Off grid design check

chsdiyer · September 2017

Hello, we recently bought ten acres and are looking to build off grid. I am somewhat ignorant to all this and somewhat not. I've done a lot of reading on the subject and have MSEE degree and PE, which I'm aware can mean little seeing as how I've never done an off grid system which is not trivial. I only say that to mention I have some degree of understanding on the components involved.

Our house is a one story design roughly 2600sqft located in coastal South Carolina. We're going to focus heavy on energy efficiency in the construction with 2x6 walls, R25 insulation, high efficiency doors/windows, etc. Propane water heater (tankless or tank), propane range, and propane fireplace. Here's my plan:

-Likely install geothermal heat pump with propane supplement
-Deep well (well driller said 1/2hp 240V pump - looking at doing grundfos pump instead)
-Water pumped from well to holding tank as needed, then smaller pump to supply house.
-(30) 330W LG panels pole mounted (15 panels per pole)
-Schneider XW 6848 inverter
-Schneider XW-MPPT80-600 charge controller
-48V roughly 40kWh battery (1 series string). Trying to decide between Hawker, Rolls 5000 series or Solar One HUP. Leaning towards the Hawker
-Backup generator. I was going to do propane with a 12kW with the thought that I would only use it if the batteries got too depleted and I would use the generator to recharge the batteries and then shut off. However, today I read an old post by Chris Olson that gave a different train of thought that I'm now considering in maybe getting a smaller generator and perhaps diesel.
-transfer switches, combiners, etc.

I think all the items I picked out so far were going to cost about $35-40k. I'm hoping to get at least $15k back in tax credits.

Questions I have are...
1.) Am I naive in this design? Originally I thought of doing 15kW solar array with 3 tesla powerwalls, but those aren't ready yet and I'm not sure proven safe, but scaled back to not over spend up front but add on if needed. That will also help me get the most back from my tax credit so I don't leave any on the table.
2.) Is my sizing off? I know I don't mention my load, but since this is for a house that isn't built, I don't know those numbers. Not sure what a geothermal load is but I'm thinking 3.5-4 ton unit. We usually keep the thermostat around 76-77 and cool to 74-75 at night.
3.) What's the best place to store all this? My though is either a separate shed or in the detached garage for the inverter, combiner, batteries, etc and then just run main service to the house.
4.) Any suggestion on generator - diesel vs propane?
5.) Am I missing anything or any other advice?

Thanks for any feedback provided.

mike95490 · September 2017

Do you have grid power near the property ?

You are going to need at least 2, maybe 3, of the 600V charge controllers, depending on the panels, maybe 3 pole mounts, 10 panels ea?

Build yourself 2 sheds, one for the generator(s) and supplies, the other for the solar gear. If one burns up, you still have the other. Cheap to do now, a real pain if you need to recover from an accident. Propane for generator, unless you plan on running it a LOT, maybe a 5Kw with a propane conversion?

Skip ground source heat pump, unless you get a great bargain on the underground loop warranty. Mini-Splits won't have the compressor starting surge.

Do you have a easy firewood supply? Sometimes nice to have a real fire.

Water source - do you need a well pump ?

chsdiyer · September 2017

Hey Mike, Thanks for the feedback!

There is grid power very close by. However, and I hate to mention this because last time I did the whole conversation went to how to solve my problem and not providing feedback. Believe me the problem is not solvable other than build off grid, or don't build. We bought land and the neighbor wont let us run power through or across her property which is vacant. It's a mess, but the power company refuses to run power without her permission. If they were going to run it underground it was going to cost me $6500. So I figure 40k upfront investment, get 18k or so back and save on the $6500 run (if it were possible) and i'd be cheaper than 10-15 years of paying utilities if not just breaking even which is still good. Hopefully at that point batteries would be all i need to replace.

So the pole mounts I picked out say they can hold 15 of the panels I'm getting...5W x 3H. Thanks for pointing out the need for more charge controllers. I guess it's better to put the panels more in parallel and just series enough to get the charge voltage high enough? I wasn't sure how much shading plays in when they're all clumped close together on a pole mount, but I guess it's still possible.

"If one burns up, you still have the other" Is that a likely scenario? I had someone tell me going off grid would be like riding a motorcycle. It's not if you'll get in an accident but when. With solar/batteries, it's not IF you'll have a fire, it's WHEN.

