Biomass Boilers: our sustainably targets up in smoke?

Biomass boilers pollute our cities more than cars, is this your idea of a sustainable energy source? We dig into the detail of biomass boilers.

FD Team
Climate Change
Biomass Boilers: our sustainably targets up in smoke?
    Contents ( - )
  1. What is a biomass boiler?
  2. A brief history of biomass boiler a...
  3. Residential vs. industrial biomass ...
  4. Benefits of biomass boilers
  5. The controversy surrounding biomass...
  6. Biomass boiler installation
  7. Maintenance of the biomass boiler
  8. Grants for a biomass boiler
  9. Quickfire Q&A about Biomass Boilers

As gas prices continue to rise by around 10% annually, and governments around the world are starting to ban gas boilers, more people will look for alternatives. Most people think of big industrial biomass plants when thinking about Biomass, but small residential offerings also exist. Their use has skyrocketed in the last decade because of their supposed eco-credentials when compared with gas or coal combustion.

In this article, we take a closer look at everything you need to know about the biomass boiler, the history of its use. Then we shine a light on whether biomass boilers are actually as sustainable as people think.

What is a biomass boiler?

A biomass boiler is a type of boiler that burns different types of fuel, such as wood chips, pellets, and logs. It is true that a biomass boiler can be more cost-effective than a traditional gas or oil boiler especially if you live in a rural area and have limited access to gas supplies.

Their popularity soared in the 2010s, but recent scientific analysis has a tree cultivated for biomass purposes actually will emit more CO2 into the environment than a standard tree throughout its lifecycle.

This revelation has forced Governments to re-assess their relationship with Biomass, once seen as the poster child of the renewable energy movement.

In the spring and summer of 2021, the UK Government open a Call For Evidence into the Role of Biomass in achieving Net Zero, indicating an openness to changing the strategic direction of the country's energy policy.

Here is a short overview of how a log boiler works:

A brief history of biomass boiler adoption

Through the 2010s, Biomass became more and more popular in developed countries, especially in Europe. Biomass was included on the list of renewable energy sources by the EU back in 2009, categorizing it as "carbon neutral" (this has later been disputed as is discussed at length below).

The UK has been a pioneer in the use of biomass boilers for both industrial energy generation and small-scale domestic applications. The use of biomass boilers has slowly proliferated throughout the country thanks to government grants, such as the Renewable Heat Incentive offering incentives to residential homeowners that install biomass heating systems.

Residential vs. industrial biomass boilers

While many people think of biomass boilers as devices reserved for industrial use, small-scale units can also be used to create a secondary source of heat and hot water for residential applications. While they may not be as efficient as their commercial counterparts, they can still be a good option for homeowners who want to be (more) environmentally friendly.

In the last 10 years, Drax, the UK's largest power plant operator, has transferred from using six coal-fired generators to four biomass burners. An action the company claimed shifted them "from being western Europe's largest polluter to being the home of the largest decarbonization project in Europe," writes Will Gardiner, chief executive of Drax Group, on the company's website.

However, this might not be the case, as we will detail in the Controversy section below.

Benefits of biomass boilers

Biomass heating systems make it easier for homeowners to heat their homes with a renewable energy source (to a certain extent). They can also serve homeowners not located near traditional gas networks.

Or perhaps a biomass boiler owner might not live on land suitable for ground source heat pumps. Biomass boilers can deliver efficiencies of over 90% – a similar level to modern condensing gas and oil boilers.

The controversy surrounding biomass boilers

Suffocating air quality

Recent Government data revealed that domestic wood burning (both closed-stove and open fires) was responsible for 38% of PM2.5 particles (smaller than 2.5 microns in size). This figure is three times higher than air pollution from road traffic.

Data from the Emissions Database for Global Atmospheric Research (EDGAR) show that in the EUSDR area, emissions of biomass-related PM2.5 in the sector "Energy in buildings" have increased by more than 60% since 1990.

