There is a smaller storage building next door to my house with a separate electric meter, which I plan on replacing with four 100 Watt 12 Volt Solar panels to start. So total 400W panels connected to a 1000W Pure Sine Wave Inverter.

If power goes out in my house next door in the middle of a party, and I use a long extension cord to connect a couple of music receivers to the 1000W inverter, how long can they power two large speakers each, with what's stored in a 12V 100AH LiFePO4 Lithium Battery?

If 1 receiver and 2 speakers are used, is that exactly one half of the estimate for 2 receivers and 4 speakers?
How much is the equation affected the louder the music?

Separately how is the equation affected if 20" fan or multiple 20" fans are added if it's summer... Thank you.

 

1 hour.

 

Really I initially just wondered about the ballpark. But your answer about 1 hour struck me a bit low.

So all right, I placed a splitter on a Kill a Watt P4460 gadget, reset it, connected two receivers and measured them powering two large speakers each, for 30 minutes.

0.08 kWh in 30 minutes.

So times two = 0.16 kWh in one hour.
=============================

So now to get the answer, how many of these kWh units can Kill a Watt gadget display, after going through all the juice from a 12V 100AH LiFePO4 Lithium Battery?

 

You have to determine this by running an actual test, there are too many unknowns for any meaningful calculation.

The rating of your "100 AH LiFePO4 " battery for example- marketing hype might make this an enthusiastic number by 50% - easily.
Inverters are never 100% efficient - without knowing this number you are only guessing

 

Of course. But we now have an actual measurement. I mean at the very least the battery will not even be full, so when full - it will last significantly longer, but what does the measurement tell you about the range, if the inverter is not too bad:
GoWISE Power 1000W Pure Sine Wave.

And the battery has been opened up elsewhere and tested and found to hold after time has passed, so not expensive, but tested WEIZE 12V 100AH LiFePO4 Lithium Battery.

Does my measurement not give you enough info to post an educated guess on the range?

 

connected two receivers and measured them powering two large speakers each,

Was that at a typical listening level for the music you want to listen to?
The music loudness will have a significant effect on the power used.

 

Understood. Let's rephrase the question.
Let's take a 12V 100AH LiFePO4 Lithium Battery made up of components that are decent. Just for the sake of this question.

What is Kill a Watt gadget above kWh reading by the time said decent battery is depleted from being full.
Volume level is party, so volume level is fairly loud, not normal, not low. Loud.

Of course so many factors influence this but educated guess on narrowed range?

Kill a Watt read 0.08 kWh after 30 minutes of loud listening.

 

Those power levels onthe meter are typical for high peak but low average sound levels in a residential setting. Crank up the bass levels to see more power used.

100Wh per receiver and 100Wh per 20" fan energy usage. (estimates include DC to AC conversion losses)

1200Wh for the battery energy storage (LiFePO4 Lithium is great for this but pricey). Your four panels might give you 200W average for 5 hours on a typical day sunny. 1000Wh on a good day so that's really a usage pattern of about 500Wh with some reserve for bad days.

I would buy a small 2000W generator instead.

 

We're switching topics, but your switched topic does interest me very much.

This whole thing started because of a sale on a 400 Watt 12 Volt Solar Panel Bundle Kit for $254.
I added a decent Inverter and a decent 12V 100AH LiFePO4 Lithium Battery to have everything I need for this experiment with TOTAL out of pocket cost of $654.01.

So this is an experiment for me to see how many years it would take Solar to pay off because my barn is on a separate meter from my house... House Solar I will wait a few years at the very least, to see if Solar tech advances make it finally worth it.

So this is about 2023 present day lower cost of Solar eqpmt sale prices addressing the Barn power usage monthly bills below.

I now figure I would have to get more panels but I thought what a heck, maybe learn a little about Solar Power with the experiment.

