Post
I plan to use solar only.

The battery bank 6 x Trojan 105 or about 660 amp.hour.

For 24 hours I use around 125 amp.hour

Planning to install 750 watts of solar panels and the boat is in the southern Caribbean with just about 12 hours a day of light year round.

On a grey day would this be enough solar?
No, but on the bright days before and after, you should be able to bank enough.

Keep in mind two factors: The usable band of battery power is about 30%: from 50% state of charge (SOG) to 80%. You need to have some extra bits to throw charge into a battery bank after 80% or so, and I would think it's worth it, if you have only solar as a charge source.

The second factor is draw-down. If you have a fixed draw, like a fridge, an investment in LED lights, foot pumps for water, extra insulation for the fridge and maybe a nice big alternator if you need to pump out 12 NM out and want to take the battery bank to 95%-100% or so have to be part of the plan. In the end run, you will save on NOT having a genset or burning more diesel, and you will have a quiet life in a quiet boat. But you have to make it easier on your batteries by accepting that 750Ah means about 225 Ah of actually usable power, and that you will be cycling often enough to want to clap on an equalization charge (which may be possible with the solar, maybe not) and will want hydrocaps and temperature sensors and SG readings and other care and feeding aspects in order to get a good five or six years out of your T-105s.

So the question is not just "how much solar" but "how much use and how much capacity and how much monitoring determine how much solar?".

I have gone with four 135W panels, a 400W wind turbine, two 90 amp alternators and two Honda 2000s to keep about an 1,100 Ah bank happy and echo-charging a 12 V starter battery and an 12 V windlass battery. Normally, I expect the wind and sun to cover the estimated 125Ah/daily drawdown, but the alts are there to cover the spread, and if I am running a power tool, it's simple to keep the Honda going at anchor for two or three hours to pump in enough electrons to have a "movie night" or even to run the A/C or hot water heater.
__________________
Can't sleep? Read www.alchemy2009.blogspot.com for fast relief. Can't read? Avoid www.volumesofsalt.blogspot.com, because it's just personal reviews of sea books.
S/V Alchemy is offline   Reply With Quote
Old 14-04-2013, 21:14   #8
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,033
Re: How much solar panel power is enough?

"The battery bank 6 x Trojan 105 or about 660 amp.hour.
For 24 hours I use around 125 amp.hour
Planning to install 750 watts of solar panels"

Ohm's Law is your best friend.

You have a 660AH battery bank, and the rule of thumb is not to push it past a 50% discharge, or a 30% discharge is you really want the longest battery life and best return on investment. You draw 125AH in one day, so that's no issue as long as you can recharge the batteries every day--in just one day.

750W of solar panels, at a nominal voltage around 20 volts (raw panel voltage is around 17-22 volts) would mean the panels can put out around 37.5amps at full power. You can get a specific amperage rating for each brand.

And typically, a panel puts out five hours worth of rated power in one day. You only get the full rated power for about two hours at noon, the whole day averages out to about five of those "noon" hours, possibly 7-8 in the Carib.

But if you figure 5 hours at 37.5 amps, that's 187AH from your panels on a typical day, nicely more than the 125 you need. You should be able to run an extension cord and sell the excess power to other nearby boats. <G>

I'd call it a nicely conservative fit. In theory you'll have almost 50% more power than you need. Even if you use a conventional controller, rather than a more expensive MPPT one. Since your panels will be able to shoulder some of the electrical load, you'll also be discharging your batteries less, and you'll pick up still better battery life from them too.
__________________
hellosailor is offline   Reply With Quote
Old 15-04-2013, 06:39   #9
Registered User

Join Date: May 2009
Boat: Kirié Feeling 446
Posts: 130
Re: How much solar panel power is enough?

Yes I plan to install an MPPT controller (Outback 80A.) and wire the panels in series to obtain higher voltage and so lenghten the charge period a bit, especially on gray days.

Panels would be Suntech 240 with a 30.3 Vmp. So 3 panels in series should give a max of 90 volts.

