House Battery and Energy Management

[Korishan]

So every 15 minutes, I'd be using the same power, but only 1/4 of the energy.

Well, not totally. Because what if for the hour you used 15kWh. However, in the first 15mins you used 70% of that and the subsequent 45mins the heater just idled keeping the temp stable.
So in this situation you had a surge of energy usage of 12,750 Watts. At 240V that's 54A

Now, during that 15 minutes, the power could certainly have gone lower or higher. But the average would still work out to 15kW and 3.75kWh. Not an instantaneous measurement of peak Watts or Amps

So yup. You got it here.

The reason I bring this up is because you need to also consider the "surge" periods. So with the above, if your furnace is pulling 54A currently, and you happen to turn on the electric stove (assuming you have one), then that could cause another spike that could push you into red zone.

I suppose what I aught to do is get one of those clamp meters with data logging. Something that would give me actual Amps and could measure a maximum peak.

What I would actually recommend here is getting something like an Iotta Watt or an Emporia unit. The Emporia is actually *very* well priced. For <$150 you can get 2 mains clamps with 8 circuit clamps.
The added bonus is that this unit can be reflashed with ESPHome energy monitoring to get rid of the cloud management portion (and giving data to the parent company).
You can upgrade the mains clamps to a higher rating if you need to. They also make a 3-phase version if you plan on doing that in the future.

https://www.amazon.com/dp/B08G37ML2R

The breaker labeled "blower" uses 42.5A. I think that's actually the element circuit. The other breaker labeled "furnace" uses 20A. I think that one is actually the blower circuit. I'm not sure if that's enough to calculate the BTU of the furnace. I also don't know if I'd need the same BTU for a heat pump.

Yeah, sounds like they labeled them backwards. Good thing you've checked before getting your fingers in where there might be live wires.
BTU's are BTU's. So if you have similarly rated heat pump, then the same heat will be produced. The difference is that the heat pump would, should, use a lot less power to create that heat.


*side note: I haven't read all of your previous postings in detail, so I may have overlooked some details. If so, please be kind in the corrections

 

[rebelrider.mike]

In fact I do have my eye on the Emporia device. I'm mostly just curious about the total power/energy usage of my house. I don't think it will have any practical value. Unless I win the lottery and decide to buy one of those big Generac whole-house generators. My friend Ken has one for his house. He got tired of lugging his portable generator out to power his basement sump each winter, only to have it not work for some reason during a power outage. His old generator is at my house now, awaiting diagnostics.

Well, speaking of generators, I've been looking into some that might work for backup power. I'm looking for a split phase 240V inverter generator. If possible, I'd also like it to be dual fuel and have an option for electric start.

Wen has one generator that mike work. The DF875iX has almost everything. It's not enclosed, so louder than other inverter generators. But Wen has tons of parts for sale right on their website. Other generators I've looked at don't seem to have parts available. It has an impressive THD of 1.5% at full load. (Why can't solar inverters do that?) Because it's an open frame design, it's not quiet or protected from the elements in any way. I saw one guy build a tiny vented shed for his. So this may be a candidate.

I was looking at a Google map image of my house, looking at good places for solar panels.

I think the carport would be a good place to start. It's large-ish, flat, slopes down towards the south. There's a tree that would have to come out, but I suspect it is the reason my sewer line keeps getting clogged with roots. And its right up against the fence. So it should probably come out anyway.

My back deck could really use a pergola whether I were to put solar on it or not. So it's another good place. It would also need to slope down towards the south because of wind I think. But nothing shades it all day. Hence the need for a pergola.

The roof is probably the only other place to put panels. It's not great. Its got steep slopes towards the west and east. East is facing away from the sun. West is good, but that side has so many things in the way. Vent pipes, a dormer, power lines on the other side of the dormer. A chimney. Also, this one I'd have to hire out because of the severe slope. Making it really expensive.

