Growing greener

Kent's vast Thanet Earth glasshouse complex is employing cutting-edge control systems to ensure production is as effective and sustainable as possible. Kris Collins reports.

Peppers at Thanet Earth grown using less fertiliser - photo: Thanet Earth Marketing
Peppers at Thanet Earth grown using less fertiliser - photo: Thanet Earth Marketing

The first fresh produce from Thanet Earth, the UK's largest glasshouse complex, hit retail shelves this month. In little over a year, Thanet Earth Marketing - a joint venture company between fresh produce supplier Fresca and site growers - has turned a former 91ha cauliflower farm near Birchington, east Kent, into an £80m modern glasshouse facility. At full production it will produce 2.5 million fresh tomatoes each week alongside volumes of cucumber and bell pepper, boosting total UK salad production by 15 per cent. Pepper and tomato crops were first planted in early January followed by cucumbers later in the month, with crops all coming online in early March.

Three of the site's seven intended glasshouses are now operational, along with seven vast reservoirs to cope with hydroponic growing requirements, a power generation plant able to supply electricity to 50,000 homes and substantial support infrastructure including an on-site packing facility.

The project represents a UK industry first with a joint venture between Fresca and three highly skilled grower organisations - Rainbow Growers, Kaaij Redstar and A&A Growers. Together they have created an efficient growing model with very strong environmental credentials, drawing on the latest technologies and growing concepts to ensure the site's carbon footprint, fertiliser use and water use is kept to a minimum.

As well as addressing environmental impact, efficient energy and fertiliser use within the houses is bringing huge cost savings, while at the same time maximising profit through increased yield per square metre.

The glasshouses are heated using combined heat and power (CHP). Each glasshouse has gas-powered engines which generate large amounts of electricity. The glasshouses themselves require very little operational power so almost all electricity is exported through a newly created link to the National Grid.

The by-products of the power generation process (heat and carbon dioxide) are taken into the glasshouses to support the natural growing process of the plants. Power for lights used in winter tomato production is also generated on-site.

Climate control

All aspects of the glasshouses - from ventilation to water sterilisation and air circulation - are automatically controlled by a Priva Integro computer control system.

Ventilation control in the Priva Integro is based on calculations of how much energy enters the glasshouse, taking into account glasshouse roof translucency, outside conditions, the type of glasshouse and the characteristics of the vents. The control system can then calculate how far the vents must be opened to remove surplus heat energy, resulting in a balanced temperature throughout the system.

Temperature integration ensures an optimal heating and ventilation strategy based on the available energy, with the system automatically ironing out peaks in heat demand.

Climate control and airflow within tomato production at Thanet Earth is further controlled with the use of Priva's under-gully circulation fans and air tubing. Fans are traditionally positioned above the crop but according to Priva export account manager Marcel Koole, airflow under the plants brings many advantages.

"Fans are normally installed above the crop to deal with air circulation and temperature differences in corners or in the gables," he says. "Thanet Earth tomatoes have circulation fans installed underneath them. The grow gutters are hung on the glasshouse structure, allowing for circulation fans and air tubes to be installed underneath and improve air circulation around plants and the glasshouse in general.

"This is becoming more and more common in glasshouse systems as construction moves towards taller structures. At Thanet Earth, gable height reaches 6m or more, meaning there is a large volume of air to be circulated."

Between ground level and the gutter there is a distance of up to 70cm, giving enough space to install 60cm-diameter circulation fans. Airflow from the air tubes dries the stem of the tomato plants reducing the chance of Botrytis infection - especially important in autumn when humidity is at its highest. Koole adds: "It is a bigger initial investment but the circulation system pays for itself. Lower energy costs are possible as there is no need for extra heat to dry out the crop - air flow will take care of that. By reducing the threat of Botrytis, fewer plants will die, meaning higher yields per square metre."

Heat control and energy efficiency is further increased with the use of the Priva plant temperature camera, which measures the infrared radiation emitted by plants through thermal imaging, measured on an area of 5sq m to 16sq m. In combination with the control system, it allows for improved regulation of heating, ventilation, screening, roof irrigation, misting and CO2 dosage.

Energy

The use of CHP technology at Thanet Earth has brought self-sufficient energy production, while channeling excess power to the National Grid for energy supply to local homes. While that in itself is not a new concept, the Integro system also manages the re-supply, automatically communicating with the power company, supplying a "power profile" for the following day. As a result, the quantity of electricity agreed with the electricity market is automatically directed into the National Grid.

Koole adds that even though some Thanet Earth production requires artificial lighting powered by the CHP system, there is still surplus electricity generated to put back into the local electricity grid. "A big plus", he says as businesses increasingly look to lower their carbon footprint.

