Frequently Asked Questions (FAQ) and answers
1. What are typical examples of incentives for facilitating the heat use from biogas plants in European countries?
If biogas plant is producing electricity under cogeneration regulations then in all countries of the European Union CHP plant has to comply with the high-efficiency CHP requirements. These requirements are transposed from the cogeneration directive and other related directives into the national legislation. In order to reach high-efficiency CHP requirements (certain level of primary energy savings and at least 75% of the total efficiency), biogas plants must have useful heat use.
In some European countries heat use from biogas plants is facilitated by CHP bonuses. For example in Germany the introduction of the so-called ‘CHP bonus’ in the amendment of the Renewable Energy Act (EEG) in 2004 resulted in a significant increase of heat utilization of biogas plants. In addition to the basic feed-in tariff, the law had foreseen the additional payment of 2 €ct/kWh if the waste heat of the CHP plant was also used. With the increase of the CHP bonus in the new version of the EEG in 2009, the incentive to expand the use of the waste heat was further strengthened. The law introduced the CHP bonus ranging from 2.94 €ct/kWh to 3 €ct/kWh for the waste heat use. In addition, the amendment of the EEG introduced a so called ‘positive list’ for heat recovery. The implementation of heat utilization concepts defined in the positive list guaranteed an increased CHP bonus. With the amendment of the EEG in 2012, the CHP bonus of the old feed-in tariff system of 2009 is replaced by an obligation to use the heat of biogas plants. As of 1 January 2012, biogas operators of newly installed biogas plants in Germany are required to use at least 25% waste heat during the first year of operation and at least 60% heat in the following years from the CHP plant. 25% thereof counts for heating of the digester.
In Finland a price-based mechanism or ‘heat bonus’ for CHP plants is introduced. Fixed ‘heat bonus’ is paid for heat that is produced in CHP using biogas or wood fuel.
2. Is the heat provided for heating the fermenters considered as useful heat?
It depends from the country specific legislation. For example in Germany, heat that is used for heating digesters is contributing to the total heat use requirement. In Latvia only heat that is sold to the third party is considered useful. Heating of digesters if they belong to the CHP operator do not count in the total useful heat amount.
3. What is an eligible (acceptable) heat use concept for biogas CHP?
German renewable energy act (EEG) indicates different ways to use waste heat in the so called ‘positive list’. The waste heat can be used for the following purposes:
- Heating and cooling of buildings
- Hot water supply
- Heat injection into a local heating system with a length of at least 400 meters
- Heating supply for different industrial processes
- Heating of buildings for poultry breeding
- Heating of animal stables
- Heating of greenhouses
- Heat treatment of digestate which require sanitation or pasteurization (wastes)
- Heat treatment of digestate for fertilizer production
- Use of heat to produce additional electricity, especially by ORC and CRC processes
In order to comply with the certain % heat obligation, biogas plant operators have to prove the heat utilization. An independent environmental expert has to be consulted in order to report the proof of heat use.
4. Who (which authority) is responsible for monitoring of heat use (field check)?
In Germany an independent environmental expert has to be consulted in order to report the proof of heat use. The same requirement is in Latvia – independent expert have to check and approve the annual report of the biogas plant operator before submitting it to the Ministry of the Economics of Latvia.
5. How can a bank be assured that the investor will keep its FiT level by heat consumption? Who controls that?
This is indeed considered as very high risk for biogas plant feasibility. In order to reduce it, banks may ask biogas plant project developers to provide heat use concept and provisional agreements with potential heat users.
6. What is highly-efficient cogeneration of electricity and heat?
In the EU is introduced a unified methodology defining so-called high-efficiency cogeneration. Only such a combined heat and power (abbreviated as “CHP“), which is meeting the requirements of high-efficiency CHP, can be supported by the member countries. The methodology is specified by the Directive 2012/27/EU and implementing decision No. 2008/952/ES and No. 2011/877/EU.
The basic requirement is that electricity and heat production in high-efficient CHP mode has to contribute to the primary energy saving (abbreviated as “PES“) in certain amount. For explanation, if the same amount of electricity and useful heat should be made of the same source (fuel) separately, than the consumption would be higher. Definition by the mentioned EU Directive requires at least 10% primary energy saving.
7. How can biogas plants compensate from seasonal variations in heat consumption?
Depending on the type and availability of substrates, it is possible to regulate the biogas production on a seasonal basis. However, in many situations it is most feasible to optimize the biogas production to ensure maximum electricity production, especially for farm biogas plants. If large quantities of excess heat are available, alternative applications focusing on the utilization of excess heat should be examined. The BiogasHeat project is describing and evaluating all alternatives in terms of optimization of heat use.
8. What is the value of the heat sold from district heating systems compared to heat used at the farm (when talking about farm biogas plants)?
