Grid tied inverter query

[Fazil]

should a grid tied inverter switch off when there is no grid power during the day?

[Youda]

Yes.

grid-tied inverter should either automatically switch off or disconnect from the grid, at least. It's required by the code - in order to prevent so called "islanding".
 

[Fazil]

So its purely as a cost saving install as it cannot combat load shedding right?

Are most guys using grid tied with battery backup for commercial installations to solve challenge mentioned above?

[Guest]

1 hour ago, Fazil said:

So its purely as a cost saving install as it cannot combat load shedding right?

Are most guys using grid tied with battery backup for commercial installations to solve challenge mentioned above?

Grid tied is for cost saving as the entire home / business benefits from the grid tied solution.
Next level to that is selling power back to the utilities - but that is a whole new ballgame.

Grid tied with battery backup is a hybrid solution yes. One powers the "Always On" loads using panels and / or batteries when the grid goes off.

[Fazil]

3 hours ago, The Terrible Triplett said:

Grid tied is for cost saving as the entire home / business benefits from the grid tied solution.
Next level to that is selling power back to the utilities - but that is a whole new ballgame.

Grid tied with battery backup is a hybrid solution yes. One powers the "Always On" loads using panels and / or batteries when the grid goes off.

Is it still a viable option considering how eratic and unstable our grid supply is?

[Bobster.]

There seems to be some disagreement on definitions.

My understanding is that "grid tied" means you have solar and inverter but no storage. I know that some web sites use the term to mean "retains connection to the grid".

So, using my more narrow definition, you would have an inverter and solar panels generating extra power during the day.

I think what @Fazil is thinking of is a HYBRID system, that has batteries for storage as well as solar cells for generation, and retains a connection to the grid.

I have the latter. When there is no power it continues to produce output but

1. Nothing is sent back to the grid
2. Only the "backed up" circuits in my home get power. Effectively the DB board is split and there are non backed up circuits (eg Stove) which will not receive power whilst the grid is not available.

For a couple of days, due to a problem with the inverter firmware, we ran as grid tied - solar supplementing the grid. I did test this by throwing my main circuit breaker during the day. What happened was that the solar power was still distributed to the backed up circuits.

 

[Bobster.]

PS: On the days when we ran just panels and inverter, our savings was in the 40% ball park. So that's not to be sneezed at. We would have protection against load shedding whilst there was strong sun light. 

I have two arrays of panels. One facing east, one facing north. I've a lovely, sunny patch of west facing roof. If I get the extra cash I'll put panels there too to get the most out the sun.

[Guest]

22 minutes ago, Fazil said:

Is it still a viable option considering how eratic and unstable our grid supply is?

Solar inverters are not as advance as say UPS'es that "clean up" the incoming power, but they do add a lot of stability.

Erratic / unstable grid: What do you mean by that?
1) Generally power failures - then absolutely yes.
2) Just your house / suburb having erratic / unstable grid?

I'm asking because a PF user had erratic power that turned out to be the breaker in the box in the street that fed their home.

[___]

South Africa's grid is not erratic or unstable. On a spectrum of how bad it can get, it's just not. At least yet. Sure, if you live in a small town where the municipality is bankrupt and infrastructure is crumbling, then maybe on a local scale this could be true, but as a whole our grid is pretty stable and gives clean power.

Once you get to Zimbabwe levels where you have maybe power 8 hours a week (I hear rumours of even less), then grid-tied obviously makes zero sense. And if you simply lose too much money during our own 2.5 hour outages, then the same. But overall, assuming that things don't deteriorate too much in the coming years, grid tied still makes economic sense.

[GreenFields]

22 minutes ago, Bobster said:

There seems to be some disagreement on definitions.

My understanding is that "grid tied" means you have solar and inverter but no storage. I know that some web sites use the term to mean "retains connection to the grid".

I understood the definition of a pure grid-tied inverter is one that converts solar DC power to AC power and synchronises it to the the national grid power in terms of frequency and phase. This output power connects in parallel to the grid, to power firstly the household where it is generated, but any excess power can be exported to the wider grid (your neighbour's house). Assuming Eskom or the municipality allows exporting/sell-back/net-metering.

I understood that a battery inverter with solar and grid inputs is not necessarily the same thing even if they are called "hybrid" (eg Axperts), while the "true" hybrids (Infini, Goodwe EM, Imeon) can do grid tie as well as backup power. Could be wrong.

[GreenFields]

54 minutes ago, Fazil said:

Is it still a viable option considering how eratic and unstable our grid supply is?

Looking back I think yes, the actual number of hours of grid outages during peak daytime generation have been relatively few, so it's still viable. Looking forward, if/when Eskom/grid collapses, grid-tie will not be viable. But if it comes to that, nothing will truly save us.

