Uninterruptible power supplies (UPS) are often installed to protect critical equipment and loads from power outages and other voltage and current problems. Many UPS systems constantly regulate the input power, thereby maintaining a constant and uniform power supply. UPS systems are typically used on computer hardware or other equipment where an unexpected power outage could result in death, serious business disruption, or data loss, such as in data centers, telecommunications facilities, hospitals and power plants.
Although UPS systems have batteries and obviously store energy, they are not synonymous with standard battery energy storage systems that are commonly added to the electrical grid these days. In fact, UPS systems are often not allowed to export electricity to the grid. However, that doesn’t mean they can’t be used to reduce energy bills and provide a return on investment for homeowners.
“Historically, inverters waited for something bad to happen – they were sort of insurance devices,” said Yaron Binder, vice president of product management at SolarEdge Critical Power, as a guest on The POWER Podcast. “But I think there’s a growing understanding that these could also act as an energy storage system and actually create some sort of benefit of, say, revenue for the customer, on top of just sitting there waiting for the power to go out.”
In the past, many UPS systems used lead-acid batteries, which were not suitable for cycling operations. Today, however, many inverters are equipped with lithium-ion batteries, which are much better suited to regular cycling. Therefore, there are fewer downsides to using a UPS for more than just emergencies.
Binder said there are many smart ways to use inverters. “One of the things you can do, for example, is use the inverter as a demand response component,” he said. Although, as mentioned earlier, homeowners are not able to export electricity directly to the grid, they can reduce their demand for electricity when electricity prices rise by using their inverter to meet the needs. internal. This will save money when prices are high and the inverter can be recharged when electricity prices have returned to a lower rate. Of course, a minimum load level must be maintained to support the primary function of the UPS, which is to power critical equipment in the event of an emergency.
Another innovative solution that can save homeowners money is to essentially level out power demand peaks using the inverter. “Sometimes you can use this battery to defer an increase in site infrastructure,” Binder said. He referred to a hospital he worked with and where it was done. The hospital had two medical scanners that consumed a lot of power when turned on. However, demand was much lower when patients were actually being tested by the machines.
“We had a case where installing these two scanners consumed more power than the distribution panel was capable of, but upgrading that distribution panel was very, very expensive,” explained binder. To solve the problem, the inverter was used during start-up, then when the load decreased during the test, the inverter returned to its normal standby role. “That way we were able to use that battery and defer that infrastructure upgrade. So that was another great use for an inverter,” Binder said.
UPS system designs vary. Two common types are monolithic and modular. Binder explained that a monolithic system is “just a big block” that has one of each component – a charger, an inverter and a static switch. “It usually has no built-in redundancy,” he said.
Modular systems, on the other hand, are constructed from smaller components. “So everyone scales the solution up and down,” Binder said. “The more power you need, the more modules you put in. And one of the things you can do is put in more modules than absolutely necessary. So just increase the size of your system and eliminate redundancy. It also provides the flexibility to use the inverter for more than just emergencies, potentially helping to pay for the most powerful system.
Another advantage of a modular UPS is that if one of the modules fails, it generally does not propagate to the rest of the system – the other modules will generally continue to operate and protect the load. In addition, the modules are easier to maintain. “Often you can hot-swap a unit, which means you can perform your maintenance while the system is running. So you don’t have to shut down that important machine or computer that’s backed up by the UPS,” Binder said.
The investment required for a monolithic system may be a little less initially, but the benefits of modular systems may outweigh the costs over time. Yet both types of systems are regularly installed, as circumstances and needs vary. Monolithic systems are frequently used in small (a few kW) and large (MW-scale) inverters, while modular systems have established their place in the middle.
“If you look at the very, very large systems, your mega data centers, then they’re going to put in at least two of everything anyway, so they have different ways of doing their redundancy. So they will often use monoliths,” Binder explained. “But in the middle, so between a few tens of kW and, I would say, a year and a half to two MW, I think that the modular becomes the ideal solution.”
To hear the full interview, which includes additional inverter use cases and more discussion of how solar power and storage come together in installations, listen The POWER Podcast. Click on the SoundCloud player below to listen in your browser now or use the following links to go to the show’s page on your favorite podcast platform:
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—Aaron Larson is the editor of POWER (@AaronL_Power, @POWERmagazine).