I know mini splits are the ideal situation, but we don't really like the aesthetics of them, or not having one central thermostat. I was hoping to install the geothermal myself. Or at least hope for a good deal on the install from a friend. It seems like those units could really cut down the heating/cooling cost compared to conventional heat pump.

Somewhat easy supply. We have 10.5 acres all over grown, and most of the bigger trees are oak, sweet gum or pine.

Will need a well. Driller said 1/2hp 230V pump for deep well, but I'm looking at a better pump like grundfos

Ocean · September 2017

I have a Grundfos 11SQF-2 and it's great. Just so long as you don't get grit / sand in it. I've seen them break from that. But they are great. They can run from virtually any power source - Direct from Solar 30 - 300vDC OR ac120 / 240 generator. We pump to a 3k gallon holding tank and then a 1/2hp jet pressure pump to drive pressure into our system.

Your proposal is Huge! So much power... for what??? It really pays (saves) to anticipate your needs. You may have a train sitting there with nowhere to go... Just stay expandable.... like stackable inverters. You can always add more panels and controllers. BTW most MPPT controllers have a max DC input of like 150 volts which really means you will only run 3 or max 4 panels in series. Then those strings will all be connected in parallel up to the max Amps input of your controller.

Outback makes nice stackable inverters, and they can be serviced on site - by you if you're handy. I've replace all the boards - in the field - on an Outback Inverter - and I'm not a specialist - just careful and good with my hands. Good controllers too.

Get a Solar Water Heater. It's one of the most energy consumptive tasks for a home. Let the sun do that with a highly efficient setup designed for it, rather than using your precious 18% efficient solar panels.

In fact, you might consider radiant floor heating, since your going to build from the ground up. Radiant Floor, with a good, massive solar water heater supplying the bulk of the heat (with propane backup), designed well, could keep your house nice and cozy all year round. Maybe you could run cold water through it when you want to cool things down.

Efficient lighting, fridge, HE washer and propane dryer, dishwasher... blender, coffee maker, entertainment system etc... even with all this you'll probably still use less than 10kWh's per day. Unless you plan on an old school electric range. Go propane range!

It's really worth adding up all your expected usage. It really is.

Unless you have a shop full of heavy tools you use all the time...

Unless you have a pool cycling every day...

Unless you have an electric vehicle you are charging off your system...

10kW worth of solar panels seems a little excessive... but hey, why not! Maybe you want to charge an EV! 10 kW of solar panels will get you about 40 - 60kWh per day of solar gain... pretty good! What will you do with all that power! It's like 5x what you will likely use in a day!

Sounds like fun!

chsdiyer · September 2017

Ocean, thanks for the input!

For my well I might be concerned about sand getting in. I can dig down 9 feet and find water and at least in that 9 feet it's all white sand with about one foot of top soil. What voltages have you powered you pump with? If you go low voltage, does that just translate to lower flow?

I might have to consider outback. I'm familiar with the Schneider name, but not so much outback. I do typically do whatever installs/reparis I can myself before paying someone else do it.

Hmm, I didn't think 10kW was that much power. I have two friends with grid tied solar. One has a 3400sqft house and 7.5kW array, the other has a slightly smaller house with 15kW array. The smaller array is a newer home but not built to be energy efficient and they still pay a little to the utility in the summer and winter. The larger array is on an older home built to the same standard (2x4walls, etc) and I think they actually pay a little more in the summer and winter. I figured 10kW would be a happy medium. I originally was planning for 15kW but realized that might be excessive. It's hard for me to gauge my power demand since I've never lived in an energy efficient house. My last house was built in 1839. I have a friend that just built a house roughly the same size and he's pulling about 50kWh in the day. Of course he's not trying to conserve and keeps the thermostat at 70. I figured conservatively we could get down to 20-30kWh per day in the summer...maybe less, but I really don't know how best to estimate. I'm not sure how many hours per day each appliance (particularly HVAC) would run, but I don't think we'd ever get below 10kWh/day.

For us, winters aren't too bad. We maybe get 10 nights below freezing. Most days in the winter time are in the 50s and that's only for about 6 weeks. It's usually in the 60-70s in December, so I don't plan to invest too much into heating system. Heated floors would be nice. our old house had no sub flooring, just 1" heart pine on the joists (open crawl space below). In the winter time those floors would get cold. Shoot, before we got a heat pump that actually worked, that house would get cold. Couldn't get over 60 inside on really cold nights. Hot days, upstairs wasn't getting below 85.

