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1. Lead Acid is far cheaper, though its bigger and heavier than LiFePo. 12V @12Ah is only $35 from a brand-name (https://batteryinthecloud.com/products/ps-12120

1. Lead Acid is far cheaper, though its bigger and heavier than LiFePo. 12V @12Ah is only $35 from a brand-name (https://batteryinthecloud.com/products/ps-12120 https://batteryinthecloud.com/products/ps-12120), and closer to $25 from no-name brands on Amazon. 2. Modules to charge LeadAcid are so cheap, they don't even make them. This specified PS-battery hsa a 13.5V to 13.8V "standby" voltage, meaning that 13.65V from the Solar Panel is all you need to have a UPS. Connect the 13.65V source from the Solar-panels to the + and - leads of the 12V battery, and volia. You get 13.65V when solar is available, and 12V from the battery when the solar cuts off. The end. Isn't that easy? 3. Grid-tie should be similarly easy, though I don't have too much experience with it myself. IMO, buy a professional AC->DC converter, probably at 19V or some other suitable voltage and then get a DC-DC buck converter to go from 19V to 14.35V, and then a diode (0.7V dropoff) to hook up to your batteries in parallel. You'll also need a diode in your Solar-panels cause you don't want your Grid-tie system "charging your solar panels" (that'd probably create a fire and/or damage them...). Hobbyists should NOT deal with main-power themselves, but there's a gross-many number of AC-to-DC converters available from $10 to $40. 4. Don't battery balance. Just buy bigger batteries. If 12Ah isn't enough, buy a 20Ah battery. If 20Ah isn't enough, buy a 33Ah battery, etc. etc. The limit is whatever you're comfortable with (the bigger batteries give more current which can be more dangerous)

