Home Battery Q&A

Answering the most common builder questions
Home Battery Q&A

You've decided you want battery storage. How do you go about choosing the right one for your customers? Battery makers will help you through the process, but you're more likely to make the right choice if you go into those discussions with some basic knowledge.

According to Adam Weinstein, a regional sales manager with battery-maker Sonnen, builders tend to ask a lot of the same questions when deciding what battery type and system to choose for their homes. We asked him what those questions are and how he generally answers them.


Q: What main types of home batteries are on the market today?

A: The two most common types for home storage are Nickel Magnesium Cobalt (NMC) and Lithium Iron Phosphate (LFP).

NMC batteries are made for rapid charge and discharge, and also pack a lot of power into a small, mobile package. Those qualities have made them popular with some electric vehicle manufacturers. However, news stories about thermal runaway, or explosions, in electric vehicles have made some homeowners reluctant to install them.

LFP batteries weigh more and cost more, so they're unsuitable for electric vehicles. However, this type of battery has a longer lifespan and is designed specifically for stationary applications with no chance of thermal runaway, making the chemistry inherently safer and ideal for home installation.


Q: How long do home batteries last?

A: Manufacturers' warranties are a good way to compare the service life of two batteries but the actual lifespan will depend on battery chemistry and how often it gets cycled (from completely charged to completely discharged and back). Manufacturers of LFP batteries claim their batteries to last for 10,000 to 15,000 cycles, or over 30 years on a home that charges and discharges it every day. An NMC battery, by contrast, might be limited to a few thousand cycles, or 5-10 years on the same home.


Q: How do I size the battery?

A: It depends on a few key factors: the size of the solar array being integrated into the home, the size of the loads that the homeowners intend to back up with the battery in the event of an outage and the number of daily loads needing power.

Here are three sample battery sizes along with the loads they will power in backup mode for a typical home.

Battery size: 4kW/6kWh

  • Refrigerator
  • Microwave
  • Three lights
  • One computer
  • One tablet or phone
  • Three extra outlets


Battery size:7kW/10kWh

  • Refrigerator
  • Microwave
  • Three lights
  • One computer
  • One tablet or phone
  • One television
  • Three extra outlets
  • One single-room air conditioning unit


Battery size:8kW/16kWh

  • Refrigerator
  • Microwave
  • Three lights
  • One computer
  • One tablet or phone
  • One television
  • Three extra outlets
  • One single-room air conditioning unit
  • Two fans
  • One Washer/Dryer combination


Q: Where can my battery be installed?

A: The biggest consideration is temperature and moisture. Most batteries will deliver full power in a temperature range of 40F to 120F, so if you build in an area that gets hot in summer or cold in winter you don't want to put them in an unheated room or in direct sunlight. Most people install them in a semi-conditioned basement or garage.

Batteries are available with outdoor-rated enclosures that protect them from the elements, but an outdoor rating is not a failsafe option.

Some batteries, specifically LFP, are safe enough to install in a conditioned living space with the wiring totally hidden. In fact, many of the LFP batteries Sonnen has installed in German homes are in living spaces as they're considered a status symbol.


Q: Do I have to wire the house differently?

A: If you intend to use the battery for backup power, the only difference is that the electrician will need to wire a sub-panel, called a protected loads panel, with the circuits you want to power in the event of an outage.


Q: What is the difference between an AC-coupled and a DC-coupled system?

A:  An AC-Coupled system has two inverters: one for the solar panels and one for the battery. All power flowing to and from the battery—whether from the grid or the solar panels—flows through the battery inverter.

AC-Coupled is the easiest way to add a battery to an existing PV system and also provides redundancy—if one of the inverters fails, you don’t lose both your solar and storage. Also, the AC-coupling allows homeowners to charge their batteries from multiple power sources: solar, the grid and even gas generators.

In a DC-coupled system, the battery is charged directly from the panels. The panels and the battery also share a single "hybrid" inverter. Because this system type requires one inverter, equipment costs are lower, making it popular for new construction specifically with new solar installations.

With a DC-Coupled system, the batteries will only be charged by the solar array.


Healthy Growth for Solar Battery Storage

While the West Coast still accounts for most installations, the technology is taking hold in all parts of the country.
Healthy Growth for Solar Battery Storage

It used to be that a typical grid-tied solar electric system only worked when the grid worked.  If a storm took out the power lines the homeowners ended up in the dark, despite those shiny panels on the roof.

