What is a Solar Greenhouse? Explore the Solar Greenhouse Working Principle and its Types

A solar greenhouse is a specialized structure or shed that uses sunlight and the greenhouse effect to create favorable conditions for plant growth all year round, irrespective of the weather conditions outside the greenhouse. 

It is primarily of two types: 

• Passive solar greenhouse: It uses thermal masses like concrete or water barrels to store heat from sunlight for temperature control inside the greenhouse.
• Active solar greenhouse: It uses solar technologies like solar panels and solar thermal collectors, and generates electricity that’s used to regulate temperature inside the greenhouse. 

All solar greenhouses, whether active or passive, follow the same basic principle: they trap and store solar energy to maintain a stable environment for plant growth. 

Want to understand what a solar greenhouse is (and does) in detail, why design matters in building a solar greenhouse, how it differs from a traditional greenhouse, its types, and how it works? Let’s get started.

What is a Solar Greenhouse?

A solar greenhouse is a structure that creates plant-friendly conditions using just sunlight, without relying on fossil fuels. It’s a smart solution for growing food even in extremely cold or cloudy regions all year round. 

It has a very simple design:

• The south-facing windows and roof are glazed (or have panels): The South wall (which has huge windows) and the roof of a solar greenhouse are glazed using a translucent or transparent covering (either plastic or dyed glass) or fitted with solar panels or solar thermal collectors. The reason is that the South direction receives the maximum sunshine, and the glazing absorbs and traps it.
• The northern wall is insulated: The north-facing wall in a solar greenhouse is well insulated. This is done to ensure that the sunlight trapped due to the greenhouse effect does not escape. In other words, insulation prevents heat loss, which is necessary to maintain the temperature inside the greenhouse. 
• Creating the greenhouse effect immediately: As soon as the sunlight enters the solar-powered greenhouse, it warms the air, soil, and surfaces inside. This trapped heat raises the temperature and promotes plant growth.

Solar Greenhouse vs Traditional Greenhouse

Here are the major differences between traditional/ conventional greenhouses and solar greenhouses:

Traditional Greenhouse	Solar Greenhouse
Uses propane or gas to heat the air inside the greenhouse during the nighttime	Uses sunlight to create ideal, plant-growing conditions inside the greenhouse
Depends on external energy systems which makes the operational cost high	Relies solely on sunlight which makes the operational cost minimal
Shoots up electricity bills since heating and cooling would rely on electricity from fossil fuels	Active solar greenhouses use electricity generated by solar panels for heating and cooling, minimizing any impact on electricity bills
May or may not have south-facing glazed covering	The south walls are strictly glazed or have solar panels fitted to maximize sunlight absorption

What is the Solar Greenhouse Working Principle? 

A solar greenhouse works by using solar energy to create ideal temperatures inside the greenhouse so plants can thrive irrespective of how the weather fares outside. 

Here’s a step-by-step guide on the solar greenhouse working principle:

Step 1: Solar Greenhouse Uses Sunlight

The work begins the minute sunlight enters the greenhouse:  

• Translucent or transparent glazing material allows sunlight to enter: Sunlight entering the solar-powered greenhouse is used by plants for photosynthesis.
• Solar panels in active solar greenhouses transform sunlight into electricity: The electricity generated powers ventilation, lighting, and cooling systems to prevent overheating and maintain optimal growing conditions year-round.

Step 2: Sunlight Gets Trapped Inside the Solar Greenhouse

Here’s how this happens:

• North-facing wall is insulated: While south-facing walls have panels or glazed coverings to allow maximum sunlight to enter the greenhouse, the north-facing wall is thermally insulated to prevent trapped heat from seeping outside. 
• Greenhouse effect begins: Since insulated walls prevent heat loss, the temperature inside the solar greenhouse increases. This keeps the conditions warm and stable to support plant growth.
• Temperature regulation in passive solar greenhouses: In passive greenhouses, temperature regulation and ventilation occur naturally through convection or manually controlled vents. This is done to ensure it doesn’t get too hot inside the greenhouse.

Step 3: Storing the Heat to Maintain Temperatures at Night 

While the greenhouse effect keeps the conditions warm during the daytime when there’s sunlight, what about the nighttime? Well, a solar greenhouse is equipped to deal with it, whether it’s the active type or the passive type. 

Here’s how this happens:

• Using thermal masses to store heat: A passive solar greenhouse uses thermal masses like water barrels, concrete, or rocks to store the heat that’s trapped inside the greenhouse during the day. This stored heat is slowly dissipated at night, which keeps the temperature warm at night, even during the winter season.
• Using batteries to store solar electricity: An active solar greenhouse generates electricity that’s stored in batteries and used at night to control heating, cooling, and ventilation.

What Are the Types of Solar Greenhouses?

The two primary kinds of solar greenhouses are active solar greenhouses and passive solar greenhouses. As already explained, the basic working principle is the same for both. However, these have significant differences too. 

Let’s explore both types of solar greenhouses in detail.

