Renewable Energy in Practice
The renewable energy has been and is still being introduced to the practise to achieve main aims and targets of policies introduced by UK and EU government.
The current energy policy in UK is set out in the Energy White Paper and Low Carbon Transition Plan. The White Paper was introduced in 2007 and the Low Carbon Transition Plan in 2009. The plans are led by the Department of Energy and Climate Change.
The first mentioned plan (White Paper) sets out the Government’s international and domestic energy strategy to address the long term energy challenges faced by UK. The main aims are to cut CO2 emissions by 60% by 2050 with a real progress by 2010; to maintain reliable energy supplies; to promote sustainable market in UK and to ensure that every home is heated adequately and affordably.
The UK is committed to delivering its share of the EU target for 20% of energy from renewable sources by 2020.
Achieving our targets could provide ï¿½100 billion worth of investment opportunities and up to half a million jobs in the renewable energy sector by 2020.
50% of all our energy is used for heating and hot water and 75% of domestic households’ energy consumption is for heating and hot water. The UK’s renewable energy strategy aims for 12% of heat to come from renewable sources. Currently under 5% of UK electricity comes from renewable sources. It is estimated that 30% of our electricity may be delivered from renewables with 2% from small-scale electricity generation.
Low Carbon Building Program(LCBP) The Government introduced many plans to achieve the above targets. One of the first was the Low Carbon Building Program (LCBP) and Phases 1, 2 and 2e. It was a major government grant funding programme and provided approximately ï¿½131 million in grants for around 20 000 projects (between 2006-2010). The LCBP was run by Department of Energy & Climate Change and the grant programs were administrated through Energy Saving Trust – Phase 1, Building Research Establishment (BRE) – Phase 2. The Phase mainly concentrated on schools, churches, community projects and non-profit organizations. We (SolarTech Ltd) were part of the programme and we delivered lot of solar PV installations through the program. The programme covered solar PV, solar thermal, micro wind turbines, micro-hydro, ground and air-source heat pumps, wood-pellet stoves and wood-fuelled boilers. It was very successful program and it is now closed.
Code for Sustainable Homes – The next step to achieve the main aims was to introduce the Code of Sustainable Homes. It has been prepared by Government in close working consultation with BRE and CIRIA (Construction Industry Research and Information Association). There were also involved other groups such as a Senior Steering Group and NGO representatives. The Code is replacing the building regulations and complementing the system of energy Performance Certificates which was introduced in 2007 under the Energy Performance of Building Directive (EPBD). The EPBD requires that all homes (the existing home when sold or leased) have an Energy Performance Certificate. The certificate will provide key information about energy efficiency and carbon performance of the home. There are 6(stars) levels of the Code and each level dictates things like minimum standards for energy (CO2) and water efficiency, waste management, energy generated from renewables, surface water run-off, management etc.
It is quite a complicated system and I have spent quite a bit of time studying it as it is very important to the Housing sector. I would like to show the example of a CODE 6 development which was a unique and the first multi-occupancy CODE 6 development in UK. The project was called Mendip Place/Mendip Road at Chelmsford via an Ingleton Wood HA. The solution included a dedicated PV system to each property so that all tenants would benefit from reduced bills, helping reduce the fuel poverty. The PV was specifically designed to maximise the roof space and to make sure that it meets the CODE criteria. In addition to the PV systems there was a centralised bio-mass boiler installed. The Biomass boiler is linked to a heat distribution unit in each property. The systems are monitored via GSM modems. The multi-technology approach (PV, Biomass, good insulation, and good fabric) has helped provide an industry leading integrated solution on this prestigious project.
There are currently schemes which should encourage people to introduce renewable energy in to their homes, shops, commercial buildings, school etc. One of the most important schemes in terms of producing electricity from renewables is the Feed-In Tariff.
The Feed-In Tariff (FIT) is a new (introduced in April 2010) Government scheme which should help to reduce the carbon footprint, energy bills and become more self-sufficient in energy. The scheme also allows earning some extra tax-free cash. It is also called by some people Clean Energy Cash back. The energy regulator Ofgem is the administrator of the FITs scheme. I quite like the scheme and the Government make it very clever. They learnt from mistakes of Spain, Germany where the FITs tariff ran out very quickly. Our government established the FITs in the to the Energy Act and every single energy supplier who wants to operate on UK market had to sign up to this scheme and agreed that they will pay a percentage of their profit to a “pot” of the money.
