Oversizing the system

[Sami Najjar]

I have another question: when using PVWatts, if the nearest data centre to my location is 53 miles, will it give a useful approximation? Or should I use another application?

[SunEagle]

I have another question: when using PVWatts, if the nearest data centre to my location is 53 miles, will it give a useful approximation? Or should I use another application?

Whenever you use PVwatts you are still going through some type of estimate. If the nearest location is at the same or close to the same latitude then your calculation should be the same or close.

If you are at a much different place based on latitude you can adjust your calculation by changing the panel angle in the calculation.

[khanh dam]

And as long as your separating fly frass from pepper and seeming to be attempting to start a pissing match, why didn't you capitalize the "W" in "kWh" as is customary for abbreviations of S.I. units named after people ?

Just like correct grammar, spelling and syntax in writing, if you want to be taken seriously, conventions and rules matter. Otherwise, fair or not, you'll probably look ignorant to those reading what you write and who do know the subject being dealt with. That can make it more difficult to be taken seriously.

seriously, your comments always amaze me in their ability to become more and more petty. I dont' see you making this "correction" on any one elses' posts, just mine. wonder why?

[SunEagle]

you dropped the unit of years in your calculation how did 9000kwh/year just become 9000kwh?

Getting a little pissy about what I post.

Whenever you run a pv watts calculation it provides and estimated production in kWh/year. So the "annual" or "yearly" output is pretty much not always mentioned.

But it still comes down to how many kWh will be produce for each kW of solar panels you install based on the amount of sunlight, dirt, panel angle, efficiency, etc.

[J.P.M.]

seriously, your comments always amaze me in their ability to become more and more petty. I dont' see you making this "correction" on any one elses' posts, just mine. wonder why?

Seems like your petty comment is like the pot calling the kettle black.

Since it looks like you're asking a question (while ironically making more grammatical and spelling errors as you go), I'll try to enlighten you.

1.) My option.

2.) In this case, to point out what looks to my like your hypocrisy and your attempt to get pissy with someone who wrote something you didn't like.

3.) As for what you claim you don't see, look around for some of my prior posts if you're interested. I, and several others around here I'd note, point out unit and other (mis)usage of technical terms and units on a semi regular basis. FWIW, kW and kWh are often incorrectly used. Not pointing such things out can only increase the confusion.
This obviously isn't a peer reviewed journal - and the way I see it, not much more than a lead generator masquerading as an an unvetted chat room, but some of us try to maintain some aspects of professionalism. Sue me. Your stuff is nothing special. Just more ignorance to be pointed out in an effort to avoid confusion to others who may be reading your stuff. If you can't reconcile that within you brain, consider the correction a public service from a condescending prick.

4.) If you're going to get pissy, don't be surprised at that comes back to you.

If you want to look ignorant, suit yourself, but this place would be better and more professional if you didn't stink it up so much with your crap.

If/when folks point out my errors (which certainly happen more than I'd like), and if I agree that they are (errors), I thank them, apologize for my screwup, make note/correction and move forward. Look hard enough and you'll find a few of my mea culpas.

I'll withhold comments about your grammar and spelling above so as not to embarrass you more than you seem to be doing to yourself.

I learned a long time ago that not everyone who tells me what I may not like to hear or read about my actions is trying to hurt my feelings.

BTW, if you don't like my posts, you can always ignore them, or exclude (block) them from showing up.

The last word on the subject is your if you want it.

[Ampster]

My two cents on the topic of this thread is that higher DC to AC ratios, as @Solarix mentioned, are becoming more common. Mine is 1.5 to 1 and that may be on the high side. However, even at a latitude of 38 degrees North, I am consistently getting a ratio of1500 kWhs/kW on annual results. That is based on DC panel capacity. Based on inverter capacity my ratio is over 2300 kWh/kW of inverter capacity.

[khanh dam]

Kwh/KW = hours right? I just do not understand the units. not being petty. spelllllling police, have areldy tickedted me. LOL, when someone says you aer petty and you tell them there(their?) grammer and spelling is badd, thats just icing on the cake! LOL. Couldn't have proved my point better!

[Ampster]

Kwh/KW = hours right? .........

It is actually a ratio, typically done using annual output (kWhrs) in relationship to the capacity (kW) of a system. Because of monthly variations in weather and inclination of the sun annual output is the easiest way to compare systems. I still have swings from one year to the next. Whether the denominator is system capacity in terms of DC size of panels or Inverter capacity is sometimes debated. Commercial installations are often compared using inverter capacity,

[solarix]

Solar yield in kWh/kW or annual energy output / array size can be thought of as the number of hours of effective full power operation per year.
btw, most si prefixs denoting orders of magnitude are lower case with the exception of M=Mega (1 million) as opposed to m=milla (1 thousanth)

[Ampster]

Solar yield in kWh/kW or annual energy output / array size can be thought of as the number of hours of effective full power operation per year.
btw, most si prefixs denoting orders of magnitude are lower case with the exception of M=Mega (1 million) as opposed to m=milla (1 thousanth)

You have clarified why I have occasionally seen percentage variations of that ratio referred to as a capacity factor. For example, if there are 8760 hours in a year and a one kW system produces 1500 kWhrs, then the capacity factor expressed as a percentage is 17.12328767% (1500 / 8720)

[Sami Najjar]

Kwh/KW = hours right? I just do not understand the units. not being petty. spelllllling police, have areldy tickedted me.

You are right, this "hours" unit refers the peak sun hours in your region for the entire year (because we are talking about "annual" specific solar yield)

[Ampster]

........if the nearest data centre to my location is 53 miles, will it give a useful approximation? ...........

As @SunEagle said if the latitude is close to yours it should be a reasonable approximation. In my case 40 miles to the west is the coast which is often overcast in the mornings so that microclimate could be less.

[Sami Najjar]

As @SunEagle said if the latitude is close to yours it should be a reasonable approximation. In my case 40 miles to the west is the coast which is often overcast in the mornings so that microclimate could be less.

Yes they are actually quite similar, I guess it will work then. Thank you.

[J.P.M.]

You are right, this "hours" unit refers the peak sun hours in your region for the entire year (because we are talking about "annual" specific solar yield)

I'd add that the array specifics such as orientation and inverter size or DC/AC ratio need to somehow be included in that description.

Side by side arrays in different orientations will produce a different number of "peak hours" per year as that term seems to be used here.

The way I learned and use the term "specific output" with respect to a PV system is that it is the annual output (either modeled or actual) in kWh/yr. divided by the system size in STC kW. Using AC or inverter size instead of the array STC size reduces the usefulness of specific output as a design tool.

[Sami Najjar]

I'd add that the array specifics such as orientation and inverter size or DC/AC ratio need to somehow be included in that description.

Side by side arrays in different orientations will produce a different number of "peak hours" per year as that term seems to be used here.

The way I learned and use the term "specific output" with respect to a PV system is that it is the annual output (either modeled or actual) in kWh/yr. divided by the system size in STC kW. Using AC or inverter size instead of the array STC size reduces the usefulness of specific output as a design tool.

I completely agree, the PVWatts wants you to use the DC STC array size and it will include all the specifics by itself to give out the AC output