[HN Gopher] My solar-powered blog is now on lithium iron phosphate
___________________________________________________________________
My solar-powered blog is now on lithium iron phosphate
Author : louwrentius
Score : 125 points
Date : 2023-05-19 12:07 UTC (1 days ago)
(HTM) web link (louwrentius.com)
(TXT) w3m dump (louwrentius.com)
| brunojppb wrote:
| > There was a handful of new data that had been created in the
| intervening ~30 minutes. We pulled that diff data manually, and
| uploaded it to the new database.
|
| But doesn't that mean you had some partial downtimes? How did you
| manage to keep everything running during these 30 minutes where
| data was copied from the old DB to the new one? Let's say there
| is a cron job that must be executed and its result would be
| stored back to the DB. Did you "pause" everything and reschedule
| it in the new instance once the diff copy was over?
| fgsfds028374 wrote:
| Sailors are big into LFPs these days. I just upgraded my Beneteau
| to a 11kWh LFP bank and it's been game changing. I cook with a
| 1800W inductive cooktop, use the microwave, run the desalinator,
| for multiple consecutive days at anchor without running a
| generator or the motor. Unthinkable in the days of AGM deep
| cycles, they'd be dead in months.
| mikae1 wrote:
| Also: https://100r.co/site/solar_cooking.html
| Scoundreller wrote:
| get an instapot! Save lots of energy while cooking faster.
| (depends on what you're cooking of course).
| kragen wrote:
| how long will the lfps last that way
| elihu wrote:
| In theory they should be good for several thousand cycles, so
| -- a long time. As long as you don't overcharge them, drain
| them too low, or try to charge them in below freezing
| temperatures.
|
| Also, they say that usually LFPs will last a bit longer if
| they're installed such that they're under a bit of sideways
| compression. I don't know why that is.
| jacquesm wrote:
| That only goes for prismatic cells (boxes rather than
| cylinders). The reason is that they tend to swell up while
| charging if you don't compress them so manufacturers will
| specify a clamping force required for the cells to keep
| their shape. If they change shape in such a way that you
| can observe it then your cells are toast so better stick to
| that mfg indicated compression. There are a number of
| articles out there that show how to do this the right way
| and also some that get it hilariously wrong. The direction
| to compress the cells in is in such a way that the
| electrodes remain under compression perpendicular to their
| surface. So compressing from the top and compressing from
| the front will do absolutely nothing.
| kragen wrote:
| thank you very much for explaining
|
| it makes sense that cylinders would be immune to swelling
| jacquesm wrote:
| You're welcome. I've been working for more than a year on
| a blog post about the various safety aspects of building
| battery packs but it's a never ending rabbithole of stuff
| to research and learn about so I haven't gotten around to
| publishing it.
| T3OU-736 wrote:
| Hah. Post it on HN, and let Cunningham's law help you :)
|
| Snark aside, I feel that on HN, there are enough actual
| proper experts who will point out avenues of research and
| gotchas that a single person chasing down rabbitholes on
| their own is unlikely to discover.
| kragen wrote:
| you might be surprised what this particular single person
| is likely to discover on their own
|
| one of jacquesm's previous personal rabbitholes was
| designing and building a wind turbine from scratch, down
| to cutting out the stator and rotor windings for the
| generator from sheet metal
| T3OU-736 wrote:
| Fair point. Either way, my ulterior motive was to be able
| to read what they have, and learn vicariously that way :)
| ilyt wrote:
| Maybe multi-part series would fit it better ? Probably
| better SEO for one-subtopic-per-article if you care about
| that.
| louwrentius wrote:
| It feels to me that the battery compression discussion is
| a bit of a game of telephone.
|
| I think this video by off-grid-solar explains it quite
| well. https://www.youtube.com/watch?v=63-Nx75_xXM
| Andys wrote:
| My household of 3 is off-grid, running off a 15kW PV array and
| 24kWh of LiFePO4 batteries, with 100% electric appliances and hot
| water. (Location is mid-latitude Australian, plenty of sunlight
| most of the time)
| duckmysick wrote:
| What do you use for hot water? Solar thermal collectors?