That's changing thanks to more efficient and cost-effective battery technology, as well as to utility involvement.  Greentech Media Research (GTM) estimates that for the first time, total installed home battery capacity of 15.9 megawatts has reached near parity with utility-scale deployments of 16 megawatts.

It's on track to get even bigger. "The residential [storage] market this year is going to be over five times the size of the market last year," said GTM Senior Analyst Brett Simon. And while California and Hawaii account for 74 percent of that capacity, installations are also growing elsewhere, with products from companies that include LG, Panasonic, Samsung, Sonnen, and Tesla.

Distributed Grid

Electric utilities are helping to drive this growth.  For instance, Walpole, NH-based Unity Homes recently built a home in Guilford, Vermont with a 10-kW solar system and a Tesla Powerwall 2.0 battery supplied by Green Mountain Power (GMP) at an installed cost of $1,500.  GMP Communications Director Kristin Kelly says that the batteries usually cost $7 to $8,000 installed, but that the utility wants to create a distributed storage grid it can draw from during peak demand times.  It began installing batteries in late 2017 and will have 2000 in place by the end of 2018.

Of course, most homeowners expect tangible benefits from that $1,500, so it's no surprise that most batteries are going into rural homes where winter storms often cause outages.  The batteries provide an estimated 8-12 hours of backup power, and the subsidized cost makes them cheaper than a whole-house generator.

Outage protection certainly drives demand for storage where there's severe weather, such as winter storms in New England or hurricanes in Florida and the Gulf states.  But without a utility incentive, they can still be a hard sell.  For instance, Sean Buckley, Owner of Harvest Sun Solar, a solar installer in Tisbury, Mass. says that with no subsidy only 10% of his customers have been willing to pay full price for a backup battery.

If customers in Buckley's market didn't pay a fixed electric rate, he might get more interest.  According to Energy Sage, an online solar energy marketplace, natural markets for storage are where the utility’s rate policy includes any of the following: time of use rates, demand charges, the lack of net metering, or net metering reimbursement based on avoided rather than retail costs.

Staying Under Threshold

Some utilities charge customers a higher rate if they exceed an energy use threshold.  Others have net metering arrangements that don't reimburse homeowners at the retail rate but rather at avoided cost—what the utility would pay to buy or generate that power.

Both apply in the Milwaukee area, where Tim O'Brien Homes recently broke ground on Wisconsin's first Zero Energy neighborhood.  Homes at Red Fox Crossing in New Berlin will be certified under the Department of Energy’s Zero Energy Ready Home program as 40% to 50% more efficient than a typical new home.  They will also include rooftop solar panels.

While these homes don't include battery storage, Craig North, the company's VP of Product Innovation and EEBA board member, says the company plans to include it in future projects.  "Our utility providers have put a tariff on over-production of solar electricity," he says.  "Homeowners also only get 25 cents on the dollar for excess power put back into the grid."

Avoiding Peak Rates

In time-of-use areas, the system can be configured to avoid buying power when it's most expensive.  That describes much of California.  "The differential between Summer on-peak and off-peak in San Diego is as high as 32 cents per kWh," says Michelle Mapel, Senior Director of Sales and Marketing at battery-maker Sonnen.  "If you can use the battery for the four hours of peak, you will definitely save money."

That potential savings led Bakersfield, California builder Dave Packer to complete a Net Zero Electric model home with solar panels and a Powerwall 2 battery system.  When Pacific Gas & Electric's rates are low in midday, excess power from the panels flows into the battery until it's fully charged.  The home can draw from this stored power in late afternoon and early evening when rates triple.  The battery also provides backup power but Packer says that outages in his area are rare and short-lived.

PG&E, like Green Mountain Power, offers batteries at a subsidized rate of $1,500, which Packer believes will motivate more homeowners to buy.

Even with time-of-use rates, a lot of homeowners aren't going to pay $7,000 or more for a battery option.  Gene Myers, CEO of Thrive Home Builders in Denver, and EEBA Board President, has a solution.  Rather than a battery option, put them in all homes and build the cost into the selling price.

Thrive will certify all of the 240 homes it completes this year under the Department of Energy's Zero Energy Ready Home program.  All homes include rooftop solar panels and a storage battery on a wall in the garage.

