Using logs, chips or pellets, our systems can run your central heating system, heat your hot water and even power large-scale commercial premises. They are almost as efficient as a gas boiler, they can be as convenient as an oil boiler and the fuel they burn is considered carbon neutral because every tree takes in as much carbon dioxide whilst it is grows as it releases when it burns. And because many forests are run on the principal that more trees are planted than is cut down, it truly is a renewable fuel source we can depend upon.
Not only does biomass produce huge carbon savings over more conventional sources of energy, it can also cost less too. What’s more oil, coal and gas are finite resources which means the cost will invariably rise as the available quantities reduce. The price of wood should remain more stable since it is a renewable resource.
Cost of energy
Electricity - 16.62p p/kWh Pellets - 6.86p p/kWh
LPG – 5.97 p/kWh Chips – 3.0 p/kWh
Gas oil – 3.87p p/kWh Seasoned wood – 5.55p p/kWh
Gas – 5.39 p/kWh
To encourage people to migrate away from fossil fuels, the government has launched the Renewable Heat inventive. The commercial RHI has been running for some time and the domestic RHI is due this spring. It can not only pay for the cost of the installation and reduce your energy bills, it can add an income stream to your property – see our guide to the RHI.
At 95% efficient, a modern automated boiler is a huge improvement on its ancient cousin the open fire. Using carefully controlled secondary air to produce combustion temperatures above 8000C, the burn process is so complete it produces very little ash – 3 tonnes of pellets can produce less than 5 kg of ash. The combustion chamber is surrounded by a heat exchanger through which flows the water from the central heating and hot water system. The exhaust gasses are transported away in the flue and the particulate count is so low in some boilers that they are DEFRA approved for use in smokeless zones.
With three fuel types and different styles of boiler within each, it’s worth understanding the pros and cons of each type.
This is probably the most convenient way of heating your home as the pellets allow a huge amount of automation. They can be made to light automatically and can be timed to come on and go off as required by a programmer or thermostat.
The simplest versions are stoves which supply heat to the room and have an internal pellet store which is loaded manually. Available in many modern designs they have a glass front so the flame can be seen burning in the grate and look attractive in a living room. Similar models are available with heat exchangers that power the radiators in the property.
Pellet boilers concentrate entirely on heating water for the radiators and hot water system. They can be much bigger and fed automatically by an intermediate pellet hopper positioned alongside or a bulk hopper, feeding the boiler with a vacuum system or a fixed auger. If the store is big enough, one or two deliveries can be sufficient to last all year.
The pellets themselves are made from virgin wood specifically grown for the purpose. 6mm thick, 30mm long and with a moisture content of <10%, they can be bought in 10kg bags or delivered in bulk into an appropriate hopper or bin. Storing large quantities of pellets takes up a lot of room but there are now many inventive ways of maximizing the volume of an internal space, building an external store or even burying a tank underground.
Boilers that burn chips can be completely automated too and are ideal for bigger installations where there is plenty of storage space and good access to the raw materials. The cost of the fuel can be as low as 2.9p p/kWh making it an attractive proposition for large-scale commercial installations. The chips are larger than pellets and have a moisture content of between 15 – 50%, both of which makes provision for storage and feeding the boiler, crucial. The boilers themselves are constructed differently and use stoker burners or stepped grate systems depending on the moisture content of the fuel.
It’s less common but the same style of boiler can be used for a wide variety of other fuel sources such as animal, food and industrial waste or high energy crops such as miscanthus, willow and maize.
Ideal for people with ready access to logs, these boilers are ‘batch fired’ typically once a day. They have to be loaded manually each day and rely on a large water storage cylinder (a ‘buffer’) to store the heat until it is needed. They are simple to install and operate, sometimes being the cheapest form of biomass power.
The combustion process is controlled by a fan which allows the logs to be stacked above the brazier and ensures the flames go downwards into the heat exchanger. The name comes from the fact that the combustion chamber is so hot that it doesn’t burn the wood but vaporizes it into gas which burns at a much higher temperature.
Biomass boilers work more efficiently if they can provide their heat indirectly via a buffer, accumulator or thermal store. Since they are slow to start up and shut down, the store smoothes out the abruptly changing calls for heat. It’s most obvious in the case of a log boiler which will burn once a day for two or three hours. When heating or hot water is required later in the day, the heat is stripped out of the store. Pellet boilers are much more flexible but even they are slow and inefficient in their start up and shut down periods. The store protects them from this and allows them to work in longer, continuous periods.
Allowing between 30 and 50 litres per kW of boiler capacity (50 for logs, 30 for pellets) it means that for larger boilers, a lot of space is needed to accommodate the buffer. The floor needs to be strong too since 1,500 litres weighs 1.5 tonnes, plus the weight of the cylinder.
There are a huge number of different sizes, shapes and types of boilers and all require a certain number of things worth looking out for:
1. Biomass boilers tend to be bigger than their fossil fuel counterparts so it’s important for us to check it will fit where the old boiler was or recommend a new location (in another room or the garage for instance.
2. Storing pellets, chips or logs is a major undertaking and will form a large part of our discussions with you.
3. Correctly installed flues are vital for the proper functioning of any biomass boiler, indeed, it can sometimes determine exactly where the boiler has to be installed.
4. Placing the fuel store within reach of the road and making deliveries easy is vital for the smooth running of the system
From the simplest stove which you light with a match to the automated boiler you control with your smart phone, biomass boilers have come a long way. MCS approval means that accredited boilers in the UK are inspected, tested and carefully scrutinised so you can be sure there aren’t any dodgy devices likely to quit the first time you fire them up.
With individual boilers as big as 350kW and the facility to cascade three together makes creating a megawatt of clean, carbon neutral energy an achievable proposition. Add in high efficiency, fine levels of control and lengthy maintenance schedules to see why biomass is becoming the fuel of choice for many businesses. If all this were not enough, the commercial RHI really gets financial directors attention as energy can quickly go from being a huge expense to an income stream.
Every organisation in the public sector has it’s own carbon reduction plans and biomass boilers with a ‘close to carbon neutral’ fuel source are a valuable weapon in this battle. From individual, small scale premises to large, town council buildings, biomass can save money and help you achieve the carbon targets you have been set.
Biomass boilers work best when they’re working hard and rather than have ten boilers in ten properties, it’s very efficient to have one boiler serving them all. A combination of supper insulated pipework and hydraulically separated systems means that individual properties can have as much or as little heat as they require. Every property has it’s own meter so they only pay for exactly what they use.