 

1200Wh
x 0.8 inverter efficiency =
960Wh
divide by
160W =
6 hours

 

Thanks for that.
I have been told that an average 400W solar panel getting 4.5 peak sun hours per day can produce around 1.8 kWh of electricity per day and 54 kWh of electricity per month.

So does that mean that if I plug it into the power company's system the meter rolls backwards?
The table above shows barn power costs would then be reduced, sometimes by 50%, sometimes by 100% on average in a given month... Is this reality? Or am I about to find out the hard way no.

 

Thanks for that.
I have been told that an average 400W solar panel getting 4.5 peak sun hours per day can produce around 1.8 kWh of electricity per day and 54 kWh of electricity per month.

So does that mean that if I plug it into the power company's system the meter rolls backwards?
The table above shows barn power costs would then be reduced, sometimes by 50%, sometimes by 100% on average in a given month... Is this reality? Or am I about to find out the hard way no.

Those are fairy land numbers. Your 400W is actually 300W unless you have perfect conditions and tracking. I've been doing diy off-grid for decades. IMO you will need much higher power and southern desert conditions to be practical.
https://forum.allaboutcircuits.com/...rge-controller-datalogger.194146/post-1825897

 

Thanks! I am on the opposite side of the spectrum from you, don't know much [yet].
As you can see my barn is only consuming less than 100 kWh per month, in 2023 averaging only 76 kWh per month.

Surely I don't need all that much, would a system twice the number of panels, so 800W instead of 400W be able to handle that?

And most importantly, if I produce 50% of what I consume, and pump it back to the power company, does that mean my bills are 50% less, is that how things work?

 

It's all about pay-back short and long term. Do it because you want to build something for fun and/or learning and/or for emergency power. Don't even try to justify the numbers for something that small. To 'sell' back to grid means city/utility approved electrical plans, on-grid approved equipment line inverters and a net-metering agreement with the utility.

https://www.cnet.com/home/energy-an...ou-can-get-paid-for-solar-power-you-generate/

It's not really true that feeding solar power into the grid will amount to a major payday each month, but if you educate yourself in advance, it might pay for your investment in going solar over the long term. We'll explain them all below so you can better understand how they help you save more and recouple the cost of your solar panels faster.

 

Thanks for that.
I have been told that an average 400W solar panel getting 4.5 peak sun hours per day can produce around 1.8 kWh of electricity per day and 54 kWh of electricity per month.

So does that mean that if I plug it into the power company's system the meter rolls backwards?
The table above shows barn power costs would then be reduced, sometimes by 50%, sometimes by 100% on average in a given month... Is this reality? Or am I about to find out the hard way no.

What are the chances that you are going to get 4.5 hours of peak sunlight day after day after day?

There are going to be cloudy days. There are going to be rainy and snowy days. You aren't going to get as much light in winter as in summer.

Unless you have a tracking system, you aren't going to have the panels pointed directly at the sun, either throughout the course of the day or over the course of a year. Depending on the typical climate where you are, you might easily average well under half of that ideal estimate. So let's call it an average of 25 kWh/mo.

As far as getting money back from the power company, that opens up a whole other can of worms and expenses. Your system might be fine for powering your barn from solar, but the electrical service from the utility company has to be completely disconnected from it. You get to power the barn from the utility company, or your solar system. One or the other. If you want to switch back and forth, you will need a physical switch that ensures that both can never be connected at the same time.

If you want to have them connected at the same time so that you can do net-metering (i.e., have both connected at the same time and use the energy from your panels first and the utility second, and sell back any excess to the utility company), then you have to have a suitable grid-tie device that ensures that your solar system's AC output is properly matched in voltage and phase with the utility company. That's going to significantly increase your cost. The minimum requirements for such an inverter depend on the jurisdiction you are in. But, assuming you do all of that, then (again, local laws and utility company policies will dictate) you definitely can get paid (usually as a bill credit) for months in which you produce more energy than you used.

