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Power station + solar for point of use load

H

HarryN

Solar Addict
Joined
Jul 25, 2021
Messages
1,026
Location
Pleasanton, CA
Hi, my wife is on oxygen for a bit recovering from a procedure.

She will be fine, so not a super big deal.

So they sent us home with an oxygen generator and spare oxygen tanks as "backup" in case the grid power goes down or something else fails.

This is all fine, but if I am out and the power goes out, then at least in theory there would not be anyone to re-plumb it over to the tank.

Also the label on the back of the oxygen generator indicates that it is using 300 watts, so I am thinking about setting up to supply some of this from solar.

I temporarily added a small power system to it all - - sort of like a UPS type use.

Thinking about adding ~ 1 kW of panels on the morning side of the house, and another ~ 1 kW of panels facing the late afternoon.

So to do this legally, I am assuming that I will need to add the whole external shut down arrangement for fire code ?

The system is set up to accept a nominal 24 volt type panel voltage, so 30 - 40 VDC from the panels.

I am not wanting to sell power to the grid - nor to tie it into the main panel if at all possible. I just want to feed solar power ( ~ 30 - 40 volts) from the panels to the power system to help run this particular point of use load.

Any suggestions for how people typically run the solar panel wires into the house and a simple way to implement any rapid shut down (for California) is appreciated.

I might just keep this setup going even after the oxygen generator aspect goes away.


Thanks

Harry
 
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I do not know what the rules are for rapid shutdown, but if you buy solar generator or DIY a solar generator, is there still a requirement for the rapid shutdown? I wonder about that too.
 
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HarryN said:
Hi, my wife is on oxygen for a bit recovering from a procedure.

She will be fine, so not a super big deal.

So they sent us home with an oxygen generator and spare oxygen tanks as "backup" in case the grid power goes down or something else fails.

This is all fine, but if I am out and the power goes out, then at least in theory there would not be anyone to re-plumb it over to the tank.

Also the label on the back of the oxygen generator indicates that it is using 300 watts, so I am thinking about setting up to supply some of this from solar.

I temporarily added a small power system to it all - - sort of like a UPS type use.

Thinking about adding ~ 1 kW of panels on the morning side of the house, and another ~ 1 kW of panels facing the late afternoon.

So to do this legally, I am assuming that I will need to add the whole external shut down arrangement for fire code ?

The system is set up to accept a nominal 24 volt type panel voltage, so 30 - 40 VDC from the panels.

I am not wanting to sell power to the grid - nor to tie it into the main panel if at all possible. I just want to feed solar power ( ~ 30 - 40 volts) from the panels to the power system to help run this particular point of use load.

Any suggestions for how people typically run the solar panel wires into the house and a simple way to implement any rapid shut down (for California) is appreciated.

I might just keep this setup going even after the oxygen generator aspect goes away.


Thanks

Harry
Click to expand...
There’s a voltage threshold for rapid shutdown and when the DC wire needs to be in metal conduit or MC once it enters the building envelope. I believe 30-40VDC is above one if not both.

The portable power banks I do not believe are set up to trigger rapid shutdown on their own. You would have to supply a separate rapid shutdown transmitter.

For this life critical application I would not use rapid shutdown at these voltages even if code says you should. There are two extra points of failure, the RSD module and RSD transmitter.
 
Bud Martin said:
I do not know what the rules are for rapid shutdown, but if you buy solar generator or DIY a solar generator, is there still a requirement for the rapid shutdown? I wonder about that too.
Click to expand...

I am not completely sure, but there appear to be some distinctions between temporary / emergency use vs continuous use.

From what I am reading on the forum and some other places, for longer term use, I will need a rapid shut down system ( RDS ) similar to this offering:

FireRaptor PV Rapid Shutdown Solution

The FireRaptor from IMO Automation is a module level rapid shutdown solution that works with all string inverters without using PLC. NEC 2014/2017/2020 compliant.
www.altestore.com www.altestore.com

I mostly build solar / electrical for van conversions so the RDS aspect is not considered important for those applications.

