Power to the PV People: How Evergrid keeps home solar up when the grid goes down

Power to pv people

Nothing confuses a grid-tied solar newbie more than the fact that they won’t have power when the grid goes down. Standard inverters need the grid to maintain the AC voltage waveform and provide surge power, and without the grid, a standard inverter can’t function. Sorry, that’s just the way it is, but can I interest you in this $30,000 battery system? … Hello?

That’s why we’re turning a spotlight onto the Evergrid from Maxout Renewables — a winner of Round 3 of the American-Made Solar Prize from the U.S. Department of Energy. The Evergrid is a 30-in. by 32-in. by 20-in. unit that allows a standard, grid-tied solar inverter to power a home when the grid is down with no battery system needed.

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It’s such a “duh!” idea that everyone has overlooked it, even Maxout founder Eric Cummings. “I can’t say why this hasn’t been tried before, but it took me way too long to warm up to the idea, and I am pretty open minded,” he tells us.

Cummings and the Maxout team, which owns the pending patents, stumbled into the idea for the Evergrid as they were developing their own hybrid solar inverter design to provide backup power.

“No matter what I tried, I found the design needed so much overprovisioning of power, protection and storage components that it really didn’t make economic sense,” Cummings tells us. “I kept wishing I had the benefit of a modest amount of inertia in the waveform like the grid has because of the literal inertia of its generators. That’s when I thought of using a generator/flywheel combination to solve the problem, but dismissed it pretty quickly because I reasoned that this would be widely done if it made sense.”

This article originally appeared in the Q1 2021 issue of Solar Builder. Subscribe for free, print or digital (or both!) right here.

The opportunity


The Evergrid provides surge power, voltage stabilization, load management and line balancing to power refrigerators, lights and air conditioning. You just tie it into the main panel as you would a generator. Priced at just $1,000, it is a cost-effective, safe way for homeowners to maximize the value of their solar installations regardless of grid conditions.

The idea may have remained on the shelf for the Northern Calif.-based company if not for “fire season” and “public safety power shutoffs” becoming the new norm in the state.

“Power shutoffs were never that big of a deal for us until a year ago, and then we realized how majorly disruptive they were. And in other parts of the country, this has been a problem for a while. So we got a rude awakening,” says Kristen Pace, COO of Maxout, pointing specifically to the plight of solar owners in Puerto Rico after Hurricane Maria. “There were 12,000 installs on the island, and many were leased, paying $100 a month for this solar power. And they were out for six months but still had to pay their leases. A lot people were shocked. They didn’t read the fine print because of course you’d think you’d be fine … it’s like a bug in the system.”

In California’s case, the market is now flooded with battery backup options for homeowners to add and solve this issue, but those carry a high price tag. Great business if you can get it, for sure, but it being the only option for a customer who already owns their own generation source feels unfair.

“After having weeks-long outages to protect against wildfires, we were brainstorming answers to the question, ‘what’s the least you can do to retrofit a solar array to provide backup power?’” Cummings says. “That was when we started to look seriously into the economics of generators and found them to be pretty compelling.”

Joseph Cataldo of Florida’s Goldin Solar, who is all set to be an early adopter, definitely sees this as a no-brainer.

“Nowadays, consumers tend to understand they are going to require some means of energy storage in order for their system to function during grid outages,” he says. “If they don’t know that when they first call in, my sales team makes sure they understand. However, I think it’s naturally disappointing to have lost power while you have a source of electricity production on your roof.”

This is especially true in Florida where even mild hurricanes and tropical storms can knock out power for several days, meaning spoiled food, no AC, no phone charging, etc.

“This device would make it possible to run the air conditioner, refrigerator, ceiling fans and lights, recharge tablets, phones and devices, operate small kitchen appliances such as a microwave and coffee maker during the day; all of which add a significant level of comfort, relative to the scenario of having no access to electricity whatsoever,” Cataldo says.

Design and installation

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An Evergrid would do much more than stabilize the waveform and protect power electronics though. Its surge capability means that solar arrays and batteries could be sized for average power rather than peak power.

