Advice for Off-grid Cabin

[Arrowshot]

Greeting and salutations. Not a newbie to this but not the best at figuring out requirements for an off-grid solar system in northern Alabama (above Birmingham). I am there a few days every other week. I’ve written below what I have and then what I think would meet my requirements but would really appreciate comments/suggestions that would ensure it meets my needs. Thanks in advance. Hope I provided enough info.

Current System

• (Four – only two being used for now) Renogy 100-Watt 12 Volt, High-Efficiency Monocrystalline panels (set at correct tilt and orientation for my area)
• EP Tracer 3215RN solar controller (30a and 12v/390-watt max PV input power)
• (Three) Sun X-Tender PVX-1040T sealed AGM deep cycle battery, 12V, 120Ah each (all are several years old now but appear to still be cycling)
• Volfvert 4000W Pure Sine Wave Power Inverter DC 12V to AC 110V 120V

What I want to run (but not all at same time)

1. LED lights (works with current inverter). Usually use a small battery powered lamp and don’t run LEDs.
2. TV (LED about 32 inches) (works with current inverter, have run for several hours under existing set up)
3. Small shop vacuum (works with current inverter)
4. 120v small fridge/freezer (600-watt startup and 130 running. Will only use when I am there which is a few days every other week..)
5. Coffee maker (maybe, might just use propane stove to boil water)
6. Small microwave (700-watt startup)
7. 6-gallon electric water heater (1300-watt heater element/120v plug in. This unit pulls .75 amps with 1.2 max 115 ac meaning max draw is roughly 138 watts.) and water pump (1300-watt heater element/120v plug in) Wattage = Amps x Volts. Thus, Wattage = 115 volts x .75 amps, Watts = 86.25.

What I Think Would Suffice

1. (Six more) Renogy 100-Watt panels
2. (One) 80 Amp MPPT Solar Charge Controller 48V 36V 24V 12V Auto, 80A Solar Panel Regulator Max Input Power 1100W-4500W
3. (Four) NPP NPG12-200Ah AGM Rechargeable Gel Deep Cycle 12V 200 Ah batteries.

Current Issues

1. Attempting to run the microwave off the inverter but it runs a few seconds then shuts down. Shop vacuum, TV and LED lights work fine.

Other Questions

1. How do I determine how effective my current batteries are and is there a way to utilize the current batteries and controller with any new equipment?
2. How large a wire do I want to run from my controller to my batteries?

 

[sunshine_eggo]

See link #1 in my signature. Enter your items, their power and the daily hours of run time for each.

Comments:

4kW inverter on 12V is insanity.

Item 4. Check the energy star rating.
Item 6. 700W microwave has near 1200W continuous run load. Microwaves are very inefficient and use about 60% more than they output.
Item 7. Not sure how a 1300W water heater has a max draw of 138W. Maybe you're referring to the water pump? that's a very small water pump.

2nd item 3: Which is it?? AGM or GEL. They are different types of batteries. Can't be both.

Concerning microwave:

Check connections and cable. Ensure all connections are properly torqued and of high quality.

1200W/12/.85 = 117A that calls for 2awg or better, and you'll need similarly beefy interconnects between the batteries.

If you have loose connections, insufficient wire gauge, and/or long cables, you may be experiencing excessive voltage drop that triggers the inverter to shut off. it could also be that the batteries are too old or at an insufficient state of charge to maintain needed voltage.

 

[Rednecktek]

Just a few thoughts off the top of my head...

1000w isn't horrible until you factor in that water heater. Now it's under sized. That tank running for an hour is 25% of your total capacity.

4kw on 12v is insane. Normally by the time you get above 3kw you're looking at a 48v system to keep the amperage, fuses, and wire sizes managable.

You are aware that flavors of lead acid only like to be used to 50% before you start damaging things. So factor 400ah @ 12v or 4800 watt hours.

It sounds like the microwave is drawing so much load it's bogging the voltage. How are the batteries connected? Cross wires or bus bar?

Try to avoid mixing AGM and GEL and different capacities if possible.

Do the power audit a few times and double check your work. The water heater would be my only major concern.

