Passive Solar Greenhouse Actually Possible? Solar Heater Truth Explained

Georgette Kilgore headshot, wearing 8 Billion Trees shirt with forest in the background.Written by Georgette Kilgore

Solar Panels | April 1, 2024

Woman standing next to a solar greenhouse wonders is a passive solar greenhouse practical and can a solar heater for greenhouse plants work and is there a guide for how to heat a greenhouse with solar panels?

Is a passive solar greenhouse actually possible?

Changing seasons highlight times in the year when farmers can grow crops. However, what if there was a way to combine heat, power and water to produce crops all year round?

This is where solar greenhouses come along, as they do not need external energy sources and can maintain crops even through the harshest winters using power that was generated ‘passively.’

But, is a passive solar greenhouse possible and practical on a large scale? can solar heaters work to maintain temperatures that allow food growing all year round?

This complete guide explains how a solar greenhouse works to generate heat for growing plants in a controlled environment.

Passive Solar Greenhouse

Is a passive solar greenhouse actually possible?

Definitely, in fact, passive solar greenhouses are more energy efficient and cost-effective in the long run than regular greenhouses.

A row of solar heater situated on a rooftop with the sky in the background.

(Image: singhvp9312)

Generally, a greenhouse uses natural energy from the sun as the main heating source. In situations where there is no sun, such as winters and cloudy days, the greenhouse will require external heating sources such as propane and electricity.

In contrast, a passive solar greenhouse does not require any artificial heating source to supplement the solar energy when there is no sunlight.6 Instead, this type of greenhouse relies entirely on stored heat to facilitate a consistent temperature in the greenhouse.

The passive solar greenhouses heat the building using solar energy during the day and use heat storing devices placed within the greenhouses to circulate excess heat throughout the night.7 The heat-storing devices may include large barrels of water, large bales of hay or concrete areas.

Workings of a Solar Greenhouse

Solar greenhouses are more oriented towards the sun than regular greenhouses.2

These structures are built with windows facing south for maximum sunlight since the US is in the northern hemisphere.

A row of flat-plate solar energy collector situated on top of a school building.

(Image: Joe Ryan, NREL 1969013)

The structure will have black stones on the north that help hold and absorb solar energy.

Passive solar greenhouses are built mainly with glass to maximize energy from the sun. They also have natural ventilation that reduces heat in summer and prevents heat loss in winter.

For instance, a farmer can use dark-colored barrels filled with water and placed strategically to capture sunlight during the day. Then at night, when temperatures cool, the water barrels radiate the heat back out into the greenhouse.

In case of overheating, the farmer can use fans to regulate the heat throughout the building.

Thermal mass accumulation does not necessarily have to be water. However, this is the best option since water has a high volumetric heat capacity.

Experts recommend water-filled barrels as energy sources for passive solar greenhouses because they are nice slow-release heat sources due to the unique characteristics of water.

The water warms up slowly during the day and gently and slowly releases heat when temperatures cool at night.

Solar Power for Greenhouse

In the 19th century, when greenhouses first became popular, they revolutionized how crops grow.

Greenhouses today can maintain constant temperatures throughout the year, making them ideal for changing seasons and harsh climates.

Green vegetables situated inside a greenhouse with ceiling fans.

(Image: Mark Stebnicki9)

However, despite their numerous benefits, greenhouses have one major drawback: they are very energy intensive.

In harsh climates, greenhouses need external heating sources, whether through electricity or gas.In the winter, although sunlight does warm the interior somewhat, temperatures can still drop below freezing at night, requiring external heat.

But as solar panels become less expensive and more mainstream, passive solar greenhouse options can utilize the sun’s energy to maintain a grow-able temperature.

Most solar energy facts guarantee the efficacy of this renewable energy source. Solar energy can power greenhouses in two distinct ways, they include:

  1. Using solar heater for greenhouse: in this case, the heater converts electricity into thermal energy, which is then circulated in the greenhouse.5
  2. Passive solar greenhouses: In this case, all heating in the greenhouse comes from stored energy from the sun.

Solar Heater for Greenhouse

A greenhouse shelters plants from freezing temperatures, especially during cold seasons. The greenhouse needs a heater to remove the chill, and investing in a solar heater for greenhouse is one of the many options to generating that heat.

