Solar Watts : Daily AH Consumption

[clownfishsydney]

We have 520 watts solar, 720 a/h batteries. We use about 150 a/h a day as we have two freezers and lots of electronics. Copes well so long as we do not have too many overcast days (very old panels so not as good in shade as new ones). This is based on winter in Queensland. In Sydney in summer, never a problem no matter the weather.

[CatNewBee]

A rule of thumb in the Med lattitude is nominal Wp x4 in Wh as daily average output, so 100Wp is good for 400Wh, in Ah divide by your average battery voltage. (400/13 = 30Ah).

This is pretty much what I could measure, 1650 x4 = 6600Wh average, / 13.4V = 500Ah in average. So 0.3 x Wh as average daily output in Ah for a 12V system is a pretty good estimation.

[billknny]

Originally Posted by Paul L

How do reconcile your formula with the 3.5+kw you are seeing?

Paul,

Like this:

3500 Watt-hours/13.5 Volts= 259 Amp-hours

630/259 = 0.4

Yes, it is higher than 0.3, but that’s in May. Much higher sun angle and long days than December. The 0.3 number is an AVERAGE.

[laika]

Originally Posted by boat_alexandra

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.

Setting aside the conspiracy, agreed, a lot of stuff saves and tastes better if not refrigerated. But then you get to cold beer..or the ability to drink a cold glass of water after a hot day in the tropic sun..that's bliss

[Paul L]

Originally Posted by billknny

Paul,

Like this:

3500 Watt-hours/13.5 Volts= 259 Amp-hours

630/259 = 0.4

Yes, it is higher than 0.3, but that’s in May. Much higher sun angle and long days than December. The 0.3 number is an AVERAGE.

Makes sense. May in Ft Lauderdale ought to be pretty close to peak time with the sun fairly north.

[sailormed]

Cruising the med: Installed 650 W in 2 horizontal Sunpower panels, charging 3 x 180 Ah batteries = 540 Ah. Usage is roughly 150-200 Ah daily, fridge and small freezer plus lights, electronics etc for comfort of crew. Batteries are down to 80% charge in the morning. That is 0,2 x 540= 110 Ah and not 150-200 as indicated above. However solar overproduction is feeding the fridges during the day, so the battery depletion is only during night hours, which in summer in the med is much less then 12 hours.
I totally agree with CatNewBee’s post 17 calculations.

[a64pilot]

One thing you have to remember with all these theoretical how many amps can you get from panels is this.
You have to have the banks charge low enough to accept all the power the panels can make. If you do then you’ll never get above 85% to 90% charged, and that is if you hold absorption all day and never let it trip into float.
If you regularly only return to 85% or so SOC, your banks life is considerably shorter, which is fine if that is the plan, just accept more frequent replacements.
For those that are in float by noon, you need to check your specific gravity if you can or resting voltage if you can’t or however your battery manufacturer says to check SOC, cause Im willing to bet that you shouldn’t be in float by noon, or even close to noon, assuming a lead acid bank that is.

[john61ct]

Yes, only applies to lead, while LFP will suck up output at max rate until full, therefore fill up much faster, maximize charge efficiency of whatever charge source.

To the point solar may be irrelevant for many use cases, you could say the need for solar is often driven by that "long tail" requirement of lead banks.

[a64pilot]

What I guess my point was is that more Solar does not always mean more useable power, once you get to where your bank and whatever appliances your running can’t accept what is already being made, having more wont do anything at all.
In my case, excess Solar gives me a longer Solar day, I think maybe as much as a couple of hours more, so maybe go big for a longer charge time, but not for more power, cause there may not be much more power if you say double your panels, maybe.

[john61ct]

On smaller boats, the physical space to reasonably mount panels is much more often the limiting factor, at least for those long-term cruising not practicing extreme minimalism by first-world standards.

[CatNewBee]

Its all about power management.

There is usable power (the capability to produce el. energy) and used power (either consumed or stored in the battery or somwhere else).

Available power equals used power with LFP batteries in BULK charge, ABSORPTION and FLOAT regimes already do not use all available energy.

You can easily leverage all available power by turning on devices when the SOC nears full (e.g. by the battery monitor relay) or based on switching to ABSORPTION (using the relay of the charge controller). You can then convert / store the excess energy in heat (water heater) in fresh water (watermaker) or do other useful things (dish washer, washing machine, dive compressor) even by draining part of the stored energy in the LFP by using this devices, the battery can then later absorb the power again and take what it gets from the sun.

