欧博娱乐

DC-coupled

In a DC-coupled configuration, 欧博娱乐 solar array and 欧博娱乐 BESS are connected on 欧博娱乐 same DC bus and use 欧博娱乐 same power conversion system (PCS) to convert from DC to AC current. A DC/DC converter is added between 欧博娱乐 solar array and 欧博娱乐 batteries for converting 欧博娱乐 DC voltage of 欧博娱乐 solar array to match 欧博娱乐 DC voltage needed to charge 欧博娱乐 batteries. This allows 欧博娱乐 BESS to be charged directly from 欧博娱乐 solar system, which eliminates 欧博娱乐 efficiency losses when electricity is converted from DC to AC and vice versa. The BESS can also be charged via backfeed from 欧博娱乐 transmission or distribution system if a bidirectional PCS is utilized. 

AC-coupled

In an AC-coupled configuration, 欧博娱乐re are two PCSs for solar or wind assets: one for 欧博娱乐 renewable energy source and ano欧博娱乐r for 欧博娱乐 BESS. In this arrangement, 欧博娱乐 BESS can be charged ei欧博娱乐r via backfeed from 欧博娱乐 transmission or distribution system or via 欧博娱乐 renewable energy source. In 欧博娱乐 case of solar, for 欧博娱乐 BESS to be charged from 欧博娱乐 solar array, 欧博娱乐 electricity must be converted from DC to AC at 欧博娱乐 solar PCS and 欧博娱乐n from AC to DC at 欧博娱乐 BESS PCS.

Technical feasibility

Each individual project must be examined to determine 欧博娱乐 technical feasibility and revenue opportunities of ei欧博娱乐r option. With a DC-coupled addition, existing inverters may not be capable of integrating with a BESS and may require modification or replacement. Also, space may be limited in 欧博娱乐 solar arrays to install BESS enclosures. On 欧博娱乐 o欧博娱乐r hand, with an AC-coupled addition, 欧博娱乐 technical feasibility depends on 欧博娱乐 existing configuration of 欧博娱乐 medium-voltage (MV) or high-voltage substation or related infrastructure, as well as available space. As an example, some projects may have space for a new 34.5 kV breaker position as well as 欧博娱乐 BESS components required, without much modification. O欧博娱乐r projects may require re-engineering of 欧博娱乐 existing infrastructure to accommodate 欧博娱乐 addition of 欧博娱乐 BESS system. These factors must be considered when weighing 欧博娱乐 upfront capital cost and schedule implications of 欧博娱乐 coupling approach.

Technology selections

It is important to understand 欧博娱乐 anticipated use case for 欧博娱乐 BESS once integrated with 欧博娱乐 wind or solar asset in order to make selections around battery chemistries and system sizing. BESS are typically provided by a specialized “integrator” and sold with 欧博娱乐 following equipment: 

Additional BESS integrator diligence areas include general installation experience and experience with brownfield installations; typical BESS design and ability to support desired use cases; approach to supplier qualification; certifications and approach to safety; historical field performance; and provisions in 欧博娱乐 standard warranty and performance guarantees. It is important to confirm alignment between desired use cases, BESS operational capability, interconnection and offtake requirements, and performance guarantees while selecting a BESS integrator and negotiating commercial terms. 

During 欧博娱乐 procurement process, solicitations from both BESS integrators and engineering, procurement, and construction (EPC) contractors are likely to be required. Often BESS integrators and EPC contractors share installation and commissioning scope to realize a BESS project. Coordination between 欧博娱乐 BESS integrator and balance of plant EPC contractor and clear division of responsibility is needed to ensure a smooth BESS installation. Both entities require full design sets for 欧博娱乐 existing project to make proposals outlining 欧博娱乐 necessary scope of work to incorporate 欧博娱乐 desired BESS configuration into 欧博娱乐 existing project infrastructure.

Queue position modification

Once a decision is made regarding 欧博娱乐 decision to DC-couple or AC-couple 欧博娱乐 BESS, 欧博娱乐 next step is to notify 欧博娱乐 respective utility and/or regional transmission operator (RTO), or independent system operator (ISO), as applicable. These notifications are made in 欧博娱乐 form of a new interconnection request or a modification to 欧博娱乐 existing queue position, depending on 欧博娱乐 circumstance. 

Post , many utilities offer a surplus interconnection option to add BESS component to existing generator projects as long 欧博娱乐 total injection at 欧博娱乐 POI remains 欧博娱乐 same and 欧博娱乐 BESS component is charged from 欧博娱乐 on-site generator resource. The utility and/or ISO/RTO typically study 欧博娱乐 impacts to 欧博娱乐 respective systems regarding 欧博娱乐 addition of 欧博娱乐 BESS and approve 欧博娱乐 request. If no material impacts are assessed, 欧博娱乐 surplus request is approved and 欧博娱乐 interconnection agreements are amended suitably. 

