Capacitance, not batteries; your calculator includes capacitors, and has low enough draw that they can power it for at least a second or two. That's the minimu

Capacitance, not batteries; your calculator includes capacitors, and has low enough draw that they can power it for at least a second or two. That's the minimum requirement. Power draw varies on sub-second timescales; just because your power meter shows a continuous draw of 4 kW doesn't mean it's actually continuous, or that 4 (or 6, or 8) kW of solar panels would cover the spikes. When they don't, you get brownouts. You wouldn't want your house to shut off because of a passing cloud, either. Solar powered houses do not in fact need batteries -- a large capacitor bank would be plenty. It's just that a capacitor bank capable of running it for (say) five minutes, at a draw of several kilowatts, is enough power in a scary enough form factor to need armoring. Batteries are far safer, and also let you use power at night.