I've been thinking of those three places for a while, but I just realized I have a trailer that I'll be installing 1kW of panels on. I have another thread on that project here. It's going to be 24VCD though. Seems a shame to have a 1kW array and not use it, but I'm not sure how I'd integrate it to the house system. It would have to be easy to disconnect too, as we plan to travel in it a few times a year. I'll have to think about that.

 

[rebelrider.mike]

Well, I thought it over, and I think the best way to add the trailer's 1kW solar array would be with a boost regulator. There are solar boost controllers out there, but none that I could find that would work for this. With a boost regulator, I can limit the Voltage to the battery maximum, and the current to around 20A or so. A 1500W, 30A regulator like this guy should do it. The open Voltage of the array would be less than the battery's discharged state, so that should be ok. I wonder though about having a boost regulator on the battery, when there's no sun for the panels. Maybe I'll need a diode between the regulator and the battery?

The best way I think, to get the panels to the booster is to add a transfer switch between the panels and the trailer's inverter. Add a connector and cable to send the power into the house. I've had the trailer battery sitting on a shelf since August without power, and it's not dead yet. So sending power to the house battery for a while won't hurt it.

I'm not convinced this is a good idea. It's just the best one I've come up with so far. I did manage to find a 600W boost controller, but nothing higher yet.

I've also been wondering where I'm going to put all this stuff. I mean, it's all going in the basement, but will it all fit? I drew up a little diagram to see where things might go. The wall is to scale as far as height and width, but nothing else is. Maybe the door.

The gray areas are cinder block. To the right is a window. The left ends at the corner of the house. The white area used to be a garage door. It's now framed in with wood. I can't move the Main panel. I figure the sub panel and ATS should be close to it. The generator will be out side of course, though I'm not sure yet which side of the door the cable will come in through. Kind of depends on the generator, and where the exhaust goes relative to the control panel. The red bits are where I imagine conduit might go to protect the various wires.

I figure each battery box will have its own integrated 2 pole breaker that won't need to be mounted on the wall. Not sure exactly what the batteries will look like yet though. I'm pretty sure the solar panels are required to have 2 pole breakers between them and the charge controllers. I also want to add a breaker after the boost converter from the trailer. So I plan to get an 8 space DC breaker panel.

The roof panels are the last things I want to add since I'll probably have to hire that out. But because the solar company does a free assessment, including roof structure and a whole house energy audit, I may call them in first, before I do any of these things, just to get a ton of free info.

 

[rebelrider.mike]

I've been thinking about the trailer solar for a bit. I think it would be better to send power from the trailer to the house using the on-board hardware, rather than trying to isolate the solar panels. I mean that instead of trying to switch the panels between the trailer's charge controller to one in the house, just use the trailer's controller, and tap into the battery bus to send power to the house. I can use a programmable Voltage relay like this one to keep the trailer battery from getting discharged into the house battery at night.

It also looks like a boost converter would not need a diode for reverse current protection (for when the battery is connected to the output, but there is no power from solar at the input.) They seem to have internal diodes already from what I can see, as part of their design. So power would go from the trailer panels, into the trailer's solar charge controller, and then to the battery. I would attach the voltage relay to the battery bus and set it to something near the top battery Voltage. Then only excess power would be boosted to the house battery Voltage and sent off to the house through a cable.

This will simplify things in the house a bit too. I've drawn up a diagram of the DC circuit breaker panel. My understanding is that all the PV arrays have to be on 2 pole breakers to switch both the positive and negative leads. Required by code that is. I think all the DC inputs will end up entering the house at a single hole in the wall, which would be very nice.

Power from the trailer will be set to the house battery Voltage, so will head off to the battery bus directly. At the moment, I plan to use the inverter's internal solar charge controller for the carport array. The other two arrays will each have their own solar charge controllers, which will then connect to the battery bus.

 

[rebelrider.mike]

Yet more proof that I am a nerd:

You probably can't see the details, but this is a spreadsheet I made when I first moved into my house of all the things I want/need to do to it. Green=done, yellow=significant progress, blue=started, white=not started yet. I couldn't remember dates to save my life, so I have the year of completion listed for all the done things. When I feel overwhelmed by all the stuff I have to do, it's nice to look at this chart and see all the green that's happened.

