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Solar (heating or electric) / Re: Need some math help on system production..
« Last post by tomw on April 15, 2017, 01:21:38 PM »
Yeah they are trying to screw us.

Our emails setting this up started with this response to my installer questioning how it would be done:

He is correct there is no net metering. With that said your production offsets what you buy from us. Anything that is overproduced is bought back at 3.8 cents per kw. With this size of unit, I do not see any over production being carried over to the next month.
This is a hybrid metering system we use and have seen other municipals doing the same thing
Basically it will look like this.
Your usage is 800 KWh
Your system produces 500 kwh
You pay retail for the 300 you buy from TMU
 Now let’s say your system produces the following
Your system produces 800 KWh
Your usage is 500 KWh
We buy the excess of 300 KWh back at 3.8 cents

He says "no net metering" then pretty much goes on to describe their method which sure looks like net metering? TWICE!.

They charged me X.X cents for all incoming then credited me x.x for any delivered so its definitely NOT what he described!

Or am I the nutbag who can't understand English?

Anyway only got the bill yesterday and being Easter weekend I decided to wait til after the holiday to pursue it further. It is a city owned utility and the superintendent is a blowhard who thinks he is Albert Einstein but is actually closer to Forrest Gump but not as nice.

I will go to the City council, Mayor and Press if I need to.  He also never returned our signed  interconnect agreement. Pity the guy is also responsible for the destruction of a $3/4 Million dollar diesel generator trying to save some $$ on oil changes and other maintenance oversights.

This is either extreme incompetence or deliberate and I think I have some options here.

Sadly, I shouldn't have to fight them to get what they said they would do.

Solar (heating or electric) / Re: Need some math help on system production..
« Last post by DJ on April 15, 2017, 11:01:07 AM »

I think this Time of Use and charging you one rate on what you import and a lower on what you export is a criminal scam.

The power companies say the difference between import and export is because of whole sale rate and grid maintenance etc.  PIFFLE!  Costs nothing and wears nothing out to send the power from one house to next door where it is then purchased at the full tilt rate.
I think they should be paying you MORE for you power than theirs.

Here they have all these wonderful feel good Fuzzy BS options to buy " Green" power.  How the fk they send you green power from coal power is another scam but anyway. If you are giving them green pwoer they sell for a preimum, shouldn't you at least get a fair 1:1 credit on the power you import?
 And what about the power from the power station 100-300KM away?  How much does that cost to send all that way and more over, how much is LOST through resistance, leakage, inefficencys in all the transformers etc?

There is no way in hell that could be more efficent than sending your power next door or up the street.

As for the time of use, I think that's pretty spin doctored. While you are at work and not using any power at home, you are in the office or at the factory where the power IS being used and shiploads of it. I have a hard time believing that combined domestic use outstrips commercial use.  And again, even if it does, why are they paying less to the home owner when they generate power which is supplied locally and takes the heat of the power company?
Makes no sense.

I have set up my own system and thankfully I have an old spinny meter which goes backwards as well as it goes forwards.  May not have that luxury much longer as I'm looking to move house  but I'll be setting up the same way so at least what I do use is offset by what I generate and I'll also look at going to a battery system ( forklift pack rather than non economic powerwall type ) to stick it to the power scammers a bit further.

As I'm also into Diesel generators running on waste oil, going off grid may be an option in the near future when I have the space and setup to do it.
Hoping to hell the next place wherever it is has the old style meter but given the age of the homes in the area I'm looking at, probably a very long shot and I'm not a lucky person.

First thing for sure will be a big electric Dual element hot water system with the main element hooked into the solar through an inverter.
Solar (heating or electric) / Re: Need some math help on system production..
« Last post by oztules on April 12, 2017, 06:57:49 PM »
You wrote that whilst I was editing mine.... agreed.... timing is everything.

And if we hear a massive explosion from the direction of Toms place... I'll deduce he just found out his bill was not net billing.... but the other one.....

Solar (heating or electric) / Re: Need some math help on system production..
« Last post by rossw on April 12, 2017, 06:54:41 PM »
Your calculations demonstrate how important "time of use" is.
The question not asked, was how well was he using the power he produced. This is largely a financial question (where you have 100% efficient storage, as the grid appears to be), but the sting in the tail is the cost per kWh.

If he buys power off the grid at 12c, and sells power TO the grid at 4c, the inequity is obvious:

Sold     1606 @  4c =   $64.24
Bought 2045 @ 12c = $245.40

Managing your usage to minimise what you export (and therefore what you import at a different time) may not result in any difference in your percentage of used power generated, but could hugely impact your power bill at the end of the day.
Solar (heating or electric) / Re: Need some math help on system production..
« Last post by oztules on April 12, 2017, 06:46:35 PM »
Same thing I came up with... different path perhaps. production was 2374kwh... of which you used directly only 2374-1606 exported not used by you at the time = 768kwh out of the 2374kwh produced.

