Need some opinions on my choice of equipment

[Joe_]

I hope I have successfully designed a small expandable backup system for my property located in the desert. Very hot, lots of sun.

I’d like to get an opinion on what I am planning before I spend more money buying the remaining equipment that I have decided on.

I presently have 6580 watts nominal of solar panels purchased used. They are flat mounted on shipping containers.
(at least that is what I am in the process of doing).
I understand that I will lose 14% which might give me a corrected nominal of 5659 nominal.
Then I will loose more in the summer due to heat, and the panels are used and probably partially degraded.
I'm not certain what that adds up to on a 110 degree day?
I own (28 ) 235 watt panels with and open circuit voltage of 37 volts and a rated amperage of 7.84. I am making 4 series strings and then parallel those into two strings with a voltage of 296 volts @17 amps to meet the spec's of the charge controller I selected below.

Now for equipment I plan to buy very soon, it’s on sale.
(1)Schneider context xw pro 48v hybrid inverter because of the well pump.
(2) EG4 MPPT solar charge controllers 500V/100 amp for the two array strings.
(1) Schneider insight home smart box to configure the inverter with.



For batteries. I’d like to build my own.
This inverter requires 200 AH to meet the minimum standards which I am sure keeps the warranty intact? I would likely order (2) of the lower end SOK offerings because they are user repairable. If i decide to test it once It is assembled.
The other option is to further research BMS's for 48 volt packs over 100 amps. Then I may purchase 280 amp cells at Currant Connected, build some frames and roll my own.

I believe I will need at least 500 AH of batteries but for now I am interested in getting everything up and running, then adding more batteries as I can afford them and have time to build them. I am not certain if I am high or low on the battery capacity needed. Let me know what you think.

The loads that I designed the system for are as follows.

The critical loads during an extended power outage which this is designed to prevent are:
2 x 5000 btu air conditioners (500 watt run wattage) much more to start. Likely one will run continuously at night. The other will cycle intermittently as things cool off over night. It cools a very small space.
2 small chest freezers and 2 full sizer refrigerators . At least one has automatic defrosting.
Likely one of the fridges would be combined into the other during a prolonged power outage.
The chest freezers would present more of a problem.
½ hp evaporate cooler (500 watts running)
3 ceiling fans and a couple of led lights.


Presently during the day with the evaporative cooler on, 3 ceiling fans and the 2 refrigerators and 2 small freezers cycling, and a couple of lights on , the draw is between 1500 and 1900 watts. This includes one of the small ac's cycling occasionally. Typically.

At night power draw seldom drops below 750 watts, typically closer to 1000 watts. This is just looking over some energy audits done without going out of our way to conserve power.

Additionally the system must be able to run a 1 hp well pump(11 amp/240V) long enough to pump 150 gallons of water daily. Takes aprox 15-20 minutes each day. Can be done during daylight. The time of the day when it is done is flexible.

Tell me what you think? I’d rather get the bad news now than after I spend the first 10K. Hopefully no bad news.

 

[HRTKD]

Since you're in a static (non-mobile) situation, I would tilt the panels. There are lots of solutions out there (and a few around here) for tilt mounting on shipping containers. Tilting will improve access to the sun and help with the heat problem.

I have 560 Ah of LiFePO4 in my RV. I can run the 15K BTU rooftop air conditioner for about three hours on battery alone. It's a rather inefficient air conditioner. In your situation, I would be looking to install a mini-split air conditioner instead of window units if that's what they are.

 

[400bird]

You need to spec you array/charge controller voltage for the coldest it will get. PV output voltage increases when it is cold, and the MPPT voltage limit is a hard limit, the controller might not survive if you go over that limit.

Second, if you are going with a Schneider inverter, have you looked a the Schneider MPPT? There are some nice benefits to having the both the inverter and charger on the same interface.

I think your math is a bit off.
If you have two parallel strings of 7 panels @ 7.84 amps each. Those two strings come out to 15.68 amps total.

If you went with the 600v Schneider MPPT, you might be able to run two parallel strings of 14.
You'd see some clipping on cool days and right at the upper limit of the specs for the MPPT 100/600

Will your install be grid tied?

If not, how ok are you with the power going out in the middle of the night when the small battery goes flat?

 

[Joe_]

Since you're in a static (non-mobile) situation, I would tilt the panels. There are lots of solutions out there (and a few around here) for tilt mounting on shipping containers. Tilting will improve access to the sun and help with the heat problem.

I have 560 Ah of LiFePO4 in my RV. I can run the 15K BTU rooftop air conditioner for about three hours on battery alone. It's a rather inefficient air conditioner. In your situation, I would be looking to install a mini-split air conditioner instead of window units if that's what they are.

Here are more details. I didn't want to make the post longer than it was, but I neglected to communicate some important information as a result.