In this particular case, the "solar generator" / Power station is one that I build for mobile applications - but will be in the family room or a closet.
 
The battery pack will run the oxygen generator for 6 - 7 hrs even without solar.

Then we have oxygen tanks after that.

You are right though - for health critical loads like this, codes will often protect the patient vs the equipment. In some cases, they don't even use a GFCI.
 
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zanydroid said:
2kW/30VDC = mucho amps for fusing. Have you sanity checked that?
Click to expand...

Good catch.

So the solar array on the morning side of the house will be ~ 800 - 900 watts or so and vertically mounted to catch the morning sunlight.

Because the mornings tend to be a bit overcast and the spectrum is red shifted vs mid day, this will really only be pushing 500 - 600 watts.

The similar size array on the late afternoon / vertical mounted panels will see essentially zero sunlight during the morning, and vice versa for later in the day.

There will also be some wire losses.

Roughly ( 700 watts ) / ( 25 volt system) ~ 30 amps.

The solar controller auto limits the current to 30 amps max so it should be ok.

In the winter it is pretty overcast here. I have seen the 300 watt test stand array at my shop only putting out 50 watts sometimes.

_________

There is a roof section that is more ideal for mounting panels from a direction viewpoint, but this would require a pro to do that work.
 
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If you’re concerned about RSD then you should also be concerned about the other requirements like GFP and AFCI.

The array you have in mind is substantial, I didn’t notice the size in my first post. And to me that triggers doing it as right as possible mechanically too with listed mounts and clamps. It might be noticeable from the street too.

The tricky part with doing this with inspections in California that there are stringent ESS/battery requirements.

Why not grid tie it under NEM2 to offset the cost of a plug in AC charged solar generator set up as a UPS? Nobody will check for the presence of that. While DC coupling into a solar set up with batteries is an issue.
 
OK with vertical wall mounts, city will hassle you a lot for permitted install because they are non standard.

I don’t think you are allowed to take orientation into account in some aspects of fusing parallel strings. You also are supposed to use STC etc ratings, not your analysis of what the illuminated will be.
 
zanydroid said:
If you’re concerned about RSD then you should also be concerned about the other requirements like GFP and AFCI.

The array you have in mind is substantial, I didn’t notice the size in my first post. And to me that triggers doing it as right as possible mechanically too with listed mounts and clamps. It might be noticeable from the street too.

The tricky part with doing this with inspections in California that there are stringent ESS/battery requirements.

Why not grid tie it under NEM2 to offset the cost of a plug in AC charged solar generator set up as a UPS? Nobody will check for the presence of that. While DC coupling into a solar set up with batteries is an issue.
Click to expand...

Thanks for the inputs.

I already have a power system running as a battery back up and it will run for 6 - 7 hrs in this mode.

In the photo is a power system that I build for mobile applications next to the oxygen generator. (black suitcase)

It has the batteries, inverter, solar charger, and 120 vac charger built in.

I have zero interest in selling power to the grid / PGE.

The primary driving force is that if power goes out, during the daytime, then I can run it all from solar during the daytime, then another 7ish hours into the evening. After that would switch over to the oxygen tank in the back.

Thank you for the input that I need to plan for the ground fault protection and AFCI. It is currently equipped with GFCI so will look at that aspect again.

The vertical wall installation aspect has been a real challenge in discussions with solar installers in the past.

CA is / has switched over to using pushing people to design solar systems to produce / consume power roughly at the same time of day and in general I agree with this concept. Since the major demand for power is ~ 3 pm - 9 pm, there are going to be a lot of people interested in installing solar on vertical walls.
 

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Just to clarify, GFCI is on the AC side, GFP is on the DC side. I was also referring to AFCI on the DC side. You’re adding a lot of wiring and metal in the house. Not sure what the standard level of protection is on mobile setups.

