Off-Grid equipment recommendations

Hi Everyone,
I'm enjoyed reading through the forums, but I couldn't find anything that meets my exact needs. Hoping you can help me out with some recommendations on a solar set up.

Project Details: 320 sq ft Tiny House (shipping container) underway.

Solar will need to run 5x outlets for phones, tv, accessories etc. Refrigerator. Small washing machine. Very small mini-split rarely. Water pumps. DHW and backup heat will be propane. Woodstove will handle majority of space heating. Lighting will be DC direct to batteries.

I'm hoping to have the system run off-grid for the majority of the time. I also want it to accept shore power for charging the batteries and preferably bypass when the batteries are charged.

Current Plan:

Solar = 5x 270-330W panels

Inverter = Renogy 3000w Inverter/Charger $750.00 (Looking for other recommendations)

Charge Controller = Renogy Rover Li 40 Amp MPPT $170.00 (NEED recommendations, I'm not sure this will work for 1000W+ of solar input - can I use two?)

Breaker Box = 3x 15 amp breakers wired from the inverter. (Will this work?)

Battery Bank = 3x 200AH 12V (Should I use 24V? What are the benefits?)

I appreciate any input, thoughts, recommendations, and opinions. I've done a lot of research and continue to get conflicting answers to how the charge controller, inverter, breaker box, and shore power are wired together.....

Hi Luke;  Welcome to Permies!

I have been off grid a long time (1980), so most of my info is probably out of date. But I'll try to answer a few of your questions. If I'm wrong others will bring us up to speed on the new stuff.


1)12 or 24 volt ?  I am 12 volt and always have been. If I did it over I would go higher.  Here is why: The higher the voltage the easier it is to move that power around (smaller wires). I have noticed a trend towards higher voltage systems over the years 24-48-even 72 volt setups. This allows much longer transmission distances  from the  array to battery's.
2)Inverters ;   I currently use a Magnum Energy . I Know the Outback inverters are popular. I know nothing about the Renogy inverters.  Is it Pure Sine wave ?  If not ,move on to one that is.  Modified sine wave inverters cost less … but your electronics will not work well with them.
3)Charge controller's; I can't answer about stacking them, but must support more amps than you can produce. I use a Morningstar  "tristar"  it is wired as a constant diversion charge control , as I have a hydro running 24-7. Solar only control works differently.
4) Breaker box;   Once it is 120 volt anything will work just fine.
5) BATTERYS)   Your estimate is way undersized . The batterys are the resevroir of your system. To small and your reservoir runs dry...  do that too much and you ruin your batterys (I am a master battery destroyer!) Think much larger capacity.  12 volt batterys are almost never used except in the smallest of systems. 6 volt or 2 volt are much more common.
6) Generater)  You haven't mentioned one, unless that is the shore power you refer to?  Off grid living , sometimes your batterys  need a boost and any good inverter has a built in battery charger. With a small gen set it can run your home while the inverter is charger your batterys.  I personally use a harbor freight inverter generater. (predator 3500) Its beyond awesome! I converted it to run off propane and wired in remote start and stop switches.

Hope this helps a little for you.  Others with much more experience will help you further.

EDIT) #3)  I "think" you would make 2 or 3 seperate voltage runs (12-24) to your battery.  Each run having its own charge control .
Better minds than mine may gasp in horror at that statement... Large grain of salt AND good food for thought!

Solar Electric
PV panels 6x 300W in parallel each is about $150 total $1000
PV support made of 2x4 just $70
Wires and DC breakers about $100
Solar BMS SBMS100  3kW $300
Inverter 4kw $1000
Battery 8 cell LiFePO4 from GBS 5kWH (24V, 200Ah) (10kWHr Equivalent) $2000
Backup Generator 2kw $1000

Panel
https://www.wholesalesolar.com/1930020/canadian-solar/solar-panels/canadian-solar-cs6k-275p-silver-poly-solar-panel
Charage Controller
https://www.kickstarter.com/projects/electrodacus/digital-mppt-and-solar-bms-for-a-net-zero-energy-h
Inverter
https://www.wholesalesolar.com/2923535/cotek/inverters/cotek-sp4000-124-inverter
https://www.amazon.com/Victron-MultiPlus-VE-Bus-Inverter-Charger/dp/B0054PRVAS
https://www.invertersupply.com/index.php?main_page=product_info&cPath=1304_263_268&products_id=1208
Battery
http://www.evwest.com/catalog/product_info.php?cPath=4&products_id=463&osCsid=rp0cj2i33tp2j88tnj80dto4e5
https://www.electriccarpartscompany.com/200Ah-CALB-SE-Batteries
Backup Generator
https://www.amazon.com/Honda-EU2200IC-2200-Watt-Companion-Generator/dp/B079YF1HF6?th=1

A few things to think about:

Max input voltage on charge controller. If your panels will be a decent distance from the house to get the best sun, getting a charge controller able to handle several panels in series can hugely decrease wiring costs.

