Optimized response to electricity time-of-use tariff of a compressed natural gas fuelling station

Abstract

Compressed natural gas propulsion of vehicles has been shown to have advantages over petrol and diesel propulsion due to lower carbon dioxide emissions as well as the increased durability of vehicle engines. The growth of compressed natural gas as an alternative fuel to petrol and diesel can be accelerated by implementing strategies that result in the economical operation of the distribution infrastructure. Economic scheduling of power consumption is a useful strategy for reducing the cost of energy for both industrial and domestic consumers who operate in time-of-use based electricity pricing environments. In this paper, an optimal energy management strategy is proposed for the operation of a compressed natural gas fuelling station. The compressor energy consumption, being the main component of the total operating cost of the fuelling station, presents a cost saving opportunity through which optimal scheduling of operation can be used to lower cost of operation of the station. The developed model shows potential average savings of 59.3% in daily electricity costs while maximizing compressor life through minimization of compressor cycling.

A Hierarchical Optimisation of a Compressed Natural Gas Station for Energy and Fuelling Efficiency under a Demand Response Program

“…The delay is an important quality of the realised schedule as it reduces the contribution of the CNG station to the grid comeback load associated with the surge in electricity demand immediately following the end of the peak pricing period [43,44]. A total of four switching instances occur over the control horizon, which is comparable with observed results for alternative strategies observed in [12,29]. This implies the superiority of the current method as it matches the performance of previously proposed techniques with the added benefit of fewer mathematical operations, thereby achieving the goal of reducing computational complexity of the problem.…”

“…The station was modelled as a mass balance system where the storage was modelled as a single reservoir with an outflow from a known demand profile and inflow from an optimally scheduled compressor. Further, in [29], an optimal control to determine the operation of the priority panel valves under a known demand profile for each of the three reservoirs of the cascade storage was carried out. These studies considered only the flow of quantity of gas in mass from the compressor to satisfy mass of gas demand at the dispenser.…”

“…The gas demand at the dispenser, m o , determines the cycling of the compressor and thus the total cost of electricity incurred in a TOU electricity tariff [24]. The energy cost minimisation layer is formulated as a mass flow problem, as we proposed in our previous study [29]. This means that the scheduling of the compressor operation is optimised around mass inflow to the cascade storage from the municipal supply line and mass outflow as determined by mass of gas demand at the dispenser over the control horizon.…”

“…Elsewhere, in [29], the approach is based on the introduction of an auxiliary variable s(t) [37,38] that assumes a value of 1 when a switch-on occurs and tries to minimise the summation of the auxiliary variable over the control horizon such that…”

“…where is a weighting factor. The weighting factor can be set to reduce the number of switching instances so that the minimum number possible is attained for the same energy cost incurred such as was the case in [29]. The method proposed in the current study for minimising the frequency of compressor switching involves a single mathematical operation and no additional constraints which reduces the computational complexity of the problem when compared with Equations (3) and (4).…”