Grid Neutral: How this DC transformerless inverter brings affordable off-grid power to the grid

sol-arkThe latest advancements in solar + storage systems have been a departure from the history in this category — mainly, doomsday 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 transformerless options — a sole inverter capable of handling the PV, grid and battery connections. 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 efficiency 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 solution to help families be less dependent on the grid in an affordable way. They wanted to take the autonomy and top end abilities of the off-grid inverter without losing continuous power efficiency. To do this, Sol-Ark beefed up its hardware to minimize 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 conversion 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 efficiency 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 efficiency. 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 batteries. 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.

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The reason Sol-Ark has so much peak power is it packs in twice as many components as its competitors. It is literally designed to survive a solar flare or EMP attack, which was the goal for these U.S. vets at the outset.

“We didn’t just focus on the person who wants to save on an electric bill but focused on emergency responders and state government, but in an affordable manner,” Brennan says. “To do this, we basically built a 20-kW inverter and throttled it down. We don’t have heating issues because we are not taxing the system.”

Providing the most powerful, efficient inverter for on or off-grid solar + storage does come with some new school drawbacks, at least right now. For example, Sol-Ark does not meet California’s Rule 21 criteria.

“That has not been an issue because we just don’t export power in California,” Brennan says. “We use the solar during the day, batteries at night and grid as a backup.”

On-grid extras

Sol-Ark comes ready to perform the typical on-grid capabilities like time of use and grid sell back but also has a few unique options:

Limited home mode. CTs or current sensors are placed on the mains of the house, and instead of just full grid selling or only powering critical loads, limited home mode is an in-between option. The CTs sense when any other circuit not on the critical loads panel kicks on and ramps up the solar power as much as it needs to zero the meter if it can.

“Maybe you don’t have a net meter agreement to sell back power to the grid, but you can push power to your whole house as long as the grid is up,” Brennan says. “If it’s down, you can only run critical circuits. We designed Sol-Ark 8K for seamless on-grid capability.”

A lot of people in rural areas take advantage of this because they either don’t want to deal with the electric company or have no incentive to deal with it, so they use that to push as much power as they can to the house.

Smart loads. This is a programmable load that’s not based on time but rather the batteries’ state of charge or how much PV power is being produced. Brennan explains: “We can turn on A/C or the hot water heater at 100 percent battery and solar is producing 2,000 W during the 9 a.m. to 3 p.m. time range when I’m producing excess solar. And if the solar stops producing [or batteries get to 95 percent], they shut off automatically. It’s perfect for on-grid time of use and off grid for preserving battery life.

Hot water heating takes about six panels of energy a day, and air conditioning can take about 12 panels a day, so if just those can be run from PV alone and without the batteries, that will extend the life of the batteries by at least 50 percent or more and probably reduce the battery bank size by 30 percent. The Sol-Ark system will also account for and adjust to the degradation of battery health over time.

What’s old is new again

Another question Brennan asks: Why are solar + storage customers waiting for lithium prices to drop when they will be connecting to the grid anyway? Sol-Ark’s goal is make an off-grid approach to solar + storage work on the grid without doubling the cost of a system.

“We don’t think customers need lithium if it’s just sitting there for backup; it’s a waste of money,” he says. “If you are on the grid, then take advantage of it. You can go with lower cost AGM batteries that last 10-plus years. If you have the grid where you are, get AGM batteries and use them as backup or slightly used and don’t necessarily deep cycle them. If you’re totally off grid, then we recommend lithium or carbon-based AGM that have four to five times the cycle life. You can minimize your usage of the grid, but do it to keep your battery bank at a reasonable cost/size. If you were to try going completely off grid with a traditional size home, the battery cost would make you cry.”

Chris Crowell is the managing editor of Solar Builder.

— Solar Builder magazine

Total clean energy disruption is here and three other takeaways from Intersolar 2018

Starting with the opening keynote presentations on through the innovations on the expo floor, Intersolar 2018 was all about disruption. Yes, even those of you already succeeding in solar today, if you’re not careful, you could be disrupted too. Here’s what jumped out at us in San Francisco last week.

1. Total clean energy disruption is coming, and it’s bigger than you think it is.

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Keynote speaker Tony Seba was the disruption tone setter. For those unfamiliar, Seba is a Silicon Valley entrepreneur, an instructor in Entrepreneurship, Disruption and Clean Energy at Stanford’s Continuing Studies Program and author of Clean Disruption of Energy and Transportation. His work focuses on clean energy, entrepreneurship and market disruption of the world’s major industries, such as energy, transportation, infrastructure, finance and manufacturing.

Yea, it’s a lot, but luckily he summarized it all in his presentation to kick off Intersolar. He makes the case that energy storage, EVs, ride-sharing and autonomous vehicles are on a path to converge very soon, and that the convergence of technology and business models in such a way is always the heart of true disruption.

“Every single technology has been adopted as an S curve. It is never a line,” Seba said. Consider the fact that cars replaced the horse and buggy in a mere 10-year span – and that’s in the days of, well, horse and buggy. His research shows how the tipping point for disruption has always led to a sharp S-curve trajectory, which is only getting sharper in our current time. “S curves are accelerating. It takes months or a year or two. More like J curves now. But yet there are still just straight lines in projections.”

