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Old 01-06-2018, 12:50   #1
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Solar Watts : Daily AH Consumption

I'm curious if there's a trend among cruisers that could be used as a rule of thumb/sanity check.

So, if you please, post:

Your Solar Watts (nominal) / Your Daily AH Consumption (average)

Also indicate:
-to what extent you rely on solar (contra wind, diesel, etc)
-where you cruise (tropics, high latitudes)


Thanks in advance
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Old 01-06-2018, 13:26   #2
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Re: Solar Watts : Daily AH Consumption

Really should include house bank size and type, too.


I have friends with 4 6V nom. golf carts, wet cells, 450 ah house bank, fridge and freezer with a 150 ah/day use and 170 watts of solar (Giot). They can go two days on that setup before hitting 50% SOC.


I have a meager 11W panel, mostly used for keeping the bank topped off when I'm not there after a full shorepower recharge. 390 ah house bank, 12V wet cells, daily use with fridge is 100 ah/day. I can do an overnight easy. Two is stretching it if I'm anchored, so I run the engine when the system voltage goes down to 12.1V with the fridge in an off cycle. If I'm moving around daily, no issues.


Both of us sail here in my signature.


Most of your question has been answered in other posts about solar - like, there have been a few, right?


But for a 100 ah/day load, most folks tend to go in the range of 400-450 ah house banks, maybe 600 if they add another pair of golf carts, and associated is around a minimum of 170-200W of solar.



It's a balance of space and stuff, use and loads, and generally boat sizes. Larger boat, everything increases, usually but not always.


There were some "how to do a rough estimate" of solar sizing posted here in many of the threads in terms of watts, amps, and anticipated ah/day, also depending on latitude and time of year. Here's what I collected with some links:


Solar Sizing


Calculate daily A-hrs consumed, multiply that value by 4 for battery capacity in A-hrs and for solar array in Watts. This is the minimum. That simple.

e.g. If 100 A-hrs / day consumption, then 400 A-hrs of FLA battery capacity and 400W of solar.

From: Matching solar panels to batteries to consumption - Page 3 - Cruisers & Sailing Forums



I have a simple formula for solar. If you have 400 watts of panels figure 25% of that in Amp Hours per day in average sunny cruising climes. 400w of solar = 100 Amp Hours a day. In a rainy place like Maine figure 1/5th or 80 amp hours and in super sunny figure 1/3 or 130 amp hours. That is on average. Works for me.
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We need to remember that in hot climates the panels can't produce as much, and any MPPT boost may be minimized.

That said I have done a lot of solar bulk charge data logging, usually in 7 day periods, and I come up with about 0.224Ah per watt, per day for real world flat oriented situations (keep in mind this is no shade but panels are flat mounted here in Maine with temps from 50F to 95F).

So a 1000W array, with zero shading from the boat, could be capable, on average, of somewhere around 224Ah +/- per day.. Some days it will be quite a bit more, some days less, but it will generally average out close to this unless your skies are always clear..

Some math:
  • 600Ah bank (assumption only it's likely smaller)
  • *Charge Rate - Rounded to Approx 40A or .07C (AGM's can easily take .3C to .4C and this is actually good for them)
  • Ah Consumption @ 50% SOC = -300Ah
  • Average hours to recharge at 100% Efficiency = 7.5 Hours (not enough solar hours to produce 40A continuously for 7.5 hours)
  • Average hours to recharge at 85% Efficiency = 8.6 Hours (not enough solar hours to produce 40A continuously for 8.6 hours)
  • Hours to recharge if you drop to float too early = Fagedaboutit
  • Average hours to recharge with shading = Impossible to predict but a lot less than no shade
*None of this includes for daily sun-up hour DC consumption. Your on-board consumption can chop your 40A by quite a bit.. If you use say 15A on average your time to 100% from 50% at 100% efficiency just went from 7.5 hours to 12 hours, and this is with zero shading.....