louwrentius 3y ago
Don’t do lead acid. I say this from experience. Lead acid charges too slow. You want a battery that can capture every ray of sunshine - especially with intermittent sunlight - and charge at full speed. Lifepo4 can do this. Lead acid can’t.
- dragontamer 3y ago
  A 12V 12Ah battery is 144Wh. I'm fairly certain that Lead-acid can accept 0.3C, and you're right in that a 60W panel is slightly more than the 43W that Lead-acid can accept. But sizing 12V 20Ah (ie: 240 Wh), and now 0.3C is 72W or 6A of safe charging (less than 0.3C). ------------- See #4: just buy a bigger battery if you need a bigger battery. Bigger battery provides more power and energy proportionally for the chemistry. And a 12V 20Ah lead-acid is just $40 on Amazon. --------- I guess your overall point is that "Trickle-charge" isn't enough for Solar? Which is something I admit I didn't think about earlier (trickle-charge just doesn't send as much current to the battery due to the lower voltage). But I guess there's a "simplicity of circuit" advantage of trickle-charging. A more complex state-of-charge circuit (likely a microcontroller keeping tabs on the battery) is needed to safely send 0.3C down to the Lead Acid. EDIT: On the other hand, having your "charge controller" just be like, two power diodes, is a gross benefit to simplicity. Its something you can do with Lead-Acid that's fully impossible with LiFePo (and is why LiFePo4 needs expensive charge controllers to work). For hobbyist purposes, there's something to be said about using simpler technologies, even if their specs are worse (and I'm not entirely sure if Lead-Acid has worse specs than LiFePo4 in this use case).
  - louwrentius 3y ago
    The key issue is that lead acid at these low capacities may be able to take one or two amps above 50% SoC. Especially at 80%+ if the panel can do 4 amps but you can charge only with 2, you are wasting precious sunlight. Lead-acid can charge at 0.3C but only when empty until 50% or so. In the absorption phase, current drops (dramatically). Also lead-acid means 50% usable capacity for longevity so the 12v 12Ah lithium is 12v 24Ah lead-acid (minimum). Which also means you can never charge with 0.3C. And even then is longevity of lifepo4 so much better it’s not funny. Please spend the extra money on lifepo4, save yourself some headaches.
    - dragontamer 3y ago
      > Also lead-acid means 50% usable capacity for longevity so the 12v 12Ah lithium is 12v 24Ah lead-acid (minimum). That's not a concern, is it? We're talking about battery backup, meaning the "expected use case" is that the Lead-Acid battery is sitting at near 100% capacity for almost its entire life, without significant amounts of discharge. Sure, you've got to discharge when the sun goes down but I don't expect a properly-sized battery to be deeply discharged (especially when we're aiming for multiple days worth of "worst-case" power, like multiple days of clouds/rain to reduce our power-collection). Lets just be dumb with napkin math for a second: 12-hours of charge, 12-hours of discharge on a "typical" day, with a 3-day / 72-hour period of worst-case charge. Where does this leave us? 12-hours of typical discharge / 72-hours of worst-case discharge == DoD of 100% to 83% on your typical day-to-day basis. Hardly anything that considers a "deep discharge". And if we really need deep-discharges, most Lead-Acids can survive something on the order of 300x to 500x deep discharges right? So its not like the 5 to 10 times a year where you need all 72-hours of battery are significantly hampering your lifespan? > And even then is longevity of lifepo4 so much better it’s not funny. Measured in deep cycle-counts (ie: cell phones or laptop usage), sure. (like 3000 cycles on LiFePo4 vs 500 on Lead Acid). But years of sitting on a float-charge, I don't think its that much better than Lead-Acid. ---------- That being said, LiFePo4 is a "superior" battery for sure, and its much cheaper than I remember. But Lead Acid remains significantly lower-priced than LiFePo4 as far as I can tell (2-to-1 or less) I think you have a point about Lead-Acid charging slower when its near full (and keeping it full is key to keeping Lead-Acid long-lasting). So I admit to not recognizing that (LiFePo4 also charges slower when near full, its just that it charges like 3x to 4x faster than Lead Acid so its less of a concern) > Please spend the extra money on lifepo4, save yourself some headaches. We're at the hobbyist level where the original post decided that MPPT solar charge controllers weren't needed (at least, in an earlier version of this project) Clearly no one here is talking about the strictly most optimal design, but are instead talking about simpler and cheaper solutions. -------- Simplicity here is key. LiFePo4 does _NOT_ like topping charges or staying at 100% charge for long periods of time. Lead Acid however, prefers 100% charge and UPS use Lead Acids for this reason. LiFePo4, in UPS/Standby like systems, need to stop charging, and wait for the battery to be used before engaging in a new charge cycle. Lead-Acid on the other hand, can just have a constant voltage applied (ex: 13.5V or so) and you can just hold that indefinitely, for incredibly simple standby circuits.
- deleted 3y ago
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- beachy 3y ago
