Precision FarmingPreci­sion tech for a green future

In Hamp­shire, England, Edward du Val and his father Henry have imple­mented preci­sion tech­nology to meet the effi­ciency and sustain­ability demands of green energy. On the 405ha Apsley Farms, they have switched from arable enter­prises to entre­pre­neurial green energy in just eight short years – a feat of dedi­ca­tion and resilience.

Diver­si­fi­ca­tion

Breaking ground in November 2011, the first two biodi­gesters and combined heat and power (CHP) unit were constructed to generate elec­tricity – by Christmas Eve 2012 they were producing 500kw per hour using 230m^₃ of biogas.

But by 2013 the busi­ness had to re-eval­uate its strategy to improve prof­itability and decided to inte­grate its elec­tricity produc­tion with gas-to-grid gener­a­tion. “Accessing the grid and the Renew­able Heat Incen­tive (RHI) meant we could secure the future viability of the busi­ness,” explains Edward.

 

 

As part of the conver­sion, two more biodi­gesters and a second CHP unit were erected, producing a combined total of 1,100kw of elec­tricity per hour using 505m^₃ of biogas. A gas clean-up plant also sepa­rates carbon dioxide (CO₂) from methane (CH4), cleaning 2,200m^₃ of biogas to make 1,200m^₃ of biomethane for use in the national grid.

Effi­ciency is key in sustaining the busi­ness and managing the bottom line.

Edward du Val

In 2016, to further improve economic circu­larity and sustain­ability of the AD plant, the family built a CO₂ capture and liquifi­ca­tion plant, to convert waste CO₂ into a food grade product for sale into the food and drink sector.

Today the £25m AD plant achieves the govern­ments antic­i­pated return on invest­ment (ROI) of 12% and it has almost reached carbon-nega­tive produc­tion. The plant produces enough green energy from five biodi­gesters and two CHP units to supply gas to around 8,500 homes, plus enough elec­tricity to meet the sites oper­a­tional demands.

Preci­sion

Producing sustain­able green energy is the main objec­tive of the biogas produc­tion, to meet the govern­ment tariff criteria, explains Edward. “Effi­ciency is key in sustaining the busi­ness and managing the bottom line. But we also must provide quar­terly input and output data for sustain­ability assess­ment, and undergo an annual audit across the whole oper­a­tion, including the 40 farms that contract grow biogas crops for us within a 30-mile radius.”

Accu­rate data is there­fore essen­tial, and that’s where near-infrared (NIR) tech­nology and the HarvestLab 3000 sensor come in. “We love our tech and felt this could improve field work and meet the sustain­ability and record keeping demands,” he adds. “From crop produc­tion to AD plant effi­ciency and logis­tics – it is an evolving part of our informed deci­sion-making within the busi­ness.”

Pre-harvest

The AD plant requires about 3,642ha of crop per annum, which is split equally between high yielding maize and rye vari­eties – each of which should produce around 250m^₃ of biogas per tonne of crop. Dry matter (DM) content is an impor­tant element in biogas output, so Edward aims to harvest the maize and rye at 32-42%, and 36-46% DM, respec­tively.

Harvesting too late or too early can play havoc with produc­tivity. “Where the dry matter exceeds the mid-40s the crop becomes very lignin rich, taking longer to digest and not gener­ating the crop’s poten­tial biogas in the 150-day reten­tion,” explains Edward. “Equally, too wet a crop can reduce its biogas poten­tial signif­i­cantly.”

Dry matter testing is there­fore essen­tial pre-harvest. “Depending on weather, crops can mature quickly in July with rye DM increasing by 0.5% a day, and maize around 1% per week.”

We can there­fore antic­i­pate which fields to harvest next, tight­ening up logis­tical plan­ning – saving time, fuel and labour.

Edward du Val

Edward uses the HarvestLab sensor directly in the field, with a 12v battery and laptop in the back of the truck. “We can sample the crop on-farm and have a DM content within minutes,” he says. “We can there­fore antic­i­pate which fields to harvest next, tight­ening up logis­tical plan­ning – saving time, fuel and labour – as well as fore­casting crop avail­ability for the biodi­gesters, and have accu­rate records for auditing.”

Harvest

At harvest, the NIR sensor gives real-time feed­back on the crop, and helps to stream­line contract farm manage­ment and data recording.

“The contract farm grows the crop, but we do all the harvesting, and store the crop in-situ in a sealed storage system called an ‘ag bag’ which acts like a pop-up silage clamp,” explains Edward.

The sensor is fitted to the forager and works with the RTK guid­ance system so the oper­ator can imme­di­ately see yields and constituents like DM and nutri­ents. These records then help to stream­line the invoicing and farm manage­ment process.

Once the crops are moved from storage to the biodi­gester, Edward uses the NIR sensor at the farm weigh­bridge to test for DM and nutrient para­me­ters. “In compar­ison to the oven dry matter tests of around 35 minutes, it gives us quick refer­ence when the lorries are coming in with high crop turnover.”

Spreading

The process of biogas produc­tion at Apsley farms is very circular, with the solid diges­tate by-product used as fertiliser and providing a new branch of revenue as garden mulch. The liquid diges­tate is used in two ways; recir­cu­la­tion into the plant, removing the need to draw on water supplies, and as a nutrient rich liquid fertiliser for the next growing crop.

Edward uses the sensor on the spreader tanker, to contin­u­ously read total and crop avail­able nitrogen (N) in the diges­tate – as well as phos­phorus (P) and potas­sium (K). “After setting your NPK targets and limit rates in the tractor, the HarvestLab is able to feed that infor­ma­tion into the guid­ance system, which dictates the speed of spreading. If you reach a bit of diges­tate that’s poorly mixed the system can slow or speed up the pace, giving an accu­rate and even spread of nutri­ents across the whole field – it really does make a differ­ence to not knowing and driving at one speed.”

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