Fast forwarding to the end scenario he lays out (which he originally laid out four years ago, and is right on track) is a world with little to no car ownership because of how much more economic sense it will make to “Uber” everywhere via fleets of automated ride services. This scenario upends much of our modern infrastructure — an abundance of storage on the grid, no use for parking lots, etc. I can’t really do it justice, so I’d recommend watching the full presentation for way more details.

The takeaway I’d like to highlight for the solar industry though is how winners of a disruption are rarely incumbents. Seba points to Kodak as a quick example. Kodak invented digital photography, had its best year ever, and then was basically out of business in under 10 years. Yes, despite that constant steep S curve, projection systems and experts and thought leaders are never prepared when that disruption hits. Companies you’ve never heard of are already ramping up to own the automated driving fleet space and random companies like Dyson are taking educated stabs in the dark at launching their own line of EVs.

For clean energy, the technology and economics are already there, it’s just a matter of a few other chess pieces moving into place, or dots connecting, or whatever other game analogy you’d like to use. If you smell what Seba is cooking, make your plans for this new world now.

2. You should try and win this funding competition.

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Did that disruption talk get you excited, or get the gears turning on the next big idea? Well, hurry and tell the Department of Energy about it and you might get hooked up with a network of people to help implement it, along with some cash.

The DOE’s American Made Challenge Solar Prize competition is awarding $3 million in prizes as well as support from the DOE’s U.S,-based network to help grow, build business plans, prototypes and funding sources for labs and innovators. Additional cash prizes are then awarded to the most viable concepts.

“What role does DOE want to have? To focus on early stage research and forge strong partnerships with the private sector,” said Elaine Ulrich, Senior Advisor, Solar Energy Technologies Office, Energy Efficiency and Renewable Energy, Department of Energy. “We know this is the cornerstone of our success, so a new way we speed innovation is through prize competitions.”

And speed it, it does. This isn’t a laborious grant application process, but a series of contests. Record a 90 second video with a strong pitch and answer four questions: What’s the problem? What’s the solution? Who is on the team? What’s the plan?

The field will be winnowed to about 20 to 40 winners (for a max of $50,000 each) to about 12 after the proof of concept stage (an and additional $200,000 possible), until finally two winners will emerge with $500,000 to launch company.

“Within six months, you could have $750,000 in cash and $150,000 in facility vouchers and tapped into a full network,” Ulrich said. “This is just the first, of hopefully many of these contests.”

Oct. 5 is the submission deadline.

3. Yes, there is still new ground to break in ground-mounted solar.

We saw and heard about several design changes in ground-mounted solar that can forge new paths in underserved segments or take over/grow established segments. We can’t talk about all of them right now (stay tuned for Solar Power International), but here are a few to note.

AP Alternatives Ready Rack

AP Alternatives Ready Rack.

AP Alternatives‘ Ready Rack mounting hardware is designed for both large utility-scale projects and small commercial projects. The small helical anchors and quick install cross bracing make the simple system robust even for high wind zones.

What we liked: This system is nimbly installed with an attachment that fits on a skid steer, which opens up the 20 to 100-kW market up much more for small solar contractors to grow and scale their business.

Soltec bifacial tracking

Live at the Soltec Bifacial testing facility.

We will have more on this topic in our Sept./Oct. issue, but just know that the industry is very focused on finding true, objective results for bifacial modules deployed in various tracker combinations. The price point on bifacial modules may not make sense for wide deployment just yet, but when it does, highly bankable systems from Soltec and Array Technologies, to name two, will be at the ready. Soltec has built a testing ground and is working with NREL and Black and Veatch to gather a complete data set on the harvest of bifacial modules on solar trackers.

Alion tracker

Alion Energy tracker.

This Alion Energy tracker is definitely not for all sites – it has a very specific value proposition for tough and dusty terrains by incorporating a self-cleaning function. There is a lot of concrete needed to install this system, but you could picture it opening up new sites in remote, harsh desert landscapes because of how often its panels could be cleaned with an automated system that uses much less water and no labor.

4. Solar + storage value is much clearer on both the large and small scale.


You’ll want to check out the Sol-Ark inverter.

On the small-scale side, we saw the most efficient solar + storage inverter on the market, and it isn’t from SolarEdge or Tesla but from little-known Sol-Ark. We explain DC transformerless architecture in greater detail in our Sept./Oct. print issue, but the quick story is this inverter is able to maintain an impressively high efficiency – both peak and consistent – in battery and grid tied scenarios.

On the large-scale side, more and more storage is being built into projects. First Solar recently signed a project contract for 150 MW of storage, for example. The key stat came from Joachim Seel, Scientific Engineering Associate at the Electricity Markets and Policy Group, Lawrence Berkeley National Laboratory, U.S.: At least six PPAs this year have featured PV-plus-long-duration storage that do not seem to be priced at a prohibitive premium to PV only.

Oh yeah, that reminds me of one more quote from Seba’s presentation: “At some point soon solar-plus-batteries will be cheaper than transmission,” Seba stated. Insert thinky emoji here.

— Solar Builder magazine