Renewable Energy Options

Technologies which generate electricity or heat from natural resources such as Solar Rays, Wind, Water, Biomass, Ground Source, Anaerobic and Hydropower, are considered ‘renewable’ because, unlike coal, oil and natural gas, they are not finite. Combined Heat and Power systems are not, strictly speaking, renewable, as they often rely on a fossil fuel source. They are, however, a more efficient and less polluting way to generate electricity and energy for buildings (https://www.carbontrust.com/media/7379/ctv010-renewable_energy_sources.pdf).

Photovoltaic Panels

Photovoltaic (PV) panel technology harnesses energy through the sun’s rays and is currently one of the most efficient forms of renewable electricity generation.

PV arrays can sit in the landscape or on or within the building envelope as building integrated photovoltaic (BIPV) panels. Both arrangements actively convert solar energy into electricity that can be used in commercial or residential buildings. The PV cells are arranged into modules, then into arrays and then finally placed on the land or onto buildings (https://www.carbontrust.com/media/81357/ctg038-a-place-in-the-sun-photovoltaic-electricity-generation.pdf; www.samlexsolar.com).

BIPVs are most commonly fitted to the roof of buildings and then connected to the national grid. However, in both commercial and residential buildings, they can be integrated into skylights, facades, windows, curtain walls and, in thin form, into roof tiles and shingles, although shading from surrounding buildings or trees can have an adverse effect on the efficiency of the system (http://inhabitat.com/solar-panel-roof-tiles/).

There are four principal types of PV cells:

1. 1. Monocrystalline PV (mono-si)
2. 2. Polycrystalline PV (poly-si)
3. 3. Thick-film PV
4. 4. Thin-film PV

(Elsadig, 2005: 69)

The most common PV cells on the market are made out of two silicon semi-conductors. When the photons from the sunlight hit the semi-conductors, they excite the electrons making them jump from the boron-doped p-type silicon conductor to the phosphorous-doped n-type silicon conductor (Jariwala and Jariwala, 2014: 39). This flow of electrons creates an electric field across the layers, which is then used to power the building. ‘Doping’ the silicon semi-conductors is important because it makes the conversion to electricity more efficient by increasing the energy of the outer shell electrons (Shepard and Shepard, 2014; www.gosunsolutions.com).

Once installed, PVs are environmentally ‘clean’. Sunlight is free and the cells produce no carbon, emissions or noise pollution. The cells are made of silicon, which at present is an abundant material (Jariwala and Jariwala, 2014).

PV cells’ embodied impact is relatively small and has rapidly decreased in recent years through research and development. Raugei and Frankl (2009) looked at the life cycle energy (LCE) consumption of PV systems and its environmental impact. They found that poly-si rooftop cells in the 1990s had an LCE of 167 g (CO₂)/kWh whereas in 2008 they had only an LCE of 37 g (Co²)/kWh, a fourfold improvement.

Manufacturing costs have been reduced through innovation in the production of the silicon crystals used. Previously, crystals were made in the form of an ingot and then cut into thin wafers. This was very expensive. Now, silicon crystals are grown into a ribbon shape and do not need cutting or strict temperature control (Shepard and Shepard, 2014: 431).

Energy used during transportation has also decreased in the past few years, as manufacturing has started within United Kingdom by companies such as Sharp Solar and Sunsolar Energy. Furthermore, Sunsolar Energy has stated that all the parts needed to make the product will be locally sourced (www.greenwisebusiness.co.uk, 2012).

This, however, may be an optimistic outlook when taking a more global viewpoint, as there are still significant amounts of imported PV cells manufactured in countries that have lower green taxes. For example, many EU countries continue to import panels manufactured in China (http://www.iea.org.uk, 2014).

As with the embodied impact of PV cells, the unit cost of the panels has also been reducing. Jariwala and Jariwala (2014) found that manufacturing prices decreased by 50% in 2011 alone. A 4 kWp system (16 solar panels) that used to cost £15,000 in 2011 is now available from £5400 plus 5% VAT. However, initial costs of buying and installing solar panels remain relatively high. Typically, a 4 kWp residential system in south west England will produce around 4.000 kWh per year. This will provide a year one return of around £1000, a return of just over 20% (www.comparemysolar.co.uk, 2014).

Hammond et al. (2011) found through life-cycle assessment that systems are unlikely to pay back their investment over a life span of 25 years, but that they would recover their embodied impact in just 4.5 years. However, it is likely that because there has, for example, been progression in research and manufacturing since 2011, the payback time for the embodied impact will be shorter. In addition, this study was completed when there were no government feed-in-tariffs.

