Author Topic: Need some math help on system production..  (Read 758 times)

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Offline tomw

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Need some math help on system production..
« 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?

Thanks.

Tom
Do NOT mistake me for any kind of "expert".

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24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

Offline rossw

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Re: Need some math help on system production..
« Reply #1 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? :)

Offline oztules

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Re: Need some math help on system production..
« Reply #2 on: April 12, 2017, 06:46:35 PM »
Same thing I came up with... different path perhaps.
ie...total 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 :)


..........oztules
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.
Flinders Island...... Australia

Offline rossw

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Re: Need some math help on system production..
« Reply #3 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.

Offline oztules

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Re: Need some math help on system production..
« Reply #4 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.....

.........oztules
Flinders Island...... Australia

Offline DJ

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Re: Need some math help on system production..
« Reply #5 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.

Offline tomw

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Re: Need some math help on system production..
« Reply #6 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:

Quote
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.

Tom
Do NOT mistake me for any kind of "expert".

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24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

Offline rossw

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Re: Need some math help on system production..
« Reply #7 on: April 15, 2017, 04:13:06 PM »
Or am I the nutbag who can't understand English?

No, he initially said one thing, then described exactly the opposite in examples, then done what he initially said.
His original examples are directly contradicting what he said and what it appears they do.

In your shoes, I think I'd print the email, run a highlighter over the examples, and take it to them along with your bill and say "please fix this".

If you're lucky, they'll do as per the example.
If you're unlucky, they'll put a line through the examples and say "Sorry, you were given the wrong information".
It's worth trying though.

Offline rossw

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Re: Need some math help on system production..
« Reply #8 on: April 15, 2017, 04:23:46 PM »
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.

Well, to be honest there ARE ongoing costs. Not just preventative maintenance (like they used to do in the old days), but ongoing repairs which DO need to be done. Fuses blow, insulators fail, poles get termites, transformers burn out, isolators stop working, storms damage things. There is an on-going cost to maintaining the network.
I'm not sure the disparity in prices reflects the cost however, but remember also that there is a great deal of "gold plating" done. Power companies prices are based largely on their value, not the cost of supply, and their value is increased by the infrastructure they build, buy or otherwise acquire.

Quote
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.

If you look at the energy market, as they get more "smart meters" out there, peoples time-of-use charging will probably get closer to the point of instantaneous-cost calculated. It is interesting to note that recently in parts of the USA, the wholesale price of electricity at certain times of the day was actually negative. Yes, they PAID you to take power. There was an over-supply of power (or is that under-demand?). A few hours later, it was back to costing you money. There needs to be a significant overhaul of the whole power "industry" to bring supply and demand more into line, but I'm not sure how to achieve it. Massive-scale deployment of individual small-scale generation & storage plants (ie, most homes and businesses) might help.


Offline eidolon

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Re: Need some math help on system production..
« Reply #9 on: April 16, 2017, 07:28:25 AM »
There were concessions made years back to the environmental community when RE power was estimated to never amount to anything. Read an article recently where it was stated that the utility companies want solar panels to face west when they can actually use the power. At this time there is no incentive for people for people to face them that way.  Smart meters will change all that and cause the grid to balance out. RE people are just freeloaders on the grid.

Offline tomw

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Re: Need some math help on system production..
« Reply #10 on: April 16, 2017, 08:36:43 AM »
RE people are just freeloaders on the grid.
I beg to differ!

a nearly $20K investment is a far cry from "free" anything.

The freeloaders are those that uncaringly waste energy gathered millions of years ago like it can last forever.

Takes all kinds to make a world.

Tom
Do NOT mistake me for any kind of "expert".

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I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

Offline Wolvenar

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Re: Need some math help on system production..
« Reply #11 on: April 17, 2017, 12:32:39 AM »
Our cooperative will not give out the numbers without a ton of official documentation so I have not checked into it in some time, however..
The last I looked, the mark up was almost 300% from the initial wholesaler, and the various cooperatives. Of that they had a projection of a bit over half of this to be used in operation costs (wages insurances etc), some in future infrastructure investments, machinery etc. The rest are supposedly *eventually* distributed to the cooperative members as the profit share. Seems though there is something like a 20 year delay before anyone sees these on average. A large percentage will never see these payouts is my guess.
I was not allowed full access to everything of course as I wasn't willing to do the mountain of paperwork, and clearances etc they required to get more info. I could show up at more of the meetings I suppose and gleam some info from that but time is not something I ever have much of.