  We have an off-grid cabin with 4 x trojan lead acid batteries and they have worked flawlessly for 8 years so far and still going strong, despite regular over-draining by solar-ignorant guests (who would bring their own bar heater to plug into a solar system??) They get water topped up every few months and fizzed every couple of years. Speed of charge is not everything.
  - dragontamer 3y ago
    To be fair, Trojan is an unusually durable lead acid battery. Their specs are far far beyond 'normal'. It seems like some serious chemists are at work there.
turtlebits 3y ago
Lead acid isn't that much cheaper. You can get LFP 12v 100AH batteries for $290, with a 10yr warranty. You also don't have to worry about discharging them too low.
- Gibbon1 3y ago
  Last time I tried spec'ing a lead acid battery in a product I found you have to derate the lead acid battery a lot more than would expect if it has to deal with constant deep charge discharge and temp extremes. Where you don't need to derate a LFP battery much at all. So lead acid is okay at lower temps and with only occasional deep discharges.
  - ianburrell 3y ago
    Lead acid battery can only use 50% of rated capacity. Also, they are heavy. Not a problem in fixed install or vehicle but pain if need to move.
    - dragontamer 3y ago
      We're talking about Rasp. Pi batteries here. 15lbs (6kg) of Lead-Acid is probably the biggest, oversized battery that'd be needed (Assuming PS-12200 a 12V 20Ah Lead-acid or 240 Watt-hours of battery life) > Lead acid battery can only use 50% of rated capacity. That's definitely wrong. Lead Acids lose durability when you deeply-discharge them, but all Lead-Acids have *hundreds* of deep-discharge cycles supported. The question is one of frequency. Li-ion is great because it has high-durability through deep-discharge cycles. But is this the use case of a UPS or Solar Backup? I argue no, it isn't. --------------- The key advantages of Lead Acid are its cheapness and simplicity. If you can overlook its size and weight (okay, 15lbs is heavy if you're used to Li-ion... but is it really a *problem*? I argue no), and also know that deep-discharges would be rare (ie: UPS style "backup battery" usage), then LeadAcid suddenly rises to #1 choice due to gross simplicity you can have when designing circuits. As I described earlier: two diodes and a constant 13.5V source are pretty much all you need to create a minimally viable Lead-Acid battery backup solution. None of this "LiFePo4 charge controller" crap or CC-CV charging circuits (Lead Acid _prefers CC-CV especially if you want to charge it in 20 hours or less, but it doesn't _need_ CC-CV circuits) A long-term trickle charger over days (~72-hours of charge) of use is perhaps a non-obvious usecase. But that's called "Always plugged in UPS" and is IMO, the kind of use-case that's best suited for "SolarPi". -------- You might laugh at "hundreds" of deep discharge cycles or counter with the "thousands" that LiFePo4 can support. But seriously, think about it. A 240 W-hr battery (12V and 20Amp-hours) hooked up to a 3W Rasp. Pi will give you 80-HOURS of life per cycle, that's over 3 days. Assuming ~500 Deep Cycles of durability (which is in-line with Lead Acid specs), that's 1500 days of worst-case deep-cycles, or 4 YEARS of life. And that's deep-cycling every 3 days, then fully charging on the 4th day instantly (it takes 20 hours to charge Lead-Acid in practice), so really you're looking at closer to 2000+ or 5+ years of worst-case life from something like the PS-12200. Do you _really_ need the thousands of deep cycle charges? The damn chemistry is going to fail for other reasons (temperature / humidity issues) after 5 to 10 years, rather than from the cycles. Especially in a UPS situation where you've got oversized Solar Panels keeping the Lead-Acid at near-100% charge for most of its life.
guerby 3y ago
"Lead Acid is far cheaper" By Wh of capacity may be but certainly not by Wh cycled out of the battery, LFP has many thousands of cycle life. "LFP 12v 100AH batteries for $290": let's say 5000 thousand full cycles, 121005000 = 6000 kWh out of the battery (with still 80% capacity left), that's $290/6000 = $0.048/kWh.
- dragontamer 3y ago
  No one deeply discharges a UPS system on any regular basis.
  - antisthenes 3y ago
    Depth of discharge depends on spare capacity, use case and autonomy of the system. It's entirely plausible for remote autonomous systems to be discharged deeply during a rainy period of several days.
    - dragontamer 3y ago
      > It's entirely plausible for remote autonomous systems to be discharged deeply during a rainy period of several days. And how often is that going to be, pray tell? Lead-Acid has hundreds of deep-discharges available. And these deep-discharges in the use case suggested (ie: 12V 20Ah Lead-Acid backing up a 3W Rasp. Pi) take 80-hours to happen with zero-sunlight at all. So... how many multi-day periods per year do you expect to happen where you deeply-discharge such a battery over 80-hours? Even at 100-times per year (aka: every 3 days you have a full deep-discharge), with a 500-deep discharge lifespan battery, we're looking at 5+ years of durability. Worst-case scenario.
      - antisthenes 3y ago
        I never said it's a scenario worth worrying about, but also 5+ years isn't anything to be proud of for when you're designing systems.