The “pot “of the money is being used to pay out the FITs. Basically the energy suppliers pass the cost of the FITs scheme to all electricity customers. So the bottom line is that people who do not install a renewable energy system will be paying those who do. The system is being very successful we have done over 4 000 installation of solar PV and wind turbines. The other technologies which qualify under the scheme are Hydro-power, Micro-CHP, Anaerobic digestion and existing generators transferred from RO (to 2007). I will explain each of the technology later on.
The Renewable Heat Incentive (RHI) There is a similar scheme to the FITs which is being introduce and it’s called the RHI. It helps to reduce carbon footprint and energy bills for the heating. The RHI scheme has been introduced for non-domestic installations and should be following by other in October 2012 as part of the Green Deal. There is a sub-section of the RHI and it is called the RHI Premium which is basically a one off payment for domestic installation which is in off gas areas. It should encourage householders to install renewables and targets non-gas users. It is bit un-fair to the gas users as I think it should be available to every householder. We can the pressure on our Government from the Energy companies.
The scheme is still little bit un-clear and the government did not handle it well enough. It supposed to be introduced by the end of 2010 but the government with DECC delayed it till August/September 2011. It almost killed the industry. The RHI scheme covers heat pumps (air-source heat pumps are excluded from the non-domestic RHI), Biomass boilers, Solar Thermal, Biomethane. It should also cover Biodiesel (up to 45kW), Biogas, Biome thane injection installations but it is still un-clear.
The Green Deal – Finally I have already mention the Green Deal. The Green Deal should revolutionise the energy efficiency of British Properties. Is part of the Energy Bill introduced to Parliament on 8th of December 2010? The Government is establishing a framework to enable private firms to offer consumers energy efficiency improvements to their homes, community spaces and businesses at no upfront cost, and to recoup payments through a charge in instalments on the energy bills. There are some similar schemes already available regionally. The United Sustainable Energy Agency (based in Milton Keynes) through their Cocoon websites has been offering insulations and solar PV or solar thermal panels. The insulation was free but the solar PV and thermal isn’t.
MCS – Microgeneration Certification Shceme – I also would like to mention the Micro generation Certification Scheme. MCS is an independent scheme that certificates micro generation products and installers in accordance with consistent standards. It is designed to evaluate micro generation products and installers against robust criteria providing greater protection for consumers. Basically if you want to install any renewable energy and benefit from the current schemes you must use MCS accredited product and installer. The MCS certification should be like insurance for a consumer to make sure that they receive a high standard product and series.
I believe I have summarized the main aims of the government and the main body’s to meet the targets. I would like to carry by identifying and explain each of the technology.
Solar photovoltaic technology
A Photovoltaic (PV) system works by converting the energy from the sun into electricity. This electricity is then fed directly into the existing supply of the property where it can be used. The electricity generated is free and has no carbon emissions. This is a simple explanation of the solar PV system. In fact the electricity generated by converting the solar radiation is direct current electricity (DC). It is lethal electricity. The DC is converted by an inverter in to the alternative current electricity (AC). The AC is fed directly into the existing supply. Materials presently used for photovoltaic include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide. There are lot of different panel’s size but it is unusually vary from the length of 1300-1700mm by 650-900mm with outputs from 170W – 260W. The DC output of each panel depends on number of sunshine days. The UK standard is set by SAP 2005 and it is 800 kwh/year per 1kWp system (4-8 panels, depends on an output of each panel). There is a way to get more accurate calculation via PVGIS (Photovoltaic Geographical Information System) website. 1kWp of solar PV saves around 580 kg of CO2 per year.
The AC is fed directly into the existing supply. Materials presently used for photovoltaic include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide. There are lot of different panel’s size but it is unusually vary from the length of 1300-1700mm by 650-900mm with outputs from 170W – 260W. The DC output of each panel depends on number of sunshine days. The UK standard is set by SAP 2005 and it is 800 kwh/year per 1kWp system (4-8 panels, depends on an output of each panel). There is a way to get more accurate calculation via PVGIS (Photovoltaic Geographical Information System) website. 1kWp of solar PV saves around 580 kg of CO2 per year.
There are other forms of solar photovoltaic such as solar PV tiles and membranes. These technologies are still quite expensive and the ratio between the payback and the output is not that great therefore the most preferable solar technology is solar PV panel.
