Smallscale AD: a small revolution in the making

Overshadowed by large-scale anaerobic digestion facilities, smaller-scale projects are gaining currency among policy makers. Richard Gueterbock highlights the challenges the emerging sector faces and outlines a few projects.

Historically, many of the renewable energy technologies that have been installed in the UK have been imported. However, more and more British companies are entering the market, especially in the development of small-scale on-site anaerobic digestion (AD).

Defra and WRAP have taken an interest in this emerging sector. Smaller-scale plants can be installed at the location where bio-waste is generated, whether that is on farms, in smaller rural communities or on industrial sites (see case studies on page 12). They can also offer a viable alternative to larger-scale “merchant” AD plants, which tend to take mixed waste materials and require off-site transport.

While it’s true that these smaller plants generate relatively small amounts of energy in comparison (they can achieve output levels of over 250kWh, which is enough energy to supply 400 houses), they provide other benefits. Small-scale plants cut the greenhouse gas emissions generated by the business and they are also more efficient at handling production residues than large-scale facilities.

Clearfleau has built on-site digesters in the dairy, distillery and food processing sectors, each with a power output below 500kWh, generated from liquid production residues. The renewable energy generated (heat and power) is then used on the processing site.

The advantage of these plants is that they fit on a relatively small footprint and can handle most unwanted food and drink processing residues.

The renewable energy Feed-in Tariff (FIT) incentive, as well as savings on the purchase of fossil fuel derived energy, have certainly helped support the sector’s growth.

The FIT regime was intended to encourage early adopters of renewable technology across a range of smaller-scale processes. It was only extended with higher rates for smaller-scale “on-site” AD (under 500kW electrical output) in 2010 but the knock-on effect was an increase in the number of smaller AD plants.

However, just as the market seems poised for expansion, DECC is threatening to make changes that could disadvantage the smaller-scale AD sector (under 500kW) compared to the more established market for larger AD plants (at over 500kW).
The main concern relates to changes to the incentive regime, which are being imposed from 2014. There is also an issue over the delay in bringing in the second phase of the Renewable Heat Incentive (RHI), which will extend the support for use of heat from renewable sources for industrial applications.

An emerging market such as on-site digestion needs sustained support and greater policy stability.

The small-scale AD market needs a strong policy framework to encourage adoption of all renewable technologies but also to support innovative
companies that are building smaller plants on industrial, farm and community sites.

On-site AD can provide many benefits for industrial sites, including lower energy and treatment costs. These deserve greater recognition in the food and drink industry but also by government and regulatory bodies.

As well as green electricity, industrial sites can make use of the surplus heat from the CHP engine, with both power and heat output contributing to a site’s energy demand.

As a result, the overall environmental impact of the production facility is reduced as well as the financial and environmental cost of treating production residues.

In a nutshell, on-site small-scale AD enables food processing companies to take control of effluent disposal costs, while reducing energy costs and cutting CO2 emissions.

Richard Gueterbock is marketing director at Clearfleau

Action inspires action. Stay ahead of the curve with sustainability and energy newsletters from edie