My Turn: The benefits of passive solar heating

For the Monitor
Published: 1/16/2022 8:01:07 AM
Modified: 1/16/2022 8:00:08 AM

Now that the winter solstice, the shortest daylight day of the year, is behind us I’m reminded of how important it is to let the sunshine into our lives.

There are many benefits to having large south-facing windows in a home. Among them is the warmth that the sun provides on sunny days, and that helps reduce the need for oil, gas and wood burning during daylight hours. This is called “passive solar heating” primarily because it requires no fancy technology, just energy efficient windows oriented toward the winter sun.

To make passive solar heat gains provide the most value, it’s also important to practice simple energy conservation methods like pulling insulated or heavy drapes, pleated shades or curtains over those same windows once the sun goes down. In many homes, the largest single source of heat loss is through windows, which generally have a small fraction of the insulating ability of an insulated wall or ceiling. So covering them at night is one of the most cost-effective and simple ways to reduce heating costs.

Another benefit of those south-facing windows is the potential for what psychologists call “seasonal affective disorder.” SAD is believed to cause depression and mental distress in some people when days are short and they live in homes or offices devoid of natural light. One treatment involves facing into a reflective frame lit by electric bulbs, but bringing more sunlight into the home is likely a simpler approach.

Whether one suffers from SAD or not, having more sunlight in a home or workspace is more pleasant and uplifting than being in a dark place with no visual connection to the outdoors.

Having green growing plants on the window sill is another benefit. As we all know, plants require light to thrive and daylight is in short supply in the depth of December and early January. The best windows for our houseplants are those that face south, with some exceptions. Plants that prefer indirect light (philodendron, etc.) still want plenty of hours of sun, but prefer it to be indirect, so putting them near, but not in front of south-facing windows is preferred.

But, for me, the biggest bonus of those south-facing windows is provided by our “solar greenhouse.” It’s not high-tech by any stretch, but a series of windows the size of patio doors facing south, enclosing a room full of plants. The room is reminiscent of the old-fashioned sun porch on 19th-century houses, and is open to the house during the day and closed off at night.

In our well-insulated version, we grow lettuce, spinach, basil, and yes, tomatoes, right through the winter. We also have ornamental plants including geranium, jade, asparagus fern and a couple of bougainvilleas that bring color to the view through the winter.

Of course, a major benefit of the solar greenhouse is the heat it provides our home. I’ve calculated that it provides about 60% of our annual heating energy. No high-tech devices are involved, just a small fan and a thermostat that pulls excess heat from the greenhouse into the cooler part of the house on any sunny winter day.

Unlike the old sun porch, the solar greenhouse holds enough heat at night to prevent it from freezing. In 40 years of operation, ours has never dropped below 32 degrees Fahrenheit, in large part because the planting bench is held up by a series of water-filled barrels. The floor and one wall are made of concrete which provides additional “storage” for the sun’s heat. When extreme cold weather arrives, simply leaving the door from the house into the greenhouse open a little bit keeps the plants from freezing.

Most of the ongoing news and conversation these days is about solar power from photovoltaic cells. This is a good thing, and our home now hosts a modest array of solar panels. But our biggest benefit comes from the passive solar gains through windows. Passive solar heating is as old or older than civilization, and works beautifully and simply anywhere there’s a need for heat and the sun shines.

There’s a great need for us to embrace the need for renewable energy by installing solar electric wherever it’s feasible and affordable. But my experience illustrates that for many homeowners and home builders, the benefits of embracing passive solar go well beyond saving money. It works so well and has so many benefits, why anyone would build a new home or substantial addition or renovation to an older home and not incorporate passive solar design is a mystery to me.

There are plenty of resources for learning about how to incorporate passive solar heating into a new or old house. If you are pondering investing in improving your home, consider this low-tech approach as well as photovoltaic electricity.

(Paul Doscher lives in Weare. He was trained as an architect and he and his wife built their own home in 1981.)

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