I just thought I'd share because this was on my desktop PC which has been stored away for a bit, and I've finally got it set back up. I love my laptop, but it's like a mini cooper whereas my desktop is more like a semi truck that can do 0-90mph in half a second. And it makes snow cones.

Well, ok it doesn't make snow cones, but it does have all my major data files and I can draw much nicer diagrams on it. Like this improved one I made of the DC panel:

I've been thinking lately about my list of devices I want to power via solar or during grid outages. I've touched on this before, but I'm trying to figure out some details I don't think I've gotten into yet. It's more complicated that just adding up Watts.

Factors that make this less strait forward are:
- Not all devices run all the time.
- Some devices have peak startup draw.
- Some devices would not be run at the same time as others.
- Devices often draw less power than their sticker says.
- Some devices are used less than once a day, or can be unused altogether if the energy budget is not sufficient.

Addressing all these factors in a spreadsheet is a bit of a challenge. But here is what I have so far:

So for example, the space heaters would not be run at the same time as the A/Cs. The microwave and the cloths washer are run so rarely they barely count. If I'm using my CPAP, my laptop and most of the lights should be off. Not that they use much power. To account for all this, I've only added selected devices to the total under "Listed Watts" When I'm awake and using the most power, These are the things most likely being used. With the microwave being included because it has the biggest listed power draw out of the 4 appliances I mentioned.

For peak power draw, I plan to do the same thing. I don't know all those numbers yet. But when I do, I'll do some kind of selective addition for them too. Once that's done, I can compare with the peak supply ability of the generator, inverter, and battery, to see how they compare.

As for appliances not running 24/7 (most of them) I need an idea of how much energy they consume over time. For that I want to make actual measurements of each device as it's running normally, and try to estimate how long each one will run cumulatively throughout the day. I'm hoping that will give me an energy usage budget that I can compare with how much energy I can produce from solar and/or generator.

The generator is easy as long as fuel is available. Solar is more tricky. How many panels can I fit on my property? How many Watts per panel? How many Watt-hours per day? The most practical estimation I've seen so far is to figure that for every Watt a panel is rated for, one might expect 3Wh per day during good weather. And on dark winter days, one might expect at least 3% of that. I have 10 panels already for the trailer project. I'm guessing I could fit another 48 panels around the property, and that would all add up to around 13kW, or roughly 40kWh per day. In the winter that could be as low as 1kWh/day though.

I have a solar contractor picked out to help with a few things. They can do a structural assessment of where the panels might go, an energy audit of the house as it is, and a study of where the best spots would be to put panels, and how much energy they might produce.

 

[cak]

You are on the right track. There are two things you need to know about your energy usage to guide your solar and battery sizing.

1) how much energy you use (kwh). You just add up how much each device uses and how many hours in the day it is on. For things that change how much they use over time you can do fun math or just use something like a watt meter and leave it plugged in for a day/week and see hoe much the device uses over time, most meters will give totals over time. Also keep in mind how many days you want to be able to run without any power input(solar or grid) I aim for 3-7 days of autonomy since I am off grid.

2) Figure out your peak load (kw) so that you can get a big enough inverter. This seems to be where you have more uncertainty. If you have not control over what gets turned on when then you generally want to way over size this which is why most modern homes have 100-200A 24vac grid connections. However that would be some very big and expensive inverters so if you can be strategic about when the high load items are on and make sure to not put too many on at the same time you can optimize your inverter size. Startup loads are a consideration but mostly only come into play with large motors and power tools and many modern electronics have a soft start that reduces that initial spike. I have found that the kitchen tends to be my peak use case but I am also switching everything to electric and have on demand hot water in the plan so if you have a propane/natural gas stove that will change your peak usage scenario. My method of determining a reasonable max energy usage at one time is to add up all my constantly running loads(wifi router, maybe fridge and freezer although mine are actually on and off throughout the day), then look at all the high load devices(mostly things that heat or cool >1kw) and figure out which ones would be running at the same time in a worst case scenario, and finally add in a little buffer for random small loads also happening to be on at the same time(usually 0.5-1kw is sufficient for me. So as an example for my system my high load devices are Cooktop 2 burner(3.4kw), Microwave(1kw), Oven(1kw), Instapot(1kw), On demand water heater(6kw). My worst case scenario is that I am preparing a large meal and trying to clean up the prep dishes at the same time so the water heater plus up to 4 of the cooking devices with a 12kw inverter setup would still leave me about 600w buffer for random small loads being on. I might eventually add a heat pump but would make sure to not run that while I cook