Mppt charge controllers are rated in output side amperage. So, in a 12 volt system, a 40 amp controller is only rated for a max of 480w nominal. Even used at 24v that's not adequate.

I have a Chinese cheapo mppt unit, tracer based. Destined for a secondary system... the MPPT side of it works tolerably, but it isn't great for the batteries as it fails to run a proper absorb stage, and has no manual equalize option. Idiotic. As usual for this sort of thing they did 98% of the work, and yet the missing 2% makes the unit less than half what a quality one should be.


If you can handle the cost, I would suggest an inverter-charger with shore power functionality built in. Victron is where I would look.

You can use multiple mppt charge controllers, each with its own panels, wired in parallel to the batteries. There are downsides; you are trying to size the controller/s to match the max output from the panels, with a bit of room to spare for safety. Doing this multiple times may leave you with more unused capacity... ie, if you have 60 amps output, a 70a controller is a closer fit than two 40s.

The controllers will generally not be communicating, so some will drop to float first while one stays in absorb. Fine as long as the one can provide enough current, suboptimal otherwise.. Similar awkwardness presumably ensues when trying to run an equalize charge, if you do that on solar. I would buy one controller large enough to handle the lot, figuring you can add a second larger or smaller controller when you want more power.

I think your loads suggest a 24V system, with more batteries, unless you don't mind never using that minisplit without full sun... as mentioned 6V cells are likely to make more sense, unless you got down the LiFePO4 rabbit hole...

I would look for an inverter with as low of a standby and search mode consumption as you can find. It really helps with a small system.

At 12v you will require more controller for the proposed array. 24v helps but dont let it ruin your muffin if you need the compatability with other appliances or loads. If you go higher voltage you can step down nicely, or go 12v and it is workable. A 40a controller, it can only feed 500w or so into the battery at 12v, at 24v your controller will handle double the charge current or watts

The renogy inverter you quoted has a standby draw of "less" than 24 watts but probably not much less. That kind of draw will eat a small system alive. For a charge controller find a bigger one to take the whole load. Competing cheaper mppt chargers are not a good idea as 0ne will always be slightly ahead of the other and if they dont talk one array will underperform. If you have the money a name brand there will pay off. If you can manage it using a small inverter for critical loads and your big one switched off except for charging or heavy draw works well for small systems. The morning star works well in that application ; enough for a small fridge devices and lights with a tiny standby draw. https://www.morningstarcorp.com/products/suresine/

For what it's worth... cheers,  David

David Baillie wrote:The renogy inverter you quoted has a standby draw of "less" than 24 watts but probably not much less.

For what it's worth... cheers,  David

! That was a flag to me also..... eats them alive!

Hello Luke,

I'm in South West France with a bit less sun than you have in Ohio and I've several solar systems which I've built up over the years to power our 3000² feet house which almost runs like a "normal" house. All heating is by wood.

In your position, with your needs, I'd  buy only 4 x 330 panels and connect them to produce 48v
A 60 amp MPPT controller
8 x 6v batteries (300 - 400ah) and connected in series and parallel to have a 24v bank

What will you use a 3000watt inverter for?

We use a small Victron Phoenix pure sine inverter 750VA which runs our twin tub washing machine, several computers, a Vorwerk vacuum cleaner, printer, sound system, 2.5kms of electric fence, bread machine (Summer only) etc. Our large refrigerator and small freezer (Summer only), telephone and torch charging and all lighting runs directly off 24v.

This system is running on only 800 watts of panels, a PWM 60amp Morningstar controller and a bank of 12 x 2v 620ah 4PzS (Fork lift) batteries which I've never needed to charge.

I can show you photos of wiring, fuses etc. and I'm sure the other posters will help with that too, once you've decided on the elements of your system.

Hi Luke!

I am still unsure what off-grid really means? Is it just without a landline electricity or including anything else such as water, sewerage, phone line and so on?

