Need Help Building System That Can Grow

[Devin82m]

Hey thanks so much for the great videos, I just discovered your channel and website.

I was wondering what system you would suggest for someone who wants to get their whole house completely on solar without sacrificing any usage. I bought a solar power setup from Iron Edison this summer, I haven't had time to install it, but it's supposed to be a 1.5 kw 12v system, we shall see, but I had to compromise at the time and bought 2 200 AhMK Delta AGMs, but now after watching your channel I see how easy it is to build large LIFEPO4 packs. I previously built a small 10 Ah pack, but the instructions I was following were iffy and I barely got the thing built, works great with a roll up panel I have.

Anyway, do you suggest 48 v to cover all the typical needs of a household? And since I will most likely need more than 4800 w, do you suggest a different BMS? (I see on your website you don't suggest the BMS you like pat 4800 w). My plan is to slowly build out a system a bit at a time (money), add battery packs here and there. But I want to make sure the skeleton of the system is ready to handle the growth up to the maximum I need, I live in the country in Idaho, I work from home doing IT work, and we are on the grid. The system I have currently does have a charge controller that is multi chemistry, including LiFPO4, and would barely be enough to power my home office, and it looks like it has a limit in amps that may not work. I do ham radio too. I would like to buy very durable long lasting components and buy backups to put away in case (faraday cage)...

My current system:
1.5 kw system

• 5 315 Watt REC TwinPeak2 Solar Panel
• 2 245 Ah MK Delta AGMs
• MidNite KID MPPT Charge Controller
• 1500 watt Samlex Inverter

Any help is appreciated.

 

[snoobler]

Welcome to the forum.

You need to establish your energy needs and design the final system, then figure out how to piecemeal it. If you have a utility bill that reports your kWh usage, that's a great place to start.

You have:
1575W of panels (1575/12V = 131A)
2940Wh of usable capacity (50% of total), 49-74A of optimal charge current

Your charge controller is only capable of 30A of battery charging meaning anything over 400W is completely wasted for 12V, BUT you can probably produce 400W almost all day long. If you reconfigure for 24 or 48V, it doubles each time meaning if you go to 48V, you can use all your array.

 

[Hedges]

Yes, 48V is the way to go for larger systems.

Check out the DC Solar trailers offered on Craigslist, possibly eBay, and additional bankruptcy auctions if more are held.
Those have been posted for $8k to $12k and include two SMA 5750W battery inverters, one charge controller, 2400W of panels, and a couple forklift batteries (which may be recent, may be old and half dead) totaling 50 kWh.
Some models have a diesel generator, for a higher price.
If you have parking space with sunshine, one of those would be turnkey 120/240VAC 12kW, with 12kWh/day production. You might add more panels later. The inverters can probably start up to a 6 HP motor.

There are other brands of inverter you could use to build a system somewhere in cost between what you've got and these DC Solar trailers. But the trailers give an idea of cost for a premium quality expandable system. They could be upgraded to 2x the battery inverter, and 20x the PV array (adding AC coupled inverters).

 

[Devin82m]

OK, thanks guys. I think I will build a 100 Ah pack first just to the get creativity going and have a pack for longer ham radio use then go from there.

But what I take from the both of you it sounds like I need to:

1. Figure out my usage
2. Buy and inverter that will cover that usage
3. Buy/build batteries for a 48v system
4. Buy a quality Charge Controller that can handle much more amperage

I think I may end up using the other stuff I bought for a wheel around "hand truck" system I can deploy quickly.

Hedges, that would be nice, but I don't have more than $500 a month to put towards any of my projects, so dropping $8k isn't in the cards. Hence piecing this together over time. Also I rarely buy used because I want to know the condition and state of anything I buy, but I'm most definitely not opposed to the idea, I could save money.

Please feel free to make any other suggestions.

 

[snoobler]

I think I may end up using the other stuff I bought for a wheel around "hand truck" system I can deploy quickly.

Hedges, that would be nice, but I don't have more than $500 a month to put towards any of my projects, so dropping $8k isn't in the cards. Hence piecing this together over time. Also I rarely buy used because I want to know the condition and state of anything I buy, but I'm most definitely not opposed to the idea, I could save money.

That's a great idea. A mobile solar generator is just a scaled down version of an off-grid system. While some of the details and components may vary, the concept is essentially the same.

Don't shy away from used. Sometimes exceptional deals can be had. I picked up 10kW of panels from a reputable local supplier for under $2700. That's about half the price of new, and these have a 1 year warranty.

 

[Devin82m]

Wow, yeah, that's a great deal, I will keep my eye out.

I just decided to sell my two unused MK Deka 245 Ah AGMs, I will use that money towards LiFePO4 cells. I bought them for $867, I'll try selling them for $800 since they have just sat there in my shop for a few months.

