Inverter noob wants to install a partial house system.

[rebelrider.mike]

Hi all.
I'm looking into installing a sub panel next to my main panel. As I've been upgrading my old house, I've been adding more and more circuit breakers because of codes and such. I'm actually trying to use less power. But my main panel is getting full.

I'd like to add a backup generator and transfer switch to the sub panel, and later a battery/inverter setup and maybe even some solar. I know a bit about solar, and a lot about batteries, but very little about inverters. I have a "small" battery that can run a mini fridge for several days on a single charge using a WZRELB inverter.

I'm on the US power grid, so split phase 240V. I don't plan to have any 240V appliances on the sub panel. I am thinking I'll want 8 circuits and up to 6kW available. That translates to 50A at 120V, or 25A at 240V. I don't plan on sending power back to the grid for money. Though that is an option in my area. Not sure how much solar power I'll actually be generating. We got 136 inches of rain last year.

I've watched hours of videos, and read through reams of web pages and PDF files. Though I'm learning a lot, it's all very confusing and I don't know how to translate it into buying stuff that will work for my particular system. I think I need a split phase inverter since my power requirement is too high. I'm using the grid as the primary source of power for now until I get solar installed. That could be years away though. It would be nice to power the sub panel from solar with the grid as a supplement/backup for when the solar/battery can't provide all the power.

I don't plan to use any power tools or well pumps. So I don't need a low frequency inverter. It's odd; I keep hearing that inverters are commonly high frequency, yet almost all the ones I've seen for sale are low frequency. Does it even matter?

Here's a list of things I'd "need" to have on backup power, assuming that things like cell towers and ISPs are still working:

Fridge: 6.5A 780W (2.2A 264W)
Freezer: 3.5A 420W
Laptops: 19.5V 3.3A (x2) 128.7W
Cell Phones: 0.5W (x3) 1.5W
Gateway: 18W
Router: 9W
Wifi: 18W
CPAP: 5.3W

If there's no internet or cell towers working, I suppose the various electronics become unnecessary. 1380.5W total.

Here's more things I'd really like to have, assuming I can generate the power, and if water is available. My community has until the water tower is empty before the taps quit working.

Microwave (input): 1700W
Cloths washer: 9A 1080W
120V heaters: 750W (x2) 1500W
5,000 BTU A/C: 4A (x4) 1900W
Lights: 10W (x6) 60W

6240W total. Though one could lower this by not running the microwave and washing machine at the same time. Or turn of the heaters or some of the A/C units. And we'd certainly not run the A/Cs and heaters at the same time. So more like 3660W.

Let's say it's hot out and we're running all 4 A/C units. Laptops are on, but fully charged so only using half of their total power. Maybe a couple lights are on. And we decide to heat something up in the microwave. Total would be 3730.5W. If the fridge and the freezer happened to be running at the same time, that would be 4930.5W. About 82% of the capacity of a 6000W inverter.

I could install the generator, transfer switch, and sub panel as early as this year. No point in getting an inverter right a way. I have no batteries for it yet. That's a whole other project. In fact, I started thinking about this stuff back in 2017. But I've been focused on making my old house more energy efficient with modern NEC compliant wiring.

I picked out a 6kW dual fuel inverter generator. I don't plan to have automatic switching between the grid and generator. I spent many hours trying to figure out exactly how it works (not just the theory) and came up with nothing. My electronics have their own UPSs anyway so it doesn't matter.

With the generator installed, the priority would be grid, then generator obviously.
With the battery and inverter added, the priority would be grid, then battery, then generator.
With solar added it changes up a bit. Solar, then battery, then grid, then generator.
I've read that some inverters will use solar/battery and grid at the same time. Using the grid only to make up for a lack of power from solar. I don't know which ones those are though. Would be neat if possible.

I've got a long list of inverters I've been looking at. Unfortunately, specific details are hard to find on many of them. The answers may already be on this forum, so I'll start searching here before I ask.

Well, here are the assumptions/guesses I've made so far. Let me know if I'm anywhere close?

- I need a split phase inverter (or a dual setup) because I want up to 6kW of power available.
- High frequency inverters would be better for me as I don't have any heavy inductive motors to start up.
- If pizza has something from all four food groups, it must therefore be a health food.
- I'm looking for a grid-tie inverter, but not necessarily a hybrid.
- I should get a 6kW generator if I want a 6kW inverter.

