The Geothermal and Advanced Spectral Technology for Regional Optimisation of greenhouse crop production (GASTRO) project was a collaboration between the University of Lincoln (UoL), Pilkington NSG, and NFU Energy which concluded in August 2026.
The project tested the benefits of Pilkington’s novel Near Infra-Red (NIR) reflective glass coating to reduce solar thermal load and enhance summer cooling, as well as the performance of UoL’s demonstration geothermal heat pump greenhouse.
The aim of integrating these technologies was to reduce primary energy demand and improve CO2 utilisation, for the potential of regionally decarbonising heat generation based on geothermal resource.
The Greenhouse
UoL’s research greenhouse consists of four compartments: two north-facing and two south-facing, with the roof of one compartment in each orientation glazed with NIR glass, and the other with standard horticultural control glass. The construction and management of the greenhouse emulate a modern commercial system, although the total floor area is much smaller.
The greenhouse is heated with a combination of Ground Source Heat Pump (GSHP) fed by an array of shallow geothermal boreholes (circa. 200m deep), and Air Source Heat Pump (ASHP). These deliver heat into a buffer vessel, from which heat is drawn into each compartment based on temperature sensors integrated into the Priva environmental management system.
Winter Crop
The most important aspect of a heating system is that it can achieve the minimum temperature set-points to support plant growth. The combined heat pump system was able to maintain the temperature set-points and enable a successful crop of strawberries even during sub-zero temperatures. This is particularly impressive given the high surface-to-volume ratio of the greenhouse, meaning higher transmission heat loss compared to a commercial system.
In terms of CoP, the system did not perform as well as expected, averaging 2.90 across the season. We suspect that this poor performance is in part due to a high ratio of heat distribution to heat delivery pipework, which means a relatively high proportion of heat generation is lost before it reaches the crop, and baseload electricity consumption on the measured circuit. Going forward, additional metering has been installed to quantify these points in future heating seasons.
Regardless, there are currently two large barriers to any new heat pump systems for UK horticulture, which must be addressed:
- Electricity grid connection
- CO2 use
Even when a heat pump system operates more cheaply than gas combustion, the non-commodity standing charge and Use of System (UoS) charges on electricity connections make electricity-based heating unfeasible. There are mechanisms which reduce the magnitude of these costs, which are available to many industrial sectors in the UK. However, horticulture is not currently eligible.
Natural gas combustion is a very cheap and reliable source of CO2. Additionally, since the majority of liquid CO2 is sourced as a byproduct of steam methane reformation, even if natural gas prices spike, liquid CO2 costs also rise. Therefore, a radical change in market conditions or policy would be required for natural gas combustion to be replaced as the cheapest CO2 source. In the meantime, pairing natural gas Combined Heat and Power (CHP) with heat pump is an attractive option to deliver both heating and CO2 demand.
Summer Crop
Part of the solution for the CO2 problem is undoubtedly to optimise its use, in part by CO2 losses through ventilation. Based on the measured data, Pilkington’s NIR reflective glass could contribute to this goal. In summer, the compartments with NIR reflective glass were closer to ambient temperatures than the control. This was more noticeable for south-facing compartments, and was much less noticeable across the winter period, indicating that the effect may be stronger when total irradiance is higher and angle of incidence lower.
Across the summer period, this led to the two NIR reflective compartments having their vents around 4% less open than the control. Future dedicated projects are required to relate these figures directly to reduced CO2 demand.
Additionally, this was achieved whilst maintaining comparable yields; the north-facing NIR compartment had 6.4% higher first-class yield than the north-facing control, whilst the two south-facing compartments were within 0.1% of one another.
For assistance in grant funding opportunities, or a detailed technical study into alternative heating and CO2 options on your site, contact us here: growsave@nfuenergy.co.uk
