[note: this section was split out from the gentle intro to solar in order to streamline it]
Bill wrote down each item, how much power it uses, and how long he would use it each day. Yes, this was annoying but he didn't try to do it all at once.
He read the Amps off the electrical product label, and multiplied it by the hours per day the item would be use. Amps x Hours = Amp-Hours, commonly written Ah.
This is what he plans to run each day:
| DC1) Device | Quantity | Amps | hours per day | Amp-hours |
| lights | 4 | 0.25 | 4 | 4 |
| roof vent | 1 | 2 | 6 | 12 |
| phone charger | 1 | 1 | 3 | 3 |
| laptop | 1 | 5 | 6 | 30 |
| 12v compressor fridge2) | 1 | 5 | 8 | 40 |
| cordless drill charger | 1 | 4 | 0.5 | 2 |
| total | 91 |
His daily power requirement is 91Ah.
There are calculators to help get a handle on daily power requirements.