Battery bank location advice

[Bager]

New member... hoping to absorb all y'alls expertise : )

I'm planning a small backup solar array (under 1kw) and storage system (200 aHr AGM) . To reduce the need for long runs of large gauge wires I want to look at the charge controller, battery bank and inverter all being located next to/under my solar array. Runs into the home will be with UF and NM building wire at 115v.

I am at lat. 45.7 which means January avg temps of 25ish degrees F; rarely as low as -30f. The location will be insulated, but not heated. I'll likely use AGM batteries. Definitly not Lithium chemistry.

At most this system will power my fridge and freezer full time except possibly Dec and Jan when generation will drop to almost nothing. It will also be available for my NG fired furnace in the event the grid goes down during the winter.

So, I'm looking for advice on my battery bank location. I've had success with AGM batteries outdoors on continuous charge through MPPT charge controllers.

Thanks

[Mike90250]

So, it boils down to load management, when the battery reaches 50%, you need to cut the loads off and let the battery recharge before loading it down again, leaving the battery low too long causes sulfation and reduced capacity. Who's going to unplug the inverter in the winter ?

[Bager]

So, it boils down to load management, when the battery reaches 50%, you need to cut the loads off and let the battery recharge before loading it down again, leaving the battery low too long causes sulfation and reduced capacity. Who's going to unplug the inverter in the winter ?

Thanks. I understand the part about drawing down the battery bank to no less than 50%. That's true 12 months of the year so can you explain the significance of that in an unheated storage location?

The question about unplugging the inverter? Please help me understand the significance of who unplugs it.

[Mike90250]

When the system is shut down for the winter, the battery must be fully charged. All loads must be disconnected, inverter, meters.....
Charge controller - maybe, if your panels are covered in snow, how long does the idle load of the controller, take to bleed your battery down ? 3 weeks? 3 Months, 6 months ?


Fully charged batteries dFreeze point Pb battery.jpgon't freeze. discharged batteries do freeze. 50% batteries can freeze

[Bager]

OK. Very good info.

This solar array and battery bank will not be shut down for the winter. It will be actively charging 365 days per year and actively discharging at a very low rate 365 days per year.. As far as the info from the chart (very good), since I'll never be below 50% discharge I shouldn't worry about outdoor temps.

So your last sentence tells me what I need to know. I can locate my battery bank outside in freezing weather with little worry since it will almost always be fully charged. Those other issues such as snow cover, et al... not a concern at all for me. I'm retired, I'm home most days. I'll be obsessively monitoring this system.

Now my question comes to... feom the inverter, can I run appropriate sized UF inside and NM from there to the breaker panel dedicated to emergency power and maybe my fridge and freezer (NOT TIED TO THE GRID).

[Mike90250]

OK, now that we know you are wanting to run a fridge, you need to be aware of the compressor starting surge, which is generally around 2,000w for about 2 seconds when starting. Make sure your inverter can handle that peak. That usually requires about a 1,000w pure sine wave inverter. ( you are powering a motor, which works much better on pure sine wave.)

My suggestion, use a 24V system. for 2000w, it's only 83A, where if you were at 12V, the inverter would need to draw 167A, which requires thick expensive copper wire, and carefully laid out runs, so the the inverter does not see much voltage drop. Voltage drop at the inverter is the usual failure mode and since it only lasts for a second, a meter will never see it.

Suggestion #2. Use four, 6V 200ah golf cart batteries. They should last you at least 2 years, and will be an inexpensive way to learn about setting up your system and managing loads

Will you be setting up a dedicated outlet in your house, or using a transfer switch on your main panel ?

The average energy star fridge consumes roughly 1kwh daily. A little dorm fridge will consume about the same because it has cheap components and thin insulation.

24V @ 200ah gives 4800wh stored, half of which are usable, if you want your batteries to last a longer time

[Bager]

OK, now that we know you are wanting to run a fridge, you need to be aware of the compressor starting surge, which is generally around 2,000w for about 2 seconds when starting. Make sure your inverter can handle that peak. That usually requires about a 1,000w pure sine wave inverter. ( you are powering a motor, which works much better on pure sine wave.)

****I was considering a 2500 or 3000 watt inverter with 5k or 6k surge (for future expansion needs rather than immediate needs for this small system).****

My suggestion, use a 24V system. for 2000w, it's only 83A, where if you were at 12V, the inverter would need to draw 167A, which requires thick expensive copper wire, and carefully laid out runs, so the the inverter does not see much voltage drop. Voltage drop at the inverter is the usual failure mode and since it only lasts for a second, a meter will never see it.

****Yes, smaller size wire is the goal. And, short runs from array to ch. controller to battery bank and to inverter. Then UF and NM for 115v runs into the garage and then into the basement.****

Suggestion #2. Use four, 6V 200ah golf cart batteries. They should last you at least 2 years, and will be an inexpensive way to learn about setting up your system and managing loads

Will you be setting up a dedicated outlet in your house, or using a transfer switch on your main panel ?

****Yes, several actually. One would go near my furnace for grid outage use only. Another would go to the fridge next to the grid power outlet as well as maybe a third near the freezer next to the grid power outlet. No ties to grid. I suspect in the beginning, and only during higher solar production periods I would be powering only the fridge via the array/battery bank. In January and February (maybe March and December) I would likely just store power from the array to keep from draining the battery bank. I did a detailed solar survey and I'm confident that production during eight months would allow me to power the fridge and freezer full time.****

The average energy star fridge consumes roughly 1kwh daily. A little dorm fridge will consume about the same because it has cheap components and thin insulation.

****Our current fridge and freezer each average 1.25 kWh/day measured with a Kill-a-watt meter. Furnace is being measured now, but with warm temps lately it really isn't getting good winter data just yet. Typical furnace such as mine will operate at 600 watts and 900 watts surge. Time will tell what actual use will be and that will tell me consumption while maintaining home temps in the mid 60s. During an extended grid outage period the furnace would probably need to only maintain temps around 50 so the data I'm collecting will over shoot our needs. Not a bad way to look at it vs underestimating.****

24V @ 200ah gives 4800wh stored, half of which are usable, if you want your batteries to last a longer time

****I'm looking at 300 aHr of storage to start.****


****We have experienced only two significant grid outages in the last five or six years. Significant is relative... I realize the one or two hours we went without power in those two outages is far from significant to many folks that depend on the grid. For instance, my sister Shiawassee County Michigan went weeks without poser several years ago around New Years Day.

I am only planning for a worst case scenario and realize normal energy consumption during an extended outage is not even close to what I want to accomplish. Keep a couple lights on, Make sure food doesn't spoil, keep the house at a tolerable temperature.

Again, thanks for the help. I am a beginner and maybe rushing this a bit. I originally wanted to have the equipment purchased and installed (DIY) before the end of the year for tax reasons. Not sure that will happen.****