Need some thoughts on Off Grid Tiny House equipment....

sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
Hi Guys,

I’m new to the forum and the world of off grid, and could use some hints and pointers in system selection for a tiny house with space constraints.  I’ve picked a few items that I know will fit physically, that are within budget, and should theoretically meet my electricity demands.

I’ll start with demands…

Tiny House will be stationary and parked permanently next summer, no grid available. 3hrs north of Toronto. Can see -30C in winter.  Currently parked in a place where a long 15amp run serves up about 700 watts before voltage drop is too great.

Average calculated KW usage per 24 hrs is expected to be somewhere around 2.0 to 2.5 on battery power.  I arrived at this:

-1500watt 6gal water heater. 20 minutes from cold to hot. = 500 watts-ish. One heat cycle per day for shower, well insulated, on a switch.  Extravagance = 1000watts
-5 LED lights on, 10w x 5 = 50watts, say 6 hrs a day as a composite  = 300 watts
-Efficient 4.5 cu ft AC fridge w/ mechanical t-stat = 600 watts/24hrs
-RV Water pump 80w x 1hr = 80 watts
-Compost toilet fan 2w x 24hrs = 48 watts
-Laptop computer 25 watts x 4hrs = 100 watts
-Radio 10 watts x 5hrs = 50 watts
-LED TV 40 watts x 2 hrs - 80 watts
-Incidentals ie vacuum, coffee grinder, various little battery chargers, water pik, etc.  200 watt hours?

All of the above w/ extravagance showers = 2458 watt hours x1.07 for 93% inverter efficiency = 2630 watts.

I also don’t intend to pull much more than 2000 watts continuously off the inverter on battery only, and not for long (20 minutes to get hot water + lights and stuff simultaneously).

The two infrequent appliances I’ve listed below I do not intend to run off battery.  If it’s sunny out and I can pull enough juice from the array, then I will use one of the below at a time with the batteries helping out.  If it’s winter and I need clean clothes or laundry, then I will use a generator to stuff amps back in the bank while doing dishes or laundry.

Full 24” Energy efficient new dishwasher
24” Clothes washer



Here’s what I’ve picked to start with…

Phase One Purchase (Very Soon)
Magnum MSH4024M.  24V Mobile Hybrid inverter with load support, 4000 watt 120v, but I don’t need anywhere past 3000 watts at the absolute most w/ load support, extra capacity will be nice for surge. Has automatic neutral-ground switching for shore power or genset.

Appropriate 4/0 cabling, battery monitor w/ shunt, fused w/ disconnect, etc.
Magnum advanced remote
Proper AC disconnects and breakers
AC and DC ground to trailer frame
Midnite Solar SPD wired to shore power and sub panel.  

4x Surrette Rolls 6v 335 AH AGM.  The spot under the couch only measures 24.5”w, 20.25”D, and 15”H, so these fit nicely.  I think they have a C/4 discharge rate? Should support bursts of 2000 watts for 20 minutes or more, hopefully.
http://www.rollsbattery.com/wp-content/uploads/batteries/S6-370AGM.pdf

I could also use 400AH L16’s but would have to run them on their side, with two of them on top of the other two with some spacers of some kind.  It would be tight. Thoughts?
http://www.rollsbattery.com/wp-content/uploads/batteries/S6-460AGM.pdf

The other option is to buy lead acid and store outside in an insulated enclosure, and have it close to the wall for short DC cabling. But between cold weather and the inconvenience of it, I’d rather not.  If I did, perhaps 6v Rolls 375AH flooded x8 would do the trick? (two parallel strings).  Or do I run into not enough panel?

Phase Two Purchase (Late Spring/Early Summer)
-Honda EU3000is connected through 30 amp shore power plug. (will subsist on shore power until tiny house is moved and solar and genset purchased/installed)

-Four 250watt-330 watt panels, totalling 1000-1320 watts, ground mount.

