There has never been a better time to install a woodfuel boiler. Fossil fuel prices are rising higher and higher and there are excellent rebates available from the Government’s Renewable Heat Incentive. However, there are a number of critical things that you must consider before you make a dash for biomass. Below we outline our view of the most important questions you need to ask before you make your decision:
1) Do you have the space?
This is a real showstopper. Biomass boilers have a much larger footprint than fossil fuel boilers. You will need space for the boiler as well as an additional space to store woodfuel and access for fuel deliveries. All woodfuels (logs, wood chip and pellets) have a lower energy density than fossil fuels. So you will need more space to accommodate the same amount of fuel. If space is a real issue then perhaps pellets will be the most suitable fuel as these 2-3 times as dense as wood chip.
2) How easy will it be to deliver fuel?
Getting the storage area and delivery system right is crucial to the long term viability of a project – if you get it wrong you could be looking forward to 20 years of awkward fuel delivery. The size of the store will dictate the frequency of deliveries. A small store will have to be filled more often than a larger store. You should also consider whether delivering woodfuel will cause any disruption. For instance, will an access way be blocked and cause delays to traffic? Or will there be any noise associated with the deliveries that might cause complaints?
3) What size boiler (in kilowatts) will you need?
Different types of building use heat in different ways and for different purposes. Predicting the correct boiler size depends on a number of important considerations:
- How much heating energy do you use and when is the heating load highest?
- Is heating required in the day time, night time or both?
- Is the load constant (i.e. process use such as a dairy) or is it seasonal?
- Are you requiring space heating and water heating? Do you need much water heating in the summer?
You might need professional help to do this on a large building. However, you can get a rough estimate of the boiler size by dividing the annual heat consumption (in kilowatt hours) by the number of hours used. A house might need 1300 hours of heating whilst an office or school might need up to 1750 hours. Another quick way of estimating the boiler size of a house is to multiply the length x width x height of the building by a fiddle factor of 0.035. This may seem a bit arbitrary but it gives a good ballpark answer. Most installers will have software tools that will determine the correct boiler size for your property.
One thing to remember is that an oversized boiler can lead to low system efficiency. A boiler sized at 50% of the peak load will provide between 85-90% of the annual heat requirement. Most biomass boiler systems are now specified with an accumulator tank. This provides a certain degree of flexibility in sizing the boiler and can reduce the periods during which it operates less efficiently at part load. Repeated starts and shut-downs are substantially reduced, which increases the boiler’s lifetime and minimises emissions. Tanks are normally sized up 60 litres/kW or more.
4) What level of automation do you require?
This is a very important question to consider. A cheaper woodfuel system such as a log boiler will require lighting at least once a day and frequent stockings. Are you prepared for this extra work or would you prefer a more expensive chip or pellet boiler that has automatic lighting and fuel extraction? Also, more basic budget systems will require more manual cleaning and ash removal whilst more expensive wood chip and pellet boilers often have self cleaning features and ash boxes on wheels. As a rule of thumb:
A cheaper system = more hands on
A more expensive system = more hands off
5) What can go wrong with a biomass boiler?
Around 90% of all problems with biomass systems relate to fuel and you can guard against these by using high quality seasoned woodfuel of the correct specification, carrying out regular (daily and weekly) checks and using the boiler efficiently. Biomass systems work best when they used to their full capacity rather than frequent are need to be used at full capacity. Most installers offer maintenance contracts to provide regular or annual servicing. It is also possible to specify remote monitoring with some installers to provide an early warning of faults and potential breakdowns.
6) Where’s your fuel coming from?
It is absolutely critical to match your boiler with the fuel available. We will deal with this issue in a separate blog in the future. The best potential savings can be achieved when you use your own resources such as an existing farm woodland or baled straw or use your land to grow dedicated energy crops. There are grants available (Woodfuel WIG) to help manage woodlands. You can also get grants to grow willow and miscanthus (Energy Crops Scheme). Grow your own prices range from £32/oven dry tonne for miscanthus to £105/oven dry tonne for small scale log production.
