Our Solar Electric Panels: Done!

Hi John,

Yes, I will attempt to do so after I'm set up with my user access next week. However I am sure that only total system data will be available. The monitoring tool has no way to see what individual panels are doing. Further, the two parallel strings are connected together at the input of the DC disconnect switch so there is no way to distinguish the output of one string from the other.

I asked how the panels were configured into the two strings. The answer was that the 5 panel array on the roof is connected to two of the 3 panel arrays on the patio cover closest to it, as well as one of the panels on the third array on the patio cover. Then the other string is composed of the 10 panel array on the roof plus the remaining two panels on the third patio cover array.

I'm also trying to evaluate what is the maximum power I should see reported by this monitoring tool. If the 24 panels are collectively rated at 5.4 kW DC power, then given the 100 ft run of #8 wire and inverter efficiency, what is the maximum AC power output that I should expect? I'm just wondering whether 4.5 kW of reported power is good or bad.

 

SMA has a lot of publicly viewable plant data here: SMA Solar Technology AG - SunnyPortal

 

Another thing you will never be tempted to do is to "hose down" your panels with your garden hose and ask your spouse to read off the "instant KWh" reading off the inverter to see how much it goes up when the temperature of the panels is decreased.

Nope, I've never done that.....

 

Thursday last week, the building code inspector came out to approve the system. This past Wednesday afternoon, the Tucson Electric tech came out to install the solar meter. However s/he did not announce his/her presence.

I was hard at work on Thursday morning and remained unaware that the system was ready to be turned on until the afternoon when I got a call from the Tucson Electric inspector who wanted to schedule his visit. That prompted me to look around and lo & behold, the solar meter was in place. I immediately turned on the system.

Unfortunately the web tracking has not yet been activated for me so I can't access that info yet. However my wife is logging data on an hourly basis so that we can see how the system's productivity changes throughout the day.

I was surprised to find 20 large electrolytic capacitors within the inverter: 770 uFd, 450V rating. I looked up the capacitors on Mouser and was astounded to find that the unit price was ~$40. $800 worth of capacitors? Thinking about whether it is worthwhile to pursue a warranty beyond the initial 10 year period.

I'm planning to hose off the panels tomorrow morning before the sun is out.

A few more photos of the inverter and webbox are attached.

 

You would have to consider that after 10 years, the efficiency and cost of the next generation inverter(s) might be a better way to spend the money than a warranty.

 

Good point, hopefully the inverter cost will decline as production rates increase. Looks like the current price is $2.8K at one supplier:
http://www.infinigi.com/sma-sb-5000us-sunny-boy-5000w-grid-tie-inverter-p-2559.html?ref=100

The inverter weighs 148 lb so I am going to need help to remove and replace that puppy when the time comes. I guess the power transformer, which is not visible when the front cover is removed, must be fairly massive to handle up to 5 kW of power.

The system produced 31 kWh today. It is supposed to produce 783 kWh per month, so it seems that the system is on track considering the time of year, shorter days in the winter, cloudy and rainy days, etc.

I think it is really cool that the system is quietly producing so much power during daylight hours. Our consumption of grid power during most of the day was close to zero (despite three AC systems in the mix), while some excess production was contributed to the grid.

 

The next gen of inverters that are coming out now are transformer-less - a lot lighter and should be cheaper, too.

http://goo.gl/SqBU

The efficiency level is impressive to - 98% efficiency rating compared to the 96% of the last gen inverters. The efficiency curve is impressively flat - most inverters start falling off in efficiency at 20% output or below, but these are nearly are actually most efficient at lower voltage and loads.

The inverters weigh half of yours - 77 lbs, too.

Now, these are 3-phase (208V) inverters so it will be interesting to see if the 2-phase 240V inverters have the same specs - typically they are nearly the same.

 

I figured out how to access the SMA Webbox reports and attached a Microsoft Excel file that provides recent data. We had rain this afternoon (good news as that will further wash off the solar panels) so this is why power production dropped off in the early afternoon today.

"Pac" is the important column from my perspective, and shows AC power production at that moment.

Columns A through R are provided by the Webbox. I added columns S through V to provide some analysis. Note that inverter efficiency is >96% once DC power input exceeds 2 kW.

