[rtkwe]

Correct it's massively energy intensive to filter the salt out the newest best ideas still use ~2 KWh/m3 of water and that's a lab system in perdue that batches the process instead of having it run continuously which is why current RO desalination systems require so much energy.

[masklinn]

For a real world comparison, the Perth desalination plant claims ~4kWh/m3.

[smm11]

California pays other states to take its excess solar energy. Power for a project like this isn't the issue, actually building the system is the issue.

[JumpCrisscross]

> California pays other states to take its excess solar energy

Intermittently. Essential services like water (with expensive fixed costs) aren’t a good fit for absorbing variable supply.

> Power for a project like this isn't the issue

California has the country’s most expensive power [1] in part due to policymakers constantly assuming it’s free.

[1] https://www.electricchoice.com/electricity-prices-by-state/

[rtkwe]

They wouldn't if you switched just Urban water use from natural sources to desalination. To do that you need to replace the ~5 million acre feet of water, ~6,167,400,000 m3, that goes into the Urban bucket which is all of the water used to keep people alive, clean, and all industrial uses of water. [0] That comes to ~ 12BkWh of energy needed to scale up batched reverse osmosis to take over just the life and job required water needs which is about 25% of the total solar power generated in all of 2025 via grid-scale solar farms. CA does export some during the day due to excess solar but is still a net importer of power.

[0] p2 of https://cwc.ca.gov/-/media/CWC-Website/Files/Documents/2019/...

[bombcar]

Those are the numbers I was looking for - that means that (ignoring build-out costs) total desalination for CA would be on the order of 10% of the 3 gorges dam yearly output (max).

[rtkwe]

Using a system that's currently in a lab scale only and ignoring other energy costs like moving the water to the plant, mixing the briny output back down to acceptable levels, and then pressurizing the system to replace the gravity fed design it currently uses.

For a rough estimate for replacing agricultural uses too ~6x that urban figure at least then weep at the amount of pumps you'd need to bring that water up and inland to the farm lands from the coast. At least for replacing urban use most of the population lives on/near the coast where the water would be produced.

[bombcar]

Farm use is by far the biggest, but "taking" water from the inland empire and dragging it to LA is also a cost.

But all of this is firmly in the "we could do it if we really wanted/needed to" not "needs more energy than the sun will produce in its lifetime".

[zahlman]

> it's massively energy intensive to filter the salt out the newest best ideas still use ~2 KWh/m3 of water

Am I alone in thinking that doesn't sound like a lot? That would be something on the order of 10% of what major cities charge for tap water?

[detourdog]

A scaled down perspective is….

The most efficient commercial desalinator for boats is 32 Watts a gallon.

[fhdkweig]

Do you mean 32 Watt-hours / gallon?

[detourdog]

Hard to say. The spec sheet calls out 4 Amps for the 12 Volt system or 32 Watts for a single gallon.

[fhdkweig]

If it includes the time it takes to produce that gallon, there would be enough information to do the energy calculation.

[detourdog]

I guess it would be 48W/h as it makes about 1.5 gallons an hour.

[rtkwe]

Which to scale back up and complete the comparison to the state of the art in lab "batch reverse osmosis" systems I was originally talking about that's ~12.7 kWh/m3.