Saving CO2e emissions with Rooftop Greenhouses – But how to prove it?

The project GROOF aims to reduce Greenhouse Gas (GHG) emissions expressed in CO₂e by implementing greenhouses on rooftops for local production of vegetables. The reduction of GHG emissions is expected to result from the synergy effects of building and rooftop greenhouse (RTG), such as recovering heat losses from the building below to heat the RTG, and from reduced transport emissions. The questions are:

• How can we prove the emission saving from the four GROOF pilots?
• And compared to which greenhouse production do we save CO₂e emissions?

To answer these questions a review on different methods in the field of environmental assessment has been conducted. Recently, Life Cycle Assessment (LCA) is gaining importance, especially tailored to verify the environmental impact of a certain product or process in regards to different impact categories. Also for the GROOF project this method, especially the Assessment of life cycle greenhouse gas emissions from horticultural products (PAS 2050-1), offers some valuable approaches considering the calculation of the Global Warming Potential (GWP). A full LCA for the horticultural production of the RTGs would start with the seed or young plant (cradle) and end with its final stage of life, when it becomes waste (grave). The whole product life cycle is visible in the following figure.

As the project GROOF sets the focus on the greenhouse rather than the whole life cycle of the plant and vegetable product, the chosen boundary for the GHG emission accounting is the production stage in the greenhouse and the following transport. So why don’t we include the other life stages? The aim of the GHG emission accounting is to analyse in what way GROOF production is different to standard production on the ground. The young plants or the warehouse though are expected not to be different in the GROOF approach or the standard production expect for the transportation, which is the reason why this transport is included.

If we wish to compare the GROOF to standard greenhouse production, what is our reference? Our reference are four model greenhouses that differ in regards to their area, their energy carrier and their energy efficiency. Previous studies found out that in North-West-Europe (NEW) the main climate impact is associated with energy usage. So we can simulate the worst case greenhouse production and a highly efficient best case greenhouse and compare the four GROOF pilots to the variety of production GHG emissions. But why is it important to compare the GROOF pilots to horticultural production in NWE and not to production in other regions? Vegetables from other regions are produced under different climate circumstances and are facing other challenges than the ones in NWE, which aggravates a possible comparison. Therefore, a comparison of GHG emissions between NWE production on RTG and intensive farming outside of NWE cannot offer a useful result on their actual environmental impact.

For the further proceeding the pilots will need to monitor all the relevant indicators for the GHG emission accounting, whereas the involved institutions will continue to model the reference greenhouses. If you have any questions or if you are active or interested in the field of environmental assessment of the horticulture sector, please do not hesitate to contact the GROOF team for further information and discussion.