Why Not Connect MPPT to Other Xanbus Devices?

Michael57 · May 2020

Hi All

This forum has been a great source of information for me, so thank you all for your efforts. I bought a cabin that is off-grid in Washington state, about a month ago, and so I inherited the system there. The previous owner told me that the system mostly just worked, he hadn't really tweaked any of the configuration since it was setup and the only real maintenance he had done was to water the batteries. The system is about 4 years old and has the following components.

4 Sunmodule SW 300 Mono
MPPT 60 150 Solar Charge Controller
Conext XW+ Inverter
Conext Solar Control Pane (SCP)
Conext Automatic Generator Start (AGS)
8 6Volt Trojan Batteries 48V/435Ah
There is also a Cummins Onan Propane powered Generator.

So, I've been learning a lot about this system and maintenance of the components and especially the batteries, and I do think the configuration is a bit problematic, allowing the batteries to get lower than recommended and not necessarily charging at the right voltage, and the batteries are slightly over watered...but I'll deal with that later (and in different threads as I look for suggestions). Overall though, the system does work pretty well.

The most confusing thing to me, is that the Inverter, AGS, and SCP are connected on the Xanbus network, but the Solar Controller is not. It would be the most trivial work to connect it, all the devices are easily accessible and close to each other. That leads me to believe that it was excluded on purpose, and I can't for the life of me figure out why. There is a battery temperature sensor that is hooked to the XW+ Inverter, so when the generator is charging and evaluating the batteries, it is temperature compensated, but since the Solar Controller is not on the Xanbus network and doesn't have it's own temperature sensor so it isn't temp aware, and it is setup for "Warm" which would be fine in the summer but is the wrong setting for the other 3 seasons...

Aside from the Solar Controller being temp aware, it would also be convenient to control it through the SCP as it has a much friendlier interface. I don't think there are any other advantages to connecting it to the Xanbus network... But I'm wondering if there are some downsides that I'm not aware of, would it some how cause a problem to connect it with this setup? I appreciate any thoughts on why it would be a good or bad idea to connect it now.

Thanks!

Horsefly · May 2020

I would hook up the MPPT60-150 to the Xanbus. You know won't do any harm, and it is really easy to do. I've got the same Charge Controller and the Conext CS4024 Inverter / Charger, and you are right - it is way easy to configure and control through the SCP. With no temp compensation info going to the MPPT60-150, you already are not operating as intended.

To me it looks as though you are under-paneled in your configuration. 1200W for 435Ah of batteries at 48V sounds pretty light. The 1200W is also nameplate rating, so in reality you are probably getting more like 900W on a good day.

Michael57 · May 2020

Horsefly said:

To me it looks as though you are under-paneled in your configuration. 1200W for 435Ah of batteries at 48V sounds pretty light. The 1200W is also nameplate rating, so in reality you are probably getting more like 900W on a good day.

Interesting. Since the panels aren't really something configurable, I haven't looked much into them yet. But on a clear day, the MPPT output goes well above the 1200W rating, though I don't think I've noted the volts and amps it's pushing when it gets that high.

I will say though, between the design and the way the previous owner talked about it, it feels like the intent was really for the Solar to power the house during the day while storing any extra energy, and float the batteries when the system isn't being used, with the propane generator really being the primary full battery charger.

Thanks for the heads up and the recommendation to connect the MPPT.

BB. · May 2020

While using the propane genset as your primary power is fine--Do you want to use more solar power down the road and less genset?

If you are living there full time (say 9+ months a year), solar is usually pretty nice. If used as a weekend/few weeks a year place, then a large solar array may not be as cost effective.

-Bill

BB. · May 2020

Michael, it is not uncommon for solar charge controllers to give "optimistic" output readings. Confirming with a DC Current Clamp DMM can be nice (especially when things don't look right--Or too good to be true). AC+DC Current Clamp DMMs (start of your switch).

https://www.amazon.com/s?k=UNI-T+UT210E+True+RMS&i=tools&ref=nb_sb_noss_2 ("good enough" for our needs)
https://www.amazon.com/gp/product/B019CY4FB4 (mid-cost DC+AC Current Clamp DMM)

I like to use some math to size a system. Using our rules of thumbs for an off grid home/cabin (energy efficient) with your present battery bank:

435 AH * 48 volt battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 4,437 WH per day (for 2 days, 50% max discharge) daily use

Not bad... A 3,300 WH per day system is pretty close to a "normal" electric life style for an energy conservation minded family (LED lighting, Full Size Energy Star refrigerator, solar friendly well pump, LED TV, Laptop, Washing Machine)...