Due to the high demand and rapid growth the manufacturing of solar cells and PV arrays has advanced. The price has also come down rapidly in last 12 months. I mean the typically price for a 4kWp system was around ï¿½16-ï¿½20 000 and it is between ï¿½10-ï¿½13 000 at the moment. It means that the payback for the system is much quicker and the option of solar PV is being seen as an attractive investment. It was also mention in Dragon’s Den by Deborah Meaden that the PV system is the best domestic investment at the moment.
There were plans of installing a huge PV farms but the Government put a cap on big size systems so it has become less attractive from the investment point of view. The last sentence leads us to a discussion where the installation of renewable energy becomes more a business than aim to achieve government aims and target. I guess this is the only way to meet the targets as I cannot see majority of population investing their money in to renewables if it is not an attractive financial investment. As I have already mentioned I think the introduction of the FITs scheme help to meet the targets but also help to the economy so it is a win/win situation.
Solar Thermal technology
The heat from the Sun is captured by solar panels into a special solar hot water cylinder or thermal store to heat the hot water or the heating circuits. Solar thermal collectors are classified as low-, medium-, or high-temperature collectors. Low temperature collectors are flat plates. These are usually used for swimming pool heating. Medium-temperature collectors are also usually flat plates as well but are used for heating water, heating or air for residential and commercial use. High temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production.
There are two types of solar thermal panels which are commonly used. The first type is a flat plate panel and the second type is an evacuated tubes panel. Other types are High-temperature collectors – Concentrated Solar Power (CSP). These are using concentrated mirrors and lenses to obtain higher temperatures. There are other types of solar thermal available such as solar air heat collectors, solar bowls and solar towers (used in Australia). I would like to describe more into details flat plate solar collector, evacuated tubes as these are used most frequently. I shall also touch little bit the others.
Flat Plate solar collector is a most common type. It consist of a dark flat plate absorber of solar energy, a transparent cover that allows solar energy to pass through but reduces heat losses, a heat-transport fluid (we have been using any form of glycol mixed with a water to prevent freezing; it is in fact an anti-freeze but developed to enable a very good heat transfer) to remove heat from the absorber and a heat insulation backing. The absorber consist of a thin absorber sheet (polymer – most commonly used in Europe, aluminium, steel or copper) often backed by a grid or coil of fluid tubing placed in an insulated casing with a glass or polycarbonate cover. There are various sizes of panels but usual sizes are 2m2 or 2.55m2. The life expectancy of panels is between 25-35 years. There lot of manufacturers of solar flat plate collectors but I was able to visit and being trained by one of the biggest manufacturer in Europe – TiSUN. The company is based in Austria and I had chance to see the manufacturing process of each flat plate panel from the start to a final product. It was very impressive.
Evacuated tube collectors use heat pipes for their core instead of passing liquid directly through them. Evacuated tubes are composed of multiple evacuated glass tubes each containing an absorber plate fused to a heat pipe. The heat from the hot end of the heat pipes is transferred to the transfer fluid (the fluid can be a same type as for the flat plates so glycol/anti-freeze mixed with the water) of a domestic hot water or space heating in a heat exchanger called a manifold. The vacuum that surrounds the outside of the tube greatly reduces convection and conduction heat loss to the outside, therefore achieving greater efficiency than flat-plate collectors, especially in colder conditions. This advantage is largely lost in warmer climates, except in those cases where very hot water is desirable, for example commercial process water. The high temperatures that can occur may require special system design to avoid or mitigate overheating conditions.
We have been having long discussion within the company if flat plates are better than evacuated tubes or the other way around. The conclusion is that taking in to a count all pluses and minuses of each technology the winner is flat plate panel. I agree that usually evacuated tubes are “more efficient” but if you look in to it more closely the different is only 5-7% in winter months. This conclusion is based on a practical measuring and monitoring systems for last couple of years. Flat plate panels are more robust and require less maintenance.
Solar Air Heat Collectors heat air directly and almost always for a space heating. They are also used for pre-heating make-up air in commercial and industrial HVAC (heating, ventilation and air-conditioning) systems.
