Enphase micro-inverter system

I'm getting my 3.24 kW Enphase powered system inspected tomorrow. Designed, installed myself with the help a friend who works in the solar industry designing/installing systems along with my brother and father who also have a good amount of construction/electrical experience.

Couple comments:

• Price of system is pretty good.
• Installation will probably be 2-3 times more than $2k if you want it done right.
• You'll need more equipment than what they include, primarily electrical wiring equipment/supplies. That will add $500+ to the price depending on your install.
• Can't assume it will last 30 years without some sort of failure / maintenance - Enphase inverters have a 15 year warranty. Panels have a 10 year product warranty and a 25 year performance warranty.
• Can't take the DC output numbers - those are lab based numbers. Your actual output will vary a HUGE amount depending on location and installation specifics (angle/direction the panels are mounted and shading). Even best case, you can typically expect at most about 80% of the nameplate at peak power. You can usually get pretty close using PV Watts to calculate your output.
• If you get the Enphase, you really want the Envoy/EMU with monitoring. More $. I'm not particularly tickled by the yearly monitoring fees, but there isn't any competition right now for the type of monitoring they offer, so they are getting away with it. There is a competitor called SolarEdge with a similar product - I'm hoping that they will be able to drive the monitoring fees down.

Either way, no matter how you look at it, PV is getting cheaper all the time. The price of the equipment has gotten to the point where now labor costs are getting to be the dominant factor - and if you want it done right (you want it to last 25 years, right?) you'll likely have to pay for it.

BTW, check out 1BOG. They pool buyers together to work out deals with installers to get the buyers a better rate. The rates they are getting are pretty good and might be a good way to go if they have a program in your area.

Finally - how much shade are we talking about here?

 

If you can avoid most of the shade during the primary production hours (10am-3pm), you probably won't lose too much from the system, especially if you are using micro-inverters (or SolarMagic). Of course, if you can ground-mount and avoid shade completely between those hours, even better. And as you mention, it will make cleaning the panels a lot easier - dirty panels will suck up about 10% of your output.

You'll get bonus production if you can manually adjust the angle of the panels for the season as well. Even just adjusting the angle twice a year (spring/fall) can make a big difference. PV Watts will help you determine the optimal angles.

I went with Enphase for a couple of reasons:

• Ability to monitor each panel - I love pouring over data, so this alone was worth it to me.
• No extremely high DC voltages to worry about. That shouldn't be an issue with a proper install, but only having 240V AC instead of up to 500V DC at the very least gives me warm fuzzies. And knowing that the inverters will shut down if they lose the grid means that I won't have those high voltage DC lines active down to the inverter all the time if I need to do any maintenance.
• Potentially higher output. Being able to have each panel product maximum power at all times is nice, even though I only have minor shading on a couple panels early morning and across the panels later in the afternoon.
• Easy to upgrade/flexibility. If I want to upgrade the system a couple years down the road because I'm using more electricity, it's easy as you don't have to worry about panel mismatch should my original panels become unavailable. Right now I'm limited with the number of panels/inverters I can install because of the size of my service panel (100A, can only backfeed with a 20A breaker which means 16A maximum, or 20 panels/inverters). But If I upgrade my panel to handle a 30A backfeed breaker, I have room on the roof for another 8-10 panels without upgrading any of the wiring (it was sized to handle 30 panels total). Or, let's say they come out with some very high efficiency/cheap panels 10 years from now - as long as they match the specs of the inverters, should be able to just swap them in. Also - my current panels are 180W units - Enphase recommends up to 230W units - that alone would give me nearly another kW of power - but in my case, I got such a good price on the 180W panels it was more economical to use the lower price panels for now.

Primary drawbacks for Enphase Inverters are:

• Cost - they are a bit more expensive than traditional inverters - not to mention basic monitoring is usually free with other inverters, I think.
• Potentially more failures - simple statistics since we have 17 more inverters now, though supposedly they are designed to be ultra-reliable. But then again, they have a 15 year warranty when most inverters have a 10 year warranty.

For me - the Enphase Inverter positives outweigh the negatives. So I'm wiling to pay a bit more for them.

 

Drees has it pretty well dial.

"Cost - they are a bit more expensive than traditional inverters - not to mention basic monitoring is usually free with other inverters, I think.
Potentially more failures - simple statistics since we have 17 more inverters now, though supposedly they are designed to be ultra-reliable. But then again, they have a 15 year warranty when most inverters have a 10 year warranty."

