House Battery and Energy Management

[rebelrider.mike]

The Misc. circuit has an interesting story. And by interesting, I mean long and boring. When we first moved in, the Misc. circuit was a collection of branches that seemed to feed about half the house. The whole upstairs minus the bathroom, but including a 120V Cadet heater. All the lighting on the main floor, the bathroom receptacle, and the two receptacles in the kitchen. Needless to say, it tripped a lot.

We had the refrigerator in the dining room, and pretty much couldn't use the kitchen or bathroom outlets for quite a while. I found that pretty much all the wiring was made of the old insulated knob and tube stuff. Some of which was in perfect condition, some of which was deteriorating from obvious overheating. When I remodeled the kitchen in 2016, I found hidden junctions in the wall without boxes, and mostly held together with wire tape. It all got upgraded, and the kitchen has 5 new circuits that are up to code. The range and the dishwasher already had their own circuits.

I've also been upgrading other parts of that Misc. circuit, to take more load off of it. I've since found more junctions in the attic with no boxes or wire nuts. Some wires are simply wrapped around exposed sections of other wires and covered with tape. The goal is to eventually make the whole circuit go away.

In other news, I decided to get myself an NEC 2020 code book. Now if only I had the decoder ring too... Well I may not be able to interpret it, but I'll at least be able to reference it when asking questions. Washington only adopts every other code update, so It should be good for another 3 years I think.

I've collected enough information now to know what circuits I want on the solar sub panel. Some of the circuits aren't finished yet, and some don't exist yet, so I've been planning things out a bit. I've been thinking about how circuits on sub panels are supposed to be "paired" so that the sub panel can be as balanced as possible. It's caused me to rethink the positions of all the circuits I have everywhere. I've color coded each circuit position on each panel so that I can easily see which positions would be paired so that one space is on bus A while the other space is on bus B. I hope that make sense.

2 Pole breakers are self balancing of course, but an example of a good pair would be the fridge and freezer. Both run often and take kind of vaguely the same amount of power. And with all these circuits on the sub panel, the main panel is freed up for future stuff.

I've also used colors to show which circuits need what. White are ones I'm still not sure about. Blue are ones I'm sure of, but haven't started yet. Yellow are in progress, and green are finished. I don't know when I'll be getting a heat pump or replacing the conventional water heater with a heat pump water heater. So for now, those are just sort of place holders.

Just for fun, here are the other two sub panels I'm working on:

The second floor sub panel is for all the wiring I'm replacing in the attic. When I moved in, the carport had an old Zinsco breaker panel feeding an outlet and a big ol' yard light. I'm sure that panel wasn't rated for outdoors, and it was pretty corroded. I took it out, but I need to replace it with a proper outdoor load center. I'd also like to expand the outdoor lighting and receptacles, so I'd like them to be on two separate circuits.

I'm down to choosing between a 16 space panel and a 20 space panel for the solar sub panel. 20 would give me spaces for future circuits, but I'm limited to 40A total, and I don't want to overload it. The main panel will have plenty of space for new circuits, just not powered by solar. The main and solar sub panels will be within inches of each other, so it physically wouldn't matter which panel I used for new circuits. 16 would save space, but then I'd be limited. The cost is about the same. I don't know.

 

[rebelrider.mike]

Continuing with the idea of balancing the two phases, I'm also thinking about the solar inverter and inverter generator, and how they have certain limitations because they'll be making split phase power too. So each phase of a 6kW inverter can do 3kW per phase. So you can't just have a limit of say, 4kW total on the inverter. It has to be split up. Also, the neutral wire has a 3kW limit too. As I learned recently, if the load is balanced, the neutral will see very little current.

I made a table based on my best guess for maximum current for the sub panel. Some were easy like the freezer or water heater. The lighting circuits I counted up how many Amps would be used if all the lights were on at the same time. The convenience outlet circuits were more difficult. I used data I've been getting from the Vue, and added in some specific devices like the air conditioners that haven't been running yet but will be at some point. Anyway, I came up with this:

These are not positions on the panel. Rather, these are circuits separated by which bus or phase they are using. Assuming all the circuits are running everything at the same time, I get some theoretical but very unlikely totals.

