Looking for Battery & Solar sizing spreadsheet

Auditing DC loads, like lights, 12V radio and DC circuit of propane fridge? They account for less than 40 AH a day.

Your converter recharges the batteries via the shore power cord, right?

So what is extracted from the batteries is replaced by the converter.

If an adapter is used to allow the shore power cord to be plugged into the Kill-A-Watt meter then the meter can be plugged into a 15-amp wall socket.

Flip off ALL the AC breakers in the rig except for the dedicated AC breaker to the converter.

NOTHING AC should be switched on including wall sockets, refrigerator, water heater, etc. The refrigerator must be working, set to gas.

Two or three days @ 24/hrs day should accumulate "X" number of kWh on the meter.

It is important to live in the rig like you normally do and not go bulimic all of a sudden. Lights, television, fans, porch light. Everything used like it was SUMMER vacation. Some thought should be given to the amount of time that is normal for dining room, kitchen lights and fan, bathroom including fan, and bedroom lights including Fantastic roof fan. Don't Scrimp or your reading will not be worth ten cents.

Shut off all the loads. Shut down the converter after -exactly- 48 hours

Read the kWh accumulated on the Kill-A-Watt meter. Write it down

Calculator time...

Divide total kWh accumulated then divide by 12.5

This will give you approximate amp hours energy used for the 48 hours

Divide the amp hour figure by a factor of 2

This is a nominal average of ampere hours used daily.

Your battery bank must not be less than TWICE the number of amp hours accumulated for 24 hours. Actually 2.5X minimum would be safer

Your solar requirement will be roughly 5-Times or 500% of your daily amp hour accumulation.

This estimate needs more caveats that the RV.Net server can hold. But it is a better-than-nothing guesstimate that beats the tar out of spreadsheet pure guesswork.

If you plan on using an inverter, get it now and add it's hunger from start to finish with the Kill-A-Watt.

Be prepared to add panels and batteries when reality arrives.

smkettner wrote:

johnm1 wrote:
I'm trying to figure out how much battery I "need" and then size the solar to recharge them.

What do you have now and how does it work for you?
ALL solar or generator backup?

Here goes the spreadsheet. Why calculating when you can ask at Rv.net :)...

I agree, not enough input data provided. Generator for high-current loads changes the picture. N8GS spreadsheet gives a good ballpark figure for all-solar system.

Today panels are cheap, and the cheapest per watt are the biggest ones, over 220W each. The cost of controller jumps abruptly when you cross over 300-400W because at this point you need more expensive MPPT controller. Then it's pretty much proportional to panel wattage.

Get as much panel wattage as you can, unless you are a minimalist and can live without MW and other high-current loads (and then you could stay within 300W range and low-cost PWM controller).

It's a brand new 30' travel trailer toy hauler (no slides, all LED lights) with the wimpy dealer installed Interstate group 24 so I don't know about THIS RV. However, in the past the group 24 wasn't nearly enough. We've always had LED lights, never use AC powered things and use battery powered lanterns inside at night to conserve the battery.

Right now, I have zero solar but I have 2 x 2k Champion inverter gennys which I'd rather not bring anymore.

I want to start using solar since we dry camp way more, and for longer, than we used to. I want to start with batteries and a Victron BVM-702 battery monitor. But I want to size the battery area to fit what I think I need and not what I might need. Heck, I could put (6 or 8) 6v batts up on the tongue, but do I need that? I highly doubt it.

I sort of/kind of understand what Mex said (though I think I would have worded it a little differently) about monitoring usage but I need to start some where even before that stage. It's called planning.

Thanks all for the help so far.

two possible ways.

1. If the converter is modern and can operate without the battery bank, plug the converter into the kill-a-watt and turn the battery disconnect switch to the OFF position. Turn on all the loads you wish to power. Measure for 12 or 24 hours.

2. Fully charge the existing battery bank, then plug the converter into the kill-a-watt unit. Turn on all the loads you wish to power. Measure for 24 hours.

johnm1 wrote:
pianotuner - how do you use a kill-a-watt meter on 12vdc "stuff"? I'm not worried about AC things.

johnm1 wrote:
pianotuner - how do you use a kill-a-watt meter on 12vdc "stuff"? I'm not worried about AC things.

With a fully charged battery, put the kill-a-watt between your rv and your shore power outlet. Switch the meter to watts mode. Watts are watts no matter ac or dc.

Roughly:
Watts to amps in AC divide by 120
Watts to amps in DC divide by 12

johnm1 wrote:
I'm trying to figure out how much battery I "need" and then size the solar to recharge them.

What do you have now and how does it work for you?
ALL solar or generator backup?

Gale has updated the spreadsheet--so use the link below.

Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT.

Here is a link to the rather special spreadsheet that N8GS has created to help size solar battery charging systems!

Solar spreadsheet by N8GS

johnm1 wrote:
Hey all,

I had a link to one that I liked but can't find it now and apparently I'm not using the correct search terms either because nothing turns up in a search.

I'm trying to figure out how much battery I "need" and then size the solar to recharge them.

Thanks,

scrubjaysnest wrote:
Try this one Solar sizing by N8GS.
It is in xls format.

This is the one I ws looking for - thx!!

pianotuner - how do you use a kill-a-watt meter on 12vdc "stuff"? I'm not worried about AC things.