Passive solar heating: What you need to know

Electricity is not the only thing that can be created by harnessing the sun's energy. One of the most economical ways to take advantage of the sun's power is to design your property with passive solar design in mind, or to say, to take full advantage of the site, materials, and climate of your home to maximize efficiency and minimize energy usage overall.

Passive solar heating is using the sun's rays to heat a living space by exposing the area to sunlight. Passive solar buildings take advantage of how the sun moves throughout the day (with attention to seasonal changes in sunlight) to warm living spaces. This process is called "passive" because it doesn't involve any solar panels or other technology to convert sunlight into usable energy - the sun's thermal energy is being stored and used as is.

This process involves more than just sun shining on your house; passive solar heating designs typically involve five important factors to collect thermal energy during the day and disperse it at night. These include an aperture for the sunlight to pass through, absorbers and thermal mass to absorb and retain the heat, distribution for heat circulation, and a fixed control that will provide shade during the summertime.

Apertures

The apertures, or collectors, in passive solar buildings, are often large windows facing south (for buildings in North America)\ for maximum sunlight exposure. In some cases, designers will build a property that has an entire wall made of windows to maximize exposure. Sunlight flows through the windows throughout the day, gets absorbed, and then dispersed. These windows often have a specialized coating that reflects harmful ultraviolet (UV) rays away from the glass, preventing them from entering the space.

Absorbers and thermal mass

In passive solar heating design, the absorber is a surface exposed to a lot of sunlight (such as a wall or floor). Absorbers are often dark surfaces so that the maximum amount of sunlight possible is soaked up. Once the absorber captures heat, the heat is retained by a thermal mass below. As sunlight flows into the room, absorbers, and thermal capture and hold the heat so that it warms the space into the evening and night after the sun goes down. Absorbers and thermal mass are commonly made of concrete, ceramic tile, brick, or stone because they have high heat capacity.

Distribution

Throughout the day and into the night, the sun's heat absorbed into the thermal mass is distributed throughout the living area. This can be done mechanically with small fans or blowers, but they are not necessary – heat will naturally move throughout spaces. Whether you have passive solar heat or not, warm air will move towards colder areas and disperse through convection, conduction, or radiation.

Control

Control is a vital component of passive solar heating design, especially if you don't want your living space to be too hot during the warmer months when the sun is highest in the sky. Different control components include awnings or roof overhangs, blinds, and shutters. These elements can also help offset any costs of cooling your home in the summer, as they help keep your living space cool and can reduce your air conditioning needs. When they are implemented into passive solar heating design, all of these components can help ensure that your home or commercial building is producing passive solar energy in the most efficient way possible.

There are a number of benefits of using passive solar heating. First and foremost, it can save you money on energy bills. By using passive solar energy, you're taking advantage of a natural process and utilizing free, renewable energy from the sun to warm your building. This allows you to dramatically decrease (or possibly eliminate) your purchase and use of gas, wood, or electricity for heat, which saves you money and reduces your footprint. There are also no operating costs for passive solar heating, while other traditional heating technologies have a limited lifespan and require maintenance over the years.

Passive solar heating is also environmentally friendly – there are no greenhouse gas emissions or pollutants released into the air as a result of sunshine entering your living space. Most traditional methods of heating a building (such as furnaces, electric resistance, or space heaters) use fossil fuels for power, which release greenhouse gases and pollutants into the air when used.

Passive solar designs also have a number of comfort benefits. For one, there is no noise coming from rumbling radiators or furnaces when you use passive solar heating. You'll also get natural light in your living space and better views from your home due to the use of large windows.

Not every property is perfectly suitable to take advantage of passive solar energy. If you're building a property and looking to adequately heat your property with the sun's thermal energy, here are some important factors to keep in mind:

Insulation and energy efficiency

In order for a passive solar design to be as effective as possible, your building needs to be well-insulated so the thermal energy absorbed by your system can stay in a designated space for as long as possible. If your home isn't properly insulated and has lots of air leakage, passive solar heating won't be a sufficient source of heat during colder months.

Obstructions to sunlight

Large windows won't do a lot of good in providing passive solar heat if there isn't a lot of sunshine streaming through them. Large trees, hills, or nearby buildings may be situated south of your property, therefore blocking sunshine throughout the day. Even if you're building a home in an area that currently receives an abundance of unobstructed sunshine from the south, you have to consider if these conditions will remain the same down the road: how large will smaller trees end up growing? Is there any chance your neighbor may invest in a property addition that would prevent your solar access? Before investing in passive solar design, make sure you'll have access to sunlight for the foreseeable future.

Geography

Your geography is also an important factor. Passive solar heating is reliant on the position of the sun on a property throughout the various seasons, and this position will vary depending on your location. In the northern hemisphere, apertures should face south, while northern facing apertures are ideal in the southern hemisphere. The size and position of your control component may also depend on your latitude, as the angle of sunlight on a given date will be different in southern California than further north in New England. An architect that's experienced as a passive solar heating expert will recommend an awning or overhang that will be the optimal size to ensure that you get the right amount of shade during the summer.

One downside of passive solar heating is that if your property was not originally built with it in mind, it can be an expensive renovation. Because passive solar requires a deliberate design in regards to building location, apertures, and construction materials, it's easiest to build a passive solar home design from the ground up.

That being said, if you are planning an addition to your home, there are steps you can take to utilize passive solar energy, even if it's not suitable to be your primary heating system. Many property homeowners consider using passive solar design in isolated additions to their homes, like a sunroom.

If you're just starting out in designing and building new construction, now is the perfect time to consider passive solar heating for your property. During the design phase of your new construction project, it's best to work with a qualified green building architect or designer who has experience with these types of heating systems to ensure you're receiving the maximum amount of benefit the sun has to offer.

If you're interested in seeing passive heating in action, take a look at case studies of passive solar on EnergySage. These case studies include pictures, testimonials, and advice straight from property owners utilizing passive solar design themselves.

If your property isn't suitable for passive solar heating, consider installing solar photovoltaic (PV) panels as another option for saving money on energy bills. By joining the EnergySage Solar Marketplace, you can obtain multiple solar quotes from pre-screened, vetted installers to compare. These custom quotes will include savings estimates that take into account electricity rates in your area, how much electricity you use, and the details of the proposed solar panel system.