This article focuses on building-integrated options rather than large-scale utility solutions such as wind farms, which are addressed separately, and provides an analysis of where they may be best installed.
The legislative background, imperatives and incentives
In recognition of the causes and effects of global climate change, the Kyoto protocol was signed by the UK and other nations in 1992, with a commitment to reduce the emission of greenhouse gases relative to 1990 as the base year.
Thefirst phase of European Union Emission Trading Scheme (EU ETS) covered the power sector and high-energy users such as oil refineries, metal processing, mineral and paper pulp industries. From 1 January 2005, all such companies in the EU had to limit their CO2emissions to allocated levels in line with Kyoto. The EU ETS is now in its third phase, running from 2013 to 2020 and covers the 27 EU Member States, as well as Iceland, Liechtenstein, Norway and Croatia. The main change from previous phases being that additional sectors and gases are now included. Key principles of the EU ETS are that participating organizations can:
Meet the targets by reducing their own emissions (e.g. by implementing energy efficiency measures, using renewable energy sources), or
Exceed the targets and sell or bank their excess emission allowances, or
Fail to meet the targets and buy emission allowances from other participants
The EU ETS is designated as a‘cap and trade’ system, where participation is mandatory for the sectors covered and it accepts credits from emission-saving projects carried out under the Kyoto Protocol’s Clean Development Mechanism (CDM) and Joint Implementation instrument (JI).
In the UK, the Utilities Act (2000) requires power suppliers to provide some electricity from renewables, starting at 3% in 2003 and rising to 15% by 2015. In a similar way to the EU ETS, generating companies receive and can trade Renewables Obligation Certificates (ROCs) for the qualifying electricity they generate.
The focus is on Greenhouse Gases (GHG) and Carbon Dioxide (CO2) in particular as the main direct contributor to the greenhouse effect. The goals set by the UK government are:
34% GHG emissions reduction by 2020 (below 1990 baseline)
Around 30% of electricity from renewables by 2020
80% GHG emissions reduction by 2050 (below 1990 baseline)
Four years after the introduction of ROCs, it was estimated that less than 3% of UK electricity was being generated from renewable sources. A‘step change’ in policy was required, and the Office of the Deputy Prime Minister (ODPM) published‘Planning Policy Statement 22 (PPS 22): Renewable Energy’ in order to promote renewable energy through the UK’s regional and local planning authorities. PPS 22 was replaced by the National Planning Policy Framework, published in March 2012 by the Department for Communities and Local Government (DCLG), which encourages the use of renewable resources.
Local planning & building regulations
More than 100 local authorities embraced PPS 22 by adopting pro-renewables planning policies typically requiring a percentage (e.g. 10%) of a development’s electricity or thermal energy needs to be derived from renewable sources. Government is developing further guidance to support local authorities addressing the sustainability of planned developments and to ensure a level playingfield across the country.
Government is also committed to successive improvements in national new-build standards through changes to the Building Regulations, Part L, Conservation of Fuel and Power. In October 2010, new regulations introduced a 25%
improvement on 2006 standards. The next review, due in 2013, is expected to further strengthen standards, in line with developing zero carbon policies.
Energy performance certificates (EPCs)
A Recast of the 2002 EU Directive on the Energy Performance of Buildings (EPBD) was published in 2010. It requires that EPCs be produced for buildings constructed, sold, or rented out to new tenants. For buildings occu-pied by public authorities and frequently visited by the public, the EPC must be displayed in a prominent place clearly visible to the public. These provisions enable prospective buyers and tenants to be informed of a building’s energy performance, ensure the public sector leads by example, and raise public awareness. The Recast was transposed in the UK by national Governments, for example in England & Wales through the Energy Performance of Buildings (England & Wales) Regulations 2012 and other regulations. Other requirements of the Recast include:
adopting a method to calculate the energy performance of buildings, setting minimum energy performance requirements and for new buildings to be Nearly Zero Energy Buildings by 2020.
Assessing the regulated carbon emissions associated with new buildings is now an important part of the design and building permitting process with the regulatory approach set out in Part L of the Building Regulations (Con-servation of Fuel & Power), the associated National Calculation Methodology (NCM) Modelling Guide and the Standard Assessment Procedure (SAP). On-site renewable energy sources are taken into account and there are limits on designflexibility to discourage inappropriate trade-offs such as buildings with poor insulation standards offset by renewable energy systems.
Technology options and applications
Wind generators – In a suitable location, wind energy can be an effective source of renewable power.
Without grant, an installed cost range of £3000 to £5000 per kW of generator capacity may be achieved for small building-mounted turbines. A common arrangement was for a turbine with three blades on a horizontal axis, all mounted on a tower or, for small generators in inner city areas, on a building. Such arrangements typically compare poorly against other renewable options, as they are highly dependent on wind speed at the turbine, obstructions (e.g. nearby buildings and trees), turbulences, the elevation of the turbine above ground, and mitigating other impacts such as aesthetics consideration for planning permission, noise, and vibrations. With suitable conditions, average site wind speeds of 4 m/s can produce useful amounts of energy from a small generator up to about 3 kW, but larger generators require at least 7 m/s. A small increase in average site wind speed will typically result a large increase in output. There will be a need for inverters, synchronizing equipment, and metering for a grid connection.
