Negative power factor and PV systems

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gar

Senior Member
110527-0038 EDT

Around here the installed cost appears to be about $7 to $8 per watt. The resulting production is about 1.1 KWH per year per watt rating. Maybe somewhat higher with microinverters.

A major problem. In our town the tax rate is about $47 per taxable $1000 value. Divide actual value by 2 to get taxable value. So $7 becomes $3.5 taxable. Divide 47 by 1000 and multiple by 3.5 and the result is $0.165 tax per year per installed 1 W of rating. The cost to buy the 1.1 KWH per year from Detroit Edison is about $0.13*1.1 = $0.143 .

The tax on the equipment to generate the electricity is greater than the cost to just buy the power from the power company. Thus, if the equipment was free but you had to pay at this tax rate you would be losing money.

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tallgirl

Senior Member
A lot of jurisdictions don't tax renewable energy equipment, so it's essentially a free "upgrade" to your property.

There are a lot of reasons to argue that solar power equipment shouldn't be taxed, not the least if which is that it isn't "permanent".
 

gar

Senior Member
110527-0859 EDT

tallgirl:

I agree that PV systems should not be assessed property taxes if you want to grow the industry and reduce fossil fuel consumption. In Michigan it takes an act of the state legislature to exempt PV systems, and this has not occurred yet.

Even if you don't tax PV systems they are in most places not economically competitive.

There is talk of getting these systems down to $1 per watt. So how do you do that? What is the cost breakdown between equipment, installation, maintenance, and equipment life?

In the SME daily briefing for today is the following quote:
GE Predicts Solar Power To Become Cheaper Than Nuclear, Fossil Fuels In Five Years.
Bloomberg News (5/27, Wingfield) reports Mark M. Little, the global research director for General Electric Co., said that "solar power may be cheaper than electricity generated by fossil fuels and nuclear reactors within three to five years because of innovations." Bloomberg New Energy Finance said that the cost of solar cells "has fallen 21 percent so far this year, and the cost of solar power is now about the same as the rate utilities charge for conventional power in the sunniest parts of California, Italy and Turkey."
Note the word may, and no cost breakdowns to justify the claim.

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kingpb

Senior Member
I guess you can boldly make those claims when you state they "may" and based on "innovations".

So what that means is that with current technology it is not cheaper, and won't be for at least 5 more years.

Yes, I'm sure they are trying to improve the efficiency of the panels, but they have a long way to go before these systems can stand on there own without subsidies.
 

tallgirl

Senior Member
A lot of "when will solar be cost effective?" depends on what you mean by "cost effective."

Those of y'all who remember when I was pulling on wires in New Orleans post-Katrina may remember that I got fed up with power outages. We had a 40 or 50 minute outage here last week -- I know we had the outage because I happened to see a log entry saying we had an outage and my partner mentioned his son's school had a power outage.

What's the worth?
 

gar

Senior Member
110601-1558 EDT

tallgirl:

I my lifetime the total number of days I have been without power is probably less than 10 and 5 of these were the great eastern blackout.

I have a 5 KW portable generator, Honda and that means expensive, about $2400. This can service more than one location and does not cost $100,000 of capital equipment and have a city tax burden of $2350 per year. The amount of electricity generated with PV will not fully pay the tax bill it creates.

If you ignore the tax problem, and do not have incentives, PV in our area is not competitive with buying power from the power company.

In our area production is about 1.1 KWH per watt of panel rating. Assume a useful life of 20 years, and at $7 per watt installed, the cost per year per watt is $0.35. Or about $ 0.32 per KWH. I pay the power company a little over $ 0.13 per KWH.

Thus, the cost for generation is considerably above my cost from the power company.
 

mivey

Senior Member
Tallgirl,

You seem to be smarter than the average bear. Why are you so sold on solar and solar technology? Have you personally run some of the economics as compared to other options?

When you say things like promoting the use of a battery bank as an economical choice it makes me wonder if you have been focused on one area and are forgetting to evaluate other choices.

If you have been deeply involved in solar projects, don't forget to get your head above water every now and then and don't necessarily buy into all of the hype from the solar company sales people. Not all of it is hype but you have to drink from more than one well to be able to evaluate the differences.
 

iwire

Moderator
Staff member
Location
Massachusetts
I got fed up with power outages. We had a 40 or 50 minute outage here last week --

That is what they make home generators for, much more cost effective IMPO, than trying to purchase and maintain a set of batteries with enough capacity to be helpful.
 

gar

Senior Member
110602-1440 EDT

I forgot to also mention the additional insurance cost.