Combustion is inherently a dirty process, even with "renewable fuels". In domestic settings, the emission of carbon monoxide from the combustion process is possible, and therefore it is essential to fit a carbon monoxide monitor near the boiler.

Biodiversity loss

The relationship between forestry of biomass forests and biodiversity is still being explored in detail. However, research from the tropics suggests that forests cultivated purely for biomass fuel have a drastic impact on biodiversity in that area.

Carbon footprint: what the current research says

In 2011, a Columbia University report summarised well the controversy around the "carbon-neutrality" of Biomass as a fuel when it said:

Whether or not Biomass is truly carbon neutral depends on the time frame being studied, what type of Biomass is used, the combustion technology, which fossil fuel is being replaced (since the combustion of both fossil fuels and Biomass produces carbon dioxide), and what forest management techniques are employed in the areas where the Biomass is harvested.

Then, in 2017 independent research by Chatham House, a UK research agency made similar conclusions:

It is often argued that biomass emissions should be considered to be zero at the point of combustion because carbon has been absorbed during the growth of the trees, either because the timber is harvested from a sustainably managed forest, or because forest area as a whole is increasing (at least in Europe and North America). The methodology specified in the 2009 EU Renewable Energy Directive and many national policy frameworks for calculating emissions from Biomass only considers supply-chain emissions, counting combustion emissions as zero.

These arguments are not credible. They ignore what happens to the wood after it is harvested (emissions will be different if the wood is burnt or made into products) and the carbon sequestration forgone from harvesting the trees that if left unharvested would have continued to grow and absorb carbon. The evidence suggests that this is true even for mature trees, which absorb carbon at a faster rate than young trees. Furthermore, even if the forest is replanted, soil carbon losses during harvesting may delay a forest's return to its status as a carbon sink for 10–20 years.

Another argument for a positive impact of burning woody Biomass is if the forest area expands as a direct result of harvesting wood for energy, and if the additional growth exceeds the emissions from combustion of Biomass. Various models have predicted that this could be the case, but it is not yet clear that this phenomenon is actually being observed. For example, the timberland area in the southeast of the US (where most US wood pellet mills supplying the EU are found) does not appear to be increasing significantly. In any case, the models that predict this often assume that old-growth forests are replaced by fast-growing plantations, which in itself leads to higher carbon emissions and negative impacts on biodiversity.

The carbon payback approach argues that, while they are higher than when using fossil fuels, carbon emissions from burning woody Biomass can be absorbed by forest regrowth. The time this takes – the carbon payback period before which carbon emissions return to the level they would have been at if fossil fuels had been used – is of crucial importance. The many attempts that have been made to estimate carbon payback periods suggest that these vary substantially, from less than 20 years to many decades and in some cases even centuries.

  • Woody Biomass for Power and Heat, Impacts on the Global Climate.

In 2018, researchers at the Massachusetts Institute of Technology (MIT) backed up this assertion with their research to show that when taking into account the full lifecycle of a forest in the United States, the burning of Biomass within this lifecycle adds to the carbon emissions released into the atmosphere:

The appeal is intuitive: burning fossil fuels injects carbon sequestered in geological reservoirs for millions of years into the atmosphere, causing global warming. In contrast, biofuels recycle carbon from the atmosphere, so, people argue, there are no net emissions. Unfortunately, science shows otherwise. Burning wood to produce energy can actually worsen climate change, at least through the year 2100 – even if wood displaces coal, the most carbon-intensive fuel.

Biomass boiler installation

For a homeowner, the biomass boiler installation process can be broken down into several steps. First, your home will be inspected to determine the type and size of the boiler and the most efficient system for your home. This portion of the installation process could take a few hours or a few days, depending on the layout of your home. Once the inspection is complete, your boiler will be installed.

More and more homeowners are installing biomass boilers in their homes, but many are put off by the upfront biomass boiler cost. The initial cost of a biomass boiler is significantly more expensive than conventional boilers, but they also decrease your monthly energy bills.