“There are a few tricky things the Evergrid needs to do,” Cummings explains. “It needs to balance average production and consumption. It needs to keep the AC voltage that the inverter sees tightly in spec, regardless of load transients. It needs to spin up the generator from a standstill. Fortunately, it turns out the electronics to do this are not expensive.”

The Evergrid has a PV input terminal, a PV output terminal and a generator output terminal. To install the Evergrid, you wire the PV inverter to its PV input terminal and the PV output terminal to an appropriately rated breaker on the main panel. If you are doing a retrofit, you can use the original PV circuit breaker. You wire the generator output terminal to a separate 50-A breaker that is mechanically interlocked with a service disconnect switch or to an automatic transfer switch.

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Wiring the generator output is the same as wiring a gas-powered backup generator. There is no need for a critical-load subpanel, but there is no problem with using one. The Evergrid uses openHAB to integrate with smart home devices and controllers. You can also monitor and control it directly from a smartphone. It is compatible with Rule 21 and legacy inverters.

“This device is designed to absorb excess energy from the array, more than the home is consuming in that instant, or supply a deficit of energy, if energy production from the array drops momentarily due to cloud cover,” Cataldo explains, “So, consumers will need to monitor their rate of electricity consumption and make sure that it is less than their array’s rate of energy production at that time of day; and for smoothest performance, they should aim to use electricity at a significantly lower rate than the array is capable of generating .”

The Evergrid makes this easy. If an appliance turns on when there isn’t enough reserve power, the Evergrid immediately sends an alert to your phone to turn off the appliance and avoid a blackout.

The battery backup’s backup

The Evergrid does more than just provide backup power. For systems equipped with an AC- or DC-battery backup system, taking the Evergrid’s surge power into account lets you size a system for the sustained load rather than maximum load. That could be huge upfront cost savings. Evergrid can handle most of the transient surges, which also extends the life of the batteries.

“We were initially just looking at using this instead of batteries but now we realize it would be a good complement to someone with a battery backup,” Pace explains. “If you’re someone who wants or has a Tesla Powerwall because you need overnight power or time-of-use, this will augment that by giving you extra surge capacity, and it will also help extend the lifetime of the batteries. There are several recent studies that show that fast discharge, such as that from a surge load, is damaging to lithium-ion batteries.”

There will also be applications for customers who do purchase battery storage and wish to increase the surge capacity of their system, without increasing the energy storage capacity.

“There will be applications where the array is larger than the maximum charge rate of a given battery pack, and historically, a section of the array would need to be removed from the backup system and installed ahead of the isolating relay or transfer switch, so that the battery pack would not be charged too fast during backup operation,” Cataldo says. “Instead, it would be possible to add an Evergrid to the backup system to absorb excess power, such that the entire array could be available to charge the battery system, substantially expanding the amount of energy available throughout the day, especially in the morning and afternoon.”

What’s next?

Prototype units are being tested at Sandia National Labs in the first quarter, followed by pilot testing with some installers after that, and UL testing over the summer. The goal is to take orders in the summer and commercially debut by the end of this year. Pace says the first production run of a few hundred units will hit some early-adopter installers in California, Florida and Puerto Rico. After that, they’ll get back to finishing what started this all: a solar inverter.

For just $1,000, it barely registers on the final price tag and seems like a no-brainer addition to any new or existing home PV system.

“We will likely solicit all our existing customers and let them know when this becomes available, and I think we would include it as a standard feature, but still itemize the cost of the Evergrid such that it could be removed, if a customer elected to,” Cataldo says. “I wouldn’t recommend that anyone do so, because the added functionality is an incredible value, but we want our customers to be able to evaluate the cost of the PV array versus quotes they would be receiving from competition and fully understands that they are getting an added feature.”

— Solar Builder magazine

[source: https://solarbuildermag.com/featured/power-to-the-pv-people-how-evergrid-keeps-home-solar-up-when-the-grid-goes-down/]


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