Note: all these extra costs are already in my current electric bill for electricity.

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Negative power factor. it can't happen. The grid tie inverter copy's the line voltage, when its in the normal range it allows the inverter to push back with a slightly greater voltage. This is the cleanest power you can produce. Var's, VA, out of balance conditions come from what uses the electricity, not what produces it.
If power company's want to reduce the var's to their system, (out of balance sine wave), all they have to do is to introduce is an incentive to reduce this condition in large electric users, mostly motor loads. Install capacitor banks equal to the induction load thru proper engineering.
Its like propaganda, throwing pop aginst a wall and see what sticks. Solar power is the best and cleanest power there is, don't let anybody tell you otherwise. PV
 

gar

Senior Member
110603-0859 EDT

perry vogler:

Negative power factor. it can't happen. The grid tie inverter copy's the line voltage, when its in the normal range it allows the inverter to push back with a slightly greater voltage. This is the cleanest power you can produce. Var's, VA, out of balance conditions come from what uses the electricity, not what produces it.
This comment makes very little logical sense.

There are three separate subjects in this one paragraph.

The use of the terminology "negative power factor" is a side issue, and simply relates to a definition. I believe tallgirl uses this to mean a leading power factor.

Your second sentence is correct but says nothing about the phase of the current from the inverter.

I do not know what you mean by "cleanest power". It is a statement without any support information.

Your last sentence of the first paragraph is somewhat correct, but misleading.

From the power company's perspective of looking at a home with inductive, resistive, and PV inverters that home is a load even if it pushes energy back into the power company's system.

If you view the home as a load and this home has some inductive loads not balance by capacitors or some other mechanism within the home, then that home looks to the power company as a lagging power factor.

Now add to this home an operational PV inverter that has a unity power factor output and that inverter supplies all of the home's resistive load, then to the power company this home looks like a load of 0 power factor. In other words the power company is supplying all of the reactive current and none of the dissipative current. This is a loss to the power company. No revenue, but supplying current that causes power dissipation within the power company network.

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PaulWDent

Member
"Power Factor" as it applies to grid-tied PV systems

"Power Factor" as it applies to grid-tied PV systems

Am I correct in assuming that the POCO would prefer a PV system produce a more-negative (closer to -100%) power factor than just a small (further from -100%, but still negative) power factor?

There's a lot of stink about PV and power factor and I'm trying to understand what the heck the utilities want. Normally "smaller" is bad, but is it smaller in absolute value, or just plain smaller?
It is less confusing just to understand that the utility wants the current that is delivered to the grid by a PV system to be substantially in-phase with the grid voltage.

This current is flowing back to the grid, i.e. in the opposite direction to the direction current would flow from the grid to a load, hance "perfect" power factor is -100% instead of +100%.

It is illuminating to consider what would happen if PV systems were supplying a very large fraction of the total power consumed from the grid, and they were all delivering current in perfect phase with the grid voltage; that would leave the utility having to pick up all of the reactive part of the load current, while the resistive part of the utility's load current was now much smaller. As a result of the utility then would be seeing a higher ratio of reactive to resistive current, i.e. it would seeing a much worse power factor. At that point, the utility may one day ask PV systems to pick up their fair share (or more) of the reactive current by specifying a PV output current phase that was slightly advanced or slightly retarded with respect to the voltage. They may even want one day to control that phase remotely.

Even now, a PV system suppying current exactly in phase with the utility voltage may not be what the utility wants. The problem is, the load (if it is not local) may be some distance away, and the current from the PV system reaching the load is then delayed, i.e. retarded in phase. So it may be better if the PV system slightly advanced its phase to begin with. However, this is so hard to figure, and would be different in every case, that I think it is not worth debating at this point.
 

gar

Senior Member
110603-1417 EDT

It is important to have a definition of power factor and limitations. I do not have any very old books on AC circuits and machines. Mine date to 42, and 52. It is quite a nuisance to go to the Engineering Library because of parking, but I may do it if convenient at a later time.