The maintenance of solar panels is easy and requires relatively little work since there are no moving parts (Shepard and Shepard, 2014: 427). This makes the monetary payback quicker as the service charge, once installed, is small.

Government feed-in-tariffs did mean that home owners could get economically rewarded for installing PVs. For example, in a residential property that has a system size of 4 kWp, the feed-in-tariffs could save homeowners approximately £750 a year (http://www.energysavingtrust.org.uk).

However, such incentives can be withdrawn as a result of changing government policy and the state of the national economy.

The clearest practical constraint for using BIVPs within United Kingdom is the amount of sunlight a year received and its intermittent nature. Although solar panels can produce energy under cloud cover, peak performance is with maximum sunlight intensity hitting the cells. Shepard and Shepard (2014) found that the mean annual solar power received was about three times more in countries like Egypt than in Great Britain; 300 rather than 100 W/m². It was also found that the distribution of solar radiation is much ‘flatter’ annually in Egypt, whereas in England, solar radiation is the highest in June when demand for energy is the lowest.

The Heron Tower in London has an area of 3200 m² and 855 modules on the façade of the building. This is estimated to have a power output of 34 kWp (Solar Technology Centre, 2014). However, another tower has been given planning permission to be constructed on the South side of the building. This means that it will shade the PV modules and significantly reduce the power output. This clearly highlights the practical constraints that could occur with PV’s.

Although some PV arrays can suffer low social acceptability through poor aesthetics and high capital costs (Raugei and Frankl, 2009: 294), this is slowly changing, as it becomes more fashionable to be seen to be ‘going green’. In particular, companies are putting more investment into renewables to ensure their business is viewed as being ethically and environmentally responsible. This can be seen at Marks & Spencer's Donnington Park distribution centre where they have started to install 24,272 solar PV panels in order to further enhance their sustainability credentials (www.greenwisebusiness.co.uk, 2014).

BIVPs have a high cost compared to conventional energy sources. To be competitive with the normal route of generating electricity through burning fossil fuels, the cost of generating electricity needs to be £0.07 per kWh (Shepard and Shepard, 2014: 434). In order to be the product of choice, solar panel technology needs to become cheaper so that there is not such a big lag time from installation until their economic value is realised, at present, many years later (www.gosunsolutions.com, 2014). Increased efficiency and increased ability to integrate PV’s into new and old buildings are happening at a rapid pace, with new thin-film photovoltaics being designed that reduce manufacturing costs (www.gosunsolutions.com).

Some ‘solar slates’ for houses have also been designed in order for PVs to be more aesthetically pleasing and less obtrusive, but at present, cost significantly more than the normal roof BIVPs (http://www.energysavingtrust.org.uk, 2014).

However, such innovation could mean that PV will become increasingly easy to embed into the buildings of the future.

Carbon costs of transportation can be significant depending on the location of production, the sources of raw materials and the main markets for the product. For example, a 190 W solar panel weighing 22 kg can create 57 kg of CO₂ if it is transported by air or 7 kg if transported by ship.

The total cost for a 1 MW solar farm is just under £50,000 and payback takes around 7–10 years at 12% interest, not taking into account the purchase of the land (Mandal, 2014). The carbon cost of disposing of the PV is still unknown, as it is such a new technology and few have reached the end of their life span (Shah et al., 1999). The UK government reduced the feed-in-tariffs in 2012 to 10 p/kWh for schemes greater than 250 kWh and this subsidy has since dropped to 6.38 p/kWh (Ofgem e-serve, 2014).

Combined Heat and Power (CHP)

As can be seen from the diagram and video clip below, heat is the waste product created by the movement of the electricity generating process (http://www.theade.co.uk/what-is-combined-heat-and-power_15.html).

Combined heat and power is a system that produces heat and electricity at the same time. This can be done on a large scale with co-generation power plants or for smaller projects with micro-CHP’s in commercial and residential buildings. CHP’s are made from four elements (IEA, 2011):

1. 1. Prime mover
2. 2. Electricity generator
3. 3. Heat recovery system
4. 4. Control system

[www.energysolutionscenter.org]

There are many different types of CHP’s normally depending on what ‘prime mover’ is used. Prime movers can be a reciprocating engine, a heat recovery steam generator, steam turbine, gas turbine or a micro-turbine (www.centreforenergy.com).

The three main micro-CHP’s are Stirling engine, internal combustion and fuel cells. Fuel cells are new to the UK market and are not yet used commercially (Shepard and Shepard, 2014: 89–90). Micro-CHP’s in residential buildings look like a typical boiler (www.energysavingtrust.org.uk; https://en.wikipedia.org/wiki/Stirling_engine).

