Grid Offset vs. Sell Back

off-grid tiny house

Grid-tie inverters – those without batteries – are key components of a broad range of PV systems for residential, commercial, and utility-scale applications. These systems are popular, in part, due to high reliability and low maintenance needs. At the residential and commercial levels, these systems connect at the building power panel(s), and they enable customers to locally generate electrical energy during the day. The local electric utility, building inspector, and fire department may require design drawings and calculations, applications, reviews, permits, inspections, and/or special meters before such a system can be installed and switched on.

PV array and inverter size, solar radiation, location, orientation, and various environmental and seasonal factors affect how much energy a system produces. A “small” system may generate enough energy to reduce (“offset”) consumption from the grid. A “large” PV system may generate enough energy to not only meet a customer’s electrical demand during parts of the day – effectively reducing part-time consumption to zero – but even have excess energy available to “sell back” to the utility grid.

Either way, customers realize reduced monthly energy bills as returns on their investments, utility generation station pollution is reduced due to lower energy demand, and the need to build additional utility generation stations is similarly reduced. System costs may be reduced by federal, state, local, and/or utility incentives, and Time-of-Use (TOU) rates and tariffs may affect the cost of energy bought and sold.

Going a step further, a “net zero” PV system configuration is a goal for some, where the total amount of energy generated by the grid-tied PV system over a year essentially equals the total amount of energy consumed by the home or business during the same period. In short, energy generated less energy consumed equals zero.

Note, however, that the “net zero” customer still relies on the utility grid to one degree or another for all or some power during some parts of the day (i.e., at night or during cloudy daytime periods) or times of the year (i.e., in the winter when the days are short and the sun is low), and then sells excess energy back to the grid when the sun is shining brightly. Put another way, “net zero” systems still require electric power stations.

An awkward limitation (possibly) of this architecture is that due to “anti-islanding” safety features, virtually all of these PV systems stop generating power and disconnect from the grid during brownouts or blackouts, be they local or regional. It’s frustrating for many to sit through a blackout with a costly alternative energy system on the roof literally doing nothing until at least five minutes after stable utility power is restored.

Battery-based inverters offer useful and even intriguing alternatives to the grid-offset vs. sell back discussion.

Like battery-less grid-tie inverters, battery-based off-grid inverters can be installed on a home or business to reduce utility energy consumption. Ideally, the inverter loads are powered from the PV array and the batteries are recharged during the day. These loads are powered from the battery bank at night. If the battery state-of-charge drops too low, then the inverter automatically connects to the grid to power its loads and help recharge the batteries.

A unique benefit of this configuration is that (assuming sufficient battery SOC) the batteries represent a backup energy source and will continue to power the inverter loads while the grid is down. For example, these loads might include some CFL or LED lights, an energy-efficient refrigerator, a microwave, and a cell phone charger. And, this type of architecture does not require special utility connection approval since it doesn’t sell back to the grid.

For those who want to sell excess energy to the grid and have a battery backup, battery-based grid-tie inverters are available.

Grid offset, sell back, and battery backup systems require different design strategies, component configurations, and permitting. Give Inverter Service Center a call at 800-621-1271, and we’ll be happy to discuss your goals and the possible solutions.

Sizing an Inverter for Mobile Applications


Inverters are indeed handy for powering a wide range of AC loads from your DC power sources while “off the grid.” You can run everything from laptop chargers to microwave ovens to refrigerators and, just like sizing an inverter for stationary applications such as in an off-grid home, the loads will greatly determine the necessary inverter size and specifications. However, mobile applications may also warrant further analysis and consideration.

Particularly in mobile power systems, house batteries often power many DC loads such as phone chargers (through USB connections), LED lighting, and even some entertainment systems. While these loads must be considered when correctly sizing the battery bank and charging systems, they do not need to be factored into the total mobile AC load for inverter size calculations.

A mobile inverter’s major loads may, therefore, be limited to large appliances such as a microwave and a refrigerator. And while these are not trivial loads, they’re also not usually continuous. For example, a 1000 W microwave may actually be rated as an 1800 W load, but its power level setting will also vary the actual load. Similarly, a modern fridge may be specified as a 600 W load when starting the compressor, but the running load may be just 100 W or less the majority of the time.

In many cases, a 2500 W true sine wave inverter along with a healthy and well-sized battery bank should be able to comfortably handle such a load combination. The inverter’s typical specifications should indicate sufficient surge capacity for these dynamic loads, and, under normal operating conditions, it would also operate at relatively high efficiency.

