Aiming for Zero: How to Build a Zero-Carbon Home

It was never the number you wanted to see at the top of a math quiz, but homes with zero carbon footprints are scoring big.

| January/February 2009

  • Architect Jim Logan reflects on our energy future in front of a solar-powered home he designed in Colorado.
    Photo by Michael Shopenn
  • Wild Sage Cohousing Apartment Complex faces north and south, which allows significant heat gain through southern windows in the winter.
  • Habitat for Humanity House features a long axis that faces south, with enough windows to gain some passive solar heat.
  • This American "dream" home is insulated and sealed with urethane foam in the roof, walls and basement.

A long-time environmentalist, Colorado-based architect Jim Logan has been building solar and low-energy homes since 1975. Feeling the growing need to combat global climate change, Logan now focuses exclusively on carbon-neutral buildings—those that release virtually no CO2 into the atmosphere. We asked him to talk with us about how regular people can reduce their homes’ carbon footprints to zero.

Q: How does a grid-connected, zero-carbon footprint house work?
A: A zero-carbon footprint house supplies more energy to the energy grid than it takes. The grid, in this case the public service company, is used as a storage device. We try to generate enough energy to run the building and produce some excess. On a bright sunny day when your solar panels make more energy than you can use, you can sell the excess back to the public service company. On cloudy days, you take power from the grid.

Q: Can any residence have a zero-carbon footprint?
A: Yes. The first step with any building—new construction or an existing building—is to do as many things as possible to lower the building’s energy consumption so less energy is required to power the building. This is often referred to as “reducing the load.” It’s possible to build super-efficient new homes fairly economically by using high levels of insulation and highquality windows. With existing construction, you can reduce loads by adding insulation wherever possible and by reducing air leaks.  Once you’ve reduced the load, it’s time to add some alternative energy system—in our case, solar thermal panels for hot water and/or photovoltaic panels to make electricity. You should implement conservation strategies such as increasing insulation and reducing energy use before investing in solar thermal and photovoltaics; it’s less expensive to buy light bulbs or add insulation than to buy and install more solar panels. Once you’ve done all you can to conserve, you may find you need fewer panels than you thought.

Q: Can you explain in more detail the difference between solar thermal panels and photovoltaics?
A: There are two basic types of solar panels. Solar thermal panels are used to heat water, whereas photovoltaics produce electricity for the home.  Solar thermal panels are composed of three parts: a solar thermal collector; a fluid system to move heat from the collector to its point of use; and a tank for heat storage. Solar thermal panels are particularly cost-effective for heating hot tubs and swimming pools, which require huge amounts of heat. In certain parts of the world, code requires that a substantial portion of your hot water be provided by solar. Israel has mandated solar heating systems since 1980, and Spain requires new and renovated buildings to obtain 30 to 70 percent of their hot water through solar power. Starting in 2010, Hawaii will be the first state to mandate installation of solar water heaters on new homes.  The most widely available photovoltaics (PVs) are thin strips of silicon, sliced up and glued onto glass, which generate electricity when the sun shines on them. One of the great things about PVs is that their life span appears to be indefinite. We see no dropoffs in their production after 20 or 30 years, so they will likely make electricity forever.

Q: Based on current energy costs, how much would it cost to install PVs on a 2,500-square-foot house?
A: Let's assume you have tidied up your energy consumption by getting an Energy Star refrigerator, replacing all your light bulbs with compact fluorescents, and turning off your TV and cable box with a plug strip so they aren’t running all the time. A 3-kilowatt (or 3,000-watt) system will handle the needs of most families; the national price of PV is currently about $9 per watt. If you live in a state that offers rebates, the cost would be about $12,000, installed.

Q: What kind of cost savings could be realized?
A: We've seen the cost of these systems drop about 5 percent a year, so it’s continuing to cost less to install them. In states like Colorado, New Jersey, New York, California and Florida, where homeowners get rebates from the energy company as well as tax breaks from the government, a system will pay for itself at the current utility rate in about seven years. It’s difficult to say what future electrical rates will be, but once you buy PVs you’ve essentially paid for all of your home’s electricity until the end of time.

5/15/2014 9:09:53 AM

Jim Logan level of expertise is huge and his practice in building low-energy homes would surely help anyone considering installing photo voltaic solar panels. I on some websites about the best money saving ideas so I decided to install an alternative energy system like PVs because such panel’s life span is indefinite.



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