Off-Grid Build - Thoughts?

[atrain0007]

Hey all, first post here, after reading a fair bit. Was looking for feedback on my build on things I may have overlooked or things I'm doing wrong.

Im in San Diego County and looking at trying to run a 2br 1100 sq ft weekend place on all electric. Big loads include a well pump, heat pump water heater, mini split, washer/dryer, stove/oven, fridge, and then the usual lights and stuff and some security cameras, and starlink service. Im thinking:

11,000 watts of solar through 24 - 460 watt BluSun bifacial panels on a solar carport with 3-8 panel strings producing 406 volts and 11.8 amps, running two of those paralleled into the
1 - eg4 18kpv inverter
1- eg4 powerpro

The carport is about 110' away from the inverter and planned to run the 12AWG from the one string and 10AWG for the paralleled strings through conduit from the panels with a ground back to the house/inverter.

I have a 12500 watt generator I'd like to wire up as a backup, but havent dug to deep into that yet. My goal would be when we are there for the weekends, or maybe some longer trips, we arent relying on the generator much.

I appreciate any feedback you guys see fit. One concern is whether the appliances might draw more than the 12k watts the inverter can put out? Also, when the inverter is wired to the load panel, do you run it into the main 200 amp service lugs, or is it supposed to go through a smaller breaker on the panel? if so what size to allow it to use all its available current?

Thanks,
Adam

 

[JWLV]

This is just my assumption without knowing your power usage.

You should do a power audit to find out exactly how much power you use. If you are thinking that one EG4 18kpv is insufficient, that would mean that your usage might exceed 12kw. And if you are using 12kw at any time, a fully charged Powerpro will only be enough to power that load for only one hour. If that's the case, you'll need half a dozen or more Powerpros.

 

[scrubjaysnest]

Do an energy audit. This defines battery bank size which then defines solar array size. A 900 sq ft 2 bedroom with propane heating and cooking will require about a 25kwh battery bank. And that is probably conservative.

 

[LywWyr]

I wouldn't pay for a hybrid if no grid is available.

 

[Spartan]

The most cost effective thing to do is to first figure out how to use less power. Electric stove, house-heat, water heating and clothes dryer can all be converted to propane / natural gas. The upsizing of solar panel capacity, generator size and inverter capacity to do all these things via electric are really going to start adding up system costs.

I'm successfully running a 3 bedroom, three bath house of about 2,500 square feet with a 4200 watt solar array, 8,000 watt inverter and 840 amp hour led-acid battery. Water heating, clothes drying, cooking and house heating is all by propane which means I don't have to have an even bigger generator, inverter, battery capacity and solar array to try to create heat with electricity which is very inefficient. A Grundfos AC/DC well pump will cut power demands even further.

Are you committed to building a system that can run these big electrical loads at any time of day or are you willing to move big electrical heating loads to gas?

 

[atrain0007]

This is just my assumption without knowing your power usage.

You should do a power audit to find out exactly how much power you use. If you are thinking that one EG4 18kpv is insufficient, that would mean that your usage might exceed 12kw. And if you are using 12kw at any time, a fully charged Powerpro will only be enough to power that load for only one hour. If that's the case, you'll need half a dozen or more Powerpros.

Thanks for that feedback. Since this place is a new build, we dont have any historical data to go off of. Im kind of looking at appliances that I'm considering buying but dont have yet (and their max wattage) to guess how much output I might need at any time. Since we are in a pretty sunny area, and would not likely have big overnight loads, I was hoping it would be ok. Maybe wishful thinking.

 

[atrain0007]

Do an energy audit. This defines battery bank size which then defines solar array size. A 900 sq ft 2 bedroom with propane heating and cooking will require about a 25kwh battery bank. And that is probably conservative.

That's certainly bigger than I was estimating based on new appliances, mini-splits, etc. I was thinking the wattage picture looked something like this:

	standby	running	peak
well pump	0	1800	5400
mini split	10	3000	4000
stove/oven	5	2000	8000
water heater	2	2500	9000
lights	0	500
fridge	0	1061
starlink	20	75
cameras	10	160
dryer	0	3000	5600
washer		300

So obviously that goes over the 12,000 watts the inverter can handle, but I dont know that we'd be running all the major draws at once. Appreciate the feedback!

 

[atrain0007]

I wouldn't pay for a hybrid if no grid is available.

This is a fair point. The grid is not an option at our location (and I'm happy about that). The two reasons I was considering the 18k were: 1. It seemed like an easier setup that the eg4 6000xp; and 2. The warranty is 10 vs 5 years on the 18k.

The warranty piece is the bigger mover of those two factors, since I'm sure I can manage the extra cabling/settings. Its hard to know what the extra 5 years of warranty would be worth...

 

[atrain0007]

The most cost effective thing to do is to first figure out how to use less power. Electric stove, house-heat, water heating and clothes dryer can all be converted to propane / natural gas. The upsizing of solar panel capacity, generator size and inverter capacity to do all these things via electric are really going to start adding up system costs.

I'm successfully running a 3 bedroom, three bath house of about 2,500 square feet with a 4200 watt solar array, 8,000 watt inverter and 840 amp hour led-acid battery. Water heating, clothes drying, cooking and house heating is all by propane which means I don't have to have an even bigger generator, inverter, battery capacity and solar array to try to create heat with electricity which is very inefficient. A Grundfos AC/DC well pump will cut power demands even further.

