OFF GRID POWER; various thoughts on...

[MountainDon]

Hi. Too bad there is too much theft risk to install those panels at your cabin. Our system has worked well for about ten years now,with the exception of the lightning strike. 

Yes, lithium batteries have advantages over lead acid. If the lithium batteries do last at least as long as the 
 manufacturers and sellers claim, they can even save money in the long term, even with the big initial expenditure.  Flooded lead acid batteries like the T105 do have one nice thing... the ability to take sp gr readings of each cell. That can tell you exactly what the condition of the cells is.  I keep a log book of the readings of each cell.  Lithium have to be charged when the battery is above 32 F.  Not a big deal but in my case, I will have to do something about that when I change to lithium. But that is a few years off as I just put new lead-acid into service this summer.

If your plan is to have the solar and batteries as a backup to operate the well pump as well as use solar power "to run a fridge or some outbuilding lights etc. and cut back on our grid use", those items will need to be separated from the other grid-tied circuits. There can not be any way the power grid and power from a generator or inverter can be "mixed". 

AC power has a sine wave. Viewed on an oscilloscope good AC power is represented by a wave ...


Simply put the peak and valleys of two AC sources to be combined must be matched, otherwise, damage is going to occur to at least some of the equipment. Your equipment or the power company equipment.  When generators that are designed to be parallel connected the engine speed, the waveform, the voltage is all matched. If the voltage is off a bit between the two sources damage can occur.   Same with inverters, some are are designed to be parallel connected, many are not. The ones that can be paralleled will sync the waveform, etc. None of those can easily be sync'd to the power company system as far as I know. The inverters and other equipment used in a grid tied solar system are designed to be compatible. The power company will have a list of approved equipment. The AIMS are almost certainly not on the list.

So, if a portion of your home is grid-tied and a section is not, you would need to totally separate the non grid powered fridge or whatever circuit from the grid powered balance of the system.

Or you make a proper grid-tied connection between your solar panel system and grid approved inverter and use the grid as a battery. This needs to be coordinated with the power company and all equipment approved and the installation inspected. FWIW, most grid-tie systems don't have any batteries, but backup batteries may be included with proper design, approval and proper automatic safeguards to keep your power completely separated from the grid when the grid loses power. Many people hire this out but with guidance, a DIY person can do it. Member Dave Sparks can help with system design and equipment purchase. Dave charges a fee for his services and really knowsHis contact emailis on his website.  his off-grid power.

There is a very real danger to power company workers if a non-authorized power source like a generator or solar inverter system is supplying power into a power grid that is not powered by the grid system.

Another member here has a standby, automatic start generator, that will take over and supply power to the home when the grid goes down. It has automatic controls to maintain isolation from the grid.

We reduced our power company bill by replacing the old furnace, the old A/C and the appliances and old electronic gear over several years time, as well as changing every light bulb to an LED. Our power company has a three-tiered rate system as many do. We seldom ever get into the second tier and never into the third and most expensive tier. We have lower total power use/costs than even some of our neighbors who opted for a solar lease or power purchase agreement.  Of course, we also go dark if the grid fails, but in our area, the grid has been very reliable. If it wasn't I would probably go with a good generator system running off propane or natural gas.

I hope you find all that useful. More questions welcomed.


Yes, that is a shameless plug for Dave, and no, I do not consider this spam as we know Dave to be qualified and honest.

[LastO]

MtnDon, I had planned to pull any circuits that I run on this solar system away from the grid and keep this system off the grid completely. The location I have chosen for the panels and the electronics and batteries is very close to the panel that my well and outbuildings that I want to run on this system so it would be pretty easy to just install a breaker panel and rewire these circuits directly to this off grid panel.

Here is the old design that you worked up for me back in 2014:
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Here's a thought that works with 1 Kid charge controller

4 of the 300 watt panels; 2 series strings of 2 panels each and those series strings connected in parallel

48 volt battery bank
buy 2 more of those batteries; 2 series strings of 4 each, connected in parallel

Then when those 12 volt batteries die buy some real RE batteries (like L-16's) or at least golf cart batteries

MtnDon
Member    # Posted: 15 Sep 2014 18:22 - Edited by: MtnDon
Reply Quote

That has the Kid working at half capacity (amps) more or less. Better than working close to the maximum, as far as theory goes. It also cuts the parallel batteries down to only 2 deep; much better than as is now.

If those batteries are about 115 amp hours each then you would have 115 x 2 = 230 AH @ 48 volts = 11040 watt hours. At 50% max discharge = about 5 Kw usable power.

230 AH would be served well with a 20-25 amp charge input. The 4 panels on the Kid would supply 21 amps at 57.6 volts (equiv to 14.4 on a 12 volt battery). Just about ideal for charging.

Now find a 48 VDC inverter.

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So here is my plan, tell me if I have this right.

I will lay everything out the same as above except rather than the 12 volt trolling motor batteries I plan to buy 8 of the Trojan T105s  (225AH) and wire them the same in two series strings of 4 batteries each and then connect those strings together parallel. (6v x 4=24 volt series strings x2)  This should be a 24 volt setup instead of the 48 volt but should make 10800 watt hours which is very close to your original design that you did for me in 2014.

