Potential and Impact of Incorporating Roof Photovoltaic to Enhance Environmental Sustainability of Historic English Churches in the United Kingdom

The Church of England (CofE) is responding to climate change by taking measures to reduce their CO2 footprint under its flagship programme -‘Shrinking the Footprint’, to facilitate the CO2 emission reduction target of 80 % by 2050. Meeting this target will require both energy efficiency measures and zero carbon energy generation of which solar PV technology is a frontrunner as it has a substantially lower CO2 footprint than grid’s electricity, with no moving parts, low maintenance and a long service life. Conventional church roofs built along the East-West axis offer the ideal pitches and orientation for collecting solar energy. However, within the CofE’s vast estate of over 15,000 church buildings, 78 % of these buildings are listed and hence care must be taken to protect the building fabric. With this context in mind, this study identifies the benefits and concerns associated with the application of rooftop solar PV on historic English Churches and evaluates viable technologies currently available. The specific design and procedural requirements have been investigated and the process map of the implementation methodology established and illustrated through a case study of an existing church. Results showed that rooftop solar PV system has the potential to reduce the GHG emissions substantially, ranging between 75 %–84 % for electricity and between 20 %–27 % for gas based on the current demand and the choice of technology option. Findings on the issues, design options and life cycle environmental impacts are analysed with discussion and recommendation of future adaptation at a national level.


Background
The Church of England's church buildings form the nation's largest 'estate' of built heritage encompassing 45 % of the grade-I listed buildings in England. Of the 15,779 churches, 78 % are listed [1] The Church of England (CofE) recognizes the significant role it could play in building a more sustainable future and is evaluating environmentally friendly approaches toward every day activities [2].
Online energy audit by CofE collected from 430 CofE buildings across England in 2012/13 indicated the total annual carbon emissions (CO 2 e) from energy use in the Church estate (including churches and other buildings) was between 608,706 and 1,013,490 tonnes of which nearly 50 % was used by churches, 18 % by offices and 15 % by schools. [3]. The Church of England aims to build on its many policies and projects as part of the global effort to tackle climate change, leading with its flagship programme Shrinking the Footprint, which committed CofE to a carbon reduction target of 80 % by 2050, with an interim target of 42 % by 2020 [4].
To radically improve the sustainability of Historic English Churches, a transformation in the way church buildings are maintained and operated is required. The sources of low carbon or renewable energy most likely to be employed by churches are bio-fuels, ground source heat pumps, or electricity generated by solar photovoltaic cells (PV) [5]. Solar PV has the greatest potential with its very low life cycle energy payback time and carbon footprint. In a benefit unforeseen by medieval architects, the traditional east-west church structure, with the altar at the east end of the nave that forms a long pitched south-facing roof is ideal for capturing sunlight. Despite it being accepted that the CO 2 emission reduction goal can be achieved by the application of on-site solar PV systems, with sporadic examples already exist, there is no in-depth study to demonstrate how such a potential resource can be practically and widely utilized. This study therefore seeks to investigate and establish the process of installing roof PV systems in historic churches and the associated economic, environmental and heritage implications with the aim that the methodology developed could be adopted for wider applications.

Sustainability and the Historic Environment
Historic churches are a trademark of the English town and countryside. These historic buildings are material expressions which have significance to present and future generations, and form part of the tangible cultural heritage [6]. An important factor in the preservation of historic buildings in the present context is sustainability. Schoor, et al [7] appropriately state that preserving historic buildings does not always align with the ambition to promote sustainability in the built environment. The aesthetic considerations and structural integrity of historic buildings have a direct impact of the retrofit and sustainability measures. Scognamiglio, et al. [8] reiterate that photovoltaics offer a huge potential in terms of cost and CO 2 savings, but their application on historic buildings is still a critical issue, since the coordination between photovoltaics and historical buildings is perceived to be striking from the "aesthetical" point of view. Longo et al. [9] argue that the idea of protecting and preserving historic buildings in its entirety is only philosophical, however, not recognizing the value of their preservation is injudicious. Visual impact and conservation issues play an important role in choosing the scenario which provides a well-balanced solution for improving energy efficiency likely to be adopted [10].
Retrofitting a historic church roof with PV for solar energy generation cannot ignore the associated conservation issues. Relatively few attempts have been made on methods for decision making to deal with the problem of balancing energy retrofits and cultural heritage values in historic buildings. However, the EU funded project Energy Efficiency for EU Historic Urban Districts' Sustainability (EFFESUS) is in the process of developing a software tool, with six impact assessment modules to support such location-specific decision-making process for the retrofit of historic buildings and districts. The methodology involves (a) heritage significance evaluation and (b) heritage impact definitions, which are compared using a heritage balancing process.
Designated heritage assets in the UK are protected by a range of planning laws and acts. Various guidelines, such as English Heritage Guidance and local planning guidelines to provide a defined framework for the preservation, rehabilitation, restoration, and reconstruction of historic properties. Listed Building Consent is required for installing solar PV on listed buildings [11]. In addition, the CofE buildings require permission from the Consistory Court of the Diocese, called a Faculty, and is preceded by an application to the Diocesan Advisory Committee (DAC) [12].
It can be claimed that not installing PV will have the least impact on Historic English Churches, but this is not a long-term solution and will reduce the ecological value of the building. More importantly, in the long term, the economic and functional value of the building may reduce which fundamentally impacts its heritage significance. A pragmatic approach is therefore required in retrofit policies for historic buildings, as we are approaching a turning point where marginal aesthetic or traditional reasoning may have to give way to the current environmental obligations.