Rx - Use the genset early in the day for bulk, lengthen solar absorption duration, and you should be able to get to 97-100% SOC in all but the worst conditions. If you don't run the genny daily, and actually drop to 50% daily, you are going to be experiencing some PSOC walk down....
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Old 01-06-2018, 13:47   #3
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Re: Solar Watts : Daily AH Consumption

420 amp hours, although batteries are long in the tooth so lets call it 320 ah.

350 watts of solar, virtually unshaded.

I use 75-100 ah per day. How much is largely a function of how hot the water I'm in is and how hard the fridge has to work due to heat infiltration through the hull.

I get to float by around 1pm on an average day.

I'm still monitoring usage and generation and have only had the panels since mid-winter so don't have a full year of data to look at yet.
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Old 01-06-2018, 14:08   #4
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Re: Solar Watts : Daily AH Consumption

capacity: 40ah
daily usage: 10-15ah
solar: 200 watts


I have 8 year old batteries with only about 40ah usable capacity now.

My largest load is a screen that draws 0.35 amps, and then a raspberry computer that draws 0.15 amps. In total this amounts to about 8ah a day, I turn the screen off when I"m not using it.

When sailing I am using pypilot autopilot. It used about 0.3 amps running in 6 knots of wind off cape hatteras, but less than 0.1 amps sailing in protected waters.

On sunny days I have a fan that draws 0.5 amps. I also have an electric cooker that draws 6 amps, and takes 45 minutes to boil 2 cups water, and a soldering iron that uses just under 2 amps.. a 12 volt drill that uses a few amps. The total consumption from all of these is small because I don't run them for long periods.

I don't understand the purpose of a refrigerator. The shops refrigrate stuff like squash that can keep a whole year on purpose just to force people to buy a refrigerator, since the thing will go off once it's been refrigerated, and it doesn't taste as fresh either.
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Old 01-06-2018, 14:08   #5
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Re: Solar Watts : Daily AH Consumption

Quote:
Originally Posted by KISS View Post
I'm curious if there's a trend among cruisers that could be used as a rule of thumb/sanity check.

So, if you please, post:

Your Solar Watts (nominal) / Your Daily AH Consumption (average)

Also indicate:
-to what extent you rely on solar (contra wind, diesel, etc)
-where you cruise (tropics, high latitudes)


Thanks in advance
I have 290W solar. I average about 100-150AH/day use. The solar on a good day makes up for the it, especially if we aren't on the boat. We are full time cruisers and before we left that amount of solar kept the batteries charged in the Boston area with the refrigerator on all week on the mooring.

I feel I need to double the solar. BUT if the mboat motors or I run the generator for an hour each day the solar is enough. So far I figure the extra solar cost would pay for 3+ years of generator time and that probably really works out to about 5 years of cruising time.
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Old 01-06-2018, 14:14   #6
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Re: Solar Watts : Daily AH Consumption

Old boat: Seawind 1000 catamaran
240 watts (2 x 120) solar panels w/3-stage MPPT controller
315 amp-hrs AGM batteries
Don't know daily usage, but overnight was ~25 amp-hrs from lights, water pump (showers and dishes), refrig/freezer, DVD player, etc. By noon the solars had completely made up for overnight usage, and covered daily hourly usage, and system on float until sundown
No generator or wind. Solar panels only. And small alternators on outboards (never used solely for charging).