| Andys wrote:
| A 250L tank with a 3.6kW electric heater element, programmed
| to turn on when batteries hit 98% full (and off again when
| batteries fall below 95%).
|
| We really only use it for short showers, and it stays warm
| enough for that, for about 3 days without power.
| originalvichy wrote:
| I'd be curious to know if an inland Aussie would like hot
| water at all besides for cooking. Some nightmarish temps
| there.
| Andys wrote:
| It gets cold at night :)
| louwrentius wrote:
| That is really cool and would be my dream.
|
| In the Netherlands it's near impossible unfortunately to
| achieve 100% off-grid due to the winter months, when you
| basically have no solar. Maybe there are Dutchies who have
| somehow achieved it (with overprovisioned solar).
|
| Do you still have a grid connection for backup or are you 100%
| disconnected from the grid?
| Andys wrote:
| 100% disconnected; it was cheaper this way (grid was too far
| away).
|
| What is the typical kWh/day consumption of a household there
| in winter months?
| sgt wrote:
| Well done for going off-grid. But what do you do if you've
| got a whole week of rain?
|
| A lot of people here in South Africa are keen on off grid
| but it's unreasonably expensive since you'll have to cater
| for those rainy days, and that means you'll need to build a
| very large system.
|
| BTW kWh/day consumption here in the winter (which is
| probably typical) is around 25kWh per day.
| Andys wrote:
| We have a diesel generator but its only needed a few days
| a year; even with regular testing it only goes through
| about one jerry can a year, far less than we use for
| transport (would love an EV!)
| adrianmonk wrote:
| > _unreasonably expensive since you 'll have to cater for
| those rainy days_
|
| I wonder if it would make sense to get a generator[1] to
| supplement solar on rare occasion.
|
| If you want to build solar, but the cost of achieving
| reliability is the one thing stopping you, then maybe a
| generator could remove that obstacle.
|
| Yes, it emits carbon, and the fuel costs money. But if
| you only use it a few days each year, that might not be
| very significant.
|
| However, it makes the system design more complicated, and
| generators require maintenance.
|
| ---
|
| [1] I'd use propane since it can be stored 10+ years,
| whereas gasoline and diesel last 6-12 months. Also
| propane can be used for emergency heat.
| sgt wrote:
| Fair point. Having a test schedule every 3 months is
| probably a good idea to ensure that it'll start up.
| louwrentius wrote:
| Thanks for sharing.
|
| To be frank, I've looked in my Energy supplier app
| (Vattenfall) and it states for December an average usage of
| 122 KWh (all households) and energy efficient households
| (solar) of 91 KWh.
| Andys wrote:
| No problem, I'm happy to share all the info. People need
| to hear how easy it is to do this with the latest
| technology.
|
| 122 kWh per _day_ ? That can 't be right.. does that
| include gas or something?
| louwrentius wrote:
| Sorry, per month. So around 4 KWh a day on average. Gas
| is not included.
| Andys wrote:
| OK. we're using about 20 to 30kWh per day (depending how
| much heating or cooling is needed). But with no gas.
| zo1 wrote:
| I'm not OP, but I would look at this tool I found a while
| back. Ridiculously useful and underrated. I think someone
| on HN linked it, as I've not found a tool so useful via
| googling despite many attempts.
|
| https://re.jrc.ec.europa.eu/pvg_tools/en/
|
| What you're looking for is the "Off Grid" tab, plug in
| your details. e.g. solar array size, size of battery,
| etc. Then click visualize results. After visualizing,
| there are a few tabs to help you make some decisions.
|
| For your case (Netherlands, it looks like a 5.4kWp solar
| array and 4kWh (I assumed 5) used per day, and with a
| single 5kWh battery, you should be able to go off-grid :)
| In fact, during summery months, you could even push to
| the grid.
