Great analysis, Chris. There's no way I'd use any lead acid battery technology in a new off-the-grid solar power system.
A friend of mine replaced his old lead acid batteries with a home brewed Tesla Power Wall, built from the battery from a wrecked Tesla Model S automobile. Part 1 (23 minutes): https://www.youtube.com/watch?v=qpPYkqpe-Ms Part 2 (13 minutes): https://www.youtube.com/watch?v=U3PM2Ndu0zg For small solar powered devices, there are LiFePo4 batteries that are sized to replace sealed lead acid batteries. LiFePO4 technology is the much safer form of lithium battery. These sealed battery modules have internal cell balancing, and some of them have under voltage and over voltage protection. A cheap imported DC to DC converter can be used in lieu of a charge controller. That makes it very easy to design a solar power system. For most applications, simply size the battery for the maximum energy needed for use at night and cloudy days and then size the solar panel to be sufficient for the desired charge time without being so large that it can charge the battery at an excessive rate. I just got the components from Amazon to power a 100W amateur radio station that's entirely off-the-grid. Hopefully I'll get that built and tested this week. On 5/14/19 1:36 PM, Chris Albertson wrote: > If you are building a battery-based power system and space and weight are > not issues then what you should care about is the "total watt-hours per > dollar". > > Here is an example,... You have a 100 amp-hour lead-acid battery at 12 > volts. If it is lead-acid then you can only discharge to 50% if you want a > reasonable lifetime. If it is a cheap batery it might last only 100 > charge cycles. so 50% x 100 cycles x 100 amp-hours x 12 volts is 60 KWH. > The cheap battery might cost $100 to you pay $1.60 per KHW for battery > power based on the replacement cost of the battery. You can buy a higher > quality battery for more money but your cost is going to be between $1 and > $2. per KWH > > So the cost of the battery power is 4 to 8 times high than the cost of > power from the utility company. > > But what if you buy higher quality batteries? > > A Tesla "Power Wall" cost $6,800 (They used to be $10K) it is a 13 KW > capacity and is good for more than 3,000 charge cycles and is actually > warrantied for 10 years. It is maintenance free for 10 years. Use with > a waentry you have an incentive to use it for the full 3,650 cycles. > Lets assume you only cycle it 3,000 times. That is under 20 cets per > KHW for battery power. It is dramtically cheaper then lead acid. > > This is why Tesla is selling b'zillions fo power wall systems. If you do > care about space, these Power Wall units cn be mounted to an exterior wall > and actually look attractive. > > > > > > > On Tue, May 14, 2019 at 9:32 AM Dave Cole <linuxcncro...@gmail.com> wrote: > >> I've been planning to put up an array on my roof. But I have plenty of >> space so I may do a ground level install. >> It would be a lot easier to maintain. >> >> FLA batteries seem to be the general recommendation for a constant use >> residential install. >> >> I've had chargers trash batteries when they failed. I sure wouldn't >> want that to happen to $10K worth of Lithium batteries! >> >> Weight isn't an issue. >> >> Dave >> >> >> >> On 5/9/2019 10:37 PM, Erik Christiansen wrote: >>> On 09.05.19 10:24, Dave Cole wrote: >>>> Erik, >>>> >>>> Do you have a blog going on your build? >>> Now that's an idea. All I've started is the seeds of an article for >>> "Owner Builder" magazine - the editor was interested when we last spoke. >>> >>>> I'd be very interested in your solar and battery setup for your off-grid >>>> home. >>> The existing home, from the 1950's & extended, only has a little 2 kW >>> petrol generator. The new roof which will carry the solar arrays goes up >>> in June, if the framing carpenters turn up on time. (Just off the phone >>> to 'em half an hour ago.) There's 6 or 7 kW of equator-facing panels, >>> but the west-facing hipped roof can only take 9 panels, so only 2.5 kW >>> or so - but still enough to keep pace with a modest aircon. >>> >>> The best trick for allowing high power consumption straight from the >>> arrays, yet limiting battery charge rate to permissible maximum, is to >>> use a hybrid inverter - they're beginning to become more available now. >>> The Redflow ZnBr battery has a limited max charge rate (44A), and pretty >>> much any other does too, e.g. 20A/100AH of capacity for LiFePO4. The >> hybrid >>> inverter looks after that while delivering to load first. >>> >>> I like the Redflow, as it's a long-life unit, unkillable by 100% >>> discharge. It does though need that once a fortnight to regenerate, so >>> it can be handy to have another battery. For off-grid, just one 10 kWh >>> battery is maybe enough for one occupant, but a second is great for >>> visitors from the city. But the reflow is about A$14k (US$10k), so I've >>> even been looking at old technology like NiFe. They're also robust, but >>> can drink a lot of distilled water, emit quite a bit of hydrogen, and >>> put out a bit of mist. About 80% energy recovery is common for a lot of >>> battery chemistries, these included. Li-Ion, or better LiFePO4, are >>> better efficiency-wise, but cycle life on deep discharge is less. Do >>> your machining in sunlight, and only run lights, computers, tv, and a >>> microwaved egg sanger at night, then they'll do well enough, I reckon - >>> certainly long enough for a better technology to reach a better price. >>> >>> We know from laptops that Li-Ion loses capacity with age. The ZnBr unit >>> is claimed to retain capacity, just losing efficiency. If a few (cheap) >>> extra panels are put in the array(s), then that's pretty much covered. >>> >>> One thing - the hybrid inverter should have two MPPT string inputs - one >>> for each PV array, as their voltage at max power will never be equal, >>> given widely divergent orientation. >>> >>>> You must have a substantial setup to be able to run your AC off your >> battery >>>> bank. >>> I'm hoping to be able to get the roof up in time to qualify for a >>> current A$5k government rebate on batteries. Systems with only 6.3 kWh >>> battery capacity are selling well here for on-grid customers. I'd like >>> twice that, as without that, running the mill for hours after half a week >>> of overcast winter days could mean arcing the generator up for a charging >>> burst. But a litre of petrol now and then is a darn sight cheaper than a >>> big battery. >>> >>>> What do you do for domestic water? A deep well? >>> For 55 years it's just been rainwater tanks. I'll be putting in another >>> 90,000 litres of tanks, to catch it when it does come. There'll be >>> nearly 400 m² of roof all up. (But yes, years ago in a big drought it >>> really was bathe the baby in a bucket of water, use that to wash her >>> clothes, then wash the lino floor with it, then put it on the few garden >>> plants you could keep going.) The concern is that a tight rain deficit >>> might be shaping up to be the new norm for SE Australia, not improving >>> at all while we go from the current 1°C warming, through 1.5°C maybe as >>> early as 2030, to 2°C a bit later. (Accelerated warming at the poles >>> does not bear looking at, unless you've had a stiff drink first.) >>> >>> The neighbour had a drill rig in before easter, to drill for stock >>> water. It was expected around 70 feet down. I haven't heard the results. >>> That's a finite resource though, only buying limited time. Slabs of >>> India is hundreds of feet down now, and heading for a brick wall. More >>> roof, more tanks, and live on what precipitates is more viable for >>> longer. >>> >>> Erik >>> >>> >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
