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  #1  
Old 01-25-2011
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solar recommendations please

I have figured my daily usage at between 200 and 300 watts. i have 2 spots for solar panels measuring 23" by 48". I'm looking to put as much as i can fit in the spots. any recommendations? I have a single 225 ah 8d battery. also am in process of building a 225 watt wind genny to augment as needed.
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Old 01-26-2011
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well 300 watts is 24 amp hours so your battery should be able to handle it. but most here will say you need more, including me.

just so you know 24 amp hours is only a 20 watt anchor light for the night plus two or three inside lights at night. i would bet its higher than that, unless you run nothing except lights when needed.

now for your answer you want to aim for, in my opinion, for 3 days of battery. so you would need a 300 amp hour battery if your use is accurate. then size charging for 150 to 200 % of your daily use. this buys you 3 days of clouds, before you need to go shore power or engine. but it will allow charging at a rate faster than you use incase you just have one day of no sun. ie one day of shade and the next day you would be fully charged ( assuming 200 % of use ). if you get two days of no charging on the forth day you would be fully charged.

i know this is for solar only, and you are going with wind too. but for solar you will get about 70 to 80 watts out of a 100 watt panel unless you use an mppt controller. assuming you use an mppt controller you will get about 40 amp hours a day out of a 100 watt panel. or about what you would need.

personally if i was going all solar in your use i would put 150 to 200 watts of panel, for those days you want to use more power. do you use a laptop, fan, auto pilot etc on your boat or just lights. because once you see that you have more power you will find a way to use it, ie a radio. also you can use the extra power for a 12 volt water heater as a dump load when fully charged.

Last edited by scottyt; 01-26-2011 at 01:05 AM.
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Old 01-26-2011
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Are there any good books or websites about solar and wind power?
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Old 01-26-2011
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Quote:
Originally Posted by scottyt View Post
well 300 watts is 24 amp hours so your battery should be able to handle it.
Watts is a unit of power, which is energy per time. Amp hours is a unit of electrical charge. Therefore I'm afraid you can't equate 300 watts to 24 amp hours as the units are different.

Newhaul, the phrase "daily usage at between 200 and 300 watts" is a little ambiguous, as watts is an instantaneous measure. Did you mean that:

1. Your peak power consumption is 200 to 300 watts? If so, this is not terribly relevant as you can use your battery to smooth out fluctuations in consumption.

2. Your sustained power consumption over many hours averages 200 to 300 watts? If so, your solar panels need to provide at least this power to avoid net battery drain.

3. Something else, perhaps involving different units such as amp hours?

Last edited by acunningham; 01-26-2011 at 01:48 AM.
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Old 01-26-2011
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Quote:
Originally Posted by newhaul View Post
I have figured my daily usage at between 200 and 300 watts. i have 2 spots for solar panels measuring 23" by 48". I'm looking to put as much as i can fit in the spots. any recommendations? I have a single 225 ah 8d battery. also am in process of building a 225 watt wind genny to augment as needed.
First off, you need to get your units straight. A watt is a unit of power, or energy per unit time. If you average 200 watts for 24 hours, that would be 400 amp-hours (@12V), which seems incredibly high for an I24.

Now, if you really mean that you average 200/24 watts, or 8.3 watts, that would be about 0.7 amps (or about 16.8 amp-hours); a much more reasonable figure for your boat, and also in line with the previous answer. Let's round that up to 20 amp-hours, and then double it to take cloudy days and such into account. Now, you need about 40 amp-hours of charging capacity to keep you even. A solar panel only charges at its rated capacity right in the middle of the day, so on average you get about 4 hours of the rated capacity per day. That means you need a panel (or set of panels) with an output of about 10 amps (or slightly less, since you charge at high than 12 volts). Put it all together, and you need about 100 to 120 watts of solar panel. For modern solar panels you get about 150 - 160 watts per square meter, so (using the most conservative numbers) you need about 0.8 square meters of panel. One 23"x48" panel would be pretty close to that. I would split the area (for a bit of redundancy) in two and get two 2' by 2' panels.
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sbs our numbers are close but i used charging volts at 13.5 and load volts at 12.5.

it is something that needs to be taken in to effect when running the numbers
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Old 01-26-2011
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Quote:
Originally Posted by scottyt View Post
sbs our numbers are close but i used charging volts at 13.5 and load volts at 12.5.

it is something that needs to be taken in to effect when running the numbers
I wasn't trying to give an exact answer. That's why I did a lot of conservative rounding and such. Yes, loads are usually taken out of a battery at an average of 12.5V, but manufacturers rate their panels at all sorts of voltages. As a result, solar panels are almost invariably over-rated by at least 10%. For that matter, loads are often under-rated by the user (e.g., lights often get accidently left on, but rarely go completely unused). An area of 0.8 m^2 will most likely provide all the power he think he'll need, plus a bit extra. In cases like this, that's as good an answer as anyone can reasonably give.
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Old 01-26-2011
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Quote:
Originally Posted by SlowButSteady View Post
In cases like this, that's as good an answer as anyone can reasonably give.
I agree with you on the numbers 100 % you just used the lower side of his uses and that thru me off. Thats what i get for reading at 3 in the morning
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Old 01-26-2011
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Quote:
Originally Posted by newhaul View Post
I have figured my daily usage at between 200 and 300 watts. i have 2 spots for solar panels measuring 23" by 48". I'm looking to put as much as i can fit in the spots. any recommendations? I have a single 225 ah 8d battery. also am in process of building a 225 watt wind genny to augment as needed.
First, you really need to get a good handle on what your actual electrical use is. Getting a battery monitor, like a Victron BMV 601, is really one of the best investments you can make. It will give you a real idea of what your use is and then you can plan what battery bank size and how much passive charging you really need.

You can probably fit two 80 watt panels in the space you've got. Two 80 watt panels will give you about 55 amp-hours of passive recharging per day (based on 5.5 amps per panel * five hours full power per day). You'd probably want to have a decent MPPT charge controller to do this with.

I would recommend you read the article on Solar Power on Boats I have written on my blog.
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Old 01-26-2011
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Thanks SD you are actually the only person that even actually answerd my actual question for the rest of you thanks for the solar info. to clarify some i have 2 3 watt cabin lights i only use one at a time ocasional use of running lights (led) and a solar self contained anchor light my radio is a crank charge type. i have been a camper most of my life. i also have a self contained solar table/tent lantern. what i am looking for is size (wattt output) and brand/ makes that will fit in the space i have available ie: 23"x48" so 200 to 300 watts daily use is actually on the high side.
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