Aidan J D'Arcy
1.1 Abstract
Modern Farming is seeing rising costs in all areas. This forces farmers to examine these costs to see where savings can be achieved. One of these areas is in electricity costs where up until recently there would have been no alternative. This page will examine the feasibility of converting a modern farms power provision from a commercial supplier such as the ESB to a self provided system such as production of Biogas through anaerobic digestion (AD).
This is becoming a real option for the modern agriculture sector as it looks to use every possible resource at their disposal to make savings and even generate revenue. If large enough quantities of power or heat energy are generated it could be possible to transfer this energy on to supplement the savings and possible contribute to recover some of the capital cost of installing the anaerobic digestion system and ancillary equipment and machinery.
This method of power generation has added benefit in reducing the dependency on fossil fuels for power generation. While it will probably not eradicate the requirement for traditional power supply methods such as connecting to the national grid, it could prove to be a significant first step in reducing fossil fuel consumption and emission of greenhouse gases.
In addition to the benefit of supplying power by a renewable energy method, there is a significant opportunity for employment to be generated. to construct each of these AD plants, there is a requirement to construct large concrete tanks which are made from specialized materials. There is the need for a system which will allow the power to be distributed to a number of locations including the local facility (eg the farm), a residential dwelling cluster like a local village or the electricity power supply grid. There will be a need for an ongoing O&M skill-set to ensure optimum performance of the system for its lifetime.
irish farmers journal - 20-10-2011 - page 34 & 35. Subscriber only
2.1 Anaerobic Digestion (AD)
Anaerobic digestion is a series of processes where microorganisms break down biodegradable material in the absence of oxygen. It is used to produce energy but also to manage waste.
Anaerobic digestion facilities have, however, been recognized by the United Nations Development Programme as one of the most useful decentralized sources of energy supply, as they are less capital-intensive than large power plants.
There are four stages to anaerobic digestion to produce biogas. These stages are outlined below at a high level.
i) The digestion process begins with bacterial hydrolysis of the input materials to break down insoluble organic polymers, such as
carbohydrates and make them available for other bacteria.
ii) Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.
iii) Acetogenic bacteria then convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon
dioxide.
iv) Finally, methanogens convert these products to methane and carbon dioxide.
The methane produced is can then be passed onto a CHP (combined heat and power) engine. This piece of machinery can extract heat for transport to a local heat dependent facility (a residential home would be the simplest example) and also produce power for supplying local power dependent facilities (such as a farm or cluster or residential homes).
(http://en.wikipedia.org/wiki/Anaerobic_digestion)
2.2 Methane from Biogas - Anaerobic Digestion
Anaerobic digestion of wastes provides biogas. Biogas contains about 60% methane that can be used to generate electricity or used for heat or for fuel for vehicles. Any animal manure, human sewage or food waste will produce methane during anaerobic digestion. Natural gas is methane. Biogas can be "cleaned" to yield purified methane that can be used in the natural gas pipelines.
Methane from biogas is an excellent alternative energy source. Using methane for energy helps the environment by replacing the use of non-renewable fossil fuels with renewable energy and by taking the methane out of the atmosphere. Methane is a green house gas that has 21 times the heating effect as carbon dioxide. Biogas methane is renewable unlike natural gas which is mined from underground wells and is a non-renewable fossil fuel.
There is also a large amount of heat energy dissipated from the Anaerobic Digestion system which can be channeled into localised heating systems for water, housing or possibly other agricutural functions such as grain drying.
(http://www.learningjoyresources.com/AD.html)
Learning Joy Resources - Year Unknown -
3.1 Anaerobic Digestion in Relation to Farming
Recently hundreds of farms in Mexico and South America have installed anaerobic digesters to collect and use methane from manure to provide energy for farm use. Many of these digester's have been paid for by a company that aggregates and sells carbon credits to factories and utility companies in countries that signed agreements under the Kyoto protocol to reduce greenhouse emissions. Carbon credits are earned by reducing greenhouse gas emissions such as carbon dioxide and methane. These credits have considerable value in Mexico and South America.
3.2 Example: Overview - Blakiston Heuston Estate Co Down
The Anaerobic Digestion (AD) plant is designed to produce and store both biogas and heat. The biogas is used to product power which will be sold onto the electricity grid. The heat produced in Blakiston will be used to partially supply heat energy to an adjoining residential development. This heat supply can be used as a supplement to individual housing heating systems and should produce a significant reduction in the requirement from the grid to these residences.