-MPPT Charge Controller 150v.  Trying to decide between outback, magnum, and morningstar.  Leaning towards morningstar, has no fans, and has ethernet/http hookup for advanced config/monitoring.

-Midnite SPD on combiner box and one inside tiny house for DC.


I am prepared and hoping under ideal conditions for two days of autonomy (light usage) on battery without doing dishes or laundry, which is easy for a single guy.

Any help, thoughts or inputs from the experts would be awesome and much appreciated.  I really look forward to hearing from you!




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Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited December 2016 #2
    just did a quick calc on those batteries and you will probably not get your 2 days autonomy out of the as @ 50% DoD you would get ~ 4000W....this is without all of the deratings applied..  Suggest you look for a higher Ah rated cell or get a second string...  more later.
    Oh get the gen set first then the Solar goods.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • PhotowhitPhotowhit Solar Expert Posts: 5,503 ✭✭✭✭✭
    I'm surprised you can heat 6 gallons of water in 20 minutes. I'd want to look that one up/put a Kill-A-Watt meter on it. I guess you are doing it.

    The inverters peak efficiency would be 93%, I'd use 85% in general and might be higher than that. Your 2 watt fan will keep the inverter running at what ever it's bas rate is 18-35 watts.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    Photowhit said:
    I'm surprised you can heat 6 gallons of water in 20 minutes. I'd want to look that one up/put a Kill-A-Watt meter on it. I guess you are doing it.

    The inverters peak efficiency would be 93%, I'd use 85% in general and might be higher than that. Your 2 watt fan will keep the inverter running at what ever it's bas rate is 18-35 watts.
    Roughly:  6gal @8lbs temp rise 60deg = 2880btu /3.4 = ~850wh.  With a warm ambient and cooler shower, 500wh in 20mins is maybe doable, but doubtful on a 15a 120v cord with unacceptable voltage drop > 700watts.  My first though is to consider whether to heat water with propane and/or as an opportunity load (when running generator or have solar available but batteries are nearly full).   Heating stuff (even toast) off-grid with electricity is costly. 

    You can certainly design a system that will run large occasional loads, but it costs both in terms of $$ and space.  You could run almost all your other loads off a 12v 300w Morningstar inverter very efficiently in terms of tare loss.  A larger inverter could have tare losses on the order of a third of your daily wh budget and will likely be quite inefficient overall with small constant loads.

    I assume you've measured the fridge's consumption with a kill-o-watt.  Small fridges are often surprisingly inefficient - maybe yours isn't.  It would also be helpful to know the starting/running amp draw.  

    Do you haul water to a cistern/tank then use the RV pump for pressure?

    Also, I agree with wb about getting the genny first.  You don't want batteries with no way to charge them.  I'm in the boonies, so I wouldn't have batteries without at least two ways to charge them, as I'm well acquainted with Murphy's law.


    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mvasmvas Registered Users Posts: 383 ✭✭✭
    edited December 2016 #5
    All of your calculations of "watts x hours" produce results with Watt-Hours (units)
    What is the total instantaneous watts need for this scenario ...
    Your Hot Water Tank is ON and then you have the inrush from the refrigerator STARTING ?
    The Inverter must handle worst case scenario (peak watts) not just average watts.
    Does your furnace have a blower?

    Valve regulated battery enclosures should at minimum be passively ventilated

    The Rolls Surrette 335AH AGM battery is estimated at 1,500 (laboratory) cycles at 50% DOD = 4 Years.

  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    Hi Guys,

    Thanks for all the responses!  

    westbranch, I appreciate the input.  I am okay with doing 70-75% DOD on the batteries as surrette says I should get 1000 cycles doing that.  Using my worst case load that should give me two days, and based on that I ought to get 5 years out of them, which I’m okay with.  But if that doesn’t work out, then yeah the whole thing gets too costly.  I can potentially upsize to 400ah cells in that space, but those batteries would be a tight fit.  I would have to stack two on two, horizontally. Do you think they would be ok sitting on their side (the long side), with 3 pieces of 1/2” strapping between the bottom one and the one sitting atop? Would the cases take it?