As for electricity I'd suggest to first measure anything and reduce your consumption as far as possible. Everything which heats with electricity is usually a heavy consumer.

Such as warm water, washing machine (about 90% of its consumption is usually used to heat the water)'. So if you can use solar (tubes/etc) and/or wood/gas to heat and make hot water you already safe lots of electricity. As solar system are quite expensive you can get away with a smaller (cheaper) system. Just be aware that it needs quite some dry firewood, most people not used to fire with wood, do not realize one might need 10-20 m³ of it yearly!

OK some people have whatever small food stove in their otherwise central heated home, but they use it only occasionally, for the fun of it, emergency (24-48h until someone comes on site to fix the system) and so on. This doesn't need much firewood, though if you depend on it, you need to have the space. Even if you just buy it.

Hi Mike;
Traditionally off grid simply meant no electricity.   To me it still does. You still had water , heat, lights, a phone... I live on a county road. Snow plows, school busses, power lines going by right out my window....

33 years ago I made them remove the lines from my property!  Only person to ask them to remove electricity ever...  I make my own and it never goes out!   That is off grid.


 

thomas rubino wrote:Hi Mike;
Traditionally off grid simply meant no electricity.   To me it still does. You still had water , heat, lights, a phone... I live on a county road. Snow plows, school busses, power lines going by right out my window....

33 years ago I made them remove the lines from my property!  Only person to ask them to remove electricity ever...  I make my own and it never goes out!   That is off grid.

T_h_x, we live more then a kilometer from the next paved road. The only thing public we have is electricity, which works quite stable. Of course it would be great to make your own, though after droping down consumption by 75%, only with a wood powered boiler, which also "powers" the washing machine, the remaining bill is about 25 US$/month. I am planning on a small hydro powered system, as those are inexpensive and run 24/7. But even with this it takes a few years to arrive at the so called ROI. Can't imagine how long it would take with PV, guess things will brake before.

Sure from a survival viewpoint it makes much sense. But then if you do not have water, sewage, firewood/stove and so on, electricity won't help much.

Everyone here has offered great suggestions so I wont repeat any of that, but I have one thing for you to think about.

When you buy your inverter, consider one with a integrated battery charger that you can use with a generator to charge the battery bank.

The sun doesn't always shine, and a bank at a low state of charge for several days is hard on the plates in the battery.  It's nice to be able to fire up a generator and charge the bank quite easily

Mike Homest wrote:

thomas rubino wrote:Hi Mike;
Traditionally off grid simply meant no electricity.   To me it still does. You still had water , heat, lights, a phone... I live on a county road. Snow plows, school busses, power lines going by right out my window....

33 years ago I made them remove the lines from my property!  Only person to ask them to remove electricity ever...  I make my own and it never goes out!   That is off grid.

T_h_x, we live more then a kilometer from the next paved road. The only thing public we have is electricity, which works quite stable. Of course it would be great to make your own, though after droping down consumption by 75%, only with a wood powered boiler, which also "powers" the washing machine, the remaining bill is about 25 US$/month. I am planning on a small hydro powered system, as those are inexpensive and run 24/7. But even with this it takes a few years to arrive at the so called ROI. Can't imagine how long it would take with PV, guess things will brake before.

Sure from a survival viewpoint it makes much sense. But then if you do not have water, sewage, firewood/stove and so on, electricity won't help much.

What is the roi on a boiler heat plant or washing machine, our cars and clothes, a glass of water, dvd player or new computer etc.? I say use and enjoyment is cash positive on day one, just like the dvd, except solar will leave you with free kilowatt hours year after year and cost the same as electricity now.

If your bill is 25$ a month and probably half or more is connection fees, then you would need 10-12$ worth of electricity and your system would be small and inexpensive, it is possible that 2 panels and microinverters would leave you net zero and your bill would be half.

If you used 25$ worth of power at, say 20 cents (i have no idea, it could be 10 cents or 45 cents or anywhere....) 3 panels could do and could have 1500 or less dollars invested and in 7 ( or less....incentives) to 10 years it would pay for itself. The equipment could last 45 years. So if this were done when a person is young, its a lifetime of nearly free electricity use, plus the service fee for an endless battery (utility) and your grankids might end up with the same.

It will not be attractive to many, but i say, if you plan on using electricity for 10 years or more, it makes perfect cents, even without incentives.