New boat: Seawind 1160 Lite (Nov 2018 delivery)
800 watts (4 x 200) solar panels w/MPPT controller
450 amp-hr AGM house battery. May add another 225 amp-hr Mastervolt to house, or run switch on "both" to include 130 amp-hr AGM start battery in house system.)
Usage will be higher as refrig is front opening, and freezer is much higher volume counter style than SW1000 combined frig/freezer.
Nothing else other than solar, and alternators on twin outboards.
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Old 01-06-2018, 15:50   #7
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Re: Solar Watts : Daily AH Consumption

I have a kilowatt of Solar, and a 660 AH bank that is about 600 now, I think.
We use likely about 250 or so AH a day sometimes as much as 300 depending on what we are doing. Panels supply a lot of that cause we tend to use most of our power during the day of course.
If we leave for town all day and only have the fridge on, the panels largely take care of things, but if we stay and watch TV etc. then not so much.
We run the generator twice a week to make water, wash clothes etc, one longish run and one shorter run, during those times we get back to 100% SOC. Longish run is when we are making water / washing clothes, washer uses a phenomenal amount of water, but does get them good and clean.
We could get by with less of course, but I believe power is like water or money, if you have more, youíll use it.
If I could have fit more Solar, I would have
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Old 02-06-2018, 08:52   #8
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Re: Solar Watts : Daily AH Consumption

We have a 1000 amp-hour 12v battery bank, and use about 250 amp-hours/day, mostly refrigeration and computers.

Our boat is equipped with 500 watts of solar and a D400 wind generator. In the Eastern Caribbean, this is almost enough to keep our batteries topped up. We get lots of wind around the winter solstice, and lots of solar the rest of the year. We run a Honda generator maybe once every 10-14 days to get to full charge.
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Old 02-06-2018, 09:16   #9
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Thumbs up Re: Solar Watts : Daily AH Consumption

MOJO has 1,000 watts of solar (10 panels, 100 watts each) controlled by an Outback Flexmax80 feeding 10 6v golf cart batteries. We use about 250 amp-hours per day. With the MPPT controller, the panels can supply in excess of 300 a-h per day on sunny days even as far north as Rhode Island, so the genset isn't needed except for hot water and running the water maker for 2 hours every week or so. We run the genset 10 min per day for hot water. Once we left the boat on a mooring for 6 weeks and when we returned the batteries were 100% and we still had ice in the freezer. The panels are going on 16 years old and still seem to put out 100%. Total installation cost was right at $4K. Pre-solar panels, we ran the genset 3-4 hrs per day. At the time diesel was a little over $1/gallon and I calculated that the solar set up would break-even in roughly 4 years. A couple years later the cost of diesel doubled and subsequently doubled again. The panels have paid for themselves many times over in fuel savings, not to mention reduced maintenance costs of the genset. Solar rules!
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Old 02-06-2018, 12:12   #10
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Re: Solar Watts : Daily AH Consumption

1x 100w semi flex plus 2x 32w flex panels strapped to the bimini so 164w max through a 20amp MPPT controller.
Panels lie flat so not at optimum angle but under full sun we see between 7.5 and 9 amps charge. This is probably lower due to the connecting cables possibly being a little under gauge so we lose some voltage but I plan to rectify that in the autumn. At 13v we should see 12.5amps.

2x 140amp-hr 12v sealed Lead Acid batteries (brand new) in parallel to give 280amp-hr capacity.

Average drain is difficult to calculate as it depends on if we are sailing or on anchor. I'd estimate around 50 to 60amp-hr per day which kind of looks right given our last trip out we were on anchor for a couple of days and still at 12.5v on the monitor the 3rd morning.

Fridge has been massively insulated inside and out with closed cell foam and sliver, air bubble insulation. Runs for 10-15mins to keep the bottom 1/3rd between 0 and 6C for between 60 and 90 mins (on average, takes a wee bit longer to chill if we've topped up the beers obviously).

When the 32w flex panels give up the ghost I will replace them with another 100w semi flex panel to give us 200w capacity.

Try to avoid using the diesel when at anchor so we don't disturb the peace so generally rely on the solar to keep us going for as long as possible. As we tend to move around every few days the engine is used to get in and out of marinas/harbours/anchorages so topping up the batteries and giving us a tank of hot water.

