Confusion over PV connection to grid

[Doing it for the kids]

our supplier has confused me today.

I was under the impression that if the sun was out and we were producing more than we were drawing, the meter from our electrical supplier measuring our usage from the grid, would stand still.

I have not installed an export meter (to get paid to feed our spare power back in to the grid) because we use most of what we produce and I thought it was not viable. I think if I did I would get paid 3 - 5 p / kwh.

last year we used 44,000 kwh but produced 45,000 kwh. I was thus expecting a small bill.

However, I have been told today that all PV generated leaves the panels and goes straight into the grid, not via any farm demand first. This cant make sense otherwise there is no benefit in producing it, getting paid export prices then importing it back in regardless!?

can someone please clarify!?

I understand my thought princess is correct for Resi but not commercial..

 

[Aceface]

I may be wrong, (it wouldn't be the first time), but the stuff you produce should be at a slightly higher voltage (think of voltage as "pressure"}, and therefore even though you are open to the grid your own produced electricity will rush to your own local demand for current which is your side of the meter thus being used ahead of any "lower pressured" current turning the meter flowing inwards from the rest of the grid. If you are only producing part of the current needed, then the grid will automatically top up the required amount and the meter will only measure the short fall.
I think something is amiss.

 

[warksfarmer]

our supplier has confused me today.

I was under the impression that if the sun was out and we were producing more than we were drawing, the meter from our electrical supplier measuring our usage from the grid, would stand still.

I have not installed an export meter (to get paid to feed our spare power back in to the grid) because we use most of what we produce and I thought it was not viable. I think if I did I would get paid 3 - 5 p / kwh.

last year we used 44,000 kwh but produced 45,000 kwh. I was thus expecting a small bill.

However, I have been told today that all PV generated leaves the panels and goes straight into the grid, not via any farm demand first. This cant make sense otherwise there is no benefit in producing it, getting paid export prices then importing it back in regardless!?

can someone please clarify!?

I understand my thought princess is correct for Resi but not commercial..

Think something is wrong somewhere. Ours is wired from the inverters back to the main farm supply. It's a 70kw system and we have an annual use of around 95,000 kwh. Last year we exported about £1000 worth at 6p/kwh and spent around £6k on importing.

Although to be honest I've questioned this in the past and think we need it checked out to make sure it's working as it should as the original installer was a cowboy and has since gone bump.

 

[akaPABLO01]

I've been awaiting this question from you lot, a very interesting one as well, and many a disagreement I've had with nearly everyone I've told.

Every spark of electricity produced by all electric generation stations is put on the grid. This is transferred by your inverter at a higher hz ensuring export otherwise its just circulating around your yard.

For example, those of you with digital meters will have a symbol (reverse) appear when your demand is less then your production. Your meters calculate the difference and either add a kW or freeze.

Those of you crafty buggers who still have the disc spinners will be enjoying rebates/account surplus on your electricity bills as those little money savers reverse spin auditioning credit - this is illegal operation btw, and you must have these upgraded to digital.

Your meter will calculate the difference in usage and export which is why the generator needs to be wired back to the main board not secondary.

Now, if you're scratching your head thinking I've produced X and imported Y but my bills are high then you are using more electricity then you originally thought to power your yard. Having a generating station is learning how to use it to its maximum efficiency, split down time at lunch. Don't have multiple drains of electrical equipment running at the same time for e.g.

11am - overcast - all machines running
12 - sunny - lunch
1 - machines off
2 - machines off
3 - milking

Scenario
Producing 70kW at 12
Producing 30kW at 12:30
Producing 10kW at 12:45
40kW produced in one hour (guesstimate)
Your yard has used a steady 50kW in 1 hour
You have not used 100% solar/wind

Ok, ready for the naysayers and disagreements, come on.

 

[Doing it for the kids]

not much to disagree on. I just wanted to know when the power leaves the invertors does it turn left straight to the grid or right via the farm before it turns left to the grid.

Most say it turns right but you and SSE are saying left.

does this mean I have to have an export meter fitted? I don't think I will export enough to make it worth while?

 

[warksfarmer]

I've been awaiting this question from you lot, a very interesting one as well, and many a disagreement I've had with nearly everyone I've told.

Every spark of electricity produced by all electric generation stations is put on the grid. This is transferred by your inverter at a higher hz ensuring export otherwise its just circulating around your yard.

For example, those of you with digital meters will have a symbol (reverse) appear when your demand is less then your production. Your meters calculate the difference and either add a kW or freeze.

Those of you crafty buggers who still have the disc spinners will be enjoying rebates/account surplus on your electricity bills as those little money savers reverse spin auditioning credit - this is illegal operation btw, and you must have these upgraded to digital.

