Linear useage of excess power generation
Sounds like he has micro inverters. Micro inverters directly attach to each panel and are wired in parallel. They simply turn DC into AC and feed it to the homes electrical system and to the grid depending on load. The smart meter tracks how much power is consumed from the grid vs fed back to the grid (excess). They also do not work in a blackout, they must see grid power to turn on.

How about storing that excess energy in a battery bank? The higher the excess, the more charge current is delivered to the battery (via PWM switching). The picaxe can monitor the excess and control a charge circuit to compensate for the load. Then you can use an off the shelf inverter to power appliances from the battery bank. The benefit of this system is that not only is it simple, but also gives you battery backup for blackout protection. Your friend can also use relays to switch certain appliances between battery and grid depending on the time of day. So during the day excess is dumped to batteries. At night when there is no more excess, relays can switch certain appliances or lighting circuits to battery and when the batteries run low, switch back to grid. Examples of relayed appliances could be: refrigerator, air conditioner, well water pump (if he has), lights, washing machine etc. The same grid->battery charger can also detect cloudy or low PV producing days and keep the battery bank charged in case of a blackout.

The batteries can get expensive but its a simple way to catch the excess and you have blackout protection.