    Photowit, I should put a meter on it.  But it’s being fed room temperature water and it’s a little on the plus side of 20 minutes I guess.  I should be more scientific about it.  

    The fan is DC and will be wired to the bank w/ fuse.  I’m hoping for 12-14 hrs of search mode per day except for fridge starts.

    Estragon, I currently don’t have the ability to run the tank on the shore power, the 700 watts is way short.  I’m still in construction and not occupying, so it’s fine for now.  I had it hooked to a generator to test it out.

    I haven’t measured the fridge, but I will, and I’ll get back to you.  The long term plan is to get a novakool type fridge with a danfoss compressor and run it on DC, but that’s down the road.

    I have an onboard 250L storage tank inside that I pump water into, and in the summer it will have collected rainwater pumped into it.  I set up a nifty water treatment system that uses no electricity, if anyone is interested I can share info about it.

    mvas, I’ll put a meter on it and find out it’s behaviour.  It’s not in service yet so I don’t know, I just went by the energuide sticker.  There is no furnace as of yet and won’t be for some time, if ever.  The place is heated with a wood stove.  I have a spot for the furnace and propane is plumbed, and if I put one in it would be an Atwood RV 12v, and the blowers use 55 watts.
  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    The only other option is to put a large flooded bank outside in an insulated enclosure.  I can get the enclosure real close to the wall that the inverter is on to minimize the run, and I could insulate it really really well.

    What do you think of having a flexible insulated pipe going from the house to the box with a thermostatically controlled fan to pump room temperature air into the box when needed?  The house will always be warm.  I would ensure to have a one way flap in that system and a vent at the top of the battery box.  The bank and box setup would need to be able to weather a potential -35C.  Has anyone done this before?

  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    What about using a DC water heating element, like 600 watts @ 24v? with a new thermostat?  or a smaller 1000watt 120v element?

    https://www.amazon.com/dp/B0006IX8AA/ref=psdc_2232427011_t2_B00KO32AB0
    https://www.amazon.com/Watt-Submersible-Water-Heater-Element/dp/B00KO32AB0

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited December 2016 #9
    Since this is a "New Build" you should use the opportunity to lower all your electrical demand as much as possible...  use lots of ambient lighting (windows) where possible. 
    Use 'Light Tunnels'  http://www.velux.ca/products/sun-tunnels.
    Use LEDs,
    Use propane , not electricity for the DHW...  Unless you have over-paneled at the 10% charge rate, say by a factor of 1.5 ..??
    Heating anything with solar power is poor planning, especially with a small array... Conservation is essential... followed by judicious use! Each Watt saved in consumption is worth a lot of PV array and battery dollars.
    Write everything down and assess it load...
    Could not find the 400 Ahr AGM's but most commercial models are able to be mounted on their side. Ask Rolls

    hth

     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • mvasmvas Registered Users Posts: 383 ✭✭✭
    I think an Almost-Instant-Use Hot Water tank is most efficient.

    Are you OK with replacing $2,000 worth of batteries every 4 years?
    Maybe, look for a battery with more rated cycles => 5 years or 6 Years ?
    By then you might be installing Lithium-Ion batteries

    A load shedding idea ...
    If you could disable the fridge whenever the 3000W water heater is ON and then
    automatically after 20 minutes (a timer) shut down the water heater and re-enable the fridge.
    This would keep the peak load on the inverter at a low level.
    Something like this device ...
    http://www.rvcruzer.com/docs/EMS_Brochure.pdf

    Also, very few AC fridges are as efficient as a 24V DC fridge.

  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    edited December 2016 #11
    Westbranch, I did my best with regard to lighting, I've got about 100 sq ft of windows in a 286 sq ft place and it's all open concept. My illumination consumption is a worst case scenario with friends over in the winter where it starts to get dark at 5pm. During the day no lights are needed whatsoever.

