Review: Net Zero – the past and future role of domestic building energy efficiency

by Henry Irvine, Aether

View the associated event for this review

50 years ago, energy efficiency in the domestic sphere was all about getting more useful energy from lesser quantities of primary energy sources. In more recent decades, the focus has shifted to getting more useful energy for fewer carbon emissions. And now, another slight shift with transformative implications: domestic energy efficiency in a net zero world means having more used energy for less power, with all the power being from decarbonised sources.

The UK government target of net zero by 2050 naturally extends beyond the buildings we live in. However, addressing the greenhouse gas emissions from domestic energy is one of the most significant obstacles to reaching the target. Setting aside the nature of the challenge ahead (likely involving significant changes in all households, all happening in close succession), the magnitude of it (26 million homes in the UK – and rising) can seem daunting. To gain insight into how we may achieve it, historical context and experience – stretching back to a world before climate emergency – is as necessary as it is revealing.

To help us navigate the route from 1970s energy security to 2050 decarbonisation, Professor Tadj Oreszczyn from the UCL Energy Institute was well-placed, with over 30 years of research into building energy efficiency. He presented on Tuesday 21st January at an event organised by the Oxford Energy Network. Throughout the talk, as Professor Oreszczyn wove together a compelling narrative of events and developments, we could explore the wisdom that the failures and successes of the past may bring to the new age of domestic energy efficiency.

Looking back: the UK’s unique path to present

We began in the late 1970s, and more specifically the Low Energy Strategy of 1979, by Gerald Leach. This was formulated in a different era: one prior to climate change where energy security came first. The strategy suggested, for the first time, that growth could continue while energy use reduced. In fact, it envisaged a 2010 with domestic delivered energy halved. To reach these targets, the UK would rely on a very similar suite of technologies that are available today, such as cost-effective insulation, heat pumps and district heating.

However, measurements indicate that change in delivered energy has not transpired as modelled in 1979; instead it now sits at a slightly higher level, having peaked in 2004. The reasons for this discrepancy can only be speculated, in part due to a historical lack of concern in measuring the simplest details of domestic energy efficiency. The advent of smart meters and more sophisticated building stock models should provide useful data sources to address that in future – but to learn from the past, some educated guesses are required.

These educated guesses swept us through a much longer history, ranging from the Great Fire of London and Brick Tax through to successful condensing boiler regulation. Professor Oreszczyn took us through a detailed breakdown of where and why Leach’s models had underestimated, overestimated and accurately projected various elements of delivered energy between 1970 and 2010. As we did so, it was striking how the trend of actual delivered energy reflected factors well beyond the buildings sector – divorce rates, man sheds and global warming all merited our attention.

Modelling uncertainties equally came to the fore. Older homes demand less gas for heating than modelled, while new homes demand more than expected in housing stock models. The diversity in solid brick wall heat loss values, which is not generally captured in models, is believed to be partially culpable for such discrepancies. As the mantra goes: “All models are wrong, some are useful” – and all could surely benefit from grounding in more data.

The assumptions from the modelling are available, which can help to explain the predictions wide of the mark. Where service was underpredicted, for example, the assumption indicates an expectation of widespread district heat networks and heat pumps by 2010. It is perhaps worth dwelling on why this hasn’t happened: perhaps the storage space required for such heating systems is too expensive with floor area now at a premium; or maybe the co-benefits of the technologies have not been made sufficiently clear to persuade consumers. Equally, technological innovation is not always embraced. Just as central heating battled for acceptance over the open fireplace, heat networks and pumps have not attained far-reaching public acceptance yet.

This brings us to a key observation: the technology of domestic energy efficiency has changed little in the last 50 years. Evidence points to glacially slow progress in the sector in this country. If we do see any major changes, beyond the iterative evolution of some technologies, they will likely be in the controls and monitoring systems used. Nevertheless, if net zero is to be achieved, it will be achieved with all the technologies that exist today – and probably in the 1970s too.