 

[snoobler]

Make sure you tell them you kept them on float the whole time, though 3 months isn't that big a deal for fully charged AGM...

 

[Hedges]

Most of the DC Solar trailers are unused. With $1 Billion in their piggy bank (almost "real money") they bought/build a lot more than they could find customers to lease.
Also new-in-the-box Sunny Island, saw $1500 recently. That would be 3 months of your budget (or 6; best to get two), so you might consider ramen or beans and rice so you can reallocate funds.

Inverters are a bigger investment so you want them reliable and possibly under warranty.
Panels, O.K. if there's an occasional bad one, so long as you have enough to rearrange within the voltage range you need.

 

[snoobler]

I posted the link to the auction for those trailers. There were some in Vegas that were well worth the money. I think they were "H" types - pure solar... about $4000 for 2.5kW of solar, lotsa batteries and a lot of split phase 240.

 

[SolarQueen]

Also be careful with the number of solar panels you get. A lot of people don't think about string sizing when they buy them. You have 20V nominal panels. If you are doing a 48V system, you need to have at least 3 in series for efficient charging in the summer. So for a 150V charge controller, you need two strings of 3, which is 6 panels. You have 5. You'll have to get a 250V charge controller like the Midnite Classic 250 to fit one string of 5 in series. It can output 63A, so with a 48V system, you'd be able to get another 5 in parallel with those in the future. (315W x 10) / 48V battery = 65A (it's ok to be a little over).

 

[snoobler]

Also be careful with the number of solar panels you get. A lot of people don't think about string sizing when they buy them. You have 20V nominal panels. If you are doing a 48V system, you need to have at least 3 in series for efficient charging in the summer. So for a 150V charge controller, you need two strings of 3, which is 6 panels. You have 5. You'll have to get a 250V charge controller like the Midnite Classic 250 to fit one string of 5 in series. It can output 63A, so with a 48V system, you'd be able to get another 5 in parallel with those in the future. (315W x 10) / 48V battery = 65A (it's ok to be a little over).

Listen to her. This is advice I didn't take (okay, well, it's advice I never got because I didn't ask, and I didn't RTFM thoroughly enough) and spent another $1000 on a 250V capable charge controller. Price of tuition.

 

[Devin82m]

Well, technically I bought 4 panels, but they didn't pack them well and the one on the bottom of the pile laying on a thin piece of cardboard was shattered. It looks like there are no breaks in or between the cells so I bought silicone encapsulate. They sent me another panel to replace that one and told me to keep the old one.

I'm a little confused by the charge controller. So you said that it's 150v and I will need two strings of 3 panels to make 6, then you said that I will need to upgrade to the 250 so I can handle a string of 5. So can my charge controller handle 6? The specs for the panels show 33.7v nominal, are you saying 20 because that's a more conservative estimate?

I will remind everyone that I want to produce enough energy to cover all my current needs, but over time. So would a 250v charge controller work or should I buy and even larger one?

Also I looked real quick and I don't see any evidence that the MidNite KID MPPT Charge Controller can charge LiFePO4 batteries, so that may not work for my mobile solar generator I plan I using LiFePO4 on or my house. The description just says Lithium and all the other typical types, not specifically LiFePO4. I bought the package above not knowing as much as I know now, and I still don't know a lot, I thought they would sell me something that fits in the specs, but after reading some of their responses in emails I wonder if the sales guy really knew much.

I plan on buying Fortune cells if I build my own packs. If I end up buying packs already built I may go with SOK.

Also, I assume I will have to either heat or store the LiFePO4 batteries indoors since it can get cold here and we have long winters? I thought about building a very well insulated shad eventually.

 

[Hedges]

I think the 250V model has lower output current limit, can't expand to as many watts.
250V would only be a suggestion for 5s1p configuration of panels, or 2 strings of 5. The 150V model would be for 3s2p, could support 3s3p maybe 3s4p.

 

[Devin82m]

So I watched a video on the charge controller I have, I still don't know if it can do LiFePO4, but the lady said that you can chain multiple Midnight Kid controllers together to handle more amperage... Not sure if that translates to more input though, you would think it would. One controller had as 5s1p and another has 5s1p. Am I understanding that right?

 

[snoobler]

If you can program the absorption and float voltages and disable equalization, or has compatible "canned" settings, it will work with LFP. Remember that in a lot of cases, LFP is a drop-in replacement for FLA/AGM.

A charger will work provided it bulk/absorption charges at 14.6V or less and floats at 13.6V or less.

One can chain any number and brands of SCC together on the same bank, but each SCC has a dedicated part of the array connected to it. During bulk charging (constant current, before absorption, peak, voltage is reached) multiple SCC equate translates to more input. Once the battery hits absorption voltage, it doesn't matter how much power you have, it can only accept so much current.