The inverter can actually invert a total of 25A per phase, but with load sharing, can send up to 40A per phase through to each bus. In the case of these maximums, that means around 10A would come from the grid to make up the difference that the inverter can't produce. But I'm well within the limit of how much the inverter could directly pass through from the grid to the panel.

Of course with a power outage, I wouldn't be able to use this much current. I'd have to do some budgeting. But that's easy. Looking at bus A, I'd never use the dishwasher and clothes washer at the same time. I already don't do that. Don't want to overwhelm my sewer connection. It also works out that each bus will have 2 window A/C units using about 4A each during the summer. Those could certainly be turned off for a bit to run other stuff. And the microwave only has a cumulative usage of maybe 5 minutes each day.

Something I didn't think about at the time I chose to have a split phase system, but I think is pretty cool, is that high peak loads will be separated between the phases. So having the freezer and refrigerator on separate phases will always keep their peak startup power separated, even if they were to activate simultaneously. I think it's extremely unlikely that that would happen, but still...

I counted the water heater twice, because it's a 2 pole circuit running on 240V. The heat pump on it uses about 400W, so each bus would see around 1.7A I don't know the peak current draw for it since I don't own one yet. It's 4,500-ish BTU, so I imagine about the same as a window A/C unit. Mine are 5,000 BTU.

 

[rebelrider.mike]

I've been watching the circuits on my Vue, and I'm seeing something curious about my freezer. It uses 13-15W of power the whole time it's compressor isn't running.

Is that normal? My fridge uses nothing between cooling cycles except the light bulbs and the ice maker. The freezer has nothing extra in it. No defrost function; not even one light bulb. I verified with a multimeter, and made sure no other things were on that circuit. It was made in 1988, so after 35 years, maybe it's time to replace it. It sure keeps the food frozen after all these years.

At least part of it's life was pretty rough. My church owned it before me. It lived in a small room with no air circulation along with other freezers and fridges storing food for the food bank. Seems every year they had to replace one from burning out. No wonder. The room was like a furnace year round. Anyway, this freezer they couldn't get the door to shut anymore so they gave it to me for free. Turns out it just needed to be defrosted, and then the door shut fine.

In the last 24 days it's used 78.6kWh. I figure that's about 1,195kWh per year. Home Depot has some nice ones that only use 227kWh per year. Might safe me a few dollars. More importantly, it would free up some Amps on the solar sub panel for other circuits.

 

[Redpacket]

I've been watching the circuits on my Vue, and I'm seeing something curious about my freezer. It uses 13-15W of power the whole time it's compressor isn't running.

That'll probably be the heater elements (go figure, heaters in a fridge??!!!) they put around door edges to get the ice down...
Mine has these too. Can feel warm bits where they are. Got to be a better way!

 

[rebelrider.mike]

I've been concerned lately that a 6kW inverter may not be enough for what I'm trying to do. The problem isn't Watts, but Amps. Using a split phase inverter, I'm limited to 3kW or about 25A per phase. That makes it difficult to add some of the more power hungry devices like the clothes washer and the microwave. I've started looking at inverters in the 8-12kW range, even though I don't plan to use that much power for the vast majority of time. The good news is that they're not much more expensive, and many have better features than what I was considering settling with.

One in particular that has caught my eye is the PowMr POW-SunSmart 10K. It's grid-tie, but I can still use it as an off grid inverter. It checks a lot of boxes for me, including being able to send over 40A to each phase continuously. 60A peak. So now I have two inverters on my short list.

In the meantime, I've been attempting to decipher the rapid shutdown requirements described by the 2020 NEC. Since my panels won't be on my roof, it makes things a bit complicated. Seems all solar arrays now need rapid shutdown capability, but only the roof mounted ones need remote shutdown capability. My plan at the moment is to install a lockout switch that shuts off both the positive and negative conductors. I haven't figured out yet whether to put it up in the array itself, or down by the rest of the electrical stuff as it enters the house. I think it just needs to shut off any conductors before they enter the house. But I'm not sure yet.

