3.2 KW Residential install w/Enphase Micro-Inverters

drees · February 2010

Background

I've been working on this project for my house with my brother and one of his friends who works in the solar industry for a number of months now. We are finally getting close to the install date (estimate 2-3 weeks). We are currently waiting for approval of the plans to get our permit which has been a bear as my city farms out it's PV plan reviews to a 3rd party consultant. It has been over 3 weeks now since our original plan submission (granted 1 of those weeks was us modifying the plans to their liking) and are still waiting to see if they like the latest plans.

My house is a two story house facing nearly directly East - the front half has the garage and living room with cathedral ceiling with one story. The back half has two stories with a nearly flat roof (fairly new rolled bitumen roof in good shape). There is no attic space.

The panels will be installed flat on the 2nd story half of the roof.

The goal of the design was to nearly eliminate our electricity bill while giving us room to use more electricity in the future (such as for air conditioning and/or a plug-in car) without having to pay 33c/kWh or more for electricity. In addition, we wanted to have a flexible system should we decide to augment the system a few years down the road.

Hardware

Panels: 18 ET Solar M572 180w - 157.7 PTC
Inverters: 18 Enphase M190 micro-inverters
Panels/Inverters will be arranged into two strings.

The CSI calculator estimates that the system will generate approximately 4,380 kWh/year which is slightly under our annual consumption of 5,000 kWh/year.

Limitations/Compromises

Ideally, we would have a south facing roof where we could tilt the panels at 17* for maximum energy production - the CSI calculator indicates that with the same system we'd get an additional 450 kWh/year or 10% more output from the system that way. Unfortunately, the city has indicated that the system must remain under the highest portion of the roof. As it is, the center gable is about 7-8" high. The "flat" portion of the roof measures about 22' x 45' with the shorter dimension facing west. With rise over run of approximately 1 over 25 (~3*), I am pretty much limited to mounting the panels flat.

Additionally, our house only has a 100A service panel. This limits us to 20A backfeed - or 16A/3.8kW AC of usuable power production without upgrading the service panel. We looked into upgrading the service panel to 200A - but because our lines are buried and the existing conductors/conduit not rated for 200A service, we would have to dig a trench to the handhole at the street at the street at considerable expense.

Each Enphase mico-inverter is rated at 800mA max output which would in theory let us add 2 more inverters down the road should we want a bit more power output. Otherwise we will have to upgrade the service panel which should give us more flexibility.

Design Plans

As mentioned, we will have two strings of 9 panels running from north to south. They will be situated near the middle of the roof space due to existing roof penetrations (Solar tubes/sewer vents). The panels will be using ProSolar Rooftrac rails mounted on 3" FastJack standoffs.

One the end of one of the rails will be a junction box to terminate one end of the Enphase inverters along with an AC disconnect switch for each string.
From here, 3/4" EMT conduit holding 6 10GA wires (3 for each string, 2 hots and a neutral) and a 8GA ground will be run though the roof, into the rafter space, though a wall and into a junction box in the garage.
From the junction box in the garage romex will be run into a sub-panel mounted on the inside of the garage with two 15A 2-pole breakers (one per string).
The sub-panel will run to an AC disconnect mounted next to the main service panel, which will backfeed into a 20A breaker in the main service panel.

Maximum current per string is 7.2A - both strings combined 14.4A.

Comments - questions?

My only reservation at this point is that I already kind of wish I had gone with bigger panels instead of the 180w ET panels. Enphase recommends 230w (DC) panels even though the AC output of the inverters is 190W. If I had used 220W+ panels I could have gone with 15 panels and one string, but the ET panels were so much cheaper per watt (50c+/watt) than the other panels I had available to me it wasn't cost effective.

BB. · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Regarding Enphase--Have you decided on how you will monitor (local hardware and your own computer, or website subscription)?

If you decide on local monitoring hardware/software and don't use the subscription program--Look at the available data from the server you buy from them. From one earlier story here, there was a software update by Enphase that reduced the amount of data available through the local interface... I would get the minimum required local data set/access written into the sales/support contract.

