Confused on solar specs \ Grape Solar

[dziedzicmj]

I think that you should not try using complex math to solve that problem. Use the calculation given above (Ipmax times 3-5 h/day). Anything else would probably lead you to a disappointment, because you won`t get the charging capacity you need. If you invest in an MPPT controller, your effectiveness of the system would be better. The rest is a bonus.

 

[Skipper]

The end is that I'm calculating requirements for long range coastal cruising with no shorepower, with the boat's estimated consumption as equipped, during both sailing and mooring, and estimated durations of each.

Edit: Using amp hours as the basis.

 

[Skipper]

So with all this info, I'm coming up with a guess of about 31.3 amp hours per day.

4.5 hours (So Cal) times max rating of 6.95 amps, on the 100 watt panel @ MPPT- controlled voltage of 14.4.

So if I'm only consuming about 20 amp hours per day, which is what I've calculated based on equipment ratings and estimated usage periods, the 100 watt panel should be sufficient. eh.....yes? :-D

This has been fun to analyze, and solid info for building an appropriate solution.

 

[Stu Jackson]

sorry, but I'm way past 11th grade.
I understand the math. It's solar and controllers I'm fuzzy on.

Wanted to know what the true specs were that might be getting to the batteries, given a standard of operational protocol for mppt controllers and the specific panel specs.

It can be a complex question apparently. But I was hoping for a simple answer. That is: does the controller change other specs like a power supply/transformer, or is it only voltage. --couldn't find those specific specs-- If it is only voltage, then I can assume that current at 12v for 100 watts is 8.3 amps, and make further calculations based on that. The calculations will be analyzed with your and others' expert additional variables.

The end is that I'm calculating requirements for long range coastal cruising with no shorepower, with the boat's estimated consumption as equipped, during both sailing and mooring, and estimated durations of each.

I'd like to get a flexible panel for the Bimini top, with no other used space. LED lights, low draw G76csx GPS. No refrig or air cond, nor any other high draw equipment, with the AP and maybe VHF/AIS being the most.

But I was hoping for a simple answer. That is: does the controller change other specs like a power supply/transformer, or is it only voltage. --couldn't find those specific specs-- If it is only voltage, then I can assume that current at 12v for 100 watts is 8.3 amps, and make further calculations based on that. The calculations will be analyzed with your and others' expert additional variables.

That's where we need to avoid being ships passing in the night and talking past each other.

Solar panel to controller to battery bank.

Solar outputs variable voltage at variable current (pressure and flow, volts times amps = watts). Charging voltage to controller gets high voltage depending on the panel selection.

Controller regulates voltage to maintain an output voltage that is limited to avoid overcharging the bank. Your controller manual explains how they do that.

Battery acceptance then takes over.

If your panel output thru the controller in ah/day exceeds your energy budget, then you're cool.

The "shortcuts" offered by one of the skippers is simply a way to get you int the RANGE of ah/day you can get. Remember my last post?

So you'll have maybe two or three DIFFERENT numbers for potential input from your panels.

Then reality hits. If you have a coulomb counter monitor wired properly, you'll actually be able to see how much. If you only have a Smart Gauge, you'll know sooner or later if the SOC goes UP after a few days.

Like the rest of life, once implemented the hardware will perform within a RANGE of inputs based on reality.

Good luck, sounds like a wonderful idea and from everything I know from extensive reading you're on the right track.

Can you provide pictures at 11?!?

 

[Skipper]

But I was hoping for a simple answer. That is: does the controller change other specs like a power supply/transformer, or is it only voltage. --couldn't find those specific specs-- If it is only voltage, then I can assume that current at 12v for 100 watts is 8.3 amps, and make further calculations based on that. The calculations will be analyzed with your and others' expert additional variables. That's where we need to avoid being ships passing in the night and talking past each other. Solar panel to controller to battery bank. Solar outputs variable voltage at variable current (pressure and flow, volts times amps = watts). Charging voltage to controller gets high voltage depending on the panel selection. Controller regulates voltage to maintain an output voltage that is limited to avoid overcharging the bank. Your controller manual explains how they do that. Battery acceptance then takes over. If your panel output thru the controller in ah/day exceeds your energy budget, then you're cool. The "shortcuts" offered by one of the skippers is simply a way to get you int the RANGE of ah/day you can get. Remember my last post? So you'll have maybe two or three DIFFERENT numbers for potential input from your panels. Then reality hits. If you have a coulomb counter monitor wired properly, you'll actually be able to see how much. If you only have a Smart Gauge, you'll know sooner or later if the SOC goes UP after a few days. Like the rest of life, once implemented the hardware will perform within a RANGE of inputs based on reality. Good luck, sounds like a wonderful idea and from everything I know from extensive reading you're on the right track. Can you provide pictures at 11?!?

