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Old 02-10-2023, 02:38 PM   #1
Almost There
 
Join Date: May 2021
Location: Santa Barbara, CA
Posts: 75
Solar idea question

Want to make sure I have this idea right:

1. The wattage on my solar charge controller is reading what the panels are currently bringing in, live. The controller itself, and the inverter, when on, have a constant power draw. Let's make those numbers 0W to make it easier.

So, if I have a device that costs 100W in power, when device is running, my solar charge controller display should read 100W input as well, correct? The panels are pulling 100W to power the device, correct?

2. OR to power device AND keep batteries topped off at 100%, simultaneously, the panels would have to pull 200W total: 100W to device power, and 100W to charging batteries (since they're losing 100W while powering device thru inverter. Essentially, to keep batteries topped off simultaneously, panels have to pull double the power of devices.

3. I guess from a practical stand point, if you match your total device wattage for all devices being used at same time, and then doubled your array wattage, you could theoretically run all devices while keeping batteries topped off, correct? Ex. All devices combined power draw = 1000W while they're all running, so I'd need 2000W of solar to run all devices AND charge battery at same time.

Have to consider time of year, latitude, cloud coverage for panels and inefficiencies from charge controller, inverter, and potential voltage drop with longer wire runs. I'm in Santa Barbara, CA (north of LA), so it's pretty sunshiny for most of the year. I realize in winter, sun is lower in sky, and sun is hitting at angle on almost flat panels that don't adjust. I think the average is 5hrs of good usable sunlight for panels for most places in the US.

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Old 02-10-2023, 04:30 PM   #2
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Join Date: Apr 2020
Location: Northern California (Sacramento)
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Quote:
Originally Posted by Kwest364 View Post
Want to make sure I have this idea right:

1. The wattage on my solar charge controller is reading what the panels are currently bringing in, live. The controller itself, and the inverter, when on, have a constant power draw. Let's make those numbers 0W to make it easier.

So, if I have a device that costs 100W in power, when device is running, my solar charge controller display should read 100W input as well, correct? The panels are pulling 100W to power the device, correct?

2. OR to power device AND keep batteries topped off at 100%, simultaneously, the panels would have to pull 200W total: 100W to device power, and 100W to charging batteries (since they're losing 100W while powering device thru inverter. Essentially, to keep batteries topped off simultaneously, panels have to pull double the power of devices.

3. I guess from a practical stand point, if you match your total device wattage for all devices being used at same time, and then doubled your array wattage, you could theoretically run all devices while keeping batteries topped off, correct? Ex. All devices combined power draw = 1000W while they're all running, so I'd need 2000W of solar to run all devices AND charge battery at same time.

Have to consider time of year, latitude, cloud coverage for panels and inefficiencies from charge controller, inverter, and potential voltage drop with longer wire runs. I'm in Santa Barbara, CA (north of LA), so it's pretty sunshiny for most of the year. I realize in winter, sun is lower in sky, and sun is hitting at angle on almost flat panels that don't adjust. I think the average is 5hrs of good usable sunlight for panels for most places in the US.
The way my Renogy solar charge controller works is it charges the system up to a particular voltage, in my case, 13.4 VDC. If the batteries are topped up and there's a device using 3 amps, if the panels can produce it the charge controller feed the system 3 amps.

If my batteries are down a bit, that's an additional voltage sag, but the charge controller is monitoring voltage and again, if there's sun, the charge controller provides the amps until the voltage gets back up to 13.4. If on top of that the fridge is running, that current draw is added to the demand, sagging voltage, and the charge controller monitors that demand-by seeing the voltage has dropped and upping the current passed to the system to the degree it can, to bring the voltage back up to par.

If the solar system doesn't produce enough amps for the load, the rest of the amps come out of the battery.

If you have no load on the system and the batteries are topped off you won't see any current on the charge controller because there's no demand, again, as determined by voltage-charge controllers measure demand by voltage.
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Old 02-10-2023, 05:29 PM   #3
Skoolie
 
Join Date: Mar 2022
Location: Middle TN
Posts: 155
Year: 2008
Chassis: IC RE (PB30500)
Engine: Maxxforce DT
A) If your solar produces more wattage than the devices use and your battery is at 100% - Power goes from solar to controller to inverter to devices with no excess power generated.

In an example:

Solar is capable of producing 500W
Batteries can hold 1200W and currently charged to 1200W
Devices use 100W

In this case the charge controller would limit solar input to 100W, with all 100W going to the inverter to power devices. The batteries would see no negative or positive wattage.

B) If your solar produces more wattage than the devices use and your battery is at less than 100% - Power goes from solar to controller to inverter to devices, any excess power goes from solar to controller to battery.