225AH x 2 = 450 AH @ 24 volts = 10800 watt hours. At 50% max discharge, This should still be about 5 Kw usable power. Hopefully my math is correct.

Unless I'm better off wiring all 8 batteries parallel for a 48 volt system. I do plan on adding 8 more batteries and 4 more panels at a later date but it will probably be awhile to come up with the funds.


Correct me if I'm wrong please.

[LastO]

Then I'm looking at this Inverter/charger as a possibility:

https://theinverterstore.com/product/6000-watt-pure-sine-inverter-charger/

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6000 WATT PURE SINE INVERTER CHARGER 24Vdc / 240Vac INPUT TO 120/ 240Vac SPLIT PHASE OUTPUT

6000 Watt, 18,000 Watt surge, 24 Vdc, 120 & 240 Vac, Inverter, Charger & Transfer Switch. 50 amps @ 120 Vac. Input charger 240 Vac.


This AIMS Power Low Frequency 6000 Watt 24-volt Split Phase Power Inverter Charger is not your average every-day power inverter. What you see here is our top-of-the-line power inverter, built for the purpose of running your whole house (smaller home), business office or large RV. This inverter charger is perfect for your off Grid system or for use as an emergency backup supply.

Split Phase Power Inverter

The 110/220 split phase inverter is capable of producing 2 legs of 110v, making this inverter perfect for home and shop applications with a 220 panel in place.

However, the inverter can utilize grid-power to charge the batteries and send the power out to your application using the built-in 85 amp charger. If the grid power is lost, this inverter is equipped with a seamless transition transfer switch, becoming a true UPS (Uninterruptable Power Supply) when you need it in emergency situations and natural disasters (battery required).

This inverter charger has an on optional LCD remote showing you of any abnormalities on all parts of the system, giving you ample time to fix the issue and exactly where to look. This inverter charger also comes with an Auto Generator Start mode that can tell a generator to start up and begin providing charge to the batteries (through a separate charger on 120v gensets) or providing power to the home.

Need to use this in a different country or with 50hz electronics? This whole house inverter comes with Auto Frequency Detection software, providing you with the correct power frequency on either 50hz or 60hz.

[LastO]

Am I better off with a 48 volt bank?
So 8 batteries in parallel because I'm going to add another string later on?
Is 2 strings of 8 batteries better than 4 strings of 4 batteries?

[LastO]

Or will my charge rate be insufficient? In hind sight looking at the numbers I think it will be insufficient.

Sorry about all the different posts. Just trying to figure out all of this as I wait for your vast knowledge on the subject...LOL. I'm learning as I go and want to get it right. I sure don't want to ruin my batteries from an insufficient charge rate or order the wrong inverter or some other issue that I have wrong.

[MountainDon]

Sorry, I'm not ignoring you but have found myself in the middle of some neighbors with frozen pipes and a leak or two.

[LastO]

I didn't think you were... no problem at all. I'm busy with livestock myself! LOL

[LastO]

225AH x 2 = 450 AH @ 24 volts = 10800 watt hours.

or 225AH @48 volts =10800 watt hours

Wouldn't the charge rate of 21 amps at 57.6 volts  be better suited for the 48 volt system @ 225AH rather than the 24 volt system recieving 21 amps at 57.6 volts for 450AH?

The only question is ...Is an 8 string of six volt batteries  better than two strings of 4 batteries?  Of course if I expand into double the solar panels and double the batteries I would be looking at two strings of 8 batteries or four strings of 4 batteries. 

Seems like the 8 battery string would be better and the charge rate better suited for the 48 volt battery bank.

[MountainDon]

A series string of those T105 batteries is better than having the same number of T105's in two series-parallel strings.

The panels you have work out well to charge the 48 volt battery bank with a KID MPPT controller. MN has a string sizing tool for checking that.   

If the same 2S 2P configuration of solar panels was tried on a 24 volt battery bank, the KID will be overpowered with too many watts. 24 volts won't work.  If you wanted more panels you would also need another controller as with the 4 panels in 2S 2P it is at about 75% of capacity. Or buy a larger capacity controller.

I have no idea how much surge capacity you will need to start that well pump. No easy way as far as I know for determining that. It would sort of be a shame to have to get a huge inverter only to cover the pump surge.  But maybe unavoidable unless you can fund a new low surge well pump. There are some you could run right off the panels without any inverter.

As for running other household items as long as they are completely on their own system so your system cannot power up a dead grid you should be fine.   How old is the fridge you might power?  If it is anywhere near time to replace it you could buy an inverter compressor fridge and not have any startup surge there either. LG and Samsung sell some fridges like that. Often it is hard to find what tech the compressor uses when looking at fridges or the spec pages. Those new compressors all have a 10 year warranty on the compressor so that can help weed out the old style compressors. Some of those compressors are also known as linear compressors. No surge, virtually silent, I really like them. With a new well pump and fridge the inverter could be made much smaller.  Just a thought.

[LastO]

Thanks MtnDon. BTW, I traveled near the mountains where you live a few years back on a run to pick someone up in Oregon from Central Texas. Beautiful country for sure!