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Since you have a solar system now, you may know the variables that are involved with calculating usage and determining system size.
If you have a grid tied system now, you will not have electricity on when the main grid goes out. You enjoy a rebate on your consumption now, but there is no back up resilient benefits to you personally for such a system in the event of a grid failure.
The best way I have figured out to determine how much electricity I will need came as a two step process. The first step was a solar survey to determine the amount of sunlight available and my current usage. I learned that a $55,000 system would cover about 35% of my usage at that time. That was shocking to say the least. From that I learned that for every dollar invested in becoming more efficient I would be saving many more dollars on the cost of a system. Basically at $2 per watt for a solar panel, for every watt I could scrounge out in efficiencies, I could save myself at least $2 on my system. It became a game for me.
The survey included my average usage report in terms I could better understand than what my utility was sending me as a bill at that time. This gave me a jump off point for trying to figure out my biggest consumers of juice, and how to mitigate or eliminate them.
I decided to purchase a watt/ amp meter that plugs directly into the wall socket and allows the device being used to plug into it. WIth this I could see exactly what was being used by the device, and I could compare that reading to the data plate on the device to compare numbers and see if they were close. Most were pretty close.
Next I had to try to figure out how much I was using on each device. I literally checked everything in my home and my shop, including my welder. I took notes on the amps/ watts and volts while it was turned on and functioning (like the fridge running) when it was not actively functioning but still “on” and when turned off but still plugged in. Most items continue to draw while plugged in and this can be a large source of savings when you go to find efficiencies. For example my son’s Playstation is 120 volts, 5.3 Amps and consumes 30 watts while it is being played. While it is off, but plugged into the wall it still consumes 3 watts. Thats 3 watts 24/7 and it adds up. For comparison most of my LED lights now only use 2.5 watts each. I realized that using a surge protector on those type items and turning it off when I wasn’t using them would save substantially.
Then I needed to know HOW LONG my family used each item on a daily, weekly and monthly basis. Once I had those numbers I could average the amount of electricity each item would need to perform as required for a month. That was my Kilowatt Hour Bank Account. The less I had in it, the more I saved.
In the process of getting every bit of efficiency out of my home’s electrical system, I realized there were quite a few things we could completely do without on a survival basis. I conferred with my wife and older boys and we came up with a list of items we would use if we were going to subsist only. We narrowed that list down to:
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chest freezer,
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refridgerator,
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1500 watt microwave for no more than 10 minutes per day,
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3 LED lights per night, total of 7.5 watts for 3 hours per day.
Most cooking could be done with the microwave, the wood stove, BBQ or solar oven. Wash could be done by hand and line dried. Food processing would be limited to jerking meat, drying fruits and canning over an open fire. This brought the realization that the one most needed survival item for my family was going to be a large pot and a large metal tub, for cooking, canning, bathing and laundry.
So my solar system was downsized to a 1.4 kw, battery based, grid tied system. That sized system had enough excess in the system to run my welder for 5 minutes once a month, and other smaller tools more often. This gave me the excess to create other energy producing devices like a gasifier, water wheel etc if needed.
The point of my sharing all of this with you is to show you that each system has to be a custom fit based on YOUR family’s needs. If I did not have a wife and four children, I could get by with much, much less.
Best of luck to you. THis is a very rewarding path you have set yourself upon. Congratualtions on starting.