Maintenance of the biomass boiler

If you're thinking about installing a biomass heating system, you're probably wondering about the maintenance requirements. In general, wood chip boilers require more maintenance than a gas boiler, but nothing too strenuous. Here are some of the important steps to take to keep your system healthy, efficient, and long-lasting:

  • The residue from the burning process (ash) must be removed from the furnace periodically. You can also get a wood boiler that is completed automated, but you can expect to pay more. They come with self-cleaning burner heads. Check out this boiler manufacturer for some examples.
  • You should also carry out regular inspections of all the moving parts, for example, the hopper, the heat exchanger and flue, and the stoves. Ensuring these boiler sections are regularly cleared and cleaned will help keep your boiler running at maximum efficiency.
  • On top of these informal checks, it is recommended you consult a specialist technician to do a proper internal clean and check annually.

Grants for a biomass boiler

Depending on which country you are in, grants are sometimes available from your Government. As the scientific and public opinion shifts on biomass boilers, it can be expected that support for these specific types of boilers will be withdrawn in the future.

In the UK, you can apply for the Domestic Renewable Heating Incentive grant.

Quickfire Q&A about Biomass Boilers

What are Biomass boilers? Biomass boilers are very similar to conventional gas boilers that you will be familiar with, providing you with space heating and hot water for the entire home. Still, instead of using gas (or oil) to produce the heat, they combust sustainably sourced wood pellets.

Carbon dioxide emissions from biomass boilers - are they carbon neutral?

The short answer is no; the sustainability credentials of energy production from Biomass have recently been disputed. Researchers have proven that over the lifespan of a tree, more CO2 is emitted in trees used for biomass energy than normal trees. Unsustainable deforestation and biodiversity loss are two other further drawbacks - cleaner alternatives are available.

Can biomass boilers be used for central heating? How is the heat output?

Absolutely, smaller residential biomass boilers are available for space and water heating. With a moisture content of less than 10%, heat output from biomass fuel of 5,000kW/tonne can be achieved (source).

Should I buy a wood pellet boiler?

Much cleaner energy sources are available. It is also possible that governments will ban the sale and use of biomass boilers (as has recently happened with gas boilers in some jurisdictions).

What's an average biomass boiler price?

Difficult question to answer, as the range is high. The lower-end biomass boilers can start at around 5000 GBP, and can cost up to 15,000GBP for a top-of-the-range, automated, high output boiler.

How does the price of biomass fuel compare to fuel costs from electricity and gas?

Figures courtesy of Biomass Energy Centre Fuel Type: Pence per kWh* Woods Chips: 2.9p Woods pellets: 4.2p Natural Gas: 4.8p Electricity: 13.4p

*The price of wood varies depending on supply and demand.

What's the difference between wood pellets and wood chips?

Wood pellets are formed by compressing very fine wood shavings (sawdust) into a pellet shape, whereas wood chips are simply small chips of forestry wood like you might find on the floor in a playground. Due to their compression, more wood pellets can be stored in a small space, but they are also more expensive (as shown in the chart above).

What are the dangers of using a biomass boiler?

Biomass burning can emit carbon monoxide, so it's vital to install a carbon monoxide alarm before you start using a domestic biomass boiler.

What is the size of a biomass boiler?

Biomass boilers usually are substantially bigger than their fossil-fuel-burning counterparts, as you have to burn a solid (rather than gas), this requires more storage space.

Where can I find a biomass supplier?

In the UK, you can use the UK Government's Biomass Supplier List to find a supplier near you.

Can I feed waste wood into the boiler to generate heat?

Waste wood can be fed into the hopper, but its best to keep the input consistent.

Does the type of fuel, type of biomass, or moisture content of fuel matter?

The short answer is yes, we recommend this great resource to learn more about the selection of different Biomass for different use cases.