The California Energy Commission is using a recently completed microgrid project at Las Positas College to show how battery energy storage can mitigate the “duck curve”—despite a couple of hitches.
Las Positas’ utility power demand curve, similar to a statewide curve, is called a “duck” because of its shape: a large midday drop due to solar generation followed by a steep ramp in late afternoon and evening as solar generation slows and people return from work to their homes.
The school’s demand curve is similar to the statewide curve, a July 16 report to the CEC said.
Las Positas currently has a 2.3-MW-capacity solar array that supplies 55 percent of its electricity. With a CEC grant, the campus added a 1-MWh battery storage system, including software that allows the school to forecast its microgrid’s capacity availability and deliver that capacity when signaled.
The project cost about $1.8 million and has a payback period of 10 to 12 years. It is projected to reduce the college’s energy cost by $120,000 a year.
Las Positas’ square footage has nearly doubled since 2004, resulting in a corresponding increase in energy use and cost, according to the school. As campus buildings were added, peak power demand increased to more than 2 MW, the CEC’s report said.
Most of the campus’ energy use happens in the evening, around 8 p.m., which is also when electricity in Pacific Gas & Electric’s service territory, where Las Positas is located, costs the most.
The project team identified opportunities to flatten the school’s demand curve, including increasing consumption of on-site renewable energy in the morning hours; evaluating the cost trade-off of reducing electricity export to the grid between noon and 6 p.m.; and implementing ways to predict and automatically reduce demand peaks.
The team tried to manage the times when the school’s large mechanical equipment turned on and off. The goal was to have thermal storage equipment operate from about 4 p.m. to 9:30 p.m. and then switch to chiller units in the morning. However, the plan failed: The on/off signal that was supposed to be sent between the thermal storage equipment and the chillers never made it through, the report said.
Prior to the battery storage project, Las Positas was sending about $30,000 worth of solar-generated electricity each year back to the power grid at no charge, due to previous net-metering tariff regulations that only allowed a solar generator to be paid for power from a 1-MW solar system. The battery now captures a portion of the excess solar power and stores it for use at other times.
California schools and colleges have installed about 1,000 MW of solar capacity in total, but often use the local utility grid as a battery, the report said, to mitigate the duck curve.
Los Positas’ microgrid was supposed to be a blueprint for other California schools; however, the project team did not publish an official blueprint, even though the requirement to do so was stated in the grant funding award.
Instead, the team said it presented the information at conferences and seminars attended by educational facilities managers and energy managers. The microgrid blueprint was going to be used by educational institutions statewide to evaluate, plan and install their own microgrids, and to help manage the output of their existing renewable-energy assets using energy storage systems.
The battery storage project grant was awarded in 2015 through the CEC’s Electric Program Investment Charge program.