That's a valid approach. At a certain point when you're off grid you just have to make it work anyways.
what components for my first build for max efficiency
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Dagoth Ur Does Solar
Solar Enthusiast
Honestly, if you REALLY have no interest or capability to learn this stuff over time, you really can just buy something like one of the nicer EcoFlow units and their solar panels, and you instantly have a battery backup and solar system that requires no real assembly or knowledge on how to use.
Plug it into a wall outlet, plug in the solar panels, and plug in whatever the hell it is you want to run.
Just to clarify, I'm not trying to sound demeaning- there's absolutely nothing wrong with buying one of those consumer style units- it sounds like you're in the target market for that. They do what most people need during a power outage in a clean package.
Bluedog225
Texas
- Joined
- Nov 18, 2019
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- 2,959
It will be a lot less expensive if you learn some basic stuff.
krby
Solar Enthusiast
I know it's tough showing up here and asking questions as a beginner. Glad you're here!
The reason everyone keeps harping on "what do you need it to do" is that enough new people have shown up here asking for help that we've seen that there isn't a good "average case" for how much people need to run off their system. Some people consider keeping the Internet and TV and a PC desktop up critical, others just assume they'll of course be able to use a microwave or a hair dryer. Others have a really old fridge that uses 4kWh per day, while mine uses ~1.5kWh per day.
So, step one is to make a list of the things you need to run, then the things you want to run, then the things that would be nice. Then go figure out how much much power (in watt-hours or kilowatt-hours) those things will use per day. I bought a Kill-A-Watt meter and used it to measure the fridge, coffee maker, wife's hair dryer, etc. Averages are fine, I took the fridge measurement over 48hrs to get an average. For the hair dryer, I measured her using it twice and averaged that.
What you're trying to end up with is a "how much power will I use in over X days". Then decide how long you'd want to go without power. That helps you size the battery bank (how many kWh "kilowatt-hours" can you store?) and helps you decide how much charging from solar you need each day (how many watts in panels?)
MichaelK
Solar Wizard
I would say no. I'd expect 530W would be good enough for a 12V system, but I'd say a minimum of four of those panels for a 24V system. Batteries perform best when charged at a certain rate. Of course there are exceptions, but here are some VERY broad guidelines for different battery chemistries.
traditional flooded lead-acid: 1/10th to 1/8th of C
sealed AGM: 1/8th to 1/5th of C
Li: 1/5th to 1/4th of C.
So, in your case, you have two 100Ah strings of Li batteries at 24V. That means YOUR "C" is 200Ah at 24V. Looking at the math, a charge rate between 1/5th and 1/4th means...200Ah/5 = 40A to 200Ah/4 = 50A. So, for your particular battery bank, it most likely will be most happy getting 40-50amp of charging. The 60A controller would be fine for that.
Now, if you assume the minimum charging voltage the batteries will see is 25V, it becomes a simple math problem. 40A X 25V = 1000W of panels 50A is 1250W. So really, at least doubling the number of panels you want is the proper way to go.
There's a second way to look at how much solar you need to have, and that is to base it on what your loads are. A good rule-of-thumb that I've used a long time is use the 1.5X to 2X rule. That is for every watt of load you want to support, have at least 1.5X that sized load in solar panels. It's not carved in stone, but over the years it has worked very well for me in real-world applications.
Let's say you want to run a 1 Liter hot water kettle. It consumes 1000W. Using the 1.5X rule, you should have at least 1500W of solar. So, either scale your solar to your battery, or scale your solar to your load, but both are significantly higher than just 530W.
Now, depending on which controller you choose, you have the choice of wiring four panels as either 2S2P, or as a single 4S1P string. The 6415 controller would be able to handle at least three in series, but for four, you need the 6420 controller.
Now, finally, one more way of determining solar is based on your sunhours (sh). That is, the amount of time per day you can expect to get FULL POWER out of your array. If you are located in South Carolina at about 33-34 degrees North, I'd suggest you'll get about 3 sh in December, and maybe 6sh in June, on clear sunny days. You simply multiply your sunhours by your watts of panels to determine how many watthours (or kWh) of power you can make. So, for example, with four panels totaling 1060W, you could make 1060 X 3sh = 3180Wh in December, or ~6.4kWh in June. On cloudy days, with rain, don't expect to get more than maybe 0.5sh per day. That is NOT going to keep a refrigerator running.
I guess Id just like to have a small amount of backup power stored for whatever I may need it for.. If it won't provide the power, I suppose Id just have to improvise or do without. I just can't imagine a mini fridge that's NOT on a continuous cycle would require SO MUCH knowledge to function. Im so confused about all this that Im probably just going to run my Ecoflow Delta 2 with my extra battery and hope for the best. Anybody need any components? ha
I would expect 400ah of batteries would keep a mini fridge going for a good few days, even without solar.
You've explained what you want to achieve and people keep ignoring that for some reason. So probably better off to ignore them, or at least filter them out.
If you wish to proceed with the installation then I suggest working on a diagram so you can formulate a plan and get feed back. The diagram should include batteries, chargers, inverters, busbars, wire gauges, fuses/breakers, panels, pretty much everything that a system needs
This stuff isn't rocket science but it can take a bit to absorb enough relevant information to feel like you aren't totally lost. So don't be afraid to take your time getting your head around it.
