A rate structure in which the retail price of electricity increases incrementally as a customer reaches certain thresholds (or ‘tiers’) of total monthly usage. In other words, at ‘Tier 1’ (up to XXX kWh/month), a customer pays $0.0X/kWh; while at ‘Tier 2’ usage (above XXX kWh/month) a customer pays $0.XX/kWh.