Understanding Solar Energy

The bit how about incredibly quickly PV has grown is a figurative slap in the face to Vaclav Smil. He had just ten years earlier said PV wasn't going to grow quickly because historically energy replacements took a long time.

https://vaclavsmil.com/wp-content/uploads/2024/10/scientific...

This retrospective on Smil's predictions four years ago is notable:

https://www.quora.com/Is-Vaclav-Smil-right-in-his-criticisms...

"To get 1 PWh/year of electricity you need to install about 450 GW worth of solar panels. You need dozens of years to acomplish such task. Reality check: 3 years in current speed, in the future probably faster."

Indeed, as the thread top link shows in 2024 the world installed 595 GW of PV.

As John Kenneth Galbraith said, "If all else fails, immortality can always be assured by spectacular error."

What people tend to forget is, that coal, oil and gas are all restricted by mining or drilling as the old are consumed, and it gets harder to access new oil wells etc. For PV there is no such limit (only copper basically, but this is recyclable and aluminum can do many tasks.) For batteries, there is lithium (lifepo4) and even that is questionable (sodium batteries) and again there is the potential for recycling. Hence, I do not see anything stopping the exponential growth of PV and batteries.

You are right.

But one misconception I often read is that everyone focuses on batteries. It would make more sense in general to talk about energy storage instead of just batteries. Like Kinetic, chemical, thermal and so on.

Batteries cannot be solely responsible for back-up. You need different types of storage: short term, medium term and long term storage.

There are different concepts for each application. Batteries, compressed air storage, pumped storage, kinetic, thermal storage as well as power-to-X systems are able to absorb the increasing summer power and provide the energy again in the medium term or seasonally shifted.

https://doi.org/10.3929/ethz-b-000445597

There are only three energy storage forms that are relevant for the next decade. All the others looked promising, but the learning curve on batteries has rendered them irrelevant. Your link is from 2020, it is out of date.

The best energy storage form is "final form". Some energy products can be stored. For example if you are using the energy to create heat, you can store heat for use in the future. Heat storage sucks as a way to store energy destined for electricity, but is a great way to store energy destined for use as heat.

The utility of batteries for daily storage is obvious and well proven.

Thirdly, the best annual storage is pumped hydro. It's the cheapest and it can be used pretty much everywhere -- all you need is water at one end of an elevation change and a way to build storage at the other end.

All the other forms that you'd think would fit in between the two are being quickly subsumed by the rapid price drops in battery pricing. The cutover points are rapidly shifting -- batteries are now cheapest for biweekly-ish.

And the primary sources are getting so cheap that overbuilding is an alternative to storage. Rather than storing for the reduced amount of daylight in the winter, just overbuild. More overbuilding and a few days of storage will let you handle a stretch of cloudy, windless days in January. No annual storage required.

> Thirdly, the best annual storage is pumped hydro.

I strongly dispute this. E-fuels like hydrogen would be much superior to PHES for annual storage.

https://x.com/iain_staffell/status/1722544993179504965

Only if we have more than enough renewable energy to spend making hydrogen. Hydrogen storage has a round-trip efficiency of 40%-50%, leading to significant energy losses. Partly by: Electrolysis requires 50-55 kWh to produce 1 kg of hydrogen, which only contains about 40 kWh, resulting in a 20%-30% energy loss upfront. It’s low energy density requires high-pressure or cryogenic storage, increasing costs and energy use, while leakage further reduces efficiency. Limited pipelines and refueling stations make hydrogen adoption costly and complex. Highly flammable hydrogen demands a lot of safety measures adding even more cost and complexity.

At the current exponential growth rate, PV will reach the point of supplying the entire world primary energy demand in a decade and a half.

Yes, hydrogen has low round trip efficiency. But it comes out cheaper than PHES. The "cost of inefficiency" is proportional to the number of charge/discharge cycles. For annual storage, efficiency is 365x less impactful than it is for diurnal storage. What matters for annual storage is capex of storage capacity.

> What matters for annual storage is capex of storage capacity.

Which is exactly why PHES wins the cost comparison for annual storage. Open air water storage is ridiculously cheap compared to hydrogen storage.

I dispute this as well. From what I see, the very best case per kWh cost of just the reservoirs and waterways for PHES is about $10/kWh. Hydrogen stored as compressed gas in solution mined salt caverns would be an order of magnitude cheaper. For storage of liquid e-fuels in tanks, tank capex would be another order of magnitude cheaper still. This assessment is consistent with the link I posted earlier.

If you want something that may compete with hydrogen for annual storage, consider bulk thermal storage (using artificially injected heat, not naturally occurring heat). The thermal time constant of a very large object increases quadratically with radius, if everything is scaled proportionally, and can easily reach many years. This is why geothermal works at all -- there's plenty of heat stored in the near crust ready to be mined.