Okay, How did I do? First system for an off grid cabin.

[Flatpicker]

Hello All.

I’ve been fortunate enough to have found this forum just as my panels, mounts, inverter and batteries arrived. That said, I was committed to the equipment as I ordered it - might have made a change or two in retrospect, especially after some digging thru the wealth of knowledge here.

Here’s what I’ve got:
(4) 550 Watt Bifacial panels. 50.1 VOC
(2) EcoWorthy dual axis tracking mounts
(2) Sungold 5.1 kW LiFe Phosphate wall mount batteries
(1) Sungold 8 kW split phase inverter (dual MPPT inputs, 500 volts max)

My goal was to be generating at the worst time of year for solar production (i.e. Winter solstice) and I nearly made that by generating on the 29th of December. The highest input I’ve seen from the 4 panels (wired in series) was 1.5 kW and so far I have produced about 20 kW according to my inverter. Production is obviously hit or miss and my main objective was to get both batteries up to 95% SOC before putting a load on them so I could calculate real world “worst case” runtime.
I have a 9000 BTU Senville split unit, a 1953 Philco refrigerator, and LED lights throughout the cabin. Total load with everything running is just under 1000 watts, so I’m thinking I’ve got a good 7.5 hours from 95% SOC down to 20% SOC. Would like to add more batteries (I’ve ordered two more 5.1 kW wall mounts), but this brings up the question: Should I add more panels?
Which brings up the NEXT question: I’m only using one MPPT input with input voltage running about 180 VDC from the four panels in series - do I add another four panels on the other MPPT input or series them with the input being used to boost the voltage to about 360 VDC? Is the inverter more efficient with one input of 360 volts or with two at 180?
Your feed back is much appreciated!

 

[JBoffgrid2022]

Right off the bat, I can try and answer a few of these. You would want to start your calculations with the load or needs of the camp first. If you calculate these properly, you can then come up with the amount of daily watts you'll need (usually measured in kWh). 1000 watts seems low to me, is this the amount of watts used per hour?

(4) 550 Watt Bifacial panels. 50.1 VOC
(2) EcoWorthy dual axis tracking mounts
(2) Sungold 5.1 kW LiFe Phosphate wall mount batteries
(1) Sungold 8 kW split phase inverter (dual MPPT inputs, 500 volts max)

8kW inverter would ideally have a 9600kW array (1.2 x inverter size).

Battery bank would depend on the amount of power the camp needs. This is factored by measuring your kWh for one day, less the amount of powered used by the inverter itself, times how many days you want in reserve.

Hope this helps

 

[Flatpicker]

Right off the bat, I can try and answer a few of these. You would want to start your calculations with the load or needs of the camp first. If you calculate these properly, you can then come up with the amount of daily watts you'll need (usually measured in kWh). 1000 watts seems low to me, is this the amount of watts used per hour?


8kW inverter would ideally have a 9600kW array (1.2 x inverter size).

Battery bank would depend on the amount of power the camp needs. This is factored by measuring your kWh for one day, less the amount of powered used by the inverter itself, times how many days you want in reserve.

Hope this helps

Thanks for the reply. First off, 1000 watts is the instantaneous load, so worst case, that is my maximum load. There fridge won’t run 24/7, probably closer to 240 minutes per day @ 300 watts so, lets say 1.8 kW hours. Next would be the LED lights. Running them 24/7 would be 1 kW hour. Actual use would be nominal. Last is the Seville split system. When running it pulls 6.8 amps in heat mode - that’s 816 watts. Depending on outside temperature, it could run a solid 20 hours a day if it’s 15 degrees outside, so there’s 16.3 kW hours. Total kWh needed could be 20 kWh per day. That is definitely WORST case scenario. Honestly, it just plain won’t happen if we are occupying the cabin. As a caveat, if we are in the cabin and need heat, we have a wood stove which we crank up. The split unit is only used for heat when we are absent/lazy. It will be used for cooling in the summer, and I’m hoping that my increase in battery plant size will carry the air conditioning load in the summer when we are making decent power from the PV arrays. That’s what got me thinking about adding more panels.
The info on the inverter size is good to know. Didn’t realize there was a formula for sizing. I went with the 8 kW because it is a split phase and interfaced easily into my 240 V panel. Regarding the 500 volt maximum of the MPPT inputs, should I series the next four in with the existing four boosting the voltage to 340-360 volts (well below maximum for the inverter) or set up another string at 170-180 volts and use the second input of the inverter? Is one way “more efficient” than the other?
The panels (as I understand) are “capable” of up to 760 watts because they are bifacial so absolute best case, I could produce as much as 3 kW from my existing arrays/mounts. I realize that will rarely (if ever) happen. Adding another 4 panels could potentially grow my PV to 6 kw. Not the 9.6 ideal maximum you mentioned but a good size array nonetheless for the application. My main question is hook up.

 

[JBoffgrid2022]

Ok, as always with this type of thing, there will always be more questions than answers lol!
That being said, I will do my best here. I too have an off grid camp that i've been struggling to provide enough power so I might be of use here. ("Might")
As I mentioned before, you'll need to start with the amount of power you'll need. Theoretical usage (calculating watts) is often a best case scenario, not a worse case scenario. In other words, you may never know the actual usage until you have everything set up and can measure this over time. That being said, you will need to identify the "power hogs" and limit or eliminate their use entirely. Otherwise you will need to come up with another solution to your power supply problem. You could as you mentioned install more solar panels to your setup or alternately supply the needed power with a back up generator. At the end of the day, you'll need to be realistic on the demands of the loads you are powering.

Regarding the additional solar panels, you could submit a specific post on the forum of how best to arrange your strings with that particular inverter. That has been the best way to get my own answers here.

You should consider installing a propane heater that does not require any power. We have installed a few of these at out camp up north and haven't had any issues. They have their own built in thermostat that detect the temperature and turn the heater on and off on their own. I also installed a wireless router via my cell phone carrier to monitor the different systems from home I have wifi thermostat, Reolink camera, and wifi connections to my inverter/solar array. This is very handy when you have an off grid camp that you need to keep an eye on!

Hope this all helps

 

[Flatpicker]

Ok, as always with this type of thing, there will always be more questions than answers lol!
That being said, I will do my best here. I too have an off grid camp that i've been struggling to provide enough power so I might be of use here. ("Might")
As I mentioned before, you'll need to start with the amount of power you'll need. Theoretical usage (calculating watts) is often a best case scenario, not a worse case scenario. In other words, you may never know the actual usage until you have everything set up and can measure this over time. That being said, you will need to identify the "power hogs" and limit or eliminate their use entirely. Otherwise you will need to come up with another solution to your power supply problem. You could as you mentioned install more solar panels to your setup or alternately supply the needed power with a back up generator. At the end of the day, you'll need to be realistic on the demands of the loads you are powering.

Regarding the additional solar panels, you could submit a specific post on the forum of how best to arrange your strings with that particular inverter. That has been the best way to get my own answers here.

You should consider installing a propane heater that does not require any power. We have installed a few of these at out camp up north and haven't had any issues. They have their own built in thermostat that detect the temperature and turn the heater on and off on their own. I also installed a wireless router via my cell phone carrier to monitor the different systems from home I have wifi thermostat, Reolink camera, and wifi connections to my inverter/solar array. This is very handy when you have an off grid camp that you need to keep an eye on!

Hope this all helps

Yup! Got the propane heater. Been there since 2013 when I built the cabin. Works great but I usually leave a ceiling fan running if it’s the sole heat source to move air around and reduce condensation during really cold spells. The load is VERY manageable - literally the refrigerator and LED lights.. Will post a more specific question regarding array wiring.