What is Passive Solar Heating?

A solar water heater on a roof.
  • 20-200 hours
  • Intermediate
  • 500-50,000

Solar power has been used since the beginning of time. We use it to warm spaces, grow and cook food, and create water condensation.

In the modern area, we mostly think of the technology we use to funnel solar power into our homes, namely solar panels.

But, there are myriad ways we can harness and direct the sun’s energy without any mechanical devices at all. It’s called passive solar, and it can provide huge energy savings for the home.

Easily explained, passive systems take advantage of structural location and building materials to optimize heat directly from the sun.

Passive systems do not rely on any external devices to function. They are ‘passive’ because they don’t require electricity in order to collect or transfer the sun’s heat.

Reduce Your Heating Bills

Since passive solar techniques garners warmth from the sun, it means you’ll need less reliance on the mechanical heating in your home.

In other words, you won’t need to turn the heat on as often, if at all. That adds up to major savings on the utility bills.

In many cases, you can cut your heating costs by more than 50 percent compared to the cost of heating the same house without passive solar design.

Home Placement for Optimal Passive Solar Heating

An overall passive solar house design begins with the placement of the home. Of course, if your home is already built, this is a moot point. But if you’re in the planning stages, it’s worth consideration.

Orienting large windows towards the south (in the northern hemisphere) is a foundational idea when it comes to passive design. It’s called passive solar collection.

Windows on the south side of the building take maximum advantage of the gifts the sun has to offer. Turn it into a sunroom on the south side and you’ll gather even more solar warmth.

Be sure to keep these windows clean for optimal function. Check out How To Build A Solarium to learn more.

If your home is due for a remodel and south-facing windows are a possibility, it’s an investment where you will see money-saving returns. However, the expense often outweighs the rewards for an existing home so this idea is better fitted to new construction.

Maximize Passive Solar Heating

In conjunction with sunshine, the building materials you use have a huge impact on the quantity of solar heat you can gather. Carefully selected glazed windows will optimize passive solar absorption. This is the second step in passive solar heating.

Insulate and Choose Materials to Retain Solar Heat

After collection and absorption, the third step is to retain the heat. This is done through careful material selection. Think of a hot sidewalk during the summer. That surface is retaining heat from the sun. Materials inside your home can do the same thing.

Choose stone, brick, tile, or concrete surfaces, which will hold the heat in during the middle of the day and release it during the evening when the sun goes down. This results in ambient temperatures regardless of the time of day.

You’ll also want to invest in the best insulation you can find for every space in the home. Insulation throughout the building reduces the amount of cold and hot air transfer. That helps keep the area cool when it’s hot outside and warm when there’s a chill in the air.

Insulation can be placed in the roof/attic, flooring, and walls. Additional insulation around doorways, windows, and even outlets are another form of passive solar heating.

Using Trombe walls, which are made of dark materials such as concrete, is another effective use of passive heating.

On the outside of the Trombe wall, a glazing is applied, leaving a gap between the glazing material and the wall to act as a greenhouse. This process naturally stores heat during the day and slowly releases it at night for passive temperature control.

Another passive heating technique is the use of natural landscape to shade the building against intense heat or to open the building up to receive sunlight as needed.

Inside or outside the home, window blinds or curtains are another way to moderate the heat.

Passive Solar Heating

All of these methods of collection and absorption lead to storage, which is called thermal mass. That thermal mass then releases the heat into the home through radiation, convection, or conduction.

As stated, collecting solar energy is only one side of the process. Without the proper systems in place, the harnessed energy would just dissipate.

So in conjunction with southward-facing windows, the home will be equipped with other passive design elements, such as roof overhangs that provide shading, and window and door placements that allow for natural ventilation through airflow.

These processes of managing how much heat there is and where it flows is the step in the passive solar heating process known as control.

Advantages of Passive Solar Energy

In addition to significant cost savings in heating and cooling the home, once established passive solar heating is free and requires no additional hardware to maintain.

A more subtle benefit is that passive solar heating doesn’t come with any potential health risks.

Obviously, passive solar design is also exceptionally good for the environment. A passive solar house reduces consumption of electricity, which means using less of the planet’s limited resources and reducing your carbon footprint.

Plus, it’s cleanly produced energy, meaning it doesn’t require burning fossil fuels and doesn’t pollute the air.

Disadvantages of Passive Solar Heating

If you’re not considering passive solar heating for a new home, it’s likely to be cost prohibitive. It’s much more affordable to incorporate during the initial build than it is to renovate in favor of passive design.

Another disadvantage is the limited quantity of energy produced. Passive solar collection only gathers a fraction of what the sun has to offer.

Since a strictly passive system doesn’t store energy long-term, additional heat or energy ends up not being consumed before it once again escapes into the atmosphere.

Passive solar heating is rarely the only form of heat for a home so you’ll still need other heating options.

Active Versus Passive Solar Heating

We’ve detailed the attributes of passive solar, but how is it different from active solar?