Some people have considered another strategy using multiple inverters. In the example above, a large inverter could be turned on to power just the microwave, and then turned back off when finished cooking. A second smaller inverter – one with sufficient surge capacity – could then be used to continuously and efficiently power the fridge. While this approach may help reduce low load losses and conserve a bit of battery energy when the microwave is off, it would also require creating two separate AC wiring systems within the coach or vehicle. One side benefit of this approach is that the larger inverter could serve as a back up for the smaller one, or to handle unexpected loads.

Also, keep in mind that inverter specifications are typically based on limited temperature and other environmental ranges. Accordingly, a mobile inverter’s more dynamic operating environment may warrant further analysis and consideration. If the inverter is going to be installed in a confined space, then adequate ventilation may be a concern. Deployment in very cold or hot conditions may require environmental protection and/or power derating. Operation at high elevation may also require power derating, which could mean specifying a larger inverter.

Power requirements, load types, and dynamic operating conditions must be factored into sizing an inverter (or inverters) for an efficient and reliable mobile system. Give us a call at 615-285-0663, and we’ll be happy to discuss your application and help you identify a solution that fits your particular requirements.

About the Author – Jim Goodnight – also known as “crewzer” — is a retired solar industry application engineer, product manager, and forum moderator and has previously written for Home Power and Solar Professional magazines.

Pure Sine Wave Inverter vs. Modified Sine Wave Inverter


Power inverters are, well, powerful devices which help you live with independent mobile power systems and improve your comfort level whether you’re on a boat, RV or living off-grid.  With an inverter, you don’t have to rely on hard-to-find DC-powered appliances or a noisy generator when your home or business loses power due to a strong storm.

One of the big questions when choosing to buy an inverter is which do I buy — a pure sine wave inverter or a modified sine wave inverter?

This article points to the pros and cons of both types and will help you make the best choice for your application.

Choosing the Best Sine Wave Inverter for Your Mobile Application

Inverters are generally electronic devices that convert DC voltage to AC. For example, you can use an inverter in your RV to convert 12 Vdc power from the battery to 120 Vac power to charge a laptop computer.

There are two popular inverter types: Pure Sine Wave (aka True Sine Wave) and Modified Sine Wave (aka Modified Square Wave). PSW inverters generate a sinusoidal waveform similar to that of AC voltage from the grid. MSW inverters generate a chunky waveform resembling steps.

On a per watt basis, PSW inverters are generally more costly than MSW inverters. However, PSWs will power any device designed to operate from the grid at home or in the office.

Sensitive devices like microwave ovens, CPAP machines and other medical devices, clocks, some chargers for cordless tools or laptop computers, radios, audio equipment, and similar products may require a PSW inverter to operate properly.

High-quality PSW inverters often have the surge capability required to start a high-surge load like a fridge compressor. Sizes typically range from the 120 W range to several kW.

MSW inverters are less costly per watt than PSW versions. They are popular built-in or add-on accessories in vehicles and are often good enough for powering non-sensitive loads like fans and lights, and some may be compatible with battery chargers for cordless tools, laptops, and cell phones. However, some of these loads may buzz, and they may run hotter (less efficiently) than normal. Sizes range from 20 W to several kW.

Give us a call at 615-285-1734, and we’ll be happy to discuss the appropriate solution for your particular needs. Visit Inverter Service Center today!

About the Author – Jim Goodnight – also known as “crewzer” — is a retired solar industry application engineer, product manager, and forum moderator and has previously written for Home Power and Solar Professional magazines.

Meet Mitul Chandrani – Xantrex Guy From Day One

Mitul Chandrani-Xantrex

A Conversation With Mitul Chandrani, Sr. Marketing Manager, Xantrex

With vision and purpose, Schneider Electric in 2008 bought a Canadian company called Xantrex. They were interested in the renewable division because of its market potential, which was rebranded under Schneider Electric. But Xantrex’ mobile unit (boats, RVs, and trucks) remained independent.

“Xantrex was one of those fortunate acquisitions” where the business benefited while still retaining its core teams and values, said Mitul Chandrani, Sr. Marketing Manager. “There was no bureaucracy or red tape you normally associate with a global company.”

In essence, Xantrex enjoys the autonomy of an entrepreneurial arm within a large but supportive organization which speaks to the strength and confidence of Schneider leadership in leaving a well-established brand alone.

Xantrex Guy From Day One

Mitul was a “Xantrex guy” but didn’t miss a step when Schneider Electric acquired the company. In fact, there was virtually no change in his day to day or with the people in charge. The General Manager,  the head of Product Development, the OEM sales manager and Mitul are all still with Xantrex today, 10 years later.

Trained in civil engineering, Mitul uses his master’s degree in marketing to design and conceive solutions for dealers, serving more as an outside sales person than a traditional marketer. He thrives on being on the front line understanding how Xantrex can help its partners, like Newmar, Keystone, Highland Ridge, Jayco, and Forest River.

