# My head hurts!



## TxGypsy (Nov 23, 2006)

I am a reasonably intelligent person. I have experience with house wiring. I am really good with math.
The more research I do the more conflicting information I find. I have a 320 sq ft cabin that will be fully shaded in humid east Texas and want a 9,000 btu mini split. One source says 600 wh. A different source gives a much higher wh. 
The energy star information rates efficiency now rather than estimated power usage. Not at all helpful.
This should not be this hard!
I will be using led lights, fan, adjustable bed, laptop, and very low energy usage water pumps for hydroponics. Oh and a water pump for rain water collection tanks.
If y'all would be kind enough to point me to an actually useful solar and battery calculator and or a helpful page or video I'd be grateful.
I thought I had a pretty good grasp on what I need but today my brain just released it into the aether.


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## MichaelK! (Oct 22, 2010)

I have a 8000 BTW air conditioner that I run on my solar system, so I can give you some numbers. The unit runs non-stop when first turned on and consumes about 750W continously till the set temperature is reached, ~3 hr. After that it cycles on and off with about a 50% cycling average, so let's say the total watthours consumed overnight is going to be (750W X 3hr) + (375W X 8hr) = 5250Wh. The inverter itself will be consuming power just staying on, maybe 1000Wh depending on the brand, so including everything else including the lights, TV, and computer, let's call that 7500Wh.

Assuming you get about 5 sunhours per day in Texas in summer (not the number of hours of daylight), you would need 7500Wh/5 sunhours = 1500W of solar panels.
Assuming you don't want to consume more than 25% of your battery per day, that would mean you need a battery with 7500Wh X 4 = 30,000Wh of power. At 12V that would be a 2500Ah battery, at 24V a 1250Ah battery, and at 48V a 625Ah battery. Rolls-Serrette makes a battery in that Ah range that one adult male can lift. 4 CH 23P | Rolls Battery You would need 12 of those 4V batteries to make a 48V system.

My air-conditioner consumes 750W while running, but you have to account for the conditioners motor that might consume 4X the running power right at startup, so that means a 1 second startup power draw of ~3000W. I'd suggest getting at least a 4000W inverter to power it, and since it's powering an AC motor, you MUST have sine-wave to protect the motor from damage. Take a look at this Schneider SW4048.





Schneider Electric Conext SW4048-120/240 Inverter/Charger - RES Supply


Free Shipping! Schneider Electric Conext SW4048-120/240 Inverter/Charger, 4000W, 120/240VAC, 50/60Hz, 30A Transfer, 48VDC, 45A Charger, RNW8654048




ressupply.com




It's a tier-1 brand, and has lots of bells and whistles that lesser inverters won't have. It has split-phase 120/240V AC, a built-in generator charging circuit, and an automatic transfer switch. It does not have NEMA sockets, this inverter must be hard-wired directing into the electrical panel.

For the panels, I recommend you get 250W+ grid-tie panels, matched to an MPPT charge controller. 1500W/50Vcharging = 30A, which is not that high, but you might want to upgrade the number of panels later. Those big batteries will enjoy charging at 60+amps, so I'd suggest getting at least a 60A controller to handle future expansion. Look at Epever's Tracer 6420AN as a good match. You could wire all four panels in series to get 120VDC and feed that into the controller, then the controller transforms the voltage down to battery voltage, making extra amps out of the extra volts. I myself am using a Midnight200 controller, with about the same specifications.

So, here is the list I think you need

6 250W grid-tie panels, 30V each. (perhaps later upgrading to 12 panels) I bought 260W REC panels for 65$each last month. 390$ total.
Epever 6420AN charge controller ~270$ on ebay
12 Rolls 4V 23p batteries (expensive!!!) the battery is going to be your single biggest expense
Schneider SW4048 sine-wave inverter, 1700$
main electrical panel for the inverter, ~350$ (this has the breakers and switches for binding the batteries, inverter, and charge controller together. Schneider Electric 865-1016 Conext SW DC Breaker Panel - RES Supply 411$
wires, breakers, spit, and other stuff, another 500-750$


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## TxGypsy (Nov 23, 2006)

@MichaelK! 
Thank you!!!! 
I'm going to study this more in the morning and make notes. This helps a lot!

It looks like my solar generator may be able to handle everything except the A/C pretty easily. I have a Bluetti AC200P. It's 2000 wh/2000 watt output/700 watt pv input/4,800 watt surge. 
I also have a 3500 watt gasoline generator for back up.


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## RJ2019 (Aug 27, 2019)

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