Solara & Los Vecinos: Net Zero Energy Affordable Housing

Solara and Los Vecinos are affordable housing projects that were designed with the goal of net zero energy performance with a very small increase in the incremental cost per unit. The projects also have a number of other “green” features.

More information on Solara and a link to a case study is on the Global Green website here. Information on Los Vecinos and a link to a case study is here.


ACEEE 2012 – Think Bigger: Net Zero Energy Communities

One of the first panel sessions I went to featured a talk by Jeff Harris, of the Alliance to Save Energy.

He covered a lot of ground in defining “net-zero energy,” covering state and federal goals around NZE, detailing many of the appeals of NZE, and then focusing on the potential of NZE communities.

What I found most interesting during his talk was the specific examples of the military’s focus on getting a number of bases to NZE. He noted that there are more than 6 pilot sites targeting ZNE (often used interchangeably with NZE) by 2020. Two of the sites have the additional aggressive goal of being “triple-net-zero,” or net zero energy, water, and waste.

He also mentioned a specific site – Fort Carson – and showed some analysis (I think by the National Renewable Energy Lab, NREL) of what kinds of strategies and systems will be needed to achieve the ZNE goal.

After the session, I found an NREL report online that provides significant detail on the recommendations provided for Fort Carson” “Targeting Net Zero Energy at Fort Carson: Assessment and Recommendations” (link opens a PDF).

Snippets – Zero Net Energy

The International Living Future Institute (ILFI), owner of the Living Building Challenge, is going where no certification program has gone before with a new Net Zero Energy Building Certification program (  You can read the International Living Future Institute press release on the NZE Building Certification program here There is a zero net energy gas station in Beaverton, Oregon (  KB Home, one of the largest homebuilders in the U.S., has developed ZeroHouse 2.0, a house designed to achieve net-zero energy. The home is currently available in Tampa, Florida, and in San Antonio and Austin, Texas, but the company plans to expand the availability of net-zero options to other cities throughout 2012 (


Zero Net Energy part 1

photo credit: Alan Walker

Zero Net Energy (ZNE) is a term that is increasingly heard throughout the architecture and building sector, but it is also a term that can mean different things to the different people who use it. In this series of posts I will give an overview of the four common definitions of  ZNE, and a brief expansion on their respective implications in relation to policy structures and physical infrastructure.

The four common definitions of ZNE are: 1. Zero Net Site Energy, 2. Zero Net Source Energy, 3. Zero Net Energy Cost, and 4. Zero Net Energy Emissions. All four of  these calculations are as measured over a calendar year, or on an annual basis. The difference is in the metric (the “thing” being measured) and the boundary (what is included in the calculation). All four definitions can be applied to –and calculated at– a “community” or multiple-building scale as well. In all cases the “net” part refers to how energy is accounted for at the grid level; low energy buildings that are not grid tied would therefore not be under a zero net energy designation.

Part 1. Zero Net Site Energy

what this is: A Zero Net Energy Building is one that uses no more energy than it can produce on-site within one calendar year (this is the most commonly used definition of the term “zero net energy” at present).

what this means: A “site” can be defined as either the building footprint itself or the building and the property it sits on. In this definition, the building/ building site would incorporate a form of on-site renewable energy such as solar (most common), wind, small hydro or biogas. As mentioned, a ZNE building is still tied to the larger energy grid. For example, a ZNE building that generates energy through the use of solar panels would create a surplus of power while the sun was shining (and the excess power would be fed back into the grid), but would have to draw power from the grid in the evening or during cloudy days. The goal here is for the overall power drawn within one calendar year to be less than or equal to the power generated.

pros, cons & considerations: The chief benefit of this definition is that it promotes deep efficiency at the single building scale. This is because in order to viably (and cost effectively) achieve this definition of ZNE, it is much more desirable to build the lowest energy-use building possible and then add a source or renewable generation. In addition, ZNE sets a concrete goal to achieve and thus can be a more useful target than trying to meet or best shifting baselines as building performance codes change.

However, buildings are built in many types and have many necessary functions- not all of which are compatible with the site definition of ZNE. For example, hospitals, restaurants, industrial activities, etc., may all have a very hard time achieving a ZNE facility because of unusually high energy demands. In addition, high-rise buildings and urban infill sites have their own challenges due to physical constraints (poor solar access, low rooftop-to-building ratio, proximity and density issues, etc.)

The implication here is that if a ZNE site-definition goal is in place on a policy level, at a certain point it becomes necessary to start looking at the issue from a multiple-building, or “community”scale, that would allow energy balancing between buildings to achieve an overall ZNE outcome (this is a simplification, but that is the main point).

Further reading:

P. Torcellini et al., Zero Energy Buildings: A Critical Look at the Definition, National Renewable Energy Lab, 2006.

This post is part of our definitions series on “eco-lingo” and technical terms


The University of California–Davis has opened its West Village development, which aims to be the largest net-zero-energy community in the country  (via The bankruptcies of three American solar power companies in the last month, including Solyndra of California… have left China’s industry with a dominant sales position — almost three-fifths of the world’s production capacity — and rapidly declining costs (via NY Times).  China was the United States’ number one source of and destination for PV products in 2010.  The U.S. imported approximately $1.4 billion worth of PV products from China, while exporting between $1.7 billion and $2.0 billion.  This resulted in a positive trade balance with China with net exports of $247 million to $540 million (via Greentech Media).

The House of the Future?


In Berkeley, we are fortunate to have such events as Science at the Theater, where Lawrence Berkeley National Lab researchers give talks on their work at the Berkeley Repertory Theatre. The lectures are free and get a pretty sizeable audience. The lectures are recorded and put on YouTube.

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(The video can also be watched here – the technical stuff starts at about 10 minutes in.)

On May 10, 2010, I was in the audience as LBNL folks talked about their vision of the house of the future:

Learn what it will take to create tomorrow’s net-zero energy home as scientists reveal the secrets of cool roofs, smart windows, and computer-driven energy control systems.

The net-zero energy home
Scientists are working to make tomorrow’s homes more than just energy efficient — they want them to be zero energy. Iain Walker, a scientist in the Lab’s Energy Performance of Buildings Group, will discuss what it takes to develop net-zero energy houses that generate as much energy as they use through highly aggressive energy efficiency and on-site renewable energy generation.

Talking back to the grid
Imagine programming your house to use less energy if the electricity grid is full or price are high. Mary Ann Piette, deputy director of Berkeley Lab’s building technology department and director of the Lab’s Demand Response Research Center, will discuss how new technologies are enabling buildings to listen to the grid and automatically change their thermostat settings or lighting loads, among other demands, in response to fluctuating electricity prices.

The networked (and energy efficient) house
In the future, your home’s lights, climate control devices, computers, windows, and appliances could be controlled via a sophisticated digital network. If it’s plugged in, it’ll be connected. Bruce Nordman, an energy scientist in Berkeley Lab’s Energy End-Use Forecasting group, will discuss how he and other scientists are working to ensure these networks help homeowners save energy.

Assemblymember Nancy Skinner also spoke at the beginning, about energy in buildings and RECO programs.

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