I was sad to learn last month that David MacKay had died of cancer. He was just 48 years old. David was well known among those who study clean energy, and he had a big influence on a lot of people, including me. But if you don’t follow the issue closely, you may not have heard of him. So I want to take a minute to tell you about David and his work.

I discovered David through his eye-opening book Sustainable Energy—Without the Hot Air. He was a physicist at Cambridge University, and his goal was to, as he put it, cut “UK emissions of twaddle” by helping people think more rigorously and numerically about clean energy. His book doesn’t favor one zero-carbon solution over another. He just shows you how to do the math for yourself, so you can work out the answers to big questions like “how much carbon do cars emit?” and “how much energy can we expect to get from renewable sources?”

Sustainable Energy really shaped my thinking. A few years ago, when I gave a TED talk on energy, I bought 2,000 copies to pass out to everyone in the audience. To this day, if you want to understand the opportunities for clean energy, nothing else comes close. I still go back and re-read parts of it myself.

Revisiting his work will be a bittersweet experience now. I had the pleasure of getting to know David and learning from him. He was always generous with his time, and he was just as thoughtful and unassuming in person as he was in writing. (Although he was a knight, he never went by Sir David.) He also inspired colleagues to take on related topics with the same rigor and sense of fun. One group of Cambridge researchers followed his lead with the excellent Sustainable Materials With Both Eyes Open.

David made Sustainable Energy—Without the Hot Air available as a free download. He also gave a very good TED talk on clean energy. If you are at all interested in the topic, I strongly encourage you to take a look at the book and the talk. You will not find a more generous and engaging guide to energy than David MacKay. I will miss him a lot, but I am grateful that he left behind so much fantastic work. It is a fitting legacy.

Update: This post has been edited to fix an error. David was knighted this year, not years ago.