I am planning on installing the panels tilted approximately 1/2 to 1 degree towards the south to deal with rains.
The racking will raise them 4 to 5 inches off the roof for air flow.
The containers are set north-south. The narrow end faces south. Less than ideal. This allows 7 rows of 2 panels with 2" of spacing between them and about 1ft of length of the container left over or 6" on each end.

If I tilt the panels more than I am planning I must increase the gap between each row to prevent one row of panels from shading the next row in the winter winter months.

We get 40+ mph wind gusts frequently in the summer. I don't want the panels overhanging the containers on the ends for structural reasons.
I believe that in high wind gusts the portion of the panel hanging over the end of the container would have multiple different forces on it than the rest of that panel that is in close proximity to the roof and induce flexing at that part of the panel decreasing life expectancy.

Even a small increase in distance between rows of panels eliminates a row of 2 panels from each container decreasing nominal output by 940 watts. This is exactly the amount of power lost by not tilting the arrays. The saving to me comes in the form of labor and material necessary to mount the panels at the proper angle.
It's a lot more work. Much quicker and easier to flat mount, take advantage of the extra real-estate to add 4 more panels to make up for the losses.. Additionally because of my southwestern desert location those additional panels will produce more power in the summer when I need it the most for running air conditioning loads.

I'm thinking I have this right but I am not certain. That is why I am running this by everyone here. I really appreciate your response and your help.
If what I am doing is still problematic with this additional information or if there is a better way please let me know. That goes for anyone reading this.

Mini splits:
I'm planning on converting the house to multiple small mini-splits in the future. I recently replaced the 5 ton main air conditioner that gets us through the hot humid months of monsoon season a couple of years ago so it should be good for a while fortunately. This system I am installing is so we don't have to abandon our property if we loose power for an extended period of time in our area in the summer.

Once I get it up and running and play with it I will have some idea of where I want to go from there.

 

[HRTKD]

There are many of us in the Flat Panel Society that make the flat mounted panels work on our campers. It's not ideal, but it works given the limitations we have. More panels makes up for flat mounting.

 

[Mark Halvorson]

If you have the room, do not mount them on the container. Make a ground mount for the solar panels.

 

[Steve_S]

I would like to just provide an alternate thought given you are buying Solar Charge Controllers and not using AIO's.

A Victron MPPT 150/100 is 150 Volt Input & Max of 5800W of Panel to charge 48V/100A. Also with a Max Efficiency of 98%. Roughly $800 USD
If you work out the difference in panel voltage & amperage requirements, you'll find that you'll need less panels per controller on average.

Victron now has a Solar MPPT Calculator that let's you enter your panel specs and play with arrangements etc for optimal performance etc... works pretty well, check it out and take your time. https://mppt.victronenergy.com/

The higher voltage SCC's are intended for the newer 50+ Volts panels like the QCell 156 Cell monsters.

 

[Joe_]

You need to spec you array/charge controller voltage for the coldest it will get. PV output voltage increases when it is cold, and the MPPT voltage limit is a hard limit, the controller might not survive if you go over that limit.

Second, if you are going with a Schneider inverter, have you looked a the Schneider MPPT? There are some nice benefits to having the both the inverter and charger on the same interface.

I think your math is a bit off.
If you have two parallel strings of 7 panels @ 7.84 amps each. Those two strings come out to 15.68 amps total.

If you went with the 600v Schneider MPPT, you might be able to run two parallel strings of 14.
You'd see some clipping on cool days and right at the upper limit of the specs for the MPPT 100/600

Will your install be grid tied?

If not, how ok are you with the power going out in the middle of the night when the small battery goes flat?

On the cold increasing the power of the PV's. I used an online calculator that asked for lowest temperature that the panels would see to compute the string values.
I am hoping it did that properly. But I will check. Thanks for that. Also the EG4 charge controllers spec'd to operate with a string voltage as high as 450V and are safe to 500V. I hope not to test that.

Schneider mppt's:
My thoughts are that the 100/600 schneider would be too close to the limit. It can get very cold here occasionally.
Also the Schneider MPPT's are more than I want to invest in at this point. I'd need two 80/600's. 2x $1200. Maybe someday but not yet.


Grid tie. Unfortunately it is not allowed by my power provider. If possible I would like to power a few of our circuits off solar such as the freezers and refrigerators and the swamp cooler and one small ac used to cool a storage closet that is on the sunny side of the house. I haven't looked into the code restrictions on tying power from an out building to the main house to power a few circuits yet to see what the legalities of doing that is. I'm sure it gets complicated if it is even allowed
.
I have been a little overwhelmed just getting up to speed on the basics of this technology honestly and appreciate those on this board being willing to share their knowlege very much.

