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4400w inverter / grid assisted solar charging

Posted: Sun Dec 23, 2018 9:33 am
by ripple4
I've done a google site search for “grid assisted charging” and I don’t think that I saw this exact topic. I’m talking about grid assisted solar charging, not direct-to-battery solar, Not L1 6amp, not off-grid solar, not grid-tie solar, not anything with DCQC. The goal here is to incrementally change over from grid charging to solar without that need to get a utility permission for grid tie and still get 2012 full-power 3.8kw L2 charging. I've heard that this is called 'selfish solar.' Where I live, in coal/shale country, grid tie is discouraged and requires the full system to be running on day 1 and repermitting for any changes.

What might be new information here is this so-called hybrid inverter product which is grid/generator interactive without grid feeding.

They key feature is that it cannot feed the grid, which in this case is a requirement, but it can interact like a UPS with grid priority or it also can preferentially use solar/battery and then go to grid when the battery is flat. When the battery is flat and solar is off-line it can allow utility pass through with >98% efficiency, so its not a net loss when beginning with low power PV. And as solar and battery is added it can use more and more renewable before switching over to grid. The total solar input for this unit is 80amp*48v with a single mppt, which is around 4kw. I had read on this sub-forum and understand the benefit of the 1 inverter per panel arrangement, this product is not setup like that, but with add-on mppt charger from paralleled inverter units the array could be split up into up to 6 mppt segments. The one I linked to is stackable up to 6 units, which would be whole house capability. For 120v loads a cheap, used 240x120/ 480x240 single phase industrial Xmer could be used.

The one I’m researching (link) has three stage battery charging and compatibility with lifepo4 cells which tells me it has CC/CV capability, 18s LiFePo4 and 14s LiPo have the exact same max cutoff voltage as 24s (48v) lead. There are many 14s BMS options for cell balancing but I cannot find one that allows me to tailor max charge voltages to 4.1 or less, but that can be set by limiting the maximum charge cutoff voltage to 57.4 on the mppt inverter. Also I was not able to find inexpensive 14s BMSs that have much more than 60ma balance current, which in a 14s 10p module (1.4kwh each) would provide 6ma on average per 18650 cell, is that enough?

realistically, this inverter could be part of a system that may included many 10’s of kwh of lipo batteries with several 14s10p BMS strings of 18650’s like a DIY powerwall, and maybe 2-4kw of used solar panels. What kind of problems could come up with such a system? Am I missing a fatal flaw?

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Fri Dec 28, 2018 8:06 pm
by ripple4
Here is the manual for one version of this grid-assisted solar device and verified it can do CC/CV battery charging with custom charge voltages for a lipo storage battery. the 48v model has a bulk charging range of 48 to 58.4v, a float charging within the same range and the low battery cut off is 40-48v. I would think that a bulk charge voltage of 4.05v/cell 56.7v/pack, a float voltage of 4.1v/cell 57.4v/pack and a low battery of 3.3/cell 46.2v/pack would give long life and are within the range of this unit. if I was not in another project at this time I would try it out myself.

*link removed, I can no longer recommend this item*

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Tue Apr 02, 2019 6:01 pm
by ripple4
I’m posting this so that the experts can criticize this plan and tell me what’s wrong with it. Don’t hold back, the faster that I’m corrected the less time I spend being wrong.

While it cannot all be used, this system could produce $950+ worth of electricity per year according to the NREL website (5040w installed, 175 azimuth, 24 degrees elevation). My annualized average usage after my electric car purchase is $1621/year so that’s enough to erase 57% of my electric bill. To start, I want to extend my existing south facing screen porch room from 12x14” to 12x28” with material I already have from when I bought it screen room kit from Costco. The 18x solar panels (77”x33” each) will be at a 24 degree angle up from horizontal face 5 degrees east of due south. So that the top edge of the array will be flush to the house and just at the bottom of the second story windows. The idea is that the panels charge 8x large 6v or 12v deep cycle batteries in the basement, also power other A/C loads during the day, and then once I get home i charge my car up from any afternoon sun and then the 6-9KWH of energy stored in the batteries. if its cloudy or the car needs more power than was available that day, the 5000w inverter will see that there is no solar and the batteries are low and automatically switch over to the utility power pass though (or an auto-start natural gas/propane generator in a grid-down situation) and provide power to my car, the batteries, and any other loads connected to it. The lead batteries will last 10 years with proper maintenance and all other parts of the system 20 years. the system will cost ~$4000, the payback will be 4.5 years, and in the systems 20 year life it will save $14,400 of spending on power, an equivalent to a >10% APR if I invested that $4000 in vanguard. Not to mention it will work with no grid power forever, its off-grid, stand alone.