I've also been looking at how to ground the array. The aluminum frames I guess can have their own ground rod, though it still needs to be connected to the house ground rod. Seems the negative conductors of the whole DC system are also supposed to be grounded in one location. Assuming all the negative conductors have continuity. I'll have to be careful exactly how I do that.

 

[not2bme]

Going larger is probably safer at the cost of more idle power consumption. But that is just what's baked into your calculation (just throw a couple more panels it's not really an issue once you go big ie. over 20kwh batt). If I was to start over, I would probably consider getting a Model 3 battery and hook it up to a HV inverter. 85kwh battery can be had for around $5-6k. That brings it down to around $60-70/kwh. BMS controlled from SimpBMS. Water cooled/heated. Dala here has shown hooking it up.

But as for the split phase thing, my Schneider does something neat when grid tied. If I try to pull 3kw from one leg, it only supplies 1.5kw from the inverter and uses 1.5kw from the grid. It then sends out 1.5kw through the other leg.

L1 = 1.5kw(inverter) + 1.5kw(grid)
L2 = 1.5kw(exported)

So technically the inverter is supplying a balanced load on both L1 and L2. It just sends one to load and the other leg to the grid. As far as the meter is concerned, no power is used since it was a net zero. This could be a Schneider thing, so I can't vouch for other inverters.

Another thing with inverters are how well it handles overloads. You can check out DavidPoz on youtube on his overload videos. He has done quite a few test on many inverters, such as starting miter saws where the surge kills most inverters. So my Schneider units can go 25% overload for 30 mins and 50% overload for 5 mins as long as the temp is within spec. That's common for most inverters that uses a toroidal transformer vs the other kind that's mosfets or whatever it's called, like my old mppsolar unit, which is light and cheaper to make, but god forbid if I had to go 25% over for more than a couple of seconds. So in that case, size appropriately.

 

[rebelrider.mike]

I'm subscribed to David Poz and also Will Prowse. Trouble with them and many other reviewers is that they do their reviews off grid. So we rarely get to see how the inverters behave when connected and interacting. I know that Schneider and Victron use toroidal transformers. Many others use low frequency brick shaped ones. The high frequency ones use the tiny "electronic" transformers and don't have the overload capacity like you said.

That balancing feature on the Schneider is a neat trick. I don't think it's common. I've seen several videos of people "fixing" their Sol-Arc phase imbalance with auto transformers. Something interesting is that the PowMr actually uses less idle power than the EG4, even though its 4kW bigger. I'm still looking for reviews on it, and haven't seen any.

With 5kW to work with on each phase, I shouldn't have any overload situations. Even the peak startup current on my various loads will be less than the max continuous current. Here's a table of specs I put together comparing the two inverters that are pretty close to what I want:

One thing I'm curious about is that I don't know the PowMr's transformer type. They also don't say how long the inverter can hold the peak output. I'm assuming a fraction of a second. That's something I'll want to try to find out at some point.

Switching gears a bit, I've been attempting to understand rapid shutdown requirements. My situation is a bit different than normal, as I plan to have a pergola on my deck with the solar arrays as the roof. I'm not sure exactly how rapid shutdown should apply. I made a diagram (surprise!) to try to get my ideas across:

I've got three shutdown locations in mind. Lockout switch 1 would be located at the array and directly shut off the output there. The concern I have is that I think the shutdown is supposed to be grouped with the other shutdown locations. For me, that's utility, battery, and the generator inlet over by the house.

Lockout switch 2 would also directly disconnect the array before any conductors enter the house. And it could be located near the other shutoffs. But my concern there is that the conductors from the array to the house would still be live. Though they shouldn't be anywhere that a firefighter would ever need to take an axe to.

Lockout switch 3 would disconnect the solar array indirectly by controlling a set of relays. This allows the conductors to be shut of at the array and keeps the switch near the other shutoffs. This introduces extra parts and makes me feel like it would be more likely to malfunction. I know they make wireless devices that operate remotely. Those seem to be expensive and are even more complicated that using relays. They also require that I buy a control unit for each panel or every two panels. I'd like a single relay for the whole array. I think code allows that. There's also no reason for a firefighter to ever have to hack through an individual panel since they're not on my roof.

