Desperate for sound advise. I have 8-375 watt, 48 volt, 9.47 amps solar panels. A 600 AH Fortune lifepo4 battery bank. I plan to get a charge controller from overkill solar. I have a 3000 watt inverter. I don't want to have to buy a monster solar charge controller. My existing.ambulance system is 12 volt. How can I configure things so I have minimum amount of power loss, expense and run my 12 volt system?
Sizing a solar charge controller.
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Hedges
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You have 3000W of panels, so 250A into a 12V battery.
First question, what is the maximum charge rate your battery can accept? too much current would cook it.
For a 600 Ah battery, 250A would be 0.42C, but I don't know the specs for your battery.
Of course the BMS would have to accept the current as well.
If the panels are oriented in multiple directions, to spread power over the day, you can probably knock the peak down to 2000W for a smaller charge controller and lower current into battery.
I'm seeing BMS at Overkill, but not charge controllers.
Midnight has a charge controller than can put out 96A. Would take 2 or 3 of those
If your system was 24V or higher, then the current would be lower.
Charging the battery 100% is 2.5 hours from PV seems excessively fast to me. I would rather spread it out of 5 to 8 hours. The trick is how to use PV generated power as it is being made to feed your inverter, but only put the desired amount in the batteries. Some inverters & chargers can take care of that (e.g. Victron) but you already have an inverter.
First question, what is the maximum charge rate your battery can accept? too much current would cook it.
For a 600 Ah battery, 250A would be 0.42C, but I don't know the specs for your battery.
Of course the BMS would have to accept the current as well.
If the panels are oriented in multiple directions, to spread power over the day, you can probably knock the peak down to 2000W for a smaller charge controller and lower current into battery.
I'm seeing BMS at Overkill, but not charge controllers.
Midnight has a charge controller than can put out 96A. Would take 2 or 3 of those
If your system was 24V or higher, then the current would be lower.
Charging the battery 100% is 2.5 hours from PV seems excessively fast to me. I would rather spread it out of 5 to 8 hours. The trick is how to use PV generated power as it is being made to feed your inverter, but only put the desired amount in the batteries. Some inverters & chargers can take care of that (e.g. Victron) but you already have an inverter.
Standard charge current is 50 Amps for my batteries. My mistake, I plan to get a bms from overktill and a charge controller from Victron. I do not want to reduce the solar panel energy produced because I can always dump it into an electric hot water heater, etc.
Is the above the Isc (short circuit current) and Voc (overcurrent voltage) if your panels? If not it would be useful if you provided this info it can be found on the back of the panels, on the datasheet or in the product specifications.
Remember the largest overkill solar BMS is 120A, so you will need at least 3 in parallel to cover your inverters continuous power rating. With 24 cells your choice is 2P4S x 3, or 1P4S x 6. The advantage of the former is lower cost, the advantage of the latter is redundancy/fault tolerance/more safety margin.
I wouldn't want to either, those suckers are pricey. Unfortunately you made your bed when you paired 3000W of solar panels with a12V system ?? This means to take full advantage of the array you'll need a 250A controller (more likely smaller controllers totaling roughly 250A), or if you are willing to over panel a bit and buy a quality controller maybe a 200A controller or 2 x 100A controllers or 3-4 x 50-80A controllers.
I see three options:
- Pony up the $$$ for 220-250A worth of SCC, or a few smaller but still large ones that add up to the same current rating
- Use less panels (I doubt 8 x 72 cell panels can fit on an ambulance roof unless you are planning a dual slide out mechanism.
- Switch to a higher voltage system, since you haven't bought a BMS yet, it would require switching out your inverter, and reconfiguring your cells for 24V (I believe you have 24 cells so 48V is not an option unless you buy 8 more). You could use a higher voltage and hook into your ambulances 12v system using DC-DC converters and chargers.
Strongly consider 24V, it would cut the cost of the charge controller and the wiring nearly in half
Assuming you do not take that route
- For the high current circuits (SCC --> Battery and Battery --> Inverter) Use very large wire and make the wire runs as short as possible
- Max out the voltage rating of your controller (without exceeding it, and account for cold weather). If your panel Voc is 48V, you could series connect two with a 150V controller, or 4 with a 250V controller.
- If you will have a complex array arrangement (slides, or side facing panels, etc) consider multiple controllers in parallel.
50A per 100Ah, so 300A for your 600Ah bank.
Fortune cells are quality and made for moderately high currents compared to standard cells. They will not be the limiting factor here.
Hedges
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What you want is SCC able to handle all PV power, but controlled so it curtails output whenever battery current would exceed 50A (i.e. reduce production by 80% if full sun and no power draw by inverter.)
I think many all-in-one do that. Don't know which models, especially for 3kW PV input.
Victron ecosystem uses a battery shunt and commands charge controller to accomplish this. When inverter needs more, shut detects reduced charge current and more power is requested.
SMA (what I have for home) has an AC inverter/charger which regulated battery current. PV is AC coupled with GT inverters, and are commanded by frequency shift so they adjust their output.
Either of those would have a response time before they could command reduced PV power after an AC "load dump", large load suddenly turning off. In the case of DC coupled Victron, that would show up applied to the battery (unless SCC has internal dV/dt limit). SMA would experience AC voltage rise and I think tries to stuff excess current into the battery momentarily. SMA recommends a minimum battery size as a function of PV wattage; I think the GT inverters would drop off line if AC voltage rose too far.
If either of those put too much current into lithium battery, BMS would disconnect. It probably has a short-term tolerance for over-current.
All good then!
Hedges
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Midnight Classic 150 is rated for 96A output, 150V max input.
You have 8 panels, so it you put 4 panels on each of two Midnight (panels 2s2p), they would exceed it's capacity for feeding a 12V battery by 25%.
But, if each series string of two was oriented differently, that would drop the peak down so no power clipped.
Will these be flat on the roof of the vehicle? Angle isn't optimum, so they would produce less than rated power except in summer. Probably all power would be used most of the time.
At $925 each, they'll cost you a pretty penny.
Consider switching to a 24V system; then you only need one charge controller, not two.
Put the $925 you saved toward a 24V inverter.
(48V is another option.)
You have 8 panels, so it you put 4 panels on each of two Midnight (panels 2s2p), they would exceed it's capacity for feeding a 12V battery by 25%.
But, if each series string of two was oriented differently, that would drop the peak down so no power clipped.
Will these be flat on the roof of the vehicle? Angle isn't optimum, so they would produce less than rated power except in summer. Probably all power would be used most of the time.
At $925 each, they'll cost you a pretty penny.
Consider switching to a 24V system; then you only need one charge controller, not two.
Put the $925 you saved toward a 24V inverter.
(48V is another option.)
I still think before you go too far down the road of trying to figure out how to handle ~230-250A of PV input, you need to determine whether you can actually realistically fit 3kw of solar on an ambulance roof.
The footprint of your 8 panels assuming just 1 inch gaps is roughly:
6.5 ft x 26.5 ft
Possibly the cheapest option for near full output would be 4 x 60A budget Epever charger controllers. This would be about $1100. I have no experience with them and don't know if there are any caveats to using them in parallel. But people who do own them seem to have a decent impression of them as far as budget controllers go. They are one of the cheaper brands Will recommends.
The footprint of your 8 panels assuming just 1 inch gaps is roughly:
6.5 ft x 26.5 ft
Possibly the cheapest option for near full output would be 4 x 60A budget Epever charger controllers. This would be about $1100. I have no experience with them and don't know if there are any caveats to using them in parallel. But people who do own them seem to have a decent impression of them as far as budget controllers go. They are one of the cheaper brands Will recommends.
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