It depends on national policies, especially tax regulations. In Denmark, the value of the heat delivered for private households through district heating grids have a substantially higher value than heat used for industrial/process purposes. This is because tax is higher for heating used for private purposes, as compared to heat used for industrial purposes.
9. Is it more feasible to upgrade biogas for natural gas grid injection than to use it in CHP units?
It depends on a number of factors. The most important are: The size of the biogas plant (annual production), distance to the nearest natural gas grid, feed-in tariff for electricity production, possibilities of using heat from cogeneration. A feasibility study has to be completed to tell.
10. What is the status of development of mobile heat transport in containers?
The use of mobile heat storage containers in not yet widely implemented in Germany. Only few technology providers exist and some pilot projects are implemented. However, most installations are set-up in connection with other heat sources than the heat from biogas plants.
An example is the heat storage container of the German company LaTherm which implemented mobile biogas heat storage containers in Berlin and soon also in Leipzig. Further containers are used in relation to landfill gas and waste incineration plants.
The main bottlenecks for the use of mobile heat containers are as follows:
- The heat demand (and the size of the biogas plant) needs to be large enough (> 1.000 MWh heat demand) to be supplied with at least 2 containers (Source: LaTherm). The minimum capacity of the heat source shall be 300 kWth, better 500 kWth (digester heating of biogas plants is not yet included!). Many biogas plants are too small.
- The distance from the biogas plant to the heat consumer shall not be too far. It shall not be more than 20 minutes away by truck. Optimum distances are below 5 km or 10 minutes. (Source: LaTherm)
- The available temperature level is relatively low (58°C) (Source: LaTherm). Many applications need higher temperature levels.
- Investment costs are still relatively high.
Opportunities exist as some technology manufacturers also provide services such as leasing. Furthermore, depending on the framework conditions, public support may be received. The clustering of several biogas plants that are close to each other may facilitate to set-up a mobile heat transport system.
11. At which size of the biogas plant is it economically feasible to upgrade biogas to biomethane?
Technically it is feasible to upgrade biogas to biomethane at nearly every size. However, on a commercial level it is only feasible for larger plants. Thereby, the costs for the production of the raw biogas are a crucial factor. Currently, only upgrading facilities with a capacity of about 250 m³ to 500 m³ upgraded biomethane per hour are economically feasible in Germany. This is equivalent to an installed capacity of 1-2 MWel, is the biogas is used in a CHP unit.
12. When can biomethane be used for farm-owned tractors?
In case that it is possible to upgrade biogas to biomethane, the produced biomethane could be used in transport, e.g. to fuel farm owned tractors. This can be done in tractors with modified diesel engines to be suitable for biomethane (or natural gas) or by dedicated tractors that have a gas engine. However, only very few manufacturers provide these tractors, such as Valtra or Steyr.
13. How can the heat be used to generate extra electrical energy?
An example of a system which allows generating electrical power from a heating vector (at a temperature of 70-90°C) is the ORC (organic Rankin cycle). An ORC allow generating from a heating source of 980 kWth an electrical output power of 125 kWhel. In the case the use of the ORC generates an increase of the electrical power which cause a decrease of the feed-in tariff value it can be considered better to avoid to work at full power and so it would be better to reduce the feed (in the case the feed represents a cost). If the feedstock doesn’t represent a cost (like for waste) and the power increase generates a loss in the feed-in tariff, the ORC option should not be considered.
14. We have been thinking about using heat for drying the digestate, but have heard that this is not sustainable option. Could you explain why?
Digestate is very valuable fertilizer. Some biogas plants are thinking about drying the digestate to decrease the amount of digestate that needs to be transported back to the fields and to lower the transportation costs. European Biogas Association in their position paper state that drying of digestate is a relatively old technology and was first introduced and tested in 1980‘s. The technology was supposed to transport concentrated mineral content of digestate from areas with intensive agricultural production to areas with shortages of organic and mineral supply in agricultural land. However, this concept was shortly rejected because of the dramatic reduction of nitrogen content during drying, which resulted in the degradation of fertilising effect of the digestate. For more information please read the paper: http://www.biogasheat.org/wp-content/uploads/2013/05/EBA-opinion_Digestate-drying_220513.pdf
15. As a wastewater treatment plant we need viable options for the use of digestate. Can you specify possible uses? Can you think at possible heat use in this context?
In many cases the use of heat to reduce the quantity of the digestate is not a viable solution due to the reduction of nitrogen content, difficulties to spread the digestate, etc. In the case of waste water treatment plant the situation is totally different as the chemical content of the digestate is sometimes very difficult to describe and it could contain detergents, and other harmful chemical compounds. Then the only solution is in fact to store the resulting digestate and to reduce the environmental risks. The solution in this case is to use the heat to reduce the water content of the digestate and allow a proper storage.