Solar heating systems are nothing new: we humans have been applying the concept for millenia. The ancient Greeks, for instance, had ‘sunrooms’, indoor spaces kept warm through the efficient capture and storage of solar energy.

Today, 1 out of 3 American families struggle with paying their energy bills. The largest chunk of the bills — 45% — goes towards heating costs. With that said, households can benefit hugely by exploring the different ways solar heating panels or systems can be used to keep us warm and drastically reduce those exorbitant bills.

There are different ways you can use solar to generate heat, including:

In this article, we will focus on solar space heating. Here’s a quick look at the potential benefits of using solar heating panels for your home:

Benefits of a solar heating system

If you’re sure not what your solar heating options are, this comprehensive solar heating guide is for you.

Table of contents

What are active and passive solar heating systems?

Utilizing energy produced by the sun is the best way to keep your home warm during winter. There are two solar heating methods — passive solar heating and active solar heating.

Passive solar heating

Passive solar heating refers to the technique of using the abundantly available energy to keep your house warm during winter. In this approach, the walls, windows, and floors of the house must be thoughtfully designed to collect and store heat from the sun during daytime, and gradually distribute it to each room. 

In passive solar heating, no active mechanisms are used to gather or distribute the solar heat through the living spaces. Rather, it involves:

  • Building rooms with large, sun-facing windows to let the sun’s energy into the rooms
  • Using concrete floors and a thermal-mass masonry to capture and store heat
  • Applying thick, airtight insulation on the outer walls to seal in the heat
  • Opening and closing windows and vents to regulate temperature, and
  • Using insulated blinds, drapes, or shutters to trap the heat in cold weather conditions

If you incorporate passive solar heating techniques when building a new house, you can see savings of up to 30-70 percent on your heating bill, depending on your location and climate.

Active solar heating

Active solar heating systems (unlike passive solar heating systems) use mechanical devices, like pumps, collectors, and storage tanks to circulate the heat throughout a home.

In an active solar heating system, a collector (made up of flat-plate PV panels) collects solar energy from the sun. The air or water (or antifreeze) inside a pipe gets warmed up by the heat transferred by the collector. This heat is either carried directly to the interior space by a pump or a venting mechanism, or is stored in a storage system.

Here’s a quick video that explains how active solar heating systems work:

Both active and passive solar heating systems supplement your home’s heating system by bringing warmth to exactly where you need it. With solar space heating, you can avoid paying the huge electricity bills that come with conventional heaters. The natural energy from the sun acts as a cost-effective supplement to your current heating system.

The main differences between active and passive solar heating

  • In active solar space heating, pumps, collectors, storage tanks, and other mechanisms are used to circulate heat in homes
  • In passive solar heating systems, the collectors are used to gather energy and heat is trapped and circulated naturally, without involving mechanical devices
  • Active systems are more complicated than passive heating systems 
  • Passive systems are typically less expensive than active space heating systems
  • Passive systems work best with new buildings, whereas active systems can be used with both new and retrofitted homes

Passive heating systems can only be implemented in new homes, so it’s only relevant for those who are about to build a new house. By contrast, active heating can be retrofitted in existing homes with traditional heating systems, in many different ways.

As active solar heating is a more practical option for most of us, let’s take a closer look at how we can use it for our homes.

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What are the different ways to use active solar heating in homes?

There are 2 basic types of active solar panel heating systems — solar air space heating and solar water heating systems (hydronic systems).

#1 Solar air space heating

Solar air space heating directly heats your living space using room air heaters. A roof-mounted or wall-mounted air heater pulls cold air into a solar collector, where it is heated and then warm air is blown back into the room.

With roof-mounted heaters, ducts are used to push heated air into the room. And with wall-mounted room heaters placed on south-facing walls, holes are made through the wall in order for the air to pass into the room.

Since 2010, the US has produced some record-breaking solar air heating installations, with systems up to 10,000-50,000ft² being installed on a single wall.

#2 Solar water heating systems

Solar water heating systems (hydronic systems) have solar collectors that absorb solar radiation and convert it into heat. Either a non-toxic glycol antifreeze or water flows through the solar collectors so that the heat energy from collectors is transferred to the fluid.

As the liquid quickly passes through the solar collector, its temperature increases up to 10°–20°F (5.6°–11°C). The warm fluid then flows to a heat exchanger or a water storage tank.

There are 3 main types of liquid-based solar space heating systems — radiant floor systems, hot-water baseboards, and central forced air systems. Let’s find out how these systems work.

A) Solar water heating: radiant floor systems

In a radiant heating system, the heated liquid moves through a system of pipes that are embedded in a thin concrete floor. The solar-heated liquid from the pipes then radiates heat into each of the rooms.

The following factors should be kept in mind with radiant floor heating: The radiant floor system’s efficiency can become compromised if the floor is covered with thick rugs or carpeting. The floor should ideally be finished with tiles.

If the radiant flooring is carefully designed, the need for a separate heat storage tank can be eliminated.

A conventional boiler or even a standard domestic water heater can be used to supply back-up heat.

To heat a space from a cold start, radiant slab systems take longer than other heat distribution systems. However, once operating, they provide consistent heating throughout the home.

Sunlight hits panels on the roof, which transfers heat into floors inside the house

B) Solar water heating: hot-water baseboards

Baseboard hot water systems are installed at the baseboard or typically at a point close to the ground, allowing heat to rise naturally and for even distribution of heat within a space.

A system of pipes installed in the baseboard pumps hot water, transferring the heat from the heated water to the room. The cool water is piped back to the boiler room to reheat and to quickly influx hot water. The fin-shaped pipes in the baseboard are usually made of copper to ensure faster heat dissipation from their surface.

Illustration demonstrating design and heat flow of hot water baseboards

To heat a room effectively, hot-water baseboards/radiators require water temperature to be between 160° – 180°F (71° – 82°C). As flat plate collectors can heat the liquid between 90° – 120°F (32° – 49°C), a backup heating system (or evacuated tube collectors) is used to increase the temperature of the solar-heated liquid.

C) Solar water heating: central forced-air systems

A liquid heating system is converted into a forced-air heating system by placing a heating coil (liquid-to-air heat exchanger) in the air-return duct of a room. As air is pulled into the duct from a room, it heats up from the solar-heated liquid in the heat exchanger. Additional heat, if required, is supplied by the furnace. The heating coil must be large enough to transfer the required amount of heat to the room, even at the lowest operating temperature of the collector. Liquid solar thermal energy systems work the best for central heating in homes.

Air changes temperature as it flows through the house with a forced-air heating system

Conclusion: Are solar heating panels good for your home?

There are several reasons to believe that active and passive solar space heating systems are good for your home:

If you think that active or passive heating systems are not viable options for your home, there is a way you can still significantly cut down on your electricity bills.

By installing PV panels on your roofs, you can use free energy from the sun to power your heating — without spending a big chunk of your income on electricity bills every month. 

See how much you can save with a standard rooftop solar system