Solar greenhouse heaters convert energy from the sun into thermal energy and distribute it all through the greenhouse.

These solar greenhouse heaters need collectors to convert and distribute thermal energy. Such collectors can be solar heat absorption panels or photovoltaic (PV) panels.

(Image: Tobi K10)

Using PV panels also means including electric heaters that convert electricity into heat. In this setup, it’s best to use an efficient heater with active air circulation.

On the other hand, using a solar heat absorption panel produces heat directly and distributes it by convection or through 12V circulation fans powered by auxiliary PV panels.

Additionally, PV collection systems should include the following components:

  • Collectors
  • Heater
  • Batteries
  • Thermal mass storage

Alternatively, the farmer can use solar furnaces, which are simpler setups than PV panel systems. These solar furnaces come as single units and consist of black panels that heat up as they absorb sunlight.

The furnace absorbs cold air from the greenhouse, which circulates in the panel and is released back into the greenhouse as heated air. The panel has a hot air vent at the top, while the cold air intake happens at the bottom because hot air is lighter and rises higher than cold air.

The air circulates naturally via convection, and using fans improves heating and circulation.

What To Consider Before Buying a Solar Heater for Greenhouse

It’s important to note that using only a solar heater to heat a greenhouse is only practical if the farmer includes a way to store energy.

Even so, solar heaters reduce the cost of running electric or gas heaters.

A cartoon illustration of a model of a solar power for greenhouse with plants arranged inside with semi-transparent solar cells as roofing.

(Image: Brendan O’Connor11)

Additionally, solar energy is among the most effective renewable energy out there. When shopping for a solar heater, the interested party should consider the following:

  • Greenhouse size: The larger the space, the more heat is needed. This means the farmer will invest in either more efficient panels or bigger heaters.
    PV panels with mono-crystalline cells provide better heating efficiency than panels with poly-crystalline cells though the former is more expensive.
  • Greenhouse purpose: The farmer will need a lot of heat to grow some products, such as tropical plants, in winter as opposed to starting seeds early in the spring.
  • Available panel space: The farmer will need a south-facing, clear space next to the greenhouse to set up the heat-absorbing or PV panels. The panels should not be set up on the greenhouse roof, or they’ll block the sunlight.

Types of Solar Greenhouse Heaters

Commercial solar greenhouse heating systems offer three options:

  1. PV panels: These absorb solar energy and convert it into electricity which then powers the space heater. The farmer should look at a solar panel size chart to determine the size and number of solar panels they need.
  2. Solar furnaces: These are attached to the greenhouse walls, and the panels take in heat and sunlight and regulate the temperatures inside the greenhouse.
  3. Hot water panels: This involves using a solar absorption panel that heats water pumped through pipes in the walls or floor of the greenhouse.

Advantages and Disadvantages of Solar Greenhouse Heaters

These are the pros and cons of solar energy no matter how solar is used. The major advantage is that barring the cost of purchase and installation, the farmer will get free heat and energy throughout the solar system’s lifetime.1

The Cons include:

  • Limited energy: Solar energy is only available when there is sunlight. The farmer must include backup heating or a battery storage system for solar energy during cloudy days and nighttime.
  • Can be costly to install: These panels are hard to install as they depend on the configuration of the property and the greenhouse.
  • Periodic cleaning: The panels must be periodically cleaned for proper (and maximum) functioning, for example, clearing off snow so the panels can absorb sunlight.

Passive Solar Greenhouse: How To Orient Your Greenhouse To Increase Solar Energy Capture

In the northern hemisphere, technicians recommend orienting passive solar greenhouses to:

  1. Use south-facing glass roofs and walls to allow maximum sunlight. The structures can be made of poly-carbonate, glass, and other clear materials, usually called glazing.
  2. Reduce heat loss on north-facing roofs and walls made of non-transparent building equipment (shingles, siding etc.)

Technicians place dark-colored water barrels inside along north-facing walls. Sunlight will come into the greenhouse through the south-facing side and heat up the barrels in the daytime.

Image that shows the comparison between passive solar greenhouse with south wall and solid insulated wall and conventional greenhouse.

