Are watts watts, 24 or 48 volts? I know that amps go down as the volts go up, 10 amps at 24 volts is 5 amps at 48 volts, is it the same with watts?

I believe amps multiplied by volts equals watts, so 10 amps at 24 volts = 240 watts and 5 amps at 48 volts = 240 watts. Hopefully someone will correct me if I am wrong.

Tom

Exactly correct. Some of the relationships for electricity:

V = I * R (Volts = Amps * Ohms)
I = V / R
R = V / I
P = I^2 * R = V^2 / R = V * I

And work is Power * Time

P * Hrs = Watt*Hours = V*I*Hours = etc.

KiloWatt = Watts / 1,000
KiloWatt*Hours = Watts*Hours / 1,000 (kWhr is what your utility charges you)

Amp*Hours = I*Hours (voltage needs to be known to be be work)

Many battery systems folks will talk about a solar panel that puts out 35 amp*hours per day into a 200 amp*hour battery bank to be consumed by a 1 amp load running 24 hours per day (24 amp*hours per day) (which would be the same as a 24 amp load running 1 hour per day)...

As long as the panel, battery, and load are all running at the same voltage (i.e., 12 volts). To calculate power, you would need to take the amp*hour number and multiply it by the system voltage). Example of "same amp*hours" but different bus voltages. One ends up being a 12 watt load, the next 24 watt load, and the final is a 48 watt load.

1 amp load * 24 hours * 12 volts = 288 watt*hr = 0.288 kiloWatthrs
1 amp load * 24 hours * 24 volts = 576 watt*hr = 0.576 kiloWatthrs
1 amp load * 24 hours * 48 volts = 1,152 watt*hr = 1.2 kiloWatthrs

So, the answer is if you have a 24 watt 12 volt bulb, it will take 24w/12=2 amps. A 24 watt 24 volt bulb will take 24w/24v=1 amp...

-Bill

Volts are "transported" more easily than amps. Amps require thicker copper wire ($$), where volts only need more rubber insulation over the wire.
Rubber is cheaper than copper.