Battery vs. Propane Generator - Why Wouldn't Batteries Work For Me?

[Shootr]

I've been watching Will's videos for a while and now I'm ready to install some sort of power backup in a cabin we just bought. It will be grid charged and used for outages for now, when we aren't there - to keep the temp around 45F . When we move up there permanently in a year or two, then I will be doing solar panels as well.

Ideally I think a 20kWh (48V x 400Ah?) bank would suit my situation pretty well. My problem is I don't have relatively accurate power usage rate for the furnace. The furnace and a few LED lights could be about 40kWh/day (20,000W@240V x 2Hrs/day). Talking to the neighbors - they remember only 1 multi day outage in the past 5 years. Monthly 1-5 hour interruptions is the norm.

During an outage when we aren't there - the furnace and a few LED lights are all that would be on. When we are there, the wood stove will reduce the electrical need so much that we can live pretty comfy on 7-10 kWh/day.

Being that the cabin is in a rural area, frankly - the electricians are pretty stuck in their ways and don't seem care too much about newer technologies. So far 2 of them have said I'm crazy and propane generators are the way to go - at $15K to install.

So...

If anyone is willing to check my math I'd appreciate knowing if I'm overlooking something in my power use to storage estimates. I'd much rather spend $10K-$15K to have a battery/soon-to-be solar system installed.

PS: I'm heading up there this weekend to do some chores, so if there is anything specific that would help narrow this down - let me know and I'll get the info.

 

[Brucey]

Are you saying you heat with an electric furnace and it takes 20kW for 2 hours out of every 24?

 

[Shootr]

As far as I can tell. I'll know for sure this weekend when I get a look at the tags on it. Everything I'm reading says a furnace my size (for a 1500SF home) draws about 20,000 watts. Seemed plausible if the little room heaters are 1500 watts max.

If that is correct, the wood stove is high on the to-do list. The place seems pretty well insulated. I'm keeping it at 45F because that's where the dart landed when I was determining a temperature to keep the plumbing out of danger. Outside temps have been 30F to 50F. This weekend it'll go down to the low 20's - which is as low as it goes there.

 

[Madcodger]

First, If you truly have an electric furnace (not a heat pump) I'd get rid of that, FAST. A heat pump is dramatically more efficient. Our 1200 SF living quarters heated with a heat pump to 68F (in Maine), over a garage of the same size, uses only about 50 Kwh/day to keep at 68F with three refrigerator/freezers running and all the other stuff people use, so your usage for an unoccupied house at 45F seems high to me.

Next, having been in your situation (remote vacation place that we later moved to), here's what I learned (hope it helps):

- Don't trust advice from the neighbors. Most people have terrible memories. We found that some would say, "Oh, we never get long outages", only to later find out that they were away during the last week-long event, or just plain forgot. After moving here, I actually heard our closest neighbor say this to a newcomer, after having heard both our generators run for almost 5 days straight the winter before. Neighbors are horribly unreliable for this type of info.

- A battery backup is awesome until the moment it is depleted and you have no way to recharge. From what you're saying, you'd have about a day of power even if you spend $10K or so on batteries. That's not much time when the only thing between you and frozen pipes is your energy source.

- For critical things/systems, "Two is one, and one is none." Redundancy saves your rear when the SHTF. This is why each of our main buildings have at least two sources of heat that require different primary fuels (electric/propane), and why there's a portable gas generator in the garage in case the automatic, propane, whole house generator fails to start, or breaks down. I'd suggest you think about a smaller (under $15K) generator that can power just critical loads, and make one of those loads a Rinnai Direct Vent wall furnace connected to the same decent-sized propane tank as the generator. That'll give you days of power and heat in a power failure, and if you are really set on no generator, I'd consider the Rinnai as the heat source rather than any electricity-fueled heat source during an outage, as the Rinnai will require only about 40-50 watts when running. We're building another home next year, and even if we connect to grid power and have 2-3 days worth of battery, it'll have an autostart generator and an automatic (not just wood stove) backup heat source to the mini-split heat pumps. Two is one, and one is none, in a bad situation.

My two cents...

 

[Vigo]

I agree that if you have a purely resistive heating element you really need to upgrade to a flow-reversing heat pump style of heater, such as what a mini split does. If you don't want to swap out the entire existing system you could just install a separate mini split, which if you do it yourself should cost less than 2k for a fairly large BTU unit. That will pay for itself in money saved on batteries to achieve the same amount of actual heating.

