It is vitally important to constantly review where, how and why energy is being consumed in your business and what sensible economy measures can be made
How can I save energy in the greenhouse?
Improvements in the greenhouse structure will provide the biggest opportunity to save energy. Things to bear in mind include air leakages, thermal screens, air circulation, and accurate heating controls.
Review energy consumption
Understanding energy consumption by reviewing energy invoices in the basis of good energy management. Review how cropping is organised and ensure any heated areas are used efficiently.
Heating
Thermal screens can reduce heat loss by up to 30%. New designs optimise energy retention whilst minimising light reduction, materials can be used that closely match the need of specific crops and greenhouse types. Investment in thermal screens can qualify for tax relief in the form of Enhanced Capital allowances (ECAs). Glass, measuring boxes and sensors should be cleaned regularly to maximise light and heat capture, and climate control equipment should be used.
Building structure
Improvements and regular maintenance can allow for better temperature control and lower expenditure. Heating costs can be reduced by 25% in a well-sealed greenhouse
Boiler efficiency
Boilers should be checked using a flue gas analysis kit. There are options available to increase the efficiency of your boiler, perhaps by fitting an automatic air inlet or a flue damper which will improve performance slightly.
Insulation
This can include insulating the boiler and distribution pipes, any oil storage tanks for fuel oil, and soil warming equipment.
Greenhouse controls
Consider using temperature integration (TI), in which the average greenhouse temperature is managed over a given period and is crop dependent. Reliable energy savings of 10% can be produced on a wide range of crops with no effect on crop quality or scheduling.
Air circulation and ventilation
Air circulation and ventilation can account for 25-30% of energy bills. Use efficient fans and ducts, consider installing circulation fans to redirect warm air and minimise heat lost from access points and consider fitting variable speed drives to reduce costs. The “heat then vent” approach to controlling humidity is reliable, but can waste energy. During late spring /summer a “vent then heat” approach can be better, relying on the properties of external air to control humidity.
CO2 enrichment and heat storage
Tomato growers can use this spreadsheet based calculator to determine the best economic strategy for CO2 enrichment. Click here (please enable macros).
Combined heat and power (CHP) units
CHP units should be used in conjunction with boiler equipment so that the CHP satisfies the base load heating requirement while the boiler is used to satisfy any peaks that may occur throughout the year. To be economical, generated electricity should meet the heat and CO2 demands of the greenhouse. Any surplus electricity should be exported via the network to other consumers
Lighting
Lighting can account for 20% of energy used and represents 50% of total energy costs. If it good practice to regularly maintain and clean any supplementary lighting and use appropriate bulbs and lighting for the designated tasks.
Alternative approaches
Alternative approaches may include reorganising the timing of crop production to reduce energy consumption; operating the greenhouse at a reduced temperature for part or all of the growing season; improving the use of space in the greenhouse, or reducing the wind speed in the greenhouse with the use of windbreaks.
Major redesigns
Consider the use of a combined heat and power system or improving the efficiency of your current boiler by fitting various devices.
Strategies to reduce energy
Source: Grow Save, and The Carbon Trust – Introducing energy saving opportunities for farmers and growers
Energy Benchmarking
Energy benchmarks are a measure of energy use intensity. The most common units are energy use per unit area (kWh/m2) and energy use per unit yield (kWh/kg)
Measuring my energy consumption
Below are some figures you can use to measure your energy consumption against. Key crops have been chosen to illustrate typical performance benchmarks. The information is based on methods and techniques that minimise energy consumption whilst maintaining crop performance at an economically acceptable level
| Energy consumption kWh/m2 |
Edible Crops |
|||
| Intensive e.g. tomato, cucumber, pepper, aubergine etc | Extensive e.g. lettuce | |||
| Heat | Electricity | Heat | Electricity | |
| Best practice | 520 | 10 | 225 | 8 |
| Typical | 675 | 15 | 250 | 12 |
| Energy consumption kWh/m2 |
Ornamental Crops |
|||
| Intensive e.g. chrysanthemum, begonia, poinsettia, young bedding plants, foliage plants etc | Extensive e.g. summer bedding plants, summer cut flowers, hardy nursery stock etc | |||
| Heat | Electricity | Heat | Electricity | |
| Best practice | 350 | 60* | 155 | 8 |
| Typical | 450 | 60* | 175 | 12 |
*includes energy uses for supplementary and night break lighting
In order to measure my energy usage what must I do?
Carry out a simple assessment to establish energy use: collect information on the amount of energy used and calculate the energy intensity. This can be done by gathering information of the total energy use for the previous year and dividing it by the total greenhouse heated area to calculate the intensity in kWh/m2
To monitor energy use, make sure you take regular meter readings, and relate the information collected to production levels and external factors i.e. the weather
How can I calculate energy/m2?
Divide total energy input by the heated area. N.B. Ensure all fuel inputs are converted to a common energy unit
How can I calculate energy/yield?
Divide total energy input by production (ensuring all energy inputs are converted to a common basis)
Source: Energy Benchmarks and Saving Measures for Protected Greenhouse Horticulture in the UK ECG091 (Carbon Trust)