Or if you have a fancy smart meter or add an AC monitor yourself you could also just look at your real world usage patterns to find what your peak load and daily usage is.

Solar production and sizing: Check out this resource for figuring out how much 1kw(or whatever size of panel system you can fit) would realistically produce in your area. It using daylight data and weather data and is industry standard for solar production estimation. It breaks things down by month so that you can aim for equaling your usage over the whole year or in my case size up the solar to meet my need on the worst production month. https://pvwatts.nrel.gov/

 

[rebelrider.mike]

Yep we're on the same page. Though with solar, I'm looking at it from a perspective of how much can I generate, and then budget that number. As opposed to starting with how much power I want. Like budgeting a paycheck. Of course, I get to use the grid to make up the deficits instead of a credit card, LOL.

Thanks for the link. I filled out what I could and it gave me these numbers:

These are way better than the numbers I was estimating. I added the kWh/day average to compare with the numbers I had previously. 13.7kWh/day is way better than 1.2! I can do a lot with 13.7kWh. Especially with a 14kWh battery.

I'm really bad at generating graphs in Excel. Despite many instructional videos, mine seem to be just flat lines with nonsensical data on the y axis. But somehow I accidentally made this:

Blue is kWh of projected solar production.
Red is whole house kWh usage for 2022.
Green is the difference if I'd had the solar hooked up last year.

It's not particularly useful since I'm not trying to run my whole house from solar. Just the key circuits. But this is the first graph I've been able to make in probably 20 years.

Speaking of key circuits, I've been building up that chart I made a couple posts ago:

I've got the cloths washer running now, with a couple meters on it. But check out the microwave. I was surprised to see a higher number of Watts being used than is posted. I made sure the sticker said "Input Power" too. It wasn't even using the integrated range hood lights or vent fan. I was also surprised that there was not much of an inrush current. I did some digging around on the ol' net, and didn't find much about microwave inrush current. Maybe it was over so fast the meter didn't catch it? Perhaps there are clever technologies built into newer microwaves that limit inrush current?

I added the generator, Solar, Battery, and an example inverter so I can compare Wh/day that I'd like to use vs. Wh/day that I can potentially store or generate. (Or manage in the case of the inverter.) My refrigerator is still running, so I can't measure the peak Watts until I've caught it.

I did a separate calculation to see how little power I could potentially live off of. Worst case, no grid, no generator, no solar. It wouldn't be fun, but I could get away with about 1200 Wh/day. That's about 12 days on just the battery. But that means even with a busted grid, I should be ok even on lean solar days.

The generator is not going to be run 100% for 24h/day. I just wanted to see the theoretical maximum. I hope to run it at 50-75% for just long enough to compensate for low solar days.

 

[rebelrider.mike]

I've measured enough stuff to start making some comparisons. I'll spare you the spreadsheets today, and just tell you that it looks like the peak power draw will be fine for the inverters I'm considering. In fact, looking at that and the constant power draw, I could add a few more items to the list.

It's also looking like I've over estimated the number of panels I'm going to need in order to power my selected devices for most of the year. I went back and crunched some numbers as far as kWh/month, based on which devices I'll use each month. What I mean is that I separated the year into 3 sections: Winter, Spring/Fall, and Summer. The differences are that in winter, my wife will be using a space heater in her office. In the summer, we'll have 3 air conditioners running. (Actually 5. But two are upstairs on circuits I can't power from solar.) In Spring/Fall, we'll be using neither heat nor cooling.