For example, they just launched at the OEM level a new electrical system for Class B motorhomes called Freedom eGen as an option for the end user which eliminates a generator altogether.

Why an Inverter Upgrade Just Makes Sense

Mitul’s enthusiasm for Xantrex solutions was evident as he told me about projects he’s been working on. One major marketing campaign over the past couple of years has been to encourage consumers to “Upgrade to an Inverter Charger.”

He detailed impressive statistics while explaining market opportunities.

Most of the RVs sold from the factory come equipped with a converter which is an AC to DC charger. It charges the batteries. That’s all it does.

Conversely, not only does the inverter/charger charge the battery it also provides an AC power source. So any AC-powered electronics and appliances in an RV can be powered easily using an inverter.

Xantrex makes inverter/chargers. They don’t make converters. Hence, the “Upgrade to an Inverter Charger” campaign targeted to RV dealers.

Instead of replacing a broken converter, Xantrex recommends the dealer offer a choice to upgrade. While an inverter/charger is slightly more expensive than a converter, it offers two distinct features: (1) a two-year warranty vs. a one-year warranty on many converters and (2) an AC power source, which is not available in a converter.

The campaign has worked so well that sales for inverter/charger models they’ve targeted to promote for the aftermarket have more than doubled, Mitul said.

Another campaign which has enjoyed great success is called “Your Gateway to Worry-free Dry Camping.”

The goal of running a print campaign in Trailerlife and Motorhome was to educate RV end users to the limitations of relying on a converter. In addition to the benefits mentioned above, an inverter/charger

  • Lasts longer.
  • Charges the battery better.
  • Powers any downstream loads while plugged into shore power (which you can’t do with a converter).

Everyone has a smartphone these days, but you can’t plug in your phone charger into a converter. You need an AC power source to do that. In educating dealers, Xantrex is not only offering end users a practical solution to their connectivity needs but also improving the bottom line for dealers with incremental revenue and improved customer satisfaction!

Freedom X for the Win

Xantrex expands the Freedom Series with new sine wave inverters.

“Freedom is like a Corvette. It’s so strong it’s become a sub-brand across multiple industries,” Mitul said. There are more boats, trucks, and RVs with the Freedom product than any other make or model. Almost every class of RV built in the U.S. between 1980 and 2004 has a Freedom product on it. The majority of boats over 50’ built in the late 90s and early 2000s have a Freedom installed.

Like any technology, Freedom has evolved. In 2017, Xantrex launched the Freedom X. Their marketing message needed to speak with one voice across the various market segments. What symbol would communicate the same thing to different audiences? They decided on the horse because of its strong connotation of Freedom and Power. In using the stallion, they were able to tie everything under one brand. (Freedom SW was launched in 2011 for the marine market.)

Power Technology Market Trends

Inverter Service Center’s Ray Barbee and Xantrex both agree that lithium-ion and solar are two areas where consumers will see rapid growth over the next five years.

“Manufacturers are way more open to lithium-ion than they were two years ago,” Mitul said. In the next few years, he believes that “a lithium-ion option will be standard on almost all RVs and boats.” That’s why the new Freedom X and Freedom SW are both compatible with lithium-ion batteries.

In addition, Coachman and Midwest, two massive RV companies, already have endorsed and are offering Freedom eGen. After extensive testing, they’ve decided to offer it as a factory option.

Of course, solar is big, Mitul said. Every RV wants solar panels on it. It’s also becoming popular in the truck and marine industry. Xantrex manufactures solar-charged controllers which work with the solar panel and inverter/charger and helps capture this market. The Freedom SW and Freedom X also integrate into a solar power system.

Finally, Mitul sees Bluetooth integration allowing for one single control panel managed from one place. Soon you’ll be able to control all instrumentation and accessories through your phone or tablet.

Personal Relationships Matter

Mitul works closely with everyone at Inverter Service Center and enjoys a strong relationship. “If they don’t hear from me for a week or two, they shoot me an email or Jordan will give me a call or PJ would say ‘where the hell have you been,’” Mitul said with a laugh. “That’s the kind of close relationship we have.” He credits PJ Gonzalez, ISC Manager, for cultivating a family atmosphere.

PJ Gonzalez, Jordan Hall and Ray Barbee

The team at ISC is also direct about issues that need fixing. PJ is very clear and transparent about his expectations and doesn’t hold back. He gives Xantrex a chance to make changes.

“Xantrex had some issues early on and after working closely with PJ the turnaround has been amazing,” Mitul said.

“Now we are so strong I think ISC is the closest partner we have.”

Thank you Mitul for being an equally great partner!