For an off grid solar powered system, suggest 5% to 13% rate of charge for battery bank. 5% can work OK for a weekend/sunny weather system. 10%-13%+ for full time off grid rate of charge:

435 AH * 58.0 volts * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,638 Watt minimum
435 AH * 58.0 volts * 1/0.77 panel+controller deratings * 0.10 rate of charge = 3,277 Watt array nominal
435 AH * 58.0 volts * 1/0.77 panel+controller deratings * 0.13 rate of charge = 4,260 Watt array "typical" cost effective maximum

So, you certainly have room to add solar panels (and a paralleled MPPT solar charge), if you wished.

Then there is sizing the array to your daily loads and where you live... Since I don't have any "real numbers", just use the 4,437 WH per day based on battery bank capacity, and guessing near Federal Way, WA state, fixed array:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Federal Way
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 43° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
1.69	2.80	3.53	4.16	4.56	4.77
Jul	Aug	Sep	Oct	Nov	Dec
5.22	5.19	4.70	3.14	1.96	1.52

Around 3 hours of sun per day or more is pretty good... Don't know where your system is, but to start, toss the bottom three months (need genset), and use February 2.80 hours of sun per day (long term average) for the "break even" month:

4,437 WH per day * 1/ 0.52 off grid AC system efficiency * 1/2.80 of sun (Feb) = 3,047 Watt array (Feb break even)

So, based on my above guesses... A ~3,277+ Watt array would be a nice full time off grid array for the battery bank you presently have (assuming 4,437 WH per day average loads).

Just to give you an idea of what a 1,200 Watt array should output:

1,200 Watts * 0.77 panel+controller derating * 1/58 volts charging = 15.9 Amps into battery bank (best cool/clear day, bank needing charging)

Average daily harvest for May (this month):

1,200 Watt array * 0.52 off grid system eff * 4.56 hours of sun (May average) = 2,845 WH per day

And, on a 435 Amp*Hour 48 volt battery bank, generally a maximum AC inverter would be:

435 AH (at 48 volts) * 1,000 Watt inverter * 1/100 AH (at 48 volt battery bank) = 4,350 Watt inverter (suggested maximum)
4,350 Watt inverter max / 2 (just a fudge factor) = 2,175 Watt AC inverter minimum "good fit"

Anyway... Some math and lots of guesses.

Your thoughts? These are just starting points.. Your needs and location are what matters.

-Bill

Michael57 · May 2020

Oops, your second post must have posted as I was typing this one. Let me take some time to digest that...Below is my original reply to your first post in the thread...(Sorry about that).

That's a good point Bill. Today it is more of the former, weekends and a couple of weeks here and there. So far, I can get through the weekend, if it's partly cloudy or better, without the generator running but given how often it's worse than partly cloudy in western WA, I can certainly see how a bigger array would have some advantages. If my math is right, even if it's tight and a bit slow, this array should be able to fully charge the batteries given that the array often gets several days to do so with no load on the system. If I'm wrong about that, please let me know.

Since I'm a novice and maybe being overly cautious, I'm a little worried about some weird side effect of adding the MPPT to the network when it hasn't been for so long, and it seems deliberately so. Though, I can't actually think of a way that it would cause a problem, but maybe it would lose its config or have some weird conflict with the Inverter...I'm just not sure.

mcgivor · May 2020

Michael57 said:

Horsefly said:

To me it looks as though you are under-paneled in your configuration. 1200W for 435Ah of batteries at 48V sounds pretty light. The 1200W is also nameplate rating, so in reality you are probably getting more like 900W on a good day.

Interesting. Since the panels aren't really something configurable, I haven't looked much into them yet. But on a clear day, the MPPT output goes well above the 1200W rating, though I don't think I've noted the volts and amps it's pushing when it gets that high.

I will say though, between the design and the way the previous owner talked about it, it feels like the intent was really for the Solar to power the house during the day while storing any extra energy, and float the batteries when the system isn't being used, with the propane generator really being the primary full battery charger.

Thanks for the heads up and the recommendation to connect the MPPT.