Those living in the southern hemisphere must orient the passive solar greenhouse inversely. In this case, sunlight is maximized on north-facing surfaces, and heat loss is minimized on south-facing surfaces.

The farmer must know how solar works to plan installation effectively.8

A passive solar greenhouse generally keeps the interior temperature 11-30 degrees (Fahrenheit) warmer than outside the structure in cold months. This temperature differential is affected by the following:

  • Location: Those in the far north will not experience the full benefits of a passive solar greenhouse. (This structure won’t operate effectively in Alaska and will be much hotter in Kentucky than in Maine.)
  • Weather conditions: Sunny days will yield different temperatures as opposed to cloudy days.
  • Proximity to the winter solstice.
  • Thermal mass quantity: The more water barrels, the more effective the structure.

The hardest time maintaining the greenhouse temperatures is on cold and cloudy days near the winter solstice, as there’s minimal capture of solar heat.

Solar Greenhouse Cost

Is passive solar greenhouse actually possible cost-wise? The cost of such a structure varies from hundreds to thousands of dollars.

The variation depends on the following:

  • Labor costs
  • Amenities included
  • Structure size
  • Type and quality of materials used

Experts recommend getting a plumber, electrician and licensed builder when building a passive solar greenhouse.3 The installation is the most expensive part of the whole system.

However, in the long run, the structure will save the farmer on heating costs and contribute to carbon footprint recycling. Solar energy is one of the most popular carbon offset source out there.

Solar Greenhouse Kit

Is DIY passive solar greenhouse actually possible? Anyone who wants to own a passive solar greenhouse needs six key pieces of equipment used in the planning and implementation phases.

They include:

  • Transparent material for south-facing walls and ceilings: As mentioned previously, the south side of the greenhouse needs to let in as much sunlight as possible. The farmer should invest in greenhouse glass that does not need constant replacement.
    This glass material is expensive, so anyone on a tighter budget should get twin-wall poly-carbonate with great insulating value.
  • Solid and insulated north-facing walls and roofs: As mentioned previously, these two structures in the north should minimize heat loss as much as possible.
  • Dark-colored, heat-retaining water barrels or thermal mass material: These barrels should be placed along the north wall to absorb maximum light from the winter sun and minimum heat from the summer sun.
  • Fans/ Air circulation: The farmer should get specialized greenhouse fans connected to electricity or a solar panel. Air circulation in the greenhouse is important because:
    • It helps even out cold and hot spots.
    • It moves air past the water barrels to bring heat into the structure.
    • It helps grow healthy plants.
  • Venting: A greenhouse absorbs heat and moisture, but too much of these properties can kill or stress the plant or cause fungal illnesses. Greenhouse venting lets out moisture and heat and allows fresh air for the plants to breathe.4
    In most cases, these vents have openers with wax cylinders.
    Temperatures of 65-75°F expand these cylinders, which then push the vents open. Vents should be located at the sides and top of the greenhouse to improve air circulation and cooling efficiency.
  • Water/irrigation/plumbing: A good greenhouse requires a dedicated water line plus any additional plumbing structure.

How To Heat a Greenhouse With Solar Panels: Solar Heater for Greenhouse DIY

Anyone who wants to heat a greenhouse with solar panels will need the following equipment to get started:

  • Solar panel
  • Housing
  • Alligator clip
  • Charge controller
  • Temperature sensor
  • Fasteners and handles
  • Battery voltage sensor

Step 1: You should determine where and how you want to place the solar panels. Before purchasing solar panels, you should know the dimensions you need and whether you have enough installation space.

You should also know how many solar panels you need.

Step 2: Install support. The second step after planning is to install the handle, locks and brackets that will be used to attach the panels to the roof or whatever structure will support the panels.

Step 3: Connect the wires. Connect all the panels and ensure all cables are waterproof and sufficiently insulated.

Then connect the grounded fasteners to the ground wire first to prevent electrocution.

Step 4: Connect the Solar Panels: The panels should be placed on their designated structures once the wires are assembled.

Step 5: The last step is to connect the inverter to the circuit breaker panel of the greenhouse AC. Then connect the PV system components and the circuit breaker to the PV lines.