So this new graph shows our power usage from the sub panel instead of the whole house:

Truthfully though, this is the same graph from before. I've been learning how to modify it. Still don't know how I managed to bring it into being. The red bars are kWh used, the blue bars are kWh generated by solar, and the green is the difference. So positive green means I have to buy from the PUD to make up the difference. And negative green is potential solar energy that would go unused.

I've actually been reducing the number of solar panels and running the kW through the PVWatts website. I'd like to strike a balance between having to buy in the winter and having wasted potential in the summer. I think the next thing I'll do is get one of those home energy monitors to have a better picture of what my individual circuits are doing. Getting a heat pump should also reduce or eliminate the need for A/C units. Even though the heat pump won't be on solar, the A/Cs are. I don't know when I'll get a heat pump. Hopefully in the next year or two.

 

[italianuser]

Very good stats . It's important to validate your models (your spreadsheets) by checking if the numbers are correct. Your laptop power usage comes from the label on the PSU, I suppose 65W; that's a typical notebook PSU but my laptop uses around 20W during 90% of the time. Also my fridge is labelled 150W but uses 75W most of the time.

Having more panels than your estimated number would be OK for me, your could one day add more battery storage.

 

[rebelrider.mike]

Same. My laptop power usage varies depending on what I'm doing. I picked what I thought was a reasonable amount, with the internal battery charged, and me watching a You Tube. I got the original value from the back of the laptop itself. I figured it would be the the maximum the laptop could use. The fridge has auto defrost and an ice maker with a door dispenser. So it could use a lot more power but with those things off, it doesn't.

I've got two priorities going on that I think I need to separate better: Power during an outage, and reducing the electric bill during normal times.

So first, the highest priority: having some power during an outage. A generator would do the job, but I'd have to run it all the time, and be constantly feeding it fuel. With a battery/inverter setup, I'm hoping the generator could spend most of its time not running. And with a few solar panels, I'd need the generator even less. I added up a few things and got this:

-Running a 7,000 Watt generator at about 75% capacity for 2 hours a day will get me 10,500 Wh per day.
-In December, the worst solar month of the year, I could average about 5,613 Wh per day.
-A house battery could provide up to 14,000 Wh of extra power during lean solar days, or make up for extra power used.

The way I figure it, between the generator and solar I'd have 16,000 Wh per day to use, and the battery would be a buffer between times of extra usage and low power generation, vs. low power usage and high power generation. I've also determined that I can get away with using less than 2,000 Wh per day, so on an average winter day I wouldn't need the generator at all. Long duration power outages usually happen after wind storms around my place. Those are usually in January or February.

One other thing to note, though I'm not sure where it goes, is that the inverter has an internal battery charger. Limiting the current of the charger so that the generator is still at 75% capacity, I can charge the battery from dead to full in about 3 hours. Rounding up a ways since batteries take more power in than they give back out. And the inverter would only be charging at about 85% of its maximum current. So no one is being stressed.

I completely forgot until just now that inverters use their own power just to be on. The unit I'm looking at uses 115W. I haven't factored that into any of my calculations yet. I gotta go fix that.

 

[italianuser]

I completely forgot until just now that inverters use their own power just to be on. The unit I'm looking at uses 115W. I haven't factored that into any of my calculations yet. I gotta go fix that.

Yes, when you have a load of panels you don't feel it at all. With a few panels like me it's like having an extra fridge!

 

[rebelrider.mike]

I don't know why the inverter power usage never occurred to me. I've certainly kept track of it in my research. I've got it added in now. It does make a dent in the calculations since it runs 24 hours/day. But it's not catastrophic. In fact, it caused me to look at the power outage situation a bit differently.

The leanest month (solar-wise) is December, and I can still produce on average over 5kW of power per day. And I can charge my 14,000kWh battery in about 3 hours via the generator as I mentioned in my last post. So I can actually use quite a few devices during an extended power outage, and still only need the generator for 3 hours per week:

With the battery as a buffer, the exact number of days between generator charging doesn't much matter. If fuel is scarce, we can turn some things off. And if the power outage is in January or February, (as is most likely) we'll have even more solar to work with.

