Solar Energy Storage: Page 7 of 14

Emerging Technologies, Markets and Applications

Leesa Lee

Senior director of marketing, Stem, stem.com

What are the components of the Stem system? How does the system operate? 

The Stem system is a modular, integrated storage solution that includes predictive analytics and advanced energy storage to reduce electricity bills for commercial and industrial customers. The system works by predicting usage and strategically charging and discharging the on-site battery to reduce peak loads. Power is not exported to the utility grid. The Stem system is installed indoors behind the utility meter in parallel with a customer’s distribution equipment.

How does the Stem system assist grid-direct PV systems?

Stem helps PV customers in three ways. The system reduces demand charges, particularly with respect to the volatility of solar production. It provides energy during the “shoulder” peak periods when consumption is still high but PV production has diminished. Finally, it future-proofs against tariff changes.

In what markets and regions does Stem offer storage systems? What is the installed capacity?

Stem currently focuses on marketing to the Californian and Hawaiian markets and has more than 7 MW of storage under contract to be deployed. We’re also working with utilities to deploy aggregated storage.

What are the key drivers in customer interest?

Demand charges currently are the key driver. To reduce demand charges, businesses need to manage peak usage effectively. Despite detailed rate-structure information, it is challenging for even the most conscientious business owner to manage peak loads. Deploying PV can reduce base loads, but peaks that result in high demand charges can still occur, especially if the PV production is volatile. As utilities need to recoup more of their infrastructure costs through higher charges on peak loads, behind-the-meter storage can play a large role in addressing the resulting demand charges experienced by end customers.

What battery technology does the Stem system use? What is the expected cycle life of the battery pack? 

The Stem system uses lithium-ion phosphate batteries. They were chosen for their combination of energy density and safety. These batteries are under warranty for 10 years.

What financing opportunities are available for the Stem system?

The Stem Zero program offers zero-down financing. Customers can get a Stem system with no money down, a fixed, low monthly payment and flexible options after the term ends. Given the nascent nature of the solar storage space, customer awareness and education are the biggest tasks that we have ahead of us at Stem. Awareness among solar developers and installers is a vital part of our marketing efforts for 2014.

Tom Leyden

CEO, Solar Grid Storage, solargridstorage.com

What are the components of the Solar Grid Storage PowerFactor solar-plus-storage system?

Solar Grid Storage PowerFactor systems have building blocks of 250 kW and 500 kW. A combination of these can be deployed for PV projects with arrays starting at 150 kW and building up to the MW scale. Our enclosures include all the components needed for solar plus storage, including a dual-use inverter, battery storage, controls, disconnects and safety devices. We typically use lithium-ion batteries that can be sourced from several well-known and bankable suppliers such as LG, Panasonic and Samsung.

Article Discussion

Related Articles