Definitely shopping for appliances with the best energy efficiency. Won't have a pool but would like a small electronics & woodworking shop (not together). No electric vehicle, the electric house is enough.

I figured the 10kW would be enough to power us and hopefully recharge the batteries often as I don't plan to size them to carry us through more than one cloudy day or so.

Estragon · September 2017

Pumping from well to a tank is a good idea - fill the tank when the sun shines and minimize battery storage losses.

10 kw of pv in a warm coastal environment may give you 7kw or so real-world, which isn't overkill IMHO.

Assuming getting propane delivered isn't a problem, and you'll be using it for other stuff anyway, that might be the way to go on the genny. Diesel isn't as bad as gas, but still does have issues with being stored too long. Aside from fire risk, another reason to put it in a separate shed is they make a lot of heat. Solar gear hates heat.

I like the idea of geothermal, but couldn't make the numbers work off-grid. I may have been able to do a lake loop, which is much cheaper than boring holes, but even though efficient, it still took too much power. You're in more moderate climate though. You'd have to work the numbers based on you local heat/cool degree days. Radiant/hydronic is nice, and fairly cheap to do during initial build. In-floor works especially well with woodstove, as stove heat tends to stratify and leave the floors cool.

BB. · September 2017

From what I have seen, ground loop thermal systems use a significant amount of power to pump the water through the wells/ground loop.

Is the solar array mounted a fair distance from the home? High voltage solar charge controllers are very nice, but usually expensive devices. If the array is hundred or more feet away, a high voltage controller may be the optimum choice. If the array is closer to the home, a standard voltage (~140-150 Vpanel max) controller may be more cost effective (and give you more options).

Fuel choice--Will you have propane or natural gas on site? If so, then using that fuel is usually a better choice than having to tank diesel (or gasoline) too.

Some issues with cold weather and propane (need larger tank to vaporize fuel for larger gensets). And the issue with diesel starting and very cold weather. But very cold weather should not be an issue for you.

Last time fuel prices got expensive and cheap--There were issues with propane suppliers and tank rental pricing and such (going from "free tanks" and fuel contract to fairly expensive tank rental pricing--As I recall).

Another device that is used in some climates are Heat Recovery Ventilators. Great for "sealed homes". Conditioned air is exhausted through the HRV and that air heats or cools (depending on season) the outside fresh air coming into the home. Have to be a bit careful--HRV can draw a fair amount of electrical power to run the circulating fan.

Solar hot water (thermal collectors and storage tank) will be great for hot water, and heating. But they can be plumbing nightmares.

Link 1
Link 2
Link 3
www.arttec.net/Solar/BarnHeat.html
low tech home made heating system.

And/or using a heat pump for hot water (down to ~50F for fairly efficient water heating). Use desuper heater on central A/C system for "free" hot water. Can reduce the plumbing nightmares of solar hot water. And modern heat pump water heaters can be pretty cost effective for solar electric power (~2-3x BTUs from electric+heat pump vs electric+resistance heating).

Heat pump hot water, give "waste" cold/dehumidified air. In warm climates, a bit of "free" A/C. In colder climates/during winter, many folks have to have ducting to outside to avoid over cooling the room/home during winter.

-Bill

Dave Angelini · September 2017

10 KW is not that much power as you thought! As the others have said, it becomes an issue when you have to replace it during winter.
Geo-thermal is pretty much like buying a big motor boat these days. You better have plenty of denaro to feed it. It made alot of sense before the mini-split for offgrid. There are many different ways to use them besides the standard wall hanging unit. Schneider system below.

Image: https://us.v-cdn.net/6024911/uploads/editor/cv/c8gko09srmaz.png

chsdiyer · September 2017

Thanks for all the feedback!!

I do plan do bury a 1000 gallon propane tank and don't think refill will be too hard. Our land is close to everything. I thought about diesel because if I'm using the generator frequently it might be a better source, and if we have a tractor it could be a shared source and not risk going bad before using.