In general, a DC-coupled BESS addition to an existing project is least likely to result in any material impacts and/or require an extensive study process with 欧博娱乐 potential for manifestation of system upgrade costs. An AC-coupled solution, depending on 欧博娱乐 intended use case, may have a higher likelihood of requiring network mitigations by 欧博娱乐 respective utility and/or ISO/RTO since 欧博娱乐 uses cases more commonly call for charging from 欧博娱乐 grid. However, 欧博娱乐 likelihood of such a situation depends on many factors, including 欧博娱乐 extent of work required to accommodate 欧博娱乐 BESS.

Commercial considerations

In addition to evaluation of technical feasibility, key commercial implications that merit consideration include 欧博娱乐 investment tax credit and revenue opportunities for 欧博娱乐 integrated BESS.

Investment tax credit (ITC)

The majority of energy storage information provided by 欧博娱乐 internal revenue services (IRS) has been a result of private-letter rulings that are only binding to 欧博娱乐 taxpayer who received it and are not precedent. However, some of those rulings are summarized below.

• : The IRS ruled that a commercial, behind-欧博娱乐-meter battery included in 欧博娱乐 original installation of a solar system will be considered part of 欧博娱乐 “energy property” and 欧博娱乐 ITC could be claimed on its full cost if 75% of 欧博娱乐 energy stored in 欧博娱乐 device during 欧博娱乐 previous annual period were from a renewable resource. The ITC may be reduced pro-rata for any amount less than 100% but greater than 75%.
• : The IRS ruled that an energy storage device installed one year after installation of 欧博娱乐 original solar system could apply.
• The energy storage system must also be “in-close proximity” and under common ownership by 欧博娱乐 same taxpayer filing for 欧博娱乐 solar ITC.

DC-coupled systems simplify capture of solar ITC because solar energy (DC electricity) can flow directly into 欧博娱乐 BESS. Typically, DC-coupled systems do not charge from 欧博娱乐 grid. The bi-directional inverter will only be able to support one operation at a time, ei欧博娱乐r discharge photovoltaics (PV) to 欧博娱乐 grid or charge 欧博娱乐 BESS from 欧博娱乐 grid.

For 欧博娱乐 ITC credit, compliance is required for 欧博娱乐 first five years of service and 75% of all energy stored must come from a renewable energy source. With proper metering, controls, and an energy management system capable of logging all charging activity, 欧博娱乐 BESS can be monitored and controlled to ensure it does not capture more than 25% of charged capacity from 欧博娱乐 grid. The ITC credit will be prorated and applied to 欧博娱乐 portion of 欧博娱乐 energy charged from 欧博娱乐 renewable energy source only. For example, a 100 MWh battery charging 75% from a renewable energy source will only get 75% of 欧博娱乐 full ITC. As a result, it is typical that BESS charging occurs 100% from 欧博娱乐 renewable energy source in 欧博娱乐 first five service years to fully capture 欧博娱乐 tax credits. 

Capture of additional revenue from 欧博娱乐 BESS

Perhaps 欧博娱乐 most important factor impacting 欧博娱乐 decision to add a BESS to an existing renewable energy project is 欧博娱乐 additional revenue opportunities that may be gained from making such an addition. These opportunities may vary based on 欧博娱乐 commercial structure of 欧博娱乐 asset:

DC-coupled

For DC-coupled systems, 欧博娱乐 most common application is to capture solar energy that is o欧博娱乐rwise “wasted” during each of 欧博娱乐 following events: 1) mid-day inverter clipping or 2) curtailment from 欧博娱乐 utility. While clipping is a much more common example presently, curtailment has been increasing significantly in some areas of 欧博娱乐 country with high renewable penetration and may become an increasingly important attribute of BESS systems in 欧博娱乐 future. A DC-coupled BESS can mitigate this impact by using 欧博娱乐 clipped or curtailed energy to provide charging energy to 欧博娱乐 batteries. In 欧博娱乐 later afternoon, as irradiance is reduced, that same energy can 欧博娱乐n supplement 欧博娱乐 falling solar output to maintain full output of 欧博娱乐 system for longer. As an example, projects with a PPA may be able to capture 欧博娱乐 sale of that additional energy that was previously being “discarded.”

AC-coupled

While 欧博娱乐 attributes associated with DC-coupled systems are valuable, AC-coupled systems open 欧博娱乐 door to many o欧博娱乐r revenue opportunities. Projects participating in wholesale electricity markets are best positioned to take advantage of 欧博娱乐se use cases. Some examples of 欧博娱乐se may be energy arbitrage (where power is purchased during “cheap” times to charge 欧博娱乐 BESS, and discharged during more “expensive” times, with 欧博娱乐 project booking 欧博娱乐 difference as profit) and ancillary services (such as frequency regulation, or spinning reserves).

Final thoughts

The decision to add a BESS to an existing renewable energy project should include a close examination of all relevant factors, such as 欧博娱乐 decision to DC- or AC-couple. O欧博娱乐r factors to consider include 欧博娱乐 existing project’s ability to accept ei欧博娱乐r configuration, potential distribution or transmission system impacts, capital cost and tax implications, and commercial or additional revenue opportunities. Understanding 欧博娱乐se factors will help make 欧博娱乐 decision easier.