Running out of battery:
Running out of battery in the middle of the night is fine at this point. As long as it is an orderly shutdown that does not damage the equipment.
The house is well insulated. The refrigerators and freezers are able to coast as long as they aren't opened. Probably get to sleep in till it gets too warm in the house because of zero noise. Things could be worse.

I'm planning on adding more battery soon. I don't know what the implications of having batteries of the same chemistry but varying ages in the same bank is. Is that actually a real problem or more a theroetical problem?

 

[Joe_]

I would like to just provide an alternate thought given you are buying Solar Charge Controllers and not using AIO's.

A Victron MPPT 150/100 is 150 Volt Input & Max of 5800W of Panel to charge 48V/100A. Also with a Max Efficiency of 98%. Roughly $800 USD
If you work out the difference in panel voltage & amperage requirements, you'll find that you'll need less panels per controller on average.

Victron now has a Solar MPPT Calculator that let's you enter your panel specs and play with arrangements etc for optimal performance etc... works pretty well, check it out and take your time. https://mppt.victronenergy.com/

The higher voltage SCC's are intended for the newer 50+ Volts panels like the QCell 156 Cell monsters.

Thank you I will run the numbers. That is a great calculator. Thanks for the link.

 

[400bird]

I would like to just provide an alternate thought given you are buying Solar Charge Controllers and not using AIO's.

A Victron MPPT 150/100 is 150 Volt Input & Max of 5800W of Panel to charge 48V/100A. Also with a Max Efficiency of 98%. Roughly $800 USD

Good point, going with a 150 volt MPPT is a good alternative.
The Schneider 60 150 would stay in the same ecosystem as the inverter. $650

If you work out the difference in panel voltage & amperage requirements, you'll find that you'll need less panels per controller on average.

Interesting, I've never seen any math one way or the other. At 150 volts, you're forced into a few parallel strings and a combiner, that adds cost.

I am planning on installing the panels tilted approximately 1/2 to 1 degree towards the south to deal with rains.

That angle is going to hurt winter production.

The racking will raise them 4 to 5 inches off the roof for air flow.
The containers are set north-south. The narrow end faces south. Less than ideal. This allows 7 rows of 2 panels with 2" of spacing between them and about 1ft of length of the container left over or 6" on each end.

Any chance of turning the containers long side south? You could then use them as a wind break and ground mount at a decent angle to increase year round production.

We get 40+ mph wind gusts frequently in the summer. I don't want the panels overhanging the containers on the ends for structural reasons.
I believe that in high wind gusts the portion of the panel hanging over the end of the container would have multiple different forces on it than the rest of that panel that is in close proximity to the roof and induce flexing at that part of the panel decreasing life expectancy.

Yeah, I'll agree with that, overhanging the panels doesn't seem like a great idea.

 

[Joe_]

Good point, going with a 150 volt MPPT is a good alternative.
The Schneider 60 150 would stay in the same ecosystem as the inverter. $650

Interesting, I've never seen any math one way or the other. At 150 volts, you're forced into a few parallel strings and a combiner, that adds cost.

I ran the numbers and also considered the additional labor, materials and time required to add additional strings, combiner boxes conduit ect.
For a 4 % increase in efficiency. It doesn't seem worth it to me at this point. I have a lot of work ahead of me already.

The Eg4's shut themselves down at dark and restart themselves when there is enough solar to charge. I'm hoping that helps. Perhaps that is figured into their efficiency already? I have no way of knowing.

Any chance of turning the containers long side south? You could then use them as a wind break and ground mount at a decent angle to increase year round production.

Unfortunately they can't be rotated or moved at this point.

 

[Shimmy]

As someone that likes Schneider, I feel like it would be remiss to not ask why you aren't going for an AIO; a big enough unit or parallel units will provide you with the capability on the well pump.

I can think of a few reasons to go one direction or the other... but it is worthwhile to make sure you have done the exercise.

 

[Joe_]

As someone that likes Schneider, I feel like it would be remiss to not ask why you aren't going for an AIO; a big enough unit or parallel units will provide you with the capability on the well pump.

I can think of a few reasons to go one direction or the other... but it is worthwhile to make sure you have done the exercise.

Schneider has a reputation for building solid industrial equipment. I’ve stumbled on to some of it when I was working. They have been around for awhile too.

I have many inductive loads that I would like to run but a very small system with very limited capacity.
Though most of the inductive loads are relatively small they aren’t interconnected and could in theory all start at once. There is nothing in place to prevent that and sooner or later it will happen. Because it can. Hopefully this inverter has the best chance of not faulting when that happens of the ones I have considered.

Also I need a resilient system my wife can handle and won’t hate. She is quite capable electrically but I’m going to look bad if she has to go outside in the heat daily to restart the system more than once in awhile. She won’t be impressed.

With freezers full of meat in the desert I really need something I can trust to persevere when I am away for a few days.

