How Much Solar

[dandrews]

Originally Posted by Maine Sail

Don,

Knowing your boat is on a mooring I will give you a run down of how I size for mooring re-charge systems. If you want larger for "cruising" then you'd need to go larger.

For mooring charging I size like this:

Ideally you want the alternator, or generator, to handle "bulk" and some absorption charging and bring the bank back to 80-85% state of charge. From there you can let the solar panel do the rest and bring the bank back to 100% SOC, when you're not there during the weekdays.

If you want to satisfy cruising needs such as refrigeration, instruments, AP etc. then your array can get quite large. You did not specify so I will give an example of hos I size for a mooring re-charge.

The faster you can bring the bank from less than 100% to 100% the less sulfation you will have and as a result the longer battery life you'll get.

I'll use an example of a bank of 300 Ah's for a "mooring recharge".

The last 20% of capacity of a 300Ah bank is 60 Ah's. However, you ideally need to take charge inefficiencies into account too so you'll really need to put back in about 70Ah's +/- to get back to that elusive 100% state of charge that boats on moorings need.

For moored boats the panels are usually left flat when you're not there so that you can capture "most" of the sun. In a land based solar array the panels are fixed, the property is not moving like a boat does, and can be angled at the sun for the best performance. For this reason alone land based solar calculations rarely if ever apply or translate well to boats. On boats the panels are rarely oriented at the sun for optimum solar gains and the stick, rigging and other appendages get in the way on swings or at different times of the day causing shading which can drastically limit array performance..

Having the ability to "aim" the panels at the sun, on a boat, is not usually a workable solution when swinging on a mooring, or at anchor if cruising unless you are there or are attentive to it, so, panel position is very often a compromise and most leave them flat.

If you are at a dock you can rig the panels and aim them more appropriately but not on a mooring, like you are, or off cruising where your boat will swing at will unless you pay really good attention or the wind & tide always come from the same direction, not so with 10+ foot tides... If you might someday wind up at a dock then articulating panels can help the output.

Because of these aiming restrictions I find, after lots of monitoring here in the North East, you can figure on about 3.5 - 4.5 hours of full rated output per day on average. In the summer our insolation numbers are actually pretty good up here.

Some folks use 5 hours per day in the Northeast but after lots of monitoring of my own panels, and customers, I found that to be a little to generous. Some days it will be more some less but here in Maine 3.5 - 4.5 hours at full output, is an average sizing number that seems to work best.

So, a 300 Ah bank @ 20% down = 60 Ah's that need to be returned + charge inefficiency = 70 Ah's total needed for a "full" bank. Note that I don't care what your load calculations are because you are doing this with no loads, when you;re not even there, other than some parasitic loads. if you were a live abord this would be different but I don't think you are as you live in Merrimack, NH which is about an hour to your boat..

A 2.5A output panel X 4.5 hours = roughly 12.5 Ah's/Day returned to the bank. If you have phantom/parasitic loads, like a propane sniffer or other "always on" loads, subtract those and this is your "net" average/day.

Next divide 70 amp hours (or what ever your bank is) by 12.5 and you can see that it will take approximately 5.6 days to go from 80% SOC to full on a 300 Ah bank with a panel capable of 2.5A. This is in PERFECT conditions though.

I personally feel that's a little long, especially accounting for weather, so would prefer to see a panel in the 3.5A minimum range on the example 300Ah bank. Bigger is always better but this becomes a "real estate", budget and let's admit it, an aesthetic compromise with many boats and boat owners. A 3.5A panel shaves a full day off the time it takes to hit full when compared to a 2.5A panel, 4.5A faster yet and a 7.5A panel you're full in just about two days from where the alternator stopped..

For cruising figure the maximum amount of time you want to run the engine or gen set per day, or every other day, then base your array size on the difference needing to be made up while accounting for loads. If you only want to run your engine for an hour per day, when you hit 50% SOC, and your alternator can get you from 50% to 70% in an hour then you have a 30% deficit to make up plus charge inefficiencies. You can size your panel to make up this deficiency if you know your average loads, which you do. There are always worst case and best case scenarios too and a best case is not always going to happen..

For your bank I would think a single 140W Kyocera, or other comparable panel, (AltE has great prices, are in Webster, MA and can ship one to Maine UPS for $23.00 in one day at ground rates BTW) would be a good base to start with. Going with two 140W panels would be really nice but a single 140W should top you up fine during the week. I just ordered two Kyocera 140's last week from AltE and they were here the next day (with ground shipping) for short money and it they are a premium panel..

