How much power SHOULD you get ?

Skippy

Well guys, I have been on here a while , and have seen a whole bunch of posts asking - Is it worth it ? - How much power ?  . . .  You know all the usual newbie questions - that we have all asked at one point or another .. .

So I thought I would post this thread and ask all you guys out there who have monitoring systems to show us how bad is bad, and conversely How good is good . . .

So here goes,

JUST connected my 2,000 watt array to my envoy system, ( and I mean - like - the day before yesterday ! ) and for the next 2 days we had nothing but clouds. . . a solar nightmare !  In the last 2 days I think I made about 2.65 kwh . . for the whole 2 days !



BUT . .. as you can see, it is really cloudy outside, and in the 2 minutes it took me to go out and take the picture - then come back inside - the system registered an output of 161 watts - a small rise, but not a whole lot . . 



Here is where it gets interesting.

On the third day of connection I have had intermittent clouds - which means a whole lot more sun than the last two days. . . .
I don't have pictures, but I can say, that the output climbed too a high of around 1,500 watts, and I have produced around 5 KWH in one day.

So, for all you guys out there, who wonder - " how much power can I get with my panels ? "
I have too answer - " How much sun do you have ? "

Anybody else ?

zoneblue

Weather can be suprisingly local in its variability. We live at 500m asl on a mountain, and get over 3m of rain each year. And yet, the rain often comes from the opposite direction from the sun, and it can be raining and sunny at the same time. Others get coastal fog, and whatnot. When in doubt find and download the hourly irradiance dataset from your local met provider. These come in what they call TMY, "typical meteorological year" format typically, kind of an average of the last 10 years data. Not only do the monthly averages for each month of the  year tell you at a broad level about what you might expect, but the daily variation, will tell you what your chances of long spells of bad weather are. Kinda geeky, i know. But it suprised me how accurate my calculations were about theoretical system performance, compared to how they actually work out in practice.

The other way to start small, monitor your system and make your local assessment.

Skippy

There are ways to "ball park" how much power you can get, I am just looking for other examples of the wide variety of power outputs you can get.  For me, 107 watts for a 2,000 watt array - at 12 noon - so far - is the worst output yet . .  I am sure that next summer, when it is 30 degrees out and it is sunny for months at a time, it will really crank out the power.

That is what I am looking for - examples of worst and best case scenarios . . so a new guy won't think it's all sunshine and roses (pun intended     )

Anybody else ?

Photowhit

I take it your 2000 watt array is grid tied?

Off grid is a different system, with needed losses. Indeed if your system doesn't shut down (reach float) on sunny days likely you have problems. Often added energy input is needed for continuously cloudy days.

FWIW- I think last year, in late Nov early Dec we had 14-15 days with 1 hour of direct sunlight, in Mid Missouri. About as bad as I can recall in my 14+ years off grid.

Skippy

Today, I broke a record. 

I really hoped that I would see 1800 watts - from a 2000 watt array . .  given system losses and stuff like that, and I was looking at the meter today at around 11 30 - intermittent clouds - and had  a reading of 1.91 kw . .  or I am guessing - 1,910 watts . .  RIGHT ON !





While I was playing with things, I was outside looking at the net - meter - meter . .  . and noticed that the two little black bars under the numbers were not moving . . . hmmm . .

So, I went inside, and I turned everything off in the house . . unplugged the fridge - turned down the heat pump . .  you know that kind of stuff . . .
Went outside, and the two little black bars underneath the numbers where marching from right too left . .  meaning that I was putting power into the grid . . .

Went back inside . .  turned on EVERYTHING . . . went outside and sure enough, the two black bars were marching from left too right...




So, when it's sunny, I know by the black bars, that I am using as much as I am making . .  the bars don't move. . . or slowly go backwards . .

Why do I feel like putting up more panels ? 

Skippy

Photowhit said:

I take it your 2000 watt array is grid tied?

Off grid is a different system, with needed losses. Indeed if your system doesn't shut down (reach float) on sunny days likely you have problems. Often added energy input is needed for continuously cloudy days.

FWIW- I think last year, in late Nov early Dec we had 14-15 days with 1 hour of direct sunlight, in Mid Missouri. About as bad as I can recall in my 14+ years off grid.

