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The Technical Case for Hybrid Solutions

Photo credit: GI Energy

 

  1. The technical case for a hybrid CHP-BESS solution

 

The figure below explains how a Battery Energy Storage System (“BESS”) can enhance the benefits of a Combined Heat and Power (“CHP”) solution. It depicts a typical summer day load profile of a large commercial building in Northern California. The building is simulated with a 2,000 kW CHP system that dispatches against its load. This system is subject to two operating restrictions: a turndown in case the load falls below 40% of the rated net capacity, and a requirement to maintain a minimum utility import of 10% of CHP net capacity always.

Figure 1: Optimal day for hybrid solution

As seen in figure 1, the CHP can run at its max rated net capacity during the middle of the day when the building’s energy consumption peaks. Early morning and late at night however, the building’s load is low which leaves some of the CHP capacity on the table that could instead be used to charge a BESS.

The thesis for integrating a BESS to this solution is as follows: The BESS can be charged during low consumption hours and discharged during peak consumption hours. In this way, the CHP can theoretically have smooth and predictable output throughout the day (maximizes fuel efficiency) and gets the most demand reduction value. Depending on the host load profile, sizing the CHP system to cover the peak electric load may result in an oversized system for a significant portion of the year. By downsizing the CHP system and adding a BESS, the hybrid system can better supply most of the host building load with the CHP and use the BESS to extend its capacity above and below the operating range of the CHP system alone.

The thesis above is contingent on predictable load profiles. If every day in the peak summer periods resembled the optimal shape in the figure above, an integrated solution is technically possible. Figure 2 below explains what a “sub-optimal” day for an integrated solution looks like.

 

Figure 2: Sub-optimal day for hybrid solution

On a “sub-optimal” day, the CHP has ample opportunity to charge the BESS, but the BESS has limited opportunity to discharge.

  1. Does a hybrid solution make technical sense for your business or property?

 

The technical feasibility of a hybrid solution is informed by the customer’s load profile and physical asset siting constraints. If the building’s load profile over the course of the peak summer months is erratic, oscillating between optimal and sub-optimal days for a hybrid solution, then hybrid solution is not technically valid. BESS assets have strict operating requirements regarding their charge and discharge cycles which would be violated if the load profile across the year is erratic. If two optimal days are interspersed by several suboptimal days, the BESS stays charged for an extending period. BESS cannot hold charge for indefinite periods of time and must have periodic charge and discharge cycles as per the manufacturer’s warranty terms. One solution to this could be to program the BESS to discharge slowly while ramping down the CHP on such suboptimal days; however, that would result in suboptimal performance of CHP at part loads in terms of its fuel consumption. A sophisticated balance needs to be struck between maintaining optimal operating parameters for both assets for a hybrid solution to succeed at delivering value.

GI Energy has extensive experience and expert analytics capabilities to conduct feasibility studies and evaluate the opportunity to deploy hybrid solutions. For questions about the comments discussed in this article or to explore whether CHP coupled with a BESS solution is right for your business, reach out to us at info@gienergyus.com.

The author of this article can be reached directly at achandar@gienergyus.com.