How cutting-edge passive solar design keeps homes cool

By SolarCity

August 26, 2015

Our recent posts on how historic homes stayed cool without air conditioning generated a ton of great feedback.

Now, a cutting-edge design approach is focused on the same goal in modern homes.

It’s called “passive solar design.” It was pioneered in the U.S. in the 1980s, refined in Europe in the 1990s, then reintroduced stateside in the early 2000s.

With passive solar, the home is designed to be comfortable with little or no use of an air conditioner or furnace. Instead, the home relies on the science of climate, thermodynamics and fluid mechanics, along with high-tech home features, to keep occupants cool or cozy.

15423582330_6c92a88d23_kImage: Jeremy Levine via CC

Passive solar energy follows a set of basic design principles:


Orientation to the sun

The home is carefully positioned based on its latitude and the known path of the sun across the sky. The passive solar design incorporates a large, usually south-facing, bank of windows. The windows are placed to allow as much sunlight as possible to enter the home in the winter, and as little as possible in the summer. The latter is usually aided by various control features (see below).


Thermal mass

The home’s interior includes some form of thermal mass—a feature that absorbs heat. A typical thermal mass is a concrete slab or stone floor. Insulated masonry walls can serve the function, too. In the winter, the thermal mass absorbs heat from the sun, and releases it as air in the home cools. In the summer, the thermal mass “scrubs” heat from the air during the day, and releases it only when the home cools at night.


Air circulation

Solar heat is distributed throughout the home via the principles of conduction, convection and radiation. Circulation is key for both cooling and heating. A passive solar home is also well insulated and nearly airtight. It allows for controlled ventilation outside only through a small, powered heat exchanger. In very hot climates, where the focus is on keeping cool much of the year, the home may incorporate additional ventilation features.


Control features

The home has mechanical and non-mechanical features that help regulate sunlight and circulation. These might include roof overhangs, shutters or awnings, blinds, vents and dampers.

Ideally, a passive solar home provides comfort without any mechanical air conditioning or heating. In practice, many have small, auxiliary systems, especially in very hot or cold climates. Still, even where these systems are needed, a passive solar home stays comfortable at a fraction of the usual energy cost.


Applicable to big and small, new and old

Passive solar energy can be applied to buildings of all sizes—from small homes to large buildings. The features are most easily integrated into new construction. But, some or all can be retrofitted into many existing homes.

According to Passive House Institute US (PHIUS), a passive building currently costs five to 10 percent more than a conventional building. It expects those costs to drop in the future, as technologies like triple-pane windows—which are frequently incorporated into passive solar design—become more common.


Passive solar certification

PHIUS has developed certification standards for those interested in passive solar construction. The standards vary by geographic region, owing to differences in climate.

As of 2015, PHIUS estimates more than 200 homes in the U.S. will meet the standard. While a small number, certifications are growing exponentially year-to-year. The PHIUS website offers resources for homeowners, including links to energy consultants who are versed in the principles.


A powerful combination

All this seems to beg the question: What if you combined passive solar design with active solar technology—electricity from solar panels? Working together, they would make for undoubtedly the greenest home on the block.

Installing a SolarCity system can make a significant impact on your energy use. And, we make it easy and inexpensive. Find out why there’s no better choice for going solar.

Power to Give

By SolarCity

August 12, 2015


The story of the GivePower Foundation starts in 2010, in the aftermath of the massive Deepwater Horizon Oil Spill in the Gulf of Mexico. In an area still recovering from the devastation of Hurricane Katrina several years earlier, the spill severely hampered the local seafood industry and put a lot of people out of work. Elon, Pete and Lyndon wanted to try to do something to help, and at the same time demonstrate the potential of energy without oil in an area that had seen very little renewable development.

With funding from Elon’s Musk Foundation, SolarCity donated a solar panel and battery backup installation to a hurricane response center in a town in southern Alabama—Coden—whose lifeblood had been commercial fishing prior to the spill. The donation was meant to ensure that local residents would have a safe, well-lit and air-conditioned place to gather should another disaster strike, with the added bonus of lowering the response center’s ongoing electricity costs.

