So, I have some 540w solar panels, a 1500 w inverter and a 100 amp 12 volt lithium battery with a .5C charge rating. I want to run my swamp cooler from it this summer and it takes about 400 w. What I'm wondering is, what should the specs of the mppt charge controller be and will one of these panels be enough or should I use two? I'll put a picture of the solar panel specs below.
How do you use large panels for a smaller system?
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BentleyJ
Solar Wizard
2 panels definitely because during the day 1 panel worth of power is going to be consumed by the cooler and the other panel can charge the battery if it had been discharged from running the cooler the night before.
As far a charge controller something like a Victron 150/45 but this is only going to output 650W at 12V. Would be much better to go with a 24V inverter.
Before purchasing any more equipment, it would be a good idea to test the 1500W inverter and make sure it can start up the induction motor in the cooler as this will require considerably more inrush than the 400 running Watts to spin up.
As far a charge controller something like a Victron 150/45 but this is only going to output 650W at 12V. Would be much better to go with a 24V inverter.
Before purchasing any more equipment, it would be a good idea to test the 1500W inverter and make sure it can start up the induction motor in the cooler as this will require considerably more inrush than the 400 running Watts to spin up.
Q-Dog
¯\_(ツ)_/¯
Is that battery's .5C charging rate the maximum rate or the recommended rate?
I feel like you will need a little bit more than one battery.
With that battery alone. You'll be lucky to get three hours of use out of it. With the inefficiencies of the inverters and losses in cables, connections, etc your probably looking at two hours or less. But, it is a good buffer for the solar and production fluctuations
Solar rarely produce their rated output unless under ideal conditions. As they heat up in the sun they drop in output. Two panels might keep up but three or four would likely do much better
Maybe start with two in series and use a victron 150/100 or something equivalent. If it proves to not keep up, add two more in parallel / series to double the wattage. Then if you find you want to keep running the cooler after the sun is too low to provide enough energy then up your battery count
Solar rarely produce their rated output unless under ideal conditions. As they heat up in the sun they drop in output. Two panels might keep up but three or four would likely do much better
Maybe start with two in series and use a victron 150/100 or something equivalent. If it proves to not keep up, add two more in parallel / series to double the wattage. Then if you find you want to keep running the cooler after the sun is too low to provide enough energy then up your battery count
The charge rate is what they recommend. It's what's in the manual.
Q-Dog
¯\_(ツ)_/¯
Very good. My battery lists a different rate for maximum charge and recommended charge.
BentleyJ
Solar Wizard
If the correct charge controller is chosen and set up properly, it cannot exceed its rated amperage output. Realistically a 100Ah LFP battery should be charged a little slower than 50A IMO. Something like 35A at 12V which is 420W. The charge controller data sheet will list the maximum output at 12V.
Do you have one that you would suggest?
BentleyJ
Solar Wizard
Yes, in the first response to your question yesterday, I mentioned the Victron 150/45. The 150/35 would also work but is limited to 500W at 12V while the 150/45 is good for 650W.
So, would the rest of the 1080w be sent to the swamp cooler or, would the solar charger only be putting out 500 watts total?
BentleyJ
Solar Wizard
Solar panels do not normally output their full STC rating except under certain rare conditions. Most PV datasheets give NMOT values for Watts, Amps and Volts. This is what can be expected at normal operating temp. Unfortunately, the pic of the sticker posted in your OP does not show these values.
Figure about 800W to 850W is what to expect as normal output. That said the 150/45 would be a limiting factor. The next step up would be Victron 150/60 would output up to 860W at 12V. It will cost a bit more but probably would be a better choice to maximize usage of the panels.
It seems like I either have to add another battery to spread out the charging amperage going to the pair or I have to buy an expensive charge controller like the victron that you can set a current limit going to the battery. I hope that makes sense. Are there other brands that are less expensive that you can set the current rate going to the battery? I can't set up the whole 20 panel array of these 540 watt panels right now because I need to move some shit around on my property to make room first. I just don't want to buy something expensive and then, buy more shit for the actual 10 or 12 kilowatt system that I want to have, eventually.
BentleyJ
Solar Wizard
Here is a less expensive charge controller.
Not sure of the specifications on this model, would be a good idea to look up the datasheet or manual before purchasing. A second battery would help quite a bit as they could take twice the current and you wouldn't have to worry about throttling the charge controller when the cooler wasn't on taking some of the power.
As you no doubt discovered, 12V systems are severely limited by Amperage. This is why we recommend 24V for medium sized systems and 48V for larger systems.