 

[SolarQueen]

Solar panels are referenced by their nominal voltage. A 12V solar panel has the right output voltage to charge a 12V battery. The actual output is 22Voc, but it is called a 12V panel for its ability to charge a 12V battery. Likewise, a 24V nominal panel outputs 44Voc. It is the right voltage to charge a 24V battery. A 20V nominal panel is high enough to charge a 12V battery with an MPPT charge controller, but not high enough to effectively charge a 24V battery in the summer when it is hot and the panel's voltage drops. It may work better for lithium than it does for lead acid, as lithium is OK with not being fully charged, unlike lead acid.

I gave several examples in my previous post, that may have been confusing and smooshed together. You have options. If you want to use your Kid, you can have a 48V battery bank, and have 3 panels in series. 3 x 315W / 48V = 19.6A out. 4 in series would be too high of a voltage. You could do 2 strings of 2 in series for a 24V battery bank. Some will argue you can do it for 48V, but again, maybe for lithium, since it can handle partial state of charge better than lead.

The Midnite Classic has a 63A output. It lets you put all 5 in series, and for a 48V bank, can handle 2 strings of 5. For a 24V bank, only 1 string. A Midnite Classic 150 has a 96A output, but you can only do up to 3 in series, but you could grow up to 5 parallel strings of 3. Lots of design choices that your salesman should have gone over with you.

 

[Rocketman]

For Solar Chargers there are two voltages. The output voltage - which is to charge your batteries - a 12v battery/system. The other voltage that is critical (never exceed - or get close) is the input voltage. This is what SolarQueen was referring to as 150v or 250v. You get this by putting panels in series. In her example a panel with a Vcc of 22 will have 22 volts output - if you string 3 in series you get 66 volts - she said 4 in series would be too many. In the winter when the solar panel is cold - it becomes much more efficient, so if you get a bright sunny cold day - the voltage the panels produce can go up. If you exceed the voltage on the Solar Controller you fry it.

The second number on the Solar Controller is the Amps it can produce. A 150/65 can handle up to 150 volts input and can produce 65 amps of power output.

 

[Devin82m]

Thanks a lot for explaining SolarQueen! Yeah, that makes more sense, I am SLOWLY understanding more. So do you suggest the Midnight brand, or is something like a Victron better? From what I can tell the Midnight brand is quality and is rated well, not some cheap Chinese charge controller, but I don't know much.

Thanks for the extra explanation Rocketman. So I believe I saw in a demonstration video for the Kid that it has a automatic cutoff if the input voltage is exceeded. From the video I saw it sounds like the Kid has a lot of smart features.

As for batteries I was thinking of building my own LiFePO4 packs, I've built a smaller 12v 20 Ah before, the larger ones seem easier. I've look at the Battleborn batteries, but they seem overpriced, even for their awesome build quality. The DIY cells I was looking at were the Fortune cells, I know there are cheaper ones out there but buying quality is more important, and I don't like dealing with Aliexpress or Alibaba, I always feel like I'm going to be cheated and I'm buying cheap crap. Does anyone suggest I go one way or another?

As for inverters that would handle my needs, I suspect I will need several kilowatts, I'm waiting for my electricity bill to see what my usage is. We have 2 refrigorators, an upgright freezer, user 1 large and 1 small space heater on and off, and I want to be able to use my 240 welder and plasma cutter and or a table saw, and of course all the electronics, stove, water heater, washer and dryer, and lights. Our electricity bill is not bad, it's typically between $100 and $200.

 

[Hedges]

If you got a Victron inverter, then I think Victron charge controller would be the way to go because they communicate, coordinate charging better.

Your electric bill won't tell you what inverter you need, just how many watts of PV panels and maybe how big a battery.
The panels will give you watt hours per day. The battery will store watt hours to last the night or however long (so you need to identify nighttime usage.) The inverter will deliver peak running watts and surge current to start motors.

You can size the inverter by adding up nameplate ratings of things you'll run at once, and for surge current use 5x the rating for motors. (Fridge not so much because rating includes defroster, motor is about 400W and 2000W surge)

Hard to do this in bite-sized chunks of $500, however. Maybe use the inverter and charge controller you've got for modest loads like the fridge and washing machine, use a generator for higher power equipment while you save up for an inverter that can run everything.

 

[snoobler]

If you got a Victron inverter, then I think Victron charge controller would be the way to go because they communicate, coordinate charging better.

This is only true if you get a GX device. It's basically a hub they all connect to and provides remote access, logging and control. Any of the bluetooth units can work in a bluetooth network, but the inverters aren't included. An SCC and a BMV monitor can share/coordinate voltage/temp data via bluetooth, and multiple bluetooth SCC can coordinate charging with each other.

I agree though. He should get Victron.