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Old 01-26-13, 04:02 PM   #1
Trevor
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Default Micro-Inverter vs Standard

New to Solar PV so any comments suggestions will be appreciated.

I am putting together plans for a garage. I would like to add a significant amount of PV on the roof (anywhere from 5kw-10kw). I have been reading about PV and looking at online pricing for the last couple of weeks. One of the big questions I am having involves whether to go with Micro or standard inverters. I like the warranty and seemingly easier install that the Enphase inverters. I have read the pros and cons of both. I live in Vermont and it seems the micro may be a little better if one or more of the panels is covered (like with snow). So, my first question is: What sort of expierence have people had with the MicroInverter?

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The second question is more about the cost of grid tie systems. I can go to
wholesalesolar.com(which I am not affiliated with at all) or other websiite and find a 9kw-10kw system with all the roof mounting hardware for $16k to $20k, but my first conversation with an installer in my area had the price of a 8kw system at $40k. I have heard an install on a roof would only take a few days (3+) so I am confused at how it gets to $40k. To be honest the conversation was on the phone with not a lot of specifics.

Vermont state details - Vemont has a 50 cent per watt grant, but it needs to be installed by a "licensed solar installer". So if I go with having someone install it for me I would be eligible to get the $5k for a 10kw system. But if the installers are charging a 30% markup on the panels, inverters, and other hardware it doesn't make sense.

So here is the second question. What does it take to put in a new system from a labor perspective from a person who knows what they are doing. I am willing to pay someone for his/her knowledge, but for $15k+ they should probably build my garage for me.

Details about the Garage - Still looking at plans but right now I have the garage being either (36 x 36) or (36 x 32). The roof will be 8/12 pitch which will get me as close to my best angle for maximizing solar power. I will also be using an attic truss to give me additional space for storage.

Thanks for any input.

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Old 01-27-13, 08:06 AM   #2
herlichka
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I would think that you should be able to find a licenced electrician that would be willing to work with you. The inverter and line voltage side of the system ar the focus of the licensed install- you can't connect to the grid without a permit, and most jurisdictions only issue permits to licensed electricians. Installing mounting rails and carrying panels up a ladder is usually a labourer's job, even the low voltage connections on the panels can be done by a non licensed labourer.

If you can find an "enthusiast" organization locally, you'll likely find a willing contractor. We have such a group here, Simcoe Huronia Alternative Renewable Energy, SHARE, and it is comprised mostly of curious electricians and hobbyists, and features regular presentations by vendors, government agencies, utilities, and owners of succesful installations.

One of the neat things about doing an install on on a brand new building is that you can install your racking or rails as you apply your roofing material, ensuring a good seal at your fasteners, and your conduit and/or cables can also be routed and sealed easier.
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Old 01-27-13, 09:32 AM   #3
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You haven't built the garage yet? do a standing seam steel roof and you will never have to replace the roof and you will save $1,000's on the solar install, a big chunk of that cost in the quote you got was most likely installing the roof mounts, out of the 3 day install I would guess that 2 of those days would be spent cutting holds in your shingles, installing brackets and installing expensive flashing boots, on a standing seam metal roof you don't cut in to the roof, instead the panels attach right to the standing seams and clamp on, saving the installer days, preventing them from buying expensive flashing boots and it saves on panel racking because the roof becomes the racking.

To answer your original question, I don't know of any situations where a single large inverter makes sense any more, other then in off grid or battery back up houses, personally I'd go with something like Helios Solar Works Solar Module Description and Specifications and use their A/C panels that have the micro inverters mounted right to the panel, I can't find the price right now on them, but when I looked before they were around $2 per watt! They are also made in Wisconsin, not China.

Around here the panels do not need to be installed by a "solar installer" to get grant money, but the grant money is based off of estimated output and that output is figured based off of location and shading, so you'd first have to have a site assessment done and they would give you a very accurate output figure.
At least here, if you own the house and live in it you can do electrical work, you still have to get it inspected by the building inspector, the other option is to find an electrition that is willing to work with you, they are not likely to want to let you do much of the electrical work, but they will most likely let you do a large chunk of the non wiring labor.

So talk to someone in your area that does site assessments and they should be able to tell you more about what you need in your area.
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Old 01-28-13, 08:55 PM   #4
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Thank you for the input, I had not thought about standing seam metal roofing. I will do a little research on that.
I am hoping to have a meeting with a "Solar Installer" later this week to get a better idea on the installation costs.
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Old 01-29-13, 06:39 PM   #5
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I install solar for a living and as far I am concerned, unless you have major shade issues that keep some of the panels producing less than others, a string inverter (SMA, Fronius, Power one, etc) is your ticket. If you have the shading issues, the Enphase is good.

About roofing, a proper racking system is the same cost for a shingle roof as for a metal standing seam roof. I can install a bracket on a shingle roof in about 2 minutes and just slightly less on a standing seam metal roof and the brackets are about the same cost. I like the metal roof because it is a longer lasting roof and there is often less embodied energy in them but the decision is yours.
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Old 01-29-13, 09:21 PM   #6
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Hi,
I have a 2.2 KW Enphase inverter system -- going on 3 years old.

Have not had any problems or failures.

At the time I did mine, the microinverters cost about the same as a single string inverter, and I liked the flexibility to add panels later, the separate MPPT for each panel, and the simple installation.

I've been happy with them, and have grown to like the web page they setup for you to get reports on the system. Their monitoring system (which is now free), also lets you know when any inverter is having problems -- kind of strange when you get an email from your inverter I've received a handful of notifications that something was wrong with the advice to just give it an hour and see if it clears itself -- it always has.

It gives you a separate power report for each panel/inverter, and I think this is useful -- for example, if you think power output for the system is down, you can look at what each panel is doing, and see the one that is causing the problem.