Here is a complete system diagram, but some of these system components already exist and work correctly, like to 10 circuit transfer switch that’s connected to NG generator and the L2H works which I talked about in a different post:

*system layout changed away from inferior components.*

In the December, the lowest production month, the system will make ~281KWH, and this is just a little bit less than my car used last December. My leaf soaked up 11KWH/day or 336KWH. However in summer, when the solar panel and inverter system will be producing 450KWH extra per month after charging my car. I can use that excess energy to run an little AC unit. My central AC unit takes too much power to run, it’s on a 30a breaker or at least it needs 30A/7200w+ to start. So instead i could install a "mini split" system that only runs on 220V/5A or 1100w. These systems have an exterior unit, just like a normal central AC system and an indoor unit like a hotel or apartment. my idea is to install that indoor unit in the basement and the outdoor unit just outside the house, but in close proximity to the indoor unit. the solar power system will charge the batteries first, and then when they are full I’ll have the system automatically start running the AC unit as long as solar power is available. this will have two main effects with the indoor unit in the basement it will eliminate the need for running a dehumidifier, which costs me $30/month to run a 70 pint unit in the hot humid summer, also i can set it up to run the furnace fan so it will suck all that cold basement air in and blow it around the house. The existing AC system will function normally and will be controlled with the existing thermostat and run on Edison power just like normal, its just it will be getting a boost with this system. In general everything has to work exactly like how you would expect, in case if someone comes after me they will need everything to work in an intuitive way, so I cannot make myself too built into it.

costs first the solar panels
18x used 280w (5040w total) solar panels $1400 delivered
5000w inverter, $530
8 deep cycle batteries $680
220v mini split system $400
Various electrical parts $400
screens/frames FREE
roof frame, steel uni-strut $500

*not recommended*

panels: ... 2459000473

mini split: ... 3107553841

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Wed Apr 03, 2019 12:42 pm
by SageBrush
^^ Fantastic

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Wed Apr 03, 2019 3:03 pm
by Oilpan4
Any chance you can go bigger on the panels?
Unistrut is good. Some people pay around $50 per panel to rack them on the cool aluminum racks. Unless it rains all the time you don't need it.
Used panels are good.

Get as much battery as you can afford.
Right now all I have a little 255ah @24v warehouse tug battery for my inverter.
48v is a great choice it seems like it has the most stuff available for it.

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Wed Apr 03, 2019 4:57 pm
by ripple4
Any chance you can go bigger on the panels?
the seller informed me that 5000w PV input was the max for this charger/inverter. I was debating going up to 5300w (295w*18) and getting some protection against output degradation in the multi-decade time frame.

Also this comment really got me thinking. can I supplement the PV input into the battery, bypassing the large charger/inverter, with a standalone 60A/48V MPPT charge controller? this would allow me the chance to put some panels facing due west, giving me the desired afternoon power. the classic trade off is if I collect more in the AM I need more battery to save for the PM when I need it for leaf charging and air conditioning. but if I collect from west facing panels I'll generate it just as I need it, but at the cost of overall production. 1200w on the roof of my garage gets sun late into the evening, over my neighbors arborvitaes, and would give me 50 more KWH in December, filling the $7 gap I had going to 100% carbon-free, off gird transportation.

If getting 1200w more into the battery is good, then I wonder if I could get a grid-tie 1200w inverter and have it directly supplement the 240v pure sine wave output of the off-grid charger/inverter.

here is the orientation of my house showing the south facing 5000w and the idea about 1000+w more facing west.

Get as much battery as you can afford.
Right now all I have a little 255ah @24v warehouse tug battery for my inverter.
48v is a great choice it seems like it has the most stuff available for it.
I looked at Fork truck units, nothing under $3K at 48v that I found, got a link? also any used lithium, even G1 leaf, is 3x as much as the following options.

One high capacity battery option is 12x of the crown 31DC130, I can get these for $85/each. I would do three parallel and 4 series to get 48v 390AH/195AH@50%DOD for $1000. the other high capacity option is 16x crown CR-205 @$74/each which is 6v, if I did 2 parallel and 8 series I would get 410AH/210AH@50%DOD, but it would be $200 more than option 1 for just 15 more AH. the KWH/$ is less on the GC2 than the marine option. The main benefit of GC2 6v is the stock water caps are easy to use, the 31DC130 has the rectangular caps that covers 3 cells each and would be a pain to water the battery 4 times a year.

