The plant owner pays 100% of the PV system cost upfront. This model allows industrial and commercial consumers to own the system and claim tax depreciation benefits.
Under a RESCO model, a third party investor comes in to invest into a PV plant on a rooftop and sells solar power to a power consumer. There is no investment required from the consumer. If solar power is viable, the consumer can benefit from savings on the electricity bill right from the start. Under this model, the investor and the consumer agree on a tariff (per kwh of solar power)
and timeline of a power purchase agreement (typically between 15-25 years). Operations, repair and maintenance of the system could be carried out by the RESCO company rather than the consumer.
Building owners will be able to generate new income through leasing their roofs for a period of time (e.g. 15 years).
In the OPEX model, a 3rd party energy service providing company (RESPCO) invests the CAPEX and the Operator pays for the energy usage. Since the RESCOs have to make money from this model, for a 10 year business case, usually the Operator ends up paying a little higher than the renewable CAPEX model the OPEX model is still more cost effective than existing diesel based solutions.