[Fazil]

36 minutes ago, The Terrible Triplett said:

Solar inverters are not as advance as say UPS'es that "clean up" the incoming power, but they do add a lot of stability.

Erratic / unstable grid: What do you mean by that?
1) Generally power failures - then absolutely yes.
2) Just your house / suburb having erratic / unstable grid?

I'm asking because a PF user had erratic power that turned out to be the breaker in the box in the street that fed their home.

Erratic meaning loss of grid regularly regardless of the cause (load shedding or system upgrades or cable theft).

This is national so im not concentrating the problem to a specific area.
I observed grid supply on 1 of my installations going as low as 208V and 51Hz.

[Fazil]

7 minutes ago, GreenFields said:

Looking back I think yes, the actual number of hours of grid outages during peak daytime generation have been relatively few, so it's still viable. Looking forward, if/when Eskom/grid collapses, grid-tie will not be viable. But if it comes to that, nothing will truly save us.

difficult to offer grid tied solutions with fear of the unknown.

So i always offer hybrid with minimal backup so loss of grid doesnt affect business continuity at a large scale.

[Guest]

31 minutes ago, GreenFields said:

Looking forward, if/when Eskom/grid collapses, grid-tie will not be viable.

Yeah, if Eskom collapses, whole new ballgame.

Must not forget that a hybrid grid tied still uses what the panels can produce, when Eskom is off.

So we win, with Eskom and without Eskom.

Edited July 22, 2019 by Guest

[Guest]

12 minutes ago, Fazil said:

Erratic meaning loss of grid regularly regardless of the cause (load shedding or system upgrades or cable theft).

Hybrid grid tied gets my vote.

[Bobster.]

20 hours ago, Fazil said:

Erratic meaning loss of grid regularly regardless of the cause (load shedding or system upgrades or cable theft).

This is national so im not concentrating the problem to a specific area.

Actually I think the problem does vary considerably with locality. Load shedding is load shedding, when Eskom do that, it affects everybody. 

But if you look at Johannesburg the last few months, when there has been no actual load shedding (I didn't say "no outages"), Blairgowrie has been pretty stable,  whilst Linden, Emmarentia and Northcliff have had a lot of problems that are caused by the local infrastructure.

Further south, Ennerdale has more than their fair share of problems because of illegal connections from a near by informal settlement.
 

[Fazil]

20 hours ago, The Terrible Triplett said:

Hybrid grid tied gets my vote.

price various substantially between grid and hybrid.
Would you still go hybrid for a business park?

[Fazil]

Client wants to save costs and has a genset on site which they want to retain. They specified because of costs no batteries required and their business only runs during the day.

So objective is to meet client request.

[Guest]

50 minutes ago, Fazil said:

Client wants to save costs and has a genset on site which they want to retain. They specified because of costs no batteries required and their business only runs during the day.

I would go pure grid tied for the entire business park to save on Eskom charges each and every sunny day.

And when the power fails, have each business install small affordable UPS'es to take care of the critical always on loads whilst the generator starts up and settles.

UPS loads I envisage are computers, switchboards, routers, not kitchen and geysers, so the cost would not be high per business. And it is for each business to take care of. Simplifies the system to boot.

Because the biggest cost as the client indicated are indeed the batteries if you want to power a business park. Spread that cost, mitigate it with off-the-shelf-stock-standard cheaper UPS'es.

Generator would probably be cheaper over time than a huge battery bank. Small UPS'es spread all over just need to deal with 5-10 min backup whilst the big genny starts up and settles.

AND the UPS'es also protects the devices connected to them from spikes and brownouts and all that.

 

Edited July 23, 2019 by Guest

[Guest]

10 minutes ago, Pietpower said:

So can you run a generator and grid tied together?

Jip, because a generator is installed COMPLETELY separate from the grid. Like having two power sources, one being Eskom and second one being the gennie.

You need a UPS to carry the load for the switch over.

Some gennies auto start in the absence of Eskom. 

So no need for inverters, just small cheap off-the-shelf UPS'es all over the business park on or under desks.

[___]

6 hours ago, Fazil said:

Would you still go hybrid for a business park?

I would not. At least not yet. If you do go hybrid later (I've seen such a system in Austria), you can always add the inverters on afterwards and keep your AC-tied PV.

The rule is that if you use most of your PV directly, then you should AC-tie it. If most of it goes into the batteries for later use, then DC-tie it.

So I would most definitely start with grid-tied PV inverters for a business park, and then maybe add some backup later. The system I saw in Austria use theirs for peak shaving. Everything above 100kW is shaved off using PV and/or batteries. They have more than 100kWh of battery storage too.