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Will the MPPT 100/20-48V charge controller function without a battery connected? In other words, if I connect a PV panel input and a purely resistive load output (e.g., a submersible heating element) to the load output, but no battery, and there is ample irradiance, will the MPPT tracking algorithm still function to deliver maximum output power to the load?
Not recommended. The battery is needed so as the MPPT can auto sense the voltage setting, and can absorb the charge current from the PV system and to supply current to the load if the pv power is insufficient. A purely resistive load would have such terrible voltage regulation that the MPPT would likely fail.
No per the Victron 250/70 manual, the MPPT would NOT be damaged. Page 61 quote:
"Also, refrain from using the solar charger as a power supply without batteries connected. Although this operation won't harm the solar charger, it might not support all types of loads. Some loads may function, while others may not, particularly at low load power, where the solar charger's response might be too slow to maintain a constant voltage. Please note that support is not provided for such situations."
So just clearing things up here. The SCC will be fine, of course due to the sun conditions stuff may or may not be able to turn on/stay on if solar pwr drops. Going through an inverter you will at least get a clean AC source, if you wanted to give up a bit of your wattage you could use a DC step down converter the kind where you can set the output DC current and voltage. That way the DC power to your inverter is regulated and constant (unless you fall below your settings due to solar power dropping). So it is pretty simple to get a regulated DC output from the SCC with some very basic electronics on Amazon, your inverter will do the rest ensuring a nice clean sine wave.
This allllllll depends on your PV array suffice to say. If you are willing to sacrifce some of its power through a step down converter you'll have a clean DC output. However you would need to buy/build a fairly high wattage DC regulator/step down converter or build your own. The loss of wattage is going to be significant if you are trying to power devices that require high wattage. If its very low wattage stuff and you have a decent PV array you can power those devices until your PV array caves to loss of sunlight.
But it WON'T hurt the Victron controller its in there own manual!
Extended use like this likely will eat up your step down converter due to the high amperage, unless you get something real nice. Not something I would leave running if I wasn't home to keep an eye on it. The inverter should be fine with a regulated DC output via a step down.
You just need to REALLY know the absolutely lowest level your PV array at 48V can perform at during the day. Know your worst case (but still running an inverter + load) value and the highest output (peak sun performance) and ensure your step down converter is good to handle those numbers. You can probably pull off 1 to 1.5KW steady during the day based on cheap step down converters on amazon until the sun runs out. Assuming you have the PV array to put out the power all day.
Interestingly enough, Epever makes a new model SCC that does DC regulation and specifically supports connecting an inverter straight to the battery outputs of the SCC. I have one, and it works fine, only used it for a couple hundred watts right now as I am waiting to get my PV panels I've ordered. In this case this SCC is doing what the step down converter is doing...regulating the DC output (not necessarily stepping down). The problem with this charge controller is that its limited to 150Voc from your array and the "no batteries" mode requires it run at 48V (not a problem for me I have both 48/24 battery packs and inverters). Also this SCC is limited to 40A. So you would have to play around with your PV array setup to get as close as possible to the max limits in the manual to get all the perfomance. In this case I believe its 2080 watts it can do without batteries.
I've got a few of the step downs, I think one of them is 1800watts, I may try that with the victron 250/70 when I get my panels delivered (eagerly awaiting). 18000 watts is more than enough to power my fridge during the day, and the goal is even if its not a super sunny day based on PV layout.
Solar is a hobby for me, I build 24/48V battery packs from LFP batteries from EV's or just plain 3.2V LFPs and build packs, put a BMS on em ect... I have a bunch of 24/48 inverters and SCCs.
I don't "need' to go without batteries on my SCC to power the fridge, I just WANT to be able to do it :)
Saves my packs for other parts of the house to power!
Stay safe but have fun!
To be fair, the spirit of the original answer was entirely correct. Not recommended (in fact Victron specifically tells you not to) and not supported, which means that even if it does say in the manual that the MPPT won't be harmed, if it was harmed there'd be no warranty on it since you'd be doing an unsupported thing that Victron specifically told you not to do.
So, over here on the "supported" side of the Community, the "No" answer was correct. Over in the Modifications side of the Community, well... that could be a different story :)