Looking forward: the possibilities for net zero

As we aspire to decarbonisation in the net zero age, it is encouraging to see that GHG emissions per capita have nearly halved since 1990. Grid decarbonisation, amongst other developments, can be thanked for this; though so can outsourcing the emissions to other countries. The decreasing trend must continue and accelerate in order to make a ‘fair’ contribution to a 1.5OC world. However, the law of diminishing returns likely applies – meaning future reductions will be increasingly difficult to achieve.

If we have already picked most of the low-hanging fruit in emissions reductions, many building energy efficiency measures represent harder-to-reach coconuts. The changes required for net zero buildings are more complex, less cost effective and perhaps more transformative than the changes that we have become accustomed to (or indeed, have not had to become accustomed to).

A revealing insight into the scale of change required in our national building stock comes from an unexpected source: temperature data. Year-on-year variability in climatic conditions can usually explain the year-on-year peaks and troughs in UK energy consumption. Even more pronounced is seasonal variability – from summer to winter – which can be represented by quarterly data. Indeed, plotting quarterly energy consumption data against temperature reveals that, in winter, buildings can account for over half of all UK energy consumption.

The high peak demand over the winter quarter in particular indicates the challenges we must meet. What hope for net zero by 2050 then? In an attempt to persuade himself that net zero is within the realm of possibility, Professor Oreszczyn conducted a thought experiment.

If everything across all sectors (in transport, industry and buildings) were to be electrified, the UK would need a 29-fold increase in wind power capacity to meet average quarterly national energy demand. This (arguably) does not seem beyond the realm of possibility. Add some measures to reduce demand: efficient electric motors for cars, domestic heat pumps, efficient lights and household appliances and a 20% reduction in heat loss – and it only leaves us requiring a 14-fold increase in wind capacity.

This was not an argument in favour in wind energy; but rather a demonstration that there are many technically feasible, albeit challenging, routes to net zero for the country. The second scenario, for example, would require a trebling in the rate of installation of wind turbines, and widespread installation of heat pumps. Daunting, but perhaps doable – 1 million boilers are replaced per year as it is.

Most importantly, these imagined scenarios should not be taken to confer ease of deployment. Deployment will likely be slow but result in too many changes in rapid succession, all while exceeding all estimates of cost. In what Professor Oreszczyn termed a “Betamax moment”, the exact route taken to net zero in buildings will most certainly not be the best route as we navigate through the complexity of our situation.

Throughout the talk, parallels were drawn to other similar challenges, to illuminate the stage at which building energy efficiency currently sits in the UK. We may be about to undergo a transition in our homes as we have done with our cars, in that the new systems and sophisticated controls that we can expect are far more complicated and perhaps counter-intuitive than, say, our beloved gas boiler. Heat pumps offer a natural illustration in this regard. Equally, as we move away from quick wins to deeper decarbonisation initiatives, the support required may mirror that required for nuclear energy deployment. High up-front and ongoing costs, high chances of unintended consequences in the long-term, a shortage of quality skills, case-by-case variability that necessitates tailoring of solutions – and (maybe) one disaster away from being derailed or critically delayed.

The challenges don’t stop there. The population will rise, with more homes increasing demand for service. Further energy efficiency measures may not be as popular as previously, as we become increasingly comfortable with the heat in our homes. Further measures are also not valued proportionately to their long-term benefits by existing market structures. All of that before even considering the logistics of deployment, which has historically suffered from poor field efficacy. And what if demand for cooling suddenly picks up?

However, the challenges of net zero must not blind us to the crux of the issue. It helps to simplify the problem – as in the thought experiment – and choose a handful of interventions with big impact. The problem here: a sluggish sector emitting significant quantities of greenhouse gas, with a few too many known (and unknown) unknowns to tailor our solutions by building. As for the big impact? No other sector in the UK lends itself so well to big impact interventions, purely on account of its predominance in total emissions. By retracing footsteps to learn lessons from the past, along with closer attention to actual performance, the many possible paths must be explored – and ultimately delivered – for net zero 2050 to become a reality.

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