The peak output may exceed the rated wattage for very short periods when clouds pass, a phenomenon known as edge of cloud effect
https://solarhomenews.wordpress.com/2009/09/03/edge-of-cloud-effect-may-not-be-what-you-think-it-is/

The Schneider 60 150 will record the peak in the history log, press enter 3 times then scroll down or up using the center buttons. The highest iv seen was 1760W from a 1500W array immediately after tropical downpour, the rain cooled panels suddenly being hit by midday sun, it soon was back to its regular 1000-1100W when the array heated up again.

Definitely hook the controller to the Xanbus network, there is only need for one RTS as the information will be shared, by the way.

Michael57 · May 2020

Bill, first of all, thank you for taking the time to lay that out, that is really helpful. I'll check into the clamp meter as well so that I can get some accurate readings on the array.

The location of this property is pretty remote so no city within 30 miles is listed on that site, but Longview would be the closest. I wish project Sunroof covered it, but it doesn't. Longview is probably a good enough proxy for our needs. I'm not sure on the angle of the array, my guess is 43ish, but I'll see if I can verify that. It's on a post, so I can adjust that part pretty easily, if I remember right. The property is pretty remote, but it is on top of a plateau around 1200' with a good view of the southern sky. The array is facing south and slightly west.

It is a pretty efficient home, even the refrigerator is run on propane and all lights are LED. The washing machine, dishwasher, microwave and well pump the big hitters. Really on that list, only the well pump is a necessity, so we try to be pretty sensible with the others.

I can definitely see that I have the capacity to add to the array, so I will keep an eye on my usage (the propane bill shows that pretty clearly) to help educate me if the investment would be worth it. Again, thank you very much for all of that information!

@mcgivor
Thank you as well. I actually have looked through the history, the highest listed was around 1600W. I routinely see it above 1400 in person when getting hit hard with the sun, which from what I'm hearing here, sounds like hogwash. Admittedly, I'm very ignorant about solar arrays, I just thought the 300w was equivalent to like a nominal rating, like the 48 in a 48 volt battery bank. I think all the more reason to grab a current clamp and also to educate myself on arrays.

Seems like the consensus is to connect the MPPT to the xanbus network too, so that makes me feel better.

BB. · May 2020

Micheal,

Yea, I typed that second post a bit later... For Longview:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Longview
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 44° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
1.90	2.91	3.67	4.29	4.58	4.72
Jul	Aug	Sep	Oct	Nov	Dec
5.18	5.27	4.72	3.25	2.01	1.59

You can try PVWatts and see if they have any data closer to you (PVWatts is a different interface, and it does have more features):
https://pvwatts.nrel.gov/pvwatts.php

You have the existing system... So a bit of monitoring (energy usage, battery usage, propane usage, etc.) can point you for future changes.

Many folks have transitioned from propane to Energy Star refrigerators--Many propane fridges eventually become a bit of a maintenance nightmare (and if you have to haul propane to your place--That 1 lb per day (or whatever) for the fridge becomes an issue.

-Bill

Dave Angelini · May 2020

The person before could have had lightning damage to the mppt. I have seen them lost the ability to "network" and since mppt-60 does not supply network power like it's big brother it could be a problem. It will not hurt to try and you should. If the SCP goes dark you will know why he did it. I did the initial offgrid field test for that about 13 years back. Totally bullet proof as long as you SPD it.

Michael57 · May 2020

None of the knockouts on the MPPT have been, well, knocked out. So I don't think it was ever connected or left connected for very long. I wonder if the fact that the MTTP doesn't supply power is why it wasn't connected? What is SPD?

Bill I do have a 500gal propane tank and a service keeps it topped off, so that part isn't a big deal but I'm not the biggest fan of the propane fridge since the temperature is a little tricky to keep where I want it. It can run off of electricity too, but the cooling mechanism is the same, so I'm sure I'll still have the same temperature challenges (which is that it keeps the fridge too cold). The one advantage is that we can leave stuff in it and cut the power completely to the cabin and it's fine. I do have a temperature monitor on it that lets me know that it stayed within a safe temperature range while I was gone.

I have been thinking about getting the conext gateway for better monitoring and the ability to upgrade the firmware, at which point I'd probably leave a few outlets on anyhow, so I can keep the electric fridge option in the back of my mind.

Why Not Connect MPPT to Other Xanbus Devices?

Comments

Federal Way
Average Solar Insolation figures

Longview
Average Solar Insolation figures

Categories

Why Not Connect MPPT to Other Xanbus Devices?

Comments

Federal WayAverage Solar Insolation figures

LongviewAverage Solar Insolation figures

Categories

Federal Way
Average Solar Insolation figures

Longview
Average Solar Insolation figures