Solar Bowles is a type of solar thermal collector that operates similarly to a parabolic dish but instead of using a tracking parabolic mirror with a fixed receiver, it has a fixed spherical mirror with a tracking receiver. It reduced its efficiency but makes it cheaper and easier to operate. It is also commonly called as a Fixed Mirror Distributed Focus Solar System. The designers are arguing with the fact that the reduction in overall power output compared with tracking parabolic mirrors is offset by lower system costs. I was lucky enough to visit couple of projects in the Czech Republic and see them in the operation.
I think I have covered the solar technology in to a detail and I would like to describe other renewable technologies – heat pumps.
A heat pump is a machine or device that diverts heat from one location at a lower temperature to another location at a higher temperature using mechanical work or a high-temperature heat source. A heat pump can be used to provide heating or cooling. Even though the heat pump can heat, it still uses the same basic refrigeration cycle to do this. In other words a heat pump can change which coil is the condenser and which the evaporator. This is normally achieved by a reversing valve. In cooler climates it is common to have heat pumps that are designed only to provide heating. The heat can be used for space heating, space cooling and the heating of a domestic/commercial hot water. There were question marks if heat pumps (mainly air-source) are renewable energy but heat pumps even in a reverse mode are classified as a renewable energy technology.
There are few types of heat pumps such as air-source and ground source (brine and water).
Air source heat pump (air to water) extracts heat from the outside air either to a heating/cooling circuit or to domestic/commercial hot water tank. They are relatively easy and in-expensive to install and have therefore historically been the most widely used heat pump type. However they suffer limitations due to their use of the outside air as a heat source. Air-source heat pumps have been also suffering from a bad press due to the under-sizing and bad designs. They were also very noisy and low efficient. However the air-source heat pump manufacturers have improved the technology in last couple of years and some of them are really good with a seasonal coefficient of performance (COP) between 3.2-3.8.
There are 2 common types of air-source (water based) heat pumps. Mono-blocks and split versions. Each of the type is divided into a low temperature and high temperature (generates up to 65 with mono-blocks and up to 80 with split versions degree of Celsius flow temperature with no need of an electric element). Mono-blocks are commonly used for new builds with low heat losses and low water flow temperature based heating (under-floor heating, low heat convectors, fan-coils). The mono-block heat pump benefits for the fact that there is no need of refrigerant pipework and an internal unit. The downside of this heat pump is that the heat pump needs to be close to the internal heat exchanger (usually up to 2.5 metres) otherwise there are huge heat losses during the heat transfer (usually around 15 degree of Celsius) between the external unit and the internal hot water/accumulation tank. It means that the heat pump needs to run more frequently and therefore it becomes more expensive to run it.
The second type – split version – is becoming more popular. The heat pump has to have minimum of two units, one outdoor (evaporators) and one indoor. The outdoor unit is connected to the indoor unit with refrigerant pipework (the most common refrigerants are R410A and R407C – both environmentally friendly). The indoor unit through a heat exchanger distributes the heat to a heating circuit, accumulation or hot water tank. The heat loss during the heat transfer is between 2-3 degree of Celsius. There are also some downsides of the system. It is not that easy to install as mono-blocks, there is a legal requirement to be F-gas certified and to hold a safety handling refrigerant certification. There is also a space requirement for the internal unit which can be either wall or ground mounted.
Both types are having inverter driven compressors and circulation pumps which allows a lower running cost. It means that a heat pump runs as it needs. I can see the future in split high temperature (HT) versions. The HT split version is easy applicable to existing heating systems and it is an ideal solution to off-gas and on-gas properties. The CO2 emissions are significantly lower but again it all comes to a fact that the design of the system and correct heat losses are being a crucial fact to a successful application.
Ground source heat pumps which are also referred to as geothermal heat pumps are typically have higher efficiencies than air-source heat pumps. This is because they draw heat from the ground or groundwater which is at a relatively constant temperature all year round below a depth of about 9 meters. This means that the temperature differential is lower, leading to higher efficiency. Ground-source heat pumps typically have COPs of 3.5-4.0 at the beginning of the heating season, with lower COPs as heat is drawn from the ground. The downside for this improved performance is that a ground-source heat pump is more expensive to install due to the need for the digging of well, trenches or boreholes in which to place the pipes that carry the heat exchange fluid. When compared versus each other, groundwater heat pumps are generally more efficient than heat pumps using heat from the soil. There are high temperature ground source heat pumps which can generate a flow temperature up to 65 degree of Celsius and therefore suitable for some existing properties. The main and the key are to size the heat pump well which leads us again to a conclusion that a heat loss of a property is a key factor. The next very important factor for ground source heat pumps is to size a ground loop, borehole and well correctly.
