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Old 13-08-2015, 12:29   #1
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What size and number of solar panels needed

I am putting solar panels on my 420 which I intend to live aboard and cruise in the Caribbean. How much solar do I need and where is a good place to get what I need?
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Old 13-08-2015, 12:43   #2
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Re: What size and number of solar panels needed

I'm afraid this is an impossible question to answer accurately without more info. What are your loads/batteries/usage/charge controller etc.?
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Old 13-08-2015, 12:47   #3
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Re: What size and number of solar panels needed

Very simply, bought a use bare bones charter boat with only Refrigerator, Freezer, and basic navigation equipment. Only charging is from the engines, everything is factory at this point.
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Old 13-08-2015, 13:02   #4
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Re: What size and number of solar panels needed

What do you plan on adding and how many amp hours per day does the fridge/freezer consume?


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Old 13-08-2015, 13:04   #5
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Re: What size and number of solar panels needed

Unfortunately, I am heading home and have not taken down that information. I guess I need more to even post this question, sorry.
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Old 13-08-2015, 13:09   #6
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Re: What size and number of solar panels needed

From a small load standpoint, of led lights, fridge, laptop/tablet and/or tv, I find that having about 300 watts of panels gives enough to charge the batteries up well each day when on the hook. That's very roughly a kilowatt a day.

This allows for some cloudy weather too. So one 270 watt panel or three 100 watt panels will do you well. Ideally 4 6V GC2 batteries will give you enough capacity for a few days of cloudy weather.

It's what I use and it works well.
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Old 13-08-2015, 13:12   #7
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Re: What size and number of solar panels needed

What many suggest is for you to first determine your energy consumption, if you know how much you use, then you know how much to replace of course.
Maybe first try to conserve, a great way is to replace all lights with LED's, You would be surprised how much current a regular bulb uses.
Myself I'm starting with 750W, with the idea of if I need more, I'll add more. I got my panels from a local installer that specializes in large residential installations, they had a few left over panels that they sold me for .50C a Watt. I found that shipping costs were high, so I started looking local for panels and got lucky.
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Old 13-08-2015, 13:17   #8
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Re: What size and number of solar panels needed

Please do post more information about what your boat and loads actually are. Having a similar sized boat with similar loads, I'd guess your consumption to be about 8 amps per hour, which means you'd need to size for 100 watts/hr.

Do you use an autopilot? Do you use LED lighting throughout (including anchor/nav lights)?

A good rule of thumb for solar capacity is 3X typical consumption. This is because solar doesn't charge at night or efficiently in the early morning or late evening, so essentially you only get on average about 8 hours of effective charging time for a 24 hour period.

So I'd say 300 watts is sufficient for these loads, presuming there's nothing you've not mentioned, and presuming you live in the U.S.

If you intend to run some power intensive loads such as a watermaker, microwave, hot plate, electric coffee pot, etc., you'll need considerably more.

You can't put enough solar on a boat to run an appropriately sized AC unit; you'd have to motor or use a generator for that.
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Old 13-08-2015, 13:25   #9
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Re: What size and number of solar panels needed

We have a 40' monohull with 500 watts ( 4 x 125) of solar panels and 627 amp hours of battery capacity. We cruise in SoCal, Sea of Cortez, and Western Mexico and have not needed to plug into shore power or use the Yanmar propulsion diesel to charge the batteries, while at anchor, since we installed the panels in early 2000. We do have a 135-amp alternator that charges the batteries while we motor, but we frequently sit for weeks at a time, on the anchor not moving. One summer we went 3-months with no alternator and never got close to a dock.

We make no attempt to conserve or limit our electrical usage:

- 4 amp refrigerator compressor that runs 8 - 10 hours a day
- 40 watt computer/monitor that runs 12 hours a day
- 27" LCD TV that runs 12 hours a day
- lots of incandescent and fluorescent light bulbs
- 750-watt microwave for 15-minutes a day
- Spectra water maker that runs 1.5 hours/day at 16 amps

Over the long haul we use about 150-amp hours/day.

Our batteries are fully charged by 2 PM and we then run the watermaker and lower the thermostat on the refrigerator to pull down the cold plate.

