1% clipping too high?

[Hv&Lv]

OK. I'll demonstrate my abysmal ignorance once again.
Why clip at all?

Oh! I want to try to answer but I’m sure others more experienced will set me straight...

Utilities limit the maximum KW pushed on their system per solar site.
if you never clipped, your not getting the biggest bang for your buck.
look at the picture I posted when you asked what clipping was.
notice the grey area of power produced on clipping vs not clipping.
Maximizing the TIME you are producing max KW amounts to more money in your pocket.

 

[Besoeker3]

Maximizing the TIME you are producing max KW amounts to more money in your pocket.

That's what I thought. So why clip and reduce the kW output?

 

[Hv&Lv]

That's what I thought. So why clip and reduce the kW output?

Because the utility limits the maximum MW. (kW)
on our system we are limiting all new installs for solar farms at 2 MW.

while we limit the MW, we don’t limit the MWh

 

[ggunn]

That's what I thought. So why clip and reduce the kW output?

If your system is inverter limited, i.e., if you have a maximum AC system size, then loading the inverter to clipping and beyond can make sense. What you lose at the top of the power curve due to clipping can often be more than made up for by the increased available power at off peak times. You have to run the numbers to see if it's worth the expense of more modules.

 

[Hv&Lv]

If your system is inverter limited, i.e., if you have a maximum AC system size, then loading the inverter to clipping and beyond can make sense. What you lose at the top of the power curve due to clipping can often be more than made up for by the increased available power at off peak times. You have to run the numbers to see if it's worth the expense of more modules.

And there’s that from the other point of view...

we we have one that I had to watch until I set directional power elements in the relay.
they max out quick and clip to our max for about 5-8 hours on a good sunny day.
others clip for about 2-3 hours.

 

[Besoeker3]

Oh! I want to try to answer but I’m sure others more experienced will set me straight...

Utilities limit the maximum KW pushed on their system per solar site.

The obvious question is why?
Solar is still peanuts compared to total system capacity.
What am I missing here?

 

[Hv&Lv]

The obvious question is why?
Solar is still peanuts compared to total system capacity.
What am I missing here?

Not all solar... we have two 10 MW sites on our system.
Pushing back too far and too much at one time. There is the infrastructure to look at. We build to our load on circuits. Solar can push enough to take care of the entire circuit and then to the Substation and beyond.
I have actually seen our POD go negative. The solar was pushing back through two substations.
push too much at one site the wire that goes to the Substation won’t handle the amps.

and the solar people want us to pay for the upgrades when there is no profit on our side. Not gonna happen...
They want all the profit for themselves.

as for residential, we build for the load, not the solar. 15 kVA XF will still only take or deliver so much...

 

[wwhitney]

OK. I'll demonstrate my abysmal ignorance once again.
Why clip at all?

It's all about the relative cost of inverters versus panels.

If inverters were free, and panels were expensive, you'd never clip, you'd always want enough inverter capacity to handle the panel output. That way you are "wasting" inverter capacity but avoiding any loss of panel capacity.

If panels were free, and inverters were expensive, you'd maximally clip, you'd want enough panels to max out your inverter almost as soon as the sun comes out. That way you are "wasting" panel capacity but avoiding any loss of inverter capacity.

In reality neither inverters nor panels are free, so the economically optimal configuration is have some clipping and to be "wasting" some inverter capacity away from solar noon, and wasting some panel capacity near solar noon. The cheaper panels are relative to inverters, the more clipping is economically optimal.

Cheers, Wayne

 

[electrofelon]

Not all solar... we have two 10 MW sites on our system.
Pushing back too far and too much at one time. There is the infrastructure to look at. We build to our load on circuits. Solar can push enough to take care of the entire circuit and then to the Substation and beyond.
I have actually seen our POD go negative. The solar was pushing back through two substations.
push too much at one site the wire that goes to the Substation won’t handle the amps.

and the solar people want us to pay for the upgrades when there is no profit on our side. Not gonna happen...
They want all the profit for themselves.

as for residential, we build for the load, not the solar. 15 kVA XF will still only take or deliver so much...

What is a ballpark capacity for a 15KV class line? I think you said your system is 12.47. Here in upstate NY the newer lines are usually 13.2, which often feed the older 4800. The sub that feeds me starts on a 13.2, runs about 5 miles (picking up a 2 MW solar along the way) to a 3x500KVA pole bank that re-feeds the older 4800 system. I am about 4 miles from that. By the time it gets to me it is a single phase spur.

 

[Hv&Lv]

What is a ballpark capacity for a 15KV class line? I think you said your system is 12.47. Here in upstate NY the newer lines are usually 13.2, which often feed the older 4800. The sub that feeds me starts on a 13.2, runs about 5 miles (picking up a 2 MW solar along the way) to a 3x500KVA pole bank that re-feeds the older 4800 system. I am about 4 miles from that. By the time it gets to me it is a single phase spur.

We have both 12.47 and 24.9 kV
It isn’t the system as much as the wire between the solar farm and the Substation.
Our 10MW farm is on a 24.9 kV line. That’s about 240 amps. That maxes out any 1/0 wire we may have on the circuit.
we have a couple of 2MW sites on the same 12.47 kV circuit at another station.

we limit the new ones now to 2MW per our provider contracts.

 

[jaggedben]

The obvious question is why?
Solar is still peanuts compared to total system capacity.
What am I missing here?