And, whatever the power cost is now per kWh, would be "frozen" and your assets would only be subject to service fees and not rate hikes.

My two sense!

frank li wrote:

Mike Homest wrote:
[..]

Sure from a survival viewpoint it makes much sense. But then if you do not have water, sewage, firewood/stove and so on, electricity won't help much.

What is the roi on a boiler heat plant or washing machine, our cars and clothes, a glass of water, dvd player or new computer etc.? I say use and enjoyment is cash positive on day one, just like the dvd, except solar will leave you with free kilowatt hours year after year and cost the same as electricity now.

The ROI of the wood powered boiler is pretty easy to calculate:
Cost incl. all stuff to self-mount about 400 US$/75 US$ (monthly electricity bill) saving == 5 1/3 month and it has itself paid off. It is now >2 years and seems still like new. I do not take the fire-wood into account as I make it on my own.

Just in the same way you can calculate a PV-System, where you need to take into account that the most expensive parts are the batteries, which will not last forever.

Sure a car/dvd and alike is something different, for many people there is some emotion (thanks to mind control/advertisement) connected to a car. Though if you take a shower it doesn't matter how you heated the water, as long as it is warm and enough.

thomas rubino wrote:
If your bill is 25$ a month and probably half or more is connection fees, then you would need 10-12$ worth of electricity and your system would be small and inexpensive, it is possible that 2 panels and microinverters would leave you net zero and your bill would be half.

If you used 25$ worth of power at, say 20 cents (i have no idea, it could be 10 cents or 45 cents or anywhere....) 3 panels could do and could have 1500 or less dollars invested and in 7 ( or less....incentives) to 10 years it would pay for itself. The equipment could last 45 years. So if this were done when a person is young, its a lifetime of nearly free electricity use, plus the service fee for an endless battery (utility) and your grankids might end up with the same.

It will not be attractive to many, but i say, if you plan on using electricity for 10 years or more, it makes perfect cents, even without incentives.

And, whatever the power cost is now per kWh, would be "frozen" and your assets would only be subject to service fees and not rate hikes.

My two sense!

The problem with solar, one needs most power when it has the least sun. Needs big batteries. I am looking into setting up a micro-hydro system, though not a very high priority. It seems I might get from a little measuring about 300W, though this is 24/7 and even more during non summer times. This means about 7.2 kWh/day. Though we need just 3-4 kWh. I might get away with pretty small batteries, perhaps just 2 100 Ah car batteries, dirt cheap. But I have not digged deeper into it.

There are ready to go china made small turbines for the purpose with generator, directly supplying 220V. It is just said the bearings are a piece of crap, but as those are normed you can simply stick in some quality ones before mounting.

I will setup some solar tube system to aid with hot water, so one doesn't need to fire up the boiler or kitchen stove during the summer to get hot water. But this is just for convenience, even a self made dirt
cheap solution might not pay off in 5 years, not because it is so expensive but because the time/money to make that little extra firewood needed for hot water is negligible. It needs 4-5 kg to heat 80l water from 5-15 to about 90C, taking below 1h. Though about 20-30 minutes and you can take a shower. Some electric boiler would need 10 kW power to get this done!

In addition you'd pay much more fess and per kWh for a connection allowing you to get 10 kW! ;-( You only get a cheap contract with single-phase and are limited to 3.5 kW.

Peoples cost and values are generally different. Like a 400$ wood fired boiler. I would estimate 4k$ to start unless you are speaking dhw only, and or diy, even then... unless you are talking about a heat exchanger and controlled circulation, id still be at a loss to buy that for 400 dollars.

Scavenged or donated items are another teritory again, like my pv system.

The mounting enclosures connectors flashings, wiring and cabling fusing switching battery enclosure screws plywood conduit sealants zip ties etc, all came on horse trade and leftovers of my work over the years. I defy most people to have the quality of parts and workmanship cheaper. It still cost 4200$ full told. Panels in 2008 were 3$/watt now .65$ for far superior solarworlds. That was 2200 dollars for 4 185w panels at my door. 200$ shipping. A have a great charge control and battery and  chepo inverters with nice breakers busses shunts and and stuff. My mounts would cost 2200, i got it for 250.

And all kinds of blather! At 5500 dollars it would take 35 years to get this thing which you speak to make bean counters happy at 2kWh per day. But that day will never come because it will need possibly several batteries over that time.

Still all our utilities are awesome and i am the company!

