Passive solar greenhouses and low-cost solutions

Energy plays a crucial role in passive solar greenhouses. Temperature, light and humidity control are essential for efficient crop production and agriculture throughout the year.

Energy is used to heat the interior of the greenhouse, especially during cold seasons or cold nights. This is essential to maintain a proper temperature for plant growth, as many cold-sensitive plants require higher temperatures than those found outdoors. Lamps or artificial lighting systems are sometimes used in a greenhouse to provide additional light to plants. This is especially important in regions with low sunlight during certain seasons or in greenhouses where plants are grown that require high light intensity to grow optimally.

Energy is also used to maintain adequate humidity levels in the greenhouse. This is achieved through irrigation systems, misting systems or fans that help control the relative humidity within the greenhouse.

Renewable energies and greenhouses

The use of renewable energy in greenhouses is an increasingly common practice to reduce environmental impact and operating costs. Implementing these renewable energy sources not only reduces the greenhouse’s carbon footprint, but can also reduce long-term costs by reducing dependence on non-renewable energy sources.

The choice of the most appropriate renewable energy source depends on the geographical location, climate, available resources and specific needs of the greenhouse:

• The installation of photovoltaic solar panels on the roof or near the greenhouse allows the energy of the sun to be captured and converted into electricity. This electricity can be used to power heating, lighting, irrigation systems and other electrical devices in the greenhouse.
• Solar thermal collectors can also be used to provide additional heating by capturing solar heat.
• In areas with consistent winds, wind turbines can be installed near the greenhouse to generate electricity. This wind energy can be used to power lighting, ventilation and other electrical equipment.
• Biomass, such as wood, agricultural waste or organic waste, can be used as a source of renewable energy to generate heat. Biomass boilers can be used to provide heating in the greenhouse using these natural resources.
• If in a suitable location, geothermal energy can be used for heating and cooling. Geothermal systems take advantage of the heat stored in the ground to maintain a constant temperature in the greenhouse throughout the year.
• In areas with nearby water streams, micro-hydroelectric systems can be used to generate electricity. This electricity can be used to power various electrical equipment in the greenhouse.
• Anaerobic digestion of organic waste, such as animal manure or plant debris, can produce biogas. This biogas can be used as a heat source for heating in the greenhouse.
• It is also possible to combine several renewable energy sources, such as solar and wind, to create a hybrid system that ensures a more stable and reliable energy supply for the greenhouse.

Implementing these renewable energy sources not only reduces the greenhouse’s carbon footprint, but can also reduce long-term costs by reducing dependence on non-renewable energy sources.

In remote areas, where energy infrastructure may be limited or non-existent, innovative greenhouses using renewable energy can be particularly beneficial for food cultivation and sustainable development. Here are some examples of innovative greenhouses with renewable energy and other low-cost systems:

Passive solar greenhouses

These greenhouses are designed to maximize solar heat capture during the day and retain it overnight. They use specific building materials and techniques to create a warm atmosphere without the need for additional energy. Passive solar energy may be sufficient to maintain temperatures suitable for plant growth even in remote areas.

A very interesting example is the Agrosavia passive solar greenhouse in the savannah of Bogota. In Colombia, the active climate control of greenhouses is not feasible for economic reasons, both for the investment and the energy consumption required. Passive heating systems are much cheaper and rely on the use of renewable energy sources, particularly solar energy.

This type of greenhouses incorporate thermal storage systems, such as large water tanks or phase change materials, to capture and store solar heat during the day and release it at night to maintain a constant temperature.

In the case of Agrosavia, the greenhouse is 40 m2 and has plastic cover with an improved ventilation system. It has 2 passive heating systems, one of bedrock where hot air is supplied during the day and extracted at night. The second system is spent in underfloor heating, which heats the environment by hot water stored in a thermotank.

In other regions with access to reservoirs, greenhouses have been developed that float on the water surface and use the reflection of sunlight from the water surface to provide additional light to plants. In addition, solar energy is used to power irrigation systems and other electrical needs.

In areas with consistent winds, small wind turbines can be installed to generate electricity. This wind energy can be used in combination with solar systems to provide continuous energy to the greenhouse.

In areas with geothermal resources, solar passive greenhouses can benefit from the heat stored in the subsoil to provide heating and cooling in a sustainable manner.

These examples demonstrate how the combination of innovative greenhouse technologies with renewable energy sources can help establish sustainable farming systems in remote areas, contributing to food security and energy self-sufficiency in these communities.

Greenhouses built with plastic bottles

Passive solar greenhouses built with plastic bottles are a sustainable and economical solution that has been implemented in various communities in Latin America.

The use of plastic bottles to build part of the walls of the greenhouse allows lower costs and provides good thermal insulation. A good example is the greenhouse built in the province of Córdoba (Argentina) by a group of students of the Agricultural Specialty, within the National Institute of Agricultural Technology.

Source: portalfruticola.com website

The greenhouse is designed to grow vegetables during the winter and is aimed at lowering costs in comparison to the high price of traditional greenhouses. This project began as an experiment with students, ended up hosting a great and varied plantation of vegetables grown in the coldest months of Argentina.

In addition, vertically placed bottles, assembled together as a column, isolate better than polyethylene and create an indoor air chamber that allows cultivation in winter. Bottles are better able to withstand winds, blows and scratches, according to their inventors.

For a greenhouse of 4 x 2.5 meters, you need between 1,500 and 2,000 plastic bottles preferably transparent, wire, slats and posts for the doors and fastening of the bottles.

There are other innovative ways to passively heat the greenhouse such as using water-filled flexible bottles or sleeves inside. Due to thermal inertia they absorb radiation during the day, heating the water inside, and return heat to the greenhouse during the night.

Source: ecomercioagrario.com website

Tests have been carried out in Almería observing increases in temperature values between 0.5 and 2.2 degrees Celsius over the night lowest temperatures. The increase could be even greater (up to 5 degrees) avoiding that the sleeves are not shaded by the plants themselves and can absorb even more energy.

Los sistemas de recogida de agua de lluvia

These systems are a good complement to passive solar greenhouses.

Ekomuro H2O+ is an innovative rainwater collection modular system made with 54 PET bottles of 3 or 2.5 liters. These interconnected bottles form a vertical, compact and pressure-resistant water tank. The system occupies a minimum of space and is oriented to saving water in homes or other uses such as irrigation in greenhouses.

Source: negociosenelsur.net website

The rainwater collector made of plastic bottles is easy to manufacture and has a very low cost. With a water filter, people can get drinking water. This solution guarantees a minimum life span and can significantly improve the quality of life of vulnerable communities and the sustainability of greenhouses.

The project addresses two environmental issues:

• The circularity of PET containers, which once converted into waste, are recycled but a large amount becomes garbage, plugging drains, generating flooding and environmental pollution.
• The need to innovate in saving water, due to the pressure of climate change on water sources. In this sense, the collection of rainwater should be a positive step.

Conventional systems for rainwater collection are made of plastic and fiberglass, have a high cost and do not exist in the local market. The Ekomuro system performs the same function in an innovative, eco-efficient, economical and easy-to-make way, based on the appropriate technology from the reuse of a solid waste, the three-liter pet container.

This project received the first prize of the challenge that sought innovative ideas for the use of natural resources at the Seventh World Water Forum, held in South Korea.

Second Generation Ekomuros have a dual purpose, on the one hand they store rainwater and on the other they recover gray water, which once treated independently, can be reused. They are made from the recovery of bottles of 20 liters, allowing a greater volume of water tank in a minimum space.