|
| This tool even looks at cloud data based on various
| databases. I don't know of it's accuracy, but I'm
| inclined to trust it.
| skc wrote:
| Really curious to learn more about this.
|
| Have you had to scale back usage of certain appliances such as
| irons, air conditioners, washing machines etc?
| Andys wrote:
| Amazingly, no. I thought we were going to have to, but our
| natural usage peaks at about 20 to 30kWh per day, and we can
| generate far more than that on a sunny day.
|
| Thanks to the oversized PV array, we generate power even in
| cloudy conditions. The PV array is also split in half and
| oriented east+west so it catches more sun through the entire
| day instead of a midday peak.
|
| For things like clothes washing, drying, and hot water
| heating, those are the heavy users but can be moved to times
| of good sunlight.
|
| We only run out of power if we have 2 or more days of heavy
| rain in a row, which only happens a few times a year.
| langsoul-com wrote:
| Isn't it easier to just have solar panels on the roof and an
| actual battery pack for the house?
|
| Though, I suppose this is more of a challenge thing
| unwind wrote:
| I think the OP lives in an apartment, where that kind of
| invasive mod is not possible.
| csteubs wrote:
| Not OP but I rent and have to use my deck for solar. I only
| have 2 x 100W panels that sit on the ground, and that feeds a
| 135Ah AGM battery in a box. The box has a 500W inverter on top
| connected to the battery and powers a mini fridge, deck
| lighting, and a few other things out there. I would love to put
| them on the roof and my landlord would probably be cool with
| it, but I take it camping all the time so it's nice being able
| to pack them up quick.
|
| Panels and batteries are relatively cheap (and getting cheaper)
| to the point that it can makes sense to have purpose-built
| setups.
| nvy wrote:
| Which panels are you using?
| jondwillis wrote:
| I recently went from deck solar to landlord-permitted roof
| solar.
| Gigachad wrote:
| From an actual practicality sense, the whole setup doesn't make
| that much sense. You could drop the files on a static site host
| and it would use 0 watts while not in use and a negligible
| amount while in use.
|
| Another interesting case would be to use an API to get your
| areas power generation stats and when the wholesale pricing is
| low due to solar/wind generation peaks, charge your battery off
| the grid.
| louwrentius wrote:
| See the previous article I link at the top about my situation.
| ttul wrote:
| I bought a low speed vehicle last summer that the previous owner
| had outfitted with a home made 24-cell LiFePO4 pack, complete
| with a cheap Chinese BMS and balancer unit. Within a week of
| purchase, his haphazardly installed balancer wires had melted in
| various places where they pressed against the high current
| conductors. Long story short, balancing didn't work properly on
| account of the sensor wires being shorted together and,
| resultingly, many cells went to zero and I suppose I'm glad it
| didn't also catch fire.
|
| These things are fun, but they pack a whole lot of energy!
| jacquesm wrote:
| This is a pretty common error and the reason why in my long
| distance e-bike pack I spent a lot of time getting the balance
| wire routing done without any wires crossing.
|
| Even Bosch got this wrong on their pannier mounted battery
| packs, I've opened up a whole pile of failed Bosch packs to see
| how they fail as a guide to my own pack design and the most
| common failure was water ingestion due to bad seals followed by
| burned out balancing wires that some how got worn out or
| pinched. This stuff is very critical and I would (1) never buy
| a pack that some other hobbyist made and (2) never sell the
| pack that I made to someone else.
| louwrentius wrote:
| Building batteries like these based on LiFePO4 is very easy to
| do, but you have to think about safety, especially if you put a
| battery in a moving vehicle.
|
| If something goes wrong with these kind of batteries, it's
| never the batteries themselves (specifically LiFePO4) but it's
| always a bad connection or an undersized wire causing high
| resistance and thus heat --> fire.