I would add that there is some concern amongst some that there is a risk that they may have higher than average failure rate in large measure due to the fact that they are going to be subjected to abnormal high temperatures being under PV panels.

IMHO, the advantage of Enphase is that it allows one to build a PV system slowly as budgets allow.

If you are interested I suggest the following link: Grid Tie and Grid Interactive Systems - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun Search around this page and there are several threads about enphase inverters.

 

I don't think it's much of a risk.

Temps under the panels are cooler than you think - not much above ambient as long as you have adequate airflow under your panels. I will try to get on my own roof on a sunny day with my infrared thermometer to measure.

Additionally, the inverters are built to be much more rugged than your typical central inverter.

Finally, Enphase has backed it up with at 15-year warranty - that's 5 years longer than your typical inverter warranty. Does anyone else offer a 15-year warranty on their inverter? From what I've heard, you can pretty much expect to replace your central inverter after 10 years of service.

 

Drees,

I am not arguing with you, and in fact I agree that the Enphase is a rugged unit, I am just relaying information that I have read on other learned forums. One other concern is what ever headache factor that would be involved in replacing a bad inverter in the middle of a large array. In other words, if an inverter in the middle row of a multiple tier array would you have to un-bolt a number of PV panels to get to the one that is bad? Same issue with a single panel failure, but panel failure is a very rare event.

 

And all of it was from people who have never used Enphase before. Basically fear, uncertainty and doubt because it's something new. Sure, it's good to be a bit sceptical of anything new, but so far all of those "issues" you mentioned are pure speculation. I know you've done a lot of solar installs, but how much hands on experience do you have with Enphase?

I just installed my array last weekend. (Yay, passed city inspection yesterday, now need utility approval before turning it on which should happen early next week!)

To pull a panel out, you have to remove 4 bolts. This literally takes about 30 seconds. If your panel is grounded using lugs, add another 30 seconds to loosen the lug, otherwise add 30 seconds to replace the WEEBs when replacing the panel. Unplugging the MC4 connectors takes another 30 seconds at most. You can easily remove and replace a panel in under 10 minutes.

Unless we are talking about a huge array with 10 rows and the inverter that failed was in the middle - it's not a big deal to replace a failed inverter. How many residential installs have room for more than 2-3 rows of panels in one array, anyway?

 

Is a ground mount install cheaper than a comparably sized roof install? Seems that if you can swing the ground mount system in the back yard, that might be favourable for a lot of reasons. The increased efficiency of being able to adjust the angle of attack, easier maintenance, and a cheaper install (if that's actually the case) seem to make it a no-brainer. What say you, installer blokes?

 

We had our PV array ground mounted, installer stated ground mount was more expensive than mounting the panels on the roof.

 

Ground mounts have some advantages, some disadvantages. In the real world, I suspect that the price is fairly comparable between ground and roof. The advantage of ground mount is that you can, if you design for it, change the azimuth angle with the season if your array is small enough to be able to manage it. It comes at the cost of installation and engineering. Panels also tend to run a bit cooler adding to harvest a bit. That said a tracking ground mount is less and less competitive as the price of PV drops. The old rule of thumb was, two axis tracking was especially important for water pumping applications as it allowed any give array a longer time to produce useable current to pump with. For most grid tie (or battery based systems) the cost/benefit is not there. Another old rule was, for the money you would have to spend to invest in tacking mounts and hardware, you would be further ahead to buy a couple more panels. This is especially true as raw panel prices drop to ~$1-$2/watt.

Of course, one other disadvantage of ground mounts is the real estate they use! That said, if you have a place, looking at ground mounting is certainly an option.

As a side note, as you design Pv for residential applications, don't overlook the idea of wall mounting arrays. The further north you are, the smaller the penalty for the incorrect azimuth angle, especially in the winter. Wall mounts can also be used in snowy climates to reduce or eliminate snow accumulation on the panels. I have several panels mounted on hinges on the wall so that I can prop them at the proper angle for the season, and then leave them vertical when we get heavy snow.

 

Of course, one advantage of ground mount is that when you have to replace your roof, you don't have to take the panels off.