Our cooperative says its all for RE, but makes it almost impossible to interconnect.

I am in the process of rethinking/designing our system and looking for the much larger knowledge of those on this site.


Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline DJ

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Re: Need some math help on system production..
« Reply #12 on: April 17, 2017, 10:25:06 AM »
I'm not sure the disparity in prices reflects the cost however, but remember also that there is a great deal of "gold plating" done.

Quote

Gold Plating?
Seems to me like it's solid 24Ct!

While I agree logically there has to be a maintenance cost, That cost is nothing like the highway robbery Difference between the (here) .06c Kwh they give you for what you generate and the .30C they charge the guy next door or down the street for his " Green " energy that comes straight out of my panels.
The poles, wires insulators etc are going to last 20-30 years least they have in my street because I have been here longer than that and the ONLY one they ever worked on was across the street when a stolen car  hit and snapped in.  Took them barely 90 Min from the time the repair crew arrived till the time they drove off job done.

I take exception to being treated like an idiot when they say it's maintenance cost instead of being honest and calling it what it is, Profiteering.
I understand businesses are there to make money but it's one thing for an essential service to cry poor mouth, Always make out they are hard done by and blame their customers while at the same time continually posting record after tax profits.

They then want to go on about how green and environmentally friendly they are  while, like everyone else, gouging anyone silly enough to fall for it and milking it for all they are worth.
If they were fairdinkum about RE and all the rest them lie through their teeth about, they would give you Equal return on what you generate as a matter of course because all this maintenance would be paid for by the built in cost of what they sell.


Quote

If you look at the energy market, as they get more "smart meters" out there, peoples time-of-use charging will probably get closer to the point of instantaneous-cost calculated. It is interesting to note that recently in parts of the USA, the wholesale price of electricity at certain times of the day was actually negative. Yes, they PAID you to take power.

Smart meters are nothing but yet another way of gouging the customer.
Does anyone REALLY think they would be spending ten of Millions on these things just to help their customers save money?
Please no one tell me you are that silly!
The ONLY reason they are investing in these things is so THEY can make more money and spin doctor it off as helping the customer.  What a load of Horse Ship!

If they were genuine about helping clients save money, they would be saying  " Off peak hot water costs 11c KWH to buy from us but we only pay you 6c KWH so make sure you get a timer that switches you hot water over to the day when you are generating solar power for nothing.
Anyone ever seen that from a power company? No.  Any why not? Because they aren't going to cut their own throat on making profit are they and who would expect them to?

So why do people believe they are installing smart meters?  ::)

Offline MadScientist267

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Re: Need some math help on system production..
« Reply #13 on: April 21, 2017, 11:29:43 PM »
Seems to me, the definition of "net" is all borked up.

Using numbers just plucked out from somewhere above that seemed to stick... I fail to see what is net about paying shy of a nickel for what you overproduce, then hit you for near enough a quarter when you pull it back. Whatever the numbers are, if they're not equal, I don't call that net.

I guess my post here should be taken purely as editorial, because obviously I'm not going to be able to change the wording in the industry's dictionary... assuming they even have one... (I know it's referring to the kWh count and not the rates... and let's face it, they're out to make money... if they provide you with something useful in the process... "that's great"... ahem)

That said... I consider something "net" when it's "overbalanced but weighs equally"... a disc meter that spins the other way, qualifies in my book. Not this buy at one rate sell at another crap.

Might as well go back to a battery bank and give "profit" up to the intrinsic losses of local storage if that's how they roll it. At least you know physics isn't taking you for some kind of devious ride that way.

Sounds to me like trading a headache for nausea... Ridiculous.

I've been wrong before tho...

Carry on then...  ::) lol

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