Our solar panels make 22 - 28 amps at 13.8 to 14.4V from 11 AM until 2 PM (88 amp hours in mid-day) and 10 to 20 amps at 13.5 V for another 6 hours a day (90 or so amp hours).

The Caribbean may be a little different because we seldom see a cloud in the sky when in Mexico.

Do an energy budget if you want real numbers for your situation - that will give you a pretty good answer. We found that 500 watts of solar works for a couple on a 40' boat in bright sunshine.

A very important consideration in the answer is - how many panels can you install that will not be shaded at any time? Shadows on the panels make a big difference in their output.
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Old 13-08-2015, 13:37   #10
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Re: What size and number of solar panels needed

Panels are pretty cheap, I'd set up a simple efficient panel setup similar to ours. Advantage is rain protection, sun protection, minimal shading, out of the way and ample power. We have 1.2 KW, 4 x 280W panels. Panels are 1m x 1.6m. Controller is a victron 80A
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Old 13-08-2015, 13:56   #11
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Re: What size and number of solar panels needed

There is no answer because there are so many variables. If you use your engine an hr or 2 each day and have an high output alt with a smart regulator then you can probably get by with small or even no solar.. if you don't use lits of amps. I have had 2-55 watt panels which keep my batts topped up when the boat is left on a mooring for 5 days. I cruised and lived aboard with only the 2 55watt panels for years. I do motor in and out of the mooring field because my refer is engine drive and we get hot water as well as amps and refer cooling. the alternator is a 120 amp with a Balmar 614. We are not misers with cabin lighting but only have the lights on were we are doing something. LEDs save amps.
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Old 13-08-2015, 14:15   #12
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Re: What size and number of solar panels needed

Quote:
Originally Posted by sailorchic34 View Post
From a small load standpoint, of led lights, fridge, laptop/tablet and/or tv, I find that having about 300 watts of panels gives enough to charge the batteries up well each day when on the hook. That's very roughly a kilowatt a day.

This allows for some cloudy weather too. So one 270 watt panel or three 100 watt panels will do you well. Ideally 4 6V GC2 batteries will give you enough capacity for a few days of cloudy weather.

It's what I use and it works well.
300 watts a hour equals twenty-five amp per hour @ 12VDC, so using 300 watts for 24 hours equals 600 amp-hours. How many amp-hours are 4 6V GC2 batteries?
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Old 13-08-2015, 14:39   #13
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Re: What size and number of solar panels needed

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300 watts a hour equals twenty-five amp per hour @ 12VDC, so using 300 watts for 24 hours equals 600 amp-hours. How many amp-hours are 4 6V GC2 batteries?
Ah the sun does not shine at night. Realistically your only getting good output for 5-6 hours a day. Also, there is a difference between rated output at STP and actual output when used on a sail boat with lots of shading opportunities. I find that the actual output is roughly 70 percent of the nameplate output. Least wise on my boat.

Don't forget that temperature coefficient. Rated Panel output is based on 25 degrees C. Every 25 degrees C (45 degrees ish F) increase in surface panel temperature drops panel voltage by ~1v. Luckily this happens in summer when there is more daylight. It's also why MPPT's don't give a higher output in summer.

So it's only about 75-85 amps in the world I live in. Which for my boat is just a bit more then I use in 24 hours. It's also about 20% of the 400amps in batteries I have connected to it.
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Old 13-08-2015, 14:46   #14
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Re: What size and number of solar panels needed

My point of view is you cannot have too much solar energy on your boat. for me it would come down to how much space do I have and how much money can I afford to spend . I think if you live aboard full time and do not want to live like you Are camping you will use as much as you have. and you can always devote extra power to heat hot water or something else extravagant
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Old 13-08-2015, 15:05   #15
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Re: What size and number of solar panels needed

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300 watts a hour equals twenty-five amp per hour @ 12VDC, so using 300 watts for 24 hours equals 600 amp-hours. How many amp-hours are 4 6V GC2 batteries?
It seems that 1000 watts per day @ 12VDC would need a minimum 84 amp-hours capacity.
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