In any case, I would review that the local interface has enough information for you to monitor and determine if you have a bad panel/inverter (without the website subscription). Figuring out if anything fails in your installation is near impossible without good data logging.

Also, from my days in design engineering--I would ask them if they have any second/alternate sources for inverters that would interface with their existing monitoring system. If you want to add more panels/inverters a few years down the road--you would want to ensure your existing monitoring hardware/software supports future needs.

Regarding mounting: Flat panels will need maintenance--you with soap and water+squeegee for cleaning the array (few times a year--depending on how much dust in your area). So--make sure you have access, walkways, and water for the job.

Ideally, you would want something like 15 degree minimum tilt to make them self cleaning. So, I would look into if this is an "unreasonable restriction" with respect to California state law:

The Solar Rights Act (CA Civil Code 714), enacted in 1978, bars restrictions by homeowners associations (HOAs) on the installation of solar-energy systems, but originally did not specifically apply to cities, counties, municipalities or other public entities. The Act was amended in September 2003 to prohibit a public entity from receiving state grant funding or loans for solar-energy programs if the entity prohibits or places unreasonable restrictions on the installation of solar-energy systems. A public entity is required to certify that it is not placing unreasonable restrictions on the procurement of solar-energy systems when applying for state-sponsored grants and loans.

The Act was amended again in September 2004 by extending its prohibition on restrictions to all public entities. Additional key changes minimize aesthetic solar restrictions to those that cost less than $2,000 and limits building official’s review of solar installations only to those items that relate to specific health and safety requirements of local, state and federal law. Assembly Bill 1892 of 2008 further amended the civil code to nullify any restrictions relating to solar energy systems contained in the governing documents of a common interest development. A common interest development includes community apartment projects, condominium projects, planned developments and stock cooperatives.

If you are in the City of San Diego, make sure you got your building plan rebates:

The County of San Diego has a Green Building Incentive Program designed to promote the use of resource efficient construction materials, water conservation and energy efficiency in new and remodeled residential and commercial buildings. As part of the program, the County will waive the fee for the building permit and plan check for a photovoltaic system. In addition, for qualifying resource conservation measures, the County will reduce building permit and plan check fees by 7.5% and grant expedited plan checks, saving approximately 7 - 10 days on the project timeline. To qualify for these conservation incentives, the project must comply with the program requirements for either natural resources conservation, water conservation, or energy conservation

Other rebates and incentives may be available to those building greener and more efficient homes and buildings. For more information, see program website above.

I pulled the above off of this site--check through it for any rebates/etc. that may be of benefit for you.

-Bill

drees · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

BB. wrote: »

Regarding Enphase--Have you decided on how you will monitor (local hardware and your own computer, or website subscription)?

Will be using the Envoy box and have a 5 year subscription to their monitoring services. I'll also look into getting the raw data off the Envoy box - I'm a software engineer with some Linux embedded systems experience so should be able to figure it out.

BB. wrote: »

Also, from my days in design engineering--I would ask them if they have any second/alternate sources for inverters that would interface with their existing monitoring system. If you want to add more panels/inverters a few years down the road--you would want to ensure your existing monitoring hardware/software supports future needs.

Not too worried about this - I imagine that they will have to keep on producing the same/compatible inverters for years to come to satisfy warranty requirements, so obtaining compatible inverters shouldn't be an issue.

BB. wrote: »

Regarding mounting: Flat panels will need maintenance--you with soap and water+squeegee for cleaning the array (few times a year--depending on how much dust in your area). So--make sure you have access, walkways, and water for the job.

Yep, this was one of my concerns as well. They will be mounted same as the roof slope ~3* angled at 280*, nearly due west - I might be able to increase the angle slightly, but we'll see once I start playing with the racking hardware.

