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Comment by sandworm101 | Hacker News Reader

Great ideas if you are dead against batteries, but there are massive downsides. Batteries are not evil or expensive, at least if you go with traditional lead-acid ones. They are a thousand times more reliable and efficient than compressed air storage. Compressed air storage has many dangers, from explosions (metal fatigue) to fire (compressing gas creates heat).

The best and most reliable method of non-battery storage of energy is the traditional water tower. It used to be standard practice for buildings to maintain water storage tanks on their roofs. Mate a water tank with some solar panels and you can create an energy storage system without heat, high pressures, chemicals, high voltage or even moving parts (the pump has only one moving part).

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Pumped hydro storage is great. The difference between it and batteries is that batteries can be constructed off site by a third party and then transported to your location.

Water towers have to be built on site, which can be difficult. Not to mention, to get appreciable storage, you have to build a really tall tower or a really big one. This is difficult too. Especially if you are in a location where the soil shifts or you get high winds. Because now your tower has to survive the elements.

There is definitely a strong case against water towers for distributed energy storage.

Conversion to or from electrical power is one option, but an elevated water storage (tower or simply up hill) reduces the need for larger water pumps. It means you don't have to run your well during dark hours. So it saves on electric use rather than provide actual electricity.

Why not dig a pit? You can even load a big mass on top of the water for extra potential energy.

Similar system from the age of steam:

https://youtu.be/aKmi0PN7LxM

I'm not dead against batteries, we've got an off grid cabin that runs on 4 6v Trojan lead acid batteries and they are great.

However there's something about living off grid that makes one want to simplify, and batteries are one of the big, expensive, and limited life time components of a solar system. If you can reduce the load on, and the required capacity of your battery bank, then you have improved reliability significantly.

As you say, pumped hydro is certainly a great storage system if the situation permits. It just takes a very large storage system to store as much as batteries. If you have a pond or lake and an easy supply of water it would certainly be my choice.

> batteries are one of the big, expensive, and limited life time components of a solar system

On the other hand, so is a big chest freezer!

A lot of the household energy load is either heating (water, cooking, surviving winter) or cooling (fridge, feeezer, surviving summer). You don't have to be dead against batteries to see a lot of potential in using thermal energy storage to decouple renewables energy sources from energy use.

Lead-acid batteries die after only a few hundred cycles.

No they don't. Case in point, I live off grid with a 24v system composed of 2v lead acid marine batteries. They were 2 years old when I got them and have put them through over 1000 days of use since.

Mind you, I don't discharge the system past 23.5v ever, and I check my electrolyte levels weekly adding distilled water as needed, but lead acid are cheap, effective, long lasting, and recyclable with minimal effort. The only thing against them is maintenance, and they are big and heavy. My house doesn't seem to care.

I appreciate the anecdata, but do you have an actual cycle count on the batteries? It's not clear to a non-expert (me) how you've disproven the GP.

The cycles you get is dependent on the depth of discharge (and more).

See the chart in [0], where 100% discharge nets 200 cycles, 50% gives you ~500, 30% is ~1200. One would expect that if you discharge 50%, thats half a cycle, and therefore get 400 cycles, but in reality you get 500.

[0]: https://pvcdrom.pveducation.org/BATTERY/charlead.htm

Lead batteries can be rejuvenated, with a device mostly called "A pulser/desulfator/refresher" Short story: I had a completely dead 12V car battery. It was at 0V and would not accept a charge at all. Connected it to a bench power supply and slowly cranked the voltage up until it charged with a couple mA @ 30V. Slowly it accepted more amps so I constantly dialed the voltage down until it was charging at 14volts. Then hooked up the desulfator and left it for couple of weeks. Every other day checked voltage and hooked it up to a charger for couple hours. After that it was perfectly able to start my car(oldtimer) again.

This kind of work requires a supply of power though, which is something of a catch 22 if the battery you are rejuvenating is your power source.

That said, this thread has descended from a comment about apocalyptic scenario planning and this general principle of maintaining batteries makes sense. Learning how to build and repair lead acid batteries doesn't seem to be beyond the realms of possibility.

You always have a power source if you are using a battery long term. Be it a solar panel, generator, mains or some other turbine.

A good MPPT charge controller will handle stepping up and down the voltage as need to provide optimum life.

I believe desulfating is based on trickle charging, so doing it via just solar might work. And if we're talking apocalypse, it'd be good to have a secondary source of power like something that can run off of organic material such as wood gas.

The desulfator i speak about is powered by the 12V battery itself. It's a small box with just get hooked up to positive and negative. Technology differs but basically it charges a capacitor and produces very short high voltage charging pulses that break the formed sulfur crystals. Yes, this will deplete the battery if it's not charged otherwise.

If you don't discharge below ~60% of system capacity, use flooded cells, and keep up with balancing charges, etc, you should be able to squeeze ~1,000 cycles out of a deep cycle/marine lead acid battery. A partial discharge only counts as a partial cycle, so you're within the expected range by your description.

https://batteryuniversity.com/learn/archive/advancements_in_...

For comparison: A Tesla Powerwall v1 has a warranty for 5000 cycles.

At well above the cost of lead acid batteries. And the Tesla battery pack is very difficult to recycle. Recycle companies will pay for old lead acid batteries. They are of value even when dead.

I disagree with the 1000 cycles concept. Modern battery controllers are very good at preserving oldschool batteries. I don't see every off-grid house replacing their batteries every few years, just as I don't see automotive or marine batteries die so quickly.

Lead acid batteries also recycle in to reloaded bullets. You can use subsonic loads with just cast lead or swag the bullets into casings and get into higher performance hunting loads.

Assuming off grid prepper mentality is being used.

I fully expect to get another 5 years out of this set. As long as we get back to float the next day, capacity diminishing doesn't really matter for a house. That's more a function of sizing the input and output to the system than battery capacity.

Out of curiosity, technical question: do you use catalytic caps on the cells to recover water from the hydrogen outgassing?

>the Tesla battery pack is very difficult to recycle.

Are you sure about this? Lead-acid batteries are highly recyclable, but lithium cells are straightforward to recycle, too. I know that Tesla has a recycling center set up at their gigafactory.

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