The project began what would become the first of a series of disaster relief efforts. SolarCity and Elon’s Musk Foundation teamed on a similar project in Japan in 2011 in the wake of the Fukushima nuclear disaster, and in 2012, SolarCity worked with partners to provide portable solar power stations for victims of Hurricane Sandy in the Northeast.

SolarCity went public in late 2012 and grew into a better position to make a broader impact. In the fall of 2013, Hayes Barnard joined SolarCity as chief revenue officer when his own company—Paramount Energy Solutions—was acquired. A few years earlier, Hayes had been exposed to the challenges that schoolchildren in impoverished areas of the globe faced through buildOn, a nonprofit that builds schools in the developing world.

Hayes spearheaded an effort to create a charitable foundation within SolarCity to address energy poverty for schoolchildren around the world, and recruited David Reichbaum to lead the organization. At the end of 2013 SolarCity officially launched the GivePower Foundation to provide light to schools in the developing world that lack basic access to electricity. 

In 2014, GivePower exceeded its goal of lighting 400 schools, helping a total of 511 schools in Africa and Central America expand their potential. Power can instantly make a difference to the 1.3 billion people living off the grid.

“These schools are often the central meeting place in the communities,” says Reichbaum, GivePower’s Global Program Manager. “Whether it’s a health clinic or adult literacy classes in the evening, or a spot for the community to gather, by bringing electricity these schools are now empowered to lift the community from some of the worst poverty imaginable.”

GivePower targets areas of the world most in need—such as sub-Saharan Africa and parts of Central America and Asia, home to nearly 97% of the world's people currently living without access to power. Schools with power can attract superior teachers, increase the number and type of classes, and help students connect with the world. 

The simple to use, solar-in-a-box kits GivePower provides include batteries, panels, and lights; they allow many schools to have interior lighting for the first time.  Working with partners such as Intel, buildOn, World Vision and GRID Alternatives, last year the GivePower program sent teams to four countries to build schools from the ground up and install solar systems.

SolarCity employees were able to join on three of these trips, and see firsthand the changes connectivity can mean for a community. In Mali, where only 1/4 of the population has access to electricity, recipient schools can now attract more teachers to the rural area. In Nicaragua, where more than 1.5 million people don’t have power, the remote 250 person-strong community of El Islote no longer lives in the dark. And in Kenya, the school in the village of Kirindon can now power the laptops donated by Intel.

The solar kits are designed to last at least a decade, and much longer for the larger build projects. The SolarCity teams also train locals to troubleshoot equipment, and provide long-term support to ensure schools remain powered. 

GivePower continues its goal of providing light to one school for every megawatt of solar power installed in the U.S. This year, thanks to a $500,000 donation from the Bank of America Charitable Foundation, the organization’s goal has doubled to over 1,000 additional schools. 

GivePower has also achieved 501(c)(3) public charity status; now everyone can give the gift of light regardless whether they’ve gone solar with SolarCity or not. Corporations and individuals can help bring light and opportunity to communities in need with GivePower through donations

Reichbaum says with more backing, GivePower has its sights set on expanding to light up medical clinics and libraries, as well as expanding people’s expectations of solar energy.

“The goal is to demonstrate to the world that solar is not only for developed countries, it’s something the rest of the world has adopted to skip over the traditional energy infrastructure. We’d like to inspire people to consider solar as the new norm.”

8 reasons we love Vermont

By SolarCity

August 10, 2015


We announced today that we’re entering Vermont, bringing our money-saving, sustainable, solar power services there for the first time.

The Green Mountain State is now the 19th we serve. And we’re delighted—for many reasons—to be part of it. Among the things we love:


It’s sweet. Really. 

Vermont is home to the venerable Ben and Jerry’s Ice Cream. The company was started in 1978, in a renovated gas station in Burlington. Vermont is also the country’s leading producer of maple syrup—by far. The state accounts for 42 percent of production countrywide. 

Put that on your pancake: Vermont produced 1.32 million gallons of maple syrup in 2014. That’s enough to fill more than 85,000 standard beer kegs.


A unique history. 

During the Revolutionary War, Vermont declared independence separately from the 13 colonies. The move effectively made it a sovereign nation. Nevertheless, Vermonters—particularly a militia known as the “Green Mountain Boys”—were key in the fight against the British. In 1791, Vermont finally joined the U.S. as the 14th state.


