Will a 100w panel charge a 48v battery?

Yes, you are correct... Adding a second (matching) solar panel in series would give you "24 volts" for charging your 24 volts battery bank (technically Vmp~35-36 volts).

The big issue is your expectations on the amount of power you can expect from a couple of solar panels and a pair of 12 volt batteries.

For a "reliable" off grid solar system with a 24 volt @ 2kWatt AC inverter. Using "typical/optimum" rules of thumb would give you a system like this:

• 2,000 Watt inverter (4,000 Watts surge)
• 400 AH @ 24 volt battery bank (for example: 4x 6 volt @ 200 AH golf cart batteries in series with 2x parallel strings for 8 G.C. flooded cell lead acid batteries in total)

You can run 5% to 13% rate of charge for such a battery bank. Taking 10% rate of charge (full off grid, daily usage):

• 400 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,506 Watt solar array

Say you live just down the block from me near Redwood City California (across the bay from Fremont--similar weather):
http://solarelectricityhandbook.com/solar-irradiance.html

Fremont
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.83	4.56	5.70	6.54	6.71	6.81
Jul	Aug	Sep	Oct	Nov	Dec
6.61	6.55	6.30	5.74	4.42	3.59

Toss the bottom three months of winter (use less power, use genset for bad weather, etc.), 4.56 Hours of sun (February break even month):

• 1,506 Watt array * 0.52 off grid system AC efficiency * 4.56 hours of sun = 3,571 Watt*Hours per day

That is enough power to run a very efficient off grid cabin with LED lights, refrigerator, well pump, clothes washer, laptop, etc. (veryI  efficient off grid cabin/home).

I don't think this is what you want/need/were planning for... But if you want the AC inverter and to run (for example) a large grinder for 2-3 hours per day--That is what such a system would look like.

Typically, we suggest working on your loads first.. Conservation is key for a cost effective off grid power system. Using battery based power tools which are already designed for minimal power usage and to operate from small battery backs (that are typically NiCad or Li Ion--designed to supply very high amounts of current/power for short periods)--And then your solar power system only has to run the battery charger for your tools (a few hundred watts for an hour or two per battery charge per tool).

And use a Kill-a-Watt type meter to measure your AC loads to design a system that is matched to your loads.

If you have AC power on the property--It is generally much more cost effective to just bury a 100 feet of 10 AWG cable from your home to the shed for AC power. May not be as much fun--But is more practical (Golf Cart batteries are cheap at ~$90 each, last 3-5 years, electronics, charge controller, AC inverter, will need replacement after ~10+ years, etc.).

Your thoughts?

-Bill