I also agree with Madcodger about having contingencies/redundancies. I know the battery system itself IS one but consider that we're not even necessarily talking about MORE money here.. For example, with a more efficient mini split, you could not only buy less batteries to cover a given time frame, BUT the mini split's electrical load is both lower and adjustable vs being 100% on or 100% off, which means you can power it directly with a fairly small generator which could cost less than what you save by buying less batteries, <$1k. That generator also gives you the ability to recharge your batteries, possibly simultaneously with powering the mini split if the generator is large enough or you run the mini split at a reduced setting during battery charging. If you made the generator propane AND got a propane heater as mentioned, now you can use the propane to power a heater OR the generator if one or the other broke, and use the generator to power the mini split OR recharge batteries to run the big 'furnace', if the mini split broke! If the generator is 'dual fuel' you've also got gas options if your propane system empties or fails!

If done that way you would have 3 heat sources (existing furnace, mini split, propane furnace) from 4 energy sources (grid, battery, propane, gasoline) and conceivably be at the same dollar figure you originally estimated.

 

[Warpspeed]

Assuming you have not yet installed anything, and you are not living there at this stage.
What I would do first, is arrange for some data logging for both inside and outside temperatures.
Then just run a small fan heater, say 1.5Kw 24 hours on continuously (no thermostat) for maybe several days or a week.

That should give a pretty good idea of how much the averaged temperature differential, inside to outside 1.5Kw produces.
Also a good feeling for the inside temperature swings during the day/night.
This experiment will work at any time of year.
Once you have a figure for that, it will give you a basis for sizing the final system, both for providing minimal background heat for when you are not there, and max winter heating load during the coldest anticipated days.

Agree with "Mad" above, a heat pump will provide a HUGE increase in system efficiency and is an absolute must have.

 

[KITROBASKIN]

People run out of propane (or gasoline) all the time. Generators require maintenance and while you are gone, seems like not a good idea for it to auto-start, possibly setting the land on fire? Maybe I am missing something.

Is there no way to drain your waterlines? Invest in the future, not short term band-aids with expensive fuel driven measures that if you figure it out, costs a lot for the amount of time you actually use it.

Crank up the wood stove when you arrive in the winter?

 

[Warpspeed]

There are other advantages to adding some minimal background heat, besides just preventing burst water pipes.
It can greatly lower the humidity, promote air circulation, and solve a lot of problems with damp, and musty smells.

 

[Shootr]

Wow, thank you all for the information!

It seems like I have a bunch of "balls in the air" juggling what I want to accomplish. It's a mobile home with 4 bedrooms, heat only - no A/C.

Furnace - Definitely not a heat pump (booo). I have an indoor thermometer monitoring it - pretty rock solid on the 45F where the thermostat is set. Adding one to the outside would be easy. Should do well for the space heater test, but I'll wait until the temps get back up to the 30's-40's. It's 3 hours away and with work/life it'd make me nervous to do it any colder. In the meantime I'll make note of the meter reading when I leave after this weekend and compare it to the reading when I return.

Mini-Split - I looked into those after I learned they are the way to go with alternative energy supplies. Embarrassed to say I lost track of that option (I've been dinking around with this project off and on for quite a while and my memory isn't what it used to be lol.) I can see now how advantageous that could be to the equation. Plus - A/C could be useful a few times a year!

Propane - It's not that I'm not a fan of it - but I think I want as much independence from outside sources as possible. I'd rather work on making the place more energy efficient to make a solar/battery system workable. They're saying in the cold, I'd need a 500 gallon tank + the generator + all the other stuff.

Freezing - I can drain the pipes but in the past my parents had a place and one copper pipe did split even after the place was winterized. Plus when the missus goes up without me - she wouldn't be keen on the process.

Luckily, this isn't an urgent need. I just want to get as much infrastructure squared away as I can before we move their permanently in 18 months +/-.

Once I get the data logging from the heater test I think it'll be much easier to make a battle plan. At first blush, the mini-split seems to be the way to go and be most compatible with a solar/battery setup.

Again - thank you all for taking the time to respond, I appreciate it!

 

[hwy17]

They're right. For occasional backup a generator is cheaper and more reliable. If you were going to be there to babysit a DIY battery then sure, but otherwise for a professional set and forget install $15k will only buy you like 10kwh of battery.

Even if you want to add solar and battery later, the generator will still be a good asset. Most of us also have generators of some shape or size. There's no power like on demand power.

 

[Vigo]

Im glad you are on board with the mini split idea.

I understand not wanting to do propane. If you want to focus on efficiency improvements first then you MAY consider as part of your outlay.. a thermal imaging camera of some sort! Cheaper ones are around $200 (except for some real low res stuff at ~$80 you may not want to bother with) and this would let you go around the house identifying all the low hanging fruit of air leaks you can fix with a $5 can of spray foam.