A renewable-energy track record. 

Vermont was the first state to enact a feed-in tariff to accelerate renewable energy technology. It’s one of only two states without a coal-fired power plant. And, it’s a leading state for methane digesters, which use microorganisms to break down biodegradable materials—in this case, cow manure from the state’s vibrant dairy industry—to manage waste and produce electricity.

Moo juice: The waste produced in a day by one cow can generate enough electricity to power two 100-watt light bulbs for 24 hours.


It’s a trailblazer for gay rights. 

In 2000, Vermont became the first state to legalize same-sex civil unions. In 2009, it became the first state to legalize marriage equality through legislative action, rather than a court decision.


Physical fitness. 

Vermonters are among the country’s healthiest people. They ranked second for health in 2014, behind only Hawaii, according to the United Health Foundation. In the rankings, the state was number one in 22 key factors, including behaviors, community and environment, policy and clinical care.


Fiscal fitness. 

Vermont routinely balances its budget, although it’s the only state in the country with no constitutional requirement to do so.


Truly great outdoors. 

Vermont’s name is derived from the French phrase for “green mountains.” The Green Mountains is also the name of the chain covering the state’s eastern half. The state’s western border with New York is punctuated by Lake Champlain. Vermont boasts 52 state parks and nearly 4.6 million acres of private and public forestland, covering nearly 80 percent of the state. Hunting and fishing are big pastimes … and moose watching is growing in popularity. Skiers also know the state well, including resorts like Okemo, Killington, Jay Peak, and many more.

Vermont’s hills really are alive: The von Trapp family, whose story was told in “The Sound of Music,” settled in Stowe after escaping Nazi-occupied Austria in 1939. The mountainous, green landscape reminded them of their beloved Alps. You can even visit and stay in their home—it’s now a popular, 96-room Alpine lodge still owned and operated by the family.


They take “quaint” seriously. 

Montpelier is the only U.S. state capital without a McDonalds. Much to advertisers’ chagrin, the state does not allow billboard advertising. And, as far back as 1970, Vermont passed Act 250. It’s an often-controversial law designed to carefully manage land development throughout the state.


SolarCity is the leading provider of rooftop solar power in the U.S. We’ve helped more than 260,000 customers across the country benefit from clean and inexpensive solar energy. And, we’re excited about the opportunity to help make the Green Mountain State even greener.

Our readers’ turn: Keeping old homes cool without AC

By SolarCity

August 05, 2015

13891666182_364593d083_o_1Image: City of Boston Archives via CC. Cropped from original.

People clearly have a passion for old homes.

Our recent post on “How homes kept cool before the age of AC” was very popular. It inspired hundreds to share their experiences and know-how, including telling us about some cooling features of older homes that we’d missed.

Here’s a sample of the best and most interesting comments (some are lightly edited):

Many wrote about features designed to help airflow.

“Some homes were built with a large central cupola, allowing hot air to rise up the center of the house and bring in cooler air through lower floor windows.”
—Barry W.
“I lived in a house built in 1901 … a wall was built into a bay window to put beds out into the breezes. This was in south Texas, where it stays hot.”
—Bobby B.
“From 1993 to 2006 we lived in a 1906 ‘dog-trot’ farmhouse … with a wide open hallway from front to back …. The term ‘breezeway’ is a more modern word. These dog-trot farmhouses were built to allow the moist, cool air to flow through.”
—Jonell H.
“I grew up in Central Texas, in a home built in about 1846. We did not get air conditioning units in the windows until the late 1960s. One feature of older homes not mentioned (in the original post) is that all the windows and doors lined up from one side of the house to the other so there was cross-ventilation.”
“Many houses in my city have south and east facing doors in the front that empty out through open rooms to doors in the back, creating airflow through the house …. There's a clear line of sight through the house if all the doors are open …. I live in Louisiana and these throughways are common architectural features in older homes.”
—Yah Yah


Several mentioned clever tricks homeowners used to stay cool.

 “(I) toured an old mansion in Jim Thorpe, Pennsylvania. They used part of the basement for the ice house (a storage room for ice, common before refrigeration). In the summer they opened a vent in the parlor. Simply brilliant!”