On to my second priority: using solar to reduce my electric bill.
Since I'm going to have solar panels anyway, may as well use them all the time, right? Well, I've gone on for quite a bit in previous posts about this, but something I realized is that when grid power is available, I'll be using a lot more than what solar can provide. Actually, a lot of stuff changes around when energy is plentiful.

So that means I could potentially put a lot more circuits on my solar powered sub panel. (I keep wanting to call it my solar panel.) Just use fewer things if there's a power outage. But the more circuits that are on the sub panel, the more likely it will be that I can get the most out of my solar array. Especially during the summer where I still have some solar energy wasted because it can't go to the whole house or back to the grid. In the event of a loss in grid power, the battery would make up the difference until I have a chance to turn stuff off.

Two features of many inverters that make this possible are grid passthrough and load sharing. I don't know if those are the right terms or not, so let me explain.

What I mean by grid passthrough is that the inverter I'm looking at can pass up to 40A from the main panel (grid) directly through to the sub panel without any sort of processing or conversion. So regardless of how much solar or battery I have available, the grid can make up the difference. I just have to make sure not to put too many circuits on the sub panel. Just like any other sub panel.

For load sharing, I mean that the inverter can set solar power as the priority and then use the grid to make up the difference if necessary. So if I'm using 4kW total, but the solar array is only producing 3kW, the inverter will pull the other 1kW from the grid. This seems to be a feature that is only available in some inverters. Reading through various user manuals, sometimes it's clear whether the inverter does load sharing or not. Other manuals are not clear. None of them have this feature listed as a specific thing, so there has been no term that I could find that specifically describes it. Searches around the internet have not yielded any cluse for me either. It's difficult to trust the exact wording of these manuals because they're pretty much all translated to English from a different language.

For a while I had this confused with peak shaving. But that is using the battery during peak energy usage times, and charging the battery during off-peak times in order to save money. My utility doesn't charge different rates for different times, so that doesn't affect me.

Speaking of money, I think I have enough figures in place to start estimating some savings. More on that later...

 

[rebelrider.mike]

It took some doing, but I managed to reverse engineer my electric bill. It looks strait-forward on the surface, but it turns out some of the taxes tax other taxes and they don't tell you which ones. Being taxed for a tax I had to pay seems a bit unethical to me. But I guess I can't do much about it.

I have the basic energy usage fee, a daily fee, a flat charity fee, a low income housing fee, two state taxes, and a city tax. The charity fee is not taxed by anyone. The other fees are taxed by one state tax, and that total is taxed by the other state tax. And that total is taxed by the city tax. Clear as mud?

Anyway, I left out all the things that would not be affected by my energy usage. What I had left was the energy fee and the three taxes. I added those up based on how much energy I'm guessing would be used by the sub panel. Then added up energy used from the solar array, not counting wasted energy in the summer. Then found the difference.

The result is a complete work of fiction based on guesses, but as my guesses get closer to real life, so will the projected amount of money I've saved. As of today it looks like I might save $375 per year. May not seem like much, but that is about what we spend on our energy bill in the winter each month. I remember when we first moved into this house, the monthly electric bill for winter time was closer to $600.

Another way to look at it is that this will be my first hobby to actually pay for itself.

Speaking of hobbies, I've been thinking on what will be my priorities this year. The weather is going to be getting nice soon I hope. So things I hope to do this year:
- Install the energy monitor.
- Buy a sub panel and ATS and install them.
- Continue working on the basement.
- Start working on the camping trailer.
- Finish the Yamaha SR500.
- Improve more electrical in the house.
- Attic ventilation and insulation.

That's probably more than enough to keep me busy. Let's see how much I can get done in the next 8 months or so.