I originally wanted to angle them at least 10* to the south for the self-cleaning, extra power harvesting and extra ventilation/cooling, (can get about 10% more electricity out of the system yearly by mounting at the ideal angle according to the CSI calculator), but fighting the city about building height restrictions wasn't something I wanted to get in to. Every 5* of angle puts the edge of the panel up ~3" if tilted on it's long axis so I might get 5* without going over the roof gable unless I had a racking system that let me put one edge of the panel just off the roof surface.

The panels will be mounted nearly in the center of the roof due to obstructions along half the top 6ft of the roof, so there will be at least 5 ft of empty roof space around all sides of the panels - plenty of room to do work on the panels should it be needed as well as satisfy any concerns the fire dept may have with roof access. Physically, there is enough room on the flat part of the roof to nearly double the size of the array while still maintaining a 4-5 ft perimeter around the panels that face a wall - the main restrictions with system sizing are figuring out how to feed all the power back into the main service panel.

What's the typical procedure with cleaning panels? Is there any worry of cracking the tempered glass in the heat of the day if using cool water to wash the panels off or should the cleaning always be done first thing in the morning or evening when the sun is low?

BB. wrote: »

If you are in the City of San Diego, make sure you got your building plan rebates:

Thanks - I'll be sure to follow that up - haven't paid any permit fees yet.

mike95490 · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

drees wrote: »

What's the typical procedure with cleaning panels? Is there any worry of cracking the tempered glass in the heat of the day if using cool water to wash the panels off or should the cleaning always be done first thing in the morning or evening when the sun is low?

I alwys do mine in the AM, after the dew has softened the grunge up, and before the sun heats them up. If you can get a Mr Clean carwash kit, with the DI rinse cartrige, that's the best no spot, no chemical final rinse.

BB. · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

I, personally, would recommend avoiding thermal shock (hot water in hose/cold panels; or hot panels and cold water)... Thermal cycling (within temperature limits) was the quickest way I had from filtering good hard disc drives from bad ones (years ago doing evaluation).

I asked Solar Guppy about the thermal shock on panels a couple years ago--and he said he never saw a problem.

SG certainly has more experience with solar panels than I...

The UL test article posted a few days ago said that humid/wet panels subjected to freezing cold (I think it was -40C) was the typical panel killer in their testing. San Diego and -40C does not go together...

I would still see what the Building Department says if you drop a copy of the law on their desk... You could possibly do the $2,000 limit by comparing output with "ideal" panel tilt vs flat (ie., $50,000 * 10% energy loss -> $5,000 loss of value/cost to make up for unreasonable/non-safety related issue)...

-Bill

Ralph Day · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Just found out some info about Enphase monitoring. I have a 10 kw system in the works, 52 inverters, and envoy. Before looking at the price per inverter for monitoring I investigated the high speed internet costs. Here in Canada the prices for high speed are ridiculous. Cheapest was $45 for 20Gb of bandwidth per month(that's antennae on the roof, not DSL). The Enphase tech support helped me figure out the amount required per month...800kb/4hr block x 3 (12 hours per day) x 30 days = 72Gb per month approximately. This puts the website monitoring out of reach for me.

One of the techs volunteered her high speed DSL service cost $25 per month...I asked how much bandwidth...unlimited! Maybe if we can bring the costs of high speed down to a realistic level I want to monitor each and every inverter, but not now.

Ralph

drees · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Ralph, so I take it you don't have DSL or cable modem available in your area?

It's fairly typical for satellite to be charged by both maximum speeds and total bandwidth cap.

All my experience with satellite internet has been very poor due to the huge amount of latency in the connection.

What type of monitoring will you be doing? Just relying on the Envoy?

Ralph Day · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Yep, just the Envoy, but setting up a LAN with my home computer. I have an email from Enphase with the instructions I can pm to you if you want it.

Ralph

drees · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

800 kB/4 hours of data sounds like an awful lot - about 4 kB/inverter/hour.

Seems like some simple gzip compression of the data would reduce data size significantly, especially since most of the data should be very similar.