Your meter will calculate the difference in usage and export which is why the generator needs to be wired back to the main board not secondary.

Now, if you're scratching your head thinking I've produced X and imported Y but my bills are high then you are using more electricity then you originally thought to power your yard. Having a generating station is learning how to use it to its maximum efficiency, split down time at lunch. Don't have multiple drains of electrical equipment running at the same time for e.g.

11am - overcast - all machines running
12 - sunny - lunch
1 - machines off
2 - machines off
3 - milking

Scenario
Producing 70kW at 12
Producing 30kW at 12:30
Producing 10kW at 12:45
40kW produced in one hour (guesstimate)
Your yard has used a steady 50kW in 1 hour
You have not used 100% solar/wind

Ok, ready for the naysayers and disagreements, come on.

Do you do site visits

 

[Doing it for the kids]

x2!

 

[akaPABLO01]

Left

Installing an export meter depends.

50kW solar electric bill annual usage 20,000kWh - install

It's difficult to suggest but I only installed them on 100kW> systems

I never put them on 50kW as farms can use about 75% of this meaning profit neutral

The analysis that was carried out before install would have suggested it with discussion on how the yard is run.

I did an analysis on a dairy post 50kW milk twice daily and they used about 75% meaning the export meter license cost them £60 loss annually

 

[Doing it for the kids]

Left

Installing an export meter depends.

50kW solar electric bill annual usage 20,000kWh - install

It's difficult to suggest but I only installed them on 100kW> systems

I never put them on 50kW as farms can use about 75% of this meaning profit neutral

The analysis that was carried out before install would have suggested it with discussion on how the yard is run.

I did an analysis on a dairy post 50kW milk twice daily and they used about 75% meaning the export meter license cost them £60 loss annually

that's my point. We have 50 kw here and I think we will use at least 40,000 all year around working 5 days under normal working hours so no point having an export meter. does that sound about right?

 

[jcb360]

not much to disagree on. I just wanted to know when the power leaves the invertors does it turn left straight to the grid or right via the farm before it turns left to the grid.

Most say it turns right but you and SSE are saying left.

does this mean I have to have an export meter fitted? I don't think I will export enough to make it worth while?

Right.....SSE are wrong.

Unless your installer connected on the grid side of the SSE meter.

Any photos of where PV connection point is?

 

[Doing it for the kids]

Right.....SSE are wrong.

Unless your installer connected on the grid side of the SSE meter.

Any photos of where PV connection point is?

so now your disagreeing with @akaPABLO01 !?

pictures wont explain it as lots of kit in there. I am fairly sure the installer did a correct job, they did an awful of work in the south of work in South England and everything got signed of correctly.

 

[Still Farming]

Your installation will use electric also so an import export meter will be required .
Sell electric waste of time unless MW's .
It's all FIT'S and they are getting worst.
As said in early days the meter ran backwards ???
Would have thought all got their acts together now ?

 

[jcb360]

so now your disagreeing with @akaPABLO01 !?

pictures wont explain it as lots of kit in there. I am fairly sure the installer did a correct job, they did an awful of work in the south of work in South England and everything got signed of correctly.

No, I'm not disagreeing with Pablo.

SSE are wrong.

Anything your PV produces reduces the amount of power you import from the grid.

Meter should stand still if PV produces more than you are consuming.

You should check that the installer hasn't connected on grid side of meter - I've seen it happen!

 

[akaPABLO01]

so now your disagreeing with @akaPABLO01 !?

pictures wont explain it as lots of kit in there. I am fairly sure the installer did a correct job, they did an awful of work in the south of work in South England and everything got signed of correctly.

@jcb360 is wrong

@Doing it for the kids although your yard is consistently consuming a steady all year power your solar isn't. It's main operation is between March/October. Within this period you'll fluctuate. Highest productivity is June.

If your usage through November to February is the same as summer then you'll have a month by month full draw give or take. Place this next to the May/August incoming draw and use your solar meter generation over these same months to get a good idea of your usage. If this works out at 50% solar usage then install an export.

You will only receive export for a 4 month period though I expect. So concluding your analysis will determine whether paying £300? Export license is warranted. Will you export £300/£0.04p= 7,500kWh?

 

[jcb360]

@jcb360 is wrong

@Doing it for the kids although your yard is consistently consuming a steady all year power your solar isn't. It's main operation is between March/October. Within this period you'll fluctuate. Highest productivity is June.

If your usage through November to February is the same as summer then you'll have a month by month full draw give or take. Place this next to the May/August incoming draw and use your solar meter generation over these same months to get a good idea of your usage. If this works out at 50% solar usage then install an export.

