**7. Barriers to the implementation of demand response strategies in the natural gas system**

Barriers and handicaps related to the implementation of DR in power systems have been discussed in many studies. One of the most recent examples can be found in Alcázar-Ortega et al. [42], which results from the European project DRIP. Among other results, this project produced a methodology for the systematic evaluation of handicaps, which prevents the implementation of DR strategies in the operation of power systems. Considering this work and based on the similarities previously identified between

power and natural gas systems, a preliminary evaluation of barriers can be assessed or referred to the gas side.

One of the main barriers is the difficulty for customer's acceptance: customers are not willing to reduce their consumption. The first reason is that consumers are not aware of the potential they may have, and they do not know that someone could be willing to pay in exchange for such flexibility. Another reason is that, when being aware of this potential, customers perceive that the economic incentives they may receive are not attractive enough. This barrier can be faced by providing customers with evidence about the economic profitability that DR actions may provide to their energy bills. While this is a difficult task, there are some tools for this purpose (some examples are provided by the aforementioned DRIP project), developed in the last years for the electricity markets that may be used for this purpose but applied to the natural gas sector.

Tools are also necessary so as to jump barriers on the side of retailers or system operators, as the potential offered by customers is difficult to forecast, and the benefits that DR may mean for their business are not easy to assess. However, the benefits of DR have been also proved in power systems for these activities, so similar results can be expected in the natural gas sector. Retailers can find in DR resources a help for the optimization of their portfolio and the reduction of imbalances, with significant cost savings. Regarding the gas system operators, the most significant barrier for them is probably the utilization of small and medium flexible consumptions. In fact, the few examples that can be found about the utilization of DR in natural gas systems are just related to very large consumers (as discussed in Section 2.3). Therefore, the empowering of the figure of the aggregator in natural gas systems is essential for the proper integration of DR resources coming from the residential and commercial sectors, as well as medium and small industries. A significant role can be played here by the managers of district heating networks, as they can provide the system operator with flexible customers willing to play not only with their gas supply but also their hot water or steam utilization. The system operator can utilize the potential offered by flexible customers so as to solve technical constraints related to the maximum capacity of pipelines in periods of peak demand. Additionally, the usage of natural gas storage can be optimized, allowing the system operator to combine both storage and DR resources to guarantee the optimum management of the whole system.

The development of the concept of Smart Energy Systems in recent times, which provides a strong metering and communication structure of the natural gas network, is definitively enabling energy grids for the easier utilization of customer's flexibility. However, as indicated in [5], the impact of DR programs, most of which would be similar to those existing for power systems, has to be evaluated and validated. At present, except for the few examples mentioned in this section, there are no real experiences demonstrating this potential. Therefore, the implementation of pilots arises as one essential step to provide credibility for considering DR.

There are some opinions against the utilization of DR strategies in the natural gas sector since some experts think that DR programs for gas consumers may be alluring but impractical [43]. Nevertheless, this book chapter proves the suitability of DR strategies applied to the natural gas sector, where similar problems to those arising in power systems can be afforded by this media.
