Net-zero homes are designed to consume no more energy than can be produced on site, usually combining a super-insulated passive solar design with active solar thermal and photovoltaic technologies for heating and general electrical use. Most cheat a little by being grid-connected, allowing the electrical utility to act a storage battery when the PV cells produce more than is needed and drawing back from the grid when they are insufficient to immediate needs. The home is considered to have achieved net-zero performance when the amount of electricity purchased from the utility over the course of a typical year is no greater than the amount sold back to the grid during that period. Net-zero homes may be built to Passivhaus standards but more commonly have a lower standard of insulation, compensated by the on-site energy production: debates over whether it makes better environmental sense to invest in the extra insulation or the PV panels are ongoing.