 

[rebelrider.mike]

Got the Emporia Vue energy monitor installed yesterday! It all went great, except one of the 16 sensors isn't working. I sent them a message, and they've already agreed to send me a new sensor. In the mean time, I've got the first 24 hours of data. Unfortunately, it's not reading the Amps accurately. I may have to open another support ticket about that. It's not just a little off, it's way off. The fridge uses 2.2A and the Vue measures 1.45A. The freezer uses 2.65A vs the Vue measuring 1.47A.

I did some math, and found that if I multiply the Vue's readings by 1.58 the numbers start to match up. I got the same factor for the freezer too. I guess it makes sense that all the inputs would be off by the same factor. I'll have to check more circuits.
Hopefully I can get it figured out soon.

The time measurements are accurate though, and I've already discovered that the fridge and freezer will likely be running more hours a day than I thought.

The fridge had 66 cycles over 24 hours and ran about 8 minutes per cycle. Roughly 8.8 hours total. By my estimate, that would have used 2.32 kWh. According to the Vue it used 1.38 kWh. With the correction factor, it came out to 2.18 kWh. So corrected, that's pretty close to the estimate. Now, I assume 120V all the time, and my actual Voltage can vary from 118V to 123V depending on the time of day. Also, I don't account for power factor. I don't know if the Vue does or not. But neither of those should affect the Amp measurement.

Anyway, I also looked at the freezer.

It had only 28 cycles, but they lasted for 24 minutes each. The freezer also uses a bit more power than the fridge. Also, I noticed that the freezer draws some small amount of current even when it's not running. Not sure what that is. It's a super simple freezer. No light bulb, no defrost. It is very old. I got it used and abused for free many years ago.

So a little disappointing that it's not accurate, but maybe it can be fixed. It's still giving lots of useful information though. I'll go see if You Tube or Google has anything to say about it.

 

[paulie]

Here in the UK, I am with OVO. I already have a grid tied system 4KW (more like 3.5KW on 21st June lol) so my energy usage is not bad. My homebrew system will initially run my workshop office. Fridge, freezer, computer, lights and cell chargers. Here is a snap shop of what info I can get from OVO

 

[Korishan]

So a little disappointing that it's not accurate, but maybe it can be fixed. It's still giving lots of useful information though. I'll go see if You Tube or Google has anything to say about it.

Interesting. I've been contemplating getting a system as well. They are very well priced for what they do. And the bonus take away is that they can be reflashed with ESP-Home and easily integrated with HomeAssistant

As for the off readings, that almost sounds to me like a calibration issue. There might be something in software, or a trim pot to dial in the readings. Something that should have been done from the factory, imho. But I suppose there's always some variances in the resistors there were used during construction that could cause some drift from one unit to the next.
The current readings are done using voltage dividers (at least that's how OpenEnergyMonitor does it), so maybe they got an incorrectly labeled reel of resistors

 

[rebelrider.mike]

At the moment, I'd still probably recommend one even with the readings being a bit off. It's still a lot of info for what you pay. Especially with the free cloud service.

Unfortunately, You Tube was a bust. Just lots and lots of unboxing and installation videos. I did read one guy saying that the Vue has separate modules inside the box that each measure 8 of the 16 inputs. I didn't really understand the details so I can't explain it, but maybe only one side is miscalibrated.

I looked at the microwave circuit which is measured on the other side of the box, and it is pretty darn close to the multimeter reading. Same with the electric water heater. I also checked the mains current. 127A on the Vue, 63A on each leg on the multimeter. So 126A and some decimal that I forgot while I was walking back to the computer. So pretty much dead-on.

I'll have to take a manual reading of each circuit and compare to the Vue to see exactly what's going on.

I did find a potential workaround. Each circuit has a Voltage multiplier that can be adjusted in the software. It is primarily for measuring 1 pole of a 2 pole circuit so that the Vue will know to use 240V instead of 120V. I used my correction factor there and it now reads about right. Doesn't affect the Amps reading, but it makes the Vue think the Volts are different so the Watts come out correct. If the time and Watts are correct, then kW and kWh will be correct too. Which is what I'm most interested in anyway. Not ideal, but I can work with it.

