Looking to add solar to house and have a reasonably short ROI

[Cowdog360]

Hey all,

I'm in Washington state, and our electricity is super cheap at 8.7cents/kwh. So any solar system that I want to do with a less than 15 year payback pretty much has to be DIY. What I was hoping to do is have a system that can have a few batteries to act as a whole house UPS, and offset some of my daily usage.

I use about 55kwh/day as my house is predominantly electric with heat pump, heat pump water heater, etc, and an EV. Here are some shots of my backyard and the roof I have to work with. The main upper roof is west facing, the lower bump out on the house is south facing, and the small roof over the garage is also west facing. In the backyard, I have considered maybe a small ground mount setup where the kid's playset is. My tiny little 4x8 shed has a pair of 235W panels on it right now and just a single 12V 100ah battery and victron controller. It's mainly for charging up the batteries in the lawn equipment, but I'm also seeing if I can work it to provide enough oomph to power the pool filter in the summer (480W).

Since it's about $350 for the utility to hook up the net meter, I was considering just starting out with something smaller that I could consume during the daytime. Like maybe 4-6 of the 400W bifacials on that smaller lower south facing slant hooked up to an EG4 6000.


Question time: Am I going to need to move my loads I want to primarily run from solar and have the option to battery back to a sub-panel? I don't need the heat pump, water heater, EV, or clothes dryer on the solar side. I have a natural gas furnace that I could kick over to in the winter in a UPS situation, so I'd mainly want to run the house loads and furnace blower on the solar to start.

Thanks!

 

[OffGridForGood]

First, I would like to say - Welcome to the DIY Solar Forum @Cowdog360 - you have come to the right place.
A few things:

I'm in Washington state, and our electricity is super cheap at 8.7cents/kwh. So any solar system that I want to do with a less than 15 year payback pretty much has to be DIY. What I was hoping to do is have a system that can have a few batteries to act as a whole house UPS, and offset some of my daily usage.

You're right, with low utility cost, there is little opportunity for ROI, although in my own thought process, utility rates are likely to increase over the coming years, can't be bad to have another option.
WA/PNW in general may give you some challenges too.
First recommendation: Seach the net for PVWatts.nrel.gov - plug in your address and it will pull up a calculator for you.
you can input the PV array size you are thinking of, or just put 1kW and the results are easy to scale up by multiplying.
PVWatts will let you put other info like the angle of that roof you considering, and if you use the compass setting on your smart-phone you can tell PVWatts the direction of the roof - ie even if you think the roof faces 'south' you may find it a bit East or West of South.

I use about 55kwh/day as my house is predominantly electric with heat pump, heat pump water heater, etc, and an EV. Here are some shots of my backyard and the roof I have to work with. The main upper roof is west facing, the lower bump out on the house is south facing, and the small roof over the garage is also west facing. In the backyard, I have considered maybe a small ground mount setup where the kid's playset is. My tiny little 4x8 shed has a pair of 235W panels on it right now and just a single 12V 100ah battery and victron controller. It's mainly for charging up the batteries in the lawn equipment, but I'm also seeing if I can work it to provide enough oomph to power the pool filter in the summer (480W).

Since it's about $350 for the utility to hook up the net meter, I was considering just starting out with something smaller that I could consume during the daytime. Like maybe 4-6 of the 400W bifacials on that smaller lower south facing slant hooked up to an EG4 6000.

I feel you are on the right track, it would be a large system to supply 55kWh per day, and PV Watts may tell you near impossible during some seasons.
A separate smaller system that can supply some loads, and give you a back up system for utility outages is a reasonable plan.
If the roof area limits your PV to 4-6 panels (1.6kW to 3kW) PVWatts will show you what you can expect per month. (divide by 30/31 days to get daily kWh)

Question time: Am I going to need to move my loads I want to primarily run from solar and have the option to battery back to a sub-panel? I don't need the heat pump, water heater, EV, or clothes dryer on the solar side. I have a natural gas furnace that I could kick over to in the winter in a UPS situation, so I'd mainly want to run the house loads and furnace blower on the solar to start.

