Off-grid device using OutBack inverter in Hawaii.

As the aging US power grid suffers more catastrophic power outages due to fire, snow, or other natural disasters, more Americans may consider the benefits of disconnecting from all power grids and living completely off the grid. This concept may seem weird and simple, but the reality of ensuring that an independent power system runs for as long as possible is much more complicated.

Although it is important to properly design and install actual solar panels on off-grid systems, sensitive power electronics must be planned more carefully. The first step is to choose a suitable inverter for the environment.

Manufacturers have been committed to designing inverters that can withstand the harshest off-grid conditions. Perhaps the biggest design choice is to create a ventilated inverter or a sealed inverter. A typical string inverter installed in a residential garage is ventilated to ensure sufficient air flow to keep it cool. Cooling is important because when inverters overheat, they will shut down to protect themselves. However, when the inverter is installed in an off-grid device, the internal fan assisting the ventilation process may suck in unwanted debris.

"Roads are basically mud, so they lift up a lot of material in the air. The inverter that will draw the atmosphere directly into the system will happily draw in all the dirt, and then you know that when you shake the box, it will A pound of dirt flows from the bottom," said John Weber, OutBack Power’s international sales manager.

The larger vents in a typical residential inverter may also invite rodents and bugs to nest inside and cause damage. For installations close to the ocean, exhaust will cause salt to enter the inverter and corrode metal parts.

Toxic visitors at off-grid installation sites in the Colorado mountains. Renewable Energy Apparel

"My rule of thumb is that if you can smell the ocean, there is salt in the air. It is very easy for people to choose this system. If you can smell the jungle, then the jungle is Will come for you," Weber said.

The solution to these off-grid environmental problems is to choose a sealed inverter design. OutBack's FXR/VFXR inverter series adopt a sealed design with only a small spiral at the bottom, allowing the inverter to breathe. This means that it absorbs as little as possible the surrounding atmosphere.

Sol-Ark also produces sealed hybrid inverters, which CTO Tom Brennan compares to the long warranty and lifetime of micro inverters.

"Most external rated hybrid inverters are indoor electronic devices inside steel umbrellas, but our outdoor electronic devices are 100% isolated from rain, dust, humidity and bugs, giving them a design life of more than 20 years," said the company. Lennan said.

The disadvantage of sealed inverters is that they do not self-cool like ventilated inverters, so their overall power rating is lower. But for longer life and less maintenance requirements, this trade-off may be worthwhile.

OutBack adds design elements that help keep the sealed inverter cool, such as an internal fan to keep the air flowing, and an external fan on the top to blow air through the heat sink outside the box.

Morningstar agrees to completely abandon fans in its off-grid inverters. Product development and application consultant Ezra Auerbach said that the manufacturer currently has a small off-grid inverter SureSine on the market, but is developing a larger product called MultiWave.

"If you don't have a fan, you won't bring dirt and dust from the environment," Auerbach said. "The sealing aspect of the device will also make it more resistant to salt intrusion. Of course, if there is no fan, there is one less fragile thing."

Morningstar must ensure that its products can operate at higher rated temperatures because there are no typical cooling elements such as fans and large vents. Morningstar engineer Doug Grubbs said that most of the company's equipment is rated for at least 45°C (113°F). The company uses passive ventilation in the form of a top radiator to prevent overheating of its unreleased off-grid inverters.

Off-grid houses are also usually located in very cold areas, which requires a completely different set of inverter design features. Aaron Mandelkorn, President of Renewable Energy Outfitters in Colorado, specializes in off-grid solar + storage projects in low temperature and high altitude areas.

Renewable Energy Outfitters off-grid installation in Colorado ski resort.

Mandelkorn first considers its operating temperature range when choosing an inverter.

"At 12,000 feet and 11,000 feet in the middle of winter, the temperature of these inverters is -15°F, not to mention the batteries and other things. Even its ability to actually function is sometimes affected," he said.

The inverters he chooses must be able to operate at these temperatures, not only for performance considerations, but also to ensure that they are installed "in compliance with specifications" and are therefore still eligible for warranty protection.

"If you have a problem, if you are too cold or too high, you won't get support from the manufacturer," Mandelcohn said. "For complex off-grid systems, we somewhat rely on the manufacturer's support to help deal with various technical issues."

He and his team still conduct numerous site visits to repair off-grid devices themselves, but they are not cheap.