louwrentius 3y ago

Don’t do lead acid. I say this from experience. Lead acid charges too slow. You want a battery that can capture every ray of sunshine - especially with intermittent sunlight - and charge at full speed. Lifepo4 can do this. Lead acid can’t.

dragontamer 3y ago
A 12V 12Ah battery is 144Wh. I'm fairly certain that Lead-acid can accept 0.3C, and you're right in that a 60W panel is slightly more than the 43W that Lead-acid can accept. But sizing 12V 20Ah (ie: 240 Wh), and now 0.3C is 72W or 6A of safe charging (less than 0.3C). ------------- See #4: just buy a bigger battery if you need a bigger battery. Bigger battery provides more power and energy proportionally for the chemistry. And a 12V 20Ah lead-acid is just $40 on Amazon. --------- I guess your overall point is that "Trickle-charge" isn't enough for Solar? Which is something I admit I didn't think about earlier (trickle-charge just doesn't send as much current to the battery due to the lower voltage). But I guess there's a "simplicity of circuit" advantage of trickle-charging. A more complex state-of-charge circuit (likely a microcontroller keeping tabs on the battery) is needed to safely send 0.3C down to the Lead Acid. EDIT: On the other hand, having your "charge controller" just be like, two power diodes, is a gross benefit to simplicity. Its something you can do with Lead-Acid that's fully impossible with LiFePo (and is why LiFePo4 needs expensive charge controllers to work). For hobbyist purposes, there's something to be said about using simpler technologies, even if their specs are worse (and I'm not entirely sure if Lead-Acid has worse specs than LiFePo4 in this use case).
- louwrentius 3y ago
  The key issue is that lead acid at these low capacities may be able to take one or two amps above 50% SoC. Especially at 80%+ if the panel can do 4 amps but you can charge only with 2, you are wasting precious sunlight. Lead-acid can charge at 0.3C but only when empty until 50% or so. In the absorption phase, current drops (dramatically). Also lead-acid means 50% usable capacity for longevity so the 12v 12Ah lithium is 12v 24Ah lead-acid (minimum). Which also means you can never charge with 0.3C. And even then is longevity of lifepo4 so much better it’s not funny. Please spend the extra money on lifepo4, save yourself some headaches.
  - dragontamer 3y ago
    > Also lead-acid means 50% usable capacity for longevity so the 12v 12Ah lithium is 12v 24Ah lead-acid (minimum). That's not a concern, is it? We're talking about battery backup, meaning the "expected use case" is that the Lead-Acid battery is sitting at near 100% capacity for almost its entire life, without significant amounts of discharge. Sure, you've got to discharge when the sun goes down but I don't expect a properly-sized battery to be deeply discharged (especially when we're aiming for multiple days worth of "worst-case" power, like multiple days of clouds/rain to reduce our power-collection). Lets just be dumb with napkin math for a second: 12-hours of charge, 12-hours of discharge on a "typical" day, with a 3-day / 72-hour period of worst-case charge. Where does this leave us? 12-hours of typical discharge / 72-hours of worst-case discharge == DoD of 100% to 83% on your typical day-to-day basis. Hardly anything that considers a "deep discharge". And if we really need deep-discharges, most Lead-Acids can survive something on the order of 300x to 500x deep discharges right? So its not like the 5 to 10 times a year where you need all 72-hours of battery are significantly hampering your lifespan? > And even then is longevity of lifepo4 so much better it’s not funny. Measured in deep cycle-counts (ie: cell phones or laptop usage), sure. (like 3000 cycles on LiFePo4 vs 500 on Lead Acid). But years of sitting on a float-charge, I don't think its that much better than Lead-Acid. ---------- That being said, LiFePo4 is a "superior" battery for sure, and its much cheaper than I remember. But Lead Acid remains significantly lower-priced than LiFePo4 as far as I can tell (2-to-1 or less) I think you have a point about Lead-Acid charging slower when its near full (and keeping it full is key to keeping Lead-Acid long-lasting). So I admit to not recognizing that (LiFePo4 also charges slower when near full, its just that it charges like 3x to 4x faster than Lead Acid so its less of a concern) > Please spend the extra money on lifepo4, save yourself some headaches. We're at the hobbyist level where the original post decided that MPPT solar charge controllers weren't needed (at least, in an earlier version of this project) Clearly no one here is talking about the strictly most optimal design, but are instead talking about simpler and cheaper solutions. -------- Simplicity here is key. LiFePo4 does _NOT_ like topping charges or staying at 100% charge for long periods of time. Lead Acid however, prefers 100% charge and UPS use Lead Acids for this reason. LiFePo4, in UPS/Standby like systems, need to stop charging, and wait for the battery to be used before engaging in a new charge cycle. Lead-Acid on the other hand, can just have a constant voltage applied (ex: 13.5V or so) and you can just hold that indefinitely, for incredibly simple standby circuits.
deleted 3y ago
[deleted]
beachy 3y ago
We have an off-grid cabin with 4 x trojan lead acid batteries and they have worked flawlessly for 8 years so far and still going strong, despite regular over-draining by solar-ignorant guests (who would bring their own bar heater to plug into a solar system??) They get water topped up every few months and fizzed every couple of years. Speed of charge is not everything.
- dragontamer 3y ago
  To be fair, Trojan is an unusually durable lead acid battery. Their specs are far far beyond 'normal'. It seems like some serious chemists are at work there.

turtlebits 3y ago

Lead acid isn't that much cheaper. You can get LFP 12v 100AH batteries for $290, with a 10yr warranty. You also don't have to worry about discharging them too low.