I wonder if I could find a 2-pole relay instead of having to use two normal ones. I also wonder if the rapid shutdown requires both conductors to be disconnected or if the positive one would be sufficient. Code just says to reduce the Voltage. Full isolation disconnect seems to be allowed separately. Like at the 2-pole breaker I plan to have inside the house. (That's the "B20A" box I have in the diagram.)

Speaking of codes and diagrams, I've been working on my whole system diagram. I decided to highlight each area as it pertains to specific articles in the NEC. I'm actually rather proud of this one:

I still need to read articles 702 and 710. Not that I understand it when I read it. The actual understanding comes from You Tube and websites, LOL.

 

[floydR]

One thing I'm curious about is that I don't know the PowMr's transformer type.

It is a high frequency inverter so it probably can't handle many more watts than it rated wattage. The max solar panel input voltage is more than most DIY solar systems. Not sure what Lithium battery activation means.
later floyd

 

[OffGridInTheCity]

Quick Disconnect - a key issue is what does you're local jurisdiction require?

In my case, for off-grid / traditional panels (non-micro-inverter) there must be 1) quick disconnect + 2) label with voltage/amps outdoors within 10ft of the array.

Roof array....

Yard array....

These quick disconnects block current from the array combiner box -> house. They also house the lightning arrestor connections (e.g. surge protection). They do NOT stop potential current within the panel wiring such as during a fire (wires melt together) or fireman using axes to break thru the roof etc.

As I understand it, some jurisdictions might require quick disconnect at each individual panel - e.g. one of the feature of panel based micro-inverters is they can offer this as an option - but my jurisdiction allows traditional arrays and this was not required at the time I did the permit.

 

[rebelrider.mike]

Thanks Floyd! Where did you find that label?
I'd prefer to have a low frequency inverter, but as large (in Watts) as this one is, I think it would do fine. It has two MPPT inputs, but I'll only need one.

It looks like I'm going to have to contact L&I directly about a couple things. One being rapid shutdown requirements of a solar array that's neither on a roof, nor on the ground. The other is about batteries. I've read through article 480, and it looks like a DIY Lithium Iron Phosphate battery may not be an option:

480.3 Equipment​

Storage batteries and battery management equipment shall be listed. This requirement shall not apply to lead-acid batteries.

From the NEC's list of definitions:

Listed. Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose. (CMP-1)
Informational Note: The means for identifying listed equipment may vary for each organization concerned with product evaluation, some of which do not recognize equipment as listed unless it is also labeled. Use of the system employed by the listing organization allows the authority having jurisdiction to identify a listed product.

I guess I could look for individual cells and BMSs that are listed. L&I has a list of laboratories that they accept listings from. Nothing I want battery-wise is listed. Or I could just buy a listed pre-built set of batteries. Or I could go with lead-acid as those have no listing requirements.

Another possible issue. I went online to see about permits. They don't have any relating to solar. Closest I could find was generator transfer equipment. Another reason to go in and talk to them directly. I fear I may have to choose between doing this without permits/inspection or not doing it at all...

 

[floydR]

Thanks Floyd! Where did you find that label?

the link you posted to the inverter powmr inverters to the right of picture if it preforms as listed it is 20,000W max much more than I thought. details under data sheet. Aparrently it is UL listed.
Later floyd

 

[rebelrider.mike]

Thanks. As my grandpa Bob would have said, if it were a snake it would have bit me, LOL. Yep, it conforms to the UL1741 requirements. They list the 20kW max but don't mention how long it can do that. I bet it's for only a second or two. Plenty of time for the startup current from fridges and freezers.

 

[rebelrider.mike]

Huzzah!
I stopped by L&I today and asked about solar permits for homeowners. Turns out they have them under additional service installation. So I can definitely do my own work. I was so excited, I forgot to ask about rapid shutdown and ESS requirements as far as safety listing. I'll figure those out later I guess. Not like I'm in a hurry. For now, I can go back to learning stuff and making plans.