New build: Choosing an inverter and Water heating

[Phil.g00]

This is my point, it is unsafe to make generalisations.
For instance you may be typical of 50% of people and I may be typical of the other 50%.
You have to contend with load-shedding in a city, but I have to contend with fairly long power cuts on a rural line every second thunderstorm.

Yes, LA’s can’t hold a candle to using the grid, but again there are still plenty users out there.

That said, I still think that even lithiums are more expensive than the grid.
If they weren’t, people like yourself with Lithiums would go off-grid en masse.
Why would you stay with ESKOM, if it was cheaper to go off-grid?
You stay because it isn’t cheaper.
So they may be getting close, but they’re not there yet.

[jykenmynie]

Going completely off-grid is a much different equation than offsetting most of your nighttime loads with batteries. You don’t need to worry about the week of bad weather in winter. To get that last 5% of your annual needs off-grid is very expensive compared to the first 95%.

[plonkster]

Also, even when those cheap cells from China land. Do I really want to go through that amount of trouble… or just pay Eskom? I mean, if I’m your average guy with a girlfriend/wife and things to get done? Until an off-the-shelf battery is cheaper than grid power, it is not happening.

There are people here with enough battery capacity to see them (almost) through the night. Those people discharge the battery every night, which means a substantial part of the PV production the next day goes into recharging the battery. Those people, who could easily be more than 50% of the city-dwellers with a Victron ESS system, will use an MPPT to do the job.

At my previous house, I cycled my batteries. At the new place, there is a pool pump that sucks up a large chunk of the PV during day time. My circumstances changed. I would be better off with a PV-inverter now.

[TheTerribleTriplet]

When one throws a curveball, or “generalize” on forums, deets come out.

Phil needs batteries because of fairly long power cuts on a rural line every second thunderstorm. WHOLE new ballgame that, lithium or te not!

Plonkster has a new house and inherited a big pool pump, one that does not run when LS takes place, so that makes a lot of sense to add a pure grid-tied inverter vs more panels and MPPT’s, his base loads are sorted.

Off-grid: Wife and I can go off-grid as is with the system, just need to go and buy a generator for Cpt winter days. But with 5, maybe 7 people soon, Not. A. Chance!

BUT, from where we were discussing PV inverters vs MPPT, my curveball, we now have more succinct details on WHY Phil and Plonkster can say, with authority, why PV inverters can work.

In a city, if I had a Solis, I would have added a cheap off-the-shelve UPS for critical loads to be powered and scheduled the charging of said UPS for when the sun shines, IF there were no further LS scheduled.

If I wanted Victron, would have gone MPPT, unless I had a case like Plonkster, and have not changed said pool pump to either solar, costly, or a smaller one that can “fit” with no additional huge expenses.

MANY options, MANY ideas MANY solutions for all the different circumstances, needs, wants … hobbies.

[Phil.g00]

You want another curved ball, I have another tiny system.
A few panels and 300W dc borehole pump with an inbuilt MPPT.
And a tank.
Wires to pump, that’s it.

[jykenmynie]

I’ve been thinking about this for a while. I have two 150/45 MPPTs filled up with 6N and 12W panels (320W ones) (Yes, if I knew anything when I got it, I would’ve gone for bigger MPPTs because my Pylontech batteries’ voltage is just too low to get 5kW out of 90A which is irritating). I have another N roof with space for 6 of those massive 500W+ panels. When I take the plunge and go that route, I’ll probably put a 3.6kW Fronius on them instead of another MPPT. This is, however, a want and not a need, so it won’t happen anytime soon (I’m good at controlling my want-urges, unlike it seems @TheTerribleTriplet )

[TheTerribleTriplet]

@Phil.g00

I have another tiny system.

I have two:
12v 100ah with MP500va and a Rpi Venus
48v MP800va and a Rpi Venus
Both 100ah lithium banks
Both feeding the house, ESS style, on schedules, me relying on the main system to “throttle” feedback to the grid.
Both recharged on “spare” solar production from the main system.

The idea was a “cheap” battery bank extension/camping system … that went HOBBY level.

Then @neliuszeeman came past with these blasted 280ah cells … so now it is becoming a moot project.

[Phil.g00]

That’s cheating, my little system doesn’t have a battery, or even switch or a fuse.
Just wires straight out of panel, chocolate block, straight onto the pump.
Ok I am lying, I did put a water meter on the pipe, that’s how I know it’s working.

[neliuszeeman]

@TheTerribleTriplet Sorry oom!

[TheTerribleTriplet]

Ek weet dat jy weet dat ek weet jy weet jy issie sorry …

[TheTerribleTriplet]

@jykenmynie

This is, however, a want and not a need, so it won’t happen anytime soon (I’m good at controlling my want-urges, unlike it seems @TheTerribleTriplet )

Bah … so I thought.