RV size panels typically don’t have the listing for mounting on a house. I always assumed they would not be as mechanically robust to wind loads etc for a 25 year service life. I’m not 100% sure what the best practice is for choosing panels in this partly code compliant partly off the books installation.
 
I wonder if I am making this all too complicated by having the box "indoors".

This particular unit is only 10 amps @ 120 vac. I have access to a different one with more power, but even that is only 20 amps @120vac.

What if instead I:
- Mount the electrical stuff outdoors (solar / battery pack / inverter / etc) in the box
- Run a 120 vac line through the wall to 1 or 2 dedicated outlets for critical items

It seems like this would not even need an electrical panel as the power levels are so low - at most a 20 amp setup.

I would like to do this to code if at all possible.

Do home code rules allow a second power sources to come directly through the walls to a "critical loads" outlet or so?

The components are all perfectly capable of operating in the temperature range that we have here.

Thanks

Harry
 
You simplify the trouble of having to worry about DC crossing into the interior of the house. A lot of the other issues around properly carrying the DC to the inverter still remain. That said this feels a lot more standard, usually solar equipment is in a machine room, garage, or outside, not in a regular living space.

Sounds like you want this configured like a generator inlet.

If the output is current limited then you probably can find a code section excusing the need to protect the wiring inside the house.

Though usually when you use a generator inlet, that first feeds into a subpanel, and then into the house. I would probably consider a subpanel with breakers in case a bigger inverter that is not output limited is used in the future. Also it’s probably easier to pass an inspection if the config is “normal”. An inlet feeding directly into a circuit is very similar to some disallowed configurations and it would smell hacky.

You have to use proper NEC wiring method for the AC. No extension cords or other flex cord through the wall.

Will the battery chemistry charge ok in your climate if placed outside?
 
Thanks for the inputs.

I am open to doing what it takes to make things work in a simple way and be code compliant. If that is easier to implement putting the box out side vs inside, then that is what I will do.

You are right that it does start to look more like a generator type design and the ability to base it on a known / typical approach is a good thing.

The box and internal build / components are what I already use routinely in conversion van electrical systems, so the internal design is fairly typical of what would be used in an RV or boat. Trying to adapt it to this if possible without too many changes - but I am sure that there will be some.

In this particular box it is just:
- 2 batteries wired in series / 24 volt
- 1 kW continuous rated inverter
- solar charger
- dedicated 120 vac charger

Breakers, fuses, etc for the tasks.

So essentially 10 amps @120 vac

The other similar version that I build is essentially the same except 2 boxes:
- 48 volt battery pack box
- Electronics box
- 2 kW inverter

Essentially 20 amps @ 120vac


So the inverter size will not change over time. It is going to be either the 10 amp or 20 amp implementation.
 
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In order to put it outdoors, I will need to run a 120 vac line over from the garage breaker box for that portion - not a huge deal hopefully - probably will have to add some conduit.

There is a possible location for mounting the box outdoors on the electrical side of the house that happens to also be right behind the wall where that oxygen setup is.

So I guess I need to have a conversation with the city on what they would require to just run this as a specific critical load outlet into the room from outside. Maybe they will allow it / maybe not.

You are probably right about putting a small panel and breakers there to seem more legit. That is a fairly low cost item.

The house ground rod is in the same vicinity.

Thanks - yes some more concept development / refining to go, that is for sure.
 
For vans I use battle born LiFe 100 batteries for 3 season use, and Lifeline GPL-27s for 4 season applications.

It works out pretty conveniently as they are both nominal size 27 so my designs are all built around this concept of easy interchangeability. A few settings changes and then testing to make sure that it all is working.

Indoors it would be an easy decision to use the BBs. Outdoors it is right on the edge. We do get frost here on winter mornings a few times a year so still thinking about that decision. It also gets fairly warm here - 110 - 115 F in the summer.

Not really wanting to go down the heated battery path on this project if possible, so might have to just accept the AGM solution. I have 4 of them at the shop already so not a big problem. Obviously the Li solution has the usual benefits other than they high and low temperature ratings challenge.
 
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