In a few years, the majority of the world’s population will live in urban centers. Already, cities are places of major global consumption and pollution; for instance, they consume 2/3 of the world’s energy and produce 70% of the world’s carbon emissions. Currently most cities only have a 3 day buffer of food supplies – leaving urban dwellers  vulnerable to increasingly common extreme weather events or other emergencies.

Among urban citizens, there is a growing awareness of the need to ensure their own food security. Balconies, roof tops, window sills and any spare piece of space of the building they stay in is being enlisted for food production.

CO2 Reuse in Greenhouses

  • Emissions trading is open to broad abuse as governments simply print certificates
  • Waiting for renewable energy to overtake fossil fuels bring short-term solutions is not feasible due to long and unpredictable scaleup times
  • Conventional green approach of “eco-efficiency” being adopted by the EU and U.S. will not work; as industrial processes become more eco-efficient they become cheaper and as they become cheaper their growth rate exceeds savings from minimization. Eco-efficiency has been shown to lead to accelerated consumption commonly referred to as the “rebound effect”, where efficiency accelerates the very problem it is intended to solve.

Scientists have been arguing for some time how to compensate for the rebound effect, but as the argument continues so do emissions.

A number of recent developments has made emissions trading schemes and EU carbon emissions taxes obsolete:

  • China banned its airlines from paying the EU carbon tax on airlines
  • Nations failed to reach significant agreement on emissions in Durban
  • Nations failed to reach significant agreement on emissions in Rio +20
  • Canada put the nail in the coffin of Kyoto by quitting it

Scientists at a press conference held September 16th, 2012 at Greenpeace New York offices presented the latest findings of the Arctic ice melt; the most since recorded history. The general mode was sombre, with scientists such as James Hansen pointing out that governments have made zero progress on addressing climate change issues.  How then, does the world solve the serious unabated CO2 emissions problem given the force of economic growth?

One of the few effective ways out of this vicious cycle is to apply the rebound effect to the re-use of CO2. This is done by using efficiency to consume large amounts of CO2 for industrial production.  Simply put, CO2 is food. Its use can be accelerated as a resource for many industrial and agricultural processes. Nature has been reusing CO2 since time began, to:

  • rebuild soil
  • grow forests
  • support life in our lakes and oceans

Through biomimicry it is possible for us to adapt and accelerate that process for profit. That basic transformation in approach and psychology leads to more productive solutions and investments.

Biomimicry for greenhouse gas reuse include:

  • Algae is one of the most effective carbon sinks on earth if the CO2 “release” side of its cycle is adapted for industrial reuse. Large scale algae production is feasible and profitable where algae is captured and reused in products before it can release its carbon back into the atmosphere. Algae can double profitably as a feedstock and purifier of agro-industrial effluent. This combination makes it financially attractive. A Florida-based company Hydromentia has been using algae to clean wastewater for two decades. Seaweed, which is a form of algae, has been harvested for centuries and the technology is now being optimized, also for removing nutrient pollution from waterways. Algae production is the focus of corporate investments globally and airlines such as Virgin prove that it works as a feedstock for biofuels, while the pharmaceuticals and agro-foods industries are lining up to produce profitable products from it.
  • Micro-algae have a very interesting characteristic: they can store fatty acids for up to 50% of their dry weight, and have 30 times more productivity than terrestrial crops (soy, colza…). They do not require any chemical additives, and can be used in the water clean-up process, acting as filters to rid contaminated water of its toxic elements. In New-Zealand, the Aquaflow company has used the 60- hectare Marlborough sewage pond to carry out its tests, proving that many industries generating waste water could produce valuable micro-algae whilst purifying their discharge, since the organisms directly consume CO2… (1)
  • Greenhouse agriculture is a bright light for feeding our growing population with its high productivity. Studies show that greenhouse production can be 5 – 10 times more productive than open field agriculture. Its existing re-use of CO2 as a nutrient for plants can be greatly expanded with the added benefit of cleaning the air.
  • Biodigestion for re-use of methane and nutrients is already being profitably expanded, instead of the counter-productive policy of subsidising burning of raw wood for “green” energy that is anything but green.
  • Substituting the use of rare resources such as metals with nano-structured carbon based materials. These are not the nano-particles which are the focus of criticism for their potential health effects, but rather carbon-based structures as stable as steel or glass.

(Source: Ellen MaCarthur Foundation and EPEA)

The Case for Rooftop Greenhouses

Why Hydroponic Greenhouses?

  • Very high yields
  • Consistent, high quality product
  • Extremely water and land efficient
  • Very lightweight – ideal for rooftop setting
  • No agricultural run off
  • Integrated Pest Management (IPM)

A recent study by the Fraunhofer Institute UMSICHT for Environment, Safety and Energy Technology department even suggests that widespread rooftop gardens can play a major role in sequestering greenhouse gases. The team applied a cradle-to-cradle approach to the CO2 emission problem. The cradle-to-cradle approach operates on the fundamental bimimcry principle that waste = food. Taking this approach, CO2, currently seen as a dangerous waste product whose excessive atmospheric concentrations are causing global warming is seen instead, as food. The project, called infarming reframes CO2 as a valuable nutrient for plant photosynthesis.