I found this on another forum and this guy has 8 tons of geothermal. When his 5 ton unit is running, I think it's only pulling about 3.5kW. That seemed pretty good to me. That's my only gauge on understanding how much energy geothermal would pull. We would do ground loops and not from our well. Dave, how else are mini splits used other than wall hanging? I'm not sure what the Schneider system is illustrated relevant to mini-splits, is that the wrong attachment?

Bill, thanks for the links and recommendations! By the way, are you the same Bill I've seen in Mike Holt videos?

Is a fire a likely scenario? Should I factor in some type of fire suppression system in the shed?
Should I plan on putting a mini split in the shed to keep it climate controlled?

The system wont be too far from the house. I'll have the house, then a 3 car garage next to it and then the shed either next to that or behind it. That equates to roughly 50-60ft from the house. But solar wont be more than 20-30ft from the inverter.

BB. · September 2017

Not me... I am camera shy.

My recommendation is to do paper designs of different system types/sizes before you purchase any solar equipment. Do a high voltage and low voltage array paper design and see figure the costs and any design issues.

Designing solar with a blank sheet is difficult. Sort of like a parts store with parts that range from a VW Bug to a Mac Semi Tractor. They are all "parts", but size/configuration matters.

And very roughly, you can "adjust" an existing system to be around 2-3x larger--But more than that, usually, you have to "start over" with new hardware to support the larger system.

Getting parts from different vendors and putting them together does work, and can work very well. If you are into integration, then staying within a family (i.e., all Schneider or all Outback/etc.) charge controllers and AC inverters can have advantages too. And if things go sideways, you only have to point the finger to one "person".

Propane has less "heat" vs diesel per gallon... So you will need larger propane tank vs diesel storage for the same energy usage. You may want to look at two different gensets too (different fuels?). A smaller one (4-6 kW) running for many hours at 80% load (battery charging after a few days of bad weather) will be more efficient than a 12 kW running at less than 50% load most of the time (use the large genset for backup to small genset/running large shop tools?). Note that diesel genset tend to be more efficient at less than 50% electrical loads vs Propane/Gasoline generators (Otto cycle more efficient).

Note that diesel gensets can have issues with long run times at less than 50%-40% loading... They can glaze the cylinders, carbon buildup, and/or have wet stacking. I am no expert, and at least one person here said that modern diesel have less issues at lower loading--Just more research.

-Bill

Estragon · September 2017

One nice thing about diesel is it doesn't burn well at ambient pressure and temp vs gas or propane, so fire is a less likely scenario. The engines can also last a long time (mine is > 30yrs old) Using a stabilizer and keeping water out of tankage diesel should last at least a couple of years. I agree with Bill on sizing. Bigger is not always better.

Air conditioning solar gear shed probably not worth it, but I'd insulate and put the genny elsewhere.

3.5kw is a pretty big load off-grid, especially for something like hvac that you want available 24x7

Dave Angelini · September 2017

3.5KW is a huge load after the sun is down and that is what my screen shot in trying to show. After sundown the mini splits are drawing about 500 watts on a slow cycling power ramp up/down. The split can be ceiling or ducted also but the best approach is a central great room. The HVAC people take a long time to understand the concept offgrid. We don't expect to come home to a hot or cold home and get it "right" in 30 minutes. We start cooling or heating once the sun is on the panels and never let the room get hot or cold. Small 1 ton or less units and the 3/4 ton can sip power 24/7 and tracked arrays give the long hours of being "off" the battery.

Avoid if you can a power shed and somehow attach the power to an outside insulated wall or garage. If you are going to use propane for cooking, and you should, skip diesel and not worry about generators for now as they can be dealt with easily down the line.

Good Luck!

chsdiyer · September 2017

Great suggestion on putting the design on paper and doing a study of alternatives. I have a spread sheet at home with all the parts listed I planned to buy and did a separate spreadsheet for batteries. I've just about got my mind wrapped around the components I'll need, and am finishing up going through the code book. Paper designs next.

I don't plan to use the generator unless the load is close to 80%. If I went diesel I'm sure between the generator and the tractor, I wouldn't have it sitting in the tank even a year. Does anyone use diesel generators powered by biodiesel or is that not all that practical? I was thinking to put the generator on a pad outside.

