Passive vs. Active Solar Energy: What Are the Differences?
Solar energy is all the rage nowadays, with solar energy expected to comprise almost 50% of new electrical installations in 2022.
That includes both residential solar panels and power plants centered around this renewable energy source. Did you know there are other ways to enjoy the benefits of solar apart from these two principal sources?
When you decide to put the sun’s energy to work for you, you can choose between active or passive solar energy.
Are you still in the dark about passive vs. active solar energy? Shed some light on the matter with this active and passive solar energy guide.
What Is Passive Solar Energy?
Passive solar energy involves using the sun’s energy in its purest form. There are no devices or appliances involved in the process.
This type of solar energy is most commonly used for heating and cooling. It relies on the heat generated by the sun or thermodynamics to function.
In the simplest terms, thermodynamics means that warm air travels from a high concentration to a low concentration, i.e. from warm areas to cool ones.
The principle of passive solar energy is simple – when you expose something to sunlight it warms up. Take away the sunlight and it stays cool.
For instance, if you leave your car parked in direct sunlight, it warms up inside. That’s because your car’s windows create a greenhouse effect inside the vehicle.
The same principle applies to your house. A passive solar space heating system relies on the building’s design to capture sunlight and heat the interiors.
Some examples of passive solar power at work include sunrooms and ordinary clotheslines.
Types of Passive Solar Energy Systems
Despite the simplicity of passive solar energy, there are three different types of systems in use today. These are:
Direct Solar Systems
These set-ups use the indoor space of the building to warm the interiors. Some examples include south-facing windows with large panes of glass and masonry or concrete walls and floors.
Indirect Solar Systems
Indirect solar systems use rooftop ponds and Trombe walls to maintain the home’s internal temperature.
Vented Trombe walls, built behind glass, allow hot air to build up between the wall and the glass. You can open the vents at night to let this warm air move inside.
Roof ponds may have insulation or glass above them, which traps the sun’s heat in the water to keep the house warm.
Isolated Solar Systems
Sunrooms located adjacent to the house with vents to allow airflow when desired work similarly to Trombe walls. The sun heats the room during the day and opening the vents at night allows the heat to stream into the house.
What Is Active Solar Energy?
Active solar energy refers to harnessing the sun’s energy and then storing it for later use. It’s the fastest growing type of solar energy in modern times, saving millions of tons of coal every month.
Active solar energy uses either air or liquid to capture heat from the sun, move it to a storage area, and then convert it to energy.
Solar panels are an example of active solar energy. They actively convert the sun’s rays into electricity which you can use just like regular electricity.
Most active solar energy systems rely on external devices to convert the sun’s energy into a usable form, as follows:
Solar Energy Collectors
Flat-plate collectors absorb solar energy and convert it to heat, using a liquid. Solar panels use PV cells to convert the sun’s energy directly into an electric current.
Some active solar systems for heating use a mirror to concentrate the sun’s rays onto a collector or insulated pipe. These pipes can reach temperatures of a few hundred degrees on a hot day.
Solar Energy Storage
Liquid-based systems rely on water tanks to store heated water, while rock bins can hold heated air. Solar panels store excess electricity in batteries connected to an inverter.
Solar Energy Distribution
Liquid-based systems use pumps, central forced air, hot-water baseboards, or radiant slabs to distribute energy, while air-based systems distribute heat via ducts and fans.
The electricity generated from solar panels travels through your home by connecting to your home’s wiring network.
Types of Active Solar Energy
Apart from solar panels, there are three lesser-known types of active solar energy. These are:
Active Solar Space Heating
Solar space heaters distribute warm air inside your home using pumps, fans, blowers, and ducts. These systems collect, store, and circulate warm air as desired.
Active Solar Pool Heating
This type of heating system works with your pool pump to warm your pool water all year round. The water flows through solar collectors and back into the pool once it’s heated sufficiently.
There are no storage tanks involved.
Active Solar Water Heating
Like pool heaters, active solar water heaters use pumps to circulate hot water or heat-transfer fluid.
Indirect water heating systems heat a type of anti-freeze mixture in the collector and transfer it to a storage tank. There, a heat exchanger moves the heat from this liquid to your household water supply.
Direct systems work the same as solar pool heaters, except they store the hot water in insulated tanks until needed.
Passive vs. Active Solar Energy Pros and Cons
Both these types of solar energy systems work very well when used in the correct context, but they do have their drawbacks, too.
Passive solar energy depends entirely on the climate in your area. That means, your interiors may become overheated on very hot days.
On cloudy days, it might not generate enough heat to warm your home sufficiently. A major drawback of passive solar is that you can’t use it to power anything else.
Active solar energy is more versatile than the passive variety. With solar panels, you can generate enough electricity to power your entire home.
Unfortunately, active solar devices are a lot more expensive than using free sunlight to warm your home, and they require specialized installation and equipment.
Finding Solutions That Suit You
When comparing passive vs. active solar energy, one shouldn’t view them as mutually exclusive. You can never have too much renewable energy, so consider your options for both when trying to find the happy medium between expense and convenience.
Passive heating solutions mean your solar panels don’t need to produce as much electricity. So, you’ll need fewer of these expensive instruments when designing an energy-efficient solution for your home.
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