Seeing a way through to low carbon salad

In the East Anglian coun­ties of Norfolk and Suffolk, a £120m commer­cial low carbon green­house project is leading the way in sustain­able high volume crop produc­tion. The 28.3ha of green­houses across two sites are the brain­child of Low Carbon Farming and funded by the UK’s largest renew­able energy investor, Green­coat Capital. They are capable of producing 12% of the UK’s tomato demand, with 75% lower carbon emis­sions than tradi­tional green­houses, by using world-first renew­able energy tech­nology and circular produc­tion.

Mark Dykes, director at Step Asso­ciates, is managing the project. “The green­house project is a collab­o­ra­tive effort to provide crit­ical proof of concept for post-Brexit food secu­rity and meeting 2030 carbon reduc­tion targets,” he says. “Construc­tion started in September 2019 – it took 14 months to build the green­houses and the heat pump system, and six months for road­works.”

Green­houses for a controlled envi­ron­ment

The seven-metre-tall green­houses are spread across two farm­land sites; Crown Point Estate, Norwich and Ingham, Bury St Edmunds, providing 16ha and 13ha of growing space respec­tively. “We have two 8ha green­houses at Crown Point Estate and a single green­house at Ingham,” explains Mr Dykes.

Each site has over five kilo­me­tres of under­ground pipeline and more glass than the Shard building in London. Constructed by Dutch glasshouse specialist, BOM Group, the green­houses provide a controlled growing envi­ron­ment where crops are grown hydro­pon­i­cally – in a nutrient-rich water solu­tion instead of tradi­tional soil.

The green­houses currently (June 2021) grow salad crops – toma­toes, cucum­bers, and peppers – verti­cally from 177km of growing gutters. In compar­ison to field farming, the green­houses can grow 10 times more crops with 10 times less water.

Within each green­house there are 16 zones which can be heated inde­pen­dently, as well as three walls which can be opened or closed to allow for isola­tion. “It allows for different crops and stages of growth to be accom­mo­dated and means crops can be grown and harvested throughout the year,” Mr Dykes explains.

“Each green­house should average four harvests per year, but that is depen­dent on crop type and rota­tion – the first harvest was taken in May 2021.”

Envi­ron­mental computers use arti­fi­cial intel­li­gence to control the envi­ron­ment, which includes scan­ning MET Office weather data. The roofs are designed to maximise natural light and diffused glass disperses light across the crops evenly. “The strin­gent control of the green­houses ensures biose­cu­rity and consis­tent, healthy growth of crops.”

Salad crops are grown hydro­pon­i­cally and verti­cally from growing gutters.

Inno­va­tion goes beyond scale

But inno­va­tion goes beyond scale, and resource engi­neering is what enables the green­houses to produce crops with 75% less emis­sions than tradi­tional commer­cial green­houses. The sites were specif­i­cally selected for their prox­imity to Anglian Water’s waste water treat­ment facil­i­ties. “Heat is extracted from cleaned effluent at the water treat­ment facil­i­ties into a heat transfer plant before being trans­ported two kilo­me­tres to ground source heat pumps at the green­house sites; these works were under­taken by specialist utility Company Clancy Group,” explains Mr Dykes.

“The ground source heat pumps are then able to inject this heat into the green­houses. Peak thermal demands are 32mw at Crown Point and 26mw at Ingham, taking green­house temper­a­tures to 55◦F. This equates to enough thermal power to heat 20,000 homes.

“The waste heat extrac­tion is a first and the devel­op­ment is home to the UK’s largest system of heat pumps. And because it is a renew­able energy project we were able to apply for a Renew­able Heat Incen­tive (RHI) grant.”

Elec­tricity for the heat pumps and sites is gener­ated by Combined Heat and Power (CHP) units located at Crown Point and Ingham, producing export capacity of 3.6mw and 2.4mw respec­tively. “The elec­tricity gener­ated by the CHP units fulfils about 85% of the site’s elec­tricity demands,” he says.

Waste heat from the units is recy­cled and enables green­house temper­a­tures to be increased when required. “Heat gener­ated by the CHP units is captured and fed into hot water storage tanks which allows green­house temper­a­tures to be taken up to 80◦F.”

The sites also have infra­struc­ture to capture and clean gener­ated carbon dioxide which is fed back into the green­houses to meet the growing crops’ require­ments. Compared to tradi­tional green­houses these save on average 1.2m tonnes of carbon from the envi­ron­ment.

Water effi­cien­cies are helped by the sheer amount of glass. “We are able to capture the rain­fall runoff from the green­houses and store it – across both sites there is 200,000m3 of water storage,” explains Mr Dykes.

To ensure unin­ter­rupted oper­a­tion the sites have control measures. “There are two gas boilers and back-up gener­a­tors, as well as two days’ worth of heat in buffer tanks – it’s been designed to cover all bases in the event of some­thing shut­ting down.”

Ariel view of the low carbon green­house site at Crown Point Estate, Norwich.

A new growing concept

The green­houses offer a new growing concept. “They are a trans­fer­able devel­op­ment – the design can be repli­cated else­where in the country and really offers an oppor­tu­nity to increase home­grown produc­tion,” he adds.

But how big do green­houses really have to be? “It comes down to economies of scale,” says Mr Dykes. “Food produc­tion effi­cien­cies and the sector’s carbon foot­print can be reduced by having these larger, low carbon green­houses. The larger green­houses reduce the logis­tical chal­lenges, emis­sions and costs of having lots of small green­houses every­where.”

And the green­houses offer oppor­tu­ni­ties beyond crop produc­tion. “Each site has provided 200 new jobs – the range of required work and skill provides broad oppor­tu­ni­ties.”