Reliance on water production by seawater desalination is growing worldwide as a means of coping with natural water scarcity. High energy demands of seawater desalination raise new challenges for both water and energy management and highlight the importance of understanding the operational dependencies of the water sector on energy supplies. While many studies have explored the need to coordinate water and energy resource management in the medium and long terms, this study highlights the need to coordinate management in the short term when dealing with maintaining the provision of critical supplies during periods of peak demand and reduced production capacity.
The Israeli water sector is heavily reliant on desalinated seawater. Over 80% of domestic drinking water is supplied from five seawater desalination plants, which collectively produce about 650 Mm3/y. Each plant has a long-term agreement with the Israeli government to supply a specific water volume ranging between 100 and 150 Mm3/y within prespecified monthly and daily limits. The total power consumption of the desalination plants is estimated at 200MW at peak production. As such, desalination plants are one of the largest energy consumers in the country. The Israeli Electricity Authority (IEA) utilizes several Electricity Load Shedding Programs (ELSPs), in which large consumers are requested to shed their power consumption during energy shortage events, usually with short notice. Desalination plants enrolled in these voluntary ELSPs are compensated for power shedding with up to 2 $/KWh. This value outweighs the loss of revenue from reduced water production, even when penalties for violations of production agreements are included.
In this work, we examined a typical energy-shedding event lasting four hours, during which desalination plants would reduce water production by 15,000 m3/h, resulting in energy savings estimated at 198,000 kWh (with 3.3 kWh/m3 energy intensity). Assuming an average compensation of 1.66 $/KWh, this translates into an income of about $330,000 for the desalination plant. Lost profits from reduced water production (revenues after deducting production costs and nonproduction penalties) amount to only roughly $25,000. Thus, with the compensation for shedding energy load 6 to 14 times greater than the water nonproduction costs, desalination plants have an obvious incentive to participate in ELSPs.
This imbalance in tariffs and penalties can create inefficiencies in the joint management of the energy and water sectors. As one example, during an extreme heat wave (May 22-24, 2019), in many areas in Israel, temperature exceeded 40℃ and humidity dropped to 10% (Figure 1a). Consequently, energy demands increased above forecasted levels, breaking historical records (Figure 1b). The IEA and the electricity system manager utilized all available electricity production units. On May 23rd, the IEA asked large energy consumers, including some desalination plants, to shed their energy consumption for four hours, and did so again on May 24th. At the same time, the National water system experienced elevated water demands, approximately 25% over the previous week. The extreme weather conditions contributed to over 1,000 fires around the country, which increased the pressure for a reliable water supply. To cope with the water stress, the National Water Company utilized its available production wells, surface water supply, and available storage.
With the existing compensation and penalty mechanisms, there was a clear discrepancy between the interests of the water sector, which prioritized reliable water supply, those of the individual desalination plants, which stood to benefit from nonproduction compensation, and the energy sector, which prioritized reliable energy supply. Considering the conflict between the water and energy sectors, the National water system operator turned to its regulator, the Water Authority (WA), and asked to intervene to prevent the desalination plants from engaging in the ELSPs. Based on contractual and legal issues, however, the WA could not mandate the desalination plants to maintain production. As such, only non-obligatory requests were made.
Figure 1c shows the desalinated water production of the five large desalination plants located in Ashkelon, Hadera, Palmachim, Sorek, and Ashdod (blue, red, orange, purple, and green lines, respectively). As can be seen, apart from the Ashkelon plant, which does not participate in the ELSP, all of the desalination plants reduced their production during the first ELSP period, while in the second ELSP period, some plants did not reduce production at the request of the WA.
The mismatch between policies aimed at addressing needs for peak energy demand management and for maintaining water production was enabled by a regulatory environment in which energy and water are managed separately, with few established mandatory mechanisms for inter-agency coordination. Collaboration between the water and energy sectors that provides integrated and comprehensive incentives and policies is critical for the efficient and reliable supply of both electricity and water resources. As extreme events are expected to intensify, this coordination is especially critical for achieving reliable and resilient supply.
Poster image: Hadera Desalination Plant and Orot Rabin Power Plant. Courtesy of IDE Technologies.