Compared to what a conventional heat pump would pull, I thought 3.5kW was pretty good. Certainly still my biggest load though. My thought is, if it's hot outside the sun is probably shining so solar will pick it up, even in summer the nights aren't too bad so if the house is efficient enough, it wouldn't run that much at night. Maybe just run ceiling fans.

chsdiyer · September 2017

Thanks Dave. I guess i'll look more into various options of mini-splits.

Our garage (3 car) interior dimensions are 24x38. Originally I thought putting the batteries and inverter and such in the back corner. The separate shed appealed to me in case there was a problem it wouldn't burn up our garage and vehicles, but it would be nice to not have to build another structure.

BB. · September 2017

Fires (genset+fuel--not uncommon. Electrical and battery fires happen too). I like separating genset+fuel from everything else. Electrical (DC side) separate is nice too. Remember access too... You start moving mutli-hundred lb batteries, or 1,000-2,000+ fork lift batteries around without a concrete pad/crane/pallet jack/lift gate truck--Gets "fun".

-Bill

Ocean · September 2017

If you want to go high tech on batteries... look into lithium. Much lighter. No acid. 70 - 80% depth of charge available vs. 50% with lead acid. and staying healthy. Also they are more efficient, so they charge up faster, and generate less heat. Also they have awesome surge capabilities with much less voltage sag than lead. You can find a 16kWh from a low-mileage Chevy Volt for around 3k. Also Tesla batteries are available. Tesla's are 6S (6 cells in series) and Volts are 12S so they need special charging parameters, which are easily accomplished with good controllers. More importantly though, you need an inverter that can have a very low voltage cutoff, like down to 36v for a 48v nominal inverter. Magnum I think can do this. Not sure about Outback.

Tesla also made batteries for the Mercedes B-Class hybrid, which are 7S. Perfect for a 24v system. put 2 units in series for a 48V nominal and any inverter can use them. 7S Tesla battereis have a high voltage of 29.2, and a low of 21. They're perfect. I have three of these (3kWh each) - wish I had four - in parallel running a 24v system (older Trace PS2524). They are awesome. Just unplug the on-board IC because some of the sensing welds went bad... and you may have to think about balancing eventually. But I'm just saying, they perform amazing, and I never deal with acid. I float around 28.8v and all my motors start with Gusto - even my 1.5hp table saw and Air compressor. They scream. And as I said, my bank is basically only 9kWh total. When you think that these batteries were designed to move a car, supplying 50kw or 100kw burst of power...for 100k miles... they will never see this kind of usage in a home... you could think they will last a long time.

But you're going to have such fun building your off grid dream home. Cheers!

chsdiyer · September 2017

Ocean, where do you get the vehicle batteries?

I considered lithium for a while...my master's thesis was on lithium BMS, and there are a lot of pros, but I still worry about the safety. I looked at LG Chem's battery and Tesla power wall but the power wall isn't installing in SC until October and they aren't ready for off grid applications probably for another year. I did look into becoming an installer for them as well since they wont let you install your self.

The lead acid batteries I'm looking at spec down to 80% DoD so they offer quit a bit of capacity...just not the number of cycles a lithium battery would...I think 2100 at that depth which isn't bad.

My thought is go with Lead acid and then down the road when it's time to replace, lithium will be more proven/available and hopefully have reduced in price.

Ocean · September 2017

I got my Lithium's on Ebay. Wrecked cars are parted out all the time. Of course in this case you are working with raw batteries - packaged as units for use in the car. Search Tesla Batteries on Ebay. Or Chevy Volt battery. You will see. People are breaking them down and selling individual 2kWh units, 4kWh units, 5.xxkWh units (tesla's)... and also entire 16kWh units as replacements for your Chevy Volt battery - like if you had 200k miles on yours, you might replace it with one from a wrecked Volt with only 30k miles on it. In this case you get a whole battery "unit" and open it up, break it down into individual blocks, re-wire them to get your voltages to match your system...

That being said, 80% DoD on a lead acid AND giving 2100 cycles under those conditions seems amazing - and unheard of - are you sure they offer that kind of performance? Perhaps they mean you get 2100 cycles if you keep your usage within the top 20%... just wondering... or maybe they can be cycled down to the bottom 20% without irreparable damage... but this still seems unlikely. Got a link for them?

-Ocean

chsdiyer · September 2017

Interesting. Thanks for the info.