Lastly, connect the inverter to the DC main breaker, and the installation is complete.

Anyone can incorporate solar energy to establish a solar greenhouse as long as you’ve done your preparation work and know your exact needs.

Frequently Asked Questions About Solar Greenhouse Options

Can You Run a 12 Volt Solar Greenhouse Fan From a Solar Panel?

Yes, as long as the output short-circuit current is lower than the fan’s capacity.

What Is the Main Difference Between a Round Greenhouse and a Ceres Greenhouse?

Besides the blatant shape difference, a Ceres greenhouse can absorb more UV sunlight and climate control than a Round greenhouse.

Why Is Investing in Solar Farms Important?

To those wondering, why is investing in solar farms important? Solar farms have a great return on investment, especially considering the saving on electricity bills and the low maintenance involved.

How Much Power Does a Solar Panel Produce?

The solar panels in the market today produce between 250 and 400 watts each every hour.

What Size Solar Panel To Charge 12V?

If a battery has 12v and 20 amps of power, it will need a 240-watt panel (12 × 20).

Do Solar Panels Work on Cloudy Days?

To those wondering, do solar panels work on cloudy days? Solar panels can still draw energy from the sun on rainy or cloudy days though not as much as on sunny days.

Why Are Solar Panels So Expensive?

To those asking, why are solar panels so expensive, solar panels are so expensive because their production require expensive raw material and advanced manufacturing.


References

1Astbury, J. (March 23, 2022). Solar Greenhouse is a Prototype for “Zero Kilometer” Food Production and Energy Generation. Dezeen. Retrieved March 27, 2023, from <https://www.dezeen.com/2022/03/23/solar-greenhouse-institute-advanced-architecture-catalonia-zero-kilometre-architecture/>

2Coulleri, A. (2021). Solar Greenhouse Prototye/IAAC. ArchDaily. Retrieved March 27, 2023, from <https://www.archdaily.com/977616/solar-greenhouse-prototype-iaac >

3Deziel, C. (February 20, 2023). Guide to Solar Greenhouse Heaters. Familyhandyman. Retrieved March 27, 2023, from <https://www.familyhandyman.com/article/guide-to-solar-greenhouse-heaters/>

4Tucher, C. (2022). Everything You Need to Know About a Solar Greenhouse. Solar Square. Retrieved March 27, 2023, from <https://www.solarsquare.in/blog/solar-greenhouse/>

5US Department of Energy. (n.d.). Active Solar Heating. Energy Saver. Retrieved March 27, 2023, from <https://www.energy.gov/energysaver/active-solar-heating>

6US Department of Energy. (2023). Sample records for passive solar greenhouse. Science.gov: Your Gateway to US Federal Science. Retrieved March 27, 2023, from <https://www.science.gov/topicpages/p/passive+solar+greenhouse>

7Bartok, Jr., J. W. (2013). Heat Storage for Greenhouses. University of Massachusetts Amherst. Retrieved March 27, 2023, from <https://ag.umass.edu/greenhouse-floriculture/fact-sheets/heat-storage-for-greenhouses>

8US Department of Energy. (2023). How Does Solar Work? Office of Energy Efficiency and Renewable Energy. Retrieved March 27, 2023, from <https://www.energy.gov/eere/solar/how-does-solar-work>

9Photo by Mark Stebnicki. Pexels. Retrieved from <https://www.pexels.com/photo/field-of-plants-in-greenhouse-2886937/>

10Solar roof Photo by Tobi K / Attribution 2.0 Generic (CC BY 2.0) . Cropped, Resized and Changed Format. From Flickr <https://www.flickr.com/photos/dragonleek/3069680570>

11Photo by Brendan O’Connor. NCSU. Retrieved from <https://news.ncsu.edu/wp-content/uploads/2020/02/OConnor-greenhouse-HEADER-1500.jpg>

12Photo by singhvp93. Pixabay. Retrieved from <https://pixabay.com/photos/water-heater-solar-sun-energy-491270/>

13Photo by Joe Ryan, NREL 19690. NREL. Retrieved from <https://www.epa.gov/sites/default/files/styles/medium/public/2014-12/7-flat-plate.jpg?itok=icNSdZb1>