When compared versus each other, groundwater heat pumps are generally more efficient than heat pumps using heat from the soil. There are high temperature ground source heat pumps which can generate a flow temperature up to 65 degree of Celsius and therefore suitable for some existing properties. The main and the key are to size the heat pump well which leads us again to a conclusion that a heat loss of a property is a key factor. The next very important factor for ground source heat pumps is to size a ground loop, borehole and well correctly.
Ground loop is a way of harvesting a heat from the ground. There are few ways to lay ground loops. The first one is called a Slinky (also coiled) type where the pipes overlay each other. Slinky type is usually more economical way but I would not recommend using it because of the fact that pipes are overlaying each other. Most of the ground source heat pump manufacturers are not recommending it as well. The second and more preferable type is a ground loop collector. It is in fact the same principal as laying the under-floor heating but it works the other way around. The ground collectors need to be minimum of 1.2m below the ground and each loop at least 1 metre from each other. This allows the collector to collect the heat from the ground and prevents freezing of the ground.
Borehole is another common way of installing ground source heat pump. A vertical closed loop field is composed of pipes that run vertically in the ground. A hole is bored in the ground, typically 23-250 m deep. Pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole. The borehole is commonly filled with a betonies grout surrounding the pipe to provide a thermal connection to the surrounding soil or rock to improve the heat transfer. Thermally enhanced grouts are available to improve this heat transfer. Grout also protects the ground water from contamination, and prevents artesian wells from flooding the property. Vertical loop fields are typically used when there is a limited area of land available. Bore holes are spaced at least 5-6 m apart and the depth depend on ground and building characteristics. If I say that a detached house needing 10 kW of heating capacity might need three boreholes 80 to 110 m deep. During the cooling season, the local temperature rise in the bore field is influenced most by the moisture travel in the soil. Reliable heat transfer models have been developed through sample bore holes as well as other tests. Obviously this is a high risk and high cost process. We are talking about ï¿½4500-ï¿½6500 per borehole which makes the ground source heat pump with boreholes less cost effective in terms of the payback for a domestic market. I am saying “domestic” market purposely because the RHI scheme (which I have mentioned early in my essay) for non-domestic installation makes ground source heat pumps more cost effective and financially attractive even by using boreholes.
If I say that a detached house needing 10 kW of heating capacity might need three boreholes 80 to 110 m deep. During the cooling season, the local temperature rise in the bore field is influenced most by the moisture travel in the soil. Reliable heat transfer models have been developed through sample bore holes as well as other tests. Obviously this is a high risk and high cost process. We are talking about ï¿½4500-ï¿½6500 per borehole which makes the ground source heat pump with boreholes less cost effective in terms of the payback for a domestic market. I am saying “domestic” market purposely because the RHI scheme (which I have mentioned early in my essay) for non-domestic installation makes ground source heat pumps more cost effective and financially attractive even by using boreholes.
Water Wells, Open Loops and Ponds are not frequently used type of ground source heat pumps even it is one of the most efficient way. A closed pond loop is not common because it depends on proximity to a body of water, where an open loop system is usually preferable. A pond loop may be advantageous where poor water quality precludes an open loop, or where the system heat load is small. A pond loop consists of coils of pipe similar to a slinky loop attached to a frame and located at the bottom of an appropriately sized pond or water source. In an open loop system (also called a groundwater heat pump), the secondary loop pumps natural water from a well or body of water into a heat exchanger inside the heat pump. Heat is either extracted or added by the primary refrigerant loop, and the water is returned to a separate injection well, irrigation trench, tile field or body of water. The supply and return lines must be placed far enough apart to ensure thermal recharge of the source. Since the water chemistry is not controlled, the appliance may need to be protected from corrosion by using different metals in the heat exchanger and pump. Lime scale may harm the system over time and require periodic acid cleaning. This is much more of a problem with cooling systems that heating systems. Also, as fouling decreases the flow of natural water, it becomes difficult for the heat pump to exchange building heat with the groundwater. If the water contains high levels of salt, minerals, iron bacteria or hydrogen sulphide, a closed loop system is usually preferable.
