With no-one apparently tailoring renewable energy sources specifically to the glasshouse industry, what is the way forward for growers?
They are under pressure to produce crops and plants at cost-effective prices while being hammered by ever soaring fuel costs. Will there be a revisiting of the compost bedding system Victorians used to heat up the pipes in their glasshouses - a method still used at some botanical gardens today?
Chris Plackett, commercial director at energy specialist Farm Energy, says: "Growing has moved beyond the scale of this method. With regard to lighting, we find few people are looking at changing because usually they invested heavily in the first place. A much higher priority is given to heating systems."
Twenty years ago, nearly everyone in horticulture was looking at gas systems. But the industry has changed as gas prices fluctuated dramatically last year. "Growers are looking at securing a competitive advantage so what heating system they use is far more confidential because this can have a major impact on overall costs," adds Plackett.
Operating from the Rhymney Valley Nursery near Cardiff, Stubbins general manager Richard Lewis says: "The climate change levy has driven growers to look seriously at using less gas. We have looked at woodchip and other technologies but the drawback is not having the by-product of carbon dioxide, which goes straight into the plants. This is vital because that is what they breathe and it increases yields to a level where it would be uneconomic to do otherwise.
"Methane is produced by an anaerobic digester so would be a sustainable heat source. In fact, I see this as the future of our industry. This may be too expensive where glasshouses exist, but moving forward with new builds, I see our industry as an attachment to a fertiliser factory or sugar plant."
By converting waste products such as food and cattle waste through an anaerobic digester, the process is twofold - chemical energy to mechanical energy, and then from mechanical energy to electrical energy (see "Changing heat source" box, p46).
Stubbins has three sites in the UK covering 18ha of glasshouses. Two of them grow tomatoes and one cucumbers, together with peppers and aubergines. This year, ochre trials are also taking place. A traditional gas-fuelled boiler heats one site and gas boilers provide combined heat and power at the others.
To reduce heating costs in the first ten weeks of the year, Lewis reports that the company uses fixed thermal screens in older glasshouses and moveable screens in new ones. This is practical because the plants are small and do not need as much carbon dioxide during this period. Savings made by adopting this practice exceeded 30 per cent.
Viable heating alternatives to gas could also include solar energy. But where carbon dioxide is needed to ensure that varieties of fruit and vegetables meet the specification demanded by supermarkets, solar panels on their own will not provide a solution.
To combat this, putting straw on the floor, which gives off carbon dioxide, could be viable for smaller production sites looking at harnessing solar energy. Due to the weight of panels, they would need to be sited next to glasshouses.
Springfields fresh produce plant nursery uses solar heating to provide the hot water needs for staff in its working and packing areas. Efficient temperature regimes should also be reviewed whether: frost free - keeping plants above 5 degsC to maintain growth; temperate - around 14 degsC to keep plants flourishing; or propagation - around 18 degsC for fruit and more tropical plants.
Electroflora managing director Gavin Willn says: "One of my clients last winter found their heating bill increased from £2,000 to £6,000 per week and soaring costs have had a significant impact on many growers." He reports that customers who grow ornamentals use pressurised hot water systems.
For non-essential crops, heating is only used for frost protection, and they go for free-standing gas or oil hot air heaters. These are simple to instal and polythene ducting can be used to give more even heat distribution. Most new builds use space heaters as a compromise between cost and speed. These generally cover 100ft square blocks. If crops are required to be heated to 20 degsC throughout winter, a more fixed heating system of hot water is used because over time this proves more economical.
"Some clients heat water with biomass such as woodchip or straw bales and this is especially true where the nursery is attached to a farm because they have bales readily available," says Willn.
Having taken over two-acre Beacons Nurseries five years ago, Julie Robinson has five greenhouses heated by gas and oil. These are used for growing seeds, cuttings of perennials, alpines and bedding plants, some of which are supplied to a local council. Partner Julie Robinson says: "No two years have been identical weather-wise and the economic climate has been very precarious."
During this period, the wholesale/retail ratio of the operation has turned from 90 per cent wholesale to more than 55 per cent retail. "We try to minimise costs as much as we can," says Robinson. "On the other hand, in this line of business, if you have to add additional heat you do it for your business to ultimately prosper.
"We have never had a winter as bad as 2009 in terms of heating but we are not looking at changing because it would be uneconomic at this time. We had to subsidise some heating costs this year as we try to balance pricing to ensure plants remain affordable."
- Have you identified where your costs lie?
- Are controls doing what you think they are?
- Do you harness the most up-to-date systems?
- Have you researched the cost of upgrades to your system?
- Do you know where areas of waste are within your current management practices?
CHANGING HEAT SOURCE
Anaerobic digestion has recently become of interest in the UK because of the feed in tariffs (FiT) that have been available since April this year. These encourage the generation of electricity from renewable sources including anaerobic digestion.
In essence, anaerobic digestion converts putrifiable waste to gas that can be used to power combined heat and power (CHP) units or fuel boilers. The digestate that is left after the process is a valuable fertiliser.
Peter Hough, director of Regreen, an agent of WELtec BioPower, says: "Putrifiable waste is turned into electrical power, heat and fertiliser. The process also produces a carbon dioxide-rich exhaust. This adds up to a process that marries well with horticulture."
In addition to FiT, from April 2011 the Government is proposing to introduce the heat incentive, encouraging digester plant owners to make proper use of the heat generated.
The gas that is produced from the digester is usually used to power the CHP unit that produces electricity.
The heat is a by-product from the engines. In the summer the gas could all go to the CHP unit and in the winter more gas could be directed to heating the glasshouse.
Anaerobic digester projects depend almost entirely on the waste streams and substrates available to them and there are significant benefits of scale.
Hough adds: "To be economic the starting point is likely to be having a capacity of around 5,000 tonnes of waste per year available to sustain the plant. This will produce around 4,700 tonnes of liquid slurry, almost odour free, with most nitrogen from this available for plant use."
In Europe, many glasshouses harness this type of energy and, depending on how good the forthcoming heat incentives are, it could pay growers to make the change.
LIGHTING UP TIME
Growers with lighting systems can find rising prices make it almost cost prohibitive to run them. Efficiency and effectiveness are the key.
Gavin Willn of Electroflora reports that to boost crops in January to March when light levels are low, his customers tend to use 400-watt sodium lamps, which cover 2-3sq m.
Hortisystems supplies technical equipment including the Hortilux Schreder range of high-pressure sodium supplementary lighting. These lights feature five reflector options for use at various mounting heights and a slim-line body that is designed to minimise crop shading.
Providing good uniformity, the reflectors are detachable for easy cleaning. Major recent developments include the three-phase 400-volt fittings coupled with electronic ballasts. These save approximately 35 watts per fitting compared to traditional ballasts.
Offering Gavita horticultural lighting, Bridge Greenhouses creates dedicated computer-designed lighting schemes to maximise the effectiveness of each light. These boast a long bulb life and high energy-efficiency together with the ability to be dimmed when full light is not required, resulting in considerable energy savings.
GlacialLight has two distributors in the UK supplying its energy-saving bulbs. Depending on the model selected, a bulb consumes only 10 to 18 watts per hour. Although more expensive initially, the company claims that over the bulb's lifetime - 20,000 hours - it provides a cheaper option.