The battery helps mitigate time of use rates and provides backup power.  One battery can handle basic lighting, the refrigerator and freezer, as well as enough outlets to charge electronic devices.  It won't run the heat pump, but Thrive's homes all have backup furnaces.

So far there hasn't been any customer pushback.  "Having a Zero Energy product is part of our brand," says Myers.  However, he also admits that given his homes' price point of $500,000 and up, the extra cost isn't the big deal it would be in a lower-priced home.

Thrive Homes in Denver is one of a growing number of builders who are outfitting homes with solar panels and storage batteries.  Shown here: the ZEN model.

Community Power

Thrive isn't the only company that has decided to make batteries standard.  Sonnen is working with Mandalay Homes in a 2,900-home development in Prescott Valley, Arizona.  Every house will have an individual solar system and a battery that together add about one percent to the home cost but save the homeowners 20 to 30 percent on electricity, thanks to a utility policy that gives a lower rate to customers who can completely power their homes for a portion of the day.

Mapel says that Sonnen is negotiating with the utility to configure storage in other communities in a way that meets the utilities' load-shifting and other needs.

In Birmingham, Ala., the utility has actually taken the lead on a community-wide storage effort.  Alabama Power is working with Signature Homes on a 62-home "Smart Neighborhood."  It will include enough solar capacity to run all the homes, which will have HERS scores of around 45, or 35 percent more efficient than standard new Alabama homes.  It will also have Samsung lithium-ion battery storage.

What makes the Smart Neighborhood unique is that rather than being installed on individual homes, the panels and the storage will be centralized in a 2-1/2 acre site, creating what the utility calls a microgrid.  Customers won't be able to switch to battery power during peak demand times but have agreed to let the utility adjust their loads to reduce total electric use via smart thermostats and other controls.

Jim Leverette, a Research Engineer with Southern Company, Alabama Power's parent company, says that the utility envisions battery-enabled microgrids as part of homebuilding's future, and is using the neighborhood as an R&D project.  "We want to evaluate the pros and cons and to get a better understanding of technical challenges."


Batteries such as those from Sonnen help mitigate peak demand charges and act as a backup power supply. They also look good.

Zero Energy Goes Mainstream

Wisconsin's first net zero neighborhood is selling ahead of schedule
Zero Energy Goes Mainstream

Do you question the appeal of Zero Energy Homes to mainstream homebuyers? Then you may be missing an opportunity. Tim O'Brien Homes, which builds in the Milwaukee and Madison, Wisconsin metro areas, is finding a strong demand for such homes if they're well designed and if buyers understand the financial and lifestyle benefits.

The company just started work on the state's first Zero Energy neighborhood, Red Fox Crossing in New Berlin. All homes in the 34-lot development will be certified under the Department of Energy’s Zero Energy Ready Home Program, a well as the ENERGY STAR, WaterSense and Indoor airPLUS programs.

Buyer interest has been encouraging. As of May 2018, before drywall work on the model home had even been completed, a full one-third of the homes had been pre-sold. That's seven months after sales opened, which is a faster sale pace than in the builder's other neighborhoods.

That success is supported by a four-legged stool that includes the right market, the right land, the right systems and the right message. Let's take a look at each.

The Market

Homes at Red Fox Crossing are priced in the mid-500's, which is move-up for the Milwaukee market. Each will have a 7-9 Kilowatt rooftop solar system that, on an annual basis, produces at least as much electricity as the home uses.

A relatively high price point makes sense for a first-time solar project, as homeowners in that niche are more willing to absorb the cost of the panels into the mortgage. But the high-end niche isn't the only market for rooftop solar. Craig North, Tim O'Brien Homes' Vice President of Product Innovation, is confident that the evolution of this neighborhood will help the company understand how to offer cost-effective solar to more price-sensitive buyers.

"We see real potential at the lower end of the market," he says. "We think rooftop solar would make sense to any value conscious buyer regardless of demographic or price point."

The homes at Red Fox Crossing don't look like "solar" homes, which is one secret to the builder's success.

The Land

Solar will work on any lot with a clear view to the Southern or Western sky, but the right land provides those views while also supporting the builder's design goals.

