Energy saving in edibles production

The potential for energy saving in crop storage has been overlooked but simple measures can bring big rewards, Jez Abbott reports.

Taking steps to improve energy efficiency in stores can lead to major cost savings that quickly pay back the investment - image: Sutton Bridge Crop Storage Research
Taking steps to improve energy efficiency in stores can lead to major cost savings that quickly pay back the investment - image: Sutton Bridge Crop Storage Research

Chris Bishop hit the light switch and was aghast. The crop consultant had just plunged the huge onion store into a sort of darkness to check for chinks of light. And there they were, loads of them, drawing the eye to wind-battered cladding panels, sagging mastic seals and creaky doors.

Bishop, a doctor of agricultural engineering and reader in post-harvest technology, knows every nook and cranny on saving energy in crop storage. Sadly many growers do not and Bishop, based at Writtle College, can see how the blindingly obvious can all too easily slip off the radar of a busy grower in his day-to-day working life.

"It's frightening how you can go into a refrigerated store, shut the doors and switch off the lights," he says. "All those chinks can really make a difference to your costs, especially with onions, relying on propane for curing as well as electricity for cooling and fans". His client, with three 2,500-tonne stores, was haemorrhaging energy and money.

Cost-effective measures

Bishop advised the grower to make £6,000 worth of changes - renewing rubber gaskets, repairing a damaged door, replacing degraded insulation - and the grower saved as much in one season. There are other ways growers can save energy that cost next to nothing, he insists.

Take all those paint pots and piles of clutter in the corner of your store. They could be blocking air movement around your compressor making it overheat. Rats, meanwhile, chew with relish and can strip cladding of its 100mm layer of polyurethane insulation. Yet a £100 infrared thermometer could help pinpoint hot and cold spots to indicate any unwanted guests.

According to Sutton Bridge crop storage research facility head Adrian Cunnington, to "improve something you first have to know what it is you need to improve". One of the first things growers could do - but so many do not - is fit meters to every store to quantify per unit how much electricity each one swallows up, he says.

"You can make an instant five to 10 per cent saving just by thinking about electricity. People who already do this are in the minority yet meters cost around £350 a store and when you spend thousands a year on energy you want to get something back." Few things, after all, are worse than being "at the whim of external influences by not repairing that cracked tin roof", he adds.

Benchmarking evidence

The Potato Council is one of several groups with software packages to help growers plug that gap by benchmarking every aspect of storage from ventilation to finance charges (see box).

South West Agricultural Resource Management (SWARM) hub is another organisation that gives information on resource efficiency. But in spite of reams of statistics from universities, Defra and the Carbon Trust, energy efficiency in crop storage is often overlooked by growers, says information officer Becky Willson.

"This is strange because the UK is the worst energy waster in Europe," she adds. "Yet a 20 per cent cut in energy costs can represent the same bottom line benefit as a five per cent increase in sales. On most farms, savings of 10-20 per cent of energy costs can be made relatively easily, often with a minimal capital outlay."

Like SWARM, Farm Energy technical director Tim Pratt has hard, raw data to prove the worth of energy efficiency. His firm worked with the Potato Council over a five-week period between late October and early December on two stores in Holbeach. A converted grain store used almost twice the electricity that a new purpose-built store next door did.

The converted store cost £1,920 more in electricity during those five weeks alone. As both stores were supplied by a single utility company, the difference was seen only once each store had its own independent metering installed. The main cause of poor performance was insulation, so 50mm of urethane foam was sprayed at a cost of around £15,000.

"The cost will be easily repaid within five years," says Pratt. "This store now performs almost as well as the purpose-built store. It can also store the crop for longer while keeping it in good condition, therefore increasing the flexibility of marketing. Overall, the payback is expected to be fewer than three years.

"Lots of growers don't know the running costs of individual stores because they are bundled together with all sorts of other things with one supplier. Unless you put meters on each store you won't know how they compare. You can also make savings by shopping around and reading the small print, especially on when to renew contracts.

"Many fail to renew within a given period and are automatically put onto a different rate, invariably much dearer. If you do nothing else but check the status of your electricity account and when you need to send in notice, it will save you money and distraught feelings. Don't buy into their pressure tactics."

Although initiatives such as enhanced capital allowances offer tax relief on kit and the recently launched Feed-in Tariff may help with growers toying with photovoltaics, the benefits of others are less clear. The new renewable heat incentive is "unlikely to offer a lot" because the emphasis is not on storage, says Pratt.

Reducing the carbon footprint

Pratt insists that renewables are "where we're going", a viewpoint given credence by PepsiCo, singled out for good practice last month in the Government's Enabling the Transition to a Green Economy document. The parent of Britain's biggest potato buyer Walkers says up to 17 per cent of crisps' carbon footprint comes from potato growing.

Best-practice guidance issued to its potato growers in its Sustainable Farming Report aims to trim emissions by half in five years (see box). Measures include a computerised carbon calculator on how to reduce footprints in storage and other areas of growing.

Publication of such reports is not a moment too soon. Crop Systems managing director Ray Andrews says around four-fifths of stores are probably past their best and even schemes such as Government grants or interest-free loans of up to £20,000 from the Carbon Trust may only scratch the sustainable-storage surface.

Farm Electronics managing director Tim Dudfield agrees: "There is a culture of naivety. People believe that if you put up a windmill it will counter the energy used in a store. It won't, crops are energy hungry. If you want 30 spuds in a brown paper bag and are not too worried about skin finish, it's not a problem. But while supermarkets demand immaculate looking vegetables on their shelves you will have to throw energy at them.

"That said, there are fewer growers these days, so the ones left are ensuring that their storage is dramatically improved. And that can only be good for the industry."

Cost reduction tips

Five key points from Sutton Bridge Crop Storage Research head Adrian Cunnington on saving on storage:

1 Tariff management Shop around for good deals, look for an alternative supplier and try to manipulate terms to suit your needs, such as off-peak contracts or timing plant to run accordingly.

2 Air mixing Make best use of ambient air availability. Mixing in cooler, night-time air can reduce refrigeration needs, while automatic control systems can mix air cost-efficiently.

3 Defrost on demand A lot of energy can be wasted through refrigeration units that defrost cycle on a time basis, rather than when needed. Changing to defrost on demand can save electricity.

4 Store design and layout Improve insulation and ensure that doors and louvres are airtight.Meanwhile, load stores to maximise airflow and reduce fan running time.

5 Storage losses Do not store a crop that is not up to the job - this adds costs that you may not recoup. Make sure that the crop meets market specification as it comes in and monitor it during the storage period.

For further details of benchmarking software, email

Know your emissions

Until recently there has been no tool to effectively monitor greenhouse gas emissions, maintains PepsiCo agricultural-sustainability manager Mark Pettigrew. But an initiative to create a farm-scale greenhouse gas calculator helps potato growers measure their carbon footprint.

Cool Farm Tool was developed by Dr John Hillier at the University of Aberdeen to monitor all areas of production in response to industry concerns. It is being trialled with growers and can be downloaded at

"The first step in reducing emissions is to develop the right tools to measure them," says Pettigrew.

"The new tool is user-friendly and provides the carbon footprint there and then."

PepsiCo's Sustainable Farming Report details another web-based crop-management tool, i-crop, developed with the University of Cambridge.

"I-crop and the Cool Farm Tool could enable PepsiCo's 350 UK farmers to monitor, manage and reduce their carbon emissions and water use and at the same time maximise potential yield and quality," says Pettigrew. "PepsiCo is trialling i-crop in 22 farms, amassing data and developing a best practice model."

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