 

True, but one other caveat. When we had our Sun Power system installed, the Sun Power people mentioned that the Taxing agencies (Ca & Fed) base a "system" off one inverter & 1Kwh worth of panels minimum. But if you feel up to arguing it ... what the heck. We may add another 1Kwh worth of panels ourself, with no additional inverter and end up having to argue the credit issue too. IOW, there's nothing in the Fed Tax Code about what constitutes a 'system' ... so as dirty Harry once said, 'do you feel lucky?'

.

 

"IMHO, the advantage of Enphase is that it allows one to build a PV system slowly as budgets allow."

This of course is somewhat irrespective of rebates/tax incentives etc. The idea of buying one inverter and one panel per month say, plugging in each one, spreading the cost over several years is pretty attractive.

I can see finding ~$1000 every few months to a total of ~20k rather than finding the $20k up front,,, that is my point.

 

Both are good points - but the tax credits are good incentive to build the system in 1 kW chunks.

Enphase inverters are about $200. UL rated panels can be had for about $2.50 / watt if you look hard. Less than $3/watt is easy to find. You'll want 5 inverters and 5 200W (minimum) panels which will cost about $1000+$2500 = $3500. That's not a large investment. Now knock off at least 30% (federal tax credit) - that's $1000+ back in your pocket, or enough to buy another panel/inverter plus some. Don't forget permit fees, which can vary widely as well - that also encourages you to upgrade in larger steps. Those numbers ignore install costs, but if you are considering adding to your system in small chunks, it's probably not going to be cost effective to hire someone unless you do it in at least 2 kW increments.

If your state has renewable energy incentives (California has incentives ranging from $1.10/w to $1.90 depending on your utility co), that knocks off another large portion of the cost.

 

What is the nature of the adjustment you are suggesting?
Most PV panels are mounted parallel to the roof and face
the sun at the same angle as the roof. Assuming a normal
installation orientation of back to back to back, raising any
given panel will cast a shadow on a neigboring panel, thereby
cutting its production.

Anyways, I ask this because I just signed off on a PV array
with Enphase inverters, and now I am wondering whether
"adjustabilty" would have any benefit.

 

Just from my experience, seasonally adjusting PV give performance increase of ~20%. (over the course of the year) The advantage is much greater the higher your latitude. For example we are north of 50 degrees, so the difference between optimal angle in June versus December is considerable. If you are only North 25, the advantage is only ~1/2 maybe.

I Actually change my panels several times a year. In my case many of my panels are wall mounted on hinges so I prop them with the proper angle, and change that angle every month or so.

In normal case roof mounting, especially fixed mounts on a pitched roof it if probably not worth the effort, but ground mounts or roof mount on a flat roof it might well be. Pretty easy to do with a small array, harder of course with a larger array.

 

Yes, as icarus is saying, the optimal tilt of the panels corresponds to how high the sun gets on the horizon.

Ideally, you'd have the panels tilted to be perpendicular to the sun at all times (a 2-axis self tracking system). 2-axis systems are almost never used due to their complexity, though.

For the vast majority of people, simply aiming to mount the panels at an angle so that annual harvest is maximized. This simplifies installation and lowers maintenance. Adjustable installs are atypical for your average residential installation. This angle will depend on your latitude, but generally an angle that matches your latitude will be very close. The exact angle will depend on your exact location, weather and power demands.

Yes the higher you tilt the angles up, the more room you need in between in between panels - how much depends on the tilt, angle of your mounting surface and how low the sun gets in winter.

 

The Sunpower PV panels offer a higher than typical
panel efficiency, namely ~18% vs 14.4%. This results
in a ~20% smaller footprint for the same wattage
panel. Obviously, anyone who has space limitations
should consider these. My installer told me that
Sunpower runs about $1/watt higher than the 14.4%
efficiency panels (his data is from a few months ago).

In the context of this discussion about Enphase, the
showstopper is that Enphase is not certified for use
with Sunpower, as my installer pointed out. I've
attached their compatability chart of March 2010.

Enphase does claim being able to capture upwards
of 9% additional power generation as a result of
their distributed architecture vs a traditional string
inverter. Attached is a slide presentation from them
which shows some actual installations. Where this
additional generation is coming from is avoiding the
string inverter's "lowest common denominator"
effect. In other words, a centralized inverter syncs
to the lowest output panel. So if a given panel is,
say, 5% low (which is within variability spec) or is
experiencing shading, that will cause the inverter
to operate all panels at the lowered power output.