    I really really like the velux tunnels, those are really cool! Thanks for sharing that!

    I know ideally you would want to have propane hot water on demand in an off grid situation, as any heating done in an RE setup is consumptive as you pointed out... but the tiny electric hot water heater was a judgement call I made to get away from propane on demand.

    Let me explain. All units except the bosch have a danger of freezing when it's cold outside (even though the unit is mounted indoors) due to cold air convecting through the direct vents. They seem to rely on heating elements during the cold weather that burn a couple hundred watts to prevent the exchanger from freezing. I guess this happens because the exchanger and unit are warm and it creates a stack effect or something because the thing is vented outside.

    The Bosch unit needs no electricity but needed a big B vent thru the roof and uses indoor air for combustion, and I already have a wood stove and a composting toilet using the inside air, and at what point do you draw the line with make-up air in such a small space. I didn't want a risk a negative draft that would suck air down the B vent and freeze the exchanger. Space was a factor too, one of those things sucks up a whole wall with the gas and water fittings, valves, etc.

    I'm stuck with the electric hot water tank, it's already in. Gonna end up experimenting with the 1000 watt AC element and I just found a 900w DC element which might be fun to play with. The thing is only going to cost a 1000 watts a day for intended consumption. A lot yes, but not an astronomical amount. I just need help sizing the system to absorb it, and I guess that's a cost of doing business that way.

    Thanks!
  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    Mvas,

    That's awesome! Thanks for the link, that is a really neat device and I will research it some more.

    On a side note, I'm not burning up 3000 watts, only 1500 on the little heater and I think I'm leaning towards getting a smaller element than that.

    I am actually okay with replacing $2000 in batteries every 4 fours.  That's only $41 /month. I live in an area where we are served by a crooked and broken hydro utility with a large and degrading infrastructure, with massive upper management issues that will charge their rural customers upwards of $100 a month for delivery for ZERO usage whatsoever.  It goes up from there.  Once you get over the basic delivery hump, you're in for about what works out to 25c/KWh for the average consumer.  Average hydro bills here are anywhere from $200-600/month, most of them being well over $300.  This doesn't include the poor folks who are dealing with the utility's billing problems where you get surprise bills for thousands out of nowhere.  Don't even get me started on the outages.

    Looking forward to replacing batteries... lol. 
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Back to DHW, have you looked into Evacuated solar water heater tubes. Can you build yourself a small (8' x 8' ?) out building to house the heat exchange tank?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Ralph DayRalph Day Solar Expert Posts: 934 ✭✭✭✭
    On the subject of Hydro One (the utility provider for rural Ontario residents), I have solar and wind with H1 as my generator usually.  The delivery charge (the charge to just have the service) for a month with no actual consumption is $40 plus 13% tax.  Not $100.  The cost of power varies. Peak time, with tax 20cents/kwhr, mid peak 15cents, off peak 9.8cents,  not 25cents all the time.  Let's be honest here.  

    When you can time shift your major uses you can theoretically cut your consumption cost in half, but who can do that?  I know I can't.  Any major charging I do overnight.  Once November rolls around I'll let H1 carry my loads, but not charge.  If there's enough wind I won't use any H1, or if the next day is forecast to be sunny.  This is helping me nurse 13year old batteries along for a few more years.  First years off grid I really aged them through ignorance.  Too soon old, too late shmart.

    Outages in can be problematic for most people.  But in eastern Ontario where I live, they are infrequent and usually storm related.  If you had accumulated outages in a year of 12 hours in total (much more than I've experienced in the last 10 years) that would only be:
    12/8760 x 100 =0.14%.  of your year without power.  Now, and ice storm that can shut you down for 3 days or 3 weeks is another story.  Generators are nice to have availble in that case...and a supply of stabilized fuel.

