Passive Cooling in a Tiny House
Originally published on RMI.org.
By John Matson
As the world warms and the demand for cooling increases, many homes will require an “all of the above” approach to keep cool without further contributing to global warming. That can include high-performance cooling systems that use climate-friendly coolants and consume relatively little energy, as well as building design approaches that offset the need for mechanical cooling in the first place.
This tiny, ultra-efficient Passive House was built in just 10 days in #Australia http://t.co/glUiZVSN1o pic.twitter.com/pjYxo496ti
— The Architect’s Newspaper (@archpaper) February 10, 2015
In this post, we look at some passive cooling strategies that help keep an innovative tiny house comfortable during California summers, without the use of a mechanical cooling system.
Brett Webster, a manager in RMI’s Carbon-Free Buildings program, lives in a 170-square-foot home in Sonoma County, California. Brett and his partner helped design and build the solar-powered tiny house as part of a graduate project, and they have lived in the demonstration home for about five years. The home itself was built on a 24-foot-long trailer and can be hitched up to a truck for relocation. So even though Brett and his partner have lived in their tiny home for years, they have moved twice in that time between Northern California locations (and their respective microclimates).
Strategic Shading
The walls of the tiny house are clad in reclaimed cedar slats over one-inch-thick panels of cork, which provides a layer of continuous insulation, reducing the thermal bridging of the wooden wall framing. Because the carbon sequestered in cork trees can exceed the carbon emissions of producing cork products, cork is often considered a carbon-negative material. The cedar siding is separated from the cork by an air gap, which allows the wooden slats to shade the cork and absorb solar radiation, while slowing the rate of heat transfer directly to the house. The walls of the structure are insulated with recycled denim to further limit heat gain in warm weather and heat loss in cool weather.
Pulley-mounted shade awnings, made from cedar slats to match the siding, cover the largest expanse of glass on the tiny house: a sliding-glass door at the entry to the home. Webster says that the shade structure extends far enough to block solar radiation from pouring through the glass entryway in summer, but it can let in sunlight and heat in winter, when the sun is lower in the sky.
The ability to shade the windows in summer and admit sunlight during the winter is critical to maintaining passive comfort in the house. The windows that the design team chose for the tiny house are well-insulated (low U-value) but are also designed to let the sun’s heat in (high solar heat gain coefficient), because the Bay Area is mostly a heating-dominant climate zone. During the summer, when that heat gain is not desirable, shading the windows is a necessity.
Ceiling and Roof
A layer of BioPCM phase change material in the ceiling acts like thermal mass to absorb and store heat that would otherwise warm the interior space. Adobe buildings and concrete-walled structures similarly benefit from thermal mass that prevents the interior from becoming overheated during the day. But phase change material is lightweight, making it more appropriate for applications like the ceiling of a tiny house, and it doesn’t have the carbon footprint of concrete. (Cement production alone accounts for about 8 percent of global carbon emissions.)
The phase change material, which comes embedded in sheets that can be rolled out between ceiling joists like high-tech bubble wrap, melts from solid to liquid at 77 degrees F (25°C). As it changes phases, the material absorbs a lot of thermal energy, preventing the temperature from exceeding 77 degrees until its heat-absorbing capacity has been reached, like a sponge that can’t soak up any more water.
The tiny house’s roof is designed to harness much of the sun’s energy and reject the rest. A 2.3-kilowatt solar array shades much of the tiny house’s roof and feeds into a Tesla Powerwall to store electricity for nighttime use. The “cool roof” is also covered with a light-colored acrylic roofing membrane to minimize heat gain from solar radiation.
Some Energy Required (But Not Much)
In addition to the passive cooling approaches described above, the tiny house relies on a few efficient electric devices to provide airflow and ventilation. Even though they don’t qualify as strictly “passive” technologies, ceiling fans and other efficient electric devices have long gone hand-in-hand with passive cooling approaches. The ventilation and airflow systems in the tiny house consume very little energy and allow the building to remain comfortable without a dedicated mechanical cooling system.
A high-efficiency overhead ceiling fan consumes 4–18 watts of electricity and ensures occupant comfort in warmer temperatures. “Airflow creates a cooling sensation that’s extremely effective,” Webster says. According to the US Department of Energy, using a ceiling fan can significantly offset the need for air conditioning, allowing occupants to raise the thermostat by about 4 degrees F without sacrificing comfort.
The well-insulated structure is designed to be closed off to the outside during hot days in the summer, so the windows do not provide any natural ventilation during the daytime. The tiny house therefore relies on an energy recovery ventilator to bring fresh air into the house. An energy recovery ventilator uses a heat exchanger to reduce the thermal energy of the outside air before it enters the house, thereby providing ventilation without flushing warm air into the building. In the winter, it does the reverse, using the heat of the outgoing stale air to warm the incoming fresh air.
Unplugging
The tiny house’s passive design and minimal energy requirements for ventilation make it fully capable of going off-grid, especially in the summer months when solar energy is abundant. And even if most of us aren’t ready to commit to living in a 170-square-foot house on wheels, the lessons from Webster’s tiny house and other passive homes provide a powerful reminder: Even for energy-intensive applications like cooling, with thoughtful design, you can do a lot with a little.
Image gallery courtesy of RMI.
Burlingame, California-based Peak Energy just scored a huge win for sodium-ion batteries. The company announced a multi-year deal with utility-scale battery storage developer Jupiter Power to supply up to 4.75 GWh of sodium-ion battery systems between 2027 and 2030.
Under the agreement, Peak will deliver 720 MWh of storage in 2027 – the largest single sodium-ion battery deployment announced so far. The deal also includes an option for an additional 4 GWh of capacity through 2030, bringing the total contract value to more than $500 million.