I suggest you consider a Critical Loads Panel - that can be supplied via utility and your planned off-grid solar set up. For a small selection of critical items it is an easy way to toggle what loads are on solar, or on utility at any time, and easy to show other family members how it works (if this is needed)
Some truely critical loads are fridge and chest freezer, lights in key rooms like kitchen and bathroom, your furnace fan as you noted, I would suggest a few key outlets for things like internet router, iphone charger, maybe your coffee pot outlet (hey coffee is critical in my home).
I have a Reliance 306 which gives me 30A to work with, and six circuits. Each can be individually toggled utility or solar as needs may be.

In your situation you may find during fall/winter some very low daily solar days, but you still want your fridge and freezer to run, so as long as the utility is available, you can toggle these onto utility and reduce the load on solar. You will come to learn how much can be on the solar half, and for how long, during crap overcast weather.
Batteries are expensive, but you can start with a small bank, and add to it over time if that suits the budget best. I started with one inverter and one server rack battery so I could play with the system, learn what it could do, and NOT do, and then built up from there. I think it is a great learning experience as well as feeling more in control over how your home can operate even during grid down.

Final comment: on the resources you will see a spreadsheet that will help you to identify and quantify all the loads you want on solar, this helps to set a reasonable target for how much the system you have in mind will be able to run.

Post questions, everyone here will help you.

 

[Cowdog360]

First, I would like to say - Welcome to the DIY Solar Forum @Cowdog360 - you have come to the right place.
A few things:

You're right, with low utility cost, there is little opportunity for ROI, although in my own thought process, utility rates are likely to increase over the coming years, can't be bad to have another option.
WA/PNW in general may give you some challenges too.
First recommendation: Seach the net for PVWatts.nrel.gov - plug in your address and it will pull up a calculator for you.
you can input the PV array size you are thinking of, or just put 1kW and the results are easy to scale up by multiplying.
PVWatts will let you put other info like the angle of that roof you considering, and if you use the compass setting on your smart-phone you can tell PVWatts the direction of the roof - ie even if you think the roof faces 'south' you may find it a bit East or West of South.


I feel you are on the right track, it would be a large system to supply 55kWh per day, and PV Watts may tell you near impossible during some seasons.
A separate smaller system that can supply some loads, and give you a back up system for utility outages is a reasonable plan.
If the roof area limits your PV to 4-6 panels (1.6kW to 3kW) PVWatts will show you what you can expect per month. (divide by 30/31 days to get daily kWh)


I suggest you consider a Critical Loads Panel - that can be supplied via utility and your planned off-grid solar set up. For a small selection of critical items it is an easy way to toggle what loads are on solar, or on utility at any time, and easy to show other family members how it works (if this is needed)
Some truely critical loads are fridge and chest freezer, lights in key rooms like kitchen and bathroom, your furnace fan as you noted, I would suggest a few key outlets for things like internet router, iphone charger, maybe your coffee pot outlet (hey coffee is critical in my home).
I have a Reliance 306 which gives me 30A to work with, and six circuits. Each can be individually toggled utility or solar as needs may be.

In your situation you may find during fall/winter some very low daily solar days, but you still want your fridge and freezer to run, so as long as the utility is available, you can toggle these onto utility and reduce the load on solar. You will come to learn how much can be on the solar half, and for how long, during crap overcast weather.
Batteries are expensive, but you can start with a small bank, and add to it over time if that suits the budget best. I started with one inverter and one server rack battery so I could play with the system, learn what it could do, and NOT do, and then built up from there. I think it is a great learning experience as well as feeling more in control over how your home can operate even during grid down.

Final comment: on the resources you will see a spreadsheet that will help you to identify and quantify all the loads you want on solar, this helps to set a reasonable target for how much the system you have in mind will be able to run.

Post questions, everyone here will help you.

Thanks, that’s all very helpful.

How do you move your critical loads of of the main panel into a new panel, do you have to pull the wires out of the old panel and drop them into the new one? Or do people just extend the wires from their old panel into the new one? Luckily my garage over the panel area isn’t fully insulated so I can get to all of the house wiring.