Did they say how often the Envoy uploads data to their servers?

BB. · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Ralph Day wrote: »

800kb/4hr block x 3 (12 hours per day) x 30 days = 72Gb per month approximately. This puts the website monitoring out of reach for me.

If I understand the numbers correctly, that works out to 720 MBytes (0.72 GBytes) per month... next stupid math trick change into 72 MB / 0.072 GB per month...

By the way, the "hidden" limit for Comast.com Cable (Xfinity now?) is 250 GBytes per month before they send the warning letter that you are hitting the limits for unlimited Internet (according to what my friend was told a week or two ago). As far as I know--you cannot find out what your monthly usage is unless you check through your router or something...

From what I have read a few years ago--If you ignore the call/letter, they will kill your account the next month (and no appeal in the cases talked about on the web).

-Bill

drees · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

BB. wrote: »

If I understand the numbers correctly, that works out to 720 MBytes (0.72 GBytes) per month...

Apparently simple math is none of our strong points.

(800 kB / 4 hours) * 3 (12 hours of sun/day) = 2.4 MB/day * 30 = 72 MB/month.

Only an order of magnitude off from 72 GB/month.

Even assuming that they send out 24 hours/day, that's still less than 150 MB/month - should not be an issue at all on any broadband plan (even satellite).

icarus · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Gigs, megs, bits, bytes, it is all greek to me! Never ask me a math question bigger than about 2 zeros!

Tony

BB. · February 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Actually--that one was a typo... Missed the "." on MS Calc. on my 10" note book (twice

)... Still wrong though..... I keep teaching my kids to do sanity checks (1MB * 3 * 30 <> 720). So--I must be insane.

:grr

Carry on.

-Bill

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Quick update - my permit was officially approved today. Planning on doing the install in about two weeks once I get all the miscellaneous parts (sub-panel, disconnect, wiring, conduit, junction box, etc).

drees · March 2010

Re: 3.2 kW Residential install w/Enphase Micro-Inverters

Worked all weekend with the help of my dad, brother and his friend to get the system installed and finally finished today.

Biggest time consumer was prepping the roof for the penetrations - being nearly flat and having hot-rolled roof proper preparation was a messy, time consuming process that included flashing and patches along with roofing "goop". Once concern is that the roof may not be as sturdy as previously thought - that's the type of thing you get the feel of after working 2 days on it, so hopefully it holds up for a while.

Next step: inspection

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Just need a couple labels before inspection:

Main panel label listing PV specs
Label indicating dual power sources (done)
Label indicating backfeed OCD
[ AC disconnect label (done)
Label for sub panel and breakers

Tomorrow I'll call for inspection once I get all the labels made up tomorrow. They say call the previous day for a next-day inspection, so hopefully Friday I will be officially blessed and can turn the system on.

niel · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

good deal on getting your system this far. i would not tell the inspector that you turned it on prior to his approval so unless he requested that you do that, say nothing.

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

The City has officially signed off on the install. Now I just need the utility (SDGE) to approve it, which should happen early next week before I turn it on.

Almost there!

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Roadblock.

SDG&E inspected the system today. Everything was go except that they require a warning placard to be displayed near the meter which shows the basic layout of the system along with the installed disconnects. The placard has to be permanently installed using rivets or machine screws.

Sample:
http://sdge.com/documents/business/warning_plaques.pdf

http://sdge.com/nem/interconnectionRequirements.shtml

Seems crazy to me given that there is a disconnect 1.5 ft from the service panel which clearly reads "Solar Disconnect". SDG&E doesn't even require a disconnect switch any more - they'll just pull the meter if you don't have one. Too bad the NEC doesn't agree. That makes 3 disconnects on the outside of the house (switch, backfeed breaker into panel, meter). Add another in the sub-panel in the garage, and another switch up on the roof.

And never mind that the inverters on the roof completely shut down as soon as the grid goes away.

Totally over kill.

