is turned off is simply lost, and this represents a significant amount of each cycle. To address this, solar inverters use some form of energy storage to buffer the panel's power during those zero-crossing periods. When the voltage of the AC goes above the voltage in the storage, it is dumped into the output along with any energy being developed by the panel at that instant. In this way, the energy produced by the panel through the entire cycle is eventually sent into the output. The problem with this approach is that the amount of energy storage needed when connected to a typical modern solar panel can only economically be provided through the use of electrolytic capacitors. These are relatively inexpensive but have well-known degradation modes that mean they have lifetime expectancy on the order of a decade. This has led to a great debate in the industry over whether or not microinverters are a good idea, because when these capacitors start to fail at the end of their expected life, replacing them will require the panels to be removed, often on the roof. Three-phase In comparison to normal household current on two wires, current on the delivery side of the power grid uses three wires and phases. At any given instant, the sum of those three is always positive (or negative). So while any given wire in a three-phase system undergoes zero-crossing events in exactly the same fashion as household current, the system as a whole does not, it simply fluctuates between the maximum and a slightly lower value. A microinverter designed specifically for three-phase supply can eliminate much of the required storage by simply selecting which wire is closest to its own operating voltage at any given instant. A simple system could simply select the wire that is closest to the maximum voltage, switching to the next line when that begins to approach the maximum. In this case, the system only has to store the amount of energy from the peak to the minimum of the cycle as a whole, which is much smaller both in voltage difference and time. This can be improved further by selecting the wire that is closest to its own DC voltage at any given instant, instead of switching from one to the other purely on a timer. At any given instant two of the three wires will have a positive (or negative)