Inverters are the electronic heartbeat of a solar system, connecting solar arrays to the grid and increasingly, to battery storage. As utilities continue to shift rate structures in ways that often harm grid-tied residential solar customers, inverter manufacturers are working to make battery integration seamless.
Solutions described as “battery-based” or “hybrid” inverters are becoming more common across the manufacturing sector. But what do these terms actually mean?
Sol-Ark manufactures both inverters and batteries and calls its solution a “battery-based inverter.”
Tom Brennan, engineering manager at Sol-Ark, said that most inverters in home installations are grid-tied string inverters. They don’t work with batteries, but instead have to sell all the power they produce back to the grid.
“A battery-enabled inverter, or battery-based inverter, is something that can do a lot more than just sell back power to the grid,” Brennan said. “It can store power, it can work off-grid, it can store power for time-of-use [rate structures].”
Battery-enabled inverters differ from traditional inverters because when there is a grid outage, standard inverters must shut down completely per Rule 21, while hybrid inverters connected to batteries can simply switch to an off-grid mode temporarily and continue to power the home.
“I think the real story here is that inverters are doing a lot more than they ever have,” said Jeremy Niles, marketing manager at Pika Energy.
They’re doing more for a number of reasons. Perhaps the biggest is as states and utilities shift away from net metering, solar customers are getting less credit for selling power back to the grid. Combining a hybrid inverter with even a small amount of battery backup can allow homeowners to self-supply power, avoid demand charges and peak time-of-use rates and still get high value for solar systems despite shifting state policies.
Time-of-use rate programs like in California charge customers higher rates for electricity used during what utilities determine are “peak” periods of the day (when power consumption is highest and solar production is low) and lower rates during off-peak times when consumption is lowest and solar is supplying plenty of power to the grid.
Solar customers with hybrid inverters paired with batteries can choose to store power during the peak solar production times in the afternoon and consume that power in the evening, when electricity costs are highest.
“Battery-based systems are exploding because they can do time-of-use shifting and get around these solar restrictions,” Brennan said.
Other utilities incorporate demand charges when customers consume energy above a certain number of kilowatts.
“In a lot of scenarios, that demand charge can make up the majority of someone’s bill,” Niles said.
Hybrid inverters paired with batteries can help avoid demand charges by storing solar energy during high solar production times, then be programmed to self-supply power from the battery instead of buying power from the grid once the house consumes a certain amount of energy. That way, the home never crosses the high demand threshold and is not charged the extra, sometimes exorbitant, fees.
Pika Energy’s Islanding Inverter is one solution that can perform demand management for customers.
“[Customers] will set the system up so that should they get close to getting that kind of demand on, the system will kick in and ease that demand, meet that demand using battery power or solar power, to prevent that demand charge from being applied to their bill,” Niles said.
Tabuchi Electric’s hybrid inverter can also be programmed to avoid both demand charges and peak times. The inverter software can be customized to satisfy different market requirements. For example, in California, Tabuchi’s inverter is customized with an “economy mode” to use stored power during peak time-of-use periods, and in Hawaii the inverter has a “customer self-supply mode” to help customers use all the solar power they produce, since they cannot sell it back to the grid.
“Each of those markets has its own advantages and disadvantages, and we try to come up with operation modes that can be unique for each market,” said Tanvir Khan, research and product development engineer at Tabuchi. “We try to make it flexible so that one solution has all these operation modes.”
Tabuchi’s hybrid inverter+storage solution is sold as one package called the EIBS (Eco Intelligent Battery System).
Since utility rate design and state solar policy is ever-changing, Tabuchi has the ability to upgrade its inverter operating modes remotely at any time. Khan calls this making inverters “future-proof.”
“The definition of future-proof is that whenever the utility changes their utility rate demand or anything they try to make more complicated with solar panels, the battery can come into play because that’s the free variable,” Khan said.
Including storage and battery-ready inverters in new installations could soon become even more fruitful than simply avoiding peak time-of-use rates and demand charges. With SEIA leading the way, solar+storage advocacy groups are pushing for nationwide incentives for adding batteries, like a federal investment tax credit for energy storage.
California leads the way with storage incentives at the state level with its Self-Generation Incentive Program (SGIP) that gives customers rebates for qualifying distributed energy systems installed on the customer’s side of the utility meter. The California Solar and Storage Association is pushing for the SGIP to be extended for another five years in the form of SB 700, which was passed by the California Assembly at the end of August.
