Solar PV Advice

Off Topic Homesteading
#1

I need a little advice on upgrading my solar PV system.

Currently, the system looks like this:

(4) 260w panels (1040w total)

Midnight Solar MPPT charge controller

2 Rolls AGM 460 AH batteries (6v)

There are some other parts, but that is the main stuff.

This is currently a DC system operating at 12v

I have 2 new batteries of the same type.

At this point, I need to make the transition from DC to AC.

In other words, I need an inverter/charger.

I would feed the “charger” part of that equation with a generator if I have a stretch of cloudy days.

I would like to be able to make 4,000 to 6,000 watts peak.

I would prefer a 240v system so that I can power both legs in a breaker panel, but I can work around that if it is a bunch more money.

I have looked at the pure sine wave invertr/chargers out there on wholesalesolar.com, etc.

Yikes. Those things are like $2,000.

What is my best option here?

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#2

Not an expert on the inverter chargers but we have had good luck with AIMs if you can go 24 Volt take a look at this one.

#3

I’m fond of the magnum inverters. Rock solid less bells and whistles and good charging on mediocre generators.
They make units that generate both legs in the same inverter instead of the more old school two inverter setups.
That said, I have thought that for Woodgas separating the charger from the inverter would be the way to go. One of the annoying things about inverters is most charge the house and charge batteries at the same time. If you have a smaller genny and a large load turns on or fluctuating ac due to less then perfect Woodgas I have found the inverters safeties can kick off the charger. The Iota chargers are a nice brand. You can get an add on to do three stage charging as well. To rebuilt with Woodgas in mind that is what I would do. The advantages of using common ac generators, as far away as you want and the advantages of steady dc charging…
Late night thoughts…
Best regards David Baillie

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#4

Yes exactly what David is saying. At first we thought DC was the way to go, but now realize DC loses a lot of its efficiency when you have to transfer that power any length of distance. Then the added expense of heavy gage cable to add. The nice thing about the DC systems is you can run with a varying rpm. But now we have the mixer control so that’s no longer an issue and even with DC you still have loading issues.

Im going to look into the Magnums as well.

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#5

IMG_0647.JPG3264×2448 1.74 MB

Solar is awesome when there is sun. Go to 48 volts if you can. This will help keep the cost of cables down. That said, the reason I am pursuing wood gas is to smooth out the edges of RE energy production. I have looked at a lot of angles for for power when there is no sun. Wind turbines, batteries, etc. Large batteries are far too expensive at this point and they start dying from day one : (

If I had the time, I would design a 3D printer that would make Edison batteries. I have had discussions with Edison experts along these lines.
Edison batteries have amazing longevity. In fact, many of the ones produced in the early 1900’s still work!

My interest in wood gas is to provide energy when solar and wind aren’t. My system will have 26kW capacity when complete. Overkill for my needs? Maybe. Considering I can easily peg 10kW when I clean my house, do the laundry, run the dishwasher, crank the music, and then the compressor kicks in, it may not be that excessive. Then again, if I shifted my power needs throughout the week, I could probably get away with a lot less.

RE is a transition. Albeit, a very challenging one. Cost creep is common. Few will ever be totally self-sufficient and the power companies are counting on that…

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#6

Thanks for the info guys.

I really like the Magnum Energy units, and imagine that they are pretty mature and bullet-proof. However, they are also over $2,000 for a 4kw inverter.

The AIMS looks like a better value at $1,200 for a 6kw inverter. But is it “Chinese junk” and does this matter?

I don’t know that I arm ready to drop that kind of money right now.

I have a 2,000 watt automotive inverter (intended for tractor trucks) that works pretty good. I bought it used for $100 (normally about $230 new). It works pretty good.

I am tempted to just use it for now.

I know there must be some good reasons why somebody is willing to pay $2,000 for an “serious” inverter when they could run out and buy a couple of automotive inverters for $400.

But so far, I have not run into a good explanation of exactly what these reasons are.

Anybody know?

Is there any reason I shouldn’t use the automotive inverters even on a long term basis? I could buy a lot of them for $2,000.