To ensure that outcome O'Brien partnered with Neumann Companies, a local land developer. "We found a great piece of land that accommodates a North-South road pattern," says company principal Matt Neumann. That means the homes will face East or West.

Wait a minute -- don't you need a South-facing front or back elevation for solar? Not necessarily, says Neumann. "Most people prefer not to have solar panels on the front of their home, and with this orientation the builder can put them on a south-facing side elevation."

The Systems

All of the community's homes will have grid-connected solar panels installed by SunVest Solar, a Neumann company and a sister company to Tim O'Brien Homes.

When it comes to systems, however, solar is the easiest one for the builder. The real challenge is engineering a home in which savings from the electricity generated by the panels more than covers the extra cost they add to the mortgage payment.

To meet that challenge the builder needs to get a lot of details right.

Take the mechanical system. Each home at Red Fox Crossing will feature higher efficiency two-stage furnaces that, according to North, will offer immediate savings for the customer. The mechanical system will also keep the homeowners comfortable year-round while providing clean, fresh air and maintaining optimal humidity levels.

The home's thermal envelope will include energy-saving features that minimize the load on the mechanical system. And it will be designed and detailed for long-term durability.

This type of high performance building is really the next step in homebuilding's evolution. It includes the elements of "green building" but also goes beyond them. Indeed, raising the bar of home performance is an important part of Tim O'Brien Homes’ culture. "We're constantly evaluating how various elements of our homes work together as a system," says North.

That constant evaluation is crucial for any builder wanting to go down this path -- getting to Zero Energy means addressing a lot of small details. Over the past five years for instance, improvements at Tim O'Brien Homes have included increasing exterior insulation levels on foundations and framing, making heat recovery ventilation a standard feature, and using spray foam to seal attics before installing the insulation.

North says that much of the company's knowledge about high-performance building came from its involvement in the Energy and Environmental Building Alliance (EEBA), where North serves as a board member. He credits EEBA with introducing the company to the Zero Net Energy concept: he learned about the Department of Energy's Zero Energy Ready Homes program at one of EEBA's annul summits and decided to adopt that program's specs.

EEBA also helps the company meet its continuous improvement goals by providing the opportunity to network with other high-performance builders. It's a community of pros -- builders, manufacturers, architects, engineers, and others -- who are committed to helping one another build better homes and grow their businesses.

"The ability to learn lessons from top industry professionals has been instrumental in helping us differentiate ourselves from the competition," says North. "And the connections made through networking have allowed us to pilot some cutting-edge products and technologies."

The Message

As part of its continuous improvement system, Tim O'Brien Homes has every one of its projects rated according to the Home Energy Rating System (HERS) Index from the

Residential Energy Service Network (RESNET). Feedback from those ratings help show the company ways to build higher quality, more durable, greener, energy efficient homes while providing strong value to the customer.

The HERS system also has marketing advantages. That's because it helps buyers understand the True Cost of Homeownership and directs them to builders who can lower those costs. The HERS Index website lists builders who commit to having their homes rated for energy performance and, according to RESNET, some Multiple Listing Services (MLS) are beginning to list HERS Index scores.

There's even data to support the payoff from a good HERS score. A 2016 study by the North Carolina Building Performance Association of more than 34,000 high-performance homes found a strong correlation between a lower HERS Index rating and a higher sale price.

In fact, a lower True Cost of Homeownership is an important part of Tim O'Brien Homes' marketing message. It seeks to help buyers understand that though a high-performance home costs a bit more to build than a code-built home, it doesn't cost any more to live in. The message is that people can get more home, more comfort and more peace of mind without spending any more money.

This understanding is especially important when it comes to solar. North points out that helping homeowners understand how Solar fits into the True Cost of Ownership model is a key making it more mainstream. The company has worked hard to address that.

Tim O'Brien Homes has found that people will embrace high-performance construction once they understand Total Cost of Ownership, and the company's marketing materials reflect that.

At the Cutting Edge of Home Warranties

Is electronic monitoring part of homebuilding's future? This builder has used building science training to get ahead of that trend.

To some builders, a perfect world is one where they get through the warranty period without issues, then never hear from the homebuyer again until it's time for another new house.

Greenville, SC builder Todd Usher calls that shortsighted, and has begun differentiating his company with a bolder approach. Usher is founder and president of Addison Homes, which builds 15-20 semi-custom homes per year, and he is rolling out a series of technology enhancements that will provide homebuyers with value for years after the sale. The first enhancements will consist of sensors that monitor critical home systems and alert Usher or his staff to potential problems that require follow up.