 

[Arrowshot]

4kW inverter on 12V is insanity. - So do I want to implement a 24v or 48v system based on how I intend to upgrade???

Item 4. Check the energy star rating. - Will check but info provided was from manufacturer.

Item 6. 700W microwave has near 1200W continuous run load. Microwaves are very inefficient and use about 60% more than they output.

Item 7. Not sure how a 1300W water heater has a max draw of 138W. Maybe you're referring to the water pump? that's a very small water pump. - That is the water pump which was recommended for the water heater.

2nd item 3: Which is it?? AGM or GEL. They are different types of batteries. Can't be both. - It is GEL

Concerning microwave:

Check connections and cable. Ensure all connections are properly torqued and of high quality. 2 gauge wire for battery connections and inverter. Everything torqued properly.

1200W/12/.85 = 117A that calls for 2awg or better, and you'll need similarly beefy interconnects between the batteries. - See above.

If you have loose connections, insufficient wire gauge, and/or long cables, you may be experiencing excessive voltage drop that triggers the inverter to shut off. it could also be that the batteries are too old or at an insufficient state of charge to maintain needed voltage. - Batteries are several years old but were not used extensively (think that might not matter as they degrade with time).

 

[sunshine_eggo]

4kW inverter on 12V is insanity. - So do I want to implement a 24v or 48v system based on how I intend to upgrade???

Just an observation. You may find that you only need a 2-3kW inverter once you've done the analysis.

Item 4. Check the energy star rating. - Will check but info provided was from manufacturer.

On/off/surge load tells you nothing about consumption. The energy star rating tells you how many kWh/year are used. Divide by 365 for kWh/day consumption - must have for energy audit.

Check connections and cable. Ensure all connections are properly torqued and of high quality. 2 gauge wire for battery connections and inverter. Everything torqued properly.

If that's the case, your batteries may be worn out. Next time you run the microwave, take a voltage reading AT the inverter terminals until it trips off.

Batteries are several years old but were not used extensively (think that might not matter as they degrade with time).

They definitely do. For those several years, they would need to be maintained flawlessly, rarely cycled, and maintained with a near continuous float to minimize degradation.

 

[Arrowshot]

See link #1 in my signature. Enter your items, their power and the daily hours of run time for each. - Generally run time for any of these will never be on a daily basis and have only ran the TV while at the camp for any extended time. Same for the water heater, it will be used intermittently (certainly never more than a few minutes) but of course it has to remain on for longer in order to heat the water for use (say 15-30 minutes).

 

[Arrowshot]

Your replies also generate another question from me, How do you maintain the best system integrity when you are only using it once or twice a month for a few days at a time?

 

[Rednecktek]

At the 4kw range, or even at the 3kw range, it's best to look at 48v so you can use the batteries later if you upgrade to a larger system in the future as well as save quite a bit on wires and fuses.

The only issue that creates is running 12v stuff as you'll have to get a buck transformer involved to feed a 12v bus. Extra planning and cost but not difficult.

 

[sunshine_eggo]

Generally run time for any of these will never be on a daily basis and have only ran the TV while at the camp for any extended time. Same for the water heater, it will be used intermittently (certainly never more than a few minutes) but of course it has to remain on for longer in order to heat the water for use (say 15-30 minutes).

Then you need to plan for the day that you run everything. The more you choose to leave things undefined, the crappier the end result will be.

Your replies also generate another question from me, How do you maintain the best system integrity when you are only using it once or twice a month for a few days at a time?

You turn everything off but the MPPT and allow the system to maintain the battery at full charge.

 

[Rednecktek]

Your replies also generate another question from me, How do you maintain the best system integrity when you are only using it once or twice a month for a few days at a time?

What I do at my camp is just have a couple panels on a small controller to keep them topped up, and disconnect the 12v bus that feeds everything else.

My camp currently is 5 FLA batteries and 400w of panels. The only draw on the batteries is the charge controller.

 

[Arrowshot]

Yep, that is what I have been doing, everything is turned off when I am not there.

 

[Arrowshot]

OK, will run through audit although will take some time to get some answers to some of the info. Thanks for assistance so far. Will revive thread when I have more info but other comments and suggestions are welcomed.