Why does the utility limit? Or why do developers choose to clip?

Either way, solar isn't peanuts. In the California Independent System Operator it's usually somewhere around 10 gigawatts mid-day, give or take a gigawatt or so. (EDIT: And that's just registered grid generators, it doesn't include something like another 2-5 GW of net metered systems.)

 

[Besoeker3]

Why does the utility limit? Or why do developers choose to clip?

Either way, solar isn't peanuts. In the California Independent System Operator it's usually somewhere around 10 gigawatts mid-day, give or take a gigawatt or so. (EDIT: And that's just registered grid generators, it doesn't include something like another 2-5 GW of net metered systems.)

For me, the question remains.
Why limit it?

 

[ggunn]

For me, the question remains.
Why limit it?

Depending on where you are and what size system you are talking about, there are many answers. At the lower end, i.e. residential systems, some AHJ's have a limit to what size system, AC rated, they will allow a homeowner to connect to their grid. Others do not have that restriction, but have a cap on what size system for which they will pay rebates. With larger systems the cost differential for the next size up inverter can be significant so it may be cheaper to overload a smaller inverter than it is to build in a larger inverter to get the same kWh/yr production.

As I said, you have to run the numbers to determine the best course, but overloading an inverter to clipping is not necessarily a bad idea.

 

[Hv&Lv]

For me, the question remains.
Why limit it?

See post 27 & 30.

its about the maximum amps dumped on the system at any given time and production contracts.

 

[Besoeker3]

OK. I'm still baffled. Free energy and clip it? But I readily accept that it is not my field.

 

[electrofelon]

OK. I'm still baffled. Free energy and clip it? But I readily accept that it is not my field.

Your question has been answered numerous times, why do you keep asking?

 

[wwhitney]

OK. I'm still baffled. Free energy and clip it? But I readily accept that it is not my field.

Post #28 answers your question. The energy is not free--it requires an upfront capital investment to be able to gather it. The question is, for a fixed dollar investment, how do you allocate that investment between panels and inverters in order to maximize the energy generation? The answer will usually be a system in which there is some clipping.

Here's a simple example with made up numbers. Suppose you have a system where each marginal panel costs $100 installed and will produce 100 kWh/year on average, given enough inverters. Each marginal inverter costs $1000 installed and will support 10 panels without clipping. Suppose the 11th panel on an inverter produces only 98 kWh/year extra; the 12th only 96 kWh/year extra; the 13th only 92 kWh/year extra, the 14th only 84 kWh/year extra, and the 15th only 68 kWh/year extra.

Now let's say that after fixed costs, you have $20,000 you want to spend on panels and inverters. You could do that by using 10 inverters and 100 panels, and you'd make 10 MWh/year with no clipping.

Or you could try 9 inverters and 110 panels, that would give you 7 inverters with 12 panels and 2 inverters with 13 panels, and it would generate 10.93 MWh/year. You'd be clipping 70 kWh/year, but you generate more energy for the dollar investment than the case of 10 inverters.

In fact let's try 8 inverters and 120 panels, that would give you 15 panels per inverter. It would generate 11.5 MWh/year. You'd be clipping 500 kWh/year, but you'd still be generating more energy for the dollar investment that the cases of 9 or 10 inverters.

Cheers,
Wayne

 

[Hv&Lv]

Post #28 answers your question. The energy is not free--it requires an upfront capital investment to be able to gather it. The question is, for a fixed dollar investment, how do you allocate that investment between panels and inverters in order to maximize the energy generation? The answer will usually be a system in which there is some clipping.

Here's a simple example with made up numbers. Suppose you have a system where each marginal panel costs $100 installed and will produce 100 kWh/year on average, given enough inverters. Each marginal inverter costs $1000 installed and will support 10 panels without clipping. Suppose the 11th panel on an inverter produces only 98 kWh/year extra; the 12th only 96 kWh/year extra; the 13th only 92 kWh/year extra, the 14th only 84 kWh/year extra, and the 15th only 68 kWh/year extra.

Now let's say that after fixed costs, you have $20,000 you want to spend on panels and inverters. You could do that by using 10 inverters and 100 panels, and you'd make 10 MWh/year with no clipping.

Or you could try 9 inverters and 110 panels, that would give you 7 inverters with 12 panels and 2 inverters with 13 panels, and it would generate 10.93 MWh/year. You'd be clipping 70 kWh/year, but you generate more energy for the dollar investment than the case of 10 inverters.

In fact let's try 8 inverters and 120 panels, that would give you 15 panels per inverter. It would generate 11.5 MWh/year. You'd be clipping 500 kWh/year, but you'd still be generating more energy for the dollar investment that the cases of 9 or 10 inverters.

Cheers,
Wayne

And on the flip side let’s say the utility limits you on your MW export. Now theres a whole other reason to clip. More MWh but less MW

 

[ggunn]

OK. I'm still baffled. Free energy and clip it? But I readily accept that it is not my field.

It's a matter of economics and design constraints. It can be a complex problem to solve and sometimes the best solution involves some clipping. As you say, it's not your field, so without understanding the details of the equation it may be counterintuitive for you.

 

[Besoeker3]

Post #28 answers your question. The energy is not free--it requires an upfront capital investment to be able to gather it.

Yes, up front. As do all power stations. The difference is the ongoing fuel cost.