Great, thanks. I can now picture the scenarios in my head.

Between you and Maine and gang, I now have enough understanding to advise others, and boast of my solar electrical prowess.
Ok I won't be doing that.

I'll put a picture but it will be awhile, will have to wait for the orders to arrive and then set it up.

 

[centerline]

sorry, but I'm way past 11th grade.
I understand the math. It's solar and controllers I'm fuzzy on.

Wanted to know what the true specs were that might be getting to the batteries, given a standard of operational protocol for mppt controllers and the specific panel specs. .

To answer this question, take the output of the panel, as stated on the spec tag, multiply it by 10hrs, then divide by 2... this will give you a good fair base number to design your system with....
some days you will get more, and some days you will get less, but it will give a good avarage that you will be very happy with.

When designing solar power grids, its not a fair option to deal with maximums and minimums, but the only fair way to do it, for yourself and the equipment, it deal with averages.
Because of the variables, which are constantly present.

Whats getting to the batteries varies thruout the day

The only maximum you need to know is what the panel is rated for, and sometimes these numbers fall short of real world measure, bucause they are based on perfect lab conditions.

And as the panel ages, it drops off a little of its potential, so for longevity and to maximize your your design efforts, use the formula that has proven to be simple and effective and without disappointments after the trial runs..

 

[keys please]

Skip
i was just on the hook (apr may) for about 6 weeks in the keys..... fridge was on 24/7 (just gotta keep that beer cold) had no access to shore power.... i have two go power 100 watt flex panals.... no matter what i had running the batts were fully charged by 2:30 every day excepting maybe two very rainy cloudy days.... i really like solar.... any travel day all instruments were on... radio, gps, wind, auto pilot, depth... no problems.... i have a good controller and also good battery monitor... both panels on top of bimini..... safe passage
brian

 

[Chief RA]

Good post Brian. Glad to hear they worked out well for you. I have had similiar results for a pair of 80w fixed panels. My Isotherm 2.3cf only draws .7a avg per hr, and yes, the beer is cold! Chief

 

[gettinthere]

Brian

Did you 'tune' your battery monitor to make sure it wasnt lying to you? After reading other threads here on sbo, I made changes to the settings of my victron. I was getting to 100% pretty quickly in the day beforehand. Now I run a low in the 85% range and tops of around 95 to 97% most every day. Several factory defaults really throw off the readings.

 

[Skipper]

Skip i was just on the hook (apr may) for about 6 weeks in the keys..... fridge was on 24/7 (just gotta keep that beer cold) had no access to shore power.... i have two go power 100 watt flex panals.... no matter what i had running the batts were fully charged by 2:30 every day excepting maybe two very rainy cloudy days.... i really like solar.... any travel day all instruments were on... radio, gps, wind, auto pilot, depth... no problems.... i have a good controller and also good battery monitor... both panels on top of bimini..... safe passage brian

Thanks, Brian.
Now I want refrigeration.
Crap, now I need a 2nd panel.
:-D

 

[jlp0217]

A PWM controller does just that, takes whatever voltage the SC is producing and turns it on and off rapidly to create a 14.4 volt output. If you measured the voltage at the cell it would probably be between the Max Power voltage and Open Circuit voltage. An MPPT controller measures the Max Power voltage of the cell at any given time and then adjusts the load on the cell to keep the cell voltage at that level and converts that voltage to 14.4 volts amplifying the current, which recovers most of the loss of a PWM controller in its Off time.