Hope that helps

Keiron
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Old 02-06-2018, 15:59   #11
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Re: Solar Watts : Daily AH Consumption

Delphine Outremer has 525 amphere of capacity from 5 fire fly batteries with a approximate daily use of 250 ampheres . 3 reefer units toaster and hair dryer .Charging is done with 920 watts of solar run through 3 victron 100/30 controllers . On float by 2 everyday. Standard altenators on the engines
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Old 02-06-2018, 16:54   #12
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Re: Solar Watts : Daily AH Consumption

I have 700watts solar 6xTrojen T105 plus 200watt wind generator so pretty good setup. My cruising area is North Queensland so plenty of sun and trade winds.
When out ( usually 8 months) I run 2x Weaco 40freezers and BD35 100ltr fridge and all the usual auto pilot when on the move stereo lights fans and 12volt water maker 2hrs every 2 days and washing machine when needed.
We spend lot of time anchored in our fav spots and never need to use gen set or run motor and most days are full batteries around lunch.

With this setup we love leaving a CLEAN FOOTPRINT its great to do this in a world that is just using more and more power. It is possible to do but I guess not every boatie has the funds I have got to this level over quite a few years so slowly slowly gets the result. cheers Jacko
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Old 02-06-2018, 19:45   #13
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Re: Solar Watts : Daily AH Consumption

The generally accepted rule of thumb, which is too simple for an internet forum because people can't argue about it is as follows:

For unshaded, horizontally mounted panels, expect the following to hold (about) true:

(Panel rated Watts) * 0.30 = Amp-Hours/ day @ 12 volts.

There will be lots of variation, but as a design rule of thumb, this works.

One of the problems with any discussion around Amp-Hours is that it is really a very imprecise measure of energy delivered and used. We REALLY should ALWAYS talk about Watt-hours. One Amp-Hour at 12 volts has a lot less energy in it than one Amp-Hour at 14.4 volts, but sailors talk about those as if they were the same.

I have 630 Watts of solar panels installed horizontally, with only occasional shading by a shroud shadow. In early May at the latitude of Fort Lauderdale it delivers between 3.5 and 4.0 kW-Hours per day. That's full un-throttled output. You get less, of course, if the batteries go into absorption mode.
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Old 02-06-2018, 20:50   #14
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Re: Solar Watts : Daily AH Consumption

Quote:
Originally Posted by billknny View Post
...

For unshaded, horizontally mounted panels, expect the following to hold (about) true:

(Panel rated Watts) * 0.30 = Amp-Hours/ day @ 12 volts.

There will be lots of variation, but as a design rule of thumb, this works.
..... .

I have 630 Watts of solar panels installed horizontally, with only occasional shading by a shroud shadow. In early May at the latitude of Fort Lauderdale it delivers between 3.5 and 4.0 kW-Hours per day. That's full un-throttled output. You get less, of course, if the batteries go into absorption mode.
How do reconcile your formula with the 3.5+kw you are seeing?
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Old 03-06-2018, 01:34   #15
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Re: Solar Watts : Daily AH Consumption

Vessel Lagoon 400S2, in the Med in France.

5 x 330Wp solar, nominal 1650Wp
nominal capacity 1000Ah LFP battery, usable / measured 1300Ah
median daily consumption 6-7kWh (500Ah) 450...600Ah
peak solar energy harvested in 24h yet 8.6kWh (640 Ah)

Most of the energy goes to the fridges/freezers (350Ah/day),
and hot water (150Ah/day), 50...150Ah/day for the galley.

Battery capacity good for about 3 days of bad weather. Lowest energy harvested due to bad weather was 4.5kWh (330Ah) by heavy consumption, endet up with -300Ah in the evening.

No other energy sources used yet since switching to solar (last 10 days).

The vessel is on the dry, at lest one panel is always shaded by the boom and boom lift line, peak energy daily around 1100W only. In a better position the system can output up to 1400W (up to 100A charging current) and probably above 10kWh peak / day.
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