Energy use in potato stores Adrian Cunnington PCL Sutton Bridge Potato Council Energy Forum Huntingdon 11 February 2010
Storage costs Fixed (capital) costs Variable (running) costs Finance costs Potato Review Nov/Dec 2009 But most visible and major running cost in potato stores is energy, i.e. electricity
Energy cost profile Electricity costs are volatile Source: FEC
Energy cost profile But general trend is upward Relative cost 1998 2003 2010 Source: NAO
Storage costs Electricity contributes around 60% of variable costs (excluding storage losses) and 10-40% of total costs, depending on circumstances Important to know how efficient your storage is and how you can improve it
PCL project: assessing use Undertaken by Farm Energy and Sutton Bridge on commercial stores Eight closely-monitored stores over two seasons Further 25 stores monitored in last year on a monthly basis Spread of store qualities and uses Analysed by store type and end market
Sub-metering FEC Just increasing awareness can yield immediate gains of up to 10%
Measurements: kwh Analyse consumption per tonne this relates directly to sales Or per tonne per day this helps to compare store performance Analysis is problematic where stores are used dynamically with partial loading/unloading or regular movement of crop in and out but it does highlight inefficiencies
Results: processing 60 0.30 55 50 0.25 45 40 Number of days stored 0.20 kwh / tonne 35 30 25 0.15 kwh / tonne / day 20 0.10 15 10 0.05 5-211 271 276 263 194 265 239 263 153 153 122 168 O I N K S Store 4 Store 1 R Store 2 P Q Store 3 Store identifier 0.00 kwh per tonne kwh/ tonne / Day
Processing stores kwh/100t/day 2007/8 70 60 50 40 30 20 10 October November December January February March April 2008/9 0 70 60 50 40 30 20 10 0 PR1 PR2 PR3 PR4 PR1 PR2 PR3 PR4
Results: processing kwh / tonne 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 trend Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Store 1 Store 2 Store 3 Store 4
Results: processing Wide range of energy usage Linked closely to crop quality Excluding problem crops, usage can still vary by factor of 3 or 4 Plenty of scope for looking at reductions or optimisation
Results: cold stores 130 120 0.60 110 100 90 Number of days stored 0.50 80 0.40 kwh / tonne 70 60 50 0.30 kwh / tonne/ day 40 0.20 30 20 0.10 10-262 304 278 265 245 265 238 277 212 169 220 265 229 304 244 195 146 82 Y W AD AH X Store 8 T AC AE U Store 7 Z Store 5 V AA Store 6 AJ AG 0.00 kwh per tonne kwh / tonne / day Store identifier
Cold stores kwh/100t/day 2007/8 120 100 80 60 40 20 October November December January February March April 2008/9 0 120 100 80 60 40 PP1 PP2 PP3 PP4 20 0 PP1 PP2 PP3 PP4
Results: cold stores 45 42 39 trend Energy consumption trend 36 33 30 kwh / tonne 27 24 21 18 15 12 9 6 3 0 Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Store 5 Store 6 Store 7 Store 8
Results: cold stores Pull-down load predominates Daily energy use can be modest in fully loaded, well insulated stores But use of stores when part-filled meant spot consumption was actually as high as 39.9 kwh/month or 4/tonne!
Results: cold stores
Champion stores Need to know factors which have greatest influence on energy costs Management is the biggest one! Season is also significant. This year our project is focusing on identifying other key attributes of lower cost stores Aim to model best stores and highlight further benefits which you can share
Trends kwh / tonne 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 trend optimal? Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Store 1 Store 2 Store 3 Store 4
Optimising stores Most efficient stores are likely to feature: Inverter drives Offer significant savings if fans are suitable eg at 80% of max speed use just 50% of power Adiabatic cooling Humidification also removes heat: allows ambient air at or above crop temperature to be used for cooling Variable differentials High quality insulation & sealing
Optimal stores Most efficient stores are likely to feature: - Positive ventilation Worth considering to achieve positive ventilation? Not with solid-sided boxes! - Separate delivery & return air This helps to prevent short-circuits and hunting in box stores without positive systems - Planned consideration of energy use
Separators
Ambient air availability 2008/9 24 20 16 12-8 4 06 Oct 13 Oct 20 Oct 27 Oct 03 Nov 10 Nov 17 Nov 24 Nov 01 Dec 08 Dec 15 Dec 22 Dec 29 Dec 05 Jan 12 Jan 19 Jan 26 Jan 02 Feb 09 Feb 16 Feb 23 Feb 02 Mar 09 Mar 16 Mar 23 Mar 30 Mar 06 Apr 13 Apr 20 Apr Average Daily hours 27 Apr Hours available* 398 319 101 49 Week commencing 9.5 DegC 8 DegC 3.5 DegC 2.5 DegC *assumes 2 C differential required
Future options Wider use of energy-saving technologies eg inverters, defrost on demand etc Smarter control Sustainable construction Renewable energy sources Wind: turbines Solar: photo volteics Ground source AD
Acknowledgements Potato Council Jon Swain, Tim Pratt & Andrew Kneeshaw at Collaborating growers and store managers Simon Alexander
Summary Move energy up your agenda Measure your usage so you know where you stand Consider your markets needs if making changes Keep up to date at www.potato.org.uk/energy