Energy Efficiency Market Study: Determining the Energy Efficiency Opportunity Potential at Minnesota Drinking Water Utilities
Minnesota drinking water treatment facilities produced 138 billion gallons of water in 2017 which used an estimated 295 million kilowatt hours of energy. This is about 0.5%1 of all the electrical consumption in Minnesota, and about 1.3%2 of industrial electrical consumption in the state. Benchmarking of this sector had not been done and specific energy savings measures were not widely known at the outset of the project. The Minnesota Technical Assistance Program (MnTAP), received a CARD grant to expand benchmarking of the drinking water treatment sector in Minnesota and to identify conservation opportunities, especially those that might be appropriate for electrical utilities to promote as part of their Conservation Incentive Program (CIP).
The general format of the project was as follows:
- Literature review: to identify potential opportunities for drinking water utilities and to better understand the base of knowledge available.
- Informational interviews with water utilities, electric utilities, and industry experts, to generate a baseline for energy use in the sector and to further identify energy conservation opportunities.
- Site assessments with select water utilities to quantify savings from both previously implemented conservation efforts and future opportunities. The specific opportunities addressed by these assessments were:
- Well/pump rehabilitation
- Pump efficiency optimization
- Customer water conservation
- Water loss reduction
- VFD installation and optimization
- Quantify the savings potential for the sector as a whole and offer guidance to electric utilities on how to incentivize the vetted energy conservation opportunities.
Opportunity Potential
Along with the identification and vetting of energy efficiency opportunities that are specifically applicable to the drinking water treatment sector in Minnesota, this project aimed to help electric utilities identify and incentivize these energy savings measures as part of CIP. The first step in this process was identifying the statewide potential for each opportunity which is show in Table 1, below.
Table 1: Summary table of opportunities and their statewide potential.
| Opportunity | % of State Water Utilities Available | Estimated Savings | Estimated Sector Energy Saving (kWh/yr) |
|---|---|---|---|
| Pump Efficiency Optimization (PEO) | N/A | N/A | 25,000,000 |
| PEO: Well Pump Selection | 87% | 5% | 14,000,000 |
| PEO: Distribution Pump Selection | 87% | 0.7% | 2,200,000 |
| PEO: Pump REdesign | 10% | 600 kWh/MG | 8,300,000 |
| Well/Pump Rehabilitation | 53% | 6% | 9,300,000 |
| Water Loss REduction (WLR): | N/A | N/A | 3,500,000 |
| WLR: Distribution Leak Repair | 95% | 2.5 – 31% of Losses | 2,400,000 |
| WLR: Hydrant Repair | 96% | 0.4 – 2.3% of Losses | 180,000 |
| WLR: Treatment Losses | 87% | 2.3 – 43% of Losses | 890,000 |
| WLR: Pressure Control | 15% | 1.4% of Losses | 31,000 |
| WLR: Storage Mixing | 15% | 0.6% of Losses | 2,000 |
| Customer Conservation (CC): | N/A | N/A | 2,700,000 |
| CC: Irrigation | 94% | N/A | 1,200,000 |
| CC: Residential Appliances | 94% | N/A | 1,500,000 |
| CC: Other | 94% | N/A | 85,000 |
| VFD Optimization | N/A | 1.5% | 1,900,000 |
Pump efficiency optimization and well/pump rehabilitation showed the greatest potential for statewide energy conservation, with modest savings potential and a fairly large number of potential sites. Pump efficiency optimization involves finding the combination of pumps that provides the lowest specific energy value (kWh/MG), and well/pump rehabilitation is the periodic maintenance of these systems. The identification of sites with greater potential for pump efficiency optimization are those with greater than five wells. For well/pump rehabilitation, sites without an existing plan for rehabilitation will provide the greatest potential. A requirement for incentivizing these opportunities is the measurement of specific energy for the pumps involved. During the interview process, no sites had the robust electricity monitoring that these two opportunities would require and would likely need to be incentivized by the electric utility. This system could emulate how compressed air leak audits are incentivized currently by electric utilities: an initial audit is completed to identify leaks and the audit is paid back once leaks are fixed. This ensures that energy savings are occurring from the investment by the electric utility. In a similar fashion, monitoring equipment could be installed to aid in pump efficiency prioritization and well/pump rehabilitation and could be paid back if efficient pumps are utilized or well/pump maintenance is completed.
Water loss reduction and customer conservation showed the next greatest potential for savings due to relatively high potential energy savings and many facilities in the state not currently planning for either opportunity. Water losses include all water that is acquired from a water source but is not delivered to a customer. This includes water lost by leaks while distributing water, water lost during treatment processes, and hydrant flushing/use. This opportunity is easily identified with Department of Natural Resources (DNR) data on leak rates and could be incentivized on a per leak fix basis. A leak rate of 10% or less is recommended by the DNR and any sites above that would be good initial targets for outreach.
Water loss reduction and customer conservation showed the next greatest potential for savings with a relatively high number of facilities in the state not currently with active plans for either and relatively high potential energy savings. This opportunity is easily identified with DNR data on leak rates and could be incentivized on a per leak fix basis similar to current compress air leak programs. A leak rate of 10% or less is recommended by the DNR and any sites above that would be good initial targets for outreach. To identify sites that could benefit from customer conservation, the water use per capita and the specific energy could be used as a way to identify higher opportunity as higher per capita use would indicate more opportunity for customer conservation and a higher specific energy would indicate a larger incentive to reduce water use. Rebate programs such as these, could be partially funded by the electric utility on a per gallon basis which can be converted to energy savings using the specific energy (kWh/MG).
The final two opportunities identified were related to VFD operation and had the lowest statewide potential. VFDs were commonly found on well pumps in drinking water treatment plants, but optimization strategies were less common. Identification of optimization activity is more challenging than the other opportunities, requiring an in-depth assessment of water utility operation. Since these opportunities have a smaller statewide potential, they should not be an electric utility’s focus.
In total, the opportunities identified above have a statewide potential of 42,000,000 kWh per year. More than half of that total is contained in the pump efficiency optimization opportunity, hinting at relatively small savings for the rest. These savings values likely do not warrant a full program devoted to this industry, but other options exist such as combining drinking water treatment with wastewater treatment facilities to cover a larger sector, combining electric utility service areas.
1 https://www.eia.gov/electricity/state/archive/2017/
2 https://www.eia.gov/electricity/state/archive/2017/minnesota/state_tables.php