Yup, grid tied . .

Thank you.  It is a real eye opener, when it's really cloudy, and you get enough continuous power for an Edison bulb . .

Hamfast

I've seen my ~2000w array crank out north of 1800w on sunny days and yep, right back down to midrange on overcast ones. Rain and snowfall cut it down to almost nothin'...:)

That being said, when I get home from work the bank is either in float (often for more than 3 hours) or absorb, depending on cloud-cover or lack thereof.    

MarkC

My 3890 watt (nameplate) grid tied system has been in operation for over a year.  The panels are somewhat compromised because they are basically direct mounted to a metal building roof that has about a 15 degree slope AND is oriented to the West of South by almost 20 degrees - a result of the building being what it is and the simplest mounting system.  I'm considering adding another two panels as they can be mounted quite easily as I have a 4000 watt Sunny Boy inverter.  The area was heavily wooded and trees partially block sun both early morning and late evening.  

Probably the "surprise" for me was that in South Texas, when the sun hits the most direct, it is also VERY hot (130 degrees plus @  panel temp). The highest production that I've seen is right at 3700 watts - on partly sunny day with bright, reflective clouds - during the summer.   I've attached a graph of the total home usage, total solar production, the "solar reduction" (how much solar energy has reduced the total home usage) which are used to calculate the energy cost savings (also plotted).  Daily fluctuations are substantial - little as a few KWH to as high as 25 KWH.  Over a weeks time, I've seen as little as 7 KWH/day to 19 KWH/day - averaged.  The overall average since startup is around 14 KWH.  

waynefromnscanada

2000 watt off grid, 1900 nameplate solar +160 watt hydro turbine. Heave overcast days, thankfully rare, and solar output can fall to a low of just  a few single digit watts. Most days that are "just cloudy" and I often get 50 % or more of what the solar is capable of, not counting scattered cloud days where tons of light from the bright clouds hit the panels and is added to the direct sunlight from the sun when it shines between the bright clouds when the solar output can skyrocket way above rated. But, during the short stormy days of late Fall / early Winter, if not for the little hydro, I'd have to shut the system down and wait for the longer, brighter days of mid to late Winter. 

inMichigan

Through sites like www.wunderground.com, have you found a nearby site with a solar radiation sensor (W/m^2)?
inMichigan

inMichigan

I have a nearby personal weather station with the solar radiation sensor.... so for several days, I tracked my PV (by CC), temperature, wind speed & direction and solar radiation.    I didn't find the air temperature and wind had a noticeable impact...   I use this graph as a quick check that I'm still getting what I expected.   For example, if I see 740 W/m^2 on the weather station, I ought to see something like 10 kw from the panels.    If not, either the weather system sensor has a problem or something's not right on my end.
inMichigan

Skippy

Thank you guys !

I wanted to show that it's not all smooth sailing with lots of output . .   and that did it . ..
Just yesterday, I had a day here that was dark cloud all day .. .  my output on the day before was 8.5 kWh, and the very next cloudy day it was 1 kWh - even.  wow - or - like my buddy at work says, nuclear winter comes, you can kiss your panels goodbye - were all finished then . ..  guess if it's dark enough - he's right ..

You have a solar radiation station ?  Interesting . . . maybe you can answer this.

Standing there looking at my solar electric meter, and it's putting out about 100 watts . . . not very much on a cloudy day . . . when behind me, the solar water heater clicks on and starts heating the house . .  HUH ?

I am guessing that the solar water heater works on thermal radiation (with the vacuum tubes it has) while the solar electric works on the light levels hitting them . . . right ?  So my idea of having a solar powered - solar water heater may run out of power - more heat than power available . ..

inMichigan

Skippy said:

Thank you guys !

I wanted to show that it's not all smooth sailing with lots of output . .   and that did it . ..
Just yesterday, I had a day here that was dark cloud all day .. .  my output on the day before was 8.5 kWh, and the very next cloudy day it was 1 kWh - even.  wow - or - like my buddy at work says, nuclear winter comes, you can kiss your panels goodbye - were all finished then . ..  guess if it's dark enough - he's right ..

You have a solar radiation station ?  Interesting . . . maybe you can answer this.

