Solar, Storage, and Software: A Three-Pronged Approach to Energy Management
Tom Lombardo posted on October 26, 2014 | 10009 views

While most residential electric customers pay for energy use (in kWh), commercial and industrial customers pay not only for total energy use but also for peak demand (in kW). It’s conceivable that a business could reduce its overall energy consumption but still have a high electric bill because of one massive power draw - possibly due to firing up a group of machines - over the course of the billing period. Energy consultants will point out these flaws and suggest more intelligent power-up procedures, but there may be times when a massive power draw is inevitable. How can businesses avoid paying high demand charges?

One way is to generate their own energy. Another way is to buy extra energy during times of low demand, store it on site, and use that energy to cover their peak loads. Two companies - one that makes solar panels and another that sells intelligent storage solutions - are saying, “Let’s do both.” Kyocera Solar’s USA division is teaming up with Stem to sell integrated packages that include photovoltaic (PV) power systems, behind-the-meter battery storage systems, and energy management software.


Image courtesy of Kyocera Solar USA

Peak demand often occurs on hot sunny days when everyone is using their air conditioners. Some utilities charge time-of-day rates, with the electric rate being higher during late afternoon and early evenings. On sunny days, a PV array can generate power when demand is highest, especially if the panels face west or southwest instead of due south. That’s great for time-of-day pricing, but air-conditioning isn’t the only cause of high demand, and there’s no guarantee that it’ll be sunny when the facility needs to pull a lot of power for a brief time. That’s where storage comes into play.


Image courtesy of Stem, Inc.

Stem sells energy management systems that include batteries, monitoring equipment, and control software. The system allows a customer to buy excess energy when demand is low and use that energy when a large power draw is needed, rather than incurring the high demand charge from the utility. And with the addition of a PV array, the customer can simply store the power that's generated on site instead of buying excess energy from the grid. This not only lowers the customer’s electric bill, but it eases the stress on the grid. It’s good for businesses and good for utilities. 

Image courtesy of Stem, Inc.

Stem’s basic storage unit - the PowerStoreTM - is a 30 kWh Lithium-iron-phosphate battery bank with an integrated three-phase inverter that’s capable of producing all standard (US) industrial voltages. It’s designed to accept an AC input, rectify it, and use the resulting DC to charge the battery bank. The PowerStore’s round-trip efficiency is over 80% - typical for battery storage -  and it’s capable of delivering peak outputs of 18 kW. The units can be cascaded to provide greater storage and demand capacities.


As I’ve mentioned before, intelligent routing of power is they key to reducing grid stress and incorporating renewable energy into the mainstream grid. Stem’s PowerScopeTM software tracks electricity rates in real time, monitors and remembers on-site usage patterns, and makes predictions based on that data. It then decides when to buy, store, and release energy.

Image courtesy of Stem, Inc.

Financial Return

Common criticisms of renewable energy and storage are the up-front cost and the long payback period. Stem took a bold move by offering zero-percent financing on its systems. The customer pays no up-front costs; instead, they pay a monthly fee to Stem over a contract period. They don’t provide details on the agreement unless you’re a prospective customer, but it’s probably something like a Power Purchase Agreement with an option to purchase the hardware at the end of the contract.

We Have the Technology...

Although I often write about new technology in the renewable energy field, the solution to our current energy problem doesn’t have to wait for any technological breakthrough; what’s needed are more creative solutions using existing technology. Sure, it’ll be great when hardware becomes more efficient and less expensive, but a little ingenuity (and the word engineering is derived from the word ingenuity) goes a long way. I hope more companies look for partnerships like this one, which blend a variety of existing technologies to solve new problems.  

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