 

[KITROBASKIN]

Seems like mobile homes can have issues with a furnace or wood stove becoming dangerous. Might be a good idea to get them looked at if you have not already.

We have a neighbor that runs his generators a lot. No one else in the neighborhood does... Our beautiful area is tainted because of him. Resentment. He has some solar but has spent money and time driving an hour round trip to get more gas, and more gas. Yeah cheaper electricity in some ways, but the nuisance noise and no pollution mitigation is repugnant as well.

Understandably there are respected members here on diysolarforum who need that method of electrical generation.

 

[Tomthumb62]

Seems like mobile homes can have issues with a furnace or wood stove becoming dangerous. Might be a good idea to get them looked at if you have not already.

We have a neighbor that runs his generators a lot. No one else in the neighborhood does... Our beautiful area is tainted because of him. Resentment. He has some solar but has spent money and time driving an hour round trip to get more gas, and more gas. Yeah cheaper electricity in some ways, but the nuisance noise and no pollution mitigation is repugnant as well.

Understandably there are respected members here on diysolarforum who need that method of electrical generation.

I have a friend who has solar with generator backup. I asked him how the system runs. He said it runs great and the only time the generator needs to run is in the deep of winter when the days are so short and it only runs for about 3 hours a night. The rest of the year it’s very quiet.

His system isn’t all that large either. I’m guessing about 2kw. They heat with wood.

 

[ElectricIslander]

Re winterizing plumbing:

To purge water lines fully often requires compressed air to blow out the lines since most plumbers who install pipe don't slope the pipe or the fittings to self drain downhill.

When we winterize our off grid cabin which isn't heated while we are away, we use two compressed air fittings on tees with valves that I installed at the high points in the system. One on the cold water line and one on the hot water line.

It takes some strategic planning and knowledge of the plumbing layout to blow all the water out effectively. Generally speaking, you want to blow air in at the top and start opening drain valves, faucets and other connections from the bottom to the top so that the air pressure continues to blow water out as you progress your valve openings.

Winterizing drains is all about preventing U-traps and toilets from suffering frost damage. There are several ways, once a year (usually in late December) we do all of these as appropriate:

• Pink RV plumbing antifreeze (alcohol and propylene glycol in toilets - put saran wrap over the toilet so that the alcohol doesn't evaporate).
• Provide some compliant material in the toilet U-trap to allow the expanding ice room to expand and prevent breakage if the temp drops below the water-antifreeze freezing temperature (we push a piece of foam pipe insulation.
• Use shop vac to vacuum out water in trap (again saran wrap over the opening prevents sewer gas from entering your home

In addition to the above we have a Williams unpowered (mV thermostat) direct vent propane wall heater that we set at 4.5 degrees C so that other stuff in the house isn't damaged during extreme cold.

 

[Shootr]

Im glad you are on board with the mini split idea.

I understand not wanting to do propane. If you want to focus on efficiency improvements first then you MAY consider as part of your outlay.. a thermal imaging camera of some sort! Cheaper ones are around $200 (except for some real low res stuff at ~$80 you may not want to bother with) and this would let you go around the house identifying all the low hanging fruit of air leaks you can fix with a $5 can of spray foam.

Ha, try single pane aluminum windows! I'm a born and raised Arizonan and every house I've moved into - the windows were one of the first things we addressed. I'll be able to do these ones myself - wood framed and every window is the same size - that'll be spring as well.

The noise issue with having a generator - I go both ways. As a full time power source, I'd be really pi$$ed listening to a neighbors droning on all the time. For temporary backup power only when needed - I can understand that. Just not for me (at this point anyways.) 10 yeas ago me and the missus camped with a self-built teardrop. Like Bryce and Zion in March camping. A lead acid 12V battery and a solar panel kept things pretty comfy. No generator in sight. I know this is an all different animal but that experience, the peace and quiet, is making me try really hard for a silent solution.

That said, the house sits on a concrete block foundation with 2-3ft of headroom. I'm going to monitor the temps in there as well as the inside and outside of the house. If there is such a thing, maybe a small direct vent gasoline generator as a backup to the solar/battery system (while we're there.)

EDIT: Yeeeaaah, maybe not lol. But storing it there and dragging it out when needed would be pretty easy,

I'm digging this conversation - thanks again!

 

[Shootr]

Seems like mobile homes can have issues with a furnace or wood stove becoming dangerous. Might be a good idea to get them looked at if you have not already.

