Mini biogas plant up to 75 kW: construction, operation and economy

Mini-biogas plants stand for one of the great growth potentials of gaseous bioenergy in Germany in the coming years. Due to the changes to the EEG amendment 2012, the newly hatched and smallest biogas plant type is becoming the focus of many farmers and investors. But for whom and under what conditions is a 75 kW mini biogas plant actually interesting? When does the construction and operation of such a small biogas plant pay off and when can an investment be rushed? The article brings some clarity to this hotly discussed market segment of the biogas industry, which is intended to promote the further expansion of decentralized and rural bioenergy in Germany.

In the past weeks I have heard different opinions about the 75 kW mini biogas plants. On this subject, I had contact with farmers who were considering whether the construction of such a mini biogas plant would also pay off in their specific case and I had discussions with project engineers who had experience in the planning and construction of biogas plants.

For me, the topic of mini biogas plants was fairly new and I was pleased with the very different feedback. The statements and moods ranged from gloomy to almost euphoric and were often a reaction to the 2012 EEG amendment.

To get you in the right mood, here are some articles on Construction and operation, or an article on Profitability of a biogas plant.

Mini biogas plants divide people's minds

The farmers I spoke to were very curious and there was a real sense of optimism for this additional opportunity to earn money with their own farm. However, there was also uncertainty and there were many questions about the new one Mini biogas plant of the EEG 2012. It was not certain whether investing around 500.000 euros, the associated risk and the time required would also be worthwhile in their case. In general, however, farmers and dairy farmers were very interested in learning more about this long-term secured source of income.

The statements of the project engineers and plant manufacturers I spoke to were much more reserved overall, as if they already knew that the construction and operation of a biogas plant up to 75 kW brings with it very special challenges and is anything but an egg-laying pig.

My impression is that there is great interest in the construction of mini-biogas plants, but the economic framework and the reasonableness of most plant planners are somewhat depressing this euphoric mood. This is despite the fact that the mini biogas plants up to 75 kW will receive the highest feed-in tariff from January 1.1.2012, XNUMX, which was previously determined in the bioenergy sector.

How can interested farmers, experienced project planners and investors / contractors still get together and jointly implement an economically successful mini-biogas plant?

In which cases are mini biogas plants an interesting option?

"8 out of 10 applications currently submitted to us for the construction of a mini biogas plant are not economically viable." So one of the project engineers I spoke to.

Of course, you can again ask the popular question of whether someone sees the glass half full or half empty. After all, 20% of the projects promise economic success. The gold rush looks different, but a carefully calculated project should generate a solid financial gain.
But what framework conditions should be available at your own location so that you are among the 20% who can achieve a successful concept for the construction and operation of a mini biogas plant?

Ideally, as many of the following statements as possible apply to you:

  • You are already a farmer or operator of animal husbandry (dairy farming)
  • You have a constant slurry flow that is collected centrally (slurry silo available?)
  • They have a few hectares of fallow or expandable area for growing energy crops
  • You have a good relationship with your neighboring farmers or residents for the establishment of partnerships in the electricity, heating and gas sectors, as well as in the trading of manure
  • Ideally, there are considerations or plans for the expansion of the energy networks (electricity, heat, gas) in the municipality.
  • So far there are hardly any biogas plants that compete for existing energy consumers

The prevailing of these framework conditions is a good basis to deal more intensively with a concept for a mini biogas plant.

Unfortunately, the effort for planning, approval and operation of a medium-sized biogas plant with 500 kW does not differ as much for a 75 kW mini-biogas plant as one would wish. The quantities implemented and the process technology used are smaller, but as far as I know, the administrative steps are hardly any.

As I did in an interesting discussion Mini biogas plants in the Landlive forum have experienced, the operator of a micro biogas plant also has the following work and costs, in addition to the day-to-day operation of the plant:

  • Control by an environmental verifier
  • Fulfillment of documentation requirements
  • Regular monitoring of the electronics (e-check)
  • Verification according to the Industrial Safety Ordinance (BetrSichV)
  • Creation and maintenance of explosion protection documents
  • Fulfillment of building law requirements
  • Fulfillment of the EEG requirements

One should not rush to build a mini biogas plant. The name "mini" quickly leads to false expectations regarding the complexity of mini-biogas plants.

