Case study: Using a BESS with photovoltaics
This building combined solar photovoltaics and energy storage to reduce its electric utility costs
The battery energy storage systems (BESS) can be a valuable system used in electrical designs in a wide range of applications. There are several benefits, including allowing energy independence of electrical systems for facilities and reducing greenhouse gas emissions.
The high-level one-line diagram (see Figure 5) illustrates a utility service feeding a service entrance switchgear. The new BESS and solar photovoltaic (PV) arrays are also connected to the switchgear and they have the capability of providing power to the site loads during a utility outage or during peak demand times. Switching to the BESS would be automatic in the event of an incident. However, without an energy management system (EMS) in place, the batteries may not be used efficiently.
This example is an existing water treatment facility that was provided with a new BESS and PV arrays. The facility averages about 40 million gallons per day of treatment. The PV arrays were sized based on the land available for installation and the BESS was sized to fully support the facility in the event of an outage for a short period of time. The facility experiences large peaks of demand for a couple of hours a day, which leads to large energy bills that are disproportionate to the total energy metered because of demand costs.
The PV arrays allow the batteries to charge in conjunction with the utility for redundancy. Energy waste is minimized with this setup. Even when the facility is experiencing low electrical load usage, the PV arrays can charge the batteries in lieu of directly providing power to the facility loads. Without the BESS in this scenario, the energy buildup with the PV arrays would be wasted because this system normally cannot store usable energy. The facility also benefits by allowing the BESS to provide peak-shaving capabilities during peak demand periods. In turn, this reduces the overall utility costs and greenhouse gas emissions.
Figure 5: A one-line diagram depicting the components of the electrical distribution system incorporating photovoltaic arrays and battery energy storage systems. Courtesy: CDM Smith
This facility was a good candidate for a BESS because of the unfavorable sell-back policy with the utility. With the growing popularity of solar, utilities have more competition in the power producing industry. In most jurisdictions, they are not required to allow a renewable energy site to connect to their power grid. In these cases, excess energy is 100% wasted without a BESS.
At the case study facility, the utility allowed interconnection but only offered to buy back excess energy at a fraction of the cost that the facility pays for it. Without a BESS, the financials of installing solar made sense only up until a certain size. With the BESS, the facility took full advantage of the land they had available for solar PV.
For the BESS, a prepackaged containerized type of battery storage was selected because of the required capacity of the site. Lithium iron phosphate battery chemistry was also selected because this was a stationary application. The containerized selection allows the flexibility for future expansions if ever necessary.
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