Keith Birchfield's posts

If I have:
(1) 170watt PV running at a net peak of 4 hours per day.
how many 105amp hour batteries can I charge ... nothing else considered.

My attempt at the math leads me to believe:
170watts*4hours=680watts generated
pushed in to 12volts=57amp hours

meaning, I can only charge .57 105ah batteries per 170watt PV running .680kwh avg per day.

Is this correct?

And If so, does that mean:
a need to maintain a relationship of
(2) 170watt panels per (1) 105amphr battery?

Thanks in advance

edited to say:
meaning, I can only charge .57 105ah batteries per 170watt PV running .680kwh avg per day.

contains a math/typo

it should have said something like:

meaning, I can only charge 57ah of 105ah batteries per 170watt PV running .680kwh avg per day.

which gives me 57/105 = .54 batteries per day.

Hey Ryan,
Actually, the batteries I'm using, do have two sets of terminals.
See:
http://store.altenergystore.com/Batteries/Batteries-Sealed-Agm/MK-8A31-AGM-105-Ah-20-Hr-AGM-Battery/p769/

And, when I test my battery, with a meter, I see what appears to be the battery voltage ... not the controller's input.  At least I think that is what I'm seeing. It definitely goes down with consumption!

James,
Thanks ... but bummer.

I'm sure that this may sound a bit silly, but ....

Why couldn't you do roughly this:
PV
-> Charge Controller
-> battery ( with primary load )
-> *Charge Controller*
-> battery or inverter?
-> secondary load

Where the second charge controller makes sure the power flows one way to the secondary load. And is ideally proceeded by a circuit that only cuts in at a set voltage level or time.

Hi Ryan,

I don't have an answer to your question, but i wanted to chime in and say that I'm looking for the same kind of solution.

But, in my case, I want the extra energy diverted to a grid tie inverter.

I love your idea of the fountain pump though, thats a great way to not let the energy go to waste!

Just in case anyone is interested, and for the archives and later searching ...

With the help of Chris from Alt-E ... I ended up starting with  the following minimal, but ready to grow set-up:

(1) Evergreen ES170 RL/SL 170W 18V Solar Panel
(1) Xantrex XW Solar Charge Controller MPPT 865-1030
(1) MK 8A31 AGM 105 Ah (20 Hr) AGM Battery
(1) Two Seas Uni-Tp/08Ll Doubletier Top/Pole-90" Sppt

and I already had a Xantrex Prosine 1000

My connections are roughly this:
PV -> 15amp breaker -> Charge Controller
Charge Controller -> 63amp breaker -> Battery
Battery -> Inverter
Inverter -> Isolated circuit

I have all of the above connected and running in a short term install.

But I have not yet mounted the PV ... its setup in an un-optimized temporary ground mount.
And I do not yet have the battery wired in a proper box ... just jumpered.

The plan for this project is to complete the install, and then follow up with adding 3 more 170w panels, and 2 ( or 3) more batteries.

As is, I'm seeing about 140-150 watts coming in to the controller during peak hours, and about .75 kwh per day ... definitely need to optimize and grow this!

I'm still learning ... the hands-on is helping ... but I'll most likely be asking the group for more advice in other threads.

Anyways, thanks to all for the help! Great Stuff!

Thomas,

Wow, good stuff. Still learning, and I so much do appreciate the help you guys are giving!

As an attempt to convert to a 12volt system to support:
600 watts for 2 hours a day for 2 days

... and with hopes of easy expansion of batteries and panels in the near future.


I've amended my list to the following:

1 - Xantrex Cm/R-50 Digitalmeter-C12/35/40/60-50'         
1 - Xantrex C35 35A, 12/24V PWM Charge Controller       
2 - Universal Ub121000 12V, 100Ah (20Hr) Sealed Agm    
2 - Evergreen ES170 RL/SL, 170W, 18V Solar Module


600 watts / 4 hours of charge time per day = 150 watt pv needed
600 watts / 2 hours a day
2*600 = 1200 watt hours / 12 volts = 100 amp-hours battery needed

times 2 days

this leads to 2 170w 18v Panels
and 2 100ah batteries

Did I get it right?

This is for a 'boot-strap' system. A proof of concept, powering a shed that currently has next to nothing running.

... But, I want it to end up an emergency back up circuit, capable of powering my 'home office' at a later date, and after upgrades.

In the interim, I also want to dump all gas powered yard tools as part of this project, and switch to electric/cordless only. ... I do realize, that I may need to size up to accommodate the yet to be purchased electric tools. ( sure would love an electric riding mower/tractor ! )

anyways, feedback on my new assumptions would be greatly appreciated!

Dennis,

Ouch. Good advice to be certain!

