Hmmm, it sounds like the neighbor did not understand the full story of what they were buying. Storing 8v out of 118v is preposterous. Alike Arct1k said, appliances use step down transformers (switching and linear) and can use whatever they are fed withing a range of around 110-120v AC. To store AC, you could use coils and caps (once AC rectified into DC), but all that would do is even out the load (remove current spikes) from motors being turned on.
However, there is "
power factor" which varies with the type of loads present in a home (capacitive vs inductive). Pure inductive and capacitive loads produce voltage to current phase shifting of 90*; -90* for inductors, +90* for capacitors. Resistive loads have 0* phase shift. A place with a lot of motor loads will have a huge phase shift. But you can add capacitor banks to offset the inductive phase shift (+90* + -90* = 0*) to get a more resistive-looking load. Of course, the amount of capacitance to add depends on how many motors are running (and how big they are), so a device can be added that measures the phase shift and adds in whatever capacitive load needed to offset the inductive load. This is probably what your neighbor bought.
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