Smart Batteries: The New Standard in Distributed Storage

As solar customers increasingly recognize the benefit of adding energy storage to secure their investment in solar power, the solar-plus-storage market in the United States is poised for significant growth. GTM Research forecasts this sector to increase from $245M (2015) to more than $3B by 2020, aligned with a nine-fold increase in installed storage on the U.S. grid.

For decades, solar has depended on net metering to drive system economics. In the emerging world of utility policy changes, solar adoption increasingly depends on the inclusion of energy storage. As GTM Research notes, “There are two big factors at play: rate changes and fees pushed by utilities concerned about net metering, and more sophisticated market rules that allow distributed batteries to play in the market.”

To reach its potential, solar-plus-storage needs the right enabling technology.

The Coral Smart Battery™ provides up to 15.8kWh of clean backup power.

The Coral Smart Battery™ is one DC-coupled option that provides up to 15.8kWh of clean backup power.

Historically, residential solar-plus-storage systems are AC-coupled with 48V batteries and multiple inverters – one for solar, and a separate inverter for the batteries. This approach, heavy on equipment costs and installation time, and with low round-trip efficiency (80% range), may work for off-grid, but isn’t well suited to emerging grid-interactive applications.

The significant opportunity in the energy storage market is to deliver distributed batteries that can reach wide-scale adoption based on the ability to provide the full benefits of solar-plus-storage, including self-supply, arbitrage, and backup power. The ultimate opportunity is winning the business of utilities and other customers who will aggregate distributed storage into virtually-controllable distributed assets.

Next generation energy storage solutions will rely on “smart batteries” to deliver these benefits and win a majority of the solar-plus-storage market.

What Is a Smart Battery?

Smart batteries are energy storage appliances that combine battery modules with sophisticated power electronics to couple directly with solar energy systems. A smart battery:

    1. Operates at a nominal range of 380VDC to accept power directly from solar over a common DC bus and deliver it to a single multi-modal inverter with minimum loss.
    2. Includes a DC/DC converter that protects the battery and delivers the correct voltage and current to the inverter.
    3. Uses higher internal voltage and lower current, for higher system efficiency.
    4. Comes as a cleanly-packaged plug-and-play unit for quick integration.

Smart batteries deliver efficiency, performance and simplicity that 48-volt and AC-coupled battery systems simply can’t. The diagram below shows the common DC bus where the PV and battery connect with smart components, before power is inverted for AC distribution.

Key Smart Battery Advantages

Installed Cost

As the cost of components like PV modules and lithium batteries decreases, balance-of-system equipment and installation costs are a target for improvement. High voltage DC-coupled smart batteries improve system economics by eliminating the need for a second specialized battery inverter. Further cost improvement is possible using compatible inverter and DC/DC converter components designed specifically for OEM integration, shrinking overall system size, weight, and part count compared to conventional products.

Efficiency

Smart batteries help to increase round-trip efficiency, which pays big dividends to the system owner and makes distributed solar-plus-storage more attractive to utilities who look to maximize energy yields.

Efficiency is a powerful driver of profitability in competitive energy markets, because losses in a single component affect the performance of the whole system. Since adding energy storage involves multiple power conversion steps, extra attention to system architecture and component design is needed to maintain high efficiency in solar-plus-storage systems.

A well-designed smart battery eliminates the losses of multiple DC/AC and AC/DC conversions, and further benefits by operating at higher internal voltages.

Superior efficiency is essential in arbitrage and other daily- cycling applications, where losses acts as a “tax” on every cycle. Increasing round-trip efficiency from 80% to 90% cuts that tax in half, while delivering improved energy yields (over 12%), and has important knock-on benefits, such as lower heating loads.

Flexibility

Smart battery-based systems offer the flexibility to serve multiple applications, including arbitrage, self-supply (using storage to minimize consumption from the grid), peak load/demand management, and backup power. Multiple smart batteries can be combined on a single bus to increase capacity – even if they have different chemistries. Stacking multiple value streams can be the key to financial success in competitive markets.

Simplicity

Traditional AC-coupled solar-plus-storage systems are complex and time-consuming to configure in the field, because they involve multiple inverters, often from different manufacturers. DC-coupled smart batteries can deliver plug-and-play simplicity to speed installation, improve profitability, and enable a broader market to benefit from solar-plus-storage.

What to Consider When Developing a Smart Battery

Design

A smart battery is less complex to develop than a fully-featured “all-in-one” energy storage system (ESS), because many of the power conversion system (PCS) and communication functions can be outsourced to the system’s PV inverter. At the same time, the flexibility of the smart battery means it can work with multiple inverters to meet an array of market needs, rather than locking the designer into a single inverter supplier.

Importantly, a smart battery is a product, not a project. In contrast to an earlier generation of 48V designs that evolved from off-grid solutions, a smart battery must be carefully engineered to enable plug-and-play connectivity, provide code compliance in key markets, and streamline installation by crews with basic skills – all critical factors to deliver the necessary balance of cost and performance.

Code Compliance

An energy storage product needs to conform to safety standards for energy storage, such as UL-1741, UL-1973 and the new UL-9540. The smart battery approach makes this simpler, because it’s not necessary to meet the stringent grid-interactivity requirements of IEEE 1547, which are handled by the PV inverter.

Key Components

While chemistry and cell selection are the focus of intense design scrutiny, less attention has been paid to power electronics. Selecting the right power converter will be increasingly important as pressures mount for cost, round-trip efficiency, and sophisticated control improvements. A smart battery uses an integrated DC/DC power converter to interface between its internal cell voltage and an external DC bus that uses common connections to solar arrays and PV inverters.

Using a DC/DC converter and islanding inverter from the same supplier saves time, eliminating the challenge of integrating components from different suppliers. Suppliers offering OEM components provide advantages in design, cost, performance and time-to-market.

Build a Smart Battery with Pika Energy

Pika Energy B Link Battery ConverterPika Energy developed the B Link DC/DC battery converter to enable the development of best-in-class smart batteries. B Link is an integration-ready OEM component with the cost, efficiency, and sophisticated control features to build market-leading energy storage products. The small (13lb), robust unit has an onboard 30A DC/DC converter and works with pack voltages up to 300V nominal, delivering over 8kW.

With B Link inside, a smart battery is ready to deliver the efficiency and power capacity that utility partners and arbitrage markets are seeking. The B Link-powered smart battery couples to the Pika Energy Island system without the need for software programming or significant integration engineering.

The B Link converter from Pika Energy makes integration simple, fast, and low-cost. A B Link-powered smart battery has 8kW of power and 30A charging.

Contact Pika Energy today to learn more about our OEM solutions.