I could get a $40/battery aftermarket battery watering system for the CR-205 but then again and I could 3D print my own easy to use polypropylene caps for the 31DC130, 1KG of PP filament cost $40. So I could go either way on maintenance, and for cost its the 31DC130. thoughts?

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Wed Apr 03, 2019 5:42 pm
by Oilpan4
If it's mppt then it should only ever accept 5kw of input. At least that was my interpretation, but I never planned on testing that idea. On a fixed fixed install made with 5.3kw of used panels you will likely never see 5kw. If you had dual axis tracking and depending on how the brand of panels you got are rated yeah you could see the full 5.3kw.

You should be able to run a mppt battery charger and a grid tie. Back around 2013 I did this with a genasun mppt for lithium iron phosphate and a cheapie mico gird tie.
The mppt soaked up around 80% of the power from the panels until the battery was full. It was just a little year long experimental grid tie vehicle to grid thing. But it worked.

Last time I was looking at hybrid inverters they didn't have a built in panel to battery charge controller. They had a battery charger that ran off AC power. I think people prefer standalone charge controllers because sometimes they quit working.
I was looking at radian and schnider.
But I will pretty much only buy Morningstar and genasun charge controllers.
There may be new ones that have built a charge controllerbuilt into the inverter but I would use a standalone one if possible.

My lift truck battery came from the scrap yard. It is a brand new battery that got tipped over. They air force weinies were afraid to use it so they scraped it. I bought it for 30 cents a pound. These batteries are fairly forklift driver proof.

I think inching your way off grid is they way to go, unless money is no object.
Occasionally I read about some one who tries to go off grid on a small budget, they buy a generator, a junk modified sine wave inverter, a few hundred watts of over priced panels and some batteries and end up back on the power grid with in a month or 2.

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Thu Apr 04, 2019 5:16 am
by BrockWI
Yes almost all the MPPT controllers will max out at whatever they are rated for. I would suggest 6000w on that south face if you can get it, there might be an hour or so the MPPT will max out and not use some of the power, but the 2 hours either side of that you will get the additional power from the panels. In winter or hazy days or mornings or evening the extra panels would help out a bunch.

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Thu Apr 04, 2019 10:46 am
by ripple4
Awesome info! I did find some info about oversized PV arrays with MPPT and it makes sense. i would have preferred to have a larger shaded area anyway covering the entire 12'x36' width x length of my patio. i'm asking the company i bought the inverter/charger from if they endorse that idea. ... stems-roi/

two other questions, the snow i get in winter often is not thick, rarely more than 6" but it does last a long time, what do we think about sticking some silicon heating pads to the back of the panels? Maybe 2 per panel, each pad 3x4" and 20 watts, they are on ebay for $2.50 each. then controlling them to turn on when there is snow on the panels. i know panel efficiency goes down when hot, but i'm talking heating them from 10F to 33F.

lastly, what precautions are common to take for surge protection on the DC side of a PV? can i install typical MOVs and thermal disconnects like AC power surge protectors at the outdoor and indoor DC breakers? i'm relatively well read on best practice for AC surge protection, DC should be the same, bubble of protection etc. the data sheets for MOV list AC and DC ratings for the same PN, with DC being a touch higher volts. My plan was going to add a ground spike in the yard, run 6awg solid to the unistrut and PV frames, and ultimately back to the edison panel ground hitting all the metal cases on the way. on the power wiring side having fused/breakers with MOVs at most wire termination. the last line of defense for my appliances was going to be high and low voltage brownout protector at the 10 circuit transfer switch.

Re: 5000w hybrid inverter for grid assisted solar charging

Posted: Thu Apr 04, 2019 10:58 am
by BrockWI
Can you get a 45* tilt on the Panels? Or are you closer to 40* north latitude? Ours at 45* will shed snow pretty quickly by themselves, as long as the snow has a place to fall off to. The 45* is perfect for winter but not as ideal for summer, but in summer we have so much more sun I just leave them at 45* all year. Most of our panels are about 18 inches off the roof except one set that is 12 inchs. Snow will sometimes pile up which then doesn't let the snow slide off anymore. But with the panels being almost black they clean themselves off pretty quickly.

I wouldn't heat them, I would think the power you use to melt snow will use more than the power you gain back from the sun. Unless they are going to be more flat? I used a square D DC rated breaker panel as a combiner box in the garage attic with all the neg fused at that point as well. Then fused again right before the inverter on both the pos and neg side.