Active solar heating requires the installation of the entire system. This may be a small plug-and-play device that supplements power to an RV, or a comprehensive interlinked system used to power a business.

In addition to the flat photovoltaic panels, the system uses either liquid or air as a conductor for the energy. Systems relying on liquid are known as hydronic collectors, while those using air are called air collectors.

One type of system traps warm air and relies on a fan to move the air around the home, while the other collects heat and relies on a radiant heating system or a heat exchanger to transfer it.

The energy produced by active solar heating systems is reliable even after the sun goes down due to the ability to store the energy in batteries for later use. However, active systems are expensive to install and maintain.

Even with the initial cost and upkeep, active solar heating will save you significantly on your monthly energy costs, with most systems paying for themselves in seven to ten years.

On the downside of active solar panels, some reports claim the fluids used to store heat in the solar panel have the potential to release toxins into the air and create a health risk.

The equipment used in active systems also wear out, and disposal is deemed an environmental hazard.

Solar power is becoming ubiquitous in all kinds of devices and systems. It’s much more than just solar panels for the roof.

By the way, there are also now solar roof tiles that look like regular clay tiles but have solar capacity built into the design.

You may already have solar power around your home, even if you don’t have a whole-house system. For example, perhaps you have string lights fed by a small solar panel or a fence-post light with a solar panel on top.

You might have solar pathway lights or a solar-charged battery pack for charging your phone and other small devices.

The point is, while there are large and expensive active solar power systems, there are also ways to incorporate low-cost devices to suit everyday needs.

You can even learn How to Make and Install a DIY Solar Pool Cover

Designing a Solar Power Home

Both passive and active solar power collection are good for the environment and your pocketbook.

Decide which elements are worth the investment and make sense with your architectural design. For example, focusing on dark colors and stone or tile floors near south windows is a small step to take.

Designing the house top to bottom to optimize solar consumption and use is a much more comprehensive task.

If you’re thinking of building a passive house, enlist the help of a professional architect with experience in the field. What it costs you in professional fees will pay you back in clean air and energy savings.

The most energy-efficient home incorporates a combination of passive and active solar processes. Some homes are so efficient they actually produce more energy than they use.

In most areas, you can sell that excess energy to the power company. They put it back on the grid for others to use, while you get a discount on your power bill.

If you decide to build a home with a combination of solar benefits, you’ll want to evaluate the different types of solar panel systems to find the best one to meet your needs. Once installed, proper care will ensure a long life of sun absorption, to the benefit of your utility bill and the planet.

Check out 6 Ways to Optimize the Efficiency of Solar Panels for more information.

Examples of Solar Systems

We’ve outlined several passive and active types of solar energy and heating. The great thing about it is it can also be used for cooling.

Passive design elements shield the southern-facing windows to protect against the sun when it gets too warm in the summer. Roof overhangs, exterior glazing and slatted cladding are other useful architectural elements.

In addition to heating the house, solar power is also commonly used to heat water within the home. Taking up less space and costing less than solar panels for the entire house, water heater solar panels significantly cut your water-heating costs.

When connected to a solar water heater, a properly designed, installed, and maintained solar water heater can meet from half to nearly all of a home's hot water demand.

Two features, a collector and a storage tank, characterize most solar water heaters. Beyond these common features, solar water heating systems can vary significantly in design.

The various system designs can be classified as passive or active and as direct (also called open loop) or indirect (also called closed loop).

Passive systems operate without pumps and controls and can be more reliable, more durable, easier to maintain, longer lasting, and less expensive to operate than active systems.

Active solar water heaters incorporate pumps and controls to move heat transfer fluids from the collectors to the storage tanks.

Both active and passive solar water heating systems often require "conventional" water heaters as backups, or the solar systems function as preheaters for the conventional units.

A direct solar water heating system circulates household water through collectors and is not appropriate in climates in which freezing temperatures occur.

An indirect system should not experience problems with freezing because the fluid in the collectors is usually a form of antifreeze.

Do Some Passive Solar Energy Research

If you are considering purchasing a solar water heating system, you may want to compare products from different manufacturers.

The Solar Rating & Certification Corporation provides a benchmark for comparing the performance of some solar water heating systems.

The SRCC publishes performance ratings of both solar water heating systems and individual solar collectors. These published ratings are the results of independent, third party laboratory testing of these products.

All systems and collectors that have been certified by the SRCC will bear the SRCC label.

Keep in mind, though, that simply having an SRCC label does not imply that the product has superior performance. Carefully compare SRCC label information on different brands and models to ensure you are fully aware of projected performance.

Just choosing a solar water heater with good ratings is not enough, though. Proper design, sizing, installation, and maintenance are also critical to ensure efficient system performance.

Although the purchase and installation prices of solar water heaters are usually higher than those of conventional types, operating costs are much lower.

It’s no surprise solar heating comes with such great benefits, including huge savings for you and a kind nod to the environment, considering the energy source is natural and eternally renewable.

If you're interested in solar power, check out our pieces on cheap panels you can buy right now, how to optimize the panels you have, and using solar shingles on your roof.