$300/kWh for home storage is readily available.
E.g. https://signaturesolar.com/eg4-ll-lithium-battery-24v-200ah/
E.g. https://signaturesolar.com/eg4-ll-lithium-battery-24v-200ah/
[Citation needed]
Typically lead acid lifespan is around 10x less than lifepo4, even if kept within spec.
But in practice it's hard to keep them in spec too, shit sulphates immediately when you look at it wrong.
LiFePo is maybe 10x the lifespan of a normal Lead-Acid battery, if you're cycling it several times a day. A car battery for instance will not do very well in this test. But I'm talking about deep cycle Lead-Acid batteries, cycled every day or couple of days down to 70% capacity (so using 30%). This is a fairly typical workload if you're (for instance) using it as a backup for solar panels. Under those circumstances, the LiFePo battery will die from time elapsed probably about the same time as or maybe even earlier than the Lead-Acid battery dies from cycle count.
Still, I would've expected that ever increasing self discharge would've made them far worse in comparison since it gets worse as the batteries age and you can end up losing major amounts of charge to it. Not sure if that's not as much of a problem for flooded as it is for AGM but I haven't heard it mentioned in the rundown.
In that case, they cost about $413/effective kWh.
In this situation, a Lead-Acid will have the full capacity that you bought, but will age like you're using 30% of the capacity most of the time.
I didn't know they could last as long as LiFePo though. Is this really true?
If this is true, why don't we just use more lead-acid batteries then?
LiFePo has a very high maximum cycle count. But after ten years, they'll die anyway. The only way that you can actually achieve a cycle count as high as the specification says is if you're cycling the battery two or three times a day, which I can believe if you're doing grid-levelling, but not if you're providing backup for your solar panels.
For lead-acid batteries, be aware of the difference between normal lead-acid, which are optimised for standby operation, and deep-cycle lead-acid, which are optimised for long life under regular cycling. Normal lead-acid batteries will die very quickly if cycled - they're designed to be charged all the time, and drawn on for very short period, like a car battery or a UPS.
Deep-cycle lead-acid batteries age by cycling, in contrast to LiFePo, which age by elapsed time. Their maximum cycle count is much lower than LiFePo, but if you're cycling them every couple of days, like in an off-grid solar project, and you're avoiding draining them below around 40%, then they can last 10 years.
So, if you want to cycle your batteries two or three times a day, then LiFePo is going to last a lot longer than Lead-Acid. But if you're cycling every couple of days and limiting the drain, then they can last about the same amount of time. It depends on the usage.
What helps with Lead-Acid is because it is that much cheaper than LiFePo, you can buy a larger capacity Lead-Acid battery for the same or less money, and then for the same performance requirements that larger battery will be drained less and at a lower rate, and therefore be less stressed and even last longer.
I think we don't use Lead-Acid as much as we do for several reasons:
1. Lead-Acid batteries have a reputation of flaking on us after a depressingly short amount of time. But that reputation has been earned from normal Lead-Acid batteries, not deep cycle ones.
2. People get scared by the lead in them, and how lead is toxic and we should be stopping using lead in everything. But really, lead in these batteries is not a danger to us, and Lead-Acid batteries are one of the best recycling success stories in the world. That lead isn't generally getting out into the environment. LiFePo batteries are much harder to recycle.
3. Electricians recommend installing expensive stuff, because then they get a bigger commission.
4. Lead-Acid batteries are commodities, but LiFePo batteries are new and exciting, and have aggressive marketing.
5. Lead-Acid are bigger and heavier for the same capacity than LiFePo. So, a LiFePo installation is going to look prettier in a nice consumer unit and be easier to install. They're heavy enough as it is.
citation needed
Perhaps 200kWh is a bit exaggerated. And yes you also need a good quality inverter for your home that synchronizes with the net, but I actually don't believe this to be expensive high tech...
Ideally I wouldn't want to put the energy I generate with solar, wind or differently back into the power net. In my country you basically give that away for free. There are reasons for that, but the most efficient way would be to use the energy yourself as much as possible.
Sure, 5kWH is enough to soften peaks and there could already be huge benefit to this. But a bit more capacity would be really nice to really safe the energy of sunny days. Reminds me if disappointing USPs that let me play Tetris for an additional 7-8 minutes before I feel like civilization has broken down completely until power comes back.
But it is only ever meaningful if you have the respective fixed voltage and it often make sense for a batteries to quickly calculate how long they should last if you know how much ampere a device draws. It could also become a sensible metric if we always talk about 120V/240V for general household appliances of course.
As a chemical battery discharges, the voltage drops, so at the same load in amps you get less watts later.
Your numbers are a little bit off though. I just googled some power bank (which is supposedly better than smartphone). It claims to provide 20 000 mAh at 5V. So it's 20 Ah at 5V or 100 Wh. I think most smartphones are around 10-20 Wh. Far from 5 kWh. But this discrepancy was already noted in other comments.