The AD system used in Blakiston is produced in Germany and is a 'ring-in-ring' system. There is a 32 metre outer ring made of concrete with a 22 metre inner ring forming two tanks, with one inside the other. The tanks are 6 metres deep providing 2400 cubic metres of capacity in the outer ring and 2200 cubic metres in the inner ring. Livestock waste (in the form of slurry) is pumped into the outer ring through a 140 cubic metre reception tank via a pumping system. Silage is also fed into this outer ring using a conveyor belt. Two types of mixing mechanisms keep the contents of the outer tank moving at all times to ensure that no stationary material blocks the system. These mechanisms operate at the surface and below the surface of the tank contents.
Once full, the digestate overflows from the outer tank to the inner tank. Gas emitted from the inner and outer tank is collected in a 'gas bag' which is installed above the surface of the two tanks. This gas is then piped from the gas bag to a 250kW CHP (combined heat and power) engine. This engine is housed in an adjoining building. Power from the engine is passed to a control panel where electricity is passed to the farm itself and out to the electricity grid.
The heat energy is roughly half of the energy output from the system so it is a significant bi-product of the system from a farm electricity supply perspective. In the case of Blakiston, its proximity to a residential development means that the heat generated by the AD system can be passed to the residences to supplement their heat requirements for water and room heating. Some farms could also use this heat energy for other farm systems such as grain drying, which is an important part of the grain production process.
irish farmers journal - 20-10-2011 - page 34 & 35. Subscriber only
4.1 Case Study: Implementation of AD System in 8 Farm Cluster
4.1.1 Overview
There are no subsidies or grants available currently to build such facilities so a manageable approach might be for a number of farms in a close geographical region to group together and finance the project as a single initiative. Sufficient power can be produced for a group of eight dairy farms each farming between 80 and 100 cows each. This would be a reasonable sized dairy producer in RoI today. Typically a farm of this size would utilize 1500 - 2000 Kw of power per month. As a comparison, a German farm with 400-500 dairy cows could feasibly take the cost of implementation of this facility itself but with the laws and economic conditions present in Germany. This is done by a 'guaranteed price' mechanism where the private producers are guaranteed a minimum price from the grid owner to supply power. This is not present in RoI today, which makes investment in renewable energy systems like biomas unattractive for most people.
(http://cosmic.rrz.uni-hamburg.de/webcat/hwwa/edok05/ch316g/DB111.pdf)
Effective Public Policy and Emerging Customer Demand - Rolf Wüstenhagen and Michael Bilharz - June 2004
pages 18-24
4.1.2 Implementation
This concept of 8 farms grouping together is based on not supplying any power back to the public power grid. This is partly due to a cost of €100k to connect back to the grid but more due to the price of power offered to private suppliers by the incumbent. This is in the region of 0.15c per watt. Other European countries like Germany as discussed above, implement conditions to attract private producers to supply the grid.
Along with the power produced to the farm units themselves, domestic power could be supplied to the residences on or beside the farms. There is also considerable heated water quantities produced by the system which can be used on the dairy farms for cleaning and also in the residential units for hot water and home heating.
Considerations for this proposal would be
- agreement on the site of the system
- agreement on the contribution of silage, slurry and other additions to the system
- regulation of the distribution of power to each farm in a ratio which matches the contributed costs. *
- agreement on the distribution of the digestate produced, which is typically used as a fertilizer on agricultural lands
- agreement from the financing body that a joint venture from the farms as a group is acceptable
* This is assumed to be equal for each farm holding
Benefit to this model would be employment generated by the construction of the plant. there could also be a significant benefit in the future is the grid owners improve their but price of power from private initiatives like this.
4.1.3 Commercials
Implementing an Anaerobic Digestion system would cost in the region of €1.6m to build in the Republic of Ireland. The lack of incentive in the Irish economy makes this a difficult proposition to justify for a single farm or even a smaller number of farms. There is a strong dis-incentive from the suppliers in the low price that they offer to purchase power from private initiatives.
In the business case attached lower on this wiki, the bi-monthly costs to each farm can be seen to be nearly 20% higher than the typical ESB bill which arrives bi-monthly. This is based on a typical farm unit of 100 dairy cows spending E1650 bi-monthly on electricity from the ESB. This strategy is based on a 20 year payback to the financing body which in itself is probably not an attractive proposition for a lender in the current economic climate.
The figures here do not include a VAT rebate of E54,000 which would be available for reclaim. There may also be the possibility that the Irish Government or the grid owner forces market conditions to make it more attractive to supply power to the grid. This could be done by a combination of the following methods
- Guaranteeing a minimum price per watt for electricity supplied to the grid.
- Licensing the technology within the state for supplying the power to the grid.
- Inserting a minimum threshold for power on the grid that must be from a (or a number of) renewable resource/s.