Some of these want-urges, they sit there dormant patiently waiting for an opportunity to blindside you before you can say “batteries” from a angle you don’t see it coming … see.

[karischoonbee]

On the SSEG application I see a requirement for a dead grid safety lock. Is this even required with a grid tied inverter without batteries? If the grid is down there will be no power mos. Anyways, what is the go-to component to install here? Surely there are other options than a R15k Ziehl relay?

[Phil.g00]

@karischoonbee

If the grid is down there will be no power mos.

I can tell you with quite a degree of certainty that myself as a worker on a power grid that if I relied on things that mos shouldn’t be live, I wouldn’t be answering this question.

@karischoonbee

On the SSEG application I see a requirement for a dead grid safety lock.

@karischoonbee

Surely there are other options than a R15k Ziehl relay?

A dead grid safety lock is a Ziehl alternative, in order to safely work on the grid a worker has to isolate and earth the plant he is working on and prevent some silly bugger from making it live again while he is working on it.
Switching it off isn’t good enough. saying it should be off isn’t good enough.
You can potentially liven the plant he intends to work on.
So it may be crude, but if the power system worker can open an isolator, earth and apply his own padlock, so it couldn’t be closed by anyone else, I am pretty sure that would satisfy the regulations. It would certainly satisfy the worker and that is the basis of how a lot of work is done on the power system.
I personally would trust that system more than any Ziehl relay and ESKOM is basically saying the same thing. It is also much cheaper.
In actual fact there are also cheap mechanical gizmo’s that accept multiple padlocks, so that multiple people can apply there own padlocks, and it will force it to remain isolated until the last padlock is removed. We use this when multiple jobs are happening simultaneously.

This kind of thing:

[mmaritz]

@plonkster

You get 95% of the power from the PV modules directly to your loads.

In my case the next viable roof PV location is 150m away from the batteries. This is a perfect PV inverter location on the AC which can charge batteries via the Multiplus which is near the batteries. MPPT not an option in this case…

[plonkster]

@mmaritz

150m away from the batteries

Same for me here, tied in with a bit of laziness. Not in the mood for dragging more thick PV cable through conduit, and the next location is a good 30 meters or more away. I already have an AC cable from the inverter output going to that building, with a bit of extension I can easily tie a PV-inverter into that.

(That’s actually a valid bit of math to do… the extra cost in the DC cabling vs the higher cost of the PV inverter vs the extra cost of labour etc etc ).

[Swartkat]

Fascinating reading, thanks to all the contributors!!!

All I can add, is a huge thanks to TTT, Plonkster and Jaco De Jongh that assisted tirelessly in getting my system finely tuned and running optimally, and with sufficient guidance by TTT from the onset that it is absolutely perfectly sized for our needs.

Obviously there is always room for improvement, and that’s why I appreciate threads like this immensely.

Oh yes Kari, very welcome here, hope to learn a lot from you as well, but always consider very carefully what our fellow forum members here has to say. And yes you probably guessed it, I also went the Victron way and couldn’t be happier with it.

Cheers everyone!

[Richard_Mackay]

Do the remote PV inverters synchronise with the AC from the main system? I presume they would have to be from the same manufacturer??

[Phil.g00]

@Richard_Mackay

Do the remote PV inverters synchronise with the AC from the main system?

Yes

@Richard_Mackay

I presume they would have to be from the same manufacturer??

No

[plonkster]

@Richard_Mackay

Do the remote PV inverters synchronise with the AC from the main system?

Yes. They use something called a PLL (phase locked loop) to time themselves to the grid frequency… or if the grid is down, then to the frequency of the inverter that takes its place.

@Richard_Mackay

I presume they would have to be from the same manufacturer??

Nope. They just need to comply with the relevant standards. If you want to use them off-grid with an inverter (one that supports it obviously), they must support GFPR, Grid Frequency-dependent power reduction. Sometimes also called “frequency shifting” though I do believe that’s not a completely accurate term.

If additionally you want to avoid feeding energy into the grid, then it gets a bit more complicated. You still don’t need to match manufacturers, but you do need to check what is supported and what not, etc. For example, right now you can have an ABB and a Fronius in the same system as a Victron and it will work just fine. And if you don’t care about feeding energy into the grid, you can also use SolarEdge, SMA or Solis.

[TheTerribleTriplet]

@plonkster

If additionally you want to avoid feeding energy into the grid, then it gets a bit more complicated. You still don’t need to match manufacturers, but you do need to check what is supported and what not, etc. For example, right now you can have an ABB and a Fronius in the same system as a Victron and it will work just fine. And if you don’t care about feeding energy into the grid, you can also use SolarEdge, SMA or Solis.

Another one of those teeny weeny gems that one finds on forums … the ones one must always keep one’s eyes peeled for.