#1 Passive Solar Greenhouse

A passive solar greenhouse is a structure that has large windows (facing true South) covered by a glazing material and thermally insulated north, east, and west walls. These can be:

• Attached to a building, which could be a barn or a house: These types of passive solar-powered greenhouses have a height in accordance with the height of the building they’re an extension of.
• An underground pit or structure sunken into the earth: These types use a solar chimney to control airflow which is necessary to ensure that it doesn’t get too hot inside the greenhouse. 

Here are the distinctive features that make a passive solar greenhouse truly unique:

• The glazed windows face true South: Since South direction gets maximum sunlight, passive solar greenhouses must face their true South, which is ~ 15 degrees to the east of South in the Northern Hemisphere.  
• There’s no requirement for mechanical cooling systems: Passive solar greenhouses have large windows, a solar chimney, or vents to control the airflow. When the air gets too hot, the windows can be manually opened to regulate the temperature.   

#2. Active Solar Greenhouse

Active solar greenhouses are modern structures that use advanced solar technologies to regulate internal temperatures, rather than relying solely on the natural climate.

They’re equipped with systems like fans and heat exchangers to manage heating and cooling. Unlike traditional greenhouses that drive up electricity costs, active solar greenhouses generate their own power from sunlight, keeping utility expenses low.  

Interestingly, active solar greenhouses may also incorporate thermal mass (like water barrels or concrete) to store heat, similar to passive solar greenhouses.

Based on the solar technology being used, further variations occur. Here’s what this means:

• Active solar greenhouse that uses solar thermal collectors: The heat from sunlight is collected by solar thermal collectors. Then, the heat transfer medium inside the collectors (which could be water or air) is circulated throughout the collectors for heat distribution inside the greenhouse at night. 
• Active solar greenhouse that uses solar panels: The solar panels produce electricity, which is used to control the temperature inside the greenhouse.
• Off-grid/standalone active solar greenhouse: This type uses solar panels to produce electricity. This electricity is used to charge batteries. The batteries provide electricity for temperature control at night.     

Active Solar Greenhouse vs Passive Solar Greenhouse

Now, let’s check out how these two primary types differ from each other:

Feature	Active Solar Greenhouse	Passive Solar Greenhouse
Energy usage	Uses solar panels to convert sunlight into electricity	Uses sunlight directly for heat without electrical conversion
Heating and cooling	Controlled using powered systems like fans, heaters, coolers	Regulated using natural convection, insulation, and thermal mass
Ventilation	Mechanical ventilation via solar-powered fans	Natural ventilation via vents, windows, and solar chimneys
Temperature control	Precise and programmable with sensors and thermostats	Depends on thermal mass and the greenhouse design
Thermal energy storage	Solar electricity stored in batteries for use at night or cloudy days	Heat stored in materials like water barrels, rocks, or concrete
Setup cost	Higher than passive type due to solar panels, batteries, and electrical components	Lower due to simpler construction and fewer tech components
Ideal use case	Ideal for regions with inconsistent sunlight or commercial operations	Best for sunny regions with stable daylightSuitable for home gardensBest for plants/ crops that are not too temperature-sensitive

What Are the Benefits and Drawbacks of a Solar Greenhouse?

Let’s walk you through the benefits and drawbacks of both active and passive solar greenhouses in detail.

Benefits and Drawbacks of a Passive Solar Greenhouse

Here’s a tabulated snapshot of the benefits and drawbacks of a passive solar greenhouse:

Benefits of a passive solar greenhouse	Drawbacks of a passive solar greenhouse
Runs without external power as it relies solely on sunlight and thermal mass	Performance drops during prolonged cloudy or low-sunlight periods
Low setup and operational costs which also results in minimal utility bills	Limited automation means more manual intervention
No carbon emissions and no batteries or electrical waste	Less control over internal climateMay not suit sensitive or tropical crops
No electronics or moving parts to maintain	Natural airflow may be inadequate during extreme heat
Fully off-gridIdeal for remote or rural areas	Requires thoughtful seasonal adjustments like shading in summers

Benefits and Drawbacks of an Active Solar Greenhouse

Let’s check out the benefits and drawbacks of an active solar greenhouse now:

Benefits of an active solar greenhouse	Drawbacks of an active solar greenhouse
Precise temperature, humidity, and airflow regulation	Dependent on solar panels, batteries, and electronic controls
Ideal for extreme climatesSupports plant growth even in harsh winters	May underperform without backup systems during extended cloudy periods
Ideal for larger or commercial greenhouses needing consistent output	Battery installation and disposal can increase environmental impact
Suitable for sensitive, high-value, or tropical crops	Not cost-effective for small-scale or hobby gardeners
Active ventilation prevents overheating more reliably	Fan and control system maintenance is required
Stores excess solar electricity in batteries for nighttime or cloudy-day use	Higher upfront and ongoing costs vs passive solar greenhouses

Which Type of Solar Greenhouse is Right For You?

The right choice of solar greenhouse largely depends on the following factors:

• Climate
• Budget
• Energy needs
• The sensitivity of crops

Choose a passive solar-powered greenhouse if: 

• You’re growing hardy plants (the ones that can withstand various environmental conditions) in a sunny area.
• You prefer simplicity and low maintenance. 

