As I am brand new in solar design, I have an important question:
My expected system is at 12 volts to provide 4 CCTV cameras, a 12volt switch, and an access point.
2 400watt Solar panels @ 24volts (Series or Parallel?)
1 Victron MPPT (Size to be determined after hearing advice here)
Cerbo GX
Smart Shunt
2 12volt 100ah batteries in parallel
PV isolator
12 volt fuse box for device distribution
ANL fuse between MPPT and battery
My question is:
Can the Victron MPPT set the output current to the battery?
If the PV is in series and sends 800 wats, 48 volts and 16amps to the MPPT
If the PV is in parallel and sends 400 Watts, 24 volts and 33amps to the MPPT
What happens to the output current to the battery? Is it controllable by the MPPT or is the current higher when you drop the output voltage to 12 volts. If in series having an output current of 66 amps (800watts/12volts =66.66 amps).
My 12volt devices will be on 24/7 and I calculate them drawing approximately 5 amps.
My goal is to get the correct size MPPT. Any help will be appreciated.
There is a handy calculator here. You could probably find your exact panels in the database drop down list. It will recommend a model for you.
Basic sizing is wattage ÷ battery voltage= amperage needed.
You have that nailed. The real question is do you want it in one controller or two smaller ones?
And then the second figure is your VOC + headroom for colder Temps.
On victron mppts the firt number is the max voltage open circuit allowed at coldest temperatures. (Panel voltage rises the colder it gets there is a co efficient figure for it)
The second figure is the max amos the mppt will output.
You will probably need a 150/60 (150v open circuit max and 60amps output to the battery if the panels are inoefect conditions.)
Your assumed 24h load of 5A in a 12V system means roughly 1440Wh (12V x 5A x 24h) energy usage daily.
Your planned batteries can store 2400Wh (12V x 200Ah).
This means your system needs a full charge every day. It can not continue to work for two days on battery power alone. Depending on where you are and how the weather is this could work, but for most places it wont. Or it means that after a day of bad weather, the system will shutdown. Whether thats acceptable to you ar not is up to you.
Based on that, your PV also needs to bring in the same 1440Wh daily at the bare minimum. By using the MPPT calculator that LX linked, you can also see an energy forecast graph. For 800W of PV, at the default Victron HQ location Almere, your system should work 24/7 between March and September. However between September and March, the forecasted daily energy is not enough to recharge what was used. It will not stay running 24h a day. Also here, you need to decide whether thats acceptable.
Raising the total PV power to 1600W would not even be enough to let the system run 24/7/365, at least according to the forecast at Almere. So before deciding on an MPPT you should decide on whether these conditions are what you are looking for.
This system will be in Florida with no shade…MPPT Wizard says a minimum of 2.5kwh a day. Sounds like I possibly need to upgrade to larger batteries or add a third..
Yeah ok, that changes things a bit. 800W will likely be enough, but yes, reconsider the battery capacity.
A point that i possibly oversimplified a bit too much is how much of the total battery capacity you can actually use. With a LiFePo you can use about 80% regularly without cutting into longevity too much. When using lead acid you should not use more than 50% on a regular basis.