#7

Kyle you can use the cheap ones but they are not code compliant if that matters. You will probably have to Crack open you main breaker box and remove the neutral bonding bar to separate the neutral (white) from the ground. In regular utilities it terminates at the ground. On the cheaper inverters you have what they call a floating neutral… they will fry if you hook them into a regular board. The advantage of the good ones would be serviceability, service life and code and safety compliance. If you go the portable route look into the iota chargers it will give you the charger functions you will need…
Best regards David Baillie

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#8

We have had excellent service from our magnum 48volt inverter, and paid the steep price because this should go us for the rest of our lives. We’ve been mostly off grid for 6 years and are now totally off grid, using a Genny to make up the 10% or so different (we use about 10 to 12 kW per day) and have 6 kW array. Hope to connect one of gary gilmore’s charcoal gasifiers to the Genny this summer. We have plenty of charcoal from sifting the last 6 years of wood stove ashes.
The trouble with buying components for smaller systems is that eventually you will be wanting to go larger and you’ve already invested in a system too small…
On the flip side, my first set of panels 7 years ago were going for $4 a watt, and all the panels we bought since then to double the array size were going for $1 a watt, but the bright side of that I suppose is that we are now well along the learning curve from starting so long ago.

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#9

A very brief comment about dc verses ac.
Its does not matter if you use AC or DC at high or low voltage and how you use it…

Here is how it works.

A 3% drop on a 120 AC system using a #2 cable drawing around 100 amps is about 3 volts.
This is tolerable, you loose a small amount of power here.
Non of the electrical codes and standards I am aware of take note of losses in the reactive power ( inductive or capacities ) on small scale power at low voltage and we can ignore them at such low voltage levels.

Next example is a 12 volt DC systems with the same cable and the same draw.
But now that small loss of 3 volts ( give or take ) is a huge issue.

The logical conclusion is to run a higher voltage.
The higher the better in fact.
But then you reach a point around 600 volts where things get complicated.
The AC systems start to develop capacitve looses between the live lines.
This can be compensated for with line reactors but they do not go away, they are still there ( only we add things to counter act them )
DC systems do not suffer from this.

Next item we encounter with AC systems is the known as the skin effect ( yes it happens at low frequency too )
We get unequal current flow in the cross section of a cable because the electrons are trying to flow around the magnetic field induced in the cable and concentrated at the core.

These losses are most important at the higher voltage and higher currents.
We deal in the low voltage and low current area.
But its still important to remember he real power losses do to resistance at low voltage high current.
High voltage DC systems on the down side can deliver some down right scary short circuit currents.
That is their biggest safety issue.

What this a means is simple.
Run the highest practical system you can.
48 DC is out there, quite common and its my first choice anything less is, well just less ( though I would prefer much higher ).

I would run 600V ac systems in my home if I could.
That is the highest voltage I think one could use before the real danger comes into play with electrical power distribution.
But this is forbidden for safety reasons ( even though its more efficient, and safety is defined by how stupid the man that uses and services the systems is )

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#10

Kyle, I discovered a YouTube video where the guy talks about the Magnum 4kw inverter (240 vac/24volt dc) and uses it’s characteristics to supply power from Enphase M215 Microinverters to his house when the grid goes down. (Normally, with a grid-tied system like mine, when the grid is down, there is no power from my solar array.) He says the MagnaSine inverter has a pure sine wave and it is AC coupled. It is bi-directional, so when the Enphase Microinverters increase the 240 vac above the spec, the power can flow back to the battery. This is what makes it different from a regular inverter. His idea is to use an AC dump load that is controlled by the voltage on the DC side of the Magnum inverter. There are 5 parts to his video that can be seen here:

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#11

Depends on what you buy, Their pure signs are completely different than the modified sign inverters, the build quality between the two are completely different. The 12 kW unit we have is made like a tank, but we have to test them yet as well. We also like the Magnums as well, but cost is an issue so we went with AIM’s to get cost down. I am going to offer the Magnums as well as a premium package. But I have a feeling the two will perform the same. The AIMs also have features that Im not the sure Magnum has, built in transfer switch and auto generator start when batteries become low.

It really boils down to what your willing to spend and what kind of features you want. Not everything coming out of China is junk these days. But non the less it is still out of China. We buy as much as we can locally and that spreads out from there. When get things abroad, I do a lot of research on those items especially if there are high ticket items. Like the Predator, I researched this engine quite a bit before choosing to go that route. This unit brang our turnkey pricing down, $6000.00 and it outperforms our original 5 kW unit. Missouri Wind and Solar also use this AIMs inverter, I dont think they would offer it if it was not a good contender.