The supply and return lines must be placed far enough apart to ensure thermal recharge of the source. Since the water chemistry is not controlled, the appliance may need to be protected from corrosion by using different metals in the heat exchanger and pump. Lime scale may harm the system over time and require periodic acid cleaning. This is much more of a problem with cooling systems that heating systems. Also, as fouling decreases the flow of natural water, it becomes difficult for the heat pump to exchange building heat with the groundwater. If the water contains high levels of salt, minerals, iron bacteria or hydrogen sulphide, a closed loop system is usually preferable.
Deep lake water cooling uses a similar process with an open loop for air conditioning and cooling. Open loop systems using ground water are usually more efficient than closed systems because they are better coupled with ground temperatures. Closed loop systems, in comparison, have to transfer heat across extra layers of pipe wall and dirt.
A growing number of jurisdictions have outlawed open-loop systems that drain to the surface because these may drain aquifers or contaminate wells. This forces the use of more environmentally sound injection wells.
I believe I described heat pumps and I would like to move on to Wind power.
A Wind Turbine is a device that converts kinetic energy from the wind into mechanical energy. There are two ways of using the mechanical energy afterwards. If the energy is used to produce electricity the device may be called a wind generator or wind charger. The second way is that if the energy is used to drive machinery the device may be called a wind mill or a wind pump.
The technology has been developed over thousand years (back to a Persia times around 200 B.C.). Today’s wind turbines are developed and manufactured in a range of vertical and horizontal axis types. The smallest turbines are used for applications such as battery charging on boats, road signs (in a combination with a small solar PV panel), and cars while large grid-connected arrays of turbines are becoming a large source of commercial electric power. Medium-range wind turbines (usually between 10-35kW) are commonly used by farmers, schools and other commercial institutions as an attractive investment due to the Feed-In Tariff. There are two design types of axis – horizontal or vertical axis designs.
Horizontal Axis Wind Turbines have the main rotor shaft and electrical generator at the top of the tower and must be pointed into the wind. Most of them have a gearbox which turns the slow rotation of blades into a quicker rotation that is more suitable to drive an electrical generator. A tower produces turbulence behind it so the turbine is usually positioned upwind of its supporting tower.
Most modern wind turbines are usually three-bladed and pointed into the wind by computer-controlled motors. The blades are usually coloured light grey to blend with the sky. The length of blades is between 1.5m-40 metres and in some case even more. The tubular steel towers are in a range from 10 metres to 90 metres tall. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes.
Vertical Axis Wind Turbines have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable, for example when integrated into buildings. The key disadvantages include the low rotational speed with the consequential higher torque and hence higher cost of the drive train, the inherently lower power and the 360 degree rotation of the aerofoil within the wind flow during each cycle. With a vertical axis, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, hence improving accessibility for maintenance.
When a turbine is mounted on a rooftop, the building generally redirects wind over the roof and these can double the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.
The wind turbine is a great technology but it needs to be designed and installed properly. There are lot of factors which needs to be taken into a consideration for a successful operation.
I would like to move on to Biomass.
Worldwide biomass boilers are the fourth largest energy source after coal, oil and gas. It is a great way of reducing the carbon footprint of any building. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel. Biomass is carbon, hydrogen and oxygen based. Biomass energy is derived from five distinct energy sources: garbage, wood, waste, landfill gases, and alcohol fuels. Wood energy is derived both from direct use of harvested wood as a fuel and from wood waste streams. The largest source of energy from wood is pulping liquor or “black liquor,” a waste product from processes of the pulp, paper and paperboard industry. Waste energy is the second-largest source of biomass energy. The main contributors of waste energy are
The main contributors of waste energy are municipal solid waste, manufacturing waste, and landfill gas. Biomass alcohol fuel or ethanol is derived primarily from sugarcane and corn. It can be used directly as a fuel or as an additive to gasoline. Biomass can be converted to other usable forms of energy like methane gas or transportation fuels like ethanol and biodiesel. Rotting garbage, and agricultural and human waste, release methane gas – also called “landfill gas” or “biogas.” Crops like corn and sugar cane can be fermented to produce the transportation fuel, ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats.