    When we expect cheap power on demand we hcave to be ready to pay for the maintenance of the infrastructure.  How much is a lineman's time worth at 2am in and ice storm?  Lots!  I don't mean what he or she is paid, I mean how much is their time worth to us?  Can you fix your transformer if it breaks?  Can you repair a transmission line?  Part of what we accept as customers using the infrastructure is the resposibility of it's upkeep.  

     Full disclosure:  I lived off grid for 6 years, then went back on grid using Hydro One as my multi billion dollar generator and phantom battery bank.  Having been responsible for my own power generation, storage and distribution for that time makes me appreciate the infrastructure and manpower necessary to keep a major utility up and running.  So, if you get your loads really low, don't expect to pay more than $60 per month for power...unless you heat with electric or have A/C.

    Ralph
  • PhotowhitPhotowhit Solar Expert Posts: 5,503 ✭✭✭✭✭
    sauerkraut said:
    The fan is DC and will be wired to the bank w/ fuse.  I’m hoping for 12-14 hrs of search mode per day except for fridge starts.
    Well planned, you likely don't need a fan in general, there are ones that don't use fans, are you in a dry climate? There are other ways to get the air flow, a tall black pipe, will create a draft during sunny days, and taller chimneys, I believe, draw better. (from my faulty old mind) 
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    The only other option is to put a large flooded bank outside in an insulated enclosure.  I can get the enclosure real close to the wall that the inverter is on to minimize the run, and I could insulate it really really well.

    What do you think of having a flexible insulated pipe going from the house to the box with a thermostatically controlled fan to pump room temperature air into the box when needed?  The house will always be warm.  I would ensure to have a one way flap in that system and a vent at the top of the battery box.  The bank and box setup would need to be able to weather a potential -35C.  Has anyone done this before?

    The flooded bank has at least three significant advantages; space limitations are less of an issue, even though AGMs are theoretically sealed you still have a potentially dangerous bank of batteries in your living space, and plain old FLAs are about 1/2 the price per amp hour.  AGMs also have the drawback of not being able to check specific gravity, which is the only way of really monitoring the health of the bank.  Given that this is your first bank, your loads are calculated with no real-world experience, and you can't properly monitor, there is a reasonably chance you'll kill a set of expensive AGM batteries.  At least with flooded you'll have a fighting chance to catch problems  before they put you out of business.

    Putting them in a box outside shouldn't be an issue as long as you keep the bank well charged.  I'm in northwestern Ontario where it gets at least as cold as your area (probably more so).  My banks are in a plywood box in a crawlspace which was unenclosed when I first installed the banks, and they handle it okay.  The bank will lose some capacity in cold temps, but won't freeze until way below -35 at full charge.  In your case I'd probably try to dig a bit of a pit to take advantage of extra thermal mass to even out temps, not so much for winter, but to keep them cooler in summer.  High heat is bad for battery life.  You shouldn't need to heat the box, but insulation would help especially in summer.  You may want to top vent it though to prevent buildup of potentially explosive gasses. 
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    Hi Guys,

    Thanks for all the responses!  

    westbranch, I appreciate the input.  I am okay with doing 70-75% DOD on the batteries as surrette says I should get 1000 cycles doing that.  Using my worst case load that should give me two days, and based on that I ought to get 5 years out of them, which I’m okay with.  But if that doesn’t work out, then yeah the whole thing gets too costly.  I can potentially upsize to 400ah cells in that space, but those batteries would be a tight fit.  I would have to stack two on two, horizontally. Do you think they would be ok sitting on their side (the long side), with 3 pieces of 1/2” strapping between the bottom one and the one sitting atop? Would the cases take it?

    Photowit, I should put a meter on it.  But it’s being fed room temperature water and it’s a little on the plus side of 20 minutes I guess.  I should be more scientific about it.  

    The fan is DC and will be wired to the bank w/ fuse.  I’m hoping for 12-14 hrs of search mode per day except for fridge starts.

    Estragon, I currently don’t have the ability to run the tank on the shore power, the 700 watts is way short.  I’m still in construction and not occupying, so it’s fine for now.  I had it hooked to a generator to test it out.

