With the growing demand for water and electricity in the world, municipalities, institutions and private industries are being confronted with rising costs. Large amounts of electricity are consumed in order to pump, treat, and distribute water resources to residential and industrial consumers. The energy associated with water management not only represents a large financial cost to the industry, but depending on how the electricity is produced in the region, it also can have heavy environmental impacts due to GHG emissions.
Water pumping represents the single largest electricity input cost for Canada’s largest city, Toronto. In fact, pumping and treating water consume enough energy to light every home in the province of Ontario, Canada. Electricity is an important factor in water pumping and in turn, water is used to generate electricity. As you can see, the management of water and wastewater treatment plants plays an important role in the water-energy nexus.
Water systems, including drinking water and wastewater, represent some of the largest storage opportunities due to the use of large reservoirs. What if we could use this storage to create a more reliable and efficient electricity system?
Balancing the Grid in Real-Time
A region’s electrical power grid can be thought of as a vast, complicated machine, where supply must match a constantly shifting demand. With the integration of intermittent renewable power sources, the real-time balancing of the grid becomes a greater challenge.
Demand can vary over intervals as short as a few seconds, a variability that generators do not like. And when the supply/demand balance shifts, power voltage and frequency shift – a condition that can be inefficiently fixed by increasing power generation.
Found within water and wastewater treatment plants is flexibility that can deliver grid balancing services to the power system. These water and wastewater systems can be leveraged to integrate intermittent renewable power generation and improve the reliability and efficiency of the power system, while offsetting electricity costs for the facility.
Capturing Demand-Side Storage
ENBALA, a North American Smart Grid company has a platform that captures process storage that already exists in the power system by tapping into the available flexibility of demand-side loads. ENBALA’s platform leverages process storage in water and wastewater treatment plants to deliver Grid Balance (the moment-to-moment balance of the electric grid) to the power system. The platform receives real-time requests from the power grid operator and then sends individual requests to network participants to tune up or down the rate at which some of their loads (such as pumps) operate. An aggregate response is then delivered back to the power grid operator.
In the case of a water pumping station, the facility operator shares with ENBALA the set-points in which its equipment has flexibility to respond to small adjustments. Additionally, the operator also specifies any constraints that need to be monitored and adhered to at the site. For example, the reservoir tank could have an upper and lower limit that cannot be exceeded, the pump could have a maximum allowable ramp rate to avoid water hammer, or that the distribution pressure cannot exceed a certain tolerance deadband.
These constraints are very important to ensure that the facility is maximizing its available flexibility to provide Grid Balance without impacting day-to-day operations.
For example, in wastewater treatment plants, aeration basins are controlled according to dissolved oxygen (DO) concentration, with a target in most facilities of 2 milligrams per liter (mg/L). In practice, actual DO concentration may range between 1 and 8 mg/L. The rate of oxygen consumption varies depending on the biological oxygen demand, and is driven by the amount and type of waste material in the water, pH, water temperature and atmospheric conditions, (all of which vary during operation). Within limits, it is OK to slow down or even to speed up the aeration process – as long as the DO stays within an accepted range.
This inherent flexibility, known as ‘demand-side storage’ is what electricity system operators can rely on to achieve a fine tuned match between supply and demand.
The Big Picture Benefits for Water & Wastewater Facilities
Today, traditional generators are paid for the fine tuning of the power system, but now large-scale electricity users like water and wastewater treatment plants can participate in this market through companies like ENBALA. ENBALA receives payment from the electricity system operator, and passes payment along to the participating organizations. In the various regions in North America where ENBALA operates, payments to companies are typically around US$50,000 to US$60,000 per megawatt year of Grid Balance.
In addition to the financial rewards for loads, the service of balancing the grid using loads has positive environmental impacts. By integrating demand-side loads from water and wastewater facilities, into the Smart Grid, the electricity system runs more efficiently and lengthens the lifespan of existing infrastructure while reducing greenhouse gases. According to an Impact Quantification report conducted by The BLOOM Centre for Sustainability, for every 1 MW of Grid Balance delivered through the ENBALA Power Network, greenhouse gases are reduced by 5,500 tonnes, smog-related emissions decrease 38 tonnes, and US$30,000 is saved in health impacts through decreased air pollution.
As described, water and wastewater facilities have inherent flexibility in how they already use electricity and their available demand-side storage is a valuable resource used for the benefit of the electricity system and the facility itself.
By participating in the water-energy nexus, demand-side loads receive a new revenue stream and the electric power system sees an increase in the grid’s efficiency and reliability.