Different CHP’s produce a different output ratio of heat and electricity. Micro-CHP’s on average currently produce a lot more heat than electricity at a ratio of about 6:1 for domestic appliances. In a residential building, micro-CHP systems tend to be Stirling engines powering CHP boilers because they are compact and less noisy (www.thegreenage.co.uk, 2014).

Fossil fuels power a prime mover which is attached to an electrical generator. This electrical generator produces the electricity that goes to the building or is sold back to the national grid. Heat produced from the prime mover is caught and used to heat the air and water in buildings (www.centreforenergy.com, 2014).

Fuel cells work differently because electricity and heat are produced and used from a chemical reaction. Hydrogen is the fuel and is placed into a cell stack that contains an anode, cathode and electrolyte layer. The hydrogen then reacts with oxygen producing the electricity and the heat (www.fuelcellenergy.com, 2014).

There are four different types of fuel cells: molten carbonate fuel cells, solid oxide fuel cells, phosphoric acid fuel cells and polymer electrolyte fuel cells. The big advantage of CHP’s powered by fuel cells is that the ratio of heat to electricity is 1:1, which is much more commercially beneficial (IEA, 2011).

Burning fossil fuels normally charge CHP’s, but they are more efficient and are low carbon compared to obtaining electricity from the national grid and cut a building’s carbon footprint by up to 40% (www.thegreenage.co.uk, 2014).

Installation and maintenance are easy for most micro-CHP’s as they are the same as a standard conventional boiler and usually mean that the service charge on the building will not increase dramatically. A typical residential micro-CHP has to be charged only every 10,000 h (www.energ-group.com, 2014).

CHP’s work well because occupiers tend to want heat at the same time that they want electricity. In a residential building for example, building users want hot water in the mornings and the evenings, therefore, electricity will also be produced at ‘peak demand’ periods (www.thegreenage.co.uk, 2014).

Due to the government’s targets of reducing CO₂ emissions by up to 80% by 2050, if CHP’s are installed in buildings, owners can benefit from government subsidies through their feed-in-tariffs (www.energysavingtrust.org.uk, 2014).

At present, a Stirling engine micro-CHP for a residential building costs around £7400, rising to £8000 for an LPG unit, not including installation costs (www.thegreenage.co.uk, 2014).

The economic payback time for micro-CHPs is relatively good. According to the Energy Saving Trust’s (2014) ‘cashback calculator’ shows the amount an average residential home owner can be expected to save annually by installing a micro-CHP boiler. Data produced by the UK government in 2013 on what figure to use for the annual generation of kWh per year for a UK domestic household has been used (www.gov.uk, 2013; http://tools.energysavingtrust.org.uk/Generating-energy/Getting-money-back/Cashback-Calculator; http://www.energysavingtrust.org.uk/scotland/tools-calculators/cashback-calculator).

The cashback calculator found that by installing a micro-CHP in a residential building, the landlord could save approximately £784 a year excluding any maintenance costs. After 10 years £7844 could be saved, thus recovering the cost of buying the micro-CHP.

A current limitation of CHP’s is that they are not hugely flexible in the ratio of heat to electricity that they can produce. Current micro-CHP’s on the market for domestic use can produce 1 kWh of electricity when the boiler is working at its maximum capacity. Putting this into perspective, a kettle needs 3 kWh of electricity to boil 1 l of water (www.thegreenage.co.uk, 2014).

In addition, in the summer when no heating is required, the CHP will not be producing any electricity. However, larger CHP’s produce more heat and, therefore, more electricity, thus making CHP’s more viable for larger commercial buildings (Chwieduk, 2003: 213).

Some companies selling CHP’s claim that they have an efficiency rate of between 80 and 90% and decrease energy consumption by around 15–45% (Smith et al., 2013). However, the word ‘efficiency’ must be deconstructed; 80–90% is the total efficiency, not the heat or electricity efficiency. With CHP’s, increasing the heat production decreases electricity production (MacKay, 2009: 149) and so, the future development of CHP’s perhaps needs to focus on making the ratio of heat and electricity production the same, as electricity is more valuable than heat.

Studies show that CHP can reduce energy costs in many different types of commercial building and that the costs of installing CHP plants can have a payback period in the range of 7–9 years (Ibid. & Maidment and Tozer, 2002).

The costs of the systems vary as they are building specific and, because this is a new technology, there is little reliable research to show if the efficiency of CHP remains the same throughout its lifetime, or indeed, how long these systems last. CHP has practical constraints, requiring planning permission for plants less than 50M (LGA, 2014), needing more space than the non-renewable equivalent system and can be noisy.