Another thing to keep in mind is that (unless local laws require differently), the utility is not going to buy energy from you at the same rate they sell it to you -- and, let's be fair, it would be completely unreasonable to expect them to. To them, you are a vendor of electricity and they are buying a product from you that they then need to turn around and sell to their customers. They have all kinds of costs that they have to cover in addition to their direct cost of buying electricity. Even if they are required to buy excess energy from you at the same rate they sell it to you at, that is not going to include the fixed costs (i.e., in most places, if you use zero power in some month, you still get a bill for having the power available for your use).

You need to talk to YOUR utility company and find out what the requirements and billing policies are where you live. This information is probably easily accessible from their website and, if not, a phone call will probably get you the information, either over the phone or by them sending you a packet in the mail.

My rough guess is that you are probably looking at, perhaps, about $0.15/kWh payback for perhaps 25 kWh/mo, making it about $3.75/mo. Take your $654 and add something like $350 for a suitable grid-tie device and you are right about in the $1000 range, making your payoff somewhere around 266 years -- and, of course, your batteries will need to be replaced several times over that period and so will your panels.

 

266 years? Wow. So... far off anywhere near reasonable...
Thank you for posting. All my equipment is unopened and has just gone up in price because the sale is over.

I am in Kansas City metro.

So if my barn meter says I use 100 kWh or less per month, how many more panels is more realistic to get completely off the grid that feeds me only about 100 kWh on average per month?

 

266 years? Wow. So... far off anywhere near reasonable...
Thank you for posting. All my equipment is unopened and has just gone up in price because the sale is over.

I am in Kansas City metro.

So if my barn meter says I use 100 kWh or less per month, how many more panels is more realistic to get completely off the grid that feeds me only about 100 kWh on average per month?

Notice the discrepancy in your numbers above -- "100 kWh or less per month" is very, very different than "100 kW on average per month". The data you provided earlier has many months that are well over 100 kWh and even has one as high as 744 kWh. That may well have been an outlier, but it happened. What would the plan be for when it happens again a few years from now?

"Completely off the grid" is a pretty high bar. That means that you have to have enough storage capacity to power your barn during the middle of winter when you happen to have several weeks with little or no direct sunlight.

You can't use averages for this. You need real data that is really relevant to your situation.

You also have to establish thresholds and contingencies.

If you are willing to have a manual switch that you can switch back over to the grid if the solar generation can't keep up for long enough, or if you are willing to put in a generator that can carry your load during those times, then you can come a lot closer to being able to put in a solar system that is sized a lot closer to your average needs. If your back up is the utility company, then you still have to pay the monthly base connection fee. In either case, you can use the back-up source to charge the batteries. This approach allows you to keep things a lot simpler because you don't need a grid-tie device. It does introduce some inefficiency because you are going from an AC source to DC to the batteries to the inverter and back to AC.

But if it's going to be pure solar, then you are going to need a lot of excess capacity.

 

I have 23 400W panels. Over 20 months of operation they have produced 600 to 700 KWh each. So average is about 32 KWh per month per panel.

 

I have 23 400W panels. Over 20 months of operation they have produced 600 to 700 KWh each. So average is about 32 KWh per month per panel.

So a W.A.G. at 25 kWh/mo wasn't too bad.

Where is that located? What is the typical climate there as far as how many bright, sunny days versus how many cloudy/worse days?

Were the remaining four months shy of two years during the summer or winter?

Are your panels statically aimed, or do they do any kind of tracking?

 

266 years? Wow. So... far off anywhere near reasonable...
Thank you for posting. All my equipment is unopened and has just gone up in price because the sale is over.

I am in Kansas City metro.

So if my barn meter says I use 100 kWh or less per month, how many more panels is more realistic to get completely off the grid that feeds me only about 100 kWh on average per month?

I just looked up some info for you.
https://www.evergy.com/-/media/docu...vate-solar/solar-customer-interest-evergy.pdf