 

[DIYrich]

You need a Transfer Switch (manual or automatic) to switch your load on the sub-panel from Grid to Generator. Isolation Relay also works. This keeps the grid from backfeeding the generator, and the generator from feeding the grid (safety of line workers). Automatic Transfer Switches are designed for generators or Solar that can run off-grid.

If you want to power 6kW, you also need to take into account startup draw (motors can take up to 3x running watts to startup). Make sure the generator has both adequate running watts and surge capacity.

If you are going to be grid tied, then you might as well have 240v inverter. You can balance the 120v loads onto the different legs.

What is your budget?

Growatt is a good system on the less expensive side.

Sol-Ark is on the more expensive side (it is an all-in-one). You can attach a generator to it, and it will isolate it from the grid (don't need the Transfer Switch). Look at the wiring diagrams in the manual to give you an idea how to wire it (generator on Gen Input line, sub-panel on Load output line). You can then add battery. And then you can add solar.

 

[rebelrider.mike]

The first part of my plan is to install a sub panel so I can separate out the circuits I want to power with solar, and have backup power to if the grid fails. To start off, I'll power it through an ATS and generator. Something like this:


I've been looking at various generators, and have come up with a list of criteria that I want.
- <5% THD.
- Dual fuel. Gasoline or propane.
- 240V split phase.
- At least 6kW.
- Field repairable. As in parts must be available for purchase.

At the moment, I have my eye on the WEN DF875iX inverter generator.

I'm building a list of appliances that I want to run on solar/backup. It's not done yet, but here's what I have so far:

Hopefully you can see it ok. I'm particularly interested in the peak startup. or inrush current for each device, and how much power each will use during normal operation. I think the totals have to be weighted though against the fact that not all appliances will be running at the same time, and most will not be running 24h/day.

Once I have all the numbers, I can compare them to what the generator, battery, solar and inverter can do. Then I'll have an idea as to whether I'm trying to use too many things, or if there's room for more. The totals on those are theoretical maximums. I wouldn't run my generator at 100% for 24 hours.

It's frustrating how many appliances don't have peak amps listed; even online. I'm having to measure it all myself. And I don't own the water heater yet. I'll probably have to be content with guessing for now. The heat pump it uses is 4,200 BTU, so I'm guessing the peak amps are about the same as a 5,000 BTU air conditioner.

Budget varies from month to month. On a good month, I could spend up to $1500 on parts or whatever. So any single part I need that's less than $1500 is fine if it seems worth the cost. Something like a Sol-Ark inverter being $6200 is way outside my price range. I'm working on a list of inverters that either I've found myself, or others have suggested. It will include specs for each unit that I think are important to know.

 

[rebelrider.mike]

I've been looking at the differences in my power needs during normal times vs. a power outage.

My first priority with all this is to have power to key circuits during a power outage. Second priority is to shave some money off my electrical bill when the grid is operational.

I did some research at a website called pvwatts.nrel.gov, and found that a single solar array might meet my power needs. December would be the leanest month as far as solar generation, but I still might average 5.6 kWh/day. I could use a little more than that, and charge up the battery every few days to make up the difference. This seems pretty doable.

As far as reducing my monthly bill. Most of the year I would be generating much more than 5.6 kWh/day. I don't plan to try to sell power back to the power company, so I'm going to try to find a balance between having to buy power during the winter, and generating more power than I need during the summer.

There's a feature that some inverters have that I think is called load sharing. It's hard to tell which inverters have it. It's not listed in any specs, but sometimes it's in the manual's settings depending on which inverter I'm looking at. Some have it, some don't, and some I can't tell. Anyway, what I mean by load sharing is that if I'm using say, 4 kW of power, and only 3 kW is available from solar, the inverter will draw 1 kW from the grid to compensate. Some inverters seem to only switch between grid and solar in an either/or situation. So I'll have to be careful to get an inverter that has this load sharing feature.

It's far from done, but I've made a graph:

It compares generated solar energy with energy used by the sub panel each month. The green is the difference. Positive green is where I have to buy to make up the difference, and negative green is unused solar energy. I'm sure this will change as I get more accurate estimates of things.

 

[rebelrider.mike]

I've researched a lot of inverter brands and models. I put together a table of inverters and features I'm looking for.

For me, the type of inverter that would work best is a single unit with split phase 120V/240V. If I were to buy one today it would be the EG4. It comes closest to having all the features I want. For now, I'll be watching to see what new inverters come to the market, and see if any will work better than the EG4.

 

[DIYrich]

Might want to add the Sol-Ark 5k to the comparison list.