The Fraunhofer team calculated that such food-producing greenhouses located atop of the 1.2 billion square meters of rooftop space available throughout Germany could sequester anywhere from 10  to 80 percent of CO2 emissions from German industry. The calculations showed that these gardens could absorb an additional 28 million tons of CO2 emissions each year in German cities.

The Fraunhofer approach is an example of a new kind of approach that will need to quickly scale in order to replace current failed attempts to reduce alarmingly high CO2 levels.

The Fraunhofer  inFarming project – which is short for ‘integrated farming’ – is a research project aimed at developing urban farming solutions to be quickly and cost effectively so that it can scale globally.

There are therefore many compelling reasons for widespread urban rooftop gardens:

  1. reduce urban food vulnerability
  2. reduce atmospheric CO2 concentrations through plant photosynthesis and reduced food miles
  3. produce crops for urban consumers
  4. develop a local economy

Fraunhofer Institute project engineer Volkmar Keuter is leading the  inFarming development effort to design cost-effective and scalable rooftop hydroponic solutions. Some of the design parameters to be worked out include:

  • reduce roof static load through the use of innovative lightweight materials
  • reduce static load as well as water resources via designing highly concentrated thin-film, nutrient stream to produce 10x higher yields than soil-grown plant
  • integrate into building grey water and blackwater (sewage) systems to recycle waste streams to extract nutrients
  • determine a large variety of edible and medicinal plants which are suitable for growing in such greenhouses
  • reduces the area required for agriculture
  • reduces transport costs to zero
  • reduces  CO2 emissions from reduced transport

If the greenhouse is designed efficiently and in a closed loop, then:

  • waste heat from buildings and additional solar modules would be enough to supply the greenhouses with all its energy needs
  • semitransparent solar cells are suited for the purpose because they do not rob the plants of the light they need to grow
  • Water consumption is minimal – in a self-contained system, water used for the plants is circulated back, cleaned and reused
  • multifunctional microsieves and photocatalytic and, thus, self-cleaning coatings keep the water quality high
  • Nutrients for the plants can even be filtered out of rainwater and wastewater

To be scaleable, outstanding questions remain to be answered:

  • which products are best suited for this venture?
  • how widely accepted are nutrient solutions as an alternative to soil

Fraunhofer has a joint venture and partnership with a number of organizations to promote the inFarming solution.

  • with U.S. based organization Brightfarms to put CO2-capturing greenhouses on urban rooftops, and Fraunhofer is building its own facility in Duisburg
  • with New York Sunworks is working with schools to put greenhouses on roofs as science teaching tools
  • In The Netherlands, the happyhealthyschool pilot project is building a rooftop greenhouse to use polluting CO2 from classrooms as a nutrient for plants

Existing Rooftop Greenhouses

 Lufa Farms vision is a city of rooftop farms. Originating in Montreal, Canada with their first 30,000 square feet facility on top of a commercial building, plans are already underway for expansion into the US. Lufa Farms business model is to produce fresh, pesticide vegetables on urban rooftops and sell them as baskets of food to urban consumers.


Lufa engineers their rooftop greenhouses to meet the rigorous conditions of an urban rooftop:

  • strong, able to withstand snow and wind loads and to meet exacting urban building codes
  • easy  integration into both new construction and existing buildings
  •  multiple growing climates to operate plant growing conditions – hot areas for some vegetables, cool areas for others, and several “micro-climates” within each
  • alternative  pest contro including: insects, certain naturally-occurring bacteria, use of weed-free growing mediums, and rigid protocols for maintaining a clean, problem-free growing area
  • several different growing methods – soil or medium the plants are grown in, nutrients they are provided, type of irrigation, amount of light they receive and temperature
  • do not use genetically-modified cultivars.Together with McGill University, developed special methods of assaying nutrition values to get best possible product
  • capture rainwater that falls on the greenhouse and recirculate water used in plant irrigation to prevent high algae growth or other plant overgrowth in water system

Brightfarms is a US company with its own unique business model. It builds rooftop greenhouses on top of urban buildings belonging to supermarket chains, hence reducing food miles to zero. Brightfarm locks in multi-year supply agreements so that it can finance it’s greenhouses.

BrightFarm Ultra-Local Greenhouses from BrightFarms on Vimeo

New York Sunworks is an NGO which has been installing hydroponic greenhouses on top of roofs in New York.
Figure 1: New York NGO Sunworks Manhattan School rooftop greenhouse project


Figure 2: NY Sunwork’s Manhattan School project

Figure 3: NY Sunwork’s Manhattan School project

Figure 4: NY Sunwork’s Manhattan School project

Figure 5: NY Sunwork’s Manhattan School project

Reference Papers

Resources for Designers