 

[Hank Waconda]

With 4K 12Volt inverter I'd be using 4/0 cable to inverter and batts at least. Other than that sound like more batt and panels good plan.

 

[12VoltInstalls]

6-gallon electric water heater (1300-watt heater element/120v plug in. This unit pulls .75 amps with 1.2 max 115 ac meaning max draw is roughly 138 watts.) and water pump (1300-watt heater element/120v plug in) Wattage = Amps x Volts. Thus, Wattage = 115 volts x .75 amps, Watts = 86.25.

Other than the math being a tad wonky, I’d probably ditch that electric hot water heater or at least configure as the primary hot water source to be ‘surplus solar’ heated and use a propane tankless water heater which can be had for as little as $200. The one I’m using was $130-ish and you can go most of all summer probably on a 30# cylinder even with daily use. Even if you need refill every three months that’s inexpensive and you won’t have to build solar to support a high resistive load.
IMHO

 

[photomankc]

Other than the math being a tad wonky, I’d probably ditch that electric hot water heater or at least configure as the primary hot water source to be ‘surplus solar’ heated and use a propane tankless water heater which can be had for as little as $200. The one I’m using was $130-ish and you can go most of all summer probably on a 30# cylinder even with daily use. Even if you need refill every three months that’s inexpensive and you won’t have to build solar to support a high resistive load.
IMHO

I'd agree. That is a terrible waste of battery.

Concerning microwave:

Check connections and cable. Ensure all connections are properly torqued and of high quality.

1200W/12/.85 = 117A that calls for 2awg or better, and you'll need similarly beefy interconnects between the batteries.

If you have loose connections, insufficient wire gauge, and/or long cables, you may be experiencing excessive voltage drop that triggers the inverter to shut off. it could also be that the batteries are too old or at an insufficient state of charge to maintain needed voltage.

I'll mirror what others have said here. 12V is pretty bad for this setup and the current draw for even 1/3 of that inverter capacity is hitting 125A from the battery. That may be a lot to ask from older LA batteries. 24V would be better and 48V better still if you plan to keep above 3000W capacity.

I am doing nearly the same thing as you cabin-wise. I head down about every 3 weeks for a few days. Similar loads, microwave, toaster, hot kettle, power tools for building, shop-vac, will be adding shallow well pump down the road.

I'm using an EG4 6500W and a single 48V 5100Wh rack battery (LiFePO). No solar yet, charge via generator. So far, the system has been perfectly able to meet my needs and handles running multiple high draw loads together. I'm really only generally drawing 250W and up to 3000W if going nuts and I know I can't max out the EG4 on the single battery so I stuck with a 40A main breaker for about 4800W max. I went LiFePO because they did not seem as cantankerous as LA for being stored for an extended time shut down in an unconditioned space and because having worked with LA for years I know the damn things are always mad about something. I went 48V in my design because I wanted to be able to handle 3000W or more of inverter without needing to manage battery cables that were thick as tree branches.

If I were you I'd give real consideration to going at least 24V for what you are talking about there. Microwaves are monsters. As mentioned that 700W microwave is quite likely wanting 1200W to 1400W and you are talking needing to deliver 125A of current and do it without voltage drop. That sounds like your batteries are flagging under that load OR your wiring and connections are under-sized leading to resistance-based voltage drop. If this is a place that is not kept cool and comfortable all year long those LA batteries are not being kept in their princess-comfort-zone and will probably need replacement more often than you would like.

If that is not feasible then you need to make sure you are using HEAVY cable and really getting good quality crimps on all the battery cables and interconnects between the batteries. Make sure they can really deliver the full rated current and sustain it. Your components are going to need to be BEEFY.

 

[Checkthisout]

TLDR

My advice is run either 12 volts or 48 volts.

24 volts is sort of becoming defunct for stationary stuff.

With 48 volts you get max wattage from all the available equipment on the market = best bang for the buck.

My current system is 12 volts, I'm changing to 24 because I got a cheap 24V multiplus. If I was paying full boat, I would upgrade to 48.

FYI, my 3 8d batteries and 3kw aims inverter run the 1500w micro no problem, while also running the dryer (motor), exhaust fan etc.