I want to install solar panels and a battery bank in my home to run a 12,000 BTU window AC, a refrigerator, and some lights.

The window unit is a 120V, 10.2A, 1224Watt unit that would run 24 hours a day. Typically its only pulling about 8 amps.

The fridge is about 20 cubic foot and my meter says it draws about 6.5 amps on 120V.

How many watts worth of panel and what size battery bank would I need to run this 24/7 in case of a power outage? I'm not really knowledgable on this solar voodoo so any help from someone who knows would be greatly appreciated.

solar facts
and
free solar

both good sites to figure out loads.

Rough guess is a 5KW array to run that AC 24/7.

If it's only running intermittantly it would be less.

A 2KW array would keep it running while the sun was shining and probably handle the fridge.

Using solar for heating/cooling isn't really economically viable, it can work for lights and coms and such but...

I have a little 320w array with a couple 220a/h batteries that are also hooked up to the DC circuit on my generator and a cheap 2kw inverter, that works really well because I can run the generator once a day for heavy loads and use the inverter for incidental stuff like lights and coffee and internet.

Of course our power hasn't gone out in 3 years since we moved but if it ever does...

Too many variable to answer you. What is your average total sunlight? How many days a year. In the winter you will get much less. Panel size, Panel efficiency come into effect. So does the system voltage (12, 24, 48) as well as the inverter efficiency.

Go take a look at Home Power Magazine, or go to Amazon and pick up a copy of Renewable Energy for Dummies...

I live completely off grid, and have a 2 year degree in Renewable. Give me more info, and I will see what I can do.

Aviator

Pure sine wave 4,000 watt inverter with built in charge controller for AC input
8 six volt, 530 amp hour batteries wired to provide 24 volts @ 1060 amp hours
2 250 watt panels
1 500 watt wind turbine
Onan 4k generator with generator auto start
Xantrex MPPT charge controller for DC input

One of those survival shows used solar to store energy in a bank of car batteries. They used the bank to run power tools. I don't think they could run the tools direct from panels. You might need an efficient bank to run a/c

double tap

It's impossible to answer your question without knowing (1.) how much power each of your anticipated loads draws, and (2.) how long each of them will run. It is unlikely that the compressor on your window unit will run all the time, and your fridge will also cycle on  and off. So, without knowing how long each of these devices actually runs, you can't proceed any further.

Using a Kill-A-Watt will help you pin down these figures.

After you know them for each load, you can add them all up, and then use them to determine how big your batteries and solar panels need to be in order to meet that estimate.

So - Step One is to fill in the blanks:

Refrigerator power consumption: _________ watts
Refrigerator hours of run-time per day: ________ hours

Window AC unit power consumption: _________ watts
Window AC unit hours of run-time per day: ________ hours

Misc. lights power consumption: _________ watts
Misc. lights hours of run-time per day: ________ hours


AN EXAMPLE:

FRIDGE: Draws 185 watts, and runs an average of 3.2 hours per day.
       185 watts x 3.2 hours = 592 watt-hours (or 0.592 KWH) per day.

AC WINDOW UNIT: Draws 530 watts, and runs an average of 9.4 hours per day.
      530 watts x 9.4 hours = 4,982 watt-hours (or 4.982 KWH) per day.

LED LIGHTS: Draw 12 watts, and run an average of 5.6 hours per day.
     12 watts x 5.6 hours = 67 watt-hours (or 0.067 KWH) per day.

Step 2 is to add them all up:

0.592 KWH +  4.982 KWH + 0.067 KWH = 5.641 KWH per day

So, your batteries and solar panels will need to supply at least 5.641 KWH per day, in order to keep up with your energy consumption.

Step 3 is to calculate the required size of your solar panels:

Assuming 5 hours of full sunshine per day, a 45 watt panel is capable of producing
    45 watts x 5 hours = 225 watt-hours (or 0.225 KWH) per day.

So, to meet your 5.641 KWH per day requirement, you would need:
    5.641 KWH per day / 0.225 KWH per day per panel = approx. 25 panels.

You will also need a solar panel charge controller and connecting wires capable of handling this many solar panels.

Step 4 is to calculate the required size of your batteries:

A pair of 6 volt golf cart batteries (connected in series to produce 12 volts) is capable of storing around 220 amp-hours of energy:
    220 amp-hours x 12 volts = 2,640 watt-hours (or 2.64 KWH).

So, in order to store enough energy to meet your 5.641 KWH per day requirement, you would need:
   5.641 KWH / 2.640 KWH per battery pair = 2.13 battery pairs.

In the real world, you would buy at least 3 battery pairs (6 golf cart batteries).

Note that this estimate assumes you get a full 5 hours of sunshine every day. If you want your system to supply the same 5.641 KWH per day even during rainy or overcast weather, you'll need to increase the number of batteries and solar panels accordingly.

Typically, battery banks are sized to provide at least several days of power on their own, in order to handle overcast or rainy days. Also, the lifespan of the batteries is drastically shortened if they're heavily discharged on a regular basis - so it pays to "go large" on your battery bank size. For the example mentioned above, doubling or tripling the number of batteries would be prudent - i.e., 12-18 golf cart batteries.

To be honest, you are better off putting the money into a Generator. The cost for a system to run the AC all day would be off the charts.

Aviator

I started to snicker when I saw the AC in his post.

The real problem is that you won't get full power out of the panels.  Even when it is high noon and sunny.

How will they be oriented?  Will they track the sun ($$$) or seasons?  Probably no, so what will you get out of a 4'x8' 750 watt panel?

At rated power you would need 3 just to keep up with daytime load.  Probably 6 more to get you fully charged for the night.  So that is 9, the double it for cloudy days and bad orientation.   So 18.  

Panels:  $15,000-$18,000
Inverter: $4,000-$5,000
Batteries: $2,000-$4,000

If you want to skimp?  Get more batteries, and far fewer panels.  A generator for extra charging.  Insulation so you don't need the AC 24x7



Posted Via AR15.Com Mobile