“Will we be able to use the energy from our grid-tied PV system when the grid power is off?” The typical answer is no—unless you have a battery backup system, which is more expensive than a batteryless grid-tied system and requires routine maintenance. During a grid failure, most inverters made for batteryless systems shut down, making energy from the PV array inaccessible. But a new inverter from SMA America can feed a load—without batteries.
When Jeff and Kathy Ball wanted a PV system that would offset all of their home’s electricity usage, backup power was one main point of interest. The Balls don’t experience frequent grid outages or have critical loads that absolutely must run during a loss of utility power, but they were interested in fully utilizing their potential solar-electric system. They considered battery backup, but the added cost of batteries and a battery-based inverter was approximately $5,000 more (about $24,475 installed cost) than a batteryless grid-tied system (about $19,000).
The decreased energy yield due to lower system efficiencies of a battery-based system was also a deterrent. The weighted efficiency of a typical grid-direct inverter ranges from 94% to 97%, while a battery-based inverter’s efficiency is lower— 91% to 93%. A standard charge controller, which is also needed for a battery backup system, incurs another 1% to 2% loss, making the battery backup system even less efficient. Over a year, the losses would add up to about 340 kilowatt-hours for the Balls’ proposed 5-kilowatt solar array.
While the Balls weighed the pros and cons of a battery backup system, another option became available: beta-testing SMA America’s Sunny Boy TL-US inverter. During a grid outage during the day, this inverter can supply up to 1,500 watts (at 120 VAC) from the PV array to a dedicated wall-mounted, switched outlet—without batteries.
From time to time, there are small technological advancements that have a large impact on the solar industry. The new TL-US inverter feels like one of those small but significant advancements.
This inverter has all the latest features—a wide DC voltage input range, which allows for more flexibility when considering array-to-inverter matching; transformerless construction, leading to higher conversion efficiencies compared to transformer-based inverters, along with a decrease in overall weight, making for an easier and safer installation. The inverter’s dual MPPT inputs allow array strings to be separated, reducing the potential for shading and module-mismatch inefficiencies and increasing flexibility in array placement. But what sets this inverter (and its series models: 3, 3.8, 4, and 5 kW) apart is its “secure power supply” (SPS) function. Given the impact of the SPS function, it will be no surprise if other inverter manufacturers introduce similar features in their own future models.