    I haven’t measured the fridge, but I will, and I’ll get back to you.  The long term plan is to get a novakool type fridge with a danfoss compressor and run it on DC, but that’s down the road.

    I have an onboard 250L storage tank inside that I pump water into, and in the summer it will have collected rainwater pumped into it.  I set up a nifty water treatment system that uses no electricity, if anyone is interested I can share info about it.

    mvas, I’ll put a meter on it and find out it’s behaviour.  It’s not in service yet so I don’t know, I just went by the energuide sticker.  There is no furnace as of yet and won’t be for some time, if ever.  The place is heated with a wood stove.  I have a spot for the furnace and propane is plumbed, and if I put one in it would be an Atwood RV 12v, and the blowers use 55 watts.
    I used the NovaKool compressor/evaporator kits in a ridiculously well insulated fridge/freezer I built myself.  Still working on the fridge door, but the bottom freezer compartment, which isn't even completely sealed yet, uses very little power (~ 100wh/day) and takes days to thaw out after I turn the compressor off.  

    Presumably you'll be using the generator or a gas powered pump to fill the 250L tank?  I just use filters for water treatment, but my lake source is pretty good to begin with.  What are you using?  Might be worth starting a new thread for that topic.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    Westbranch,

    Thanks for the evacuated water tube suggestion.  The water tank I have actually has an exchanger built in as it was built for the sailboat world and is meant to also heat the hot water by piping hot engine coolant through it.  Link below…

    http://www.thechandleryonline.com/product_info.php?cPath=3_351&products_id=139



    Ralph Day, you raise some good points and perhaps I’m being a bit unfair, but I don’t think our Hydro One situation is quite as rosy in our location as it is in yours.  Regardless, I will be in a spot where there is no grid.

    Photowit, the toilet is a Separatte Villa, made in sweden, comes with the fan and they recommend it be used all the time.  I will try it out without the fan just to see.

    Estragon, if I went with flooded batteries outdoors, I would worry about them in a partial state of charge overnight when there are no loads/charging to keep them warm when it is extremely cold.  Is this something I should be concerned about?  Theoretical 750ah x 24 volt bank.  Batteries are at half capacity at -25C or so.. so I would only be able to pull about 4500 watthours from them in this instance?  What happens if I get them down to 50% state of charge and we get a -30C night, would they freeze?  I guess what I’m looking for is data on freezing temps vs SoC.  Any thoughts would be welcome.

    As for water, I will just use a small 12v pump in the summer months to pump rainwater on board from collection barrels.  In the winter (for now until I get a well installed, and would run that off it’s own little system) I will bring water in with my pickup truck from down the road and pump it off with said pump.  Not ideal, but I won’t be using much water so I think it’ll be ok.

    I’ll start another topic on water treatment later, don’t want to derail this thread too badly.

    Thanks
  • ThomThom Solar Expert Posts: 195 ✭✭✭
    We heat all water on gas or wood stove. Pump water from a dug well with the generator every 2 to 3 days. Use a flush toilet . A 35 gallon trash can for storage. Our small system works well for us. we turn off the inverter at bed time. Use iPad for internet , TV 2 hours at night , led lighting, wifi on only when awake. Gas refrigerator. Propane is $36 month. Less in the winter. Golf cart  battery's were 6 years old in June. 
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added [email protected] 100w panel with a midnight brat 
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    Westbranch,


    Estragon, if I went with flooded batteries outdoors, I would worry about them in a partial state of charge overnight when there are no loads/charging to keep them warm when it is extremely cold.  Is this something I should be concerned about?  Theoretical 750ah x 24 volt bank.  Batteries are at half capacity at -25C or so.. so I would only be able to pull about 4500 watthours from them in this instance?  What happens if I get them down to 50% state of charge and we get a -30C night, would they freeze?  I guess what I’m looking for is data on freezing temps vs SoC.  Any thoughts would be welcome.

