Micro inverter to grid

Another solution is to have an ATS (automatic transfer switch) that monitors load vs generation, and disconnects equipment accordingly.
Its likely that it will be more expensive, which is why I again say its not really viable.

You're really better off with a hybrid unit, or complete offgrid in our country, given the laws/regulations in place.
 
You are wrong, the exSolar one is not for a grid-tied micro inverter, it's designed for the Fronius grid-tied inverter, as I have said in the past.

An ATS is an automatic electrical that switches a load between two sources. (wikipedia)
The load in this case would be the "house". So it would switch to generator, if the grid goes down, then switch back to grid when the grid comes back.

I am not sure how you see this working in a micro-inverter solution, could you please explain?

I agree, hybrid is a very nice solution, but if you want to power your house, you would typically need a 5kVa unit which at the last price I have is $ 896.52 or about R13,000 from ReneSola. You then need at least 4 x 300W panels (36.6V each) to make the minimum 120V to have it switch on. Which is another R 12,000 without installation. Then you would need batteries, lets say 4 150Ah at R 1,500 each, that is another R 6,000. Installation, including wiring and rails etc can easily come in at another R 14,000. So the hybrid solution would end up costing you just shy of R50,000.

A typical household that spends R 1,000 on electricity a month would have a base-load of about 500W, peaking in the morning and evening. So the bulk of the time the 5kVA unit will be producing 500W to satisfy the house's daylight needs, which could be done with two micro-inverters for R 15,000. The rand value of the saving would be the same, since the same number of kilowatt hours are being produced by both systems. The R 50,000 system will take 5 times longer to amortize, which is about 20 years.

(Obviously you will get load-shedding assistance with the hybrid, as the micro-inverter is not legally allowed to help during load shedding.)

If your electricity bill is R 2,500/month, theoretically your base might then be 1,250W and the hybrid would then save you 4 times as much money. We used the NASA radiation average to calculate that one 300W panel saves you an average of R 140.00 every month.

So 4 (300W panels) x 140 = R 560/month x 12 = R 6,720/year which will give you 7.5 years to amortize the R 50,000.

Going above a monthly cost of R 2,500 you would need to add more panels, so maxing out the hybrid at 16 panels, which would add R 36,000 to take your costs to R 90,000 (including a bit for installation and rails). You would then be saving:

16 x 140 = R 6,400/month x 12 = R 76,800/year and then amortize the R 90,000 in a year and a half. That is assuming you have a base load of 5kVa which is a monthly electricity bill of about R 10,000.

Thank you
Peter
Evolt Energy.
 
Last edited:
Suggest read my solar blog to see more of those exact sort of calculations in a little more detail.
I think the phrase teaching grandmother to suck eggs comes to mind here :whistle:

Thanks though.


The CHTech (ExSolar branded) unit either does voltage or frequency control to control a GTI (grid tied inverter). I haven't checked which exactly. Should work for your units also, as thats the basics of AC coupled control.


Assuming

Micro Inverter <-> DB <-> Grid Tie Feedback Limiter -> Grid

The limiter will either send voltage or frequency out of bounds to the GTI line, and it will go into shutdown mode. Anti-islanding will kick in, and it will shutoff for 600 seconds, then try to reconnect to the grid every 30 seconds thereafter (assuming it follows standards).

Alternately if using a smart ATS switch, then it could work by turning off the Micro inverter line via relay if Generation > Load.
Assuming single phase it would have 2 sensors.
One for incoming power (output from Micro inverter side), and one for grid load. If incoming power > grid load, then turn a relay on to disconnect the Micro Inverter from the grid.


Microcare also makes something similar - http://microcare.co.za/products/specialized-products/grid-tied-limiter/ , although that communicates with their own brand inverters over serial, rather than via AC coupling.


Yet another option is to have a dump load controlled via relay what kicks in when generation > power usage.
Similar concept - example here - http://www.ev-power.eu/GridFree-Inverters/Current-monitoring-relay.html

All of these options, are of course rather silly, albeit necessary given the laws/regulations in place, and the increasing abundance of smart meters that prevent feedback.

Technical kludges all the same though.
 
Last edited:
This discussion isn't all about you ;) (there might be one or two other people reading this)

I think the GWL/Power Current Monitoring Relay, PRI-32, AC 1A - 20A, CE, should work.
If you have the micro wired into your db through your 2 pole 10A breaker (as you should).
Only problem would be you are limited to 1A or 220W, they suggest looping the wire a few times, but my grid supply cable is already 6mm, the size of their hole.

You could set the device to "closed" if the current is greater than 1A, which would connect your micro inverter to your house, and "open" if the current drops below 1A which will then disconnect the micro.
(Assuming he device is direction aware) thereby preventing feedback into the grid.

You would then get a sawtooth wave as the micro ramps up production, hits the 1A limit, switches off, waits 600 seconds and starts the process again.

Legally you would be 2 for 3 (you lose 1 point if you are using the ReneSola micro, as NRS cert. is only due in 3-6 months).
This is about as close as you can come to legal, you would need a base load of 500W to make it viable, so a monthly electricity spend of at least R 1000.00.

Buying the device from the site gives:
53.79 € (unit) + 62.11 € (shipping via TNT) = 115.90 € ~ R 1,740.37 (which adds 1 year to the amortization)

Kind regards
Peter
Evolt Energy.
 
Last edited:
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X