It's the seed of what will eventually grow into a long-term warranty program that will benefit his buyers and bring in extra revenue. What has given him confidence to offer such a program? He gives much of the credit to ongoing training in high-performance building for himself and his employees.

Health Check

Usher got the monitoring idea from the auto industry. "GM sends me monthly updates on my truck's health and tells me when it needs service, so I thought 'why not do that for homebuyers?'" He realized that, done right, monitoring and notification could help him build and maintain brand loyalty.

He started with a crawlspace humidity sensor. Crawlspaces are common in the South, and Addison now installs Ultra Aire's Sentry product in all new homes. It measures humidity and temperature, and sends an alert if the numbers fall outside of pre-defined parameters. The sensor sends the data to the cloud (via the homeowner's wifi) then to a handheld app that Usher can use to keep track of multiple homes. He alerts the homeowners if anything looks like it needs a closer look.

Crawlspaces are just the start. Addison will eventually outfit homes with equipment that monitors a variety of home systems. The possibilities Usher is considering include:

  • Uponor's new Phyn Plus product to detect leaks at the main water supply
  • Navien's NaviLink to monitor system status on his homes' tankless water heating systems
  • Lennox wifi-enabled thermostats to alert him to potential problems with the heating and cooling system
  • SMA inverters to track efficiency and output of the rooftop solar panels

The ultimate goal is to offer extended warranties on all these systems. He will supplement this with warranties on additional items—for instance on termite damage if the homeowners sign up for an annual termite inspection and treatment.

While Addison does not currently charge for monitoring, that's in the works. The company will eventually give new homebuyers free monitoring for two years then offer to continue it, along with warranty protection, for a reasonable monthly fee. Usher is confident that most customers will opt-in once they get used to the benefits.

He admits that monitoring HVAC and hot water systems will take some negotiation, as manufacturers like to award that service to the dealer or installer. But he insists that homeowners prefer to deal with one trusted source. He is hoping that volume will help bring manufacturers around— Usher's company is part of the CB USA buying group, which could provide some clout —but that alone won't be enough. "We still have to demonstrate our expertise," he says.

Training Needed

Of course, before you can demonstrate that expertise you have to have it. And if you want to introduce an extended warranty program your work quality better be such that you don't get many warranty calls. That's where training comes in.

Take those Southern crawlspaces. They're notorious for condensation problems, but Usher avoids such problems by closing the crawl and bringing it into the building envelope. The benefits he has gotten from this and other high-performance building techniques have made him a big believer in training. "If you promise a durable home with no moisture or indoor air quality problems, you better learn how to deliver on that promise."

Usher's training has included Southface's Earth Craft House program as well as training on RESNET's Home Energy Rating System (HERS). But he says the most valuable ongoing education has come from the Energy and Environmental Building Alliance (EEBA), where he recently joined the board of directors.

"EEBA offers some of the best, easiest to understand building science training I've ever received," he says. "It has helped me build better homes in every way: more energy efficient, with better water and air quality, and fewer callbacks. It's also the most affordable training I know of." In fact, he now sends all of his staff through EEBA's programs.

What's the Payoff?

The bottom line, says Usher, is that learning how to build high performance homes is making it possible for him to offer value-added services he would not have otherwise considered.

As a bonus, the monitoring service is also helping him improve his product. For instance, the crawlspace moisture detector on one house was sending alerts during heavy rains. He investigated and found that while there weren't any problems, the foundation drain wasn't emptying as fast as he would like. "It told me that I needed to pitch the drain a bit more on the next house."

Monitoring also earns its keep as a marketing tool. "The feedback we've gotten from homeowners is all positive," he says.

Usher wants to grow Addison's annual volume to 30 or 40 homes over the next couple of years, and he knows that referrals from happy customers will play a big part in that growth. What better way to get those referrals than to be known as a builder who exceeds their expectations by taking care of them long after you've finished the work?

Do you want to learn how to build high-performance homes that are comfortable, durable, healthy and energy efficient? The Energy and Environmental Building Alliance offers an annual three-day Educational Summit, as well as one-day training seminars in various parts of the country. For more information or to sign up go to

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