Low Solar Power Production?

Cortttt · September 2021

I recently installed an EMC-1 Morningstar Converter to measure how much solar power is coming into the battery. I have 510 watts of solar polar on the roof of a van. The panels are lying flat on the van (not tilt enabled). The van is often in the sunlight most of the day....

The usual max array voltage is about 20.5; the average max output watt hours varies widely but is probably around 240/250.

The average amp-hours per day received is 72.

That seems low to me ?????

Photowhit · September 2021

So a lot of info is missing, I'll assume a 12 volt system.

The EMC-1 Morningstar is just a data and communication device. So you are getting data from it...

Not sure what your array looks like, but perhaps 2 panels in series feeding an MPPT type controller?

To start, Let's talk about losses;

Solar panels rated vs actual output.

Solar panels have a name plate rating. these ratings are based on Standard Test Conditions (STC). In the real world they will produce less. Some now come with Normal Operating Cell Temperature values (NOCT) They are generally about 75% of the name plate.

These means you can expect about 75 watts out of a 100 watt panel. This is what you can expect when the panels are warm/hot. You may approach Standard Test Conditions(STC), in very cold fall days with good direct sun, but it will be rare.

Here are a couple examples of STC vs NOCT provided by solar companies;

Image: https://us.v-cdn.net/6024911/uploads/editor/rw/qzvcy5fnis5l.jpg

Now lets talk about angle of the panel to the sun, you can really only expect max production in the 2 hours either side of solar noon for panels angled correctly to the sun. Any off any more than 15 degrees will result in some loss to the corrected expected output.

Charging a battery, we don't know what battery chemistry you are using, but the amps across the shunt (perhaps the data collection device is shunt based?) are affected by charging/system voltage. So if charging at 14.8 volts less current will be passing the shunt than the system voltage (12 volts). This uses the basic equation amps x volts = watts.

...and of course, does your system reach fully charged? at that point the charge controller shuts down the array and you add nothing to the battery bank which is already full. Even when the battery bank reaches absorb, the batteries reduce the amount of current they will accept.

...and system loads? If this is a shunt based monitor, loads that are running while you are charging reduce the amount of current passing through the shut to the battery bank. So if you are running 100 watts of box fans and laptop, you shuld deduct that for current that coould charge a battery.

Here's some basic info on battery charging for lead acid flooded batteries;

The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

BULK;

First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

ABSORB;

Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries.

The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

FLOAT;

Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage

Cortttt · September 2021

Thanks for all the info. Before I try to digest it - here's some more info. - 3 approx 170-watt panels in series feeding a 60-amp Morningstar MPPT controller. 12 volt system.

I had seen estimates on the internet of a 500 watt system delivering about twice what I'm getting.

The EMC-1 attaches to the controller and measures the power coming into the battery..Does not so far as I know measure anything coming out of the battery

I noticed that when I brought another 200 watt panel along and added it (on the side of the van) that it would boost the watts and amps the battery was receiving in the morning but not when the sun was high - the battery couldn't accept more. Does that mean that with 2 battery I could make better use of the solar I'm getting?

It's a 100 amp Firefly battery by the way.

I did get a shunt-based VIctron battery monitor and am trying to figure out how to read it (and set it properly) so I can read power coming out as well.

Photowhit · September 2021

Cortttt said:
The EMC-1 attaches to the controller and measures the power coming into the battery..Does not so far as I know measure anything coming out of the battery

At the controller, it CAN NOT measure the current going into the battery! Only measuring the current at the connection to the battery with a shunt can that be done. It can measure the power coming into the system, but energy used by the inverter or DC drains would have to be subtracted from the power entering the system.

Once the battery, is a flooded lead acid, reaches 80% full the battery will accept less current, until the charge controller 'times out' or reaches a minimal flow of current. Then the charge controller will turn off power coming into the system down to a trickle.

Cortttt said:

I had seen estimates on the internet of a 500 watt system delivering about twice what I'm getting.

Off grid solar MUST have lots of losses, so the system can remain healthy. It needs to be able to come to a full charge 2-3 times a week.

Cortttt said:
I noticed that when I brought another 200 watt panel along and added it (on the side of the van) that it would boost the watts and amps the battery was receiving in the morning but not when the sun was high - the battery couldn't accept more. Does that mean that with 2 battery I could make better use of the solar I'm getting?

I really don't know how you use your system, or where in the world you live. We use as a general rule what the battery manufacturers suggest. Being able to charge a battery bank at 10-13% of it's capacity. So a 100 amp 12 volt battery that would be 10-13 amps. Since you will be tied to poor orientation of the array "flat mounted on your van", you might bump that up a bit. "Firefly" is NOT a type of battery and I don't feel like looking it up to see what type of battery it is. With 500 watts of array, you should be able to provide roughly a max of 300 watts (derating for NOCT values and poor orientation) Or about 300/15 volts charging= 20 amps max. That should be all your battery would want in general.Cortttt said:

The average amp-hours per day received is 72.

Indeed 72 amp hours in a day is a huge amount for a 100 amp battery. Most healthy systems are designed to use the top 20% or 20 amps and have the rest in reserve for over cast days. I can't see your loads during the day, so I don't know how much of that is consumption, but it sounds like an under sized system for the amount of charging it's doing.

Cortttt · September 2021

Right the EMC-1 measures the power available to go into the battery - thanks...

The Firefly is an unusual battery type - it's a carbon-foam battery that can be drained to low levels and returned to charge.

Firefly International Energy (fireflyenergy.com)

Firefly states that "Firefly carbon foam design resists sulfation and corrosion (two of the primary causes of failure in lead-acid batteries), while dramatically increasing the surface area within the battery, resulting in greater energy capacity, faster recharges,and deeper discharge capability."

This seems to be true as I have at times drained the battery to very low levels only to see it rebound.

I thought the battery pack might be undersized. as I see other systems with less solar and more batteries. It was what was recommended to me and tt's worked well for about six years but the battery is clearly dying now. I will go to Lithium next. I have a Victron battery monitor and am trying to figure out the load...

The system is being used constantly to power an Engel fridge (actually 2 over the past year), a computer, cell phone and sometimes a small CD player . It was at approximately 300 watts of solar power and then I added another Engel fridge and added another panel over the past year.

I've been pretty clueless, though, as to the proper sizing of this system.. As I shift to new batteries I'm finally trying to learn how much is coming in and how much is going out and get that right.

Low Solar Power Production?

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