Are you committed to building a system that can run these big electrical loads at any time of day or are you willing to move big electrical heating loads to gas?

I hear ya!

One of the goals for the project was to move all electric. Gas is an option, but I think I'm willing to trade the extra costs for the simplicity of just the one power source. If it the house and appliances can just "work" without training spouses and friends and family about propane and generators and all that, we will get more use out of the place and enjoy it more. Its definitely a big trade off.

The plan is to use some less-thirsty appliances if possible: induction stove, heat pump water heater, mini split for heating/cooling. There are limitations for sure, but I'm hoping they close the gap a bit.

 

[Doggydogworld]

Two sources gives some redundancy. But if A/C is the long pole in the tent then heat pump is "free". Climate and house design matter a lot -- if summer nights are cool and winter days are sunny you can design with minimal HVAC. Hot nights in summer (or poor house design) require a big battery. Cold, cloudy winter stretches require a big battery and/or combustion heat.

How many days a year will it get used?

 

[Spartan]

If it the house and appliances can just "work" without training spouses and friends and family about propane and generators and all that, we will get more use out of the place and enjoy it more. Its definitely a big trade off.

I'm not sure where the training comes in when using propane? All my propane devices just work like their electric counterparts. Even the backup propane generator is fully automatic-on, automatic-off so there is no training involved.

If you're building from the ground up, you have the perfect opportunity to blend energy sources (gas/solar) in a way that balances and complements the energy needs of your off-grid home. My house was built from the ground up as an off-grid home so everything we did was designed to work together. We designed our house so that you would never know you were in an off-grid home unless we told you.

I noticed in your energy audit you listed 1800 wats for the well pump with a startup draw of 5400 watts. Had I installed a traditional 240 volt well pump, I'd be looking at about 3000 watts to pump water into my storage tanks. By installing a Grundfos efficient AC/DC well pump, I'm using 400 watts to pump water from 90 feet. Because the pump has a soft-start, there is not peak energy burst at startup.

You've got 3000 watts listed for the heat pump. By heating with a propane, whole-house system, I am only intermittently using 600 watts for the electric fan that circulates the heated air through the ductwork. Similar with the propane-heat clothes dryer. If you install a wood stove, you'll use propane heat even less. The gas oven uses zero electricity. As for refrigerators, they are so efficient now compared to a decade ago that you'll notice people aren't installing propane powered refrigerators like in past times.

So, as you can see, selecting the right alternative devices drastically reduce the sizing of inverter, battery and solar array capacity. Yes, you can design to be all electric but if you have to understand what that will cost you compared to blending in some propane powered devices. You're going to find the cost savings are significant by using propane for devices that need to generate heat. We had a fairly generous construction budget but even then it didn't make economic sense to put in electric ovens, water heating or house heating along with the size of battery bank, inverter and solar array to run them.

Building your vacation house sounds like a fun project by the way. Good luck!

 

[atrain0007]

Two sources gives some redundancy. But if A/C is the long pole in the tent then heat pump is "free". Climate and house design matter a lot -- if summer nights are cool and winter days are sunny you can design with minimal HVAC. Hot nights in summer (or poor house design) require a big battery. Cold, cloudy winter stretches require a big battery and/or combustion heat.

How many days a year will it get used?

Its in the high desert of so-cal , so we get cool at night in the summer, and it should be sunny most of the winter. I am banking on these qualities helping reduce some of the electrical needs...

We will be there a couple dozen weekends a year and maybe another week or two for a couple longer stays.

 

[Doggydogworld]

Its in the high desert of so-cal , so we get cool at night in the summer, and it should be sunny most of the winter. I am banking on these qualities helping reduce some of the electrical needs...

We will be there a couple dozen weekends a year and maybe another week or two for a couple longer stays.

OK, let's say your system averages 50 kWh a day production. You can store 14 kWh. If you fully use that 14 kWh plus half the other 36 that must be consumed in real time that's 32 kWh/day of consumption. If you're there 60 days a year that's 1920 kWh per year. $20k system cost and 20 year life is $1k/year simple cost and closer to 2k/year including time cost of money, inverter replacement at 10 years, etc.

So about $1 per kWh.

Note this cost varies directly with usage. If you only spend 30 days a year there you pay more like $2/kWh, if you move there full time it's only 17 cents/kWh.

$1/kWh is on par with the all-in cost to run a generator and more than the equivalent cost of propane for heating, hot water and cooking. So there's no strong financial reason to favor solar or to avoid it. 11 kW of solar plus a propane generator wired into the inverter and set up for auto-start is a pretty "hands-off" system. I'd use a tankless propane water heater for hot showers even if the inverter or generator fails. I'd back up the mini-split with propane space heating for the same reason. Add a propane grill outside and you can even cook without electricity.

With all that your 14 kWh battery could last an entire cloudy weekend without generator noise. You might even cut down to 18 panels in a 2x9 setup (a bit over 20' x 20') and save a few grand on panel and wire cost. Depends on how much A/C you need. Clever house design can cut A/C load -- cool roof, thermal mass, insulation, etc. Likewise, passive solar can reduce heating load.

Absent propane you probably want a bigger battery. People here tend to have 1-3 days worth of full production, around 50-150 kWh for your system.