If you not use it or store it somehow, its gone.

[Pete O Static]

My panels total 290 watts.
Located in the Caribbean.
Wired in series.
Controller Victron 100/30 MPPT.
Typically Generate 1.2kwh per day.


Each system is going to yield different results. Using a rule of thumb is very general. Wiring in series vs parallel, PWM vs MPPT controllers, Latitude and shading, there are way too many variables.

With my meager 290 watts I can sit at anchor indefinitely in the Caribbean. It will keep meats frozen in the fridge for weeks. I only start the engine to heat water and I could probably get a 12 volt diverter for the water tank. My lighting is LED, so the fridge and the stereo are my main energy consumers. On passage, totally different story and I need to charge with the engine system to supplement for autopilots, chartplotters, VHF, AIS, etc when sailing through the night.

I never get to "float" by noon and I am always suspect when people say that they do. If you notice, many people will say this, regardless of array size, bank size or energy consumption. If you are charging a 1000 amp/hr bank with 300 watts, while using computers and blenders, no way you should be in float by noon.

Typically, a controller has a setting which once "timed out" will go to float regardless of battery state. Mine was set to a default of 6 hours. Meaning regardless of energy harvested, it would be in float by noon. I removed that restriction by changing the setting to 10 hours. Now I get a full day of Bulk, Absorption and sometimes, finally float at the end of the day.


I verify this with a Balmar Smart Gauge. I am nowhere near back up to 100% by noon and I am willing to bet most are not.

[sailjumanji]

Originally Posted by Pete O Static

My panels total 290 watts.
Located in the Caribbean.
Wired in series.
Controller Victron 100/30 MPPT.
Typically Generate 1.2kwh per day.


Each system is going to yield different results. Using a rule of thumb is very general. Wiring in series vs parallel, PWM vs MPPT controllers, Latitude and shading, there are way too many variables.

With my meager 290 watts I can sit at anchor indefinitely in the Caribbean. It will keep meats frozen in the fridge for weeks. I only start the engine to heat water and I could probably get a 12 volt diverter for the water tank. My lighting is LED, so the fridge and the stereo are my main energy consumers. On passage, totally different story and I need to charge with the engine system to supplement for autopilots, chartplotters, VHF, AIS, etc when sailing through the night.

I never get to "float" by noon and I am always suspect when people say that they do. If you notice, many people will say this, regardless of array size, bank size or energy consumption. If you are charging a 1000 amp/hr bank with 300 watts, while using computers and blenders, no way you should be in float by noon.

Typically, a controller has a setting which once "timed out" will go to float regardless of battery state. Mine was set to a default of 6 hours. Meaning regardless of energy harvested, it would be in float by noon. I removed that restriction by changing the setting to 10 hours. Now I get a full day of Bulk, Absorption and sometimes, finally float at the end of the day.


I verify this with a Balmar Smart Gauge. I am nowhere near back up to 100% by noon and I am willing to bet most are not.

If it's sunny, we are at float by noon. If you are only down by 25 amp-hrs overnight, 325 amp-hr battery bank, and 240 watts solar panels, that's not tough to do. The controller counts amp-hrs both ways. When it goes into float, the counter is showing 100%.

If it's cloudy morning, it might be closer to 1-2 pm for full charge. If really sunny in the afternoon, we turn on watermaker and covers it's 8 amps with solar, and the batteries are still on float and fully charged. Take advantage of the higher voltage (13.8 volts) yields more product.

Hot water is propane. Lights led. No computer. No inverter. No blender. Although freezer used to make ice cubes and fridge keeps beer cold. Rum on ice is most efficient.

[a64pilot]

You have a fridge and freezer etc and only draw 2.5 amps?
I’m assuming 10 hours of no Solar, which isn’t much.
Also I’m sure you know, but you have to return 110% or so of the power you use to be fully charged. That number is not set in stone it’s plus or minus a little.

[sailjumanji]

Originally Posted by a64pilot

You have a fridge and freezer etc and only draw 2.5 amps?

It's a combo unit with the cold plate between, in counter style. When it kicks on it draws 5 amps. So overnight it is probably just cooling half the time, and dormant the other half. Yeah, so I guess it averages 2.5 amps.