Anyone know of a good source to have these signs made? Thinking I will probably just call up a couple local sign shops. The inspector said that most PV shops end up buying their own engraver.

mike95490 · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

drees wrote: »

Totally over kill.

There was a game I used to love playing, called Overkill

--
This PSA brought to you by the department
Department of Redundancy

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Drew up a caution plaque last night using OpenOffice Impress, emailed a copy to the SDG&E NEM guy to see if he liked it before I turned it into a sign. He liked it (very quick reply!) and I called up a local trophy/sign shop. Emailed them a copy of the sign in bmp format and they should have it done in the next day or so and will cost me about $15. Good deal!

With some luck may be up and running by the weekend!

newenergy · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Impress is their slideshow application, right?

I would think OpenOffice Draw would have been easier.

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

newenergy wrote: »

Impress is their slideshow application, right?

I would think OpenOffice Draw would have been easier.

Yeah, you're right. But the tools are nearly identical between the two, so I the end result and effort level is basically the same. It does look like Draw (can you tell I haven't used the tools much?) will be a bit easier next time.

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

The SDGE inspector approved the system this afternoon. Got to turn it on with a bit of sun left. Unfortunately, will be cloudy with some rain later this week around here so that will limit production.

Public monitoring site is available here:

http://enlighten.enphaseenergy.com/public/systems/xM8R3368

niel · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

congrats that it's finally done. i found the power monitoring link interesting and informative and would show if an inverter would fail. there were some discrepancies in the power production as shown when i clicked on today's power and it showed some pvs around 5w and the other half were at 30-40w each. that was for march 29 at 20:15 gmt. paying for that monitoring does distract from it all though.

RWB · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Enphase's online monitoring web interface is beautiful and I can't believe that Outback has not paid to have something as nice for their systems even though it can only show the total panels production vs each individual panels output which is awesome.

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

niel wrote: »

congrats that it's finally done.

Thanks! It's been over a year since I seriously started planning it, so it's nice to finally have it up and running.

niel wrote: »

i found the power monitoring link interesting and informative and would show if an inverter would fail. there were some discrepancies in the power production as shown when i clicked on today's power and it showed some pvs around 5w and the other half were at 30-40w each. that was for march 29 at 20:15 gmt. paying for that monitoring does distract from it all though.

Interesting, do you have a screenshot? I couldn't see anything like that except for shortly after I flipped it on around 17:15GMT-7 (ah, you must mean GMT-10, US/Eastern). I'm not sure what caused that - I'm sure it's some sort of issue while the system was still ramping up after turning on.

niel · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

drees,
it took me awhile to remember how to copy the browser image and to be honest, i'm not quite sure how i did it. anyway, you should be able to see what i'm talking about with this pic of my browser page. it was not the exact moment i was originally referring to, but shows variances none the less.

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Yep, that's the same time I was looking at. That was shortly after I turned on the system, I'm guessing that all the inverters hadn't synced up to the grid yet which is why some were at full output and others weren't on yet.

nvyseal · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

I'm going to watch your system today. Bet this is exciting for you. I'll compare it to mine when i get home, as i dont have internet data logging.

drees · March 2010

Re: 3.2 KW Residential install w/Enphase Micro-Inverters

Yes, definitely exciting, but could be more exciting if it was a clear, sunny day. It's been completely overcast today so far so output is down a lot (currently a bit over 600W or 34W/panel).

Earlier testing in the middle of the month of the system generated a bit over 17 kWh on a clear day with a peak of 2.4 kW just before 1pm local time - both of which are in-line with the output I expect from the system.

The output for the day was actually a bit higher than I expected - PV watts estimated 383 kWh for March. That would only take 22 sunny days of output at that rate - I'm thinking that either there is more cloud cover than I expect for March, or my PVwatts derating factor is a bit too much. Over the life of the system it's probably fairly representative, though.

3.2 KW Residential install w/Enphase Micro-Inverters

Comments

Categories