The solar one HUP batteries claim 4000 cycles at 50%, but I haven't found their 80% rating

The Hawker manual says
Warranty: 10 years
Cycles to 80% DOD: 2100 over 10 years

Rolls Surrett 5000 series shows same cycles for 80%. At 20% they claim 5000 cycles
https://www.solar-electric.com/suba8vo820am.html

chsdiyer · September 2017

Dave, I've been looking at mini-splits now as I had no idea how many options there are for them. Few questions...
1.) Can the concealed ducts be mounted in the crawl space and have a regular floor vent come up through the floor?
https://www.ecomfort.com/Mitsubishi-M5H42D0909090912-B/p57442.html

2.) That link above says that unit will pull 3.8kW in cooling mode (if I'm reading that right). That seems to be more than what the geothermal should pull and will be limited to 5 rooms. Geothermal could run to each room. I see a lot of benefits to the mini split system, I'm just wondering if it is a better power saver? Is it because that is a max rating and in all reality you wouldn't be running every unit at the highest setting? But if I have to put one in each room, I'd have to have about 9-10 zones.

3.) I liked the idea of the ceiling cassette systems but they all appear to be 22" x 22". That would mean having my ceiling framing design redone to account for that. Do you know if they make any that would fit regular 16" on center ceiling framing?

thanks!

Ocean · September 2017

Wow on the batteries!

Estragon · September 2017

A word to the wise on the batteries - it isn't all that unusual for a first bank to be sacrificed on the alter of bitter, real world experience. L.A. batteries have been around for 150 years, and still I doubt the bell curve of claimed cycles vs DOD bears up well to actual use. Maybe lithium will be different. I don't know.

mcgivor · September 2017

Manufacturer's cycle claims are just an indication of what's possible under controlled conditions, if the the conditions of the installed location differ, then actual life expectancy can vary. These controlled conditions vary, temperature being a determining factor can vary significantly, I've seen 20°C for some to 35-40°C for others, so the question is, if the cycle life is 5000 at 20°C, what would it be at 35°C. In addition are these claims based on actual cycles, or an accelerated test, the latter would then be a prediction. So would the manufacturers of lithium batteries be any different? I think not, why would they. One manufacturer of lithium batteries compared their product against lead acid, claiming LA is actually more expensive due to lithium being able to accept 100% DOD whilst LA was significantly less so a larger bank would be required, which offset their higher initial cost, but how long would a lithium battery actually last in terms of cycles at 100% DOD? Not many would be my guess, from what I've read. They the lithium manufacturer, really an assembler, later amended their claims, albeit still in their favor...........you never hear The new 2018 Chevrolet, almost as good as the Ford, no, it's always better.

Perhaps lithium is better, I guess we will hear from users when they don't live up to the cycle expectations, or exceed them, for that matter.

Ocean · September 2017

I've been using Lithium Ion batteries from a Mercedes B-Class since Aug 2016 (batts built by Tesla). 3x 3kWh modules in parallel - each module being 7S. It's a 24volt nominal system (Inverter is Trace PS2524, with low shutdown of 21V). Sometimes I run it down all the way, but usually I operate within the top 50%. Depends on weather, and what i'm up to. To date they perform very well, but it's only been just over a year. Just today I ripped a 6ft. 2x8 a couple times on my 1.5hp table saw while floating at 28.8v. I checked the meter (outback mx60) and I was still floating at 28.8 after the rips, with just under 500 watts coming in from the solar. The saw screams. I'm sticking with lithium so far so good.

mike95490 · September 2017

Another gotcha, is the propane cookstove - specifically the OVEN. What sort of ignition system does it use.
Spark = 3 watts
GloBar = 300 watts the whole time the oven is on.

Both of my backup generators are diesel, and I've had no starting issues down to +20F, as long as the crankcase oil is the right weight.

Raj174 · September 2017

@chsdiyer
Here's another option for a heat pump. Over the last couple of years, almost every major heat pump brand has come out with a variable speed compressor in their high end units. They are pricey, but very efficient with ratings up to 20 SEER and an almost nonexistent start surge. Available in sizes of 2 to 5 tons.

2600 sq. feet is a lot of space to heat and cool, even when well insulated. If might be a good idea to have an A/C service company come in at some point in construction and do a proper evaluation to size the unit. That, along with other loads will contribute a lot to properly sizing the battery.

