Solar Builder

NOV-DEC 2018

Solar Builder focuses on the installation/construction of solar PV systems. We cover the latest PV technology (modules, mounting, inverters, storage, BOS) and equip installers/contractors with tips and tools to make informed purchasing decisions.

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18 N OV E M B E R / D E C E M B E R 2 0 1 8 T he latest advancements in solar + storage systems have been a departure from the history in this category — mainly, dooms- day preppers and hippies getting off the grid, man. No, the solutions of tomorrow are grid-tied but built to reduce a home's dependency on the grid, using time of use strategies to shift loads to avoid the most punitive electric rates. The sexiest solar + storage inverter advances in this area are DC transformer- less options — a sole inverter capable of handling the PV, grid and battery connec- tions. Because these inverters will be grid- connected, they prioritize continuous power efficiency instead of peak power. This is fine unless a customer is looking for an on-grid system that also can handle battery backup capabilities because that requires high peak power. There's also the efficiency loss when converting from PV to battery and back to AC. An inverter starting at 97 percent efficiency could be at 92.2 percent or lower depending on the brand by the time the energy finally makes it to its destination. So, yes, DC transformerless is a streamlined, future-proof architecture, but you will be making a compromise in effi- ciency somewhere. Well, except with the Sol-Ark inverter. Peak vs. continuous Sol-Ark is a new inverter on the block (or grid, I suppose). It is the brainchild of U.S. veterans looking to engineer a solu- tion to help families be less dependent on the grid in an affordable way. They want- ed to take the autonomy and top end abil- ities of the off-grid inverter without losing continuous power efficiency. To do this, Sol-Ark beefed up its hardware to mini- mize conversion losses. The result: Sol- Ark can deliver 96.5 percent efficiency in on-grid and 93 percent in off-grid and time of use scenarios with minimal con- version losses. On average, Sol-Ark needs 10 to 15 percent fewer solar panels and 5 to 30 percent less storage. That is serious savings. "On our system, we have an internal 400-volt bus, and we convert high voltage solar panels to that 400 volts, and then that's converted to AC," says Tom Brennan, engineering manager for Sol- Ark. "When we go to the batteries, we focused on a super-efficient conversion method that allows us the highest effi- ciency directly into a 48-volt battery." The end result is 95.5 percent efficiency from battery to AC. Where many inverters in this space lag is in AC to battery efficiency. Outback, for example, is rated about 82 percent effi- ciency. Sol-Ark hits 96 percent efficiency because of a different methodology for pumping power in and out of batteries — a powerful 185 amp DC-to-DC charger. Other DC transformerless options out there like Pika and SolarEdge are designed for newer 380-volt Lithium bat- teries. But Brennan notes these batteries are still 50 volts internally and require a double conversion every time going in or out of the battery. It's why Sol-Ark has focused on just making 48 volt batteries more efficient. Your on-grid customers might want storage as backup and to have power when the grid is down. This again is when peak power is crucial to handle motors starting up. For example, SolarEdge and Outback Skybox are not off-grid solutions. They only deliver 5 kW on the battery and little additional peak power means they can't start up A/C or well pumps. Pika has a per string optimizer, and if you don't use it, it won't work off grid because it's not an AC-coupled system. BOS NEW IN Grid Neutral How this DC transformerless inverter brings affordable off-grid power to the grid By Chris Crowell

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