No power bill and uninteruptable and redundant, clean power anywhere i haul it.... kinda cool!
Physically removing my service conductors from the utility meter enclosure absolutely priceless. Where can i spend another 5500...... over 35 years to do it again?

A note, my origial system today would cost like 3800 store bought, plus wire and conduit with a standard roofmount.

frank li wrote:Peoples cost and values are generally different. Like a 400$ wood fired boiler. I would estimate 4k$ to start unless you are speaking dhw only, and or diy, even then... unless you are talking about a heat exchanger and controlled circulation, id still be at a loss to buy that for 400 dollars.

The Boiler (brand new) was about 300 US$, it has (iirc) 1200W electrical heating, which I haven't connected, an extra heat exchanger (8 kW), which I haven't used so far. you could attach a solar system to it or some radiator, while the last makes little sense, since the boiler is not really thought to be fired permanently. About 100 US$ for the missing tubes, water/exhaust and so on which I had not onsite already.

I have everything setup on my own. Yes it is not expensive and working like a charm, though it might not be that great in terms of efficiency, it doesn't matter to me. From calculating you get about 50% efficiency in the summer and maybe 75% in the winter, due to room heating. I like that it is very simple, what is not there can simply not break.

+++In addition it needs zero electricity and even without power, I can still take a shower and alike.+++

Mike Homest wrote:

frank li wrote:Peoples cost and values are generally different. Like a 400$ wood fired boiler. I would estimate 4k$ to start unless you are speaking dhw only, and or diy, even then... unless you are talking about a heat exchanger and controlled circulation, id still be at a loss to buy that for 400 dollars.

The Boiler (brand new) was about 300 US$, it has (iirc) 1200W electrical heating, which I haven't connected, an extra heat exchanger (8 kW), which I haven't used so far. you could attach a solar system to it or some radiator, while the last makes little sense, since the boiler is not really thought to be fired permanently. About 100 US$ for the missing tubes, water/exhaust and so on which I had not onsite already.

I have everything setup on my own. Yes it is not expensive and working like a charm, though it might not be that great in terms of efficiency, it doesn't matter to me. From calculating you get about 50% efficiency in the summer and maybe 75% in the winter, due to room heating. I like that it is very simple, what is not there can simply not break.

+++In addition it needs zero electricity and even without power, I can still take a shower and alike.+++

Mike do you have a link to the boiler or some pics...
Thanks,   David

David Baillie wrote:

Mike do you have a link to the boiler or some pics...
Thanks,   David

Boiler Wood Electric to Floor 80 LT SX Braun Bandini Water Heater

https://www.ebay.co.uk/p/Boiler-Wood-Electric-to-Floor-80-LT-SX-Braun-Bandini-Water-Heater/8009750977

It seems we have the LTE version, with electrical heating, wood and an extra heat exchanger. Though I was not sure if I'll use it, it seemed easier then not having it.

See under above link:

Read full description
See details and exclusions

Mike Homest wrote:

David Baillie wrote:

Mike do you have a link to the boiler or some pics...
Thanks,   David

Boiler Wood Electric to Floor 80 LT SX Braun Bandini Water Heater

https://www.ebay.co.uk/p/Boiler-Wood-Electric-to-Floor-80-LT-SX-Braun-Bandini-Water-Heater/8009750977

It seems we have the LTE version, with electrical heating, wood and an extra heat exchanger. Though I was not sure if I'll use it, it seemed easier then not having it.

See under above link:

Read full description
See details and exclusions

Nice device, Mike. I had no idea you could buy such a thing, i mean, someone makes them, good luck finding without your link, it reminds me to check world markets. Its like a giant samovar. Looks more like 1200 dollars shipped here plus all kinds of tax, if i could even get one here.

It would have to be smuggled in on the spaghetti boat with a lamp shade on  it!

All jokes aside it is cool amd i like the magnesium instead of aluminum anode. Too bad its full of fiber glass which places it outside of my inventory requirements for hazardous materials in the home, id love to have something like that for heating the dog shed, but they cant have one either!

This is a great example for us. I could grid tie net zero your house (if it were here) cheaper than having that boiler on my door step.

Location can drastically alter both true and percieved costs.

Mike Homest wrote:

David Baillie wrote:

Mike do you have a link to the boiler or some pics...
Thanks,   David

Boiler Wood Electric to Floor 80 LT SX Braun Bandini Water Heater

https://www.ebay.co.uk/p/Boiler-Wood-Electric-to-Floor-80-LT-SX-Braun-Bandini-Water-Heater/8009750977

It seems we have the LTE version, with electrical heating, wood and an extra heat exchanger. Though I was not sure if I'll use it, it seemed easier then not having it.