Thank you for your response. I am a newbie as well, maybe even a neonate to these things. I am drawn to your mention that 400ah of batteries will keep a mini fridge running for a good few days even without solar. I would like to know what you mean by a mini fridge.
I am also interested in setting up a system quite simple for some low energy lighting, laptop usage (two of them at 65W each), an LED television and a game console and/or a decoder. I understand the likely need to alternate their usage based on a scale of preference. I would also like something on the cheaper side, especially regarding batteries. I wonder if car batteries will suffice for such a setup. What do you think/advise?
krby
Solar Enthusiast
If you're looking to save costs, it is helpful to know how much power use. Things like lights are easy, if they're on, they're likely using the watts they say on the label, other equipment is harder. A residential refrigerator typically runs the compressor for a while, then is mostly dormant. Laptops are similar. You may have a 65W charging brick for it, but it probably isn't using 65W the whole time unless you're maxing out the CPU or graphics card the whole time. My point is you really should measure usage of various devices over a couple of days to get an average.
Search for 'Kill A Watt' or 'Electricity Usage Monitor' on Amazon or wherever you want to shop. You don't need the exact Kill A Watt brand. The idea is you plug it into the wall, set it up to record kWh (kilowatt-hours), zero the counter, then plug in the appliance or device. Go about your normal routine (or what would be normal when running off batteries). I like to average for at least a day. Write down the total used and how long you recorded so you can get an hour or daily average for that device. Then do it for the next one. When you have everything written down you can total things up and have a "kilowatt-hours needed per day (or hour, your choice). Then you decide how many days or hours you want your batteries to provide backup power and you have a baseline capacity you need.
This is the starting point. If you find you used 1.3kWh of AC power, then you'll need a system capable of providing that. You'll have to account for efficiency losses and such, but you'll never need LESS battery capacity than that to power what you want.
The reason I'm pushing the "energy survey" is that by doing that, you'll know your minimum needs, you can then price out what that would cost you to cover and because you will have the per-device usage written down, make choices like: "ok, when I'm on battery power, I'm not going to run the hair dryer for 45minutes", so you can lower the needed capacity and lower your costs.
IMO, with these systems, the needed energy storage capacity drives the cost of everything. More capacity means more batteries, which then need a source that can charge them in a time you're happy with.
One last thing:
Most actual car batteries? No. They are designed to deliver a lot of current over a short period and be recharged right afterwords. You can get deep cycle lead acid (the same chemistry used in car batteries) that are designed to be discharged down much lower than typical car batteries. These are sometimes also called "marine batteries" or gel cell or AGM.
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MichaelK
Solar Wizard
I guess this is the central part of your problem. If you don't do the math, you can't understand what you need.
You really don't need to imagine anything. The specifications of everything is available if you put in the time to look for it. So, let's look at a mini-frig. Went to the HomeDepot website, and picked a random model, made by RCA.
Clicked on the Energy Guide, on the right side of pic number two
OK, if this mini-frig consumes 219kWh per year, on average it will consume 219kWh/365days = 0.6kWh, or 600Wh.
The inverter just staying on consumes power itself. How much depends partially on the size of the inverter, and secondly on the quality of design. Let's guesstimate you get one that consumes ~ 25W continous. The Samlex PST-2000 is in that range. So, 25W X 24 hours per day = 600Wh. Let's say you keep 100W of lights on for four hours, that's 400Wh. Finally, maybe two hours of computer or TV time, maybe 50W for 2 hours = 100Wh.
Add that all up and you get 600Wh + 600Wh + 400Wh +100Wh = 1700Wh per day. That's a realistic number that I've actually seen myself with my own system. Let's say though you go with a range, and say you need between 1500Wh and 2500Wh per day. Call it an average of 2000Wh, or 2kWh.
This is an example of what people are talking about when they say "you need to do your homework". If you are located in South Carolina, at about 35 degees North, I'd guesstimate you get 3.0sunhours of light in winter and 6.0sunhours in summer. In December, a system with 530W of panels might make 530W X 3.0sh = 1590Wh of power. Maybe, just barely enough that you might break even. Maybe, barely, assuming you have clear, sunny weather. At your location, what's the likelyhood that if the power goes off in December, the weather will be clear and sunny?
Having more watts of solar means that in less than ideal conditions, you will make the amount of power you need. Here is a plan that will let your system grow if you find you've made mistakes in your calculations. Mistakes though that are fixable.
Buy a high-voltage charge controller like the Epever 6415 or 6420, and the 24V sine-wave inverter. Wire your batteries for 24V. Start out with two 265W panels, that you wire in series to get 62Vmp. Feed that into your 6415 controller that transforms it down to 25-28 charging volts. Operate the the system for a while and see if you can keep the batteries charged without the system crashing.
If it doesn't, then wire another 265W panel in series to get 795W at 93V. If you still don't get enough to successfully power the system, add a fourth panel. You could wire this either 2S2P, or 4S1P with the 6420 controller. Only 2S2P if you got the 6415. If that's still not enough power, go with all six, and wire them 3S2P. That I think will make you a reliable 24V that is not going to let you down. It WILL keep the lights on, even in December.
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