    As for water, I will just use a small 12v pump in the summer months to pump rainwater on board from collection barrels.  In the winter (for now until I get a well installed, and would run that off it’s own little system) I will bring water in with my pickup truck from down the road and pump it off with said pump.  Not ideal, but I won’t be using much water so I think it’ll be ok.

    I’ll start another topic on water treatment later, don’t want to derail this thread too badly.

    Thanks
    Figuring out the drop-off in usable capacity with lower temps is complicated by varying current rates at various states of charge.  A 50% loss would be pretty extreme though and would have to assume some really heavy rates of discharge.  It seems to me my charge controller estimates about a 25-30% loss of capacity at those sort of temps.  

    As for freezing, using this chart
    http://www.trojanbattery.com/pdf/WP_DeepCycleBatteryStorage_0512.pdf
    it looks like a 50%SOC battery would start freezing around 0F or -18C
    Assuming the box/shed is insulated and attached to a heated house, I doubt a -30C night would get the batteries that cold but it's possible.  In my experience, the battery doesn't freeze all at once like pure water.  It gets sort of slushy first.  Eventually it would freeze completely though and potentially burst the case or otherwise damage the battery.  

    At 50%SOC I would already have turned the generator on anyway.  Realistically, you have to use the generator a fair bit in winter in Canada.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Marc KurthMarc Kurth Solar Expert Posts: 836 ✭✭✭✭
    Battery freezing/case rupture/plate shorting is a very real concern in extremely cold areas if you are not careful in maintaining a high SOC.

    We do a lot of work for industrial/government entities in extreme latitudes/altitudes and it is a very real problem. Even certain AGM's can freeze up tight at -40 degrees if you let them get appreciably under 65%-70% SOC.  In my experience, 100% SOC is little more than a nice theory when it's really cold!

    And of course that's exactly when things go wrong in remote locations.........

    Marc
    I always have more questions than answers. That's the nature of life.
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    edited December 2016 #22
    Do not heat water with PV.
    Especially in canada.
    You are going to be lucky to get half the panels rated output in winter, then you are going to have serious battery numbing from the cold.
    The way I see it you could be heating water with propane at around 85% to 95% efficiency or you will be heating it with a generator at around 20% efficiency.
    With a tank less propane water heater you will have instant heat for minimal electrical input, may 100 to 200 watts when running.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    I use a Rennai tankless for DHW and also for supplemental space heat via infloor pex radiant. OP might want to consider at least running pipe during construction so the option is there to add. Sometimes the woodstove puts out too much heat when I just want to take the chill off. Also stove heat stratifies, leaving the floor cold.

    Tankless plus 5 circ pumps will run on the Morningstar 300w inverter.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490mike95490 Solar Expert Posts: 9,195 ✭✭✭✭✭
    Many wood stoves have a water heater tank/loop option.  I'd look into that for hot water at least in winter, solar in summer.  If you can mount a 30 gallon tank up in the loft, it will thermosiphon from the stove and not need a pump.  feed preheat water to your electric heater, or a propane tankless.    You can build a "doghouse" on the side and use a roof vent for a tankless, and avoid the freeze.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    The tiny house construction is actually pretty much complete, this week I’m putting the flooring down, and everything else is in place, just have to trim things out and install some things like the toilet and bath sink.

    Estragon,

    I like your idea of having a second inverter for lower tare losses, it’s at least worth thinking about for the evenings.  You mention the morningstar, but they only have a 12v.  Would you use a DC to DC converter to bring down the 24v battery bank… are there losses with DC to DC conversion?  Would assume a different inverter like a Samlex if otherwise.

    So, I’ve given up on the electric hot water tank for heating water, I’ll proceed with the solar DHW system for the sunny months and I think I’d like to try tying a boiler into the mix that I can use in the winter.