So you used 768kwh of your own electrons, but had to then import some 2045kwh from  the man... making total usage by you  768+2045=2813kwh

That makes total usage............2813kwh
and total produced...................2374kwh

And so I get the same thing with (2374/2813)x 100 = 84%... so 84% of your electrical needs came from home grown electrons, while 16% was imported from the powers that be.

Interesting that most of your generated power was exported ( 1606kwh as against 768kwh used at the time of production )...... grid makes a good battery :)

EDIT: It is interesting  that it will depend on the billing system, as to whether you need to reschedule the house power usage profile. If you get net metering, and net billing then who cares, but if you get charged at an import rate that is materially different to the export rate, then it may not look too pleasant.

Over in Aust, some providers do net billing ( Flinders Island is one  :)), but some give you only 5-8 cents/kwh for your export, and charge you up to 25c/kwh for your imported power. In this latter case, you need to get the hot water running during the day only, and any other loads you can schedule in the daylight hours.... particularly at peak solar times.

Tom needs to be on net billing, as his usage does not mirror his production timing.
Solar (heating or electric) / Re: Need some math help on system production..
« Last post by rossw on April 12, 2017, 03:55:41 PM »
Well, I might have this wrong, but my take on it is that:

You produced 2374.8
You imported 2045.51 and exported 1606.85 (making a nett of 438.6 used from grid)
So your total consumption was (2374.8 produced + 2045.51 imported - 1606.85 exported)  2813.46 consumed.

You produced 2374.8 locally of the 2813.46 total you used: (2374.8/2813.46)*100/1 = 84.4%
Or, the other way, you produced 2374.8 but consumed 2813.46, so you CONSUMED 118.47% of your production.

Anyone else want a go? :)
Oztules / Re: guess who bought a power jack inverter
« Last post by Juan Marrero on April 12, 2017, 10:44:18 AM »
hey !  thanks!
I will do just that
You have another's fan in the caribbean .
Solar (heating or electric) / Need some math help on system production..
« Last post by tomw on April 12, 2017, 10:21:23 AM »
Ok, folks.

We installed a grid tie 7,700 watt SMA SunnyBoy system.

The smart meter was installed as part of that interconnect agreement.

I gather 4 figures from my system:

Inverter data:

Total KWH produced (daily, monthly, yearly)

Meter data:

Delivered -Pushed out to the grid.

Received -drawn from the grid.

Net -Like it says, different between the above 2 figures.

Trying to sort out the percentage of our use we produce with the system.

I a just having  brain farts on figuring this out, not seeing the way. When I graded papers for a professor in college we used the formula what you have divided by what you should have times 100 for  test scores. This works great but it doesn't seem to work in this situation?

The fly in the buttermilk is that I have no way to know how much we use that doesn't go through the meter. The inverter connects to the breaker panel through a switch and breakers and excess flows to the grid and if needed power  flows in from the grid when the system is not producing enough to service loads. All thru one bidirectional "smart" meter.

For instance, I have these lifetime values:

Inverter total production:
2,374.8 kWh

Meter data:
438.6 NET   1606.85 OUT   2045.51 IN

Now, the part that stumps me.

What percent of my total consumption is from the SMA?

Careful, it is not as simple as it seems. At first I thought I could just use meter NET divided by inverter total but that completely misses the instantaneous usage that often is a large part of the inverter output.

I know that we "bought" 438.6 KWH since Nov 19, 2016 (day of meter swap and commissioning)

Late winter was very overcast / cloudy and short days but last month we produced about 300 KWH more than we used that month.

OK any ideas?


Oztules / Re: guess who bought a power jack inverter
« Last post by oztules on April 12, 2017, 04:21:37 AM »
Treat the output as 220v center tapped transformer.... so for 220v use L1 and L2 and ignore N is effectively the center tap. So you can run the pump through L1 and L2, and still use the 110v output to drive different  loads as well.

Oztules / Re: guess who bought a power jack inverter
« Last post by Juan Marrero on April 11, 2017, 02:43:05 PM »
Hello everyone.
Thanks for all the really useful information.
I request your opinion.
I am aslo an islander (40 x 100 mile island in the caribbean).
I got a power jack low frequency 8000w split phase inverter too.
ac electricity is 60hz here.
I need to hard wire the ac 220-240v to a water pump which is 3 amps but is about 100 feet away off grid.
I checked the terminals and L1+N=110v ac and L2+N=11v ac
I am planing on using a 8AWGauge(3.26 mm or 8.36mm2) to hardwire the connections.
The question is:
1) Do I connect one to each L1 and L2 and the ground to the N?
    or do I just connect the L1+L2 ?
2) Do I use a thicker wire?
3) once I use this hardwire does that mean I cannot use the 110v ac outlet receptacle?
Does anyone have a picture of a hardwired 240v ac power jack inverter?
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