It's all in what you want the system to do and you really did not specify, so I answered with what most boaters here in Maine want to do with mooring stored vessels, and that is get the banks back to full, within a few days, from about 80% SOC...

I'll pre-duck now to avoid Don's lecture on why my input may not have been appropriate to his original question...

Thank you for this post. Made more since to me than anything I have read on the subject.

Don Andrews

[dandrews]

Originally Posted by dandrews

Thank you for this post. Made more since to me than anything I have read on the subject.

Don Andrews

Don't you hate it when your iPad offers up a word for you and you don't catch it is the incorrect word for what you are trying to say. Makes more SENSE to read before you hit send.

[Khagan1227]

Great thread all around even with the amount of thread drift.

Several different ways of looking at a problem and how detail oriented some of us are in our thinking. Others... not so much.

[careka]

New types will come,
So long, silicon: Researchers create solar panels from cheap copper oxide | ExtremeTech

[Pete7]

Originally Posted by Don Lucas

Since I didn't ask anything other than how much solar do you have and is it enough, which is a very simple questions, why can not I get a simple answer?

Don, don't worry, some of us got the message about what you wanted as an answer.

The information of how much solar, what's your typical load, possibly with location* and is it enough? will be useful for those following on.

Pete

* Thread drift - whilst some feel solar isn't so useful in higher lats I disagree. Sitting at 51'N I see the panels working from very early morning to mid evening. Long daylight also lowers our need for interior lights. Finally even in the mid day sun our panels are only luke warm to the touch so efficient.

[mbianka]

Originally Posted by Don Lucas

How much solar do you have, is it enough?

Lets stay away from theory and responses that have to do with doing a demand calculation etc as we all know that theory and reality don't always match. I've calculated mine till the cows come home but that doesn't mean the answer is real life correct.

Just how much solar do you have, what size loads do you have, is your solar keeping up?

Don:

I run with two separate systems since I have electric propulsion.
I've got two group 27 Gel's in parallel which is approx 200 ah total for my house bank. I have two old Seimens 12 volt 75 watt panels connected to a Morningstar PWM solar controller for 150 watts solar. This pretty much meets my needs including running an Engel M27 in freezer mode when I'm aboard and in refrigeration mode when I'm off.

My EP system which has four 8A4D batteries in series (200 ah each) has two 60 watt 48 volt panels connected to another 48 volt Morningstar PWM controller. It also has a Marine Air X 48 volt wind turbine connected to the EP bank.

Both the 12 volt 75 watt and the 48 volt 60 watt panels are part of my solar bimini setup:
THE BIANKA LOG BLOG: SOLAR BIMINI PART SEVEN: PANELS INSTALLED
The panels do get some occasional shadow from the boom but, still meet my energy needs very nicely.

While at anchor I do tap into the EP battery bank to run my laptop via a 48 volt to 12 volt converter:
THE BIANKA LOG BLOG: AN ENERGY EPIPHANY
Any use here gets replaced quickly with the 48 volt solar panels and wind turbine. Which means I don't have to fire up a generator.

I'm on a mooring or at anchor usually. I have no engine and therefore no alternator so any supplemental charging is accomplished with a Honda 2000 generator. Which also functions to run my hookah dive setup and other things as needed.

Once my batteries have been topped up solar and wind usually keep up with demand. If I have a day or two of extended cloud cover I may have to fire up the Honda for a half hour or so to make sure the house bank does not run down too much in the middle of the night.

[belizesailor]

Working on expanding my home (off-grid) power system and found a good spreadsheet for my purposes. You can check it out here:

calculating your solar power needs

[Strygaldwir]

I have 185 Watts of solar, with Outback MPPT controller. It is not enough.

I have a Frigoboat Freezer and Seperate Refrigerator. If I turn off the Freezer and refrigerator, the 185 will keep the batteries 100% charged about 95% of the time. There will be slight draw downs on successive cloudy and rainy days. But, my battery capacity lets me go through those days without having to result to alternate charging.

