Biomass CHP – time to take note?

An ArborElectrogen 45kW CHP Unit

Small-scale biomass combined heat and power (CHP) has been a gleam in the eye of engineers and designers for 30 years. While biomass heating under the RHI has been a great success, very few biomass CHP systems have so far been developed, despite attractive ROC and RHI tariffs. That’s now changing fast.

At least 5 companies are currently offering a range of biomass CHP systems with 25 to 65kW power outputs, and around twice that output in heat. With one of these companies being Froling – the well-respected German biomass boiler company – many started to take note. The SEWF Consultancy team have been reviewing the tedchnology, and drilling deep to get to the core of the technology choices, costs and issues. Our conclusion is that while biomass CHP is not for the faint-hearted, we think that they are potentially viable and financially attractive systems, as long as you are fully aware of the key issues at stake.

Follow the Money

The design approach to most of the small-scale biomass CHP systems is fairly common. Using a high grade and consistent wood chip or wood pellet fuel, a (mainly) downdraft gasifier turns the fuel into a gas. The gas is cleaned up to remove particulates and then burned in a heavy duty engine to produce power (and waste heat). The design target of the systems is to run for 7000 to 8000 hours a year.

Biomass CHP systems currently attract biogas (mainly) and biomass heat RHI tariffs, as well as 1.9 ROCs (currently around 8.4p/kWh). Depending on whether the power generated can be used on-site (saving 10p to 12p/kWh power import costs) or just exported to the grid (obtaining around 5p/kWh), this adds up to significant income streams. Given the £175,000 to £400,000 capitals costs, these high income streams are needed to make the investment pay, but 3 to 6 year paybacks have been quoted and are in principle obtainable.

So much for the theory. What about the ‘real world’ practice and the issues a client needs to look out for?

It’s all about the fuel

A consistent problem with previous efforts to develop viable and reliable CHP systems has been inconsistent fuel quality. Most biomass systems require dry fuel – 10-15% moisture content – as well as a fine grade quality. Chip fuel that varies in moisture content or has too high a level of fines or over-size particles will cause problems with tarring up inside the gasifier and frequent halts in production. Until recently, getting consistent 10% moisture content chip was very hard to achieve. Today, the situation is different due to the proliferation of chip driers, part-funded under the RHI. With suitable chip drier and screening systems, the right fuel quality can be obtained. Several of the offerings, such as the Entrade VG system, use wood pellets to achieve the correct moisture content and quality; the only down-side being a higher fuel cost.

Reliability, Replacement and On-going support

Looking Inside the Gasifier of a Spanner CHP System

Looking Inside the Gasifier of a Spanner CHP System

Running for 8,000 hours a year can deliver really good rates of return for biomass CHP. Achieving that however requires an on-going high level of servicing and support. Our view is that expecting biomass-CHP to be a ‘plug and play’ system is probably unrealistic. A complete engine replacement or rebuild every 2 to 4 years will be needed; as will regular cleaning, replacement of filters, and daily checking of controls. The choice of servicing and support packages is hence a key decision. Going for an all-inclusive package is one route. It won’t be cheap – up to £15,000 a year for some systems – but the selling company essentially takes responsibility to for keeping the plant on-line and generating income streams. This is the main approach of Froling-British Gas, Entrade-VG and Arbor Electrogen.

The other option is to get to really know your system and build up a support team via local engineers. This is the approach taken by the Spanner CHP system. It comes with a modest warranty and more limited support from the German parent company, but the capital costs are significantly lower.

Can We Help?

CHP Ready Wood Chip

CHP Ready Wood Chip

SEWF feel that there is an exciting opportunity with biomass-CHP. It could be a really interesting investment offering great 15-20-year returns. We’ve modelled most of the main technology offerings in the market and have tested the claims of the Sales people. With our extensive chip fuel experience, we can also offer and advise on how to secure ‘CHP-ready chip’.

Can we can help you quickly assess whether biomass CHP is right for you via short site visits and quick evaluations? Drop us a line or call Stewart Boyle on 07785 726 306.