This is one brand, like I said, there are many, including Carrier and Trane.

https://www.americanstandardair.com/products/heating-and-cooling/heat-pumps/platinum-20-heat-pump-.html

Rick

Estragon · September 2017

@mike95490 - agree on the stove. I have one made for off-grid that uses a single 9v battery for ignition. It has a setting to leave an oven pilot light on, which I do if using the oven regularly. The 9v lasts ~ 1year.

Dave Angelini · September 2017

They are at 30 SEER now BTW. I was one of the first to use them in 2007 offgrid. The idea of building ducts for them is crazy! One of their biggest energy savers is the 30% gain by not having ducting loss. In an offgrid home we cool the great room. If there are bedrooms that must have their doors closed, we duct the bedroom to the main room with a very small efficient fan. Most offgrid homes do not have alot of people, but if you do, it is part of the design that I do. Anything is possible, you just have to have the experience to not screw it up. The other way is just start small and learn as you go. Stay away from the professional HVAC people until you install ! They are clueless offgrid!

In a large system like this sounds the electronic gas oven loss is not a big deal BTW.

jonr · September 2017

For anyone considering heating a closed door bedroom by moving room temperature air, I recommend running the numbers as follows:

BTU Moved = (∆ Temp) x CFM x 1.08

An open door with a 5F ∆ Temp should move ~300 CFM (1620 btu/hr).

https://growershouse.com/8-duct-fan-210-cfm

Mangas · September 2017

As posted earlier threads for larger systems, our new two zone variable speed high efficiency Trane central A/C and propane furnace HVAC systems are amazingly efficient compared to the older technology we had. Dramatic reduction in power use which adds storage capacity. Our two zones cool and heat over 3,500 square ft.

Minisplit systems rate right up there too.

Room fans improve summer HVAC efficiency.

Propane stove and dryer with heat strip ignition. Propane water heater.

Batteries and solar mechanical hardware installed in a separate dedicated shed with above and underground runs in conduit.

Propane water cooled Genset scaled to run everything if need be plus 20%.

Remote underground propane and potable water storage. Plumb water pressure tank with a dedicated hydrant and ball valve.

Our array is fixed ground mounted. We stood up enough panels to not require seasonal orientation adjustments. Panels are commodities these days. But, we're located in the Southwest.

Tractor with quick release pallet forks and bucket very helpful and economic for off grid living.

Scale system capacity to 125%. Agree, using same hardware manufacturer.

My 2 cents.

chsdiyer · September 2017

Yeah, I don't expect to get 2100 cycles at 80% DoD out of the batteries. Even solar panels are rated higher than what you can expect. I guess they took one out of the lumber industries playbook. But I figured a battery that is rated so well in cycle life is probably going to do better than one that is not. Like a 330W panel is still better than a similar quality one at 250W. I have seem a common suggestion of not getting a really nice battery your first time, but get a cheaper one to learn off first. So I consider getting some L-16s but to me that would just add more complications (parallel strings, more batteries to maintain, more wire connections, etc) than it's worth even if I don't get the full life out of the better batteries.

Mike, thanks for the tip on the oven. I wouldn't have even thought about that.

Rick thanks for the info on the newer heat pumps. I had just installed a new one in our old house and I think the HVAC guy had told me 14 was good enough and 16 was the highest. Didn't realize you could get 20 SEER. Variable speed compressor would be nice too. I did a rough manual J my self which said I needed 28000 BTUs of cooling (i think). I'm going to have the engineer I have doing my plans perform a better one. Do you know about how much power those new units draw?

Dave, there will be 5 of us. Me, my wife and three small children. Good to know ducting of mini split takes away a good bit of the pros to using them. The great room is central to the house, but I don't think the bedrooms would get much cool air to them based on the floor plan.

Mangas, thanks for the input! I'm looking to get a tractor soon and pallet forks is definitely on the list of attachments to get. Does your propane dryer leave the clothes smelling funny. A while back I looked at getting a gas stove but someone (or some reviews) told me they leave the clothes smelling funny. Why did you go on the large side for generator. I think I read in another thread you mentioned you don't use your generator that much...I may have misread though. Do you have tankless or tank water heater?

I REALLY appreciate everyone taking the time to provide feedback!!

Thank you

Off grid design check

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