PV panel orientation?

First, I would visit: Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun - Powered by vBulletin

Second, I would never use just one inverter if the panel orientation was significantly different, as you would throw away a considerable potential harvest, depending on the array size.

I know that Drees is very happy with his Enphase micro inverter system, I personally would prefer central inverters but the Enphase has a place.

 

Different orientation like this?



One side of panels (16 total) face East/North east while the other side (20 total) face South/south west. There is a separat 4Kwh (ac) inverter for each side. Configured this way, we probably loose about 15% total efficiency but we're tight on space so it's the best we can do.

 

I did my own installation, 3 2500 watt inverters, 60 solar panels. On a combination flat, and pitched roof. Planning is critical, and if you do your homework you can achieve a really good system!!!

 

Within certain limitation, partial shading, even from a wire for example will reduce the output of the entire series string. I do understand your installers point of view given multiple points of failure, but clearly you have to decide where the trade off is.

I suggest you post the same question on the Solar forum, grid tie section. There are a lot of very smart folks over there who are designers/EE's etc who have seen it all.

Icarus

 

Got some pics? Love to see PV installs.

I'm sure mwalsh won't mind me intruding on his thread since I already provided advice on the two other forums he posted on.

 

Here is an aerial shot from Bing...

Bing Maps

Zoom in, my house is the one with 3 sat dishes, and the white roof......

and the Solar, and ...Pool Heating panels....

Can't see the pool?
It's indoors.... SWEET!!!

 

Nice setup! That's a lot of solar panels! How many kWh do you generate a year? I'm guessing over 10,000?

 

Now THEM is mighty big sat dishes. Either that, or the worlds largest wok. You could cook a lot of rice in a wok that big. Or maybe use 'em for moon bounce on the ham bands.


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My panel/inverter orientation is as follows:

Array 1: orientation- East, 18 216 Watt panels, one 3500 Watt PV Powered inverter.

Array 2: orientation- West, 27 216 Watt panels, one 4800 Watt PV Powered inverter.

This system has been in service for 1 year and covers almost my entire electric usage.

 

Disclosure: I installed Enphase micro-inverters on my
PV array, which consists of two different facets.

I think that it is ironic that your contractor faults
micro-inverters' "multiple sources of failure" as his
rationale for not recommending them. Enphase touts
their products' reliability as one of their main advantages
over a string inverter. Enphase's logic is twofold: first
if a string inverter fails, your whole array goes down,
whereas with distributed inverters you only lose the one
that failed; and second, a micro-inverter has to deal
with a much lower electrical load (one panel's worth)
than a central inverter and thus should be inherently
more reliable.

Enphase's white paper on micro-inverter reliability is here:

http://www.enphaseenergy.com/downloads/Enphase_WhitePaper_Reliability_of_Enphase_Micro-inverters.pdf

But the issue of reliability aside, the day to day
benefit of micro-inverters is that you get the max
harvest from each PV module, whereas a string inverter
has to sync to the PV module that has the lowest
output. That loss gets further multipled if you have
any shading issues at all.

In my own case, I am getting a 6% increased harvest
on my "best case" facet (this is the difference in output
between my west-most panel and my east most panel;
the west-most "lights up" sooner), and a 7% increased
harvest on my worst case facet (one panel has shading
issue for a short time in early morning). There's
probably some MPPT advantage as well, but I don't
have a way to measure that.

This same logic could be applied to current string
inverters, too.

--

No one inverter solution is perfect for every situation.
I think you are making a good decision to make your
contractor consider micro-inverters for your situation
based on the facts of your situation, and not on his
comfort zone.

 

For what it is worth a couple of thoughts: First, I would be surprised if "in the future inverters would be built into panels" The reason, as I see it is that PV panels have a great many potential configurations including DC outputs that would make built in inverters less useful to say the least.

Second, If it were me, and I had consistent panel orientation I would go with a central inverter for two reasons. The first is the only single point of failure, in a package that is easy to replace. Additionally the track record of name brand inverters is pretty darn good. While I believe that Enphase is a real product and has a real future, in this business, failure of the business is not unheard of. What would you do, for example, if in ten years, you had a single (or multiple) inverter failure(s) and Enphase is no longer available? In a conventional failure, at least if brand X is out of business it is pretty likely that brand Y will be available. So in the case of a an Enphase failure you now would have to completely reconfigure your array, at considerable expense to bring the failed components on line.

All that said, I would consider a Enphase system if my PV facets were significantly compromised and different, so that the Enphase system would significantly increase production.

Just my thoughts, worth only the price you pay for them.

 

If you have a consistent panel orientation, including
no shading issues, then a string inverter's fixed cost
becomes its big advantage for large arrays. With my 13
panels, I was in a gray area, that is, a string inverter
vs 13 Enphases cost in the same ballpark. For me,
since the costs were about the same and they made
up just 13% of the total cost anyways, my decision criteria
then shifted to yield, that is, how to get the maximum
value out of the remaining 87% of my investment.

