Growing efficiency

Can the protected horticulture sector continue to reduce its energy use? Gavin McEwan reports.

Protected horticulture has exceeded original Government targets on energy efficiency - photo: HW
Protected horticulture has exceeded original Government targets on energy efficiency - photo: HW

Many glasshouse growers have already slimmed down their energy consumption in line with government targets in order to be eligible for a discount on the Climate Change Levy, a tax on industrial energy use.

But with the news in January that horticulture's target for 2010 had been upped from 12 per cent to 20 per cent, the industry appeared to be a victim of its own success in energy reduction.

The Climate Change Agreement is negotiated between the Department of Energy & Climate Change (DECC) and the NFU, then administered on the NFU's behalf by consultancy FEC Services, which manages similar schemes in the pig and poultry sectors.

FEC Services commercial director Chris Plackett says: "The Government wanted over 30 per cent - they thought horticulture could keep going on making savings. But you pick the low-hanging fruit first and eventually you reach a plateau because you've taken up all those measures. You can only insulate your pipes once."

The relationship between the NFU and growers on the question of efficiency is not all one-way, he adds. "The NFU is looking for information from practitioners on what is and isn't viable in order to project a realistic target. Such a target needs to be not too challenging from the growers' point of view, and not too soft from the point of view of the Government.

"Horticulture is doing particularly well next to other industries and the indicators are that it continues to make savings. But everyone has invested heavily in better control systems, more efficient boiler equipment and thermal screens. Those things have passed from the early adopters into the mainstream."

The Government was concerned that growers would continue to get the discount while sitting on their hands, he says. "But some measures (growers) have taken, such as thermal screens, have a payback period of several years."

The next stage will involve technologies that are less established, he adds.

"Like flat-screen televisions a few years ago, the use of renewables and closed glasshouses is still in the early years in terms of technology and people's acceptance of them. When they are picked up, the rate of change (in savings) will be faster, but until then the rate will flatten off."

Plackett says such technologies are likely to prove their worth on the Continent first.

"Holland has a far bigger public purse to put into development, so inevitably it will lead the way - we do ride on their shirt-tails a bit. But they are not that far ahead, and they do make mistakes. Our good growers are probably as good as theirs."

A current concern is that the global downturn has weakened demand for fossil fuels. A respite in the rise of fuel prices might reduce the incentive to make further efficiency gains. But according to Plackett: "The gas price is easing in the short term, but it's heavily dependent on world demand. The experts are predicting that it will be back on an upward trend by 2010."

This longer-term trend will make alternative fuel sources more appealing, but these are no panacea, he says. "The attractiveness of biomass will depend on a grower's individual circumstances - particularly the local supply chain. How secure is the supply and the price? And if gas and oil go up in price, so will biomass."

Industrial waste, underground heat pumps and combined heat and power (CHP) units "will all have their place", he adds.

Bridge Greenhouses managing director Ben Smith agrees that making further reductions will be harder. "A grower may have already installed thermal screens to meet the first target," he says. "You can put in double screens but the return will be lower. If the first screen gave you a 40 per cent saving and the second one gives you a 40 per cent saving of the remainder, that's only a further 24 per cent saving overall."

Thermal screens, already well-established in horticulture, offer 85 per cent light transmission, according to the Carbon Trust. The trust, which is part-funded from revenue from the Climate Change Levy, suggests polythene or bubble wrap as low-cost alternatives. At around £50,000/ha, these offer a payback period of two to three years.

Current advances in thermal screens focus on fire resistance and safe gaps between screens and lighting, says Smith. Meanwhile, some planners now require glasshouses that use assimilation lighting at night to use light screens to "black out" in order to prevent light pollution, he adds.

He has other suggestions for efficiencies to consider. "Some tomato growers also get higher efficiency by using 'grow pipes' - a secondary heating circuit at 40-45 degsC running near the plants and supplied from a flue-gas condenser on the gas boiler," he says. "You can also use heat stores to level out the load on your boiler - that way you can get by with a smaller boiler. This applies particularly to biomass or other solid fuel boilers - they don't like having to change their output.

"You can run them fairly hard and store the surplus in the short term, then use the heat you've accumulated at night when you need it."

Good housekeeping also has a role, he says. "Keep your glasshouse airtight and use your climate-control computer to control the temperature and humidity accurately. But after that it's difficult to see where growers can go."