The 42 book - Electrical Circuits and Machinery - by Hehre and Harness - on p 83 defines power factor as
PF = power/volt-amperes

The 52 book - Analysis of A-C Circuits - by Melville B. Stout - on p 19 defines power factor in the same way. And on p 18 is this comment ---
"The product of E by I is called the "apparent power", probably because the early workers felt that the product EI should represent power, in line with their experience with direct current. ......".

From a search via Google Books I found this reference, of 1906, which doesn't help much. http://books.google.com/books?id=3d...&resnum=1&ved=0CC4Q6AEwAA#v=onepage&q&f=false

I am going to work from the 42 book definition with some assumptions. VA can not have a direction defined, therefore it is always positive. But we can define a direction for real power, and measure its direction. Therefore, it is reasonable to use + and - to define power direction.

On this basis we can have a negative power factor when real power flows toward the normal source from the load and the load has a reactive component.

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tallgirl

Senior Member
110603-0859 EDT

perry vogler:

This comment makes very little logical sense.

There are three separate subjects in this one paragraph.

The use of the terminology "negative power factor" is a side issue, and simply relates to a definition. I believe tallgirl uses this to mean a leading power factor..
No, I mean it in the sense that the current is moving in the opposite direction from normal -- "selling" or "exporting" power, as it were.



I don't know how well this will show up, but here's an hourly chart. When L1 is "selling" power, the power factor is negative. When it's buying, the power factor is positive. That seems to be what people in the PV/DRG business use when they want to distinguish between "buying" and "selling" power factors.
 

gar

Senior Member
110603-1623 EDT

tallgirl:

Your plot shows up fine.

If the intent is to describe the direction of power flow, then I do not think it is useful. I would rather have power plotted with a sign indicating direction. I am more interested in power than power factor.

If the intent is to provide information to the power company on how the power factor to this load is seen by the power company, then it is useful.

Your usage of negative power factor, then relates to my discussion in post #96.

How did this thread get this long?

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mivey

Senior Member
110603-1417 EDT

It is important to have a definition of power factor and limitations. I do not have any very old books on AC circuits and machines. Mine date to 42, and 52. It is quite a nuisance to go to the Engineering Library because of parking, but I may do it if convenient at a later time.

The 42 book - Electrical Circuits and Machinery - by Hehre and Harness - on p 83 defines power factor as
PF = power/volt-amperes

The 52 book - Analysis of A-C Circuits - by Melville B. Stout - on p 19 defines power factor in the same way. And on p 18 is this comment ---
"The product of E by I is called the "apparent power", probably because the early workers felt that the product EI should represent power, in line with their experience with direct current. ......".

From a search via Google Books I found this reference, of 1906, which doesn't help much. http://books.google.com/books?id=3d9QAAAAYAAJ&pg=PA1207&dq=earliest+definition+of+%22power+factor%22&hl=en&ei=KCvpTc6YIM24tgei2bDGAQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CC4Q6AEwAA#v=onepage&q&f=false

I am going to work from the 42 book definition with some assumptions. VA can not have a direction defined, therefore it is always positive. But we can define a direction for real power, and measure its direction. Therefore, it is reasonable to use + and - to define power direction.

On this basis we can have a negative power factor when real power flows toward the normal source from the load and the load has a reactive component.

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I have a decent library and most of my old books that I looked at (teens through 50's) define power factor as cosΘ (or cosω or similar term) or the ratio of watts to volt-amperes . None talk about a negative power factor because there is no such thing as a negative power factor.

If you want to be sloppy, you may use the term "negative" as an indicator of "power delivered" or "power received" depending on your perspective but it is not clear. Trying to be an indicator for direction of power flow is all it is. This is popularized by Fluke power quality meters.

To take a symbol on a meter and use it as a term for power factor is silly and sloppy. How many would look at this: ~100 and say "tilde 100" instead of "approximately 100"? That is just goofiness. Don't do it.
 

gar

Senior Member
110603-2237 EDT

mivey:

I agree with you that negative power factor is sort of goofy, but I was trying to come up with some definition that might explain what tallgirl had in mind. It appears that this definition is what she had in mind.

I do not know what useful purpose this usage has. As I said in my comment to tallgirl I am more interested (negative) power than a negative power factor as a measurement tool.

Maybe what a power company might want to have is both a VARH meter and a KWH, and that with new meters this also should mean the power company could get short time average power and VAR.

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