Also, as the demand for power in buildings tends to spike at different times of the day and seasonally, unnecessary heat can be generated. However, with careful management, excess heat can be used by connecting other buildings to the system. CHP’s also require grid connection in order to get the 4.1 p/kWh UK Government generation tariff (Ofgem, 2014). The amount it receives quarterly is calculated by the tariff level multiplied by the heat generated. Recently, the UK Government withdrew its Levy Exception Certificates which reduced tax rates on buildings with CHP (LGA, 2014 & CHPA, 2013).

The global CHP market is currently increasing at a fast rate with an expectation that it will grow 20.2% up to 2019. This is because the government is funding many leading companies and experts in order to create new technologies (www.digitaljournal.com).

Development is focusing on fuel cell technology because of its ability to produce a higher ratio of electricity to heat. They are the products which utilise a chemical reaction which is more sustainable than current CHP technology. Larger systems such as internal combustion engines, can be fuelled by fuel cells rather than by fossil fuels and therefore significantly reduce the carbon emissions released into the atmosphere (Neef, 2008: 265–272).

If CHP’s can be fuelled by fuel cells or biomass rather than fossil fuels and manufacturing costs can be decreased, then CHP’s can become an excellent way for buildings to significantly decrease their carbon footprint and embodied impact.

Ground Source

Ground source heating or cooling works by transferring heat to or from the ground via a heat pump in the building and a loop of water and/or antifreeze-filled pipework buried in the ground. The captured heat is then used for water or space heating within the propertyhttps://www.youtube.com/watch?v=KE3SvNRmwcQhttps://www.youtube.com/watch?v=jzXt55ZGsNwhttp://energy.gov/energysaver/articles/geothermal-heat-pumpshttp://www.energysavingtrust.org.uk/domestic/ground-source-heat-pumpshttp://www.gshp.org.uk/documents/CE82-DomesticGroundSourceHeatPumps.pdfhttps://en.wikipedia.org/wiki/Geothermal_heat_pump).

The feasibility of these systems for particular buildings will depend on the building itself, ground conditions, plot size and accessibility for digging trenches or boreholes.

A well-insulated, thermally efficient building is essential if the system is to function correctly and whilst the payback period of these systems has been found to be cost effective when replacing electricity or coal as the prime heating source, they are less economical for buildings using mains gas.

Because of the lower water temperatures required, ground source systems are also more commonly used with underfloor heating systems or warm air heating rather than with radiators (EST, 2016).

Biomass Boilers

Biomass is organic matter which comes from plants and trees and is most commonly burnt in compressed block, wood chip or pellet form as a fuel source in boilers to provide heat to residential, institutional and commercial properties or to district heating plants such as this proposed installation in Northamptonshire, United Kingdomhttp://www.theade.co.uk/nexterra-consortium-reaches-financial-close-on-biomass-gasification-plant-in-northamptonshire_3044.htmlhttps://en.wikipedia.org/wiki/Biomasshttps://www.youtube.com/watch?v=JZak3wa8gZQhttps://www.youtube.com/watch?v=ZNVx_ndDE8Uhttp://www.carbontrust.com/media/31667/ctg012_biomass_heating.pdfhttp://www.carbontrust.com/resources/guides/renewable-energy-technologies/biomass-heating-tools-and-guidance/https://www.gov.uk/government/publications/woodfuel-guidancehttp://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-biomass-energy-works.html#.VebXvCVVikohttp://www.biomassenergycentre.org.uk/pls/portal/docs/PAGE/BEC_TECHNICAL/BEST%20PRACTICE/36491_FOR_BIOMASS_1.PDFhttp://www.energysavingtrust.org.uk/domestic/biomasshttp://www.theade.co.uk/medialibrary/2014/10/14/f8e891d8/Llanwddyn%20Biomass%20Case%20Study.pdfhttp://www.thegreenage.co.uk/tech/biomass-boilers-versus-conventional-gas-boilers/.

Whilst the initial cost of a biomass boiler is more than that of conventional gas or oil-fired boilers, the running costs per kWh can be lower compared to non-renewable sources (Berkovic-Subic et al., 2014). A study by Chau et al. (2009) found that biomass boilers for the commercial production of food in greenhouses were seven times more expensive for a 5 MW plant than the equivalent natural gas boilers. However, the same study also concluded that a biomass boiler saved 3000 tonnes of CO₂ compared to a natural gas boiler.