Combined heat and power

CHP systems are quite common in the Netherlands, but Smith says: "The economics are not particularly attractive."

Growers in the Netherlands are also moving into combining CHP units with underground heat storage, providing a low- temperature heat source for tasks such as under-floor heating, he says.

Porters Horticultural quality manager Sarah Fairhurst says the Merseyside ornamentals grower will be sticking with its gas-powered boiler for the foreseeable future. "We looked at a CHP unit but for us the payback period was too long," she says.

Fairhurst, the newly appointed British Protected Ornamentals Association chairman, adds: "The targets are achievable through measures such as: temperature integration, where you have an average set heat point through the course of the day; thermal screens; and even simple things like lagging the boiler and repairing broken panes of glass."

Although she adds that, with the cost of energy still high, "these are things we would have done anyway".

Indeed, for many of the scheme's members, the levy discount is likely to be an agreeable bonus rather than a driving incentive, as there have been moves to cut energy use in horticulture ever since the original oil shocks of the 1970s.

Tomatoes, for example, are now grown using half the energy per tonne that was required 30 years ago, thanks to CO2 enrichment and new varieties.

As the FEC Services website suggests: "Whilst the Climate Change Levy tax credits for this reduction will have been a big incentive for scheme members, the biggest benefit will come from the savings they made by the reduced consumption."

The right image

Low energy use fits in with an image that horticulture ought to be portraying, says Dr Alan Knight of the Sustainable Development Commission. "The question of whether or not to insulate your glasshouse should be a no-brainer," he says.

Knight spoke at a conference last month on energy saving at Northern Ireland's College of Agriculture, Food & Rural Enterprise. The college's Horticulture Development Centre at its Greenmount campus, in County Antrim, is putting these measures into practice. It has commissioned a 320kW biomass boiler as well as 10 solar panels, each 2.5sq m, which will pre-heat water entering the main biomass boiler.

The college's senior renewable energy technologist Nigel Moore says: "The anticipated payback for the Sustainable Energy Unit is seven to 10 years depending on oil prices, with additional savings of approximately 200 tonnes of CO2 each year."


According to Defra figures, protected crops account for over a quarter of all energy use in UK agriculture, compared to only three per cent consumed by horticultural field crops.

The Climate Change Levy (CCL), which applies to non-renewable fuels other than oil, was introduced in 2001. But growers are entitled to a rebate if they can demonstrate moves toward greater efficiency.

Climate Change Agreements have been concluded with more than 40 industry sectors. These take two forms: a "sector-level agreement" with an industry umbrella body and "underlying agreements" with individual enterprises.

For a business to qualify for an 80 per cent rebate on its CCL payments, it has to meet energy-use reduction targets set in 2005 for energy reductions by 2006, 2008 and 2010 relative to the base year of 2004. Provision was made to reassess the 2010 target in 2008, and it has now been set at 20 per cent lower in 2010 than in the baseline year of 2004.

The target for 2008 was set at 12 per cent, but a saving of 18 per cent had already been achieved by 2006. The extent to which the sector has overshot its 2008 target will be made known shortly.

Electricity generated from renewable sources such as biomass is not taxed.

According to FEC, a grower with 1ha of greenhouse space using 100,000kWh of electricity and five million kWh of gas per year would save approximately £6,500 per year through the scheme.

FEC Services provides an online savings calculator at


Glasshouse supplier Cambridge HOK technical manager Duncan Grant says basic housekeeping is as important as technical upgrades in getting energy use down. His tips are:

- Make sure roof vents shut properly. Leaking vents mean loss of heat in winter. These should be serviced and adjusted if necessary.

- Make sure all glazing strips are sound to prevent leaks. Also make sure doors are tight and replace broken glass.

- Reduce pipe temperatures - do you really need to run such a high minimum pipe?

- Have the boiler serviced regularly. This is not only a legal requirement, but a well-maintained boiler will run more efficiently. The Carbon Trust estimates that a poorly maintained boiler can cost 10 per cent more to run.

- Install energy screens.

- Install variable-speed pumps for block heating and transport circulation. In most cases there is no need to run a pump flat out to maintain temperature. Reducing the speed of the pump will cut both electrical consumption and heat loss, especially on long pipe runs.

- Install a modern environmental computer-based control system, or make sure the software on your existing system is up to date. The latest control algorithms are designed to run your nursery at optimum conditions, thus saving energy.

- Consider alternative energy sources such as biomass boilers.

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