"We came to a place where everything was frozen, we came to a place where everything was just cooking, we just saw various electrical faults because they couldn't handle it," he said. "Many times, in order to repair the construction site, it is necessary to use excavators and snowmobiles to clean the road and repair the road in winter."

This process may cost about $10,000 for the customer, but some relatively simple steps can be taken during the installation and operation and maintenance process to largely avoid those expensive visits.

OutBack’s Webber stated that if possible, installers should protect the inverter by building a strong structure around the inverter, preferably made of metal, because rodents cannot pass through it. The inverter should also be installed on treated wood, which rises from the ground and makes it difficult for animals to enter from below. Weber also recommended that installers use wire mesh to keep small animals away from insulation and wires.

Wyoming uses an off-grid device with OutBack inverters.

"At the end of the day, Mother Nature will always try to get into your system. Every obstacle you create will slow down this process significantly," Weber said.

In hot climates, the structure should be ventilated to again ensure that the inverter does not overheat. It can be drilled and covered with wire mesh as another barrier against animals. Morningstar's Grubbs also recommends installing an external fan to keep the structure cool.

Since off-grid inverters are usually paired with batteries, Auerbach said it is very important to ensure that there is enough air space between the inverter and the lead-acid battery to solve the problem of exhaust gas emissions. He also encouraged installers to invest in good temperature sensors and voltage sensors to pay close attention to the system and avoid overheating or other unexpected shutdowns.

Weber said it is also important to remove any large trees or branches that may fall on the system during the installation process and to develop a regular O&M plan to ensure that the system is not affected by nature or any other factors.

A power shed that accommodates electronic equipment for off-grid solar projects. Renewable Energy Apparel

In cold climates, REO's Mandelkorn emphasized the importance of installing inverters and batteries in conditional insulated spaces. He usually installs power electronics and batteries in a "power shed" that uses direct ventilated propane heaters for insulation and heating.

"A little insulation and a little heat can have a very, very long effect," he said.

In order to keep the system running and minimize site visits to operation and maintenance, Mandelkorn said that he chose an inverter with comprehensive remote monitoring capabilities like Sol-Ark. If the system informs him that there is a malfunction, he can remotely view the problem and determine whether the problem does not require long journeys into the mountains, such as DC overvoltage caused by sunny days, or whether it is a critical problem that can only be solved by visiting the site in person.

Sol-Ark's Brennan said that the manufacturer will remotely monitor its entire fleet and send an email to installers when they find an error.

"Although the problem is usually a setting that we can change remotely, we can find installation errors before they cause hardware damage," Brennan said.

Mandelkorn said that in his project, he put the "availability" of the inverter above the maintainability, which means that he hopes his customers can use the integrated monitoring platform to understand what is happening in the system, but he does not want them Must personally service their system if it requires any electrical work.

However, Webber stated that OutBack is committed to making its inverters easy for end users to repair because manufacturers understand that installers are sometimes far away from these off-grid systems.

Weber said: "If they have the ability to install new graphics cards in their computers, they have the ability to replace these boards and restart and run the inverter."

Off-grid solar + storage projects can be complicated, but with proper design and installation considerations and strong monitoring, installers can ensure that their customers enjoy many electrified days without relying on power lines.

Kelsey is the senior editor of "Solar World".

"If you don't have a fan, you won't bring dirt and dust from the environment," Auerbach said. "The sealing aspect of the device will also make it more resistant to salt intrusion. Of course, if there is no fan, there is one less fragile thing."

This has been the Achilles' heel of the inverter for many years. It is for this reason that I have replaced several inverters over the years. The fan brings dust into the bearing, stops cooling, and the inverter trips due to temperature. If you plan to use a fan for your design, make it easy to visually inspect, snap-in, plug-and-play, or throw it away altogether. Now using SiC or GaN transistors, people can build more powerful inverters that require almost no cooling, and have 25 years of solar photovoltaic and inverter systems. There seems to be some "promise" that sooner or later there will be battery chemistry and electrolyte pairing, resulting in a 50,000 cycle battery. Even if it is charged/discharged twice a day, it will have a 68-year-old energy storage system.

This is the key to the utility becoming an unknowable appendage of the home system. Using current HMI and tag-based programming, algorithms for power outage resilience, interactive grid operation, or islanding can be created. As the overall installation cost of the battery pack becomes more reasonable, people can “become bigger” and in most cases (most of the time), their home is out of their system.

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