- Energy Saving
- Heat Pumps
- Electricity Generation
Heating and lighting for soft fruit
On Monday 19 November, GrowSave held its first event specifically for the Soft Fruit sector.
GrowSave has previously been involved with soft fruit, having led a study group to Belgium and the Netherlands in 2016, but this was the first dedicated workshop. The focus was on heating and lighting and highlighted some of the key considerations when choosing equipment.
Jon Swain, Senior Consultant at FEC Energy, explained the advantages of using a heating system, which can include extending the growing season, as well as maintaining a healthy environment for the crop. Efficient operation of the system is important and is influenced by growing strategy. For example, a ‘vent then heat’ approach will use less energy than ‘heat then vent’ when trying to maintain target humidity levels. In these times of high energy prices, growers should seriously consider energy-saving measures. This could be as simple as insulating the glasshouse sides, repairing broken or slipped panes, and making sure vents close completely. Lower energy usage will mean lower bills, but there is a balance between what is needed to maintain a healthy, productive crop and using heat for climate control. Sometimes, though, efficient and effective production can be achieved with methods that are seen as unconventional, and growers may like to experiment with these.
System maintenance is also vital to ensure everything is operating optimally and can identify issues before they get out of hand. This is especially the case for biomass systems, where fuel quality can be variable. Renewables remain a viable option; eligible plants can take advantage of the RHI scheme until 2021. Water and ground source heat pumps are still the best-supported technologies in terms of financial incentive and potentially lend themselves well to the relatively low temperatures required by soft fruit growers.
For many, CO2 production is important; Jon spoke about some of the options for self-supply, including gas heaters and CHP engines. Biomass boilers are not well-suited, however, as significant cleaning of the flue gas is required.
While heating was the main topic of the day, the use of lights was also considered. Traditionally, lighting has not been used for soft fruit and relatively limited research has been carried out on the subject compared to ornamentals and edibles such as tomato. Some growers have experimented with trial units, but results have been mixed.
The principles of lighting in horticulture are well understood, with over 50 years of development. The importance of stimulating photosynthesis is not wasted on growers and using supplementary lights to artificially extend day length and season are the primary objectives. However, quantifying the financial benefit of an increase in production and quality can be a challenge. Without knowing the value, therefore, it can be difficult to justify the large capital expense necessary to invest in supplementary lights. For those that do, the choice is generally between HPS lamps and LEDs. The former have established themselves as the industry standard over the years, but development in the last decade has been limited. In contrast, LED technology continues to advance, but remains on the periphery of what is viable for horticulture. Despite significant (approx. 50%) reductions in energy usage compared to HPS, the capital cost means a long payback period. As such, LEDs have not seen the uptake many might have expected.
LEDs certainly have their advantages, allowing tuneable output, meaning the exact wavelengths required by the crop can be achieved, whereas HPS gives a full-spectrum output. However, producing light at wavelengths not required by the plant can be viewed as a waste of energy, although the nature of HPS lamps means a lot of radiant heat is produced as a by-product, which can go some way toward offsetting primary heat. LEDs, on the other hand, do not radiate heat, but may still require cooling via convection.
Whether or not supplementary lights are a good investment depends largely on the benefit to production. If they allow year-round production, not otherwise possible, then this could be attractive, as long as the value of the crop outweighs running costs and a return on investment is seen within an acceptable timeframe. The choice between HPS and LEDs is likely to be financial; until the price of electricity becomes too much to bear, or LEDs become significantly cheaper, the decision is likely to go in favour of HPS.
GrowSave is already planning its next Soft Fruit event, scheduled for 27 February 2019. Keep an eye on our events page for more details.