PV technologies
The key component of a PV system is the PV panels that convert sunlight into electricity. The associated components include: mounting/racking structures, inverter that converts DC into AC; meters and optional energy storage devices such as a battery unit or hot water store. Technical and physical characteristics of PV modules have major influence on the system acceptance. Their key characteristics are summarised in the following Table 1. Organic PV Developing technology that uses conductive organic polymers or small organic molecules for light absorption and charge transport. It has the benefits of low cost, high throughput manufacturing, simple in fabrication and installation. Not readily available in the UK

Implementation methodology
The implementation of PV system on roofs CofE churches is investigated and the process is divided into three key stages i) Concept and Feasibility, ii) Detailed Design Approvals and Finance and iii) Construction and Handover, as shown in the flow chart in Figure 1. Brief comments with reference to the relevant code in the chart are outlined in Table 2. Table 2. Key tasks of the processes in the methodology flow chart in Figure 2 Code Process Key tasks C1 Notify DAC Notify Diocese Advisory Committee (DAC) and follow their advice notes before undertaking any major or minor works in church buildings. C2 Advice

Results & Discussion
Summary of main results of the analysis is shown in Table 3 with highlights of the key findings explained in the following sections. Table 3. Summary of Performance of Techno-Commercially Viable Options Note: The GHG Emissions Impact of battery storage has not been considered in the above analysis 2.1.1. Consumption Pattern of Electricity and gas. The overall consumption pattern of electricity in the Vicarage is more or less the same in all the four seasons, with a varying degree of peak load ranging from a maximum of 5 kW in winter to a minimum of 3 kW in summer. The consumption pattern in Scenario1 and Scenario 2 is also more or less the same, wherein the consumption is concentrated in two parts of the day, from 09:00-14:00 and then again between 16:00-21:00. The consumption pattern in Scenario 3 is drastically different due of conversion of the Parish Hall into a café that operates the entire day from 7:00, peaks at around 11:00 and then gradually reduces to zero at around 23:00. As expected the consumption of gas is highest during winter (62 %), followed by spring (24 %), and with autumn and summer being more or less the same (around 7% each).

Broad Techno-Commercial Viability.
The preliminary design of the four options, revealed that Organic PV resulted in annual generation of around 9 MWh as compared to 60 MWh, 47 MWh and 36 MWh for Mono Crystalline, Thin Film CdTe and BIPV Slate/Tile respectively. Such low generation from Organic PV would render it economically unviable at the current levels of technology and efficiency.

Viability of
Storage. An analysis of the hourly consumption pattern of electricity across seasons and across the three scenarios, highlighted that there is a substantial consumption of electricity during evening hours whereas the generation from the PV system would be during the day. Battery storage would be useful in ensuring higher levels of self-consumption inside the church complex. Further, there is significant heating requirement in spring and winter which will enable the usage of electricity for heating purposes. However, to ensure storage through heat, proper insulation must be provided.

Conclusions and future work
It can be concluded from this study that the churches in England (15,779 in number) could potentially generate significant amount of clean solar electricity annually, resulting in a substantial reduction in GHG emissions. Out of the 15,779 CofE churches, approximately 12,600 are listed buildings that are protected by public law and require permissions from various authorities for installation of rooftop solar PV systems. Thus, the proposed rooftop PV solutions need to address the visual impact and heritage concerns that listed buildings present.
There are currently three techno-commercially feasible options for rooftop PV systems. If these options are ranked from 1 to 3 based on the three identified criteria comprising economic benefit, GHG emissions and visual impact ( Figure 2) & heritage considerations, would lead to the conclusions tabulated in table 3.
It can also be concluded that battery storage coupled with the rooftop PV system would provide significant value to churches by increasing the amount of self-consumption from the electricity generated from the PV system, which can be used both for powering the electric appliances and also for water and space heating. From the case study conducted at the St. Barnabas Church at Hove, it can be concluded that rooftop solar PV system has the potential to reduce the GHG emissions substantially, ranging between 75 %-84 % for electricity and between 20 %-27 % for gas based on the current demand, depending on the choice of one of the three technology options. Based on the consumption profile of St. Barnabas Church at Hove and the generation profiles emanating from the application of the three technologies, it may be concluded that connectivity with the grid is required to ensure flexibility of operation and to meet the demand at all point in time. Going totally off-grid will require an extremely expensive storage option which will not be technocommercially feasible. Current work builds the foundation for evaluating the potential and practical implementation of PV systems on church roofs to improve the sustainability of such buildings. Ongoing work is underway to establish the potential impact of PV implementation on all viable CofE church roofs and to develop demonstrations to showcase such viability.