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#12

Hi all ,
if you have a hour or so to read a few very interesting stories about cheap Chinese inverters it could help those on a very limited budget .
I started reading this over 2 years ago and to be honest i was so impressed with what these clever guys had done we went out and bought a 3000 a 5000 and a 8000 watt all 24 volt units . these units not one cost us more than $450 and run everyday with no problems at all , and since this discussion started the manufacturer’s of these inverters must have been watching and reading as we never had to do a thing to ours straight out of the box they were very efficient .
If money was not an issue then of course we would have bought a home country brand make , but times are hard .
PS … the latest unit i bought is a 3000watt dc generator coupled to a 5000 inverter charger i had to dig deep for that and paid $650 , but was worth every penny .
Dave
https://forums.energymatters.com.au/solar-wind-gear/topic3344.html

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#13

So which inverter are you using? The PowerStar?

I followed the link and read the first few entries.

It sounds like these guys are making a lot of modifications.

I have enough projects, without having to re-engineer an inverter.

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#14

David - Thanks for the info.

Code compliance is not an issue on this off-grid setup.

However, I am concerned about the grounding issue.

How can I tell if the unit is designed for a floating ground?

Out of curiosity, what would happen if I just ran the two hot legs off the inverter to the box with one of those three prong to two prong converter plugs?

#15

Kyle:

That could lead to trouble down the road.
Maybe you do not need it now, but if you can have an inspection done by a Utility inspector then you have something to show your insurance company.

If the unthinkable happens and your insurance company wants to deny your claim on the grounds of bad wiring practices or equipment not approved then a special inspection certificate from the Utility in your area might cover you.

You also may want to consider that somewhere down the road you want to sell your property.
That special inspection of your system is quality assurance for a perspective buyer.

I have little respect for most residential inspectors.
Most seem uninterested in anything more complicated than a quick fan through the code book can answer.
Some blow smoke up you butt to cover for a basic lack of understanding for a complicated code question.
Even when they approve or disprove of something another inspector will have a difference of opinion often overturning the decision of the other.
But they all have the power to issue a variance to the code if you can prove your system is safe and reliable even if there are difference from what the code says.
So smile, shine the man on, pretend you are in the presence of the Pope himself, and once he puts that sticker on your box never let another one of them SOB’s in you home again if you can.

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#16

So Kyle what Wallace says is true. I assume you’ve thought all that through. If your inverter is made to be portable and costs that little I can almost guarantee you it is a floating neutral type. I’m assuming here that utility power once came in and there is a 220 breaker box installed. When utility power comes in there are usually two hot legs a neutral and a ground. They all go into the main breaker area of your board and that area is sealed off from the circuit breaker area that feeds the house. If there is no utility power to it remove that cover plate somewhere in there will be a plate screwed on between the neutral wire bar and the ground bar. If you remove it a floating neutral inverter will now work on it. Tape it to the bottom of the panel if you ever want to reverse it. Feed the hot side into a secondary breaker and jumper to a breaker right next to it. Keep your main breakers off. That will connect both legs. Again understand this violates many rules… If you just run a plug to your board only one leg on a 220 board will light up. If you don’t unbound the neutral your inverter will scream and shut down or burn out… no telling which…
Best regards David Baillie

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#17

This is not my home.

It is an off grid shack.

There will be no future buyer.

There is no insurance.

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#18

Dave:
It’s very hard to follow your explanation.
I just watched as you edited it to make it simpler but its still a little hard to follow.

The Common ( white ) and the ground are bonded together in this panel board once.
Nowhere else in the system are you supposed to have a second point where you bond your common to ground ( unless there is an outbuilding with a second panel board local codes may require a bond, other may not even require a panel board depending the rules in your area ).

If you have a unit with a floating common then you can use your utility provided ground bond to bond your inverted to ground.
Most inverters I have seen have options for grounding.
I would make very sure you can get this unit bonded for safety.

Ungrounded power systems scare the hell out of me because they can be so unpredictable and can become unstable ( voltage swings with reference to ground ).
They also do not trip on a short to ground.
That is until there is a second ground and all hell breaks loose.

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#19

Dave - Yes. That makes perfect sense.

The panel appears to have originally been a 100 amp sub-panel or something. There is no “main breaker.” Presently, power is fed to a double-pole breaker from a 220v generator.

Right now, there is no earth ground, but I intend to add one, since I assume this is an important safety feature.

I would like to be able to either feed the panel from the generator, or flip that breaker off and flip another one on, to feed it from the solar inverter.

The neutral legs (white) and grounds (bare) are intermingled on the same bus bar.

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#20

Kyle:
If your completely isolated from any utility source then you should drive a grounding rod in and bond to that.
What ever the codes are in your area you should try and follow the rules for safety.

Also GFCI protection is a very good idea and it can provide a great deal of back security for you in case your ground is not quite up to snuff ( dry soil rocky ground that prevent deep rod penetration ect )

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