 

[hwy17]

When you shop for your CLP I would get one with a main breaker on it so that you can add a generator interlock, and then you can have a regular grid feed from main panel to subpanel in parallel with the inverter feed from main to sub, as a backup and for doing maintenance. The inverter's load circuit would feed into the interlocked "generator input" of the CLP.

Whether you want to move all the romex over or just splice and pipe it is up to you, the latter will be less work and is fine. "Inline" wagos are available online and make for tidy splices in the panel.

 

[ksmithaz1]

Frankly, if ROI is your main goal, Micro-Inverters and general grid tie will save you the most money for the lowest capital outlay. You can't easily run from pure solar you will need some battery, if you don't grid tie. Battery is the most expensive component of a system that can operate stand-alone. Permitting for a small grid tie system should not be that expensive.

Since you say you want backup the game is going to be time (battery) + DEMAND.

The minute you jump to the next level, I'd just drop an ATS in front of your critical loads panel, and get an AiO like the 6000XP/18KPV/SolArk15 or similar. No point in getting into all the interlock stuff, or creative wiring, just feed a 25-100A (Match your solar output) breaker from your current panel to an ATS as "backup" along with the inverter as the "primary" input. ATS out to the sub-panel and your golden. This is my exact setup. Simple to wire, no confusion, if the inverters are working they feed the panel, if not you fail over to the grid. The 6000XP has the ATS part built-in. but you would need to paralell units to grow output

I'd been using the cheapo DIN rail Chinese ATS, it just died after 2+ years, I had a couple of spares on-hand, swapped it in, annoying but straightforward. When I started It was switching frequently between grid and inverter for input, but as my system stabilized pretty much twice a day every day, off when the batteries were dry, on when the sun had them charged up enough to run things and keep charging. At this point,I've doubled my battery to 60KWH, and my system has not cut over to the grid for more than few minutes since January (I had two short manual cuts because of a maintenance/engineering issue ). My last bill was $23.

I bought a heavier duty 160A ATS that I will be implementing as I move things and add a third inverter bringing my DEMAND capacity from 100A to 150A. If you are going to get happy and parallel inverters at some point, I'd go with an independent ATS. If you use the one on the inverter now you can't just yank it off the wall, though you could put a manual bypass in front of it, but then why not just have an automatic one behind both sources instead?

I made my "Critical Loads" sub-panel a full size 100A (Derated breaker) panel. I just moved everything over once I figured out my DEMAND. Put a sensor on your primary feed and log it. See what your peak draw is. The batteries are going to be the most expensive thing, it's a vicious cycle, I'm tossing PV need more battery, can't get the battery charged need more PV, ...

Enjoy.

 

[OffGridForGood]

When you shop for your CLP I would get one with a main breaker on it so that you can add a generator interlock, and then you can have a regular grid feed from main panel to subpanel in parallel with the inverter feed from main to sub, as a backup and for doing maintenance.

Or use the inverter AC input for the generator input to the system, and avoid the interlock, allow automation if you like.
Or use a Chargeverter to allow the generator to directly recharge batteries without affecting the rest of the system.

 

[Cowdog360]

Frankly, if ROI is your main goal, Micro-Inverters and general grid tie will save you the most money for the lowest capital outlay. You can't easily run from pure solar you will need some battery, if you don't grid tie. Battery is the most expensive component of a system that can operate stand-alone. Permitting for a small grid tie system should not be that expensive.

Since you say you want backup the game is going to be time (battery) + DEMAND.

The minute you jump to the next level, I'd just drop an ATS in front of your critical loads panel, and get an AiO like the 6000XP/18KPV/SolArk15 or similar. No point in getting into all the interlock stuff, or creative wiring, just feed a 25-100A (Match your solar output) breaker from your current panel to an ATS as "backup" along with the inverter as the "primary" input. ATS out to the sub-panel and your golden. This is my exact setup. Simple to wire, no confusion, if the inverters are working they feed the panel, if not you fail over to the grid. The 6000XP has the ATS part built-in. but you would need to paralell units to grow output

I'd been using the cheapo DIN rail Chinese ATS, it just died after 2+ years, I had a couple of spares on-hand, swapped it in, annoying but straightforward. When I started It was switching frequently between grid and inverter for input, but as my system stabilized pretty much twice a day every day, off when the batteries were dry, on when the sun had them charged up enough to run things and keep charging. At this point,I've doubled my battery to 60KWH, and my system has not cut over to the grid for more than few minutes since January (I had two short manual cuts because of a maintenance/engineering issue ). My last bill was $23.

