Our Solar Electric Panels: Done!

I'm kind of jealous of the production of you guys out in the desert

I think I max out around 25-30 kwh out of my 5.2kw system. Usually, this occurs in the spring - less moisture in the air = less clouds to interrupt production. I'm also not exactly situated N-S, either and can only feasibly have panels on the front of my roof. That being said, I still get approx 50% of my annual usage from the panels, which is pretty darn good since it's an "electric house" with the exception of the oil furnace.

I'd love to get a vertical axis wind turbine to supplement the PV array, but there isn't much demand in my area and I *might* have to get home owners approval first. I say *might* because I honestly have no clue if we even have a home owners association in my little neighborhood. I've paid $25 once in the 5 years I've been here. It covers snow removal and some ice melt for the front entrance of the neighborhood. I think we may have drained those funds after last winter, though.

Patrick, you should get slightly better production in Spring, due to the lower temps you'll have compared to summer.

 

Well, during summer months when the ambient temp is 110 degrees F, we have too much of a good thing here in southern AZ regarding sunlight. Hence, installing a solar electric system is like making lemonade out of lemons.

Having spent several weeks in Newark, Delaware last fall, I know that is a beautiful area. Reduced solar electric production is a reasonable price to pay for living there.

 

Very true. As with most things in life, it's about compromise. Although, I'd almost rather have your temps of 100 with next to no humidity than the 90s we had this year with 50% humidity and dew points in the 70s. Nothing quite like walking outside at 10am and sweating from the humidity. Then again, nothing about our weather over the past year has been "normal", either.

Hopefully, once the oak tree in my back yard grows another 10 feet, my usage will drop in the summer a little. The setting sun just beams right into the back of my house for a couple hours a day and you can hear the AC running more from it.

 

Think very carefully about a small scale wind turbine, even a vat. Few people have had very good long term luck with them. The harsh reality is that if you have enough wind to be productive, you probably have too much for wind to be reliable, since the hardware has lots of live loads, and has to live in a harsh environment.

For further reading, here is a good start:

Wind Power Generation - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun

Icarus

 

Hi Ed,

It appears that the street price of my inverter (SMA SB5000US) is currently $3,200 or so.
SMA Sunny Boy 5000 US with AC-DC Disconnect - 4001 TO 7500 Watt Grid Tie Inverters @ AltE

I have a 24 panel system manufactured by Schott, 225W each panel (5.4 kW total) and was quoted a total price so I don't know how the pieces contributed to the total.

 

Disclaimer: I installed my own micro-inverter system.

In most properly designed systems, the improvement in going from a central inverter to micro inverters won't be anywhere near 20-25% increase unless you have shading or other issues with the system. 50% increase in output would mean that the original system was designed with severe deficiencies.

For installs with all panels in the same orientation and little to no shading, the difference between a central and micro inverters should be in the single digits.

Now if you do have multiple panel orientations and some partial shade issues, yes, micro inverters can significantly improve output.

Panel-level monitoring is nice for troubleshooting, too.

But cost is an issue and Enphase makes you pay a bit extra to get the web based panel-level power monitoring.

All that said, I still favor micro inverters - Enphase's next generation inverter are supposed to be even better (smaller, cheaper, more efficient, more durable) than the current ones - not sure when they will be shipping them, though. Apparently they're working with multiple panel manufacturers to get them embedded in the panel to further simplify installation.

 

Yes you are correct in that my friend who claims huge benefit may not have had his system wired up perfectly as he discovered when he tried adding panels I now hear. He had single inverter and shading issues. He added all new micro's as he was never happy with the output and was astonished.

But thats really the beauty of using micro's. The string wiring issue is taken out of the loop when using micro's which is really appealing to the novice. If you are competent in all phases of ac wiring (which I am) you can be up and running in no time without wondering if you wired up your strings correctly with partial shading issues.

Thanks for the input. For a solar novice it really sounds like the way to go.

Btw, how do Siemans panels match up with eNphase micro's?

 

Hi Ed,

1. If you can install the system so that all panels face in the same south-facing direction, at the same angle, and are not subject to shade, then there's no problem with the use of a single inverter.

2. If #1 is not possible, then use of micro inverters is a reasonable solution.

3. Regarding use of a single inverter and wiring the strings correctly, the idea is to arrange each string so that each one produces the same voltage. In my case I have two strings with 12 panels each. A neighbor with 33 panels has three strings with 11 panels each.

4. The maximum voltage produced by each string needs to comfortably fit within the inverter's spec for maximum voltage. In my case, the strings produce ~350VDC under max power production and ~400VDC when there's less sunlight.

5. I have a 100 ft run of #8 wire from the roof down to the inverter. The run consists of four wires carrying power plus a ground wire. At peak power production, those wires carry ~15A at 350 VDC. If micro inverters had been used, then the wires would carry ~20A at 240 VAC.

6. There is a power loss due to resistance in the wiring. Since the power loss varies according to the square of the current carried, the wiring power loss would be ~78% greater if 20A is flowing in the wires, vs. 15A.

 

I would say that the $1900 figure is high, and that the
way you are calculating the figure is incomplete.

First, I suggest that the apples to apples using
your numbers is $3200 vs $2800, not $3200 + $1500
installation cost vs $2800 and $0 installation cost.
In other words, you need to account for installation
costs for both approaches.

Second, the micro-inverter installation cost will be
much less than you estimated, and in fact, I think it
will be roughly the same as central inverter's
installation cost.