On average, a wood chip burner has around 70% efficiency whilst a pellet burner has an efficiency of around 80% for both residential and commercial (Hebensteit et al., 2014). According to Hebensteit et al. (2014) the payback time for a wood chip burner is up to 12 years, depending on the flue gas temperature.

Irresponsible, uncontrolled harvesting of timber can cause deforestation leading to soil erosion, loss of biodiversity and eutrophication (http://toxics.usgs.gov/definitions/eutrophication.html; http://study.com/academy/lesson/what-is-eutrophication-definition-causes-effects.html).

Consequently, all large-scale commercial UK biomass boilers have to run using sustainably sourced (FSC accredited) wood, using a variety of wood types (Ofgem, 2014). The UK Government’s Department of Energy and Climate Change (DECC) has provided a 10 p/kWh subsidy for the generation of heat from biomass boilers although this policy is of course subject to change (DECC, 2013). The financial cost of this requirement to use only sustainably sourced timber does seem to mean that only larger boilers for commercial buildings are commercially viable. Smaller boilers (in the 1 MW range) often co-fire biomass and natural gas to give a better rate of return (Saidur et al., 2011). In United Kingdom, biomass is still perceived by some as an evolving technology requiring a substantial upfront investment with an uncertain future financial payback profile.

Wind Turbines

Wind turbines use natural wind movement to generate electricity and first started generating commercial electricity in United Kingdom in 2008 when the technology provided around 1% of the total electricity generation of the country. Generally, the larger the blades on the turbine, the greater the electricity generated and therefore also determining the height of the turbine itself (Lu et al., 2002; https://www.youtube.com/watch?v=qSWm_nprfqE; http://energy.gov/eere/wind/inside-wind-turbine-0; http://www.ifpaenergyconference.com/Wind-Energy.html).

Wind turbines need to be in a position where there are constant and relatively high wind speeds. Their location in United Kingdom has been controversial in terms of noise creation, visual pollution and a claimed adverse effect on residential house prices (Devine-Wright, 2004; Sims et al., 2010).

Because of opposition from the public and local planning authority, many commercial buildings do not have wind turbines.

The 2 MW wind turbine stands 85 m tall with a blade diameter of 71 m and can power up to 1500 homes (Enercon, 2014).

Large-scale wind turbines are defined as greater than 1000 kW (or 1 MW). The 1000 kW and 2000 kW turbines both have a payback of under 5 years, whereas the 3000 kW has a payback of 10 years. This is because the project cost of the turbines increases by £2 million and because the tariff rate drops from 11.86 to 3.23 p/kWh from 1000 and 2000 to 3000 kW respectively (Renewables First, 2014).

Wave and Hydropower

Although not widely used in United Kingdom (producing only 1.8% of UK electricity and 18% of renewable energy), hydropower produces more than 70% of renewable energy worldwide and more than 16% of all electricity generated internationally. The main sources of hydropower are dams, rivers and tides.

Whilst providing an excellent source of emission-free, renewable energy, hydropower from dams has been associated with a number of negative environmental impacts resulting in the building of huge reservoirs necessary including ecosystem damage and loss of land, forced relocation of communities, flooding caused by poor construction or natural disaster and methane emissions from decaying plant material lost underwater (https://en.wikipedia.org/wiki/Hydroelectricity; https://en.wikipedia.org/wiki/Tidal_power).

Anaerobic Digestion

As with hydropower, anaerobic digestion processes whereby gas produced by the breakdown of biodegradable waste materials including food, sewage solids, paper and grass cuttings, is then burnt to produce energy, is not a major source of energy in United Kingdom. However, there are over 300 plants in the country at present with plans to develop over 450 new sites in the future (http://www.nnfcc.co.uk/bioenergy/ad-deployment-report, 2016; https://en.wikipedia.org/wiki/Anaerobic_digestion; http://www.biogas-info.co.uk/resources/biogas-map/).

Conclusion

Although renewable technologies help to reduce CO₂ emissions, to date no studies have been able to determine the full carbon footprint (including sourcing materials, production, transportation and disposal) of the renewable technologies discussed here. It can be concluded, however, that wind turbine technology has the quickest payback time (of around 4 years) but obviously depends on a constant supply of wind and can also be harder to gain planning permission for. CHP works well in commercial buildings and can reduce both financial and environmental costs. Whilst they are efficient sources of energy, biomass boilers don’t work as well on a commercial scale as they rely on large deliveries of sustainable (and therefore expensive) wood or other certified products. PV has been a huge success in United Kingdom despite the reduction in tariffs. It generates an income for the customer and has a relatively quick payback time. Current installations are, however, so new that they may be outdated and relatively inefficient within 10 years as newer renewable energy technologies rapidly evolve.

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