—Doreen P.
“We lived in a two-story home. All the windows in the upstairs would be open. There was a window in the hallway and in that we put a fan facing out. To avoid having cool air pulled up from downstairs, my father put a door at the head of the stairs. This worked quite well!”
                  —Kathy R.
“Most likely you will need to add rat sills (bottom plate of a wall frame) to prevent air from being drawn through the walls from beneath the house.”
—Priscilla R.


Shading was important.

 “We lived in Minnesota on the Canadian border. It gets hot and humid in mid- to late-summer. But it usually cooled off significantly overnight. My grandmother and mother would open up all windows overnight and blow in as much of that air as possible with fans, then shut the windows in early morning and pull the shades down. That, coupled with the shade of large oak and elm trees around the house kept it nicely cool all day long. Ahhhh…”

—Trish L.
“You omitted awnings. My grandmother had these put up each summer.”
“I spent my childhood years in a two-story house (built in 1903) with a full basement and third floor attic, and there were huge elm trees along the sidewalk. My parents installed a huge window fan in the attic that pulled cool air up through the house. Dutch Elm disease destroyed all the shade trees in the 1970s … about that time, people installed air conditioners and stayed inside. That changed neighborhood life.”
—Kathleen R.


And, when all else failed … people just dealt with the heat.

 “We lived in a one story home with lots of windows …. It had fans and a window fan in the living room. We bathed in the summer two to three times a day! Your body adjusted to the heat. And, you sweated a lot!”

—Joan F.  


Whether “home” is a 19th century Victorian … a 21st century contemporary … a Texas “dog trot” farmhouse … or anything in between, going solar can help you save energy and money year-round. Modern solar panels are designed to work with all architectural styles and roof types. And with SolarCity, installation and maintenance are affordable and easy.

How solar installers beat the heat

By SolarCity

July 29, 2015

Hot or cold, rain or shine, SolarCity rooftop installers know a thing or two about dealing with weather extremes. They brave just about anything Mother Nature throws at them as they bring clean, inexpensive solar power to our customers.

So—to continue our summertime series on keeping cool—we asked the solar installer team at our Henderson, Nevada office to share their personal advice for beating the heat. Bear in mind, they responded during a week (July 13-17) when daytime temperatures hit triple digits … pretty typical for mid-summer in southern Nevada.


“I start my day with a can of coconut water. I think it helps me avoid cramps and has lots of potassium. I also have two bottles of Gatorade throughout the day for headaches—for me, it works better than Ibuprofen or other headache medicine. And of course, I drink lots of water. My first day on the job, I wasn't prepared, and I was determined to not feel like that again. I’ve done this routine since then and have been feeling way better. I hope this helps you beat the heat! Go SolarCity!”

--Steven S.


“I try to get to the jobsite early and start work before it gets really hot. Another trick I use is to keep a couple water bottles in my tool bag on the roof—I have to constantly ask the guys on the ground to refill. And, it’s always helpful to take breathers and stay under the shade whenever possible.”

--Mark C.


“I use blue “Mission” brand neck wraps. They keep my neck and face feeling cool all day. You can get them at Lowe’s for about $20.”

--Jeremy S.


“This is kinda’ funny: I put a frozen water bottle by the ladder and I stare at it while I'm measuring the roof. It makes me work faster! Other than that, I use a cooling vest. I usually get it wet then throw it in a freezer or a cooler with ice. I also use motorcycle neck braces that I soak in water then throw on ice. And, I hydrate. Not just with water, with sugary sports drinks too.”

--Nick R.


“I stay hydrated on my evenings and days off. I like to hydrate my body at least 24 hours in advance of a job. I also wear a wide-brim straw hat. They’re not expensive—I find them for $8 at a local Chevron. I’ve even found them for $5 at a nearby O'Neill outlet. And, I like ‘Frogg Toggs’ brand wet cloths for my head and neck. I think they stay much colder, much longer than the competitors’.”

--Sean B.


What are your best heat-beating tips? Let us know in the comments. 

SolarCity makes going solar easy, and our professional solar installers are just part of the reason why. We handle everything—from designing and engineering your system, to installing the highest quality solar panels and related equipment, to coordinating the required inspections with your local building department.

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