Choosing a Biogas Contractor: References, Quotes, Contracts

To find the right contractor for a biogas plant, visit comparable reference plants, obtain at least three quotes based on the same enquiry and settle warranty, performance guarantees, payment schedule and service contract in writing. The lowest price is rarely the best offer if civil works, electrical engineering or permit planning are missing. An independent engineering firm or expert can review the quotes neutrally. The provider directory lists companies by category and region in Germany.

Which contractors you need

Different partners are involved depending on the project. For a small manure plant, many manufacturers offer standardised compact plants as a complete package. For larger or bespoke plants, general contractors, specialist planners and individual trades work together.

Clarify early who is responsible for the system as a whole. If work is split between several companies, interfaces arise where defects are hard to attribute. A general contractor takes on this responsibility but usually charges a premium for it.

Checking references properly

References are the most important selection criterion, but only if they match your project. A large energy crop plant says little about experience with a small manure plant. Ask specifically for:

1. Plants of similar size and with similar feedstocks, ideally in operation for several years.
2. Contact details of operators you can speak to openly, without the contractor present.
3. Experience with gas yield, CHP availability, faults and service response times.
4. How long the company has been in business and whether it has its own service technicians in your region.

A visit during normal operation often reveals more than any brochure. Look at how accessible agitators and pumps are, at order and documentation, and at how the operator talks about the contractor.

Making quotes comparable

Biogas quotes often differ in scope, not just price. To compare them, every contractor should quote on the basis of the same written enquiry: livestock numbers and slurry volumes, other feedstocks, target rated output, heat use and site conditions.

For each quote, check whether the following items are included or must be provided by you (by the client):

• Earthworks, foundations, concrete work and bunding
• Digester, digestate store, gas storage and agitation
• CHP unit, gas conditioning, emergency flare and heat extraction
• Electrical engineering, controls, remote monitoring and grid connection
• Permit planning, structural calculations and documents for inspectors
• Commissioning, biological start-up support and training
• Documentation, operating instructions and explosion protection document

Client-side work is often underestimated and can account for a substantial share of total cost. A first estimate of the overall investment helps you spot unusually low or high quotes. Where prices differ widely, ask why. Differences are often explained by tank sizes, materials, agitation technology or a different CHP manufacturer.

Warranty, guarantees and securities

The statutory warranty depends on the contractual basis. Under Section 634a of the German Civil Code (Bürgerliches Gesetzbuch, BGB), defect claims for buildings and structures become time-barred after five years, and for other works generally after two years. Whether and which parts of a biogas plant count as a structure has to be assessed case by case. If the German construction contract procedures (VOB/B) are agreed, their own periods apply, which may be shorter for machinery and electrical parts requiring maintenance unless the builder is also given the maintenance contract. Have the periods for all major plant components set out expressly in the contract.

Beyond the warranty, contractual guarantees are common and advisable:

• Performance guarantees for the electrical output and efficiency of the CHP unit, measured by an agreed method.
• Availability guarantee for the CHP unit, with clear rules on what counts as downtime and what follows if it is not met.
• Completion guarantee for the handover date, with a contractual penalty where appropriate.

Securities protect you against insolvency or defects: a payment schedule linked to construction progress, a performance bond during construction and a warranty bond afterwards. Agree a formal acceptance with a written record, only after a successful trial run. Warranty periods start with acceptance, and the burden of proving defects generally passes to you.

Also ask whether the contractor is certified as a specialist company under water law for work on components handling substances hazardous to water, where this is required for your plant.

Negotiating the service contract at the same time

The investment is only part of the cost. Over the plant’s life, CHP maintenance and availability largely determine profitability. Negotiate the service contract together with the plant quote, while you still have bargaining power. Settle scope, billing basis, major overhaul, response times, spare parts supply and price adjustment. Also check whether independent service companies in your region can maintain the engine, so that you are not permanently tied to one supplier.

Warning signs in quotes

Some features should make you cautious and prompt closer questions:

• Unusually high gas yields or outputs well above recognised indicative values for your feedstocks.
• Large advance payments before delivery or construction, without a bond as security.
• Pressure to sign quickly, for example citing expiring prices or funding deadlines.
• Vague specifications in which major components are only mentioned in general terms.
• No references, or only distant ones, that cannot be visited.
• No clear statement on service after commissioning.

Take enough time over the choice. A biogas plant is an investment for twenty years or more, and mistakes in awarding the contract are hard to correct later.

Checklist for choosing a contractor

1. Prepare a written enquiry with quantities, feedstocks, target output and heat concept.
2. Approach at least three contractors with suitable references.
3. Visit reference plants and talk to operators without the contractor present.
4. Compare the scope of all quotes in one table and put figures on client-side work.
5. Fix warranty periods for all plant components in writing.
6. Agree performance, availability and completion guarantees with measurement methods.
7. Agree a payment schedule tied to progress, plus bonds.
8. Provide for a formal acceptance with a written record after a trial run.
9. Negotiate the service contract and spare parts supply in parallel.
10. Have quotes and contract reviewed by an independent engineer or expert.