The theoretical maximum is that of a lithium-air battery, where people have demonstrated 1600 Wh/kg in the lab, but they are not rechargeable. The best we have on the prototype stage in laboratories is around 400 Wh/kg, but those last less than a hundred cycles. In terms of energy per weight, the best we have commercially is NCA batteries at 220 Wh/kg. If you look at the cool improvement graphs shown by battery manufacturers, it's always kWh per dollar that is improving. And that is way beyond even the most optimistic estimates of battery technology development. Having batteries small and light enough for practical large container ships, or transatlantic aircraft, would literally mean reducing the battery in a Tesla down to the size of two gallons of milk. So while David does make a good point (I think the book, overall, is excellent and I recommend it frequently), it also overstates significantly the energy required from renewables in the UK. It's also exceedingly unlikely that we'd use solar power in the UK to create fuels for aircraft or ships. Likewise his heating section doesn't take into account energy saving measures and it doesn't account for heating from heat pumps. An average electric car today might get 3 miles/kWh (4.8km/kWh) - as there's no highly inefficient internal combustion engine involved. For example, his 'Cars' section calculates 40kWh/day/person - or 0.8 kWh/km (1.25 km/kWh). His book also doesn't really take into account efficiency savings. In fact, last year the UK alone generated 11.77 TWh - which is about what the entire world generated in 2009 when the book was written. The amount of energy he's talking about - around 1200 TWh - is now only 1.4 times all the photovoltaics in the world.

He makes assumptions like 10% efficient panels (panels today are probably 18-22% efficient) and says that the required solar power would be '100 times all the photovoltaics in the whole world'. Just re-reading the part about solar panels from the perspective of 2021 is quite eye-opening. David MacKay's book is great, but it was written in 2009.

Cen tech battery charger