Solar Panels

What is the Difference Between Active and Passive Solar Energy?

By:Michael Johns

passive vs active solar energy

In this article, you will learn about the differences between active and passive solar energy. 

Solar power is a brilliant source of renewable energy. It is a way to create electricity and heat from the sun. Light and heat produced by the sun can be used as an unlimited energy source for our homes and other areas of life. There are two different ways in which the energy can be harnessed which are called active and passive.

Keep reading to compare passive and active solar panel systems, plus the pros and cons of each.

Active vs Passive Solar Energy

The difference between active and passive solar energy can be confusing to understand. Afterall, both use the sun to achieve their goals.

In simple terms, an active solar system takes the sun’s energy and actively converts it into another usable energy source. This is often converting light to electricity using the photovoltaic (PV) effect. Comparatively, passive solar energy is utilized without the need to convert energy and uses the sun’s heat or light directly.

What is Active Solar Energy?

Active solar energy is commonly used to generate heat and electricity. Examples of this are solar panels and collectors on house rooftops. These components are designed to capture the heat or light from the sun and convert it into a more usable energy form.

PV Solar Panels

This is what you will picture when you think about solar panels. These are the panels that absorb sunlight and generate electricity. They are filled with photovoltaic silicon cells. When these cells are hit with photons of sunlight it creates an electric current. The light energy from the sun energizes electronics to produce electricity. The panel is working actively converting light to electricity. There have been huge advances in PV technology over recent decades. The best panel can now make the energy conversion at a 22% – 23% efficiency. This means around 23% of sunlight energy becomes electricity. 

PV solar cell
Example of a PV solar cell

PV solar panels are very popular across the world as they can be used in a very versatile manner. You can mount them on buildings and connect them to the main grid. This allows you to send electricity to the property and any excess can be then sold to the utility grid using Net Energy Metering.

In addition, you can use this type of solar energy in an off-grid scenario. You’ll see it on RVs, boats, semi-trucks, remote cabins, and even in a portable design. The active solar energy is created by electricity and then stored in a battery to be used by electronics. For example, you could recharge a deep cycle battery with a PV solar panel.

Solar Water Heater/Collector

If you look closely at solar panel systems you’ll start to notice a different design in some cases. The panel actually consists of lots of black pipes. This is a solar collector and it is used to heat water and air. In actual fact, these can use both active and passive solar energy. An active solar collector will absorb the heat energy from the sun into a liquid or gas inside the pipes. Then this heated substance is used to heat water in a tank or pumped around a heating system to radiate warm air. This is active solar energy as the heat energy from the sun is being transferred between multiple components and pumped around to its end goal of heating water or air.

active solar water heater
Example of a solar water heater

You can also find passive energy solar collectors in hot countries. These devices will directly heat water through the sun’s energy with no need for energy conversion or mechanical transfer.

Advantages of Active Solar Energy

Let’s take a look at the benefits of active solar energy:

  • Can be used to create the PV effect. This allows you to generate electricity from sunlight. 
  • Enables you to generate electricity anywhere there is sunlight.
  • Free source of electricity and heat. The sun’s energy is almost unlimited and has no ongoing costs to use.
  • Efficiency of heating can be increased by using heat-absorbing liquids known as hydronic collectors.
  • Enables you to convert the sun’s energy into more useful types of energy.
  • Usually a profitable long term investment

Disadvantages of Active Solar Energy

Here are the drawbacks to active solar energy:

  • It is expensive as you need specialist equipment to generate electricity or heat.
  • Usually requires professional installation which adds to complexity and costs.
  • Residential and commercial solar systems require approval from the local city and utility companies.
  • Will have ongoing maintenance and cleaning.
  • PV solar panels degrade over time and become less efficient. Eventually, they need replacing.

What is Passive Solar Energy?

Passive solar energy uses the heat and light of the sun directly without the need to convert the energy. Most commonly it is used as a way to heat a property or building without the need to add active solar equipment. 

You will experience passive solar energy in everyday life. You can find an example of it in anything that the sun heats up. Think about a car on a hot sunny day. If you touch the bodywork of the car it is hot, plus the inside of the car is warmer than the air temperature outside. This is passive solar energy heating up the car.

The same concept is used to structure and heat buildings like greenhouses and conservatories. The heat and light of the sun heats the inside of the building. Objects inside these structures absorb the heat energy and increase in temperature without any help or energy conversion. Even during winter months, you will still notice that a building with sunny south facing windows is passively heated by the sun. 

solar greenhouse
A greenhouse uses passive solar energy

Often buildings are specifically designed to take advantage of this effect. Architects will design large south facing windows with thick concrete walls on the north side. The sun then passes through the glass and passively heats the thick wall. This wall retains this heat during the day and slowly releases it during the night.

Advantages of Passive Solar Energy

Here’s the benefits to passive solar energy:

  • Cheaper to use as no specialist equipment is required.
  • Can be incorporated into the design of the building.
  • An easy way to heat a building at all times of year.
  • Free source of heating with no ongoing costs.
  • Useful for growing plants out of season in greenhouses.

Disadvantages of Active Solar Energy

Let’s take a look at the drawback to active solar energy:

  • Weather dependent as it can struggle to create heat during overcast conditions. Plus it can overheat a property in the summer.
  • Needs careful design and orientation to be effective
  • Can’t generate electricity.
  • Often needs to be supplemented by other heat energy sources or active solar energy.

What is Better Passive or Active Solar Energy?

Most people use active solar energy as you can add PV solar panels and solar collectors to almost any building. All you need is a space like a rooftop that receives direct sunlight in the middle of the day. It has multiple benefits including the ability to produce electricity.

Passive solar energy is still very useful but isn’t as easy to install on every property. It needs to be incorporated into the overall plans of a building. This is because it requires large windows oriented in the correct direction, plus objects like thick walls to absorb heat. In addition, you have less control over how the heat energy is used which can lead to problems like overheating in the summer.

To be honest, one is not necessarily better than the other. It all depends on what you are trying to achieve. For example, passive solar energy might not suit a house but can be incredibly useful in greenhouses that need to stay warm all year round. Many botanical garden greenhouses, like the Eden project, use a mixture of passive and active solar energy to run their facilities. 

Difference Between Active and Passive Solar Systems Summary

I hope reading this article helps you answer the question ‘What is the difference between active and passive solar energy?’

In simple terms, you can think of the difference like this:

  • Passive = The sun heating things directly.
  • Active = Converting the sun’s energy into another form, like electricity.

You’ll see examples of both of these in everyday life, particularly in modern eco-homes. So next time you go out see if you can spot the differences in your local area.