**5. Demand response experiences in natural gas systems**

DR concepts have been used for years (with different levels of development depending on countries) in the management of power systems [26]. Thus, DR programs, either offered by system operators or utilities, contribute to solving different matters that appear in the habitual operation of the power grid. Nevertheless, and in spite of the similarities existing between the power and natural gas systems, there are few successful experiences of DR applications in the natural gas system. However, as agreed by some researchers and professionals, DR concepts could be essential for the better and more efficient operation of natural gas systems, as can be deduced, among others, from the following factors highlighted by Srinivaspura [27]:


Until now, DR concepts have been applied worldwide as predominantly pilot projects, but results achieved have been promising [29]. In Canada, residential endusers have been asked to participate in DR programs based on the gas management through the regulation of the thermostat for heating applications. The energy savings estimated were influenced by the thermal oscillation (external Temperature) and the warmness of the season and could reach up to 21% [30].

## *Demand Response Applications for the Operation of Smart Natural Gas Systems DOI: http://dx.doi.org/10.5772/intechopen.101810*

Enernoc, the most active company in DR applications for small and medium customers in the electricity sector, is also trying to develop some experiences in the natural gas sector. In particular, this company has developed a platform, which is being tested in customers from National Grid in the State of New York, in order to shift consumptions to optimize the use of fuel sources based on weather availability. Therefore, Enernoc will try to demonstrate that DR concepts may help in winter to solve the same kind of problems that the power system (closely linked to the gas consumption) has during peak periods in summer [31].

Regarding Europe, Spain was a pioneer in the approval of an interruptible program in 20069 , based on the need of establishing tools and mechanisms so as to make more flexible the natural gas system. By means of this program, the gas system operator has the possibility to interrupt the supply to large customers willing to do that in case of emergencies. This advanced mechanism has two types or modes of interruptibility:


Interruptible customers must be able to completely interrupt their consumption with a notification in advance of 24 h. The duration of the interruption may vary from 6 h up to 10 days. However, as mentioned earlier, only large customers with an annual consumption higher than 10 GWh and a daily consumption higher than 26 MWh and connected to a pipeline with a pressure higher than 4 bar can participate.

Another experience can be found in the United Kingdom, where there is a kind of interruptible program, but just at the distribution level and less developed than in Spain. Just a small group of large industrial consumers can participate, depending upon the commercial arrangements they have agreed to10. Interruptible customers receive discounted transportation charges when reducing their consumption in periods of high demand (especially in winter peaks). In 2010, just 27 customers participated in interruptible gas contracts in the UK [32].

In the Netherlands, a consortium of 11 entities called Energy Delta Gas Research (EDGaR)11 coordinates the development of different scientific, applied, and technological research projects on natural gas. However, even if there are some research lines in the field of smart natural gas systems, none of them is dealing at the moment with DR applications in the natural gas sector. Said that, it is true that for this consortium, customer's flexibility is a key value in smart grids, and some ideas have arisen about the utilization of flexibility of electricity consumers for the management of power plants fueled by natural gas, as indicated in the research of Huitema et al. [33].

<sup>9</sup> The interruptibility program is regulated in the Resolution 25 July 2006 from the General Direction of Energy Policy and Mines. Available from: https://www.boe.es/diario\_boe/txt. php?id=BOE-A-2006-14314.

<sup>10</sup> The characteristics of interruptible supplies are described in: http://www2.nationalgrid.com/uk/ Industry-information/Gas-transmission-system-operations/Interruptions-to-supply/.

<sup>11</sup> More information about this consortium is available at: http://www.edgar-program.com [Accessed: April 18, 2017].

All these experiences demonstrate the promising application of DR resources for a more efficient management of the natural gas systems, similarly to the power grid. However, most of them are just in the pilot phase at present or, in the best case, only large industrial customers are enabled to participate.