    Small diesel powered Hydronic coolant heater like this one… http://www.eberspaecher-na.com/fileadmin/data/countrysites/EB_Kanada/pdf/EB_Hydronic_D5_SC_S_E_WEB_READY_01_26_15.pdf

    Webasto also has many options, and they are widely used for heat and DHW in boats, sailboats, trucks, RV’s (more so in europe I suppose).  The one I linked above uses about half a litre of fuel per hour and spits out 17,000 btu’s, and about 50 watts.  I was thinking I would mount it outside with it’s fuel tank, and circulate a glycol solution into the hot water tank’s exchanger, then alter tie in solar collectors with some valves and things (will have to sort out the details).

    Perhaps have the boiler signal on a temperature controller.

    Thoughts?  May not be ideal, but it sure would be fun to play with, and would remove the entire DHW load from my RE system.
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    I have an Espar heater on my boat which works pretty well. It lives inside with the exhaust going out through the hull. Mine is ducted air, but I expect the hydronic ones are nice too. A big advantage on the boat is it runs on the same fuel as the engine (diesel). Pity you aren't using a diesel generator. I don't know if you could harvest waste heat off a honda like you could off a diesel, but the espar should get the job done.

    For space heating, if you aren't putting infloor radiant I would at least think about planning for water to air heat exchangers for future. You may find the wood stove overheats the small space in shoulder seasons. I've found dampering stoves down too far just ends up smouldering which leads to chimney fouling.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    I think the dc converters are pretty good in terms of idle tare. Not sure about overall efficiency. Are you set on 24v? I sure wish the Morningstar came in other voltages.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • sauerkrautsauerkraut Registered Users Posts: 9 ✭✭
    Agreed with the wood stove!  I currently heat with it as it's the only heating source and a small load of kindling and a medium split brings the inside up about 8 celcius, which to illustrate your point is a lot if you want to go from 18C to 22C to take the edge off.

    I have a space for an Atwood propane RV furnace, with the proper size hole in the wall framed out and the propane line already plumbed and I had planned on using that for bumps in temperature and while I was away.  12v units, so I'd need a dc converter anyway.

    I'm pretty set on the 24v setup, I need at least a 24v system to deal with some of the loads I am going to be working with occasionally.  I think I'll focus on DC fridge, and some DC lighting to keep the inverter in search most of the time and just see how it goes. 

    Too bad espar doesn't have a little propane coolant heater/boiler, and I haven't been able to find one elsewhere.  Does anyone have any data on using a small tankless DHW propane heater as a boiler with antifreeze in it? Like one of those cheap ecotemps, and perhaps mount it outside with a circ pump ? (weather proofed, of course)
  • PhotowhitPhotowhit Solar Expert Posts: 5,503 ✭✭✭✭✭
    Exeltech makes a 600 watt that is hardwireable and draws @8 watts idle. They also make a 250 watt, but I don't know the draw on it, I don't think it is designed to be hardwired.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • EstragonEstragon Registered Users Posts: 4,484 ✭✭✭✭✭
    I use a Rennai tankless for both DHW and radiant infloor supplemental heat. It heats potable water for domestic use and prop glycol through a heat exchanger for radiant. I think running glycol directly through the tankless would work okay. I usually run some glycol through before leaving in winter. Would be worth checking with mfg though. Apparently prop glycol doesn't play well with some kinds of rubber (like marine toilet joker valves).
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • 706jim706jim Solar Expert Posts: 397 ✭✭✭✭

    I have that identical Atwood heater in my powerboat. I have a Honda EU1000 inverter generator that will power the microwave, or stove element or battery charger on the boat. No way it would run a 1400 watt element as found in the Atwood. My solution was to replace the 1400 watt 120 volt element with a 3000 watt 240 volt unit (about $20 at Canadian Tire) which requires 750 watts to operate. You might want to consider this as an option for your tiny home. It would require a smaller inverter although the amount of energy works out to be pretty much the same to heat the tank. Or you can use a small generator as I do.

    At my summer camp, I've used a 5 gallon Atwood propane water heater for 22 years with great results.

    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
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