Using high-speed demand response of building HVAC systems to smooth cloud-driven intermittency of distributed solar photovoltaic generation

The penetration level of distributed solar photovoltaic (PV) generation is rapidly increasing as a consequence of incentives, renewable portfolio standards, decrease in the cost of devices and other factors. If the peak power rating of PV systems in a particular distribution feeder is above a certain fraction of the feeder´s capacity, it can be difficult to maintain power quality without resorting to support devices such as batteries, flywheels or capacitors. The high cost of these support devices increases the levelised energy cost of PV electricity. In this study, a method to absorb a substantial fraction of the power spectrum related to solar intermittency using controllable loads in HVAC systems is described. In particular, the focus is on modulating the speed of fan motors in such a way that, while temperature control in the building is maintained, the intermittent component of PV generation is absorbed, as close as possible to its source. First, the power spectrum of PV generation is characterized for a variety of cloud cover conditions. Second, a high-fidelity model of a building is used to optimize the operating parameters of the fan control strategy. Third, experimental verification of the strategy´s effectiveness is performed. It is shown that fan control can absorb a substantial fraction of the energy associated with PV intermittency at very low cost, thereby reducing the size of smoothing systems, such as batteries, which are nevertheless needed to absorb the high-frequency band of the intermittency spectrum.