Yes I have a 140 amp alternator with Xantrex controller, reinsulated fridge and freezer, high efficiency lighting and never take the batteries below 50% charge. I have been living aboard for 18 years.
__________________
SaltyTanned is offline   Reply With Quote
Old 15-04-2013, 06:57   #10
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: How much solar panel power is enough?

Here are the numbers for the Caribbean as observed aboard Jedi:

- 660W solar array
- Outback MPPT controller
- 6x Trojan L16 batteries in 12V config for 1,200Ah

- 24h statistics as recorded by the controller:

Sunny day: 2.5kWh
Overcast day: 1.2kWh

This changes month to month too. You can find tables that show radiation for each month of the year for each area in the world.

cheers,
Nick.
__________________
s/v Jedi is offline   Reply With Quote
Old 15-04-2013, 07:07   #11
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: How much solar panel power is enough?

Quote:
Originally Posted by SaltyTanned View Post
Yes I plan to install an MPPT controller (Outback 80A.) and wire the panels in series to obtain higher voltage and so lenghten the charge period a bit, especially on gray days.
.
Series does not have any practical effect on the length of the charge period, even for (nominally) 12v panels
The Vmp remains higher than the battery voltage under quite low light conditions. The charging stops under low light because the panels cannot produce significant current rather than a lack of voltage.

Have a look at this typical photo. The charge controller has shut down because the current produced by the panels is so low it is less than consumption of the controller. The Voc is still 18.0 v ( these are 12 v panels in parallel).
In other words the voltage is still fine, it is current that is too low. Series connection is no help.
Attached Thumbnails
Click image for larger version

Name:	image.jpg
Views:	98
Size:	124.0 KB
ID:	59238  
__________________
noelex 77 is offline   Reply With Quote
Old 15-04-2013, 07:12   #12
Registered User

Join Date: May 2009
Boat: Kirié Feeling 446
Posts: 130
Re: How much solar panel power is enough?

Thanks Nick,

Then 3 panels will not be enough on cloudy days.

It is a problem of space to mount them of course. 3 panels cover the bimini exactly. So I will need to add an arch and install 5 panels for the electrical independance I dream of.
__________________
SaltyTanned is offline   Reply With Quote
Old 15-04-2013, 07:16   #13
Registered User

Join Date: May 2009
Boat: Kirié Feeling 446
Posts: 130
Re: How much solar panel power is enough?

Thanks noelex,

Ahh there is nothing like experience. What I was told sounded logical but I realise it is as often, quite wrong. Then the only advantage to a series instead of a parrallel connection is the wire size.
__________________
SaltyTanned is offline   Reply With Quote
Old 15-04-2013, 07:17   #14
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: How much solar panel power is enough?

Quote:
Originally Posted by noelex 77 View Post
Series does not have any practical effect on the length of the charge period, even for (nominally) 12v panels
The Vmp remains higher than the battery voltage under quite low light conditions. The charging stops under low light because the panels cannot produce significant current rather than a lack of voltage.

Have a look at this typical photo. The charge controller has shut down because the current produced by the panels is so low it is less than consumption of the controller. The Voc is still 18.0 v ( these are 12 v panels in parallel).
In other words the voltage is still fine, it is current that is too low. Series connection is no help.
You don't know that. The controller will wake up from snoozing every so much minutes and then try to load the array. It is at that time that it will decide to go back to snoozing or to keep pulling power. The only way to know if it makes a difference is to try it with a series config under equal conditions

For example: your 18V might come out of one panel with 5 other panels partly shaded at 9V. A series config might be able to salvage half of the capacity of those 5 panels, tripling the output under the conditions compared to your parallel setup. Mark aboard Reach has tried this and reports 25% increase in avg daily production when in series with a string on port and a string on starboard side.
__________________
s/v Jedi is offline   Reply With Quote
Old 15-04-2013, 07:25   #15
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: How much solar panel power is enough?

The photo was taken under uniform low light.

Performance under shade is a separate issue

Here is another photo showing very low production (because of low light) with a Vmp of 15.0v still well above battery voltage.
Attached Thumbnails
Click image for larger version

Name:	image.jpg
Views:	106
Size:	141.2 KB
ID:	59246  
__________________

__________________
noelex 77 is offline   Reply With Quote
Reply

Tags
solar

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 22:37.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.