Standing there looking at my solar electric meter, and it's putting out about 100 watts . . . not very much on a cloudy day . . . when behind me, the solar water heater clicks on and starts heating the house . .  HUH ?

I am guessing that the solar water heater works on thermal radiation (with the vacuum tubes it has) while the solar electric works on the light levels hitting them . . . right ?  So my idea of having a solar powered - solar water heater may run out of power - more heat than power available . ..

Ours happens to be a Vantage Pro 2+ from Davis.  
http://www.davisnet.com/weather/products/vantage-pro-professional-weather-stations.asp 
Not so many weather stations have a Solar Radiation sensor.   Did I need such a device...probably not.  Did I want it for a long time, yes. I will certainly use it to monitor the solar system and help optimize it.  

Since I have access to live W/m^2 during any testing, it makes it easy to compensate for the sun's intensity being different.  If you could find a nearby weatherstation on www.wunderground.com, other than clouds, it's be handy.  For example, here I was testing the impact of shifting the Radian's V_sell relative to the system voltage.    Knowing the W/m^2 each time I wrote down the Output and settings, it was easy to rescale the Panel output to be all as if it was 400 W/m^2.



In fact, after I did this test, I realized with excitement that my V_sell of 56.8 used this Summer/Fall was not as efficient as using 56.4 V.

I plan to change to V_sell of 56.0V (for my CC setting of 58.6V).  It's the difference between the two, not their absolute value.

inMichigan

Ralph Day

I like your racking system.  But how many people does it take to adjust the angles?  One to lift, one to reset the pins/bolts?  KISS at it's best.

Ralph

Skippy

I built the racking system homemade . . . right now, I can raise and lower it by myself, but it is a hand full too do . .

I had too have it engineered - as per the building inspectors request (see order) . . and it is engineered for the panels too be fully upright and in an 80 kph wind . . since I do not have the final steel bars in place yet, I just leave it in the center position . .

Yaryman

Just to give an idea for output during November. This was/will be the high output for the month. 
This was right after a big rain had cleaned the panels and it was a day with a high of 66 degrees. 
5.04 kW system - 18 SolorWorld 280's with Enphase M250 inverters - All panels South facing located in SF Bay Area

Skippy

Thank you.  That is a perfect example of what I would like to show the new guys out there, even though you may have a "huge" array, sometimes - the sun just ain't there . .  

BB.

On very dark/cloudy days a couple days a year, my GT system would produce about 5% of the same energy I would see on bright spring/fall days.

-Bill

Yaryman

Here is the same system 2 days before on a rainy day with mostly clouds after the rain stopped at noon. 
Two days apart, a perfect sunny cool day produces 25.8 kWh, and the rainy, cloudy day produces 6.21 kWh. 

Skippy

I'm glad I am not the only one . . .

On a good day, with solar panels rated at 220 Watts - maximum power . . . current output power at the moment is:



That was the good news . . .

On a bad day with the same 220 watt panels -  maximum recorded . .  current output power:



Then you have a really bad day where the maximum output of the panels looks like this - this is as HIGH as it reached ALL day.




So for the newbies that are thinking "Yaa . .  full power all day every day . . "  Sorry, not going to happen . . .

But - it is kinda cool when the sun does come out !  

Skippy

Well since this is all new too me, I thought I would pass it on . ..

We had our first snow fall last week, and with 6 inches of snow on all of the panels, they do not even report too the enphase monitor in the house. . .  0 output - 0 panels connected. . NOTHING. . 

Of course, once the snow started too melt - the display started too read - 2 -3-5-7- 9

But for a while there, I was kinda worried . .  0 panels reporting . .  WHAT ??

So, I guess you can say, that if you leave them covered with snow, you get LESS than nothing. . .  