The Priva Integro control system also controls the complete water management system at Thanet Earth. The software is able to keep the water flows separate, depending on their composition, making it simple to set which tank the water comes from and which tank it must be returned to after use.

Water sterilisation equipment kills any bacteria and viruses present in the water using ultraviolet light. Previously, this was controlled manually, but Integro has been developed to automatically direct "dirty water" for sterilisation before arriving at the clean water tank.

According to Koole: "All excess water is collected, sterilised and used again. There is no longer any reason to lose money through wasted fertiliser in run-off water. Thirty per cent of fertiliser costs are saved by water recycling - a huge amount of money per year for such a big-scale operation like Thanet Earth."

Sustainability

Thanet Earth's marketing team commissioned specialist consultancy Bidwells Agribusiness to assess the overall sustainability of the Thanet Earth site and the supply of products to customers. The carbon emissions associated with the supply of Thanet Earth vegetables to customers were measured using PAS 2050 guidelines - the British Standards Institute and the Carbon Trust's recognised standard for the assessment of greenhouse gas emissions from the supply of goods and services.

The study compared all the various materials, construction processes and operations contributing to greenhouse gas emissions for Thanet Earth against alternative sources and techniques, including other UK production and overseas crops grown in Spain, Italy, Israel, Poland and Holland.

The report throws up some very positive findings, according to the head of Bidwells' renewable energy team, Greg Hilton. "There are a number of other glasshouse projects in the UK using innovative techniques, which are also positive from an environmental point of view," he says.

"But the scale of Thanet Earth allows for investment in all the latest innovative technology, showing UK horticulture can do things that until now have only been seen in Holland."

Though based on fossil fuel consumption, Thanet Earth's CHP systems score highly on their efficiency and carbon footprint, according to Hilton.

"CHP systems are key in the delivery of carbon savings as they generate electricity in a very efficient manner and use the heat created by the electricity generator to warm the glasshouses."

Again it comes down to the level of scale at Thanet Earth in creating these efficiencies. Hilton adds: "Thanet Earth has sized its CHP engines to supply all the heat required in the glasshouses. It's not unique in the UK but still very atypical. Many glasshouse growers use CHP but you find it is not of a size to generate all heat requirements. Thanet Earth is different in that regard, which is the primary reason for its very good performance in terms of carbon emissions."

Hilton continues to work with Thanet Earth Marketing to explore the opportunities to reduce the site's carbon footprint even further by using biomass-powered CHP systems. "It's an exciting opportunity," he says.

"Rather than use a fossil fuel, you are switching over to a renewable energy source which could deliver another step change in carbon performance for the site. Over the next couple of years the next 20ha of glasshouse will be installed and the management team are looking at using biomass CHP to lower carbon emissions even further.

"They seem always to be moving forward and that's very important - they use industry best practice at the time of development but are willing to adapt to new technologies as they continue to develop."

LESS IS MORE

The advanced irrigation techniques employed at Thanet Earth mean fertiliser can be used more efficiently than elsewhere, says Bidwells. Optimum levels of fertiliser can be targeted at the crop, ensuring the plant efficiently uses nutrients to boost yields. The advanced drainage systems ensure run-off is collected and recycled, reducing fertiliser wastage. This differs from other, less efficient systems, which typically waste over half of the applied nutrients through run-off.

In a direct comparison of fertiliser use against volume of crop produced, these efficiencies show that:

- Typical Spanish producers use 3.5 to 4.5 times more fertiliser on tomatoes than Thanet Earth.

- Typical Spanish producers use between five and seven times more fertiliser on peppers.

- Typical Spanish producers use up to 14 times more fertiliser per equivalent output on cucumbers.

- Traditional Spanish tomato growers use on average 17 times more water per kilogram of tomatoes compared to production at Thanet Earth. This is due to Thanet Earth using rainwater capture and recycling irrigation water.

SHOWING SUSTAINABILITY

The independent sustainability assessment of Thanet Earth, carried out by Bidwells Agribusiness, shows some key advantages to Thanet Earth production over other traditional production areas:

- Peppers and cucumbers grown at Thanet Earth have a lower carbon footprint than current alternative sources.

- Tomatoes grown without artificial light at Thanet Earth have a lower carbon footprint than the Mediterranean sources studied.

- Tomatoes grown under lights at Thanet Earth have a similar carbon footprint to UK-grown tomatoes without lights or combined heat and power (CHP).

- The use of CHP actually contributes a negative carbon emission towards the total measured Thanet Earth carbon footprint. The power is produced more efficiently than most other forms of UK power generation because it utilises both the heat and electricity produced by the fuel.


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