100% off grid modern home?

[EastTN Offgrid]

So, we live in East TN and want to build a new home on our land. There is no electric service, so we want to be 100% off grid on Solar with a generator backup. We are a family of 5, and want to be sure to have all of the normal modern day amenities. My guess is if we build it big enough, we can do this? Planning for a ground based array and then basement located batteries. About a 3000-3500 sq ft home, Heat Pump (Geothermal). Maybe the Split Phase ACs, or do we go full central AC?

 

[x98myers7]

first off... welcome!

yes, totally doable at just about any lat/long. it all comes down to budget. IMO, I would go for multiple smaller fixed ground mounts at varying heading to maximize production through the day. i would have a small climate-controlled utility building housing all the batteries and equipment, then run AC to the house. eliminates the major fire hazard of having that much lifepo4 in the main living area.

suncalc.org + PVwatts will give you the best idea for production capabilities. for load estimates you can probably just base them on your current utilization.

have fun!

 

[EastTN Offgrid]

first off... welcome!

yes, totally doable at just about any lat/long. it all comes down to budget. IMO, I would go for multiple smaller fixed ground mounts at varying heading to maximize production through the day. i would have a small climate-controlled utility building housing all the batteries and equipment, then run AC to the house. eliminates the major fire hazard of having that much lifepo4 in the main living area.

suncalc.org + PVwatts will give you the best idea for production capabilities. for load estimates you can probably just base them on your current utilization.

have fun!

Thank you! I will check out those resources. If I were to locate the batt/equipment in an out building or detached garage, can i run both AC/DC to the house? I was thinking about running most of the lights and some outlets on DC.

I am excited to tackle this part of our project as a DIY - my wife, not so much.

 

[x98myers7]

If I were to locate the batt/equipment in an out building or detached garage, can i run both AC/DC to the house? I was thinking about running most of the lights and some outlets on DC.

yes, absolutely. I dream about that kind of new build. haha. the possibilities are only limited to your budget.

 

[houseofancients]

Thank you! I will check out those resources. If I were to locate the batt/equipment in an out building or detached garage, can i run both AC/DC to the house? I was thinking about running most of the lights and some outlets on DC.

I am excited to tackle this part of our project as a DIY - my wife, not so much.

doesnt really make sense to run dc .
it will just increase complexity, and a whole lot of extra wiring, while connected devices will be more expensive

 

[Cyanlite]

3500sq feet needs probably 25-35kW of solar. With about 60kWh of batteries, you're getting in close to the $50-80k range. Maybe even more if you need more batteries and inverter redundancies. If you're running on well pumps for water, you definitely need enough batteries there to support that for extended periods of cloudy days.

There are things you can do to reduce your solar/battery needs: geothermal since it requires no compressors/condensers. Solar hot water heaters, induction cooktops or propane. Heat pump electric dryers or propane. Energy efficient refrigerators and freezers, TVs, and WiFi router.

 

[EastTN Offgrid]

3500sq feet needs probably 25-35kW of solar. With about 60kWh of batteries, you're getting in close to the $50-80k range. Maybe even more if you need more batteries and inverter redundancies. If you're running on well pumps for water, you definitely need enough batteries there to support that for extended periods of cloudy days.

There are things you can do to reduce your solar/battery needs: geothermal since it requires no compressors/condensers. Solar hot water heaters, induction cooktops or propane. Heat pump electric dryers or propane. Energy efficient refrigerators and freezers, TVs, and WiFi router.

You are in the ball park. We are thinking 25Kw array and 50Kw batt bank. The well pump will be on its own array and bank, but we are using a Grundfos SQFlex pump. It is both AC or DC powered. I have it hooked up for DC off Solar, and then a gas powered generator as backup for AC power. The plan is to also have a 1,000 gallon water tank as a reserve to pull from. So the well pump can fill it all day long on solar at 11GPM.

I would love to run a geothermal heat pump and then we might need 1-2 strategically placed split phase AC, or maybe just some of the Midea-U window units.

Propane will be the cooking and hot water fuel. But i also saw someone's setup that "dumps" the excess solar power when the batteries are full into a traditional hot water tank. Might see what can be done there. But primary would be a propane fired on-demand hot water system.

Dryer is already gas. but yeah, I am trying to figure out how to used other options and less load on the electric. For heat we plan to build a large masonry oven in the middle of the house. If that works out as planned, I might skip the geothermal heat pump (unless I use it as AC too).

So many ideas and plans.

 

[Bluedog225]

Yeah. No point in DC to the house. Your big challenge is enough batteries to last through the night running air conditioning and other loads. Figure 5-8 (max) hours of solar production. And figure how many watts you need per hour to get you through the night. That’s a good start.

Then you can layer on a few cloudy days.

 

[rhino]

but we are using a Grundfos SQFlex pump

So you already have this pump? Those are pretty pricy and if you are already going to have AC power could use much cheaper 120V AC powered Grundfos and put the savings towards the other equipment.

 

[peakbagger]

Do some research on zero energy homes or Passive Homes. If built right, they use no energy to heat or cool. Get rid of heating and cooling demand and power usage goes way down.

