How to improve energy in potato stores
© Tim Scrivener Storing potatoes is one of the most energy-intensive activities in agriculture. The Potato Council estimates electricity costs account for £3-9/t, depending on the crop type and length of storage.
While modern stores are more energy efficient, there are many ageing stores that waste considerable amounts of energy, says Adrian Cunnington, head of the Potato Council’s Sutton Bridge Crop Storage Research (SBCSR) facility.
See also: Make energy go further on arable farms
“Electricity costs will be inherently higher for the fresh market sector than for processing due to the refrigeration requirements, but a lot comes down to the efficiency of operations from the moment the crop comes into store.”
12 steps to energy-efficient potato storage
- Use meters or sub-meters on individual stores or pieces of equipment to monitor energy use and highlight possible management changes
- Ensure controls work correctly and consider ways to use cheap-rate electricity
- Consider variable-frequency drives – these can be used on fans, condensers or compressors to improve energy efficiency – take care to avoid any effect on quality by reducing airflow too much
- Calibrate temperature probes annually and verify with hand-held thermometer. Ensure correct location
- Insulation – check for gaps or damage and ensure insulation thickness is adequate (80-100mm foam or boarding)
- Fans and ducts – ensure inlet/outlet ducting allows for most efficient fan operation. Consider more aerodynamic fans
- Doors, louvres and joints – seal gaps to reduce air leakage and use brush seals, rubber flaps, spray foam or silicon sealant where appropriate
- Lighting – consider new energy-efficient technology when replacing lighting – for example, gas discharge tubes
- Consider replacing old motors on graders or conveyors with more energy-efficient models
- Get an energy audit – an independent check to highlight areas for energy saving – for example, Potato Council/FEC store check
- Layout – ensure boxes allow uniform airflow
- Hygiene – keep fans, ducts and coils clear of debris to allow good airflow
Source: Potato Council
Refrigeration costs and the efficiency with which potatoes are cooled is the key concern. “The best stores are averaging 4.4kWh of cooling for every 1kWh of electricity used, while the worst are nearer 1.6kWh,” says Mr Cunnington.
There can be a number of reasons for this variation, from the type and age of cooling and ventilation equipment to the store layout/ airflow or airtightness.
Look for leaks
Air leakage can account for up to 37% of a store’s total energy consumption (pre-pack) and 55% (processing), according to a SBCSR/ Farm Energy Centre study.
Analysis of 40 stores audited under the Potato Council’s store check (see ‘12 steps to energy-efficient potato storage’, right) service last year shows one-third fell below an acceptable standard for air leakage, while only a minority were classed as good.
The effects of air leakage is worse on warm, windy days where more energy is used, cancelling out external air coming in, says renewable energy consultant Rod McGovern, who suggests leakage can be cut significantly by relatively simple measures, such as:
- Sealing gaps around doors/closing doors properly
- Filling joints on roof eaves or ridges
- Flaps over louvres or ventilation systems
- Minimising airflow through ambient fans when turned off.
“Stores should not be airtight as potatoes need some oxygen, but minimising air leakage is a key step in controlling the storage environment and maximising energy efficiency.”
New kit cuts costs
Mounting pressure on margins makes it harder to contemplate buying energy-saving equipment, acknowledges Dr Cunnington, but he says many options are relatively cheap and will deliver long-term savings.
For example, replacing old fans with energy-efficient units should pay back in two to three years at most, while an inverter (also called a variable-frequency drive) can improve returns further, he says.
Inverters allow fans to run at variable speeds when required, such as full speed when the warm crop comes into store and needs cooling quickly, but lower speeds to maintain temperature during the holding period.
“Running a fan at 80% with an inverter drive costs about half as much as running it flat out.
“There are also other benefits to consider, such as being able to use fans at lower speeds to circulate CIPC sprout suppressant.”
More accurate metering of individual stores rather than one meter for the whole enterprise is also worthwhile, says Mr McGovern.
Meters typically cost £600-1,000 installed and can give growers a lot of information about how and where energy is used. This in turn can allow simple, cost-effective management changes.
Potato Council store check
The Potato Council’s Store Check service audits store performance and efficiency, covering energy use, refrigeration efficiency and an air leakage test. Cost is about £550-700.