Heat in buildings strategy: strategic environmental assessment

2. Heating Scotland’s homes and buildings

2.1 Introduction

2.1.1 Buildings account for around 21% of Scotland’s total greenhouse gas emissions^[9]. Around 81% of homes^[10] and approximately 30% of non- domestic buildings^[11] using mains gas for heating. Non-domestic mains gas accounts for a greater proportion of energy use in this sector. Currently gas supplied via the mains gas network is predominantly natural gas, a fossil fuel composed mainly of methane.

2.2 Strategically Important energy efficiency measures and heat technologies ready for deployment

2.2.1 At present the main strategically important energy efficiency and low and zero emissions heat technologies that are ready for deployment in Scotland and which can make a meaningful contribution towards targets include building energy efficiency measures, heat pumps and connection to heat networks.

Energy Efficiency Measures

2.2.2 Energy efficiency measures make buildings easier to keep warm (reducing the demand for heat), and can reduce the cost of achieving thermal comfort. ‘Fabric first’ energy measures include draught-proofing (e.g. blocking or sealing gaps around windows, doors, and skirting boards); loft, floor and wall insulation; insulating thermal stores and heating pipes; and improving window glazing.

2.2.3 A minimum level of energy efficiency is an important prerequisite to supporting the rollout of zero and low emission heating for buildings across all technology scenarios.

Heat Pumps and Heat Networks

2.2.4 The key zero and low-emissions heating solutions available today for Scotland are heat pumps and heat networks.

2.2.5 Heat pumps provide an efficient and effective way to use electricity to heat buildings because they use electricity to draw a larger amount of heat from either air, ground or water. Heat pumps can supply heat to individual buildings or can supply a heat network.

2.2.6 Heat pumps can also be highly effective in most buildings when they are combined with appropriate energy efficiency measures. Notwithstanding this, their characteristics mean that they are not suitable for all buildings. For example, air source heat pumps require a place outside the home where an external unit can be fitted to a wall or placed on the ground, including space around it to ensure the flow of air. The size of heat pump will also vary depending on the home’s heat demand.

2.2.7 Heat networks can heat our homes and other buildings by distributing hot water or steam through insulated pipes. The thermal energy that heats the water or steam can come from a variety of low or zero emissions sources including large-scale heat pumps, solar energy, biomass boilers, and heat captured from industrial processes such as at whisky distilleries. Estimates suggest that there were almost 30,000 homes connected to district or communal heat networks in Scotland at the end of 2018.^[12] They have the potential to not only remove emissions from heating buildings but at the same time provide real consumer benefits.

2.2.8 The Committee on Climate Change has recommended that heat networks should form a significant part of Scotland’s future heat supply. Heat networks can contribute to emissions reduction because they are source neutral, opening up opportunities to make use of low and zero emissions heat sources that otherwise could not be used such as low and zero emissions sources such as waste industrial heat and water.. Heat networks can also deliver heat to buildings that have limited alternative options (such as flats). Thermal storage is likely to play an important role in the operation of heat networks, helping to optimise operation and potentially reduce running costs.

2.3 Other heat technologies (Hydrogen and Bioenergy)

2.3.1 In the longer term, hydrogen has a potential role in decarbonising heat in buildings.

2.3.2 In broad terms there are three types of hydrogen production. So called ‘Grey’ Hydrogen is produced from the reforming of natural gas and this process produces both hydrogen and carbon dioxide. Blue (or low-carbon) Hydrogen is produced in the same way as grey hydrogen but the process is aligned with CCS systems which capture most of the CO2 produced, preventing it from entering the atmosphere and storing it safely in deep geological formations. Green Hydrogen is produced from the electrolysis of water, a process which splits water into its constituent parts of hydrogen and oxygen. When renewably sourced electricity is used, this process is completely green.^[13]

2.3.3 The technology to produce hydrogen is well understood and in the longer term, hydrogen could also be used to displace the direct use of methane in the heating of our homes and the provision of heat and industrial processes in our heavy industries. This is because domestic central heating systems and industrial applications can potentially be adapted to use hydrogen, making the conversion of existing gas networks to hydrogen and ‘greening the gas grid’ a serious consideration. ^[14]

2.3.4 Should the required demonstration and safety case trials prove successful, conversion of parts of the gas network in the longer term to carry 100% hydrogen could play an important role in reducing emissions from buildings to very near zero. Hydrogen may be particularly appropriate in certain locations, where there is local supply (for example from abundant renewable electricity) or where industrial demand creates economies of scale. Further, additional constraints including a repurposing of the gas network and replacement of household appliances so they are hydrogen ready, meaning that decarbonised gas is unlikely to play a large part in meeting our emissions reduction before 2030.

2.3.5 Bioenergy can be generated and used in a wide range of ways. Solid forms of biomass (such as forestry waste or energy crops) can be used as feedstock for combustion to produce heat. Bioenergy can be used to produce biomethane for injection into the gas grid, or further processed into liquid fuels. Certain types of bioenergy, such as food waste, may be more suitable for anaerobic digestion to produce biogas, which can then be combusted to produce heat and/or power or upgraded to biomethane.^[15] .

2.3.6 In line with advice from the UK’s Climate Change Committee^[16] it is considered that bioenergy will have only a limited role in the future of low and zero emissions heating. The Committee recommended that bioenergy resources should only be used where their carbon reduction impact is maximised or where alternative options are not available.