See under above link:

Read full description
See details and exclusions

David Baillie wrote:
Nice device, Mike. I had no idea you could buy such a thing, i mean, someone makes them, good luck finding without your link, it reminds me to check world markets. Its like a giant samovar. Looks more like 1200 dollars shipped here plus all kinds of tax, if i could even get one here.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Boiler+Wood+Electric&_sacat=0

David Baillie wrote:
All jokes aside it is cool amd i like the magnesium instead of aluminum anode. Too bad its full of fiber glass which places it outside of my inventory requirements for hazardous materials in the home, id love to have something like that for heating the dog shed, but they cant have one either!

This is a great example for us. I could grid tie net zero your house (if it were here) cheaper than having that boiler on my door step.

Location can drastically alter both true and percieved costs.

Unsure about what is wrong with the fiber glass insulation? It might not be possible to insulate it otherwise, because of the immense heat it produces?

I like it very much because of its simple technology.

What is the difference between 4 12v 105ah batteries  and 2 -6v 420ah bats?

Theoretically they store the same amount of power

the4- 12 volt come with a 2 year replacement  and cost 400$
the 2-6volt come with a 6 month warranty  and cost 600$

what am i missing? why are 6 volt bats so much more expensive and yet have less warranty?

Hi Bob;    How they are built is the difference.  Smaller  12 volt batterys will have smaller plates closer together. They will tend to sulfate up sooner and having a small case that waste product will raise up and short out the plates quickly.  
The larger cased 6Vt L-16 size battery's. Have wider spacing between plates. They have a deep reservoir to hold  waste and will not short out for years.  


There really is no comparison between them. In my opinion , the 6 vt are better for solar charging.

I thought the sulfate was a surface coating on the plates, not a waste product settling on the bottom.  I guess it's a little of both.

I  bought 8 of the 12 v bats already and have been going back and forth between the L16s and the 12v deep cycles. I suppose it wouldn't hurt to spend the extra 200$ just to have a system to compare.

I'm also going to have my trip together when 4 other truck batteries (now nearing 10 years old and still working) finally start to fail, and do the full edta treatment- empty acid, soak in edta solution, rinse a few times, refill with acid

That may squeeze a few more years out of them- or not.  The test case i saw written up was with new trojans that had been left uncharged for a couple years. likely there will be less dramatic restoration with bats that have been cycled many times, but the rinsing etc might even eliminate shorts in a bat

That boiler is totally nifty! It seems like a great fit for an application where it could also serve as backup heat, too. And really economical if you live on the right side of the pond!


Bob, hope you will post about your battery refurbishment experience. I cringe thinking about how many freaking batteries I'm relying on in all the vehicles/equipment. Of the top of my head I think it's about 14 at the moment... and it always seems like 2/3rds are getting tired at any given time.

Hello Bob, just to add to the reply that Thomas gave about 12v batteries.

He is absolutely correct but there is another important consideration when choosing solar batteries.

Take the example of connecting four 12v 100ah batteries in parallel.

Correct wiring and connections are crucial to ensure that the current going through batteries is shared equally. Every battery must benefit from the absorption period to be fully charged.

Resistance paths in six cells x four batteries creates a high margin of error, the paths are not always the same and can change over time. That's why it's important to unhook everything and check the individual cells in your batteries periodically and change their order from time to time. (Eg. Moving the first and last batteries to the inside of the string.)

I've learned my lesson by experience. Just have a look at my Flickr solar photos, you'll see that I made that mistake often, being tempted to buy cheap and easily available 12v batteries that died after just four or five years.

Now, I'd never parallel more that 3 batteries and when I'm designing a system, I try to aim for two.

To get 400ah, it's best to buy 6v batteries - connected in series, they'll get the same charge and they'll last for years. Or, if you already have 12v batteries connect them in series and parallel to provide 24v, use a dropper if you really need to for some applications but most inverters, LEDs, frigos, telephone chargers etc. we can buy now now are 12v or 24v.

For a bigger system use high ah 2v batteries connected in series. They are really expensive but worth it in the long run, not only for your purse but for the environment too.

I probably will look at some of the really destitute bats I have laying around and see what I can do. Batteries that aren't yet split down the sides from freezing in an uncharged state is always a good place to start. If I get anything that looks promising I will post it.

