Newbie from Texas

[hiteck]

Hello from East Texas. I purchased a Harbor Freight 45 watt solar kit a while back and have learned enough to know I need to learn a lot more. I quickly found that just buying a kit and hooking up a 12v battery isn't really enough to do anything with. I'm here to try and learn how to do basic solar calculations for pv arrays, battery banks, etc...

The charge controller like the rest of the kit is pretty basic so I've just ordered a Windy Nation P30L PWM charge controller. I'm hoping it will help me to see what's really going on when playing with this stuff. I also plan to pick up a Kill-a-Watt meter so that I can determine accurately what certain devices/appliances would require to run them.

I've found a guy locally with some 45 watt thin film solar panels from Solarex (manu 1998) for $25 each. I may pick some of these up to play with as well.

[Sunking]

Hello from East Texas. I purchased a Harbor Freight 45 watt solar kit

I am so sorry you did not come here first. The box the kit came in is worth more than the kit.

First and most important, easiest and fastest lesson you need to learn right now and is free; Money is no object when it comes to off-grid solar. Sky is the limit. You want to go off-grid? Then you want to pay about 10 times more for electricity the rest of your life. It is that simple. In Texas with dirt cheap electric rates maybe a little bit more than that with 8-cents per Kwh electric rates. See that was quick, painless and best of all FREE. Didn't cost you one cent and took 5 to 10 seconds to learn and be an expert.

Now you can start learning the calculations and math by reading this stickie. Once you have had a few days to figure it out, then come back and ask questions.

[hiteck]

Thanks for the free/fast lesson and link Sunking. I'm not really looking to go off-grid. I just want to setup a small system for temporary backup when the power goes out and/or possibly add to a small enclose trailer I use for camping. When I go off-grid I don't need electricity

[Sunking]

Thanks for the free/fast lesson and link Sunking. I'm not really looking to go off-grid. I just want to setup a small system for temporary backup when the power goes out and/or possibly add to a small enclose trailer I use for camping. When I go off-grid I don't need electricity

Small learning stuff is fine. Going of grid is just silly if you have commercial power and that does double in TX where power is cheap.

I just wanted you to tap the breaks before you did anything stupid and start buying stuff. You got off cheap when you bought Harbor Fight junk. Just think if you jumped in and spent $5000 only to find out it won't work. $5000 gets you 15 cents of electricity per day, and $2500 of that is in batteries you replace every 5 years or so.

Now you are off to a good start. Former Texan here, so I wouldn't let you dive in head first without telling you it is one feet deep and a rock bottom.

[hiteck]

I wouldn't let you dive in head first without telling you it is one feet deep and a rock bottom.

And I appreciate it

[hiteck]

I read the stickie and have continued reading and wanted to clarify what I think I've learned so far.

I realize my actual results will be different than the math below, but it gives me a starting point in understanding what's going on.


My 3 panels claim to be 15 watts a piece for a total of 45 watts.

Using Watts = Volts X Amps that would be
15watts/12 volts = 1.25 Amps per panel or 3.75 amps total for 3 panels

If the average peak sun hours in my area is 4.5 hours then (without factoring in for any inefficiency)
3.75 amps X 4.5 hours = 16.875 amp hours a day

Or am I way off base?

Thanks in advance!

[Sunking]

I read the stickie and have continued reading and wanted to clarify what I think I've learned so far.

I realize my actual results will be different than the math below, but it gives me a starting point in understanding what's going on.


My 3 panels claim to be 15 watts a piece for a total of 45 watts.

Using Watts = Volts X Amps that would be
15watts/12 volts = 1.25 Amps per panel or 3.75 amps total for 3 panels

If the average peak sun hours in my area is 4.5 hours then (without factoring in for any inefficiency)
3.75 amps X 4.5 hours = 16.875 amp hours a day

Or am I way off base?

No just the wrong Ball Park. Forget about amp hours does not mean anything with out a voltage. Amp hours is the very last thing you worry about once you know capacity and system voltages to be used.

All you want to know is Watt Hours. In this case 45 watts x 4.5 Sun Hours = 202 watt hours or .202 Kwh. Just understand with that system efficiency is less than 50% so in practice less than 100 watt hours. A beer fart as more energy than that.

[hiteck]

No just the wrong Ball Park. Forget about amp hours does not mean anything with out a voltage. Amp hours is the very last thing you worry about once you know capacity and system voltages to be used.

All you want to know is Watt Hours. In this case 45 watts x 4.5 Sun Hours = 202 watt hours or .202 Kwh. Just understand with that system efficiency is less than 50% so in practice less than 100 watt hours. A beer fart as more energy than that.

I dont' have a Kwh target so I guess I'm pretty much going about this backwards. I though that amp hours would determine the size of the battery bank that the panels would support. Not considering efficeincy of course.

[Sunking]

I dont' have a Kwh target so I guess I'm pretty much going about this backwards. I though that amp hours would determine the size of the battery bank that the panels would support. Not considering efficeincy of course.

Battery amp hours are the last step in the process. For example if you use 1 Kwh per day, you need a 5 Kwh battery. So what Amp Hour rating is a 5 Kwh battery?

You cannot answer the question because you do not have enough information. That missing piece of info is the nominal battery voltage. If we know that, then we can get the Amp Hours. For example:

5000 wh / 12 volts = 416 AH
5000 wh / 24 volts = 208 AH
5000 wh / 48 volts = 204 AH

5th grade math.

[hiteck]

Battery amp hours are the last step in the process. For example if you use 1 Kwh per day, you need a 5 Kwh battery. So what Amp Hour rating is a 5 Kwh battery?

You cannot answer the question because you do not have enough information. That missing piece of info is the nominal battery voltage. If we know that, then we can get the Amp Hours. For example:

5000 wh / 12 volts = 416 AH
5000 wh / 24 volts = 208 AH
5000 wh / 48 volts = 204 AH

5th grade math.

OK i guess I made an assumption that I didn't obviously share. I assumed for no reason other than 12 volt devices are readily available that I'd be playing with 12 volts. So that's why I used 12 in the Watts / Volts=Amps formula.

I appreciate the additional info and your patience.

[Living Large]

Just understand with that system efficiency is less than 50% so in practice less than 100 watt hours. A beer fart as more energy than that.

As an academic matter, I believe a beer fart would contain less energy than 100 wH, not more.

[hiteck]

As an academic matter, I believe a beer fart would contain less energy than 100 wH, not more.

Which one of you will actually put it to the test? I found you a video that might help.

[Living Large]

Which one of you will actually put it to the test? I found you a video that might help.

One source I found indicates that regular, not beer, contains about 147 J. At .00027778 wH per Joule, that is about 0.04 wH. Even with a 100% margin of error due to estimation, this is still three orders of magnitude less than 100 wH.

ps That video looks a bit odd - especially two screws driven into a metal lid and used as contacts.

[Sunking]

ps That video looks a bit odd - especially two screws driven into a metal lid and used as contacts.

As PT Barnum says: There is a Sucker Born Every Minute. Most people would never question a Dead Bolt Fault thus shortin gout any voltage to run a motor. Of course the video is fake.

[hiteck]

As PT Barnum says: There is a Sucker Born Every Minute. Most people would never question a Dead Bolt Fault thus shortin gout any voltage to run a motor. Of course the video is fake.

but it was funny