Pumping water uphill: storing energy without batteries

Ross Baldick Electric Power Consulting

Jaime Luengo shows UT professor Gary Hallock how the solar-powered water pump works.

It’s been my pleasure for the past several years to supervise a senior design project in my Electrical and Computer Engineering department at The University of Texas at Austin. The project is aimed at avoiding battery storage in off-grid solar applications by taking advantage of the storability of the final product or service provided by an electric motor.

Think of an electrically-driven water pump that is filling a raised tank, with the water then being used for domestic or agricultural use by letting it flow downhill. If the pump and tank are sized appropriately, then the pump could operate when power is available and still pump enough each day to cover the needs.

Our team’s approach to powering this system from the sun without battery storage has been to use a variable-speed drive for an electric motor and vary the drive frequency to match the power output from a solar panel. When the sun is shining brightly and more power is available from the solar panel, we adjust the drive frequency up so that the motor can use all the power. When it is cloudy and the solar panel produces less power, we adjust the drive frequency down so that the motor is still pumping, but at a lower rate, and using the available power. By adjusting the drive frequency this way, we can utilize whatever power is available from the panel without battery storage. We are storing the energy by pumping water uphill.

Ross Baldick Electric Power Consulting

This year’s senior design team included (left to right): Carly Stalder, Ankit Sharma, Ji Hoon Seon, and Max Granat. Not pictured: Jaime Luengo, Cody Scarborough, Schuyler Christensen.

(There are other potential applications, such as-available air conditioning or other mechanical loads where there is inherent storage in the end-use product or service.)

Several senior design groups have been working toward this goal over the last few years. This year the students really came together and were able to build on previous groups’ efforts to build a working prototype that could harness variable light levels.

These photos show you the results: a working prototype that pumps more when the sun is bright.

About Ross Baldick

Electricity is an increasingly complex industry in the midst of transition to renewables and decarbonization. Using my 25 years’ experience as an engineer, policy analyst, and academic, I help my consulting clients think through their toughest technical challenges and formulate their best business strategies.
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