Utility-scale Solar PV + Battery Storage

Jump to: Trends, Considerations, and Resource Potential | Description of Reference Plant

Co-locating renewables with storage helps avoid curtailment of energy, reduce integration costs, provide grid services, and reduce transmission costs by sharing a single point of interconnection. As both utility-scale solar PV, wind, and battery storage costs decline, opportunities to pair the resources together are gaining traction. The 2021 Power Plan includes a reference plant for a co-located solar PV plus battery storage system.

The Council analyzed behind-the-meter (otherwise known as distributed) solar PV plus battery storage and included it in its load forecast. For more information, see behind-the-meter solar plus battery.

Solar PV + Battery Trends, Considerations, and Resource Potential

Jump to: Technology Trends | Cost Trends Development Trends | Environmental Effects Resource Potential in Region | Opportunities and Challenges 

The following section describes high level trends in technology, cost, and development for co-located solar PV and battery energy storage. In addition, it identifies resource potential in the region, opportunities and challenges, and environmental effects.

Technology Trends

There are two major technology configurations for co-located solar and battery – AC-coupled and DC-coupled. An AC-coupled system means that there are two inverters, one for the solar and one for the battery – equivalent to two distinct systems that are located at the same site. There are cost reductions in balance-of-system costs for this type of configuration, for example shared siting, land, interconnection, and fixed transmission costs. A DC-coupled system has only one inverter for both the solar and the battery. This configuration receives all of the same balance-of-system benefits as the AC-coupled system, plus the reduced cost of one inverter instead of two. However, the major benefit of a DC-coupled system is that for solar projects with an inverter loading ratio greater than 1.0 (solar module capacity is overbuilt compared to the inverter capacity), instead of clipping the energy when it exceeds the maximum rating of the inverter, it can be directly transferred to the battery and stored for later use.

Cost Trends

There is limited data available for solar plus battery storage systems to determine any major trends. As the prices of the individual resources decline, so too will hybrid developments. In general, when co-located, there are about 10-15% savings on the storage component by using shared equipment (when DC-coupled, the battery can use the solar PV inverter).

Development Trends

There are about 4,500 megawatts solar PV plus battery projects installed in the United States and over 30,000 megawatts of proposed solar PV plus battery projects in the development pipeline (megawatts capacity number applies to the solar PV component in both cases). See map below for geographic distribution of projects across the United States.

Operating and Planned Solar PV plus Battery Storage Projects in the United States

The Horn Rapids Solar and Storage Training Center, a 4MWdc solar PV plus 1MW/4MWh battery storage system is the only solar plus battery project currently operating in the region. However, there are almost 3,000 megawatts of renewable plus storage projects in the region’s development pipeline – several of which are substantial in size and with power purchase agreements in place.

Environmental Effects

See the Environmental Effects of Generating Resources for a high-level summary of some of the primary environmental effects of solar PV and battery storage resources. For an in-depth description of the lifecycle impacts associated with electricity generation, see Appendix I of the Seventh Power Plan.

The solar PV plus battery reference plant considered and assessed by the Council for the 2021 Power Plan are assumed to comply with existing environmental regulations governing air and water emissions, siting regulations, waste disposal, and fish and wildlife protection and mitigation costs when quantifiable and directly attributable to the new resource. Extensive environmental impact statements throughout the siting and licensing process as authorized by FERC are accounted for in the overall project cost. For more information, see the section on Federal Statutes and Regulation Updates and the Methodology for Determining Quantifiable Environmental Costs and Benefits and Due Consideration.

Resource Potential in the Region

As the region develops new resources to meet clean energy policies and replace retiring coal units, co-locating renewable resources with battery storage is an option that utilities and energy service providers are considering. In terms of capital cost, these projects tend to be more expensive than other resource alternatives because you are combining two resources, but as costs decline for wind, solar, and batteries in particular, the values of co-locating renewable resources plus battery storage could

Opportunities and Challenges

There are obvious benefits to co-locating resources, saving on cost, land-use, and sharing access to the grid. To understand more of the opportunities and challenges related to development of renewable resources and battery storage, see onshore wind, utility-scale solar PV, and utility-scale battery storage.

Description of Solar PV + Battery Storage Reference Plant

The solar PV plus battery storage reference plant is a 100MWac solar PV installation co-located with a DC-coupled 100MW/400MWh lithium-ion battery storage system. Cost savings are realized by pairing the systems together, requiring only one inverter and sharing the cost of siting, licensing, land acquisition, substation, and transmission interconnection. When co-located with and powered by a renewable resource, a battery storage system is eligible for the investment tax credit (ITC). The reference plant assumes all surrounding infrastructure and necessary equipment are included in the cost, for example all in-plant electrical and control systems, on-site roads, weather stations, step-up transformers, switchgear and interconnection facilities, and security, control, and maintenance facilities.

Solar PV + Battery Storage: 2021 Power Plan Reference Plants

Reference PlantSolar PV + Battery Storage
Technology Type100MWac solar PV co-located w/ DC-coupled 100MW/ 400MWh lithium ion
ConfigurationCo-located solar + battery
Nameplate Capacity (MW)100 MW
Avg. Annual Capacity Factor
Round-trip Efficiency88%
Heat Rate – HHV (Btu/kWh)
Economic Life (Years)30
Tax BenefitsITC
Financial SponsorIOU
Development Period (Yrs)1
Construction Period (Yrs)1
Earliest In-Operation Date2021
Overnight Capital Cost ($/kW)$2,568/kW
All-in Capital Cost (pre-tax benefits) ($/kW)$2,702/kW
All-in Capital Cost (w/ tax benefits) ($/kW)$2,432/kW
Fixed O&M Cost ($/kW-yr)$31/kW-yr
Variable O&M Cost ($/MWh)$0/MWh
TransmissionIOU NT
Deferred Transmission and Distribution ($/kW-yr)
Maximum build-out (MW)10,000 MW (100 units)

*All costs in 2016 year dollars. For more details and definitions of resource attributes, see Definitions of Reference Plant Components.

Maximum buildout: The maximum buildout potential for solar PV + battery storage resources follows the maximum buildout methodology, as well as the standalone solar PV and battery storage reference plants.

Forward capital cost curves: The co-located solar PV plus battery storage reference plant forward cost curve follows the assumptions of a standalone solar PV reference plant.

More information: For background analysis, see the initial presentation on utility-scale battery reference plants from the September 2019 GRAC meeting. Please note that some of the material in the presentation may have been updated between that meeting and the draft plan. In addition, see the capital/FOM/VOM cost workbooks for all resource reference plants as well as MicroFin for supplementary inputs and analysis.