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Old 17-08-2004, 15:54   #1
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solar power

Hi all
I am looking to install a solar charging kit for my catalina 30, The electronics onboard really only consist of an auto-pilot, vhf, radio and soon a gps/radar, while underway. Dose anybodie have any suggestions on size and charging power for a solar system?
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Old 18-08-2004, 02:57   #2
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You really need to do your own energy budget to work out what you need from your equipment in the way that you sail, cause everyone is different. They are not hard, but do need a bit of research.

Start by listing all of your electrical equipment onboard

Work out how much power they use for an hours use (e.g. 10w bulb = 1 amp/hr (roughly)but round up not down). Most equipment will have a power requirement somewhere on them or in their documentation.

Work out how many hours they will be used per day. Some equipment will only be used occasionally, so work out how many hours of use per week and then divide by 7.

Dont forget that there are 24 hrs in a day!

Multiply the amp/hr figure for a piece of equipment by the number of hours and add all these together for all your equipment.

You now have a power requirement. Some of this will be met by use of your engine, and you should be able to estimate this (take daily engine use for hrs and multiply by abt half the alternator capacity (I said this was rough) . You can subtract this total from the power requirement. You are left with the power requirement for your boat, which can be made up by shore charging, solar panel or wind generation (or combination thereof). Because you have rounded up, and used half the alternator capacity, this will provide a surplus for a while, until you add that next must have gizmo!
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Old 18-08-2004, 03:12   #3
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energy budget

I suggest that you fit as much Solar Panel Capacity as you can afford (space & dollars).
You cannot have too much electrical energy on board. No matter what you calculate your energy budget at; you can (& likely will) always use more.
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Old 18-08-2004, 07:38   #4
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Don't forget to figure in the battery size.

You have to have a place to store all of this electricity you are generating. Remember that you have to figure in how much battery capacity you need as well. You need to have twice the battery capacity of your lowest discharge cycle. Discharging batteries more than 50% will reduce their life. In addition to the above power analysis, you also have to do a time based study. Look at the consumption and generation cycle times and make sure during this cycle you don't drop the stored battery power too low. If your batteries are too small for the charging system, the regulators will limit power to the batteries of sunny days, underutilizing the power source, then the batteries won't have enough power to get you through the cloudy days, or even a night of heavy autopilot use.

If you find that during the cycle you are going below 50% capacity, you might be able to alter your operating strategy to help.

For example, alternators start out charging hard and as the battery voltage increases, they taper the charge. You could use high consumption devices later in the charge cycle when the battery is taking less current than the alternator can produce. This might be the time to run the SSB to get email, or perhaps you need to operate some power tools with an inverter.

The same can also be said for solar panels. When the sun is bright and the batteries are topped up you can do all of the power consuming tasks and take power "straight from the panels". Don't do those things at night when it all has to come from the batteries.
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Old 18-08-2004, 10:20   #5
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Thank you all for the information, It looks like Ill have to get the calculator out !
cheers
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Old 18-08-2004, 14:08   #6
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And remember that the solar panels wattage size is based on a perfect condition. We don't get perfect conditions in real world. The efficiency decresses due to how much Sun light there is, the angle of the Sun, what could be casting a shadow, the temperature of the panel, dirt and salt on the panel, whether Pluto is aligned with Juipitor etc etc. So you want to fit a much larger panel than your calculations of wattage use over a 24Hr period suggests. Plus you need to be able to put the discharge of 24hrs, back in within the Most efficient Sun light hrs. In other words, just because the Sun is above the horizen, there will be little charge supply till the Sun is high enough to shine down on the panel. So you may only have 12hrs of Sunlight in the Summer and perhaps only 6hrs in the Winter. That will vary with what lattitude you are in of course.
And if you are over a panel size of 10W, it is recomended you use a charge controller and one is definatly required for above 20W's.
And lastly, if you have a very large bank of batteries, and you really flatten them, it can take a lot of current to lift them up again. Usually much higher than what a bank of panels will produce. So don't ever allow the banks to fully discharge. And fully discharge is not dead flat. As already stated, it is only 50% and that is about 11V ruffly for a 12V battery. Anything below that and you start reducing the life expectancy of the battery dramaticaly. Anything bellow 12.1V and sulfation starts occuring on the plates.
Hope this is helpful,
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Old 18-08-2004, 15:17   #7
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Quote:
Alan Wheeler once whispered in the wind:
As already stated, it is only 50% and that is about 11V ruffly for a 12V battery. Anything below that and you start reducing the life expectancy of the battery dramaticaly. Anything bellow 12.1V and sulfation starts occuring on the plates.
Hope this is helpful,
Wheels
Sorry to disillusion you, but 50% of a 12v battery is actually 12.2v according to adverc (and they should know)
!
I have a 180w panel which seems to keep my batteries reasonably well up
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Old 18-08-2004, 17:53   #8
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Ditto...
Get the most and the biggest panels ya can fit and afford.

I have 2 Siemens 75 W panels over the bimini top and behind the back stays and behind the boom.

On a good day in the Bahamas they will pump 50 amps into the battery bank.

On a cloudy day, less than half that, about 2 a/h when the sun does not shine, 8.5 when it does.

There is a give and take however....
During the winter in Florida the nights are pretty cool and the temp. inside the boat is pretty moderate, therefore the fridge and freezer burns about half the amps they do in the summer....And ya have less output of the panels in the winter due to the angle of the sun...So the total ain't too far off:

These 2 panels will pretty much run the fridge and the freezer box for free...Hell of a deal...No oil changes, no noise, no nothing.
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Old 19-08-2004, 15:34   #9
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You are quite right. That was a typo and should have read 12V even though 12V is still wrong, it was at least closer. Actually I do have a table here as well and should have been more accurate in my statements than generalisations. A percentage of a volt makes to much difference with batteries.
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Old 26-08-2004, 02:18   #10
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Lower costs coming ?

This should help to bring down the cost of solar panels ...

From The San Francisco Chronicle:

Solar power bill supported by David R. Baker

Gov. Arnold Schwarzenegger on Friday threw his support behind a bill to dramatically increase the number of California homes using solar power, reviving a legislative effort that seemed all but dead last week.

The bill calls for placing solar panels on 1 million new and existing homes during the next 13 years and offering rebates to the homeowners or builders who install them. Builders also would be required by 2008 to offer solar panels as an option on new homes in every subdivision with at least 25 houses.

The governor's plan differs significantly from another solar power bill that stalled in Sacramento last week. That bill would have used a 25- to 30-cent charge on utility bills to pay for incentives to builders and homeowners installing solar panels. Because of that proposed charge, the bill would have needed a two-thirds majority to pass the Assembly and Senate.

The new bill does not include the charge and therefore will probably require a simple majority vote. Costs will be paid by existing state funds for renewable resources.

State Sen. Kevin Murray, D-Culver City, who wrote both bills, said Schwarzenegger's backing could give the idea the support it needs.

Schwarzenegger "is able to temper and moderate any opposition from the business community, and he's able to overcome any Republican ideological issues," he said.
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Old 26-08-2004, 10:32   #11
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Lightbulb Windmills too!

So why don't they offer them windmills too. We put them on boats. Maybe it's a safety factor.
When I went to Alaska back in 75, that was my plan to build a self-sufficient house, using wind, water and solar to charge batteries. Then just be conservative.
The technology today has advanced ten fold. It would be much more feasible today to set up homes that were bio-consumers. You can buy almost everything in 12V these days. If not, electronic inverters are available which are a lot more efficient and cheaper then they were back in 75..._/)
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