I watched my contractor install Enphases on my array.
They clip onto the rack, and you plug together the
supplied, daisy chained cables. Everything is modular
plug and play. It took him about 5 minutes per unit,
so installing 16 as in your example is an hour or so
of labor. That's more like $100-200.

A central inverter installation requires labor to measure
and cut the cables, run the cables, and to mount the
(heavy) inverter on a wall. The cost for that amount
of labor would seem to me to be in the same ballpark
as the micro-inverters. You need to add the cost
of materials, since central inverters don't come with
cables, connectors, and wall mounting hardware...let's
call that an additional $100. [There would be an additional
cost for a plug-in card if you want web access, but let's
not worry about that for now.]

At this point, assuming installation labor cost is a wash,
this puts you at:

$3200 for micro-inverters minus $2800 for central inverter
plus $100 = $300 premium for micro-inverters

To this $300, you'd add $395 for the Enphase "Envoy"
control unit, which is what enables web-accessible
data display. This would bring the total additional
cost to approximately $700 for a 16 panel system.
To get to "real money," you must apply the various
government tax credits and utility rebates...for me
in Missouri, that works out to ~50%...thus the actual
premium I'd be paying for 16 panels would be $350.

A 16 panel system, or 3.7 kw, generates about $500
of power per year. If the micro-inverters happen to
be 25% more productive, then the payback period
would be slightly less than three years - not bad.
Such additional efficiency would only happen if the
array either had shading issues or consisted of
multiple strings that are mounted at different azimuths
or tilt angles. My own 13-panel installation has both shading
issues and two strings mounted at different tilt angles,
which is why I went with micro-inverters.

 

Excellent stuff thank you.

 

Hello everyone, very interesting and informative information in this thread.

For all you experts, I'd love to get your opinions on my planned install:

At my seasonal camp, I use about 1,000 KWH per year. The proposal is for:

(4) 235-watt Conergy photovoltaic panels (Conergy AG - Renewable Energy - Photovoltaics, Wind Energy)
(4) Enphase microinverters (Home - Enphase Energy)

which the company says will generate about the 1,000 KWH that we use.

Installed price is $6,200. After tax credit and state rebate, out of pocket cost about $2,200.

Thoughts? Recommendations?

Thanks!

 

$6,200 seems pretty high for a 4-panel system. The panels cost $573 each here:
Conergy P 235PA Solar Panel 235 Watts | CivicSolar

The microinverters cost $215 to $245 depending upon capacity; while the energy management unit costs $365 here:
Enphase M190 Micro-Inverter - Real Goods

I am wondering whether it makes sense for you to solicit other quotes, recognizing that you will only pocket 1/3 of whatever savings you can negotiate.

 

A simple PV watts calc using Caribou as a default location, reveals a 1 kw pv system will yield ~ 1200 kw/year, with an energy value of (at current power rates of ~$145.

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/code/pvwattsv1.cgi

My rule of thumb is that Grid tie Pv is running ~ $5-8 watt installed before rebates etc, so your price in in the ball park at least. That said, you will pay a premium given the smallish size of your system.

My biggest comment is, assuming you are using the camp ~ 60 days a year, your consumption works out to ~ 16kwh/day. I would suggest that before you invest a couple of thousand dollars in Pv you look very carefully at your consumption and figure out every conservation method you can find. As we also say in the Pv world, your cheapest energy dollar is the one you don't have to produce. It used to be that for every dollar spent on conservation, one would likely save ~ ten dollars in PV costs. That number is probably closer to 5/1 now, but he principle is the same.

Just FYI, we life off grid for ~ 1/2 the year, with 400 watts of PV. We consume on average ~ .6-.8 kwh/day. On a good day, we just about equal that in PV harvest. On an ideal day we can harvest up to ~ 1.5 kwh/day. This is with a battery based system that starts out with a much smaller efficiency curve because of the battery systems.

If you are interested in some very good PV info, I invite you over here:

Grid Tie and Grid Interactive Systems - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun

It is a very user friendly forum, populated by some very sharp folks. folks who, on balance have forgotten more about PV than most of us will ever know.

Good luck and keep in touch.

Icarus

 

Yep. $6.59/watt doesn't seem too out of line for a slightly less than 1kW system to me.

mainerinexile - make sure that quote includes the Enphase Envoy and at least 5 years of detailed power monitoring to get maximum benefit from the micro inverters. On small systems, the cost of the Envoy drives up the cost/watt for Enphase systems. It costs about $300 - about 5% of the total system cost for a $6000 system!

 

Thanks for the NA Wind & Sun link. Great forum!

 

You say "get at least 5 years monitoring etc".

Does that mean they have a license fee per year?

Thanks!

 

Yes, it's about $2/year/inverter to get the detailed monitoring and access to the monitoring portal, and there's no easy way to get detailed per-module power production without it. As an Enphase owner, I feel it's one of the biggest drawbacks with the system as the ongoing cost negates a lot of the benefits of micro inverters adding 10%+ to the cost of the inverter over 15 years.

As a Enlighten subscriber, you get a 100% uptime guarantee - they will pay you 20c/kWh for any lost production due to a failure (up to 30 days). But that's really nominal - a typical panel will usually generate about 1 kWh/day if it's sunny...

 

My system is rated 5.4 kW DC. For December month-to-date, the system has produced 672 AC kWh or 23.2 kWh per day. Today has been very overcast and the system only produced 6.4 kWh as of this writing. Peak AC production today was only 2,055 watts during the 15 minute period starting 2 PM.

During December, Dec. 1 produced the most power at 28.73 kWh, followed by Dec. 25 at 28.22 kWh and Dec. 24 at 27.99 kWh.