 

[toms]

So, we live in East TN and want to build a new home on our land. There is no electric service, so we want to be 100% off grid on Solar with a generator backup. We are a family of 5, and want to be sure to have all of the normal modern day amenities. My guess is if we build it big enough, we can do this? Planning for a ground based array and then basement located batteries. About a 3000-3500 sq ft home, Heat Pump (Geothermal). Maybe the Split Phase ACs, or do we go full central AC?

We are doing very close to what you describe. Our system consists of two separate systems, one 10kwh - one 20kwh.

The systems are installed as described elsewhere in this thread in a separate insulated / climate controlled room.

We have a bore and desalination plant,and fill storage tanks in summer to enable the pumps to be idle in winter.

We use a diesel generator to supplement energy as required. If you do your sums you will find that it is far more economical to size your batteries for nominal use, and run a generator when there isn’t enough sun.

Two independent systems allow redundancy, as well as being able to tailor your system to the loads. I run all my pumps and AC systems from my 10kw bank which has a supercap to buffer the inrush current of the inductive loads.

The main house loads run from the other system which is a SMA AC coupled system with a DIY LiFePO4 bank controlled by a REC BMS.

The secondary system can be connected to the main house via a manual transfer switch, or the generator input of the SMA to charge the primary batteries.

This system has evolved over the last decade, and my family of 6 have not worried about a lack of electricity.

 

[EastTN Offgrid]

Do some research on zero energy homes or Passive Homes. If built right, they use no energy to heat or cool. Get rid of heating and cooling demand and power usage goes way down.

Thanks. We are looks ng at a timber frame with SIPs Walls right now.

 

[EastTN Offgrid]

So you already have this pump? Those are pretty pricy and if you are already going to have AC power could use much cheaper 120V AC powered Grundfos and put the savings towards the other equipment.

Yes, we have this pump already in the well. Using it for livestock right now. But the reason I went with it (besides the AC/DC) is because the well is about 500 yards from where the house will be located. Soni just wanted to have it on a separate solar array.

 

[OffGridInTheCity]

I have a 13kw system / 2600sq ft home / zone 4 weather and I'm powering 80% of my house 9 months of the year. I get 2000kwh/month in summer and 500kwh/month in winter with 18,000kwh solar per year and 15,000kwh useable after losses. Its the 3 months of winter where I only get 25% of summer power that is the hurdle. I would need a 13kw * 4 = 52kwh pv array and/or a good generator backup but right now I rely on grid-assist. I'm in Southern Oregon and we get many thick clouds in winter.

You might check out @Wild Wonderful Off-Grid youtube (100% off-grid) and search "solar" and you'll be able to find their entire 13kw pv system -> power house + propane generator backup using Conext MPPT 80 600 Solar PV Charge Controllers - https://solar.se.com/us/en/product/conext-mppt-80-600-solar-pv-charge-controller/ equipment and costs. Not pushing Conext but rather they have a great set of youtubes on solar array, controllers, batteries, power shed build, propane install etc and might give you a checklist of things to consider for you're plans. Here's just one of the youtubes to give you an idea:

 

[peakbagger]

Thanks. We are looks ng at a timber frame with SIPs Walls right now.

Just make sure you include blower door testing in the contract and make sure you understand shading and optimal window placement. Far too many homes get built with way too much glass that overheat in the summer and freeze at night in the winter. Overhangs integrated into the building can help with summer overheating but not much can be done with radiant loss at night from too many windows during heating season

 

[Quattrohead]

Check ICF for your shell, actual R22-23 but works like R50 due to the thickness of the concrete. Spray foam the roof 2" closed then 4" open cell.
Use split HVAC system like Mr Cool with variable speed and soft start or use mini-splits.

 

[Steve_S]

I have to chime in here on this.
I'm 100% off-grid. Hyper-Efficient house, specifically designed for purpose. The house itself is mostly "self regulating" thermally. This will not be a tidy post, sorry, too much info to share so I'll be copying in from different pieces I've written up.

1). Conservation & efficiency RULE ! far cheaper & reliable to conserve vs generation and storage.

2) spending the $ up front may be scary But you reap the rewards of it every day and without inflation, so it becomes a bigger reward over time. Even decades forward.

3) proper planning & design for future mods, expansion or changes (updates) is essential. Even the small details.

I'll have to be at. Home with my PC to cross copy and finish this. Stuck in hospital and using a damned cell phone which screws up the functionality. Sorry about that

 

[NC_hydro]

Best money spent in your build will be minimizing energy use. ie 75watt 21CU ft samsung fridge, on demand gas hot water (navien)/or even better also have wood fire hot water heater. Wood heat in the winter, east TN has plenty of free or nearly free firewood which cuts your energy use in the less sunny winter months. Your highest usage will be in the hot sunny summer months when solar is more plentiful.

 

[rhino]

samsung fridge

Aren't those extremely expensive to repair and have reliability issues?

 

[NC_hydro]

Aren't those extremely expensive to repair and have reliability issues?

Haven't heard that. Maybe some of their fancy side by side $2k+ models? I have two, one for 4yrs and one for 1yr at my off grid place. Top freezer that can convert to fridge. When the compressor is running I see 75w with fridge/fridge and 90w when freezer/fridge mode. Paid $900 for my first one but the price has gone up slight since then.

Samsung-33-in-21-cu-ft-Top-Freezer-Refrigerator-with-FlexZone-in-Fingerprint-Resistant-Stainless-Steel-Standard-Depth- Model# -> RT21M6213SR