My girlfriend is moving in, so electrical loads will increase. Getting an apartment sized heat pump dryer, small mini-split heat pump for backup space heating, small microwave, etc. So I need to double my array and battery bank, and am facing a number of decisions that I suspect many others, in one form or another, may be also be facing. So I’d very much like to hear people’s thoughts. I’m totally open to suggestions, advice, and accusations of ignorance or stupidity. After all, that’s why I’m posting!
Here’s my existing system:
*Two parallel strings of 3, 295 watt panels in series, for a 1.79 kW array with a Vmp of 135 volts
*Midnite Classic 200
*Four Rolls S530 6 volt batteries in a single, 24 volt string for 10kWh of storage (3kWh usable based on a 30% dod)
*24vdc loads: overhead light fixtures (led bulbs), ceiling fan, pressure pump, SunDanzer ‘fridge.
*110 vac loads powered by a 2kw Samlex inverter: Staber clothes washer, notebook computers, medium sized flat screen TV, 40 watt receiver, C-pap machine, and a few lamps (led bulbs).
*Meanwell 24 volt battery charger and Honda 2000eu generator for the relatively few days per year when the battery bank has dropped below 70% soc.
*I consume an average of 2kWh per day. When it’s sunny the battery bank reaches float by noon. But it’s often...not super sunny.
As you can see, I’m running a number of critical load on the 24vdc side of the system. I do like the fact that those loads aren’t dependent on the inverter (a.k.a. “a fancy gizmo that can failâ€). The few times the battery bank has dropped below what the inverter needs to operate, those critical loads have kept right on cranking. And leaving aside the “All a.c. vs hybrid†debate, I have an investment in 24vdc loads, so even if I decided that all a.c. is the best approach, it’s too late to change.
I know it makes total sense to double my battery capacity by moving to a single, series, 48 volt string. This would allow me to double the array (just repeating the current panel configuration and putting the two arrays in parallel) and keep my single Classic 200. One downside right off the bat is that I’d be retiring my current bank of Rolls betteries, which are only 2.5 years old and in pretty good shape.
One approach is pretty straightforward, but expensive:
*Buy eight new 6 volt batteries to make a 48 volt bank
*Upgrade to a 48vdc inverter / charger (tempted by the AimsPower’s features and low price, but thinking it may be too good to be true; that is, that at such a low price it can’t possibly approach the reliability of, e.g., a Magnum or a Schneider).
*Buy a dc-dc buck converter to power the 24vdc loads.
But here’s the thing…there are other options. I could...
*Simply replicate the system I haveâ€"array, charge controller, and battery bankâ€"and use a great big A-B switch to run the house off one bank or the other. Resultâ€"no need to buy a new inverter and dc-dc buck converter, and I only have to buy 4 new 6 volt batteries instead of 8. Yes, I’d have to buy another Classic 200 charge controller...but you have to admit, there’s something about two completely redundant systems that adds a pretty significant degree of fault-tolerance.
*Buy 4 new 12 volt, 200ah batteries for a 48 volt string of the same kWh capacity of my 400ah 24 volt string, plus a 48 volt inverter/charger. I’d then make use of the 24vdc string by charging it from the 48vdc bank with an MPPT charge controller. In this case I’d run a.c. loads from the 48 volt string, and dc loads from the 24 volt string.
*Just go ahead an mix the old and new batteries into a 48 volt series string, and accept that the new ones won’t last as they would if the whole string was new.
So many options...that’s what makes it challenging. But on the positive side, it’s and interesting problem. Ultimately I’ll probably end up going with a new 48 volt bank, 48 volt inverter/charger, and a dc-dc converter for the 24 volt loads. But I suspect people may well have ideas I’ve not yet hit on. So...bring ‘em on. And thank you.
If your DC loads and AC loads are approximately equal you could build 2 systems one for AC one for DC. With some way to charge one from the other.
Either directly connecting the DC to the AC bank when the AC needs more. Run an AC charger from the AC bank's inverter when needed. Both would need some electrickery to do this automagically. Spelled "For the other half" ;D
Too many conversions eat up energy is one issue so sizing each bank to what it needs would be important.
It is a hard call to replace perfectly good equipment unless there are no viable options.
I would be comfortable designing and installing such a system but it would not be for everyone.
I know from personal experience that mixing batteries of different age, capacities or types in a bank is a bad idea that appears to be a good idea at first!