Sodium-ion vs. lithium-ion
Peak Energy says its sodium-ion batteries degrade less over time and have lower operations and maintenance costs than lithium-ion systems. Because the batteries don’t degrade as quickly, operators don’t need to add more capacity later in a project’s life to maintain performance. They also use a fully passive cooling system that eliminates pumps, fans, and other components used in lithium-ion setups, reducing maintenance and safety risks.
The company claims its grid-scale sodium-ion system uses up to 97% less auxiliary power, offers about 30% better cell degradation performance over 20 years, and comes with a lower total cost of ownership.
Why this deal matters
The agreement marks a significant step forward for the emerging sodium-ion sector, which has been gaining momentum as a safer and lower-cost alternative to lithium-ion for long-duration and grid-scale energy storage. It also underscores the growing effort to build a domestic sodium-ion battery supply chain in the US.
“From day one, we’ve believed sodium-ion will be the winning technology for grid-scale storage, which is essential to meet rising demand from hyperscalers and AI,” said Landon Mossburg, Peak Energy’s CEO and cofounder. “Deploying the world’s largest sodium-ion energy storage system with one of the nation’s top independent power producers proves that sodium is ready for today and will dominate the future.”
Mike Geier, CTO at Jupiter Power, said the company is “excited to support domestic battery energy storage manufacturing as we continue to increase the deployment of firm, dispatchable energy when and where it’s most needed,” and called Peak’s approach to sodium-ion “a potential game changer for the industry.”
Read more: The US’s first grid-scale sodium-ion battery is now online
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![The new 2026 Lexus ES is an upgrade in just about every way [Video]](https://i0.wp.com/electrek.co/wp-content/uploads/sites/3/2025/11/new-2026-Lexus-ES-EV.jpeg?resize=1200,628&quality=82&strip=all&ssl=1)
Lexus claims the new ES “takes sedan styling, luxury, and refinement to a higher level” with a complete redesign. With the 2026 ES arriving soon, Lexus offered a closer look at the upgrades inside and out.
The new 2026 Lexus ES debuts in EV and hybrid forms
The eighth-gen ES is bringing more than a sharp new style. Lexus overhauled its flagship sedan from the ground up for the 2026 model year, which will include battery electric (BEV) and hybrid (HEV) powertrain options.
Inspired by the radical LF-ZC show car, the 2026 ES has been fully redesigned with what Lexus calls the “Experience Elegance and Electrified Sedan” concept, aimed at further refining the driving experience.
The new design centers on a redesigned “spindle body” that extends from the hood to the bumper. It also features a redesigned grille, replacing the signature Lexus spindle grille as the brand looks for a new identity in the electric era.
Inside, the new 2026 ES features the latest version of the Lexus Interface multimedia system. The setup includes a 14″ touchscreen with wireless Apple CarPlay and Android Auto, and a 12.3″ driver display cluster.
Based on the redesigned TNGA GA-K platform, the new ES will be available in battery electric (BEV) and hybrid (HEV) powertrains for the first time.
The 2026 Lexus ES lineup consists of two models: the ES 350e, a front-wheel-drive (FWD) model, and the ES 500e, an all-wheel-drive (AWD) model.
Lexus expects the ES 350e to have a driving range of 300 miles when fitted with 19″ wheels, while the ES 500e has an estimated driving range of 250 miles.
Both the ES 350e and 500e feature a built-in NACS port to recharge at Tesla Superchargers. Using DC fast charging, it can recharge from 10% to 80% in about 30 minutes under “ideal conditions,” according to Lexus.
With its debut just around the corner, Lexus offered a closer look at the new 2026 ES inside and out in a new video.
Lexus has yet to announce prices, but the redesigned ES is expected to start at about $45,000 to $50,000, or slightly more than the outgoing model.
After launching the upgraded RZ earlier this month, Lexus said the ES would be next. It’s expected to go on sale in Spring 2026.
What do you think of the redesigned 2026 ES? Do you like the new Lexus design? Let us know your thoughts in the comments below.
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Tesla has launched a new version of the Model Y in China, and it’s achieving an impressive new range rating – thanks to a new battery cell from South Korea’s LG.
The new variant, a five-seat, rear-wheel drive long-range model, has been released with an 821-km range based on China’s CLTC standard.
While the CLTC rating is known to be optimistic, 821 km (about 510 miles) is an impressive number and the longest range Tesla has offered in its Model Y lineup to date, which is going to help it be more competitive in the Chinese market.
This new extended range Model Y version is made possible by using the 78.4-kWh ternary lithium-ion battery pack from LG Energy Solution, the same pack found in the also recently launched 830-km range Model 3 variant.
The new long-range RWD Model Y starts at RMB 288,500, which translates to just over $40,500 USD.
The launch comes at a critical time for Tesla in China, which has seen its sales slump in recent months. The automaker recorded its lowest monthly sales in October since November 2022, falling out of the top 10 list for new energy vehicle (NEV) sales.
That’s despite a continued surge in electric vehicle sales in China. Tesla is not benefiting from it amid strong competition.
According to local Chinese media reports, the new 821-km Model Y is already gaining traction with some anecdotal reports of enthusiasm at Tesla stores.
The reports are partly supported by Tesla quickly extending delivery timelines from 2-4 weeks to 4-6 weeks just hours after launch.
Electrek’s Take
I think this is going to be suitable for a decent short-term bump in demand, but it’s still on the expensive side for the Chinese market.
For example, now the Model Y beats the Xpeng G6’s max range of 755 km, but the G6 with this range costs 234,900 RMB (approximately $32,900 USD), which is significantly cheaper.
Every 10,000 RMB tranche lower means a lot more demand in China.
Tesla needs to launch its new “standard” versions to start making a difference with demand long term in China.
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