6 Improve: low carbon energy supply
Low carbon energy supply options for buildings include renewable energy options (solar PV, solar hot water, solid biomass and biogas) and more efficient heating technology (heat pumps, efficient boilers and CHP).
6.1 Renewable energy sources
Lower-carbon energy sources applicable for the urban built environment include the use of solar PV panels, solar hot water panels, heat pumps, combined heat and power ( CHP), solid biomass and biogas.
These low carbon energy sources can offer air quality benefits by displacing emissions from fossil fuel combustion (apart from solid biomass - see below). These air quality benefits can have wider reaching distributional impacts, with research (Boyce and Pastor, 2012) indicating that lower income and minority groups are more likely to live next to polluting point sources such as fossil fuel power stations. There is also the potential to improve future energy security by reducing dependence on imported energy sources, and to avoid adverse side effects associated with fossil fuel extraction, such as the landscape impacts of opencast coal mining, the risk of oil spills, and emissions from gas flaring.
Most energy supply technologies have some potential adverse side-effects. Solar PV panels use rare metals and there is a need to better understand the sourcing of materials for use in solar panels including ways to minimise environmental impacts through reuse and recycling initiatives (Smith et al., 2016).
Although solar panels and solar walls require a high capital investment, the low running costs mean that there is potential for fuel poverty reduction benefits even in Scotland, and a detailed analysis of this potential in Dundee has been undertaken (Andreadis et al., 2013). The study suggested that city level solar installation programmes could play a key role in reducing fuel poverty at an acceptable cost.
Air and ground source heat pumps are covered by UK's Renewable Heat Incentive. By 2050, the embedded carbon could be reduced by 32% when comparing heat pump systems with gas boilers (Gupta & Irving, 2014)  . However, as their operation requires electricity, heat pumps often lead to an increase in electricity consumption and therefore the extent to which emissions are reduced depends on how 'clean' is the source of electricity (Onyango, et al., 2016). One promising solution is the combination of heat pumps with thermal energy storage which would allow heat demand to be shifted to off peak time or times of renewable electricity surplus (Renaldi, et al., 2016). By integrating thermal energy storage and time-of-use tariffs, the operational costs of heat pump systems will decline and, in combination with the Renewable Heat Incentive, the system will become cost competitive with conventional systems (Renaldi, et al., 2016).
In the rural Scottish context, there is evidence on the contribution from woody biomass for private space and water heating in North East Scotland. This is a relatively low-cost energy source that can help to address the impact of rising energy prices, help to address fuel poverty (Feliciano et al., 2014) and improve energy security. Potential adverse side effects include that for solid biomass, there can be an increase in particulate and nitrogen oxides emissions if it is replacing gas. However, there are net benefits if replacing coal or oil (Environmental Protection UK, 2013), depending on the technology used. Focussing on off gas-grid uptake, i.e. replacing coal or oil fired systems, will also tend to avoid uptake in urban air quality hotspots.
The introduction of the heat planning law, whereby developers of major sources of waste heat are required to install infrastructure to capture and deliver it to local homes and businesses, will deliver benefits including reducing the ecological impacts of dumping waste heat into natural environments (Daly and Farley, 2011), and encouraging the co-location of housing and employment which will reduce transport impacts.
The quantification of air quality aspects is covered in Chapter 7. In terms of wider impacts there is comparatively limited consideration in the co-benefits literature, however, Energy system modelling could help assess the benefits of diversified energy supplies and the cost of using 'fluctuating' sources (Smith et al., 2016).
Email: Debbie Sagar