When you research solar heating options you will likely come across two different types of systems. We class these as either active or passive, but what’s the between an active and a passive solar energy system? This article looks at both types, comparing the two to give you a better understanding of the subject.
Active Solar Energy Systems
Let’s start by looking at active solar energy heating systems. When we use the term ‘active’ we mean any system that makes use of moving parts, electronic controls, or other intelligent systems.
Active solar energy systems work by heating either a liquid or a fluid inside a solar collector. This heat energy can then be transferred to water in a heat exchanger (if using fluids) or blown into a building (if using air). Both of these options help to heat a home.
Solar hot water can be used in a central heating system, helping to keep radiators warm. You can also use it directly from taps and showers as part of your hot water supply. Air can be blown into a building using a solar air heater, again helping to keep it warm.
What makes these types of systems ‘active solar’ is the mechanisms they use. This can be as simple as using a pump to move fluid around a solar hot water system. It can also include the fans that a solar air heating system uses to move warm air around a building.
Passive Solar Energy Systems
To get a better understanding of the difference between active and passive solar energy, let’s now take a look at passive solar heating.
The key difference here is that passive systems make use of no moving parts, electronics, or other controls. Instead, they rely solely upon the natural absorption of solar radiation in thermal mass. The term thermal mass means any material that stores heat. Some good examples of thermal mass include; water, concrete, clay, earth, rock, and wood.
So, how does passive solar work? Well, architects carefully design passive buildings using the right materials for thermal mass. They make use of large south-facing windows to allow solar radiation into the building.
Once solar radiation enters a passive building, it can be absorbed by thermal mass which retains heat. Over time, the building will release this energy, helping to keep the building warm.
Most modern homes are built with passive solar design in mind. This forms the basis of good energy efficiency and is often an attractive feature for those looking to buy a home.
Active vs Passive Solar: Which is Best?
When comparing active and passive solar energy systems, it’s important to remember that each has a range of benefits and drawbacks. The following sections weigh these up for both active and passive systems.
Active Solar – Pros
- Clean, good for the environment, and reduces your carbon footprint.
- It can reduce or eliminate your heating bills depending on the size of your system.
- Active solar is more efficient than passive solar. Mechanical elements increase the effectiveness of such systems.
- It often has a higher capacity than passive solar.
- Solar installation companies can retrofit solar technology to an existing building.
Active Solar – Cons
- Active solar technology is expensive. Solar collectors, heat exchangers (for hot water), and ventilation systems (for solar air heaters) can cost a considerable amount.
- The technology takes up space both inside and outside of the home.
- Active solar systems need to be maintained and can sometimes break down.
- It requires external power sources to operate pumps, fans, and any electrical control systems.
- Solar collectors can be unattractive to some people.
Passive Solar – Pros
- Clean, good for the environment, and reduces your carbon footprint.
- Passive solar technology is cheaper than active technology. It doesn’t cost much more to build a passive house than a regular one.
- It can reduce your utility bills and does not require any external power supply.
- Very reliable with no moving parts or control systems.
- It does not require any maintenance other than usual building maintenance.
- There are no solar collectors helping to maintain the aesthetics of a building.
Passive Solar – Cons
- Passive solar is less efficient than active solar technology.
- It is unlikely to eliminate your heating bills but still helps to reduce them.
- It cannot be retrofitted to an existing building. Passive solar design is built into the structure of a new building.
- May require trees and other vegetation to be cut down for adequate sunlight to reach windows.
Conclusion
So there we have the difference between active and passive solar heating systems. Active systems make use of moving parts, helping to improve their efficiency over passive solar buildings. However, passive solar is still an effective way of reducing your energy bills.
Comparing the two, it is clear that active solar systems can be more effective than passive solar systems. It is, however, unfair to compare the two directly as both have their uses. In fact, many passive homes include active solar technologies to make better use of the sun as an energy source.
Some homes feature both active and passive heating systems together with solar panels for electricity production. Using a design of this nature often results in a house becoming carbon neutral – something we should all be striving for.