One of the most common uses of biomass is for a heating. The system falls under the categories of direct combustion, gasification, combined heat and power (CHP), anaerobic digestion and aerobic digestion. The use of biomass in heating systems is beneficial because it uses agricultural, forest, urban and industrial residues and waste to produce heat and electricity with less effect on the environment than fossil fuels. This type of energy production has a limited long term effect on the environment because the carbon in biomass is part of the natural carbon cycle; while the carbon in fossil fuels is not, and permanently adds carbon to the environment when burned for fuel. The downside of the biomass heating is its cost of wood pellets, wood chips and other biomass. We have to also consider the cost/CO2 emissions of a transport of biomass to its consumers.
There are four main types of heating systems that use biomass to heat a boiler. The types are fully Automated, Semi-automated, Pellet-Fired and combined heat and power (CHP).
Fully automated systems – Chipped or ground up waste wood is brought to the site by delivery trucks and dropped into a holding tank. A system of conveyors then transports the wood from the holding tank to the boiler at a certain managed rate. This rate is managed by computer controls and a laser that measures the load of fuel the conveyor is bringing in. The system automatically goes on and off to maintain the pressure and temperature within the boiler. Fully automated systems offer a great deal of ease in their operation because they only require the operator of the system to control the computer, and not the transport of wood.
Semi-automated systems or “Surge Bin” systems are very similar to fully automated systems except they require more manpower to keep operational. They have smaller holding tanks, and a much simpler conveyor systems which will require personnel to maintain the systems operation. The reasoning for the changes from the fully automated system is the efficiency of the system. Wood fire fuelled boilers are most efficient when they are running at their highest capacity, and the heat required most days of the year will not be the peak heat requirement for the year. Considering that the system will only need to run at a high capacity a few days of the year, it is made to meet the requirements for the majority of the year to maintain its high efficiency.
Pellet-fired is the third main type of biomass heating. Pellets are a processed form of wood, which make them more expensive. Although they are more expensive, they are much more condensed and uniform, and therefore are more efficient. In these systems, the pellets are stored in a grain-type storage silo, and gravity is used to move them to the boiler. The storage requirements are much smaller for pellet-fired systems because of their condensed nature, which also helps cut down costs. These systems are used for a wide variety of facilities, but they are most efficient and cost effective for places where space for storage and conveyor systems is limited, and where the pellets are made fairly close to the facility. I have already mentioned the issue of the cost of pellets and their transport. The pellets need to have a certain level of humidity to achieve the efficiency out of the boiler.
Combined heat and power systems are very useful systems in which wood waste, such as wood chips, is used to generate power, and heat is created as a by-product of the power generation system. They have a very high cost because of the high pressure operation. Because of this high pressure operation, the need for a highly trained operator is mandatory, and will raise the cost of operation. Another drawback is that while they produce electricity they will produce heat, and if producing heat is not desirable for certain parts of the year, the addition of a cooling tower is necessary, and will also raise the cost.
There are certain situations where CHP is a good option. Wood product manufacturers would use a combined heat and power system because they have a large supply of waste wood, and a need for both heat and power. Other places where these systems would be optimal are hospitals and prisons, which need energy, and heat for hot water. These systems are sized so that they will produce enough heat to match the average heat load so that no additional heat is needed, and a cooling tower is not needed.
I have already mentioned the Code 6 job which the company I work for was involved and there has been used a communal biomass boiler heating system.
The Energy Statement for Ashton Green Sustainable Urban Extension looked into possibilities of using multiple renewable energy technologies in order to support a planning application. The main areas are energy deductions in terms of CO2 emissions and sustainability standards. The requirement was a level code 4 of Sustainable homes which means that energy generated for the each dwelling must be 44% above the PART L 2006. The local policies also require a 14% contribution to total energy demand from renewable generation in 2010.
The report also identifies incentives for Renewable energy which I have already describes. The report also considered technically feasible the integration of heat pumps, solar thermal, PV, CHP and Biomass. The report comes up with two strategies. The first is based on solar thermal and PV system and the second is based on gas CHP and biomass community heat and power. They are not considering installing of small wind turbines.
I would personally prefer either the option one and use solar thermal and PV to achieve The CODE but I would also incorporate heat pumps. The reason why I would not recommend using gas CHP and biomass is the rising cost of the wood pellets/wood chips as well as the gas. The development would also be dependent of third party suppliers. There will also be higher maintenance cost and more mechanical parts involved.
Overall I would suggest using heat pump with a combination of solar thermal and PV. I would also not rule out the option of a small (10kw) wind turbine.