I've also done some experiments with the pulsators and those are interesting and may work, but typical chargers with the pulsators included may not have the geometry right to be effective.The instructions I saw used very short leads and were placed basically right at the center of the battery, so I'm dubious about three and 6 foot leads off a charger being able to transmit the same effect.  Of course that being said, whenever I used them, they drained so much energy the bats needed to be on a charger just to keep up with the drain, and I never had that many solar panels or that much discipline. Inevitably I would end up with a battery discharged even deeper than when I started and no way to charge it back up quickly.

Thanks for the reminder Irene, I do use heavier cables and short connections, and that part of my system is something I'm constantly improving. As much as possible I try and keep the electricity paths equal in resistance, individual similar length and gauge wire running to a central distribution point.

Being on the lookout for weak batteries that may drag down the bank is always a good thing. Mostly I look for irregularities in the performance of the bank, but periodic inspections are also good. (As is matching batteries with equal age/strength in the same bank)

Hi Everyone,
Original poster is back. I've been trying to follow along whenever possible.

First, I wanted to say Thank You for all the great information. Particularly Thomas, Dillon and Irene.

Thomas -- we are now planning on a 24V battery bank built from 6V batteries. Most likely totaling 800AH. The batteries we haven't ordered yet as we're exploring the best options for these; both new and used. The minisplit will only be used for cooling, and probably only run 2-3 hours on particularly hot days. Further, the inverter/charger can be plugged in during the summer to charge up our battery bank. In the future, when we expand the amount of AH -- we will be able to use the minisplit more, without needing the shore power for backup charging.

Dillon -- We did end up choosing a Inverter/Charger. AIMS 4000W version for under $1000.00. The standby usage isn't great, but the large capacity gives us future options. Also, we chose the Renogy 60 Amp charge controller. This should give us plenty of leeway when inputting 1000 watts into 24V battery bank. We already have as many 330W panels as required. We have these sitting in the shop from another project.

Irene -- Thank you for the information and detailed responses. I used several of your comments when talking to my partners on this project.

I have several extra small 30W panels and 12V deep cycle batteries laying around. I'm considering making a separate solar system consisting of 3x 30W panels and x3 36 AH 12V batteries. This would only be used for the DC fan in the composting toilet vent. Therefore separating that from the larger solar system. Basically, even if our main battery storage drops too low, AND shower power isn't available -- the composting toilet's fan will still be exhausting. Just a thought of mine, and not sure if it's worth the time.


Any suggestions on where to obtain quality 6V batteries on a semi strict budget? We have a team of mechanical engineers working on this, so modifying and combining items can be done.

Does anyone know how to get a minisplit to operate with "soft start" to prevent a immediate large draw on the batteries?

Any recommendation on composting toilets? I'm currently considering Natures Head or Separett.

Thanks again for the ideas!

For the minisplit, perhaps a capacitor or two? Big ones... careful with these.

Composting toilet, DIY. Check out Gord and Anne Baird's book 'Essential composting toilets'.

The aims inverter should take care of itself with up to 8000w long duration and 12000w short duration surge ratings. Much of whats in there are capacitors for filtering amd power handling.

I have no idea what heat pump you have. Some have soft start.... inverters onboard. Good ones (most all?) are dc driven variable speed motors. There is a locked rotor amps specification and as long as the inverter has the kva for a few miliseconds with some overhead for other loads all will be good.

It may be worth a try with just the inverter. The aims and magnum inverters have great surge rating relative to max continuous. And even if the inverter can do, lights might slightly dim and some people will not have it.

A dedicated softstart device is great for truly large locked rotor amp loads that may be unpractical to budget an inverter for or otherwise not suitable. 90a-120a at 240vac is a heavy rotor associated with ground source heat pumps and when there are well pumps involved, co-ordination of startup of large heat pump compressors is a must and usually in the controls for the machine. When i think minisplit, a big one is somewhere around 2500w-3500w surge. I guess an airsource heat pump can be had in most any size.....

Your 24v 800ah battery will laugh at the demand load from all that the prospect inverter can muster, except when depleted considerably and that is another detail to know the relation of in your system.

If a generator is in the mix, it can be co-ordinated to assist or transfer in when needed with some accessories or the right inverter.

A seperate power supply for the composting toilet is an awesome idea. They are great when they draft in one direction and constantly!