Author Topic: Multiple Inverters New Installation  (Read 4173 times)

dodegkr

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Multiple Inverters New Installation
« on: July 14, 2013, 09:48:50 AM »
Hi,

I have been following Martin for a while now and finally took the plunge and had some PV installed.

I hope to post a youtube video soon, I am however confused and wonder if someone can help explain.

I am based in the South of the UK and have two strings of PV located on two different parts of the property as the main property roof  is too small.

7 x 240Watt Panasonic VBHN240SE10 HIT panels on the roof of my house (South Facing)

7 x 240Watt Panasonic VBHN240SE10 HIT panels on the roof of my garage (East Facing)

Due to the fact that the panels were located in different areas and rather than have to dig up the drive and run long DC cables the installers put in two Solarmax 2000S inverters

One in the roof space and one in the garage, each Inverter has a very short DC run and each Inverter has its own Board trips Isolation and Generation meters for the Feed In Tariff.

The Main house Inverter AC output is fed into the main Consumer Unit's Main Switch together with the main grid connection.

The Garage Inverter AC output is fed into a trip in the main board that feeds the garage Consumer unit.

So here's the question..

Using a bit of php code I pull the stats of the inverters as :

Main House Panel Status

AC Power now.........[Watt].: 1390
Load now................[%].: 60
AC Current now.......[Amps].: 5.65
Time 14:33

Garage Roof Panel Status

AC Power now.........[Watt].: 1159
Load now................[%].: 50
AC Current now.......[Amps].: 4.73
Time 14:33

I note the Grid Electricity Meter is stationary at this point

The washing machine is on and a few devices are in standby tv,dvd etc, computer is on..

I fire up a portable AC unit in the house which according to the wall plugin meter is pulling 1059Watts

So if we guess that everything is using 2kw why does the meter start ticking on the Grid ?

Is it possible that wiring it up this way means we will pull from the grid and not the garage panels.

To me I cant understand how the garage panels will be pulled from if we go over the house roof panels output

Is there a better way to wire it up, how on earth do we use the garage PV power in the house or are we anyway ?

If both arrays are totalling 2549 then surely the grid wont be called on for a load of less than that?

I have attached a picture of the diagram on the wall by the CU.

I still don't understand why the house pulls from the inverter and not the grid in the first instance!

Thanks for any ideas, comments

Dave
« Last Edit: July 14, 2013, 11:25:27 AM by dodegkr »

SeanB

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Re: Multiple Inverters New
« Reply #1 on: July 14, 2013, 10:07:25 AM »
From the diagram the meters on the PV cells show you are feeding power into the consumer unit, which feeds the house. The import meter does not register power being fed back ( which it should do so if it is connected in reverse it does not run backwards) so only power to the house that is not supplied by the panels is actually being metered by it. The meters on the panels show total generated, and they only count up.

dodegkr

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Re: Multiple Inverters New
« Reply #2 on: July 14, 2013, 11:14:18 AM »
Sure I get that part, but what I dont understand is an AC load larger than the house panels 1.6kw will it come from the roof and partially from the garage? how does that work ! If its DC in parallel i.e a battery I get it, but AC ?
so far best I have seen is 2.8kW from the two sets of panels & inverters combined

I have ordered 3 CT sensors to have a play on each feed into an http://openenergymonitor.org/emon/

« Last Edit: July 14, 2013, 11:27:39 AM by dodegkr »

SeanB

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Re: Multiple Inverters New Installation
« Reply #3 on: July 14, 2013, 12:29:15 PM »
Each of the panels and the grid feeds power to the consumer unit. Any load will draw power from the combined units, as they are all in phase to the common port. Any excess power draw over that the panels can supply at the moment will be drawn from the grid. Each panel and inverter just tries to give the most power into the grid and house, they just provide power and any excess will be sent to the grid.

dodegkr

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Re: Multiple Inverters New Installation
« Reply #4 on: July 14, 2013, 12:44:39 PM »
Thanks Sean, When you say in phase can you elaborate as to what that means.
I have heard of three phase 415v but with a single supply paralleled to the output of the inverter what does phase mean.

Dave

SeanB

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Re: Multiple Inverters New Installation
« Reply #5 on: July 14, 2013, 02:54:16 PM »
The inverters generate power that is a sine wave that slightly leads the incoming mains by a small amount so that they continually supply a current into the grid, like a generator unit in a power plant. This works very well to add power without needing any complex systems, as the load is going to always be a lot bigger than any individual inverter, but it adds in its best contribution to give power to the rest.

dodegkr

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Re: Multiple Inverters New Installation
« Reply #6 on: July 14, 2013, 03:58:54 PM »
So would one inverter lead another then.

I.e if the frequency was 50.01Hz of the main grid would the first inverter run at say 50.1Hz and the other one at 50.2 or something.
They are connected together with RS485 for data logging but I cant see anyway of making them aware of each other other than the frequency shift ?

SeanB

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Re: Multiple Inverters New Installation
« Reply #7 on: July 15, 2013, 12:51:06 AM »
They will both have exactly the same frequency as the grid, but both will be an independent supplier to it. To each the grid is a load that will absorb power, so both will provide power to it. They will not be aware of each other until the grid fails. Depending on the fault that disconnects, so that there is either too much or too little load to absorb the power generated, they will either shut down on overcurrent ( too much load to supply) or they will drive each other up in frequency until they trip out on anti islanding when they hit around 55Hz, then the last one running will trip on overload.

They are not going to be aware of each other as they are only a small part of many suppliers, following the grid trends to give power in if they have it available from the panels. Many small sources that are scattered around and doing the same without needing to be aware of each other.

dodegkr

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Re: Multiple Inverters New Installation
« Reply #8 on: July 15, 2013, 03:52:12 PM »
Sean,

Thanks for the replay, that makes some sense with anti-islanding in play

Cheers

Dave