On the other hand, if we were talking about, say, 50
panels, again assuming a consistent panel orientation, then
one string inverter would be the far superior solution if
cost was your decision criteria.

With regard to reliability, this is more a discussion of
future technology and warranty rather than actual
product. In the near term of, say, 1-2 years, I figure
that Enphase would be around to do direct 1 for 1
replacement if an inverter would go bad. Once you
go beyond a few years, it's unlikely Enphase would stock
today's product for warranty purposes for long, after
production had ceased. Electronic products go bad if you
sit them on a shelf for years on end. So, keeping spares
inventory of them is more expensive then just shipping
an equivalent current product. I saw this during my
tenure at a technology company (HP).

This reminds me of the extended warranty I got with my
first digital camera. The camera did go bad, and the
vendor sent me a new one. Even though only one year
had elapsed, the new camera was not the same model
as the old camera, it was the then current "equivalent."
I sense that the micro-inverter industry's maturity and
rate of innovation is analogous.

As to the possibility of Enphase not being around,
this also can be said of any component - panels,
inverter, software - that you have installed today.
Even the biggest, most successful companies can
and will exit a primary business (IBM doesn't make
PC's anymore...though that's no great loss . You
just have to take it on faith that "someone" will be there
two decades from now when you need a replacement
part.

 

Jut to hone my point a bit. Currently, there is only one choice of micro-inverters, Enphase. So if a number of them go TU in a few years and Enphase is TU, there is currently no viable replacement. The option then would be to rewire the entire string with a conventional inverter.

On the other hand, if a conventional inverter fails, and it is out of business, there is currently a Brand X or Y or Z available to replace the bum one, without any rewire of the string.

Like I said, I would consider micro-inverters given off axis array, but other than that I would use a conventional inverter system.

 

My favorite response in the solar world is the best way to get the best system is to avoid the pitfalls of "Ready, fire, Aim!" Look at it this way. You may be tired of the process, but a few hours of aggravation now might yield a much better compromise in your system.

I always suggest looking long and hard at all aspects of all options before you jump. This is a big money, long term deal, so make it as right as you can.

Icarus

 

In my mind, your desire to have one string, located in one
somewhat constrained spot, having the large capacity you
need...makes Sunpower a natural candidate. That being said,
you should be aware that Sunpower is very picky about its installer
network, i.e., installers that you may have been first working work
who are not authorized SP dealers will have no choice but to argue
for some other approach.

I sold high tech products for almost two decades. Yes, I was in
Sales. (I took early retirement in March, hence the "was.") What
I learned in sales helped me be a better solar customer, so let
me share with you how I solved the problem you describe.

My last company wanted us to strive for long term success. To
do that, we were famously urged to become a "trusted advisor"
to our customers. This became my goal, and once I was able to
achieve that status with a given customer, virtually every one
stayed with me because of the added value I brought...and price
became muted, to the point where the bar, so to speak, was to
be "competitive" and not necessarily the lowest price.

When I started to research my solar project, I wanted to find
a company who would become my trusted advisor. In Missouri,
we are, unfortunately, not too good at being early adopters, so
you can count on one hand the number of companies who have
done more than 10 installations. I did research to find the market
leaders, and even had an off the record conversation with the
"Green Coordinator" at my local utility to find out who they liked.

I then contacted the company I thought could do the job best.
I said to Dane, their President, "I want you to be my partner, not
my supplier. I want you to educate me on the technology, and to
give me choices. I want you to help me figure out the best way
for me to meet my goals. In return, I will give you: a prompt
decision to your proposal; allow you to make a fair profit;
and I won't shop your proposal, your ideas on the street."

Think about it: what good, decent company wouldn't accept
this offer?

As for the "earning trust" part, I did test our relationship: "Dane,
I just heard that Sunpower has a higher efficiency product than the
one you recommended, why can't we use those?" I looked for him
to either know the answer off the top of his head, or do research
and get back to me. Sometimes he had to do both. For the
Sunpower question, he knew already that Sunpower didn't support
Enphase, but he went back to Sunpower to get their product
roadmap, which showed that there were no immenient products
that would be compatible. I did enough research to be able to
ask some hard questions, and I gained confidence in him when he
responded back with well thought out answers.

So my advice is: do your homework...pick one or at most two
partners to work with...make them earn your trust...but you
earn their respect by not wasting their time by going around
"getting bids for the same thing". [If you feel you *need* to
get additional bids, this is actually saying you don't have the
trust yet that you need from your prospective trusted advisor.
When you get a prescription from your doctor, how often do
you go to another doctor to check that the first doctor's
prescription is right?]

Remember that you are going to have to live with the result for
maybe 25 years, so you do your job to find the person you can
trust to work with you to build the best solution.

 

That requires that no company will provide single module inverters in what has to be an industry that will grow by huge factors. Hard to believe that is a real issue. (Like asking what happens if nobody builds the chargers for the electric cars of the future.) Much more likely is that in 10 years one of the panels might be compromising the whole array.