You will only receive export for a 4 month period though I expect. So concluding your analysis will determine whether paying £300? Export license is warranted. Will you export £300/£0.04p= 7,500kWh?

Please clarify which specific part of my post is wrong?

 

[akaPABLO01]

Please clarify which specific part of my post is wrong?

When there was heavy solar farms being installed in the south the DNO froze all installs and applications because all network capacity was peaked. All the renewables were loading the grid. The network transfers electricity via hz transfer lets say 40. The inverter reads this and transfers at a higher rate to export all generation onto the grid to mix with national grid power station electricity. Your meter will freeze when you are exporting as much as you use and when you are using more than exporting it will accumulate. The meter will read reverse on overproduction.

 

[jcb360]

When there was heavy solar farms being installed in the south the DNO froze all installs and applications because all network capacity was peaked. All the renewables were loading the grid. The network transfers electricity via hz transfer lets say 40. The inverter reads this and transfers at a higher rate to export all generation onto the grid to mix with national grid power station electricity. Your meter will freeze when you are exporting as much as you use and when you are using more than exporting it will accumulate. The meter will read reverse on overproduction.

I'll ask again......Please clarify which specific part of my post is wrong.

Thanks.

Also, please clarify which units the figure 40 relates to.

 

[akaPABLO01]

SSE are wrong.

Frequency

http://www2.nationalgrid.com/uk/services/balancing-services/frequency-response/

 

[jcb360]

H

Frequency

http://www2.nationalgrid.com/uk/services/balancing-services/frequency-response/

You still haven't explained which part of my post was wrong.

I am perfectly aware that the grid must be maintained at a nominal frequency of 50 Hz.

What was the 40 referred to in your previous post?

 

[e3120]

I've been awaiting this question from you lot, a very interesting one as well, and many a disagreement I've had with nearly everyone I've told.

Every spark of electricity produced by all electric generation stations is put on the grid. This is transferred by your inverter at a higher hz ensuring export otherwise its just circulating around your yard.

For example, those of you with digital meters will have a symbol (reverse) appear when your demand is less then your production. Your meters calculate the difference and either add a kW or freeze.

Those of you crafty buggers who still have the disc spinners will be enjoying rebates/account surplus on your electricity bills as those little money savers reverse spin auditioning credit - this is illegal operation btw, and you must have these upgraded to digital.

Your meter will calculate the difference in usage and export which is why the generator needs to be wired back to the main board not secondary.

Now, if you're scratching your head thinking I've produced X and imported Y but my bills are high then you are using more electricity then you originally thought to power your yard. Having a generating station is learning how to use it to its maximum efficiency, split down time at lunch. Don't have multiple drains of electrical equipment running at the same time for e.g.

11am - overcast - all machines running
12 - sunny - lunch
1 - machines off
2 - machines off
3 - milking

Scenario
Producing 70kW at 12
Producing 30kW at 12:30
Producing 10kW at 12:45
40kW produced in one hour (guesstimate)
Your yard has used a steady 50kW in 1 hour
You have not used 100% solar/wind

Ok, ready for the naysayers and disagreements, come on.

I call rubbish.

The bits about matching demand/generation i.e. not taking breaks when sunny is valid and contradicts the rest of what you're saying. If you're right, they'd be no point.

Generation units don't run at a higher frequency to 'push' power onto the grid. If they did, within a few seconds, they'd be completely (180 degrees) out of sync with the grid and trying to push when the grid was pulling. I don't mean import/export here, just the peaks/troughs of the sine wave of AC. That's why inverters/grid synchronous generators need the grid - they need the heartbeat of the grid frequency to align to.

What all generators have to do is push out a slightly higher voltage to 'overcome' the grid. When this higher voltage is on the farm side of the meter, it will drive the farm kit first, and, if they is enough current to spare, some will be pushed back onto the grid, but this is the last resort as it's the most effort. The water analogy above (pressure is equivalent to voltage and obeys mathematically similar laws of physics) is a useful way to think of it, except water is more like DC.

My own generation significantly outweighs my usage when there is decent wind at all and my bills do as the OP expects - in a consistently windy month my import is very small and much less than my own usage (which is easily triangulated using generation/import/export readings. Yes, I do have an export meter, but this shouldn't affect how the import meter works.

If the OP is 100% sure that a good proportion of his usage is concurrent with generation, and he only has 1 import meter (some slight wooliness there), then something is amiss. PV connected to the grid side of the import meter would absolutely exhibit that behaviour - it's like it was next door's PV, but it's hard to believe that someone could be so clumsy.