Understanding the terms
Although inverter manufacturers use verbiage like “islanding,” “hybrid” or “battery-based” inverters, the inverters are still separate from batteries in most applications except the Tesla Powerwall 2, which integrates an inverter+battery in one case, and some others.
“The industry trend is not necessarily putting the battery and the inverter together like Tesla. Instead it’s having the right-size battery bank and inverter so that you’re primarily using solar power and stored solar power throughout the day and night and the grid is basically a backup,” Brennan said.
Many battery-based inverters don’t require a battery pairing from the start. If and when customers decide to add a battery to their solar installation, all the infrastructure is already in place to easily integrate storage.
That flexibility can be very helpful as new renewable energy requirements and policies take effect in different states, like the mandate of solar on all new homes in California. Homebuilders can install energy storage to reduce the amount of PV they must install or offset other efficiency requirements. If builders choose to just install solar and not storage on a new home, using a battery-ready inverter for the project can give homeowners the flexibility to add a battery at a later date.
Niles said that in the past, the type of solar modules was considered the most consequential choice for customers in a solar array. The biggest consideration now is the choice of inverter.
“Basically, the most important thing people can do nowadays is get an inverter that will accept a battery. A battery-ready inverter,” Niles said. “Because there’s a good chance you’ll need one in the future.”
“”Sol-Ark manufactures both inverters and batteries and calls its solution a “battery-based inverter.””
Over 20 years ago, this is what was used to “protect” assets like data centers or SCADA servers and is still used today. These Uninterruptable Power Supplies or UPS units are set to use continuously charged battery banks in which the D.C. buss drives the inverter and the loads connected to it all the time. With the proper balance of energy storage, solar PV and smart programming in the hybrid inverter, the home could run off of solar PV most of the time and off peak or super off peak electricity the rest of the time.
As Vern Sherwood pointed out, the old Xantrex XW6048 was ahead of its time. The XW series rolled out in about 2,000 and had the ability to be used as a pure grid tied inverter, or could be wired to a battery back system for grid tied, battery backed, or could be set up with the proper programming as an off grid battery powered system. The thing at the time that amazed me was, this one unit could do all three with programming. There was also a setting that this inverter could be used as grid tied, with the ability to sell a preprogrammed amount of energy to the grid also. Sounds a whole lot like the hybrid inverters that are promoted now-a-days.
I think worth mentioning would be as well:
Conext XW+ Solar Hybrid Inverter System
mpi hybrid series
Duane Schweigert says
How does a on grid micro inverter system adapt to hybrid solar ? Like the direction the inverter tech in going.
Sajith Kumar says
I have 500-700 V input from my PV panels producing 4K+ watts on grid. When the grid is off, can i connect the 600 Volt DC to an inverter and get AC output to my house equipments without a battery.?Do we have an inverter that can do this with 600 V input from PV?
None of these hybrid inverters provide power from your panels when the grid goes down…..they just use what’s stored in your battery for a few hours then you’re done until the grid comes back up.
All this is about to change when Enphase releases their new IQ8 microinverter in a few months.
It’s so sophisticated it can form it’s own micro-grid…..which means the energy generated by your solar panels can be used 100% of the time the sun is shining with or without the grid.
It’s a revolutionary change….and will be a God send to hurricane areas.
Ellington L Ellis says
Are any good independent commercial inverters sold that work with lithium systems. Most inverters sold are designed for lead acid batteries. Thanks
B Fehr says
The Powerwall 2 still needs an inverter. The inverter that comes with the battery cannot be used to convert the DC power from the solar panels to AC. Its primary use is to convert AC power coming from the primary inverter or the grid to DC before storing it in the battery.
Is it really new technolgy ? (Hybride inverter) , i had many proposals from chineese manufacturers since 2016.
Vern Sherwood says
Xantrex was doing this type of stuff in the late nineties with there SW line of inverters. There just more programable features now available.
This idea was thought of a long time ago and the federal government never wanted to put any money into it, because it was obvious that it was a better way to go. For the originator look up Lepcon, Lumeloid, and Alvin Marks.
Marks raised money several times and failed to produce any sort of working prototype. Lumeloid was really just an unproven idea.
Danny McCullough says
Do you know if Solar City panels can use this equipment, since I bought outright several of my panels and rebates paid for the rest.
Kelly Pickerel says
Danny, the panels aren’t usually the issue, it’s the inverter that needs to be compatible for energy storage.