In an example:

Solar is capable of producing 500W
Batteries can hold 1200W and currently charged to 600W
Devices use 100W

In this case the charge controller would max solar input at 500W. With 100W going to inverter to power devices and the excess 400W going to the battery until enough time had passed to get the battery back up to 1200W. In this scenario it would take approximately 1.5 hours. After which you would be in example "A".

C) If your solar produces less wattage than the devices use and your battery is above 0% - Power goes from solar to controller to inverter to devices, any deficit in power comes from battery to inverter to devices.

In an example:

Solar is capable of producing 120W (it's winter and cloudy)
Batteries can hold 1200W and currently charged to 1200W
Devices use 500W (more power to heat your rig)

In this case the charge controller would max solar input at 120W, with all 120W going to the inverter to power devices. The batteries would make up the deficit in power consumption by sending 380W to the inverter to power devices until the battery reached 0% (using 0% as voltage cutoff). In this scenario you would last approximately 3hrs and 10minutes. After which you would be in example "D".

D) If your solar produces less wattage than the devices use and your battery is at 0% - System shuts down

In an example:
Solar is capable of producing 120W (it's winter and cloudy)
Batteries can hold 1200W and currently charged to 0W
Devices use 500W (more power to heat your rig)

In this case the charge controller would max solar input at 120W, with all 120W going to the inverter to power devices. The inverter noticing a power deficit and not having the battery wattage as backup would shut down to protect the system. The 120W would then go to the battery to charge it until the battery reached a wattage that the inverter considers "safe". After which you would be in scenario "C".

This cycle of example "C" and "D" would continue until you were to intervene. Either by shutting the inverter off manually or providing a secondary power source that could make up the deficit, such as a generator, which would then put you in example "B".


As you can see there is no "double dipping" of power. There will be some power loss do to inefficiency that is wasted as heat. But that should be about 5% loss depending on your specific charge controller and inverter.

I hope this answers your question and isn't too confusing.
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Old 02-12-2023, 05:32 AM   #4
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Join Date: Apr 2018
Location: League City, TX
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Quote:
Originally Posted by Clouse House View Post
A) If your solar produces more wattage than the devices use and your battery is at 100% - Power goes from solar to controller to inverter to devices with no excess power generated.

In an example:

Solar is capable of producing 500W
Batteries can hold 1200W and currently charged to 1200W
Devices use 100W

In this case the charge controller would limit solar input to 100W, with all 100W going to the inverter to power devices. The batteries would see no negative or positive wattage.

B) If your solar produces more wattage than the devices use and your battery is at less than 100% - Power goes from solar to controller to inverter to devices, any excess power goes from solar to controller to battery.

In an example:

Solar is capable of producing 500W
Batteries can hold 1200W and currently charged to 600W
Devices use 100W

In this case the charge controller would max solar input at 500W. With 100W going to inverter to power devices and the excess 400W going to the battery until enough time had passed to get the battery back up to 1200W. In this scenario it would take approximately 1.5 hours. After which you would be in example "A".

C) If your solar produces less wattage than the devices use and your battery is above 0% - Power goes from solar to controller to inverter to devices, any deficit in power comes from battery to inverter to devices.

In an example:

Solar is capable of producing 120W (it's winter and cloudy)
Batteries can hold 1200W and currently charged to 1200W
Devices use 500W (more power to heat your rig)

In this case the charge controller would max solar input at 120W, with all 120W going to the inverter to power devices. The batteries would make up the deficit in power consumption by sending 380W to the inverter to power devices until the battery reached 0% (using 0% as voltage cutoff). In this scenario you would last approximately 3hrs and 10minutes. After which you would be in example "D".

D) If your solar produces less wattage than the devices use and your battery is at 0% - System shuts down

In an example:
Solar is capable of producing 120W (it's winter and cloudy)
Batteries can hold 1200W and currently charged to 0W
Devices use 500W (more power to heat your rig)

In this case the charge controller would max solar input at 120W, with all 120W going to the inverter to power devices. The inverter noticing a power deficit and not having the battery wattage as backup would shut down to protect the system. The 120W would then go to the battery to charge it until the battery reached a wattage that the inverter considers "safe". After which you would be in scenario "C".

This cycle of example "C" and "D" would continue until you were to intervene. Either by shutting the inverter off manually or providing a secondary power source that could make up the deficit, such as a generator, which would then put you in example "B".


As you can see there is no "double dipping" of power. There will be some power loss do to inefficiency that is wasted as heat. But that should be about 5% loss depending on your specific charge controller and inverter.

I hope this answers your question and isn't too confusing.
Minor correction. Batteries store electricity in units of watt-hours, not watts. Units matter greatly in math and if we don't keep them straight it all gets a bit jumbled.
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