In July, 2018, Denver became the 73rd city in the U.S. to commit to 100 percent renewable energy, joining others like Berkeley, California, Madison, Wisconsin, and right here in Portland, Oregon. A large-scale commitment to grid-connected renewable energy is surely among the most important steps in the fight against climate change, but the transition will require more than just an uptick in solar and wind installations. Integrating energy storage across the entire spectrum, from residential to utility scale, will play a key role in facilitating the transformation to grid-friendly, 100% renewable communities.
The beauty of renewables lies in their ability to capture the natural sources of energy we are readily imbued with. The photons striking Earth’s surface in Texas alone could be converted to 300 times the total power output of all the power plants in the world! Their principal limitation, however, is a lack of on-demand availability—the sun only shines for so many hours each day.
This is where energy storage comes in. By pairing solar with battery backup, the sun’s energy can be harnessed during the daytime and reserved for later use at dusk, dawn, or in the complete darkness of night. In essence, energy storage can ease or eliminate reliance on the grid, and the ever-rising utility rates that come with it.
What’s more, an increasing number of utilities are offering time-of-use billing, which offers variable rates throughout the day that are priced in accordance with demand. Prices tend to spike in the morning when most people wake up and again in the evening as people return home from work. In this billing format, a home battery, even without solar, can charge itself when rates are cheapest and save that power for use during more expensive periods.
So which battery do we typically recommend? Of course, all projects are unique and each home or business has its own energy needs and financial considerations. That being said, we’ve found that the Tesla Powerwall II is the best product on the market in terms of bang-for-your-buck, ease of integration, and flexibility.
Tesla Powerwall II has a generous rating of 14 kilowatt-hours of energy storage capacity. As a lithium battery, nearly the entire stated capacity is usable. The alternative, lead acid batteries, typically only allow 50% of its capacity to be used. Thus, a 14kWh lithium battery is comparable in usage energy to a 28kWh lead acid battery bank.
The inverter on the Tesla Powerwall II is rated in terms of the instantaneous power: 5kW of continuous use and 7kW of peak power (up to 10 seconds). For context, a fully-charged battery of this size could, on its own, power your home’s essential loads (bare-bones electrical needs such as a refrigerator, garage door and a few important outlets) for as long as a day.
Beyond sheer capacity, a built-in bi-directional inverter is what sets apart the Powerwall II from the original Powerwall and the other batteries such as the LG Chem. So, not only is the Tesla Powerwall II a battery, but it includes the necessary component which enables you to actually use the battery. The inverter can take the stored direct current (DC) electricity from the battery and convert it to alternating current (AC) while also converting incoming AC electricity to DC to charge the battery. This is convenient because it allows this battery system to be retrofitted into homes with existing solar installed.
Bi-directionality also enables the Powerwall II to power your home with solar when the grid goes down. In the event of an outage, the battery keeps the solar array online by mimicking the sine wave supplied by the grid. This keeps your system online: the solar charges the battery with DC power and the battery supplies your home with AC electricity. If fully charged, the battery will trigger the solar array to shut down to avoid supplying the offline grid with power. Once the Powerwall II drops to 97 percent capacity, it will restart the array and the entire process begins anew.
Using the sun’s power day and night will go a long way in the quest for cities and states to be powered entirely by renewable resources. But in order to have around-the-clock access to power that can only be captured during certain periods, energy storage systems must be in place. If you want to reduce your utility bills, eliminate reliance on the grid, increase your home or business’s resiliency to power outages, and aid in society’s inevitable transition to 100 percent renewable energy, a battery backup system like the Tesla Powerwall II may be right for you.