Looking for Emergency Portable Solar Solution

BB.

Re: Looking for Emergency Portable Solar Solution

Basically, it is very difficult to parallel a bunch of batteries and have them properly share current while charging and discharging.

Batteries have very low resistance (on the order of 0.010 ohms or so... About the same as some of the interconnect wiring. When you place the batteries in parallel, any little difference (dirty connection, extra long piece of wire, a warmer battery vs a colder battery in the same bank, etc.) will cause the batteries not to share the current.

With improperly wired battery battery bank, the batteries will cycle/age differently. See this website for some options on paralleling batteries:

www.smartgauge.co.uk/batt_con.html

Also, if you have flooded cell batteries, each parallel string is just that many more cells to check for electrolyte levels and more connections to keep clean.

And, if you have a weak cell (open or shorted), it can damage other strings in the battery bank too (a shorted cell can discharge the entire bank, cause the local string to over charge the other batteries; an open cell will take that string out of service, etc.).

If you do parallel a battery bank, I recommend 2-3 strings maximum in parallel. There are people that have happily paralleled more strings--but I don't think it is the best design.

Also, when you parallel more than two strings of batteries, you should have a high current fuse or breaker at each connection to reduce the chance of a short circuit/wiring fire.

Also, if you parallel battery banks, you should pick up a DC Current Clamp meter so you can monitor the current in each string during charging/discharging to make sure everything is reasonably balanced (here is relatively inexpensive and functional DC current clamp meter).

They are making larger AH capacity cells in 4 volt and 2 volt models now... This allows single strings in higher AH capacity and let you have a cell that is still something one or two people can move around without a crane or forklift.

Golf Cart Batteries are not (usually) the best performing/longest life types--but they are cheap and easy to find. Typically recommended for a first timer to play with and not feel too bad if the batteries are damaged from deficit charging, accidental power drain, over charging, etc. (been there, done that). Sometimes we joke around and call them "Training Batteries".

After 3-5 years of use, you will have a better idea of what your next system/battery bank should be without having spent a bunch of money learning.

-Bill

BB.

Re: Looking for Emergency Portable Solar Solution

Forgot to add, yes, you can find companies that make prewired systems (Midnite Solar is a major brand) and even retailers like Northern Arizona Wind & Sun (our host) will build custom pre-tested systems... I believe--None of us moderators here are connected with NAWS except as volunteer moderators here.

But, before you go there, you really need to define your power needs.

It is very difficult to, cost effectively, start out with a "small" off-grid system and "grow" it larger over time. Major increases in power (more than 2x larger) are usually best done with new battery bank and inverters (higher bank voltage).

And adding solar panels a few years down the road can be a bit painful too (matching Vmp/Imp of new panels into your existing array).

-Bill