Sustainable Energy-Without the Hot Air

David J. C. MacKay

 

Reflections by Juan A. Morillas – Founder, Share Your Green Design

 

This book was part of the bibliography of an energy course I took at the Centre for Alternative Technology (CAT) in 2017. At the time, energy was a topic I consciously wanted to understand better.

That period had a lasting impact on me. The course, together with this book, didn’t lead to an immediate decision, but it triggered a gradual rethinking of what I wanted to focus on in my work and in my career. It became clear to me that engaging with sustainability required understanding measurable impact.

How this book changed the way I think

What stayed with me most strongly was the relationship between effort and impact. The book made visible how some actions, while well‑intentioned, require significant effort yet result in very small reductions when viewed at the scale of total energy use. At the same time, it showed that the actions that really matter often involve difficult trade‑offs and operate at much larger scales.

This led me to a shift that still guides my work today. Before taking action, it is essential to understand what actually helps to reduce our impact on nature and by how much. Measurement is not something that comes after decisions. It is what allows decisions to be made in the first place.

The book and its approach

Mackay’s book isn’t trying to give one solution. It’s meant to help people clearly measure and compare different energy systems. Energy demand and energy supply are expressed using consistent units, per person, allowing direct comparison between everyday activities (such as transport, heating, or flying) and different energy sources (such as wind, solar, nuclear, or biomass).

By doing this, the book exposes mismatches between demand and supply that are often hidden when discussions rely on aggregated figures or qualitative language. It demonstrates that any solution capable of making a meaningful difference must operate at a scale comparable to the problem it addresses.

Personal and professional impact

The impact of the book became clear gradually. The same questions kept coming up in my work:

• How big is the impact?
• What’s the scale?
• Are we putting effort into the things that actually matter?

I wanted to focus on sustainable design in the sense that its performance could be measured, compared, and questioned. That way of thinking eventually led, in 2021, to the founding of Share Your Green Design.

The platform began as a small initiative with a clear intention. To create a place where professionals could share data, methods, and evidence, rather than opinions. The connection to this book is direct, even if it took time to materialise.

Why it remains a reference

This book is still a reference for me today. Not because its numbers replace current data, but because its framework remains relevant. It continues to inform how I evaluate sustainability claims, design decisions, and proposed strategies.

Whenever I step back and ask whether something is worth pursuing, the questions it introduced are still there:

• Is the impact measurable?
• Is the scale appropriate?
• Is the effort aligned with the outcome?

This book had a lasting influence on how I think and work. It helped me establish a clear priority: if the goal is to reduce our impact on nature, understanding that impact quantitatively is a prerequisite for meaningful action.

Juan A. Morillas

 

 

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