Larger, stand-alone turbines typically compare more favourably than smaller building-mounted turbines.
Third party provision through an Energy Service Company (ESCo) can be successful for larger (stand-alone) installations located within or close to the host building’s site, especially in industrial settings where there may be less aesthetic or noise issues than inner city locations. The ESCo provides funding, installs and operates the plant and the client signs up for the renewable electrical energy at an agreed price for a period of time.
Building integrated photovoltaics (BIPV) – Photovoltaic materials, commonly known as solar cells, gen-erate direct current electrical power when exposed to light. Solar cells are constructed from semiconducting materials that absorb solar radiation; electrons are displaced within the material, thus starting aflow of cur-rent through an external connected circuit. PVs are available in a number of forms including monocrystalline, polycrystalline, amorphous silicon (thinfilm) or hybrid panels that are mounted on or integrated into the roofs or facades of buildings. Conversion efficiency of solar energy to electrical power is improving with advances in technology and ranges from 10% to 20%. In practice, allowing for UK weather conditions, an installation of 7 m2of monocrystalline modules (south facing at 30° from horizontal) typically produces 1000 watts peak (1 kWp), yielding about 800 kWh in a year. Installed costs range from £1200 to £2500/kWp.
12 Renewable Energy Options
Ground source heat pumps (heating & cooling) – At a particular depth (about 10 m in the UK), the ground temperature remains substantially constant throughout the year. Heat (and coolth) may be extracted through either an‘open’ system – discharging ground water to river or sewer after passing it through a heat exchanger, or a‘closed’ system – circulating a fluid (often water) through a heat exchanger and (typically) vertical pipes extending below the ground water table. An electrically driven heat pump is then used to raise thefluid temperature via the refrigeration cycle, and low temperature hot water is delivered to the building.
Most inner city ground heating and cooling systems consist of a cluster of pipes inserted into vertical holes typically 50 to 100 metres deep depending on space and ground conditions. Horizontal systems can be used where site circumstances allow. Costs for the drilling operation vary according to location, site accessibility, and ground conditions. Geological investigations are recommended to confirm ground conditions, reduce risks, and improve design and cost certainty.
Such systems may achieve a Coefficient of Performance (COP = heat output/ electrical energy input) of between 3 and 4, achieving good savings of energy compared with conventional fossil fuels based systems.
Installed costs are in the range £600 to £1700/kW depending on system type (vertical or horizontal), its size and complexity.
Note that there is some debate on the status of ground source heat pumps as a renewable source of energy as it requires an external source of power which may not be renewable, typically electricity from the grid.
Solar water heating – The basic principle is to collect heat from the sun via a fluid which is circulated in a roof solar panel or‘collector’. The heated fluid is then used to preheat hot water for space heating or domestic hot water, either in a separate tank or a twin coil hot water cylinder. Purpose-designed‘evacuated tube collectors’ were developed to increase performance against the typical ‘flat plate collectors’. A typical residential‘evacuated tube collectors’ system has a cost ranging from £700 to £1000/m2depending on pipe runs and complexity. Such system may produce approximately 500 to 800 kWh/m2per year. Commercial systems are larger and more complex, and may achieve similar performance, providing there is sufficient hot water demand. Low-density residential, retail and leisure developments with washrooms and showers may also be suitable applications providing adequate demand for hot water.
Biomass boilers – Wood chips or pellets derived from waste or farmed coppices or forests are available commercially and are considered carbon neutral, having absorbed carbon dioxide during growth. With a suitable fuel storage hopper and automatic screw drive and controls, biomass boilers can replace conven-tional boilers with little technical or aesthetic impact. However, they do depend on a viable source of fuel, and there are requirements for fuel deliveries access (in particular for inner city or remote locations), fuel storage, ash removal/disposal, as well as periodic de-coking. In individual dwellings, space may be a pro-blem because a biomass boiler does not integrate readily into a typical modern kitchen. However, communal systems (serving multiple dwellings/flats) may be a viable domestic application. Biomass boilers are avail-able in a wide range of domestic and commercial sizes. For a large installation, biomass boilers are more likely to form part of a modular system rather than to displace conventional boilers entirely. There is a cost premium for the biomass storage and feed system, and the cost of the fuel is currently comparable with other solid fuels. Installed costs of a biomass boiler range from £200 to £350/kW.
Biomass combined heat & power (CHP) – Conventional CHP installations consist of either an internal combustion engine or a gas turbine driving an alternator, with maximum recovery of heat, particularly from the exhaust system. For best efficiency, there needs to be a convenient and constant requirement for the heat energy output and the generated electricity should also be utilized locally, with any excess exported to the grid.
Considering the cost implications for biomass storage and handling as described for biomass boilers above, biomass CHP would only be viable in specific circumstances, with installed system costs in the order of
£2500 to £3500/kW (electrical). Note that, at the time of writing, the authors are not aware of any small-scale biomass CHP system successfully operated in the UK over any significant period.
Renewable Energy Options 13
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