I had incorrectly assumed the 12/24 stood for 12 *AND* 24v capability.

My inverter is the 12volt model. :-( Bummer.

This pushes my batteries to 12 volt.

I guess its too much to hope for, that the charge controller can take 24v from the panel, and put out 12 volt for the battery?

Dennis,

Thank you for the excellent reply. It helped me quite a bit.
24 volts in the battery bank it is! :-)

Looks like I'm moving forward with my list then:
1 - Xantrex Cm/R-50 Digitalmeter-C12/35/40/60-50\'
1 - Xantrex C35 35A, 12/24V PWM Charge Controller
2 - Universal Ub121000 12V, 100Ah (20Hr) Sealed Agm
1 -Sharp NT-180U1 180W 24V Solar Panel
( already have xantrex prosine 1000 )

And hope to follow up with a few more batteries and another panel at a later date. And then at yet another later date, follow up with a parallel grid tie for the surplus ...

Anyways, I've asked the guys in the aes support for the wires and other misc items ... as soon as they reply, then this project will finally get started!

Thanks to all for the feedback.
Keith

Dennis,
Thanks for the reply. I think you are warning me that in order to charge my 12 volt batteries ... I need to have 'more than' 12 volt supply. So, I've either accidentally 'got it right', or I may have something mismatched.

I'm still trying to learn here so someone help me out.

Is it going to be ok to do the following (or should I do it a little different?)
24 volt PV ->
12/24 Charge Controller ->
12 volt Battery ->
12/24 Inverter

What I'm worried about most ... now ... is that the C35/40 will have to run in 12 volt mode in order to put 12 volts out ... meaning that I might be way under-utilizing the PV ?

Or is it instead, that I'm more likely to get my 12 volts from the 24v PV, due to not running optimum most of the time?

John,
Thanks for the suggestion. I'm guessing you have seen evidence that a simple pole mount 'is good enough' to get started?

I've suspected that, but wasn't certain. I've even seen a little bit of evidence in different posts and blogs ... that the trackers might be prone to needing maintenance ... at least more so than a standard pole mount.

My installation location is far far from perfect. Lots of tress all around, and the roof is 'off limits' per the boss (wife). So I'm stuck with a pole mount near my eastern tree line. This leaves me with 'good sun' from about noon till sundown minus an hour or two behind western tree line. This led me to believe that a tracker might help?

Am I correct in the assumption that evening sun is better than morning sun? Leading me to an eastern install to see the western sky better. ( south is reasonably clear )

Thanks Dennis, I appreciate the comment!

I'm now considering the:
Sharp NT-180U1 180W 24V Solar Panel
Which gets me half way to your suggestion ... and still works with my inverter, which is 12v/24v

Anyways, I've also switched my target (1st battery) to:
Universal Ub121000 12V, 100Ah (20Hr) Sealed Agm
It appears much cheaper with similar output. I hope there is no quality concern.

Am I fooling myself in believing I can get by with the single battery?
If I understand correctly, I think the single 100ah battery will give me about a half an hour run time on about 800w peak load,

I'm still trying to understand this, so please correct me wherever I stray ...

And since I expect the load to be very light overnight ... that this may allow me to squeak by.
The 100w flood lights (6) will only run for maybe ten seconds each ... and hopefully only about a dozen times in the night time.
The sprinkler system is offline until spring, so there is no real 'other' load on the circuit at the moment.
So, If I follow up with another battery or two in the spring, I should be good to go?

Hello all,

And please forgive my newbie terminology and question, but I'm hoping someone can do two things.

One let me know if what I'm getting ready to do is a bad idea in anyway

And two, offer alternative suggestions.

What am I trying to do?

I'm trying to power-up a standalone circuit via Solar with battery backup.

The circuit currently has very little on it:
A shed with light
3 flood lights on motion detect ( in test mode ... only run a few seconds per trigger ... to scare deer away)
An in-ground sprinkler system
and the misc. connection.

This circuit is not connected to the house in anyway right now ( except for a very temporary patch cable, that I want to remove as soon as possible )

I currently have a prosine 1000, but thats it.

I'm considering purchasing the following as additional purchases to get the project up on its first legs:
Kyocera KC125G 125W 12V Solar Panel 
Concorde Pvx-1040T 12V, 104Ah (24Hr) Sealed Agm       
Xantrex C35 35A, 12/24V PWM Charge Controller
Zomeworks Utr-020 Universal Solar Tracker


Long term goals is to run two additional circuits
The first being a well pump
The second being living room with laptops, small wireless network and entertainment center

But for now, just this 'backyard' circuit and 'proof of concept project'

Where I hope to provide near the full capacity of the prosine to that single isolated circuit.