BUT - you shouldn't get scared right away! With every major and long-term investment in a completely new technology, new administrative tasks come up. It is worth the time it takes to determine whether setting up a mini biogas plant at your own location and with your own resources is sensible and economically justifiable.

What needs to be considered specifically?

Questions and answers on the construction and operation of a 75 kW mini biogas plant

Have you decided with your head and heart that you would like to take a closer look at the “Mini Biogas Plant Project”? Here are some questions for the next stage of planning that you will likely be dealing with. The answers are suggestions and, of course, must be considered in more detail in the specific case.

What does a mini biogas plant cost, or what are the costs?

It is not easy to give a general answer à la X Euro to this question, since the total price depends on many factors.

But as the first house number, I would like to refer to a statement by Ekkehard Schneider from the Biogas Association. According to this, the plant operator of a 100 kW plant incurs costs of around € 220.000 (= € 2.200 / kW). The costs for the combined heat and power plant, the line technology and the pump technology are not yet included.

Smaller plants will tend to be more expensive. Conservatively calculated, you should budget around € 75 for the construction of a 500.000 kW plant with a combined heat and power unit, control and network connection. This corresponds to total costs of around € 6.500 / kW. In addition there are the running costs for maintenance and inspection.

At this point I would like to have an interesting forum discussion ("thread") Economy of mini biogas plants recommend that developed in the Schlattmann biogas forum.

How much substrate do I need to operate a mini biogas plant?

A mini biogas plant has to be operated with 80% liquid manure in order to receive the feed-in subsidy of 25 cents / kWh. Corresponding slurry quantities must therefore be available. The remaining substrate amounts of 20% can be covered by using NawaRo's.
In order to obtain the appropriate amount of manure for 80% of the required amount of substrate, the manure of about 75 - 150 cattle (GV) is necessary for the operation of a mini biogas plant with 250 kW. This corresponds to a manure volume of around 5.000 m3 per year, although the information I have received so far fluctuates relatively strongly.

How big should the components of a mini-biogas plant be (CHP, fermenter, digestate storage, post-fermenter)?

Ideally, the output of the electricity generation unit or the combined heat and power plant should come as close as possible to the upper limit of 75 kW, which was set in the EEG 2012.

In combined heat and power plants, the electrical efficiency decreases along with the installed power. At CHP with 75 kW elec. Power achieves an electrical efficiency of around 38-39%. For larger CHPs around 200 kW (see Agenitor from 2G Bioenergietechnik) an electrical efficiency of around 42% can be achieved. There has simply not been as much research into improving mini-CHP plants as it has been into developing more powerful CHPs. The costs for the 75 kW CHP are around € 100.000.

Here you will find an article on the 10 best-selling Biogas CHP in Germany in the year 2010.

The size of the fermenter should be 500 - 1.200 m3, which results in costs between 80.000 - 100.000 €.

700 - 1.500 m3 should be planned for the size of the digestate storage (and secondary fermenter for two-stage systems). Any costs incurred are estimated at around € 100.000 - € 150.000. Depending on the federal state, residence times of around 100 days are required by law to complete the fermentation process and thus the formation of methane as far as possible.

Which partnerships are helpful when operating a mini biogas plant?

In order to be able to operate my mini biogas plant as successfully as possible, an efficient and sustainable use of all available resources is necessary.

Above all, this includes the fullest possible use of the energy products obtained, such as gas, heat and electricity, and the full use of the digestate. Partnerships to preserve the substrates and sell the resulting main and by-products can be used to build win-win situations.

A concrete example is the free acceptance of the manure from a neighboring farmer, who in return receives the digestate and the heat produced free of charge. The plant operator retains the proceeds from the sale of electricity.

A year-round supply contract for heat will not be easy and you have to be prepared for the fact that the heat demand of the manure-powered mini-biogas plants is significantly higher in winter than in summer.

What additional tasks will I have to do when operating a mini biogas plant?

In the operation of the mini biogas plant, trial and error will certainly have to pay some tuition fees in order to achieve the best possible setting for your own biogas plant and your own CHP plant.

In addition, other legal requirements must be taken into account, but they can be easily helped to fulfill: environmental verifiers, documentation obligations, e-check, requirements of the BetrSichV, explosion protection, building law requirements and EEG requirements.