Also note on Oct 6, during the 12:15 window, the system generated an average of 5,112 DC watts. That is 94.7% of the panels' collective rating of 5.4 kW. I hope to see more of that in October as the weather cools off.

 

Pricing a system myself. I guess the hot set up today is using micro inverters at each panel. No string loss at all.

Here:
Micro-inverters vs. Central Inverters: Is There a Clear Winner? | Renewable Energy Podcast

and:
http://www.solarpanelstore.com/pdf/IAEI_jw_article.pdf


Its more costly up front but extremely efficient and each micro has lan control also. With eNphase software you can look at each panel charge efficency on your pc. No more monster inverters.

 

I'm sure Drees will chime in, as he is a big enphase guy. I personally think the advantage of micro-inverters gets lost as the array size gets bigger.

Icarus

 

Go Hill Go !!!!!!!!!!!!!!

Now, if you'd just plug in that dirty, polluting Prius of yours.

On your mention of vampire power from cell phone chargers, I charge my cell phone in my car. I have to drive to work anyway, and the alternator is going to spin anyway, so I might as well capture some of that extra energy in my iPhone battery.

Congrats on the solar panels! In my neighborhood (duck pond), there are numerous houses now with solar panels - and there's that one house on the street across from the Carls Jr at El Toro and Muirlands that has all kinds of solar and thermal stuff on his house (he has a fan-blade type thing that spins on a vertical axis and generates electricity (kind of like a whirlie bird with a generator) I forget the scientific name for that type of air current))

Congrats on the solar !!!!

 

sounds like a vertical axis turbine.

 

My solar electric system has been in service for two months, and here are some highlights:

- 1,764 AC kWh total production
- 32.85 AC kWh highest daily production, on Oct. 9
- Average daily AC kWh production was 28.56 in October and 28.83 in November
- Peak DC watt output was 5,250.66W on Oct 21 during the noon to 12:15 PM window of time (compared to rated power of 5.4 kW)
- Tucson Electric charges $7.66 per month to be connected to the grid. Right now my system is producing much more power than we are using.

I attached Excel workbooks containing Oct and Nov data to my post #109. Each workbook has a summary tab that shows daily AC kWh production and peak DC watt output in table format as well as graphically.

There are ~1,750 homes in my housing development and my guess is that ~50 homes now have solar electric systems. The largest that I've heard of consists of 33 panels, 7.8 kW DC rating. Given the very attractive Tucson Electric rebate (which has since been cut by 1/3) as well as Federal and AZ state tax credits, it made sense to buy a big system (as the owner's net cost was only ~25% of the total.)

 

True, but since TEP (and its customers) contributed $16.2K to the purchase of my system, I won't complain about the fixed charge to be connected to the grid or the relatively low payment for excess kWh. I think that the excess kWh will be paid out in the December bill, and then the cycle will reset. My guess is that the payment will be ~ $0.03 per kWh.

Following is November data regarding system production vs. household usage. I'll post December next month per hill's request:

Numbers in kWh

System produced: 859
Consumed from Grid: 320
Contributed to Grid: (675)
Household usage: 504 (was in southern CA one week out of the month)

% Surplus: 70.4%

 

- Tucson Electric charges $7.66 per month to be connected to the grid. Right now my system is producing much more power than we are using.

Patrick: Is your total TEP bill $7.66, or is that simply the surcharge?

Up here in TRICO country (North Tucson) we pay a solar surcharge of $3.38 / month, out of a total monthly bill of $19.80 - which includes "fixed charges" of $15.00, plus tax.

We just completed our first year on solar. Our 5.14 kWh system generated 9998 kw. We were rebated on our overage at $.04205.

Our peak day was in the spring at approximately 37 kw.

 

How do you figure "50% more efficient"? What constitutes a "vast improvement" on a 10 panel system?

My single inverter operates at 96%+ efficiency.

If you can mount your panels so that they are all facing the same direction, its not clear how much incremental solar panel efficiency will be gained from a micro-inverter setup.

If you need to mount your panels facing multiple directions then you at minimum need to use one inverter for each direction.

The total bill was $7.66. Thanks for the info, maybe I can look forward to improved production next spring!