We have a neighbor that runs his generators a lot. No one else in the neighborhood does... Our beautiful area is tainted because of him. Resentment. He has some solar but has spent money and time driving an hour round trip to get more gas, and more gas. Yeah cheaper electricity in some ways, but the nuisance noise and no pollution mitigation is repugnant as well.

Understandably there are respected members here on diysolarforum who need that method of electrical generation.

We got a HVAC specific inspection when we bought the place - came back perfect. I can't get over how clean the crawl space is, where all the ducting is. It is practically spotless, not even a cobweb to be seen.

 

[JRH]

Seems like mobile homes can have issues with a furnace or wood stove becoming dangerous. Might be a good idea to get them looked at if you have not already.

We have a neighbor that runs his generators a lot. No one else in the neighborhood does... Our beautiful area is tainted because of him. Resentment. He has some solar but has spent money and time driving an hour round trip to get more gas, and more gas. Yeah cheaper electricity in some ways, but the nuisance noise and no pollution mitigation is repugnant as well.

Understandably there are respected members here on diysolarforum who need that method of electrical generation.

I moved once to get away from a neighbor who ruined the silence of the mountain forest with his damn gen set…very loud….upset everyone….a year later I went back to visit a friend near there only to find that the creep didn’t run his damn 12 k genny no more…it was killed ..
rumor has it that a “squirell hunter“ missed the critter and put a load of buck shot into the gennys engine.
I have always questioned that choice of load for a squirell…makes a man wonder…

but I’m glad the critter got away.

J.

 

[ChrisG]

In the same situation you are with a vacation cabin. We bought the place three years ago, difficult to get people up the mountain to work on anything so I've done a lot of DIY. Before adding inverter/battery or generator my goal was to get the cabin as efficient as possible. Since I can't get large quantities of propane delivered, the place is entirely electric.
Steps:

1. Replace well pump with a Grundfos SQ soft start - one of the best changes I made
2. Install a larger well pressure tank - pump runs less often, but really not an issue with Grundfos
3. Install mini-splits - still have the electric baseboards as back up
4. Installed a critical loads panel - moved fridge, freezer, light and outlet circuits, microwave circuits, well pump, and mini splits to it

If grid is down and not enough solar, I have 4 40lb propane tanks that run a 240v portable generator to 1) run the critical loads and even one mini split if needed (both if summer and only air conditioning) 2)charge batteries if needed (invert/battery is always a work in progress). Redundancy is key.

My 240v inverter/generator died recently so on the hunt for one. Considering getting two of those for redundancy if the price is right. Even toying with the idea of a 120v inverter/generator with a Solar-Edge or Victron autotransformer for step-up 120v->240v. 120v generators are easy to find.

 

[Vigo]

That said, the house sits on a concrete block foundation with 2-3ft of headroom. I'm going to monitor the temps in there as well as the inside and outside of the house. If there is such a thing, maybe a small direct vent gasoline generator as a backup to the solar/battery system (while we're there.)

EDIT: Yeeeaaah, maybe not lol. But storing it there and dragging it out when needed would be pretty easy,

Oh believe me, i've thought of probably EVERY way to recoup the 2/3rd of heat energy that's wasted coming off a generator and out of its exhaust. I'm still vaguely planning to build a 'hot room' shed sort of thing that houses the generator in the bottom 2ft, and then 2 water heaters in a compartment above. One of them being a natural gas sort which has the 'heat exchanger' passage up the middle. The two would be plumbed to each other and the house. The idea being all the heat coming off the generator housing AND out of the exhaust flows up through the central passage of the gas water heater tank, into the room and circulates around both tanks before hopefully finding its way out around the bottom of that space. Then implement some sort of water-to-air heat exchanger in the house and a system to prevent the water from overheating (could just be a kill switch hooked from water heater thermostat to generator). I imagine the interior of the water heater space would get pretty sooty eventually but i dont see why i would care..

If you wanted to get real simple about trying to capture some of that heat under the home, I would just run a solid/continuous 20ft piece of pipe sideways under the house and then pipe the generator exhaust through it. Yeah it might leak where you hook the genny to it but it's not going to leak in the solid pipe under the house. That way you'd at least have a ~20ft heat exchanger pipe under the house. Honestly though with NPT gas pipe i just wouldn't worry too much about leaks.. they make muffler sealing paste and high temp epoxy, so i don't see any real failure point of just slathering some of either on the npt threads and making a whole generator exhaust system under your house.. It would take some serious leakage AND lack of air exchange in the trailer to end up with a bunch of CO concentration in the house, imo.

 

[Warpspeed]

When I was in the Antarctic we had a large communal "hot room" that we used for drying clothes.