Not sure of the specifications on this model, would be a good idea to look up the datasheet or manual before purchasing. A second battery would help quite a bit as they could take twice the current and you wouldn't have to worry about throttling the charge controller when the cooler wasn't on taking some of the power.
As you no doubt discovered, 12V systems are severely limited by Amperage. This is why we recommend 24V for medium sized systems and 48V for larger systems.
Q-Dog
¯\_(ツ)_/¯
What you want to do is not possible using only a charge controller. There needs to be something in the system that can distinguish between power going to the battery and power going to the loads.
With a Victron system you CAN limit charging to a battery while reserving the full output of a charge controller to run loads. That would require a GX device like a Cerbo or a Raspberry Pi running Venus OS, and enabling DVCC with the appropriate settings. I think a smart shunt or battery monitor would also be required.
With a Victron system you CAN limit charging to a battery while reserving the full output of a charge controller to run loads. That would require a GX device like a Cerbo or a Raspberry Pi running Venus OS, and enabling DVCC with the appropriate settings. I think a smart shunt or battery monitor would also be required.
I guess I'm still confused. Were you saying that this would work only if I went up to a 24 volt system or were you saying that I could run two 12 volt batteries in parallel to make the amperage from the solar charger split between the two batteries and still run two 540 watt panels? The specs of all the 60 amp charge controllers I see don't show that they would take enough Watts from the solar panels? They are all Limited at somewhere around 700 or 750 Watts PV input.
mikefitz
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You have 540 watt panels, typical actual output maybe 400 watts . You have a 400 watts continious power needed for the cooler. You have a single 12v battery, maximum charge 50 amps. Using a 1500 watt 12v inverter.
Connect two panels to a 60 amp MPPT controller , under very rare solar conditions You may get more than 400 watts from each panel but the controller will just limit at 60 amps. The inverter will pull perhaps 35 amps, leaving 25 amps for the battery charge current.
To ensure enough solar energy add a further panel, all quality MPPT controllers can be overpaneled.
If by some chance the battery is unloaded and receives the full 60 amps it will most likely, happly accept the charge, worst case Is the BMS shutting down the charge path.
I know where I can buy this mppt only 50 bucks. It says it can only take 100 volt input. When I measure one of these panels even on a cloudy day, it can put out 51 volts or more. Could I still use this mppt for at least two of the panels?
mikefitz
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Use panels in parallel.
Sorry for being such a scaredy cat but, did you look at the specs I showed? It doesn't say what it's input current is. Are we just saying the input current is 60 amps because it is a 60 amp mppt? If that's true, could I connect three of the panels to it as long as they were in parallel or is that just going Way Beyond the rated 720 Watts that the mppt specs say it can handle with a 12 volt battery?
BentleyJ
Solar Wizard
You have to do some math. Power IN = Power Out - Losses
The charge controller can only supply 720W when charging a 12V battery. (assuming the charge voltage is actually 14V, that is about 51A to the battery)
2 panels connected in parallel will supply 40V x 26A x.8 = 830W
So with 2 panels in series the charge controller is slightly over paneled for cloudy days. A 3rd panel will do nothing except in very poor solar conditions. However, with a low cost controller like that I would be cautious not to over panel too much.
The charge controller can only supply 720W when charging a 12V battery. (assuming the charge voltage is actually 14V, that is about 51A to the battery)
2 panels connected in parallel will supply 40V x 26A x.8 = 830W
So with 2 panels in series the charge controller is slightly over paneled for cloudy days. A 3rd panel will do nothing except in very poor solar conditions. However, with a low cost controller like that I would be cautious not to over panel too much.
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I'm sorry but, you said in series. Did you mean in parallel?
mikefitz
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It's not specified for most MPPT but it's assumed not to be greater than output current limit.
You have a 100 volt limit so the 51 volt panels need to be In parallel. Two panels is 26 amps maximum, 3 panels is 39 amps maximum. The mppt will convert panel power up to a maximum of 60 amps and what ever charge voltage the battery takes. At the typical maximum charge voltage of a lithium battery, 14.2 volts that's 14.2 x 60 = 825 watts Into the battery and load.
All mppt controllers can be over panelled, its the controller that determines what power to take from the panels.
If there is a real 720 watt limit, which I doubt , on this controller, then its not a 60 amp controller. I suspect someone did the (60 amps times 12 volts = 720 watts calculation.
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BentleyJ
Solar Wizard
Yes, sorry parallel. Post above corrected.
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