If I run my refrigerator, I'd need about another 90 watts to achieve the same results above. I'd estimate I need another 185 watts for the freezer. Thus, I am thinking of adding two more 200 watt panels. Since I use a large MPPT, I can simply add on additional panels in series increasing the voltage to 75 volts (Rated to handle 100 volts). This will give me a system that will keep pace with my usage unless something extraordinary happens.

I should note, I would not necessarily expect the panels to keep up with the regime I use for my watermaker. I like to top up my tanks about every three days. I use my portable generator for 3 or so hours while the watermaker is topping the tanks up. When I do go full panels I will probably alter this regime, might not have to run the portable as long. I'll see then.

[bob_77903]

380W solar-Outback 60W controller, its enough for me!

[ohdrinkboy]

I'm a neophite, so play nice. Hear lots of talk about watts/$$, but what about watts/square inch? Are all panels the same? I would think you want the most watts/square inch within your budget.

[senormechanico]

320 watts, Bluesky mppt, Aerogel insulation in fridge, Spectra watermaker, tons of power, enough to use inverter for hot water.

Ohdrinkboy,
On a house installation, it's usually about watts per dollar as roof space is plentiful.
On a boat however, the space is usually limited and mounting hardware is a significant cost in many installations. Therefore, it's usually best to buy the most watts per square inch/foot/meter.

[belizesailor]

Originally Posted by ohdrinkboy

I'm a neophite, so play nice. Hear lots of talk about watts/$$, but what about watts/square inch? Are all panels the same? I would think you want the most watts/square inch within your budget.

Good insight and especially relevant on a boat. Have not crunched these numbers, but let's see how it works out...
'
This is by no means a statistically valid sample, but crunching the numbers on a sample of 4 panels from the Sun Electronics site (Solar Panels, PV Systems and Inverters Distributor) ranging from 105W to 315W the answer appears to be "GO BIG". More watts per Square Inch on the bigger wattage panels (also physically larger of course). On most cruising size boats a beast like the 315W panel, at about 65" x 52" could be a challenge to find a home for, but it has the highest watts/SqIn.

Next question to answer would be is there a difference between same wattage panels across brands?

[SailFastTri]

OK let me jump in with a related question: I have 160w of solar and keep my boat on a mooring at 40-degrees north. I have an Isotherm small fridge that uses about 2.9 amps and has poor insulation, so it's mostly on. Battery bank is 240ah and I never want to go below 50% charge. Presently I'm running a daily deficit with only the fridge on, and it takes 3-6 days to reach 50%, depending on weather. I see about 7a peak charge in mid-day sun.

Got to keep the beer cold, so how much additional solar should I add? Alternate: would I be better off to buy an Engel and sell my isotherm?

[Ex-Calif]

Originally Posted by SailFastTri

OK let me jump in with a related question: I have 160w of solar and keep my boat on a mooring at 40-degrees north. I have an Isotherm small fridge that uses about 2.9 amps and has poor insulation, so it's mostly on. Battery bank is 240ah and I never want to go below 50% charge. Presently I'm running a daily deficit with only the fridge on, and it takes 3-6 days to reach 50%, depending on weather. I see about 7a peak charge in mid-day sun.

Got to keep the beer cold, so how much additional solar should I add? Alternate: would I be better off to buy an Engel and sell my isotherm?

Conventional wisdom says make the boat efficient first. So yes, efficient fridge, LED lighting, insulation etc. etc...

Also, as an observation reading a bunch of posts here most folks are in the 75-100 amps a day range.

If I were setting up from scratch I would be looking at a 100amp system as a baseline.

[belizesailor]

Originally Posted by SailFastTri

OK let me jump in with a related question: I have 160w of solar and keep my boat on a mooring at 40-degrees north. I have an Isotherm small fridge that uses about 2.9 amps and has poor insulation, so it's mostly on. Battery bank is 240ah and I never want to go below 50% charge. Presently I'm running a daily deficit with only the fridge on, and it takes 3-6 days to reach 50%, depending on weather. I see about 7a peak charge in mid-day sun.

Got to keep the beer cold, so how much additional solar should I add? Alternate: would I be better off to buy an Engel and sell my isotherm?

See the spreadsheet link I posted earlier -- it will run the numbers for you and even project out across multiple days and show the deficit/surplus.

Also, the Isotherm (Danfoss compressor?) is likely to be more efficient than one of the portables (I assume that is the Engel you are referring too). Duty cycle should only be around 25%. Might have a fridge guy look at it and consider fixing the insulation problem.