By all means I would use the current system components. Probably keep it as the AC system depending on some factors I can't easily define here.
Just tossing it on the wall to see if it sticks.
Tom
Maybe let the girlfriend move in and then measure the increased loads you have and power needed. Use the generator to tide you over if needed , and then you can realistically size your system for real world increases.
If you are upgrading lead acid batteries consider and price out larger East Penn Deka forklift type battery pack . Lots of lead and storage in those and longevity .
If I was going to 48v I would want to wait and see what pans out with the Midnite 48v inverter/controller system coming on the market - but who knows how long and how much that will end up costing.
Larry
I agree with Larry, plan for POSSIBLE upgrade but DON"T jump untill you have to... youare in a good position being planned out ahead...
You have a reasonable system now and you may only have to tweak it rather than rebuild it..
CPAP is not a critical load?
Quote from: Westbranch on April 26, 2017, 12:09:33 PM
I agree with Larry, plan for POSSIBLE upgrade but DON"T jump untill you have to... youare in a good position being planned out ahead...
You have a reasonable system now and you may only have to tweak it rather than rebuild it..
CPAP is not a critical load?
Agreed, a wait and see period might be best. I was just offering technical solution to the hardware question.
One or the other could decide they can't stand the other for some reason. (Just saying...).
My CPAP machine (Continuous Positive Airway Pressure) is a critical load. Not life sustaining but definitely necessary for good sleep.
Just from here.
Tom
Tom's idea of adding DC or AC only system to mix is interesting and might work out after the new load impact ( girlfriend - ha ha ) is evaluated.
Larry
A little negotiation (which part of NO don't you understand?) over the use of a hair dryer might be beneficial! They can be a battery KILLER!
Thanks to all for the ideas.
This forum ROCKS.
--Paul
I'd worry that even doubling the system may leave you short. Two people use three times the power. Since you have a generator, maybe just factor in 6 months of incremental gasoline to the calculation.
In my case, I went from a 400W/24-120V system to 5000W/52-240V system when she moved in. (She was not the only reason for the upgrade.)
I kept the old system running and configured all my electronics and communications on it. I also have some minor DC stuff on it, too. The big system handles everything else. Big motor starts (circular saws) then did not cause a voltage drop, which almost always dropped the Internet and had to reboot all routers and radios. The two systems are interconnected, so when the small system is low, it charges automagically. I can manually switch to run the house (except for the 240V heat pump DHW) off the small system.
There is no doubt that your power use will increase substantially, a lot more than double. While you don't have the exact numbers and honestly never will, I would be really proactive about this. Women like to be comfortable and it isn't that easy to find a woman that will put up with us under any circumstances, much less a super low power existence, so don't delay on moving forward.
I am a big fan of 48 volt systems, in fact, all I work with are 48 volt systems, mostly LiFe, but not always.
When someone has a 12 volt or other lower voltage load, I just use DC:DC converters to deal with it. As you mentioned, you could
- Move your primary setup to 48 volt
- Keep some batteries on 24 volt for the 24 volt loads, and keep them charged up using a DC:DC converter
Or
- Put in a 48 volt system with 4 kW inverter
There is no dilemma here at all - you will need at least 10 kW-hrs for your GF each day for her to live a normal life. Don't take this the wrong way, because I am really amazed at how people can live with so little power, but very few women can deal with such a spartan life and will become unhappy about it, no matter what they imagine to be true.
If you want a GF, it cost money, time and patience. She will be excited that you are making the effort to expand on your infrastructure to accommodate her. This is just the start of expanding your infrastructure, not the end. She might even enjoy being part of the effort as a joint BF / GF project. It will make it seem more like "her home" , not just her moving in as a trial run to a BF's man cave.
The more she is involved in the project, the more she will understand how it works and make the effort to work with it instead of seeing it as a limitation / life complexity.
BTW, the MN 48 volt setup does look interesting, but you can't afford to wait. Move forward pro-actively, not reactively.
Are we talking about upgrading to a girlfriend or a 48volt RE system?
This must be a first for this forum, perhaps we need a new forum area,
"How to get a girlfriend at 48 volts" :)
dgd
Can't you see the Personal Ad ?
Searching for my off grid soulmate .
Must use less than 5 kWh a day .
ha ha
Must like: candle lit dinners
: splitting wood
: sitting watching DVD's at 19:00 by an open fire
: Lights out by 22:00
: Cool showers in the morning when the stove is late getting started.......
Lol
Good one!!!!!