|
| In my case, my wires are quite oversized and I bought a proper
| lug nut crimping tool (and not use a vice or soldering (Don't
| do it)) to make the connections. I've also really made all
| connections tight, double-checking them.
| ttul wrote:
| Yeah for sure. I am redoing all the wiring and replacing
| about half the cells because they went to zero... Will be
| over-specifying everything and making the routing super tidy.
| If you have the patience for that, DIY batteries are fun!
| anonymousiam wrote:
| I ran a similar off-grid system for 10 years (starting in 2003),
| but mine was of a somewhat larger scale. The server consumed
| about 400W and I had 1280W of solar panels. I started with lead-
| acid deep-cycle marine batteries, but later switched to sealed
| AGM because they did not vent hydrogen while charging.
| Admittedly, it was not 100% off-grid. I had a 50A 12V DC power
| supply on-grid that could power and/or charge the system if
| needed.
|
| I switched the marine batteries out after about four years of
| operation.
|
| I took down the solar panels in 2013 because the roof needed
| repair.
|
| If I were doing it today, I would probably give Lithium-Iron a
| try. They weigh less, have higher power density, and last longer.
| antisthenes wrote:
| So what are you doing now in terms of renewables? Anything?
|
| Or were the renewables strictly to run the server?
| anonymousiam wrote:
| It's a long story. That solar plant was basically a UPS
| because the neighborhood where I bought a house had terrible
| power, and yes, they were just for the server. The root cause
| of the power problem was a 50-year old 4kV "last mile" which
| was finally upgraded to 16kV a few years before I took down
| the system. Power there is great right now, but maybe not for
| much longer because California keeps shutting down power
| plants. The NG plant less than a mile away will be gone next
| year. San Onofre is gone now too (https://www.sandiegouniontr
| ibune.com/business/story/2022-08-...). I hope to sell the
| place in CA soon.
|
| I now have another house elsewhere with 4kW of solar on the
| roof. I would add more, but for two reasons:
|
| 1) There might be enough space up on the roof for another
| 2-3kW, but it's close.
|
| 2) The local laws governing grid-tie are such that I can't
| just add more panels. I can put up another separate system,
| but with a separate meter. I'm concerned that two separate
| systems on the same grid point trying to sync to the grid may
| have problems where they interfere with each other. I have
| read about such problems.
| Logans_Run wrote:
| Regarding point #2) Absolutely yes that can be (and is) a
| problem for exactly the reason you say in terms of
| synchronising 2 (or more) PV setups to the local grid and
| (I would imagine) have the facility for emitting volumous
| clouds of magic smoke.
|
| Fortunately the solution would appear to be use of a GPS
| central time clock that is fed to the 2x PV arrays
| individualy... if you run your own local time server you
| can 'skew' the clock signals to each array to get them in
| sync with each other and then in to a dummy load of spare
| lead-acids or a capacitor bank (if you want to get fancy
| and don't mind the 'large gray box' emitting smoke and
| launching itself off the wall from time to time).
|
| Then you sync your 'mini-grid' to their slightly larger
| mini-grid.
|
| Oh and when synching - never forget the old-school 4-light-
| bulb trick as a visual confirmation that things are synched
| correctly before tying in to the grid. Oh and fuses, large
| ones. With spares.
|
| If you can find a friendly H.V. engineer or Linesman they
| might be able to tell you what clock source 'their grid'
| uses (GPS, Network time etc etc) which makes synching to
| the local-ish grid a whole lot easier if you have the exact
| same setup. I think the main thing is to make sure you have
| the dummy-load ready to feed/smooth what can be at times be
| a large inrush/outrush till the load equalizes.
|
| Obviously, always seek out advice from someone that knows
| what they are talking about and has knolwedge of local
| laws, quirks of the grid etc.
| anonymousiam wrote:
| Thanks for the reply. I got a few years of experience
| doing power systems in 1980, which came in handy when I
| did the CA PV system in 2003. (My embedded/web
| development skills also came in handy when
| designing/deploying the solar M&C subsystem, because no
| such products existed at the time.)