It will also be interesting to see which legal regulation is found for the cover of digestate storage in mini-biogas plants. The question here is whether the cover of the digestate must be gas-tight or not.

As a potential operator of a mini biogas plant, you must inevitably take a broad look into the future. How likely is it that you want to significantly expand your own animal husbandry in the next 10 years? In such a case, the specified power limit of 75 kW can also become an obstacle and you cannot manage the additional slurry quantities with your own system.

I would also like to give you a small report on the experience with Operation and construction of a mini biogas plant recommended by the Office for Food, Agriculture and Forestry Schweinfurt and made available by the DBFZ.

Conclusion on the economy of 75 kW mini biogas plants

We are still at the very beginning with the mini biogas plants and I hope that we will find ways and solutions to integrate these decentralized bioenergy plants into our energy supply and biogas landscape, which have to be calculated precisely.

In addition to passion and curiosity, a well-thought-out concept is an important key to the successful operation of a mini biogas plant. Let yourself be advised from various sides before you decide for or against a mini-biogas plant or a biogas plant type. The time and energy required should not be underestimated. Then an exciting business field awaits you as a supplement to the previous animal husbandry.

In one of the upcoming articles I will go over to different ones Supplier and manufacturer of mini biogas plants come in and present it as a suggestion.

Otherwise, I wish you reason, passion and creativity in your "Adventure Mini Biogas Plant".

What do you think about the 75 kW mini biogas plants? Do you have experience in handling mini biogas plants or can you give advice?

Would you like to talk about your previous concept for a mini biogas plant or do you want to hear a neutral opinion? I can advise you on your investment decisions for Pro and Contra mini biogas plant.

  • Are your substrate quantities sufficient to operate a 75 kW system?
  • Which manufacturers offer mini biogas plants and what advantages do you offer?
  • Which concepts for partnerships with neighboring farmers and social institutions are possible?

Talk to me.

5 comments on “Mini biogas plant up to 75 kW: construction, operation and economy”

  1. That you always have to think of a 75 kW system, the 80/20% control offers this option. But wouldn't a pure liquid manure biogas plant be better for the farmer because of the substrate (maize) costs? I'll call it a liquid manure refinement plant. Such a system pays for itself from 20 kW, the prerequisite is that there must be around 120 LU and about 2.500 m³ of liquid manure.

    Why are small plants funded?

    Not that you want to prefer mini systems, but the problem is food versus energy crops. A biogas plant should bring additional income without much effort!

  2. In my experience, the pure slurry plants among the mini biogas plants have so far been much more popular. The energy content of liquid manure (SG, like RG) is somewhat lower than that of NawaRos, but the operation of the mini biogas plant with 100 percent liquid manure is also less complex. The more complicated handling of plants with 20 percent NawaRos seems to deter many potential plant operators so far.

  3. Since there is no maize or other renewable resources in pure liquid manure plants, no long dwell times have to be observed. Pure liquid manure plants do not need a secondary fermenter, so the old liquid manure storage can simply be used - even without a cover (which is of course not that great ecologically) . That means you can set up such a small system, let's say with 30 kW for around 250. The only problem is: who has so many livestock units (approx. 000?) And still no BGA?

  4. Thank you for the interesting feedback on the profitability of a mini biogas plant. I absolutely agree with you that the operation of a 100 percent slurry plant should be much easier to implement than a plant with 20 percent renewable resources. The information for the costs incurred for the construction and operation of a mini biogas plant according to EEG 2012 fluctuates just as significantly as the information for the required number of LUs (230 - 600 LUs at 75 kW).

    I can well imagine the costs of € 250.000 for a 30 kW system, but I hope and believe that 400 LU will not be necessary for this. There will not be that many businesses of this size without a BGA.

    Do you know of a project started in the past few months for a mini biogas plant?

    Greetings from Berlin.

  5. Problem with the 75 kw systems, most providers say a little corn / barley etc…. with in the fermenter for the 80/20 regulation ......
    Here I see the risk of the costs for substrates. I myself am a friend of 100% liquid manure plants Residues such as manure yes, but if everyone just strives for maximum performance again ... the same problems as with Nawaro biogas plants ..... with sunny greetings Josef Simon

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