Gibbon1 3y ago
Last time I tried spec'ing a lead acid battery in a product I found you have to derate the lead acid battery a lot more than would expect if it has to deal with constant deep charge discharge and temp extremes. Where you don't need to derate a LFP battery much at all. So lead acid is okay at lower temps and with only occasional deep discharges.
- ianburrell 3y ago
  Lead acid battery can only use 50% of rated capacity. Also, they are heavy. Not a problem in fixed install or vehicle but pain if need to move.
  - dragontamer 3y ago
    We're talking about Rasp. Pi batteries here. 15lbs (6kg) of Lead-Acid is probably the biggest, oversized battery that'd be needed (Assuming PS-12200 a 12V 20Ah Lead-acid or 240 Watt-hours of battery life) > Lead acid battery can only use 50% of rated capacity. That's definitely wrong. Lead Acids lose durability when you deeply-discharge them, but all Lead-Acids have *hundreds* of deep-discharge cycles supported. The question is one of frequency. Li-ion is great because it has high-durability through deep-discharge cycles. But is this the use case of a UPS or Solar Backup? I argue no, it isn't. --------------- The key advantages of Lead Acid are its cheapness and simplicity. If you can overlook its size and weight (okay, 15lbs is heavy if you're used to Li-ion... but is it really a *problem*? I argue no), and also know that deep-discharges would be rare (ie: UPS style "backup battery" usage), then LeadAcid suddenly rises to #1 choice due to gross simplicity you can have when designing circuits. As I described earlier: two diodes and a constant 13.5V source are pretty much all you need to create a minimally viable Lead-Acid battery backup solution. None of this "LiFePo4 charge controller" crap or CC-CV charging circuits (Lead Acid _prefers CC-CV especially if you want to charge it in 20 hours or less, but it doesn't _need_ CC-CV circuits) A long-term trickle charger over days (~72-hours of charge) of use is perhaps a non-obvious usecase. But that's called "Always plugged in UPS" and is IMO, the kind of use-case that's best suited for "SolarPi". -------- You might laugh at "hundreds" of deep discharge cycles or counter with the "thousands" that LiFePo4 can support. But seriously, think about it. A 240 W-hr battery (12V and 20Amp-hours) hooked up to a 3W Rasp. Pi will give you 80-HOURS of life per cycle, that's over 3 days. Assuming ~500 Deep Cycles of durability (which is in-line with Lead Acid specs), that's 1500 days of worst-case deep-cycles, or 4 YEARS of life. And that's deep-cycling every 3 days, then fully charging on the 4th day instantly (it takes 20 hours to charge Lead-Acid in practice), so really you're looking at closer to 2000+ or 5+ years of worst-case life from something like the PS-12200. Do you _really_ need the thousands of deep cycle charges? The damn chemistry is going to fail for other reasons (temperature / humidity issues) after 5 to 10 years, rather than from the cycles. Especially in a UPS situation where you've got oversized Solar Panels keeping the Lead-Acid at near-100% charge for most of its life.

guerby 3y ago

"Lead Acid is far cheaper" By Wh of capacity may be but certainly not by Wh cycled out of the battery, LFP has many thousands of cycle life. "LFP 12v 100AH batteries for $290": let's say 5000 thousand full cycles, 121005000 = 6000 kWh out of the battery (with still 80% capacity left), that's $290/6000 = $0.048/kWh.

dragontamer 3y ago
No one deeply discharges a UPS system on any regular basis.
- antisthenes 3y ago
  Depth of discharge depends on spare capacity, use case and autonomy of the system. It's entirely plausible for remote autonomous systems to be discharged deeply during a rainy period of several days.
  - dragontamer 3y ago
    > It's entirely plausible for remote autonomous systems to be discharged deeply during a rainy period of several days. And how often is that going to be, pray tell? Lead-Acid has hundreds of deep-discharges available. And these deep-discharges in the use case suggested (ie: 12V 20Ah Lead-Acid backing up a 3W Rasp. Pi) take 80-hours to happen with zero-sunlight at all. So... how many multi-day periods per year do you expect to happen where you deeply-discharge such a battery over 80-hours? Even at 100-times per year (aka: every 3 days you have a full deep-discharge), with a 500-deep discharge lifespan battery, we're looking at 5+ years of durability. Worst-case scenario.
    - antisthenes 3y ago
      I never said it's a scenario worth worrying about, but also 5+ years isn't anything to be proud of for when you're designing systems.