I bought a heavier duty 160A ATS that I will be implementing as I move things and add a third inverter bringing my DEMAND capacity from 100A to 150A. If you are going to get happy and parallel inverters at some point, I'd go with an independent ATS. If you use the one on the inverter now you can't just yank it off the wall, though you could put a manual bypass in front of it, but then why not just have an automatic one behind both sources instead?

I made my "Critical Loads" sub-panel a full size 100A (Derated breaker) panel. I just moved everything over once I figured out my DEMAND. Put a sensor on your primary feed and log it. See what your peak draw is. The batteries are going to be the most expensive thing, it's a vicious cycle, I'm tossing PV need more battery, can't get the battery charged need more PV, ...

Enjoy.

Yeah, the more I think about things here with how long the payback is for any system, I’ll probably design it more as a whole house UPS that can run a bank of critical loads for a few hours during an outage, as they typically are infrequent and don’t last long. But it would be nice basically to have it grid tied to sell back when I’m not charging the batteries or consuming everything I generate. Even just considering 5-10kwh of battery and a small 2kwh array to start might be a good way to get started. That sol-ark looks amazing, just a bit more than I wanted to spend. I’ll have to consider all the angles for sure. I like the idea of doing 100A subpanel, and moving over a lot of things.

Are those in-line wago connectors to splice between panels code compliant? I like the idea of not necessarily removing the original wires from the original panel in case I ever want to revert things or sell the house.

I already do have an Emporia Vue monitoring 16 circuit and piping all the data into Home Asisstant, so I’ll be able to tackle that shortly.

 

[OffGridForGood]

I’ll probably design it more as a whole house UPS that can run a bank of critical loads for a few hours during an outage

Keep in mind Lithium-Iron-Phosphate (LFP) batteries should not sit long periods at full 100% SOC waiting for infrequent utility outages. If you plan to have the solar as a UPS, consider other batteries, or plan for some loads to allow the LFP to move up and down the SOC scale daily.
I found in my own early set up just load-shifting was easy and fun: we have Time of Use (ToU) rates, such that off peak rate (for charging) and on peak rate (discharging) saves a fair chunk of money off the monthly bill. Not sure if you have ToU rates in your area, but if you do, it may be worth considering as it will provide some ROI, and allow the battery SOC to move daily.

 

[MisterSandals]

I’ll probably design it more as a whole house UPS that can run a bank of critical loads for a few hours during an outage, as they typically are infrequent and don’t last long.

This is a very reasonable first step. To make it really simple, consider having your UPS/inverter be "extension cord ready". If you lose power, plug in the fridge and other necessities via extension cord. I got thru this stage needing to use it only twice over a 2 year period and it met our needs with minimal effort nicely.

But it would be nice basically to have it grid tied to sell back when I’m not charging the batteries or consuming everything I generate.

Micro inverters, which was mentioned by @ksmithaz1 is also an easy solution and gets the ROI going.

Charging/maintaining batteries from solar produced AC is easiest. Having a distinct DC solar system with SCC to charge/maintain batteries is a lot of fun, especially if you can make it portable for camping or ...

Scroll thru the "Show and Tell" section for inspiration and ideas.

Good luck, enjoy the adventure and welcome to the forum.

 

[ksmithaz1]

The monitoring is really going to help you tremendously. This will give you your demand needs for whatever you decide are your critical loads. If your willing to buy the batteries you'll want to have maybe twice what you need to run your critical loads for the desired time. This will give you some flexibility, and allow you to play around and figure out what works, and give you an idea of how much more of this cruft you will end up buying, er, I mean how much more might be useful if you decide to expand the system.

Have fun!