RyanRichardson

I certainly understand your frustration when you installed your panels, only to find that they were operating at such a decreased efficiency. I’m glad it worked out for you in the end though, and this teaches us a very important lesson about solar power—while it can be an awesome energy source, it’s not always going to be consistent. Solar power isn’t without downfalls. Here’s an article for anyone considering going solar: http://solar-to-the-people.com/solar-energy-advantages-disadvantages/ Everyone here may also find this FAQ and solar power calculator helpful. http://www.seia.org/about/solar-energy/solar-faq
http://pvwatts.nrel.gov/index.php

kspellman02

Interesting thread since this is what I came here looking for answers today. We just installed 4 REC 280 Panels....2 Serial strings in parallel feeding a Classic 150.....on the roof of our Catamaran here in St. Thomas USVI. my output seems to average about 200W at any given time during the day when the sun is out. I was thinking something is wrong, but it appears that some factors are cutting my panels performance. 1.) sail boom .....I expected at least one panel to be mostly down for much of a given day so I really think we have 3 panels operational at any given time....sometimes two.  2.) Panel Angle - Because we have a relatively flat roof on the boat, we lose some efficiency.....that was a bit of a surprise. 3.) Occasional Clouds - Again, some expected loss there.

Otherwise the system seems to be working fine....just thought we would get a bit more output  :-(

vtmaps

kspellman02 said:

2 Serial strings in parallel feeding a Classic 150.....
<snip>
my output seems to average about 200W at any given time during the day when the sun is out.
>snip>
I expected at least one panel to be mostly down for much of a given day so I really think we have 3 panels operational at any given time....sometimes two.

What voltage batteries?  If you are using a 12 volt system, you might get better results putting all 4 panels in parallel.  When two panels are in series, a shadow on one is like a shadow on both.

--vtMaps

kspellman02

VTMAPS - Battery Voltage is 12....panel voltage is 31.9....these are poly panels so I had expected the blockage to only affect certain areas/strings of cells in the panel that were shaded. I suppose I can get some higher capacity (more input) combiners and give the parallel a try. I think my issue is going to be that if I go all parallel, the 4 panels will have more voltage possibility (128v) than my Classic 150 controller can handle (96V).....

Aguarancher

@kspellman02, I think you might be a bit confused. To connect your panels in parallel, you combine all the panel + wires together and all the panels - wires together and connect individually to the charge controller. Your charge controller input voltage will be 31.9 volts.

kspellman02

Aquarancher, you are correct....I was confused. Went back an looked and will have to give parallel a try. Thanks All! And Merry Christmas!

Skippy

Update for you guys. .  .

It is now middle of summer or so . . and the panels are working at full power most of the time . . Net meter is working good, meaning that the latest hydro bill is a grand total of 4 $ .

I believe the enphase monitor is reading about 2 MWH of hydro produced  . . . give or take a bit.....

I was kinda worried about this whole "net meter" thing . .. did not really know what would happen . .  would I get a credit for the excess power ? would they "forget" about any excess ?  etc . .

Well, I have found out that in my area, while I was on regular grid power, the smart meter charges are as follows . . .

Like any other smart meter you have different prices for the high - medium -  and low demand times.

THEN : I asked to have a net meter installed for the solar panels, and found this on my bill.



So, now that it is nice and sunny outside, I was eager too look at my latest bill, and found this :



So, looking at the above bill, I generated 122 kwh extra.  Then was charged a delivery charge of 16.44 . .

I called them up,and with some humor - mentioned that I am paying 17 $ too deliver power to myself . . .

They did not see the humor ... go figure.

Johann

Skippy said:

Update for you guys. .  .

It is now middle of summer or so . . and the panels are working at full power most of the time . . Net meter is working good, meaning that the latest hydro bill is a grand total of 4 $ .

I believe the enphase monitor is reading about 2 MWH of hydro produced  . . . give or take a bit.....

I was kinda worried about this whole "net meter" thing . .. did not really know what would happen . .  would I get a credit for the excess power ? would they "forget" about any excess ?  etc . .

Well, I have found out that in my area, while I was on regular grid power, the smart meter charges are as follows . . .

Like any other smart meter you have different prices for the high - medium -  and low demand times.

THEN : I asked to have a net meter installed for the solar panels, and found this on my bill.



So, now that it is nice and sunny outside, I was eager too look at my latest bill, and found this :



So, looking at the above bill, I generated 122 kwh extra.  Then was charged a delivery charge of 16.44 . .

I called them up,and with some humor - mentioned that I am paying 17 $ too deliver power to myself . . .

They did not see the humor ... go figure.

What a shame.....You had to pay so you can dump your generated solar power into their net.
What a rip-off. Thief's.