I like building stuff, but I'm not so good about looking after it after its built and doing the routine checks to make sure everything is still working, so the automated reporting including faults is nice for me.

The install is easy -- I did mine including permits and all -- the pictures here give an idea of what's involved: Designing and Installing a Grid-Tie PV System
There are some more DIY installs here: Solar Photovoltaic Projects Tie
In particular, take a look at "Doug's New 4.6 KW..." system.

While the micro-inverters make for an easy install, I don't think the string inverter install would be much harder.

I guess some places it can be a pain for permits and inspections and meeting utility rules, but here in MT its cheap, simple and fast. I was up and net metering a week after the system was finished.

Solar Today did a nationwide survey a few months ago on what people were paying for professionally installed systems. The US average was over $6 per watt (may have dropped a bit since). Places are offering pretty complete kits for less than $2 a watt. There will be stuff to add to the $2 per watt, but not a while lot in terms of $'s per watt, so, it seems like there is still quite a bit of money to be saved for a DIY installation?


Gary
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Old 01-29-13, 10:27 PM   #7
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Gary, One of the first installs I had read about was yours. You are very thorough in you descriptions which makes it easier for us newbs. So for that I thank you.

Mike, You mention Standing Seam (which is more than I want to spend on a garage roof) and shingles which may not last as long as the solar panels. But what has been your expierence with corragated metal roofing?



Thanks again for the comments and suggestions.
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Old 01-30-13, 01:10 PM   #8
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Trevor,

As you haven't built the garage yet, be sure to site it true south when you build it. If there is to be any roof penetrations, be sure it {they?} are not on the south facing side of the roof. Also, if I was using the roof for solar panels, I would make the pitch of the roof match the latitude since I wouldn't be doing a seasonal adjustment to the tilt. Sorry, it may seem like I am talking down to you and I don't mean it that way, just wanted to be sure. You might also want to have fairly large overhang sized for passive solar and an appropriate number of windows. These add very little to the building cost and can make a huge difference in the temperatures in the building, both summer and winter.

The standing seam roof premium over a corrugated metal roof would probably pay for itself in a couple of ways (I have a metal roof with the screws visible on my house).

First off, the savings in racking materials only benefits you with standing seam, not corrugated metal because of the clamps used to pinch the seams on a standing seam roof.

Second, a few of the screws on my metal roof have somehow backed themselves out. That put me on the roof fixing them. If those screws were located under your solar array, you might not notice the problem until the water dripped off the underside of your roof. And you would almost certainly need to remove panel(s) to repair it.

All that said, I have two solar arrays in my backyard, both ground mounted. The first is 1050 watts of 6 Sharp 175w panels. I built it in two increments, 4 panels with Enphase micro inverters and then 2 more panels to fill the rack I built with more Enphase micro inverters. The first part was built in early 2009 when I bought American made Enphase inverters with the cast aluminum housings. When I added the last 2 panels in the fall of 2010, the Enphase inverters were made in China, but I had no choice for this small array. Last Spring {2012}, I had a bad inverter that Enphase made up under warranty. It was one of the newer inverters manufactured in China.

When I built the second array, 5760 watts, I went with 24 Sharp 240w panels on a DPW designed ground mounted rack running to an SMA Sunny Boy 5000 inverter. My solar designer recommended against the 6000w inverter because he said it would drop off more at the lower end of my array output.

The comparisons I have done on output say the small Enphase array does better on the really nice solar days. They have produced in excess of the panel rated wattage in really cold, for Alabama, weather. I have not observed the Sunny Boy go past 5111 watts. Typically the Enphase hits about 92% of module rated wattage where the Sunny Boy stops at 89% of module rated wattage.

My personal preference is to buy American, and I may not make quite as much power this way as if I'd gone with Enphase inverters. Twenty four separate Enphase inverters and the Enphase monitoring unit would have cost more than the Sunny Boy did also.

Whatever you decide, I'm glad you are considering solar.

Just my two cents worth,

Mark
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Old 02-01-13, 05:12 PM   #9
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I am trying to find the optimum pitch for the roof and I found this site (can't post links yet so try putting a w w w in front of) ".macslab.com/optsolar.html" . Mark you say use your the latitude. What should I be using if I am at 44 degrees Lat?

I have also found a non-standing seam metal roof that appears to allow the clamp on type of roof mount. This is a ABC SL16 metal roof. Yes you will have screws showing that hold the roof down, but I plan on using 90% of the roof for panels(at least the side that faces the road, which is south). As soon as I get a price I will compare it to a standing seam price. Can someone take a look at (can't post links yet but try putting a W w w in front of this ".abcmetalroofing.com/panels_sl16.html" American Building Components ? Metal Roofing & Wall Panels[/url] and verify the clamp on holders would work?

From a DIY perspective it seems the micro-inverters are almost fool proof, so I am leaning in that direction.

I still have a few months to plan, the garage is not going up until the May time frame, but am trying to get an idea on $ for a budget.

Thanks again for your responses. This forum is great.
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Old 02-01-13, 07:36 PM   #10
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The only negative thing about any metal roof, from a installation perspective, is a slippery roof.

To me string inverters are easier only because i can just clip them together and have one set of lines for a group of panels. Yes the micro inverter give you individual monitoring but you can get that from a TIGO optimizer module as well with a string inverter and the cost will be less expensive the Enphase.

About the slope, if you were using a battery system and you had to get the most winter time power possible, I would keep the angle close to your latitude, BUT, if everything you make is going into the grid and counts on your bill annually, put the panels on an angle that produces the most when there is the longest days. That might only be 15deg or 30 deg.

Where we are, the utility pays me $.80/kwh for everything I produce so I will have it at the angle that nets me the most over the year. Others have a month to month net metering so follow the battery rule

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