Calculation of Solar Output from PV

[john61ct]

The AH counter included in some BMs only count relative to the bank.

The ones included in some SCs only count panel output.

Shunts can be placed at any point, to measure energy used by a holding plate fridge / freezer for example.

In which case no distinction is made between energy provided from the panels in the daytime vs that coming from bank storage.

I'm not being argumentative or nit-picky here, precise discussion is required to avoid confusion.

[StuM]

Originally Posted by valhalla360

If the batteries won't absorb what the panels put out, your panel estimate doesn't mean much. It's very much related.

It does if you also have loads such as refrigeration, radio, instruments, autopilot etc in the afternoon. Having enough solar to cover those will mean you can start the evening with full batteries.

[john61ct]

Originally Posted by sailorboy1

why do these always become the same tic for tat battles over small details

Just accept that boat electrical power storage and generation doesn't care about theory or perfect and go about making it work for you. I get amazed people will spend $1000+ on solar and batteries to save $1-2/day on diesel costs. Just to find out they are going to motor or run the generator etc. anyway.

For many an outboard is the only consumer of fossil fuels aboard.

And more may have higher capacity but prefer to use it as little as possible.

Dino juice will never get the bank full anyway, unless you're burning it literally all day long.

These discussions can be helpful for those learning in a wide variety of contexts, not just those similar to yours.

If the details don't interest you, just ignore those posts / threads.

[newhaul]

Originally Posted by a64pilot

This is why I often never see the 1/3 rule. Yes my panels will supply it, but in order to fully recharge my bank, the acceptance rate of the bank is lower than what the panels can make towards the end of the day. I cheat, I will run a generator to kick start things in the morning.

I’d say that if your day to day limit on power production is what the panels can make, then it’s likely you are short cycling your bank.

It’s just reality, if you are taking every Watt your panels make and can put that in your bank, then you don’t have enough Solar or are using too much power, or just accept a shorter life out of your bank, which may be the least expensive and most logical thing to do depending on situation.

Just don’t be upset if your not making the 1/3 rule in power, watch your panel voltage, if is often at the max voltage, it’s likely that your battery acceptance is limiting power the bank can absorb, cause remember the amp counters don’t count what the panels can make, they only count what the bank can accept.

That's why I like my controller it does it all .
It shows ah in and via the load circuit ( up to 30 amp draw) it shows ah out.
It shows battery voltage, panel output voltage , also shows instantaneous amps out of he panels. And amp draw via the load circuit. All at the push of a button.

[newhaul]

Originally Posted by john61ct

The AH counter included in some BMs only count relative to the bank.

The ones included in some SCs only count panel output.

Shunts can be placed at any point, to measure energy used by a holding plate fridge / freezer for example.

In which case no distinction is made between energy provided from the panels in the daytime vs that coming from bank storage.

I'm not being argumentative or nit-picky here, precise discussion is required to avoid confusion.

That's why I chose / like the controller I have . It shows it all at the push of a button.
Ah in ah out , panel voltage , battery voltage, also shows instantaneous amps in and out .
( Amps and ah out are running thru the 30 amp load circuit on the controller)
even battery temperature if you use it/ need it for compensation charging of Fla/ agm.

[john61ct]

Sure more information at a given charge source helps.

Those with load devices not powered by load outputs, or a mix of different charge sources, will need a bank-centered monitor to get the full picture.

A central BM that "controls the controllers" is to me the ideal.

[noelex 77]

Originally Posted by valhalla360

If you are the more typical between the 45th parallels, the rule of thumb works pretty good.

I am not so sure. In Melbourne, my hometown, from the official figures you can expect almost four times the output from solar panels in the summer months compared to the winter months. Go further north in Australia and the output in winter is over three times the output in Melbourne. These are just seasonal and location differences. Then there are also shorter term variations caused by periods of atypical weather. As well, there are considerable differences in how the panels are installed on boats. Some are subject to a great deal of shade, others less so, some can be angled, some are fixed.

The ⅓ rule is good average but realise if you want to apply this rule the standard deviation is substantial.

[a64pilot]

The 1/3 rule works and is I think sort of meant for boats cruising the Caribbean, mostly during Winter.

[noelex 77]

Originally Posted by a64pilot

I think sort of meant for boats cruising the Caribbean, mostly during Winter.

Well, I am almost 4000 nm from the Caribbean and it’s summer .

[john61ct]

Just like a stopped clock, any rule of thumb works at least once in a while 8-)

[StuM]

Originally Posted by john61ct

Just like a stopped clock, any rule of thumb works at least once in a while 8-)

Any rule of thumb works reasonably well on average.
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As long as your average has a large enough sample size and is averaged over a large enough period (like a year in this case )

[a64pilot]

Originally Posted by noelex 77

Well, I am almost 4000 nm from the Caribbean and it’s summer .

I know, and if your near where I think you are you have near total sunlight. Go a little further North and it never sets, just moves around.

I was only trying to point out that of course due to time of year and how far from the equator you are, there are huge variations in the amount of sunlight you get, and that these general rules are often meant for the average cruiser, who is likely pretty close to the equator one side or the other.
I assume where you are the air temp is quite comfortable, but the water not so much?

[StuM]

Originally Posted by a64pilot

I know, and if your near where I think you are you have near total sunlight. Go a little further North and it never sets, just moves around.

I was only trying to point out that of course due to time of year and how far from the equator you are, there are huge variations in the amount of sunlight you get, and that these general rules are often meant for the average cruiser, who is likely pretty close to the equator one side or the other.
I assume where you are the air temp is quite comfortable, but the water not so much?

An interesting chart:



From Insolation ( input of solar energy) as a Function of Latitude and Season

"The blue line is for June 21, the Northern Hemisphere summer solstice, and the green line is for the Southern Hemisphere summer solstice, December 21. The red line is for insolation for both equinoxes, March 21 and September 21. Some of the notable facts of these insolation values is that the North Pole at the Northern Hemisphere summer solstice gets more solar energy on that day than any other location on Earth. At that time it is getting significantly more than locations on the equator with their twelve hour days are getting. Of course at that time points on the equator are effectively at a latitude of 23.5° South. The point on Earth that gets the highest one-day energy input from the Sun is the South Pole."

[rgleason]

Thank you.

Summer Solstice June 21, longest day, 41deg lat isolation is about 20% above the Equator.
Equinox Sept 21, (day/night are equal), 41deg lat insolation is about 10% less than Equator.

[rgleason]

Perhaps it is useful to analyze the system over a 24 hr period to plan loads and source timings. For example:

Engine/Alternator operation: Run large loads such as Refrigerators with evaporators on high, and perhaps SSB, watermakers, etc.
Solar after 100% SOC (if it happens): Run useful loads.

My experience with refrigeration and a small alternator and battery bank, is that periodic engine/alternator time is a very useful time to "catch up" while charging the batteries.