# Solar panel question (post EMP battery charging)



## A J (Oct 16, 2014)

Hi all,

One of the items on my 'prep' list is a means of charging my deep cycle batteries if fuel/generator is not available. For instance a serious EMP event, long term fuel shortage etc.

I have a few very good deep cycle batteries (group 30 AGM) that I keep charged for use with the 12v sump pump, Ham Radio emergency power and inverter for other small AC loads (CPAP).

During a power outage, we'll run one of the generators a few hours/day to keep the freezers cold and at the same time, charge up the batteries.

But in a situation where no fuel was available, I'd need 12v to keep the sump pumped out during certain times of the year (spring) and also need 12v for the inverter/CPAP.

To this end, I'm wondering if a single 200-250 Watt panel and an MPPT charge controller, both stored in faraday cages would be worth the effort?

I've never been around PVs at all.

In my reading, it seems that a 225 Watt panel in direct sunlight should provide about 15amps of charge into a 12v battery. Which would probably keep up with our usage.

1) What am I missing?
2) Am I close in my understanding of the sizing?
3) I've read that a panel doesn't 'age' when not in use, so it would have an infinite shelf life.


Thanks,
AJ


----------



## pheniox17 (Dec 12, 2013)

Sizing sounds good, but you need to know daylight times, and allow a % of tolerance 

Also at peek it produces 15A so in 1 hour you will charge a battery with 15ah of power (roughly) 

There is more, but keep it simple, get a multimeter for your kit also and learn how to use it (go analog, no need for a battery but a 9v battery in one lasts for years, the batt is for resistance testing)


----------



## A J (Oct 16, 2014)

pheniox17 said:


> Sizing sounds good, but you need to know daylight times, and allow a % of tolerance
> 
> Also at peek it produces 15A so in 1 hour you will charge a battery with 15ah of power (roughly)
> 
> There is more, but keep it simple, get a multimeter for your kit also and learn how to use it (go analog, no need for a battery but a 9v battery in one lasts for years, the batt is for resistance testing)


Thanks, yep understand that is 15ah. I figure on the low end, we get 50% sun for at least 5 hours/day. In the spring, we get more hours of sun (this is when the sump uses the power). Also one of the big batteries will last several days during the high run times, so with the multiple batteries I should be able to last past real wet times of low sun, then get caught up later.
For example, this time of year the sump almost never runs. So it's kind of nice that during the shortest days of the years, I'll need less power to keep the basement dry.

As far as multi-meters, good to go there (have real cheap ones stored in foil). my nice one is a fluke that I use for putzing around with radios/circuits etc.

I know that a single 250 would likely keep up with my usage but it will be close. 
2 would definitely make it easier, I'll have to keep my eyes open for a good deal on a pair!
After all, 2 is 1 and 1 is none.

Thanks a ton,
Don


----------



## pheniox17 (Dec 12, 2013)

Yeah just try and match charging to use... Its hard, let's say your batteries are 100 amp hour capacity to charge 1 in ideal conditions with a 15amp panel (so your getting 15amps output from the solar setup, all day) it will take just under 8 hours for a full charge, when not ideal that time takes longer (so 50% output will take 16 hours, if your getting 10 hours sunlight a day, that's 2 days from flat) that's what's the multimeter is for, you need to track solar output to battery capacity, and solar panels degrade over time, that was the main point I was getting at...

So in theory, grab your storage numbers (amp hour) and do the maths from there, then give yourself a good tolerance/leeway (a case of you can't have too much)


----------



## budgetprepp-n (Apr 7, 2013)

Red neck, answer :
Think of your solar panels as a battery charger, If the panels are to small they will still charge
up the batteries but it will take longer than if you had a bigger battery charger (more panels)


----------



## thepeartree (Aug 25, 2014)

To my mind, you want maybe 4 batteries in parallel, just to be safe. And solar panels do age (don't we all?). And batteries age. I would plan on at least two panels. Of course you need a charge controller. I would also get something larger than a 250 watt inverter. You may want to power some lights. Or some 5v device chargers. Or an ice cream machine. You should be able to pick up a 6 or 700 watt unit for under $50.


----------