|
| I'm somewhat skeptical that GPS synchronization is the
| real answer here. The problem is synchronizing the phase
| of the PV system to the grid so they can work together to
| power the load, allowing excess PV power to be sold back
| into the grid when not needed locally. To synchronize,
| one needs to control the phase of the PV system so it
| always slightly leads the phase of the grid. Determining
| the phase of the grid is the challenge. With two or more
| locally grid-tied PV systems, you cannot know the phase
| of the grid with much certainty because each PV's take on
| the grid phase is the aggregate of the actual grid phase
| and the phase of the other PV systems. Positive feedback
| and phase oscillation are likely.
|
| Using GPS to synchronize with the grid assumes that the
| grid's phase is stable, but my observations over the past
| few years have revealed that today's grid has much less
| short-term stability than the grid of old. I'm assuming
| that the lower phase stability today is caused by the
| recent massive adoption of grid-tied PV arrays. So
| instead of using GPS time to guess the current grid
| phase, you really need to know what it is (locally).
| Aside from placing grid phase monitors on nearby houses,
| I don't know how to do this.
| jandrese wrote:
| It would be so much cheaper to do it today, especially if
| you're comfortable with DIY and don't mind buying some used
| panels. Easier too, there are so many turnkey and DIY friendly
| solutions on the market now.
| yobuko wrote:
| I've been enjoying each of your posts you share here regarding
| this set up. I have two questions if you please?
|
| 1. Have you considered adding a small wind turbine (DIY of
| course) to supplement?
|
| 2. Although the costs are certainly coming down and within the
| realm of possibility for many, they are still too prohibitive for
| those that would benefit the most. Do you see any way that you
| could recreate your project on a shoe-string budget?
| louwrentius wrote:
| Thank you!
|
| Yes, I've looked into running a small wind turbine but from
| what I can tell it's not worth the money or effort.
|
| There is a reason why they build wind turbines so large and
| high. At small sizes, with our wind speeds, they barely produce
| any energy.
|
| I can't also just put one on my balcony as I'm not allowed to
| (building regulations).
|
| If I ever want to build my dream renewable energy build, I
| really have to relocate :)
|
| Regarding a shoe-string budget: it all depends on your goals. A
| key thing is doing everything second-hand, maybe except for the
| LiFePO4 batteries, unless you can find those. In the
| Netherlands, There's a lot of solar gear moving through our
| local Ebay (Marktplaats, owned by Ebay) so that's something to
| look out for.
| formvoltron wrote:
| my popcorn is made by stored solar power from my 2.2 kwh lifepo4
| pack. so what?
| coffeebeqn wrote:
| Not even mentioned is the incredible number of cycles lifepo4 can
| do before storage is degraded - thousands instead of hundreds
| cronix wrote:
| Yes, usually around 3k charges before reaching 80% capacity,
| which is around 10 years.
| megaman821 wrote:
| I have an LFP battery from EcoFlow, and now I am more worried
| about the inverter or BMS failing before the battery cells.
| End of useful life really isn't until 50% battery capacity,
| which could 30 years out.
| boulos wrote:
| Yeah, that's why all the recent sprinter van conversions are
| using them for the "house" batteries.
| louwrentius wrote:
| My cells are rated for 4000 cycles which is ~11 years.
|
| At 10% years they will have 80% of capacity.
|
| A-grade cells are often rated for 6000 cycles.
|
| It's amazing. I've updated the article with those numbers.
| nahnahg wrote:
| [dead]
| supermatt wrote:
| 3 kWh for 500$! How times have changed! Anyone know of a three-
| phase UPS I could power with such a battery?
| jondwillis wrote:
| personally my UPS is connected to a 2kWh battery (with an
| inverter) via AC. Even when something happens to the battery to
| cut power too the UPs, the UPS has enough battery to last until
| it is resolved.
___________________________________________________________________
(page generated 2023-05-20 23:02 UTC)