If you need to buy from a third part supplier it makes sense to use one that is accredited with Hetas or Woodsure as this means that they will have a quality assurance process in place. Current prices (Feb 2012) for woodfuels are as follows:
- Good quality wood chip – £100/tonne at 30% moisture content (around £143/odt or 3.2p/kWh)
- Hardwood logs – £220/tonne* at 20% moisture content (around £275/odt or 5.5p/kWh).
- Bulk Pellets – £200/tonne at 8% moisture content (around £218/odt or 4.3p/kWh).
* Don’t be fooled by thinking that a load of logs is a tonne of logs. A tonne of hardwood logs at 20% MC has a bulk density of 450 kg per cubic metre. So you would need 2.2 cubic metres to weigh a tonne. Softwood logs have a lower density so you would need 2.9 cubic metres to weigh a tonne.
7) What are you going to do with the ash?
Most boilers are very efficient so the amount of ash produced is low in comparison to the amount of fuel used. The amount of ash produced can vary greatly:
- <1% for chipped round wood
- 2% for willow coppice
- 2-4% for miscanthus straw.
Most boilers only need de-ashing every 1-4 weeks. Provided the fuel has been procured from uncontaminated sources the ash may be disposed of as fertiliser. Obviously this is a volume game. A boiler requiring 10 tonnes of fuel with an ash content of 2% will produce 200 kg of ash whilst a boiler requiring 100 tonnes of the same fuel will produce 2 tonnes of ash. Some fuel suppliers will agree to take away your ash for a price.
8) Will planning permission be necessary?
It always makes sense to ask your local authority planning department for their advice. You will probably need planning permission if you need to build a new boiler house or fuel store or a new chimney causing a visual impact. There are also more stringent requirements for listed buildings, for buildings in conservation areas, National Parks or in Areas of Outstanding Natural Beauty (AONB). Biomass boilers les than 50 kW in capacity are covered by the Building Regulations which dictates the height of flue, flue outlet positions etc.
You also need to know if you are in a smoke control zone. Biomass fuels can be burnt in a smoke free zone as long as an exempt appliance is used.
9) How can you make sure that the installation goes without hiccups?
It is really important that you aim to get at least three completed quotes from reputable installers. Do your research and ask for references as part of the quote. Ask if you can visit similar installations. You should take care to produce a very clear specification brief to make sure that all returned tenders are on a level playing field. This is important as system cost is often crucial to deciding the preferred bidder. You should make sure that any optional extras are clearly stated.
You should allow a realistic timeframe for construction and build in contingencies. Most installers are incredibly busy with the current surge in demand. Also, you should include the schedule in the contract as well as a clause dealing with liability for delays. You should maintain a contingency budget and enter contract with the installer on a fixed price basis. You might also wish to build in a clause allowing you to retain a final payment for trouble shooting to ensure that the boiler is running to your complete satisfaction.
10) Will you be eligible for the Renewable Heat Incentive?
Phase 1 of the RHI is for non domestic installations only such as schools, district heating schemes, offices etc. The rebates are very lucrative – a 50 kW system used for 1314 hours (15% of the year) could make an owner £5190/year for 20 years. Domestic installations are currently covered by a one off payment of £950 as part of the Renewable Heat Premium Payment. Phase 2 of the scheme is expected to be launched in late autumn 2012. This will probably involve domestic installations but there are whispers that the rebates will be lower and the duration of tariffs will be reduced. Also, tougher emissions limits (particulate levels and nitrogen oxides (NOx) levels) will be brought in. This might mean that some boilers that are currently covered by the scheme will not make the grade.
So there you go. There’s an awful lot to think about but the RHI rebates and savings compared to oil, LPG and electric heating should make the extra effort worthwhile.
If however, this all makes you feel a bit daunted and you would like some professional help choosing the right type of boiler for your building, assessing the opportunities to grow your own fuel or project management of an installation then please contact Crops for Energy on 0844 249 2901 or email [email protected]