I’d also like the option of occasionally running power tools or my wire feed without having to shut down the 1/2 hp evaporative cooler in the summer if possible. Or possibly start and stop the evaporative cooler while letting the well pump cycle at the same time so I am not bound to filling a gravity feed tank each and every morning to keep the house livable when it is hot outside should I want to sleep in.

That sort of stuff. I don’t know how much I will be able to get away with but will find out. I have my doubts that an inverter that lacks a substantial magnetic circuit will be up to these tasks. This one is both larger and more efficient than the lvx series AOL that was my other choice.

I have zero experience with solar. I have some experience with inverters. But not in this context.

In a post above I said I didn’t think that I wanted to do a bunch of additional construction for an increase of 4%in efficiency.
After getting off the computer I realized that a better answer would have been to ask how important a 4% increase in efficiency in a small system such as I am attempting to build is, because I have no idea.

I’m here to learn.
I want to get this right.

 

[400bird]

How did you calculate 4% difference between flat and angled mounting?
I'm seeing significantly more gains with angled panels when I run the numbers.

I'm not exactly sure on your location, you said SW desert, so I punched in Phoenix.

11% annual gain in total production at 28.5°
43% gain in December at 43.5°

Summer gain is less pronounced.

I understand the concern about summer production, in hot regions we use much more electricity in the summer.
But, winter is much harder for most (due to clouds).
I'm almost centered in California, we'll hit 110 most summers. Before solar my summer electricity bill was $300/month, winter was $50
And after adding solar, I'm buying more electricity in the winter than summer.

If you're set on the nearly flat mounted panels, that's fine, I just want to you see the benefits of pointing the panels towards the sun.

 

[Joe_]

How did you calculate 4% difference between flat and angled mounting?
I'm seeing significantly more gains with angled panels when I run the numbers.

I'm not exactly sure on your location, you said SW desert, so I punched in Phoenix.

11% annual gain in total production at 28.5°
43% gain in December at 43.5°

Summer gain is less pronounced.

I understand the concern about summer production, in hot regions we use much more electricity in the summer.
But, winter is much harder for most (due to clouds).
I'm almost centered in California, we'll hit 110 most summers. Before solar my summer electricity bill was $300/month, winter was $50
And after adding solar, I'm buying more electricity in the winter than summer.

If you're set on the nearly flat mounted panels, that's fine, I just want to you see the benefits of pointing the panels towards the sun.

The 4% efficiency difference I was referred to was the difference between use of EG4 charge controllers vs switching to Victron which has a nominal efficiency rating that is 4% higher.

I agree with you that I would pick up efficiency in the winter by tilting my panels. However because of the layout of the parallel arrays and fixed length of the containers they mount atop, as I tilt them up more I must leave more room between rows of panels to avoid shading the next row during the winter months. This causes two issues. Even a 5degree tilt costs me 4 panels lost. One row of 2 panels on each container. Because the container has a fixed length and I can’t overhang the panels because they will experience relatively high cross winds. This loss of 4 panels nullifies any extra energy gained by tilting. It’s a wash and it’s a lot more work to construct non flat mounts.

More important is I loose the shading effects of the panels on the roofs of the containers in summer.
I realized when I began using an un insulated container that I needed to put a roof over the container to shade it. Power ventilation just wasn’t enough. Building materials are expensive now, used panels seem to be a great alternative.
They provide needed shade while creating energy. I may cover the areas not covered by the panels with corrugated steel to complete the shading if needed. I’m leaving every other racking piece long so that I can do that.


Shading should greatly effects the cost of energy for both the insulated air conditioned container when the ac is in operation and the uninsulated one that runs a ventilation fan in the hotter parts of the day, everyday from 10am- 7pm.

I hope that makes more sense now.

 

[Shimmy]

...However because of the layout of the parallel arrays and fixed length of the containers they mount atop, as I tilt them up more I must leave more room between rows of panels to avoid shading the next row during the winter months.

You keep painting yourself in a box. You can do plenty of interesting things with Unistrut or other rails, including an overlapping and south-tilted array on a single plane. PV panels are generally designed to be secured at 4 points without negative impact. Without going too crazy you can easily build a rack that would hold 3W x 6L panels and a 5º slope on a 40' shipping container. As an added bonus, you create a spot on the north end of the roof where you can fit a condensing unit if the container needs AC.

 

[Joe_]

You keep painting yourself in a box. You can do plenty of interesting things with Unistrut or other rails, including an overlapping and south-tilted array on a single plane. PV panels are generally designed to be secured at 4 points without negative impact. Without going too crazy you can easily build a rack that would hold 3W x 6L panels and a 5º slope on a 40' shipping container. As an added bonus, you create a spot on the north end of the roof where you can fit a condensing unit if the container needs AC.

Yes, certainly that is possible.