I'm hesitant to open up the box just yet. Finding a calibration pot would be fantastic, but I want to get more info on exactly what it's reading before I mess with it. Maybe see what their tech support suggests. And getting all this info is just too fun to turn the thing off right now.

Another interesting observation. I don't have a sensor on my furnace, but since it's 95% of the power that my house uses, I can basically watch the mains power on the Vue to see what the furnace is doing. There are two jumps in power when the furnace turns on. I'm guessing one is the blower, and the other is the heating element. Neither have a huge startup power draw. I'm a bit surprised by this, but maybe they have some kind of soft start device built in. The Vue is able to catch the spikes from the fridge and freezer no problem. The microwave is the same way. No measurable spikes by the Vue or the multimeter I have that can measure and save max Amp draw.

 

[rebelrider.mike]

I went and measured 13 of the 16 circuits, and only 3 so far are inaccurate. The 3 I haven't measured yet I won't get to for a while. Putting in the correction factors seems to be working. Even on the data that was recorded before gets corrected.

I've also noticed that while the Vue can catch a peak draw from a circuit, it doesn't seem to be fast enough to catch the full value. Probably because it only measures in 1 second intervals where as my multimeter measures several data points per second. I don't remember how many. So I'll just have to catch it with the multimeter. No big deal, that's not really what the Vue is for anyway.

I made a new table based on circuits instead of individual devices. Theses are candidates I'm looking at for moving to the solar sub panel. The correction value is the multiplier I'm using to correct the inaccuracy of each circuit. Default is 1, so those circuits are already reading correctly. I've just realized that the water heater is actually set to 2 since it's on a 240V breaker.

Some of the circuits I want on the solar sub panel don't exist yet. And the Misc. circuit hopefully won't exist much longer. But the circuits I've highlighted in blue are ones I definitely want on the sub panel. The rest I'm not sure.

Some of this depends on when I can get a heat pump. The heat pump won't go on the solar sub panel. It will still be too big. But it will hopefully eliminate the need for the 3 window air conditioners that I've been using each summer. People on the internet say that an electric furnace's BTUs can be calculated by multiplying the Watts by 3.412. That would mean my 15kW furnace is 51,180 BTU. Folks also say that can be shortened to tons by dividing by 12,000. That would be 4.265 Tons. So it would seem I need a heat pump that is sized either 4 or 4.5 tons to replace the furnace.

I'm not sure it's so simple as that, but it gives me a starting point as far as looking at heat pumps and what they cost to install. I still want to get a professional out who can do a Manual J assessment so I don't have to guess. But that is still waiting on things that have to wait on other things. Nothing is ever easy.

 

[Korishan]

Probably because it only measures in 1 second intervals where as my multimeter measures several data points per second.

The default firmware probably does 1000sps and then averages the value over 1s. I can't imagine they are using an ADC that's slower than an ADS1115, or similar. That would be really stupid, tbh. Maybe this is one reason why there are those reflashing it with a custom firmware to unlock more potential.
It would be nice to be able to calibrate each port independently of not only voltage, but also current. By increasing voltage, it is effectively changing other calculations.

 

[rebelrider.mike]

I've gotten the impression that Emporia is still developing the software. If so, more features could be available in the future, without having to replace the software. I don't know anything about the electronics involved that you mentioned. But averaging over 1 second makes sense. These peak power draws seem to last less than a second. It's made me wonder about how to figure the peak load on a solar inverter or inverter generator. Since these peak draws last a second or less, what are the chances that two will happen at the same time? Maybe for determining peak power draw, I should add the biggest peak to the maximum constant load. I'll have to think about that.

The Vue's 1 second intervals are definitely more useful than my house meter's 15 minute intervals.

It occurs to me that maybe the sensors could be giving a low signal, and the central unit may not be to blame. I've already found a sensor that didn't work at all. At some point I'll try swapping a known good sensor with one that's reading low, and see if there's any difference.

Emporia has already set up an order to ship me a new sensor. They didn't even ask me for a serial number or proof of purchase.