Opt for an active solar greenhouse if: 

• You’re in a colder climate
• You’re growing delicate or high-yield crops
• You need precise temperature control year-round

Here’s a tabulated snapshot of everything you should take into account for choosing the right solar greenhouse: 

Factors	When to choose a passive solar greenhouse?	When to choose an active solar greenhouse?
Climate	You live in a sunny region with stable daylight	You live in a cold, cloudy, or variable climate
Crop sensitivity	Your plants are not highly sensitive to temperature / humidity fluctuations	You’re growing tropical or high-value crops
Budget	You have limited funds and prefer low setup/maintenance costs	You can invest more in automation and solar tech upfront
Energy dependency	You want a fully off-grid solution with no electrical components	You want to use solar-generated electricity for heating/cooling systems
Desired automation level	You’re fine with manual ventilation and seasonal adjustments	You want programmable, hands-free temperature and humidity regulation
Greenhouse size	You’re building a small-scale or backyard greenhouse	You’re setting up a large or commercial-scale operation

Which Are the Best Glazing Materials For a Solar Greenhouse? Instructions for DIY Enthusiasts

If you’re building a solar greenhouse all by yourself, we’ve got a list of the best materials you’ll need:

• Polycarbonate panels (twin-wall or multi-wall)
• Acrylic sheets (PMMA)
• Tempered glass
• Polyethene film (single or double layer)
• Solar panels

Conclusion

One of the best ways to utilize sunlight for food abundance even in the face of extreme climate is a solar greenhouse. It’s very much possible to control light and temperature inside solar greenhouses. Hence, they are used to grow vegetables and flowers all year long. 

Whether you choose to build an active solar greenhouse or a passive one should primarily factor from the scale of production and crop sensitivity. 

• When to use an active solar greenhouse? Commercial setups that aim to reap crops that are extensively sensitive to humidity and temperature should use an active solar greenhouse since the chances of crop failure due to less than ideal temperature and improper ventilation are next to none. 

When to use a passive solar greenhouse? For hobby gardeners and those growing plants that are not extremely temperature sensitive, investing in passive solar greenhouses is a better decision.

FAQs

Q1. What is the principle of a solar greenhouse system?

Ans. The principle of a solar greenhouse system is to harness, trap, and store solar energy to create a stable and warm environment for plant growth, without relying on fossil fuels as energy sources. Here’s the step-by-step explanation: Sunlight enters the greenhouse through transparent or translucent glazing (like polycarbonate or glass). This light is then absorbed by internal surfaces and converted into heat, raising the temperature inside. The structure is designed to retain this heat using insulation and thermal mass like water barrels, concrete, or stone. Some solar greenhouses also include solar panels to generate electricity for ventilation, heating, and lighting. These are known as active solar greenhouses.

Q2. How is a solar greenhouse constructed?

Ans. Here’s a step-by-step guide on how to construct a solar greenhouse: Step 1: Choose the Right Location: Pick a site with maximum sun exposure, ideally facing true South (in the Northern Hemisphere). Step 2: Design the Structure: Use a sloped roof for solar gain, with transparent glazing on the south-facing side and insulated walls on the north, east, and west. Step 3: Build the Frame: Construct the frame using durable materials like wood, steel, or aluminum, ensuring it supports the glazing and withstands local weather. Step 4: Install Glazing and Insulation: Fix the glazing panels and add insulation to non-glazed walls and the foundation to reduce heat loss. Step 5: Add Thermal Mass: Place water barrels, stone, or concrete inside the solar greenhouse to absorb heat during the day and release it at night. Step 6: Integrate Solar Systems (if active): Install solar panels, fans, lights, and batteries if you're building an active solar greenhouse. Step 7: Set Up Ventilation: Add operable vents or solar-powered fans for airflow and temperature control.

Q3. How does the greenhouse effect work with solar energy?

Ans. In a solar greenhouse, the greenhouse effect works by allowing sunlight to enter through transparent glazing, where it’s absorbed by surfaces like soil, plants, and thermal mass. This absorbed solar energy is then converted into heat. Since the structure is insulated, the heat gets trapped inside, warming the air and maintaining an ideal growing temperature.

Q4. What are the benefits of solar greenhouses?

Ans. The three main advantages of solar greenhouses are: A step towards sustainable living: The fact that the sun is a renewable energy source is one of the most crucial benefits of a solar-powered greenhouse. It helps in walking a step towards sustainable development. Environment-friendly: A solar energy greenhouse can curb conventional and toxic greenhouse emissions. Greenhouse gas emissions are one of the most severe and significant environmental problems. Thus, the importance of solar greenhouse increases multifold in this case. Cost-effective: Electric or natural gas-heated greenhouses can be expensive to maintain. On the other hand, a person won’t typically have to worry about the electricity bill when using a solar greenhouse. After all, there is no cost involved when using the sun as a resource. You only need to bear the installation cost, as maintenance is inexpensive.