Total Battery Output Vs. Appliances

[Sunking]

John lets start over. First thing you need to understand is battery systems are incredible expensive, and solar is a very mature technology. Solar panels are like CRT TV's, they have been around so long time since 1839 and th elast major leap was in 1941 during WW-II when transistors invented. As a mature technology there are no major leaps to be had, only small refinements. The solar panels of the late 1950's are essentially the same as today.

But here is what you really need to grasp before you do anything, it is the most important thing to know. Anything you take off-grid, and I do mean anything, is going to cost you 5 to 10 times more the rest of your life vs buying that power from the utility. The reason is endless battery replacement cost.

Here is an example of cost and physics. Let's pretend you want to take the smallest of loads off the grid, your home lighting. Typically that amounts to about 2 Kwh per day. Utilities depending on which state you live in charge as low as 7-cents per Kwh, and democrats like paying 25-cents per Kwh In other words just 14 to 50-cents per day. Let's assume you live In Sleepyville USA with average winter Solar Insolation 3 Sun Hours, and your local utility charges the national average of 11.1 cents per Kwh. Here is what it takes:


Panel Wattage = 1000 watts = $1000 to $2000)
40 Amp MPPT Charge Controller = $350 to $400
Good 5 year 24 volt 420 AH 600 pound Battery = $2000 to $2500
Premises Grade 500 watt True Sine Wave Inverter = $500

Your initial cost is going to be around $4500. In 5 years the system will have generated 3650 Kwh. That brings your first 5 year Kwh cost to $4500 / 3650 Kwh = $1.23 per Kwh or just over 10 times more than the utility would have charged you. Now it is time to replace the 600 pound gorilla battery setting in your garage at even higher cost. Lets say $2500 (I used $2200 initial) Your next 5 year cost is $2500 / 3650 Kwh = $.68 per Kwh or just over 6 times what the utility charges.

So you are retired on a fixed income. Can you afford to pay 10 times more for electricity to keep your kids from inheriting any money?

Care to guess what it would cost to take a power hungry appliance off the grid? You don't have to do you? It would be foolish to even consider it.

[SunEagle]

I think that guy is dead. Never heard from him again after he was about to do something we told him was too dangerous....

Hopefully not dead but just embarrassed enough to not come back to the forum. He was going down a short pier without a life preserver.

[Living Large]

I’ve got a lot to learn about the science and who and where to get my answers from. A lot to learn. What I wasn’t prepared for was one response that told me my question was, “ His whole question is nonsense.” Granted, from one with more experience and knowledge about the science and practicality of solar science and its use – yes that question would seem “His whole question is nonsense”, but it was the best way that I could word my question at the time.

Thanks for the responses. Good web site.

John - First step is pull on a flack jacket and grow thicker skin, as others said. There are a lot of knowledgeable people here (I am not one), so if you hang in there, you'll get what you need.

What was meant by "getting stuck in a 12V box" is, and this is important, is that if you design a system for a 12V battery bank, it will restrict the amount of power you can get out at a reasonable price. Amy's comment pertains to whether you want to also restrict yourself to 12V appliances, or maybe in the future you will want to use 120VAC loads.

So the second step, after pulling on the skin and jacket in case of a sneak attack, is to figure out what your daily and peak power needs are. And, do you want/need the flexibility to go to an inverter to power 120VAC loads at some point. These things should be decided before going further. That's my 0.02.

If your appliances have nameplates, labels, etc they should tell you what power they draw. Your objective is determining the watt hours of power you use each day. If you use multiple appliances at the same time, that could be useful as well in sizing components.

Based on what has been written, it sounds like all 12V appliances. For anything 12V, you multiply by the Amperage to get watts. So if a fridge is 12V/15A, the wattage would be 12 x 15 = 180W. To get watt hours, you multiply the watt rating by the time it runs. So if it runs 8 hours a day, it would use 8 x 180 = 1440W-hr, or 1.44kWh (one point four four kilowatt hours). kilowatt being 1000 watts.

AC works the same, amps x volts = watts.

That is where you start.