Solar Panels and Inverters, Our First Solar Repair Experience.

In 2012, shortly after moving to electric with our BMW Active E, it became apparent to us that installing a solar array on our roof was going to be beneficial for us to lower the cost of our transportation fuel as well as our consumption of energy at home.  Producing our own fuel coupled with net metering and time of use would provide us with efficiency that would provide for a rather quick payback.

As I understand it, Net Metering allows utility customers with the ability to export the power generated by their devices (in our case, our solar panels) to the utility at the retail rate of energy as a credit against our overall consumption.  Time of Use is a program that provides differing pricing for electricity depending on the time of day and week that energy is consumed by a utility customer.  When we first started on this program, our peak times for energy mapped perfectly with the hours of sunlight.  That is to say, the peak energy times were from Monday to Friday from 10am to 6pm.  This meant that during the the times that we were not at home, our solar panels would produce enough credit to be offset during our primary usage, which is after 6pm and before 10am (in SCE territory, since we installed our panels, this peak time has changed and shifted to 2pm to 8pm).  Under our original assumptions, and armed with a single EV that was capable of an 80-100 mile range, we figured our break-even for this project to be in the approximately six to seven years.  As many long-time readers have found out, it was soon after getting into our BMW Active E that we dedicated ourselves to a primarily EV existence that we went from one EV to three EVs and back down to two EVs.  With the amount of driving that both my wife and I did, this break-even point was reached sometime last year (around the three and a half to four year mark.)

When we first bid out our homes’ solar PV, we shopped it around and ended up with Solar City.  As I’ve documented before, because there was a snag in the age of our roof, we had the opportunity to re-open this to others and ended up with Real Goods Solar (RGS Energy).  We documented all this in some articles on this blog.  I did a follow up that covered the installation.  Because of how things worked out for us, we opted to pre-pay our power purchase agreement with Real Goods Solar for the 20 years of service that we signed up for, if we do this again now, we would buy the system instead, but I didn’t want to have to worry about maintenance and the like.

Which brings us to the subject of inverters.  As I understand it, the inverter is the device that converts the Direct Current (DC) produced by our solar panels into AC (Alternating Current) energy that our appliances and other domestic household devices uses. Every solar company that I spoke to during the bid process basically said that the main thing that would break in a solar installation is the inverter.   Under original solar installation designs, solar installations would have ONE or TWO inverters that connect the whole system to the home and electrical grid. This means that if the inverter failed, the energy produced by the solar panels would not be converted to AC power and be effectively out of service for the whole system until it gets repaired.  We picked Real Goods Solar primarily for financial reasons.  However, at the time, they pitched an interesting system using micro-inverters.  Instead of one (or a primary and backup) inverter situation for the house, each solar panel has its own inverter that converts the energy produced by each panel to AC.  This configuration spread the risk of outage from the whole system to just a single panel at a time.  Being a systems guy and understanding single points of failure versus minimizing this, I appreciated the pitch, but money savings really drove the decision.

One of the technical benefits we got from having the micro-inverter solution is we are able to see the production of our solar system down to the panel level.

So, on a normal day, we can see the panel production on either the website on a browser:

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Or on the mobile app.

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A few months ago, we experienced our first repair under this program.  On the weeks prior to failure, I started receiving alerts regarding AC voltage being out of range and on March 8, I noticed that one of the panels had a hard failure.

This is a screenshot of the email that I received to show the errors in one of the micro-inverters that started to occur.

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It looked minor at first, but as you can see in the graphic of our system, one of the panels is grey.  And this is a good indication of the failure AND the location of the failure in our system.

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I reported this to Real Goods Energy and received a trouble ticket on March 9th. They remotely diagnosed the problem and required me to contact the owners of the system.  Since I am on a Power Purchase Agreement (PPA), I don’t actually own the system on my roof, I effectively buy power from those that do at a predetermined rate when I signed my contract.  Traditional PPA purchasers do this on a monthly basis that have riders that increase the cost per kWh over the years, but we decided to prepay the entire contract at the time that we finalized our deal and therefore fixed our cost per kWh soon after the installation was complete.  Therefore, technically, we don’t own the system on top of our roof.  The owner to the system provided approval and we waited for the repair to be completed.

It took about a month for the full repair to be completed and I estimate that we lost about 40kWh of production from having one panel out that entire month.  To put this into perspective, the whole system produces 40kWh on a Summer day, so even though the panels were missing one of the 28 panels on the roof from producing, my outage was only equivalent to one day’s outage with a more traditional set up.

So, what does a micro-inverter look like?  Well.  Here are a few photos.

Here is the broken one getting put back in the box.

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Here it is on the roof.

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And here it is installed and in-place.

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In writing this article, I was looking for pictures of larger inverters and came across this picture of a commercial solar installation from Brightergy.com.

Solar Inverters at Cross Midwest’s solar-power installation

The picture is from an article “How Solar Inverters Work” from February 6, 2013 on the brightergy website. It also covers inverters.

Here is the picture of a more common inverter from Wikipedia’s article on Solar Inverters.

Solar Inverter from Wikipedia
Solar Inverter from Wikipedia

Why would I not want to use micro-inverters. In moderate climate, like California, it works great. However, someone in Arizona has mentioned to me that it is too hot in their climate. I don’t know if this is true, but it has been reported by one person to me.

Consider going solar, use our referral code here.   If you wish to have a longer discussion, I have access to other installers as well.  Send me a tweet and we can get that process started interactively.

Tesla Solar EVent

On Friday, October 28, 2016, approximately a year and a half since the original Tesla Energy launch EVent on April 30, 2015, Tesla improved upon the PowerWall and PowerPack, Tesla revisited Tesla Energy with the launch of the Tesla/Solar City product launch for the Solar Shingles.

Tesla Energy 2015 Launch

I did a bunch of tweets during the original Tesla Energy, PowerWall and PowerPack launch event from April 30, 2015…

(Here’s a link to the Flickr album from the Tesla Energy event.)

Tesla PowerWall

Some selected tweets from the original Tesla Energy Event:

 

 

 

 

Tesla Solar Event

The focus of the event held by Tesla this past Friday, October 28, 2016, at Universal Studios Hollywood was on the newly unveiled Solar Roofing products that were developed in conjunction with Solar City.  As impressive as this product line is, the Solar Roof is definitely not a financial fit in our current configuration.  Many who follow this blog will note that we just achieved our break-even point this past year (the fourth year of our twenty year agreement for Solar power) and paid less than $20 for all of the fourth year of energy (not counting taxes.)

One could say that neither the PowerWall nor its succeeding product, the PowerWall2 really makes economic sense for our use case either.  With net-metering still in effect in California, the economics of the PowerWall2 is not the reason to go ahead and purchase one.  However, coupled with time-of-use, and the whole-house backup capabilities of the PowerWall2, it looks like a great solution for a whole-house backup system.  With our summer peaks generating power at 40 kWh, two units may be all we’ll ever need.  I intend to recharge the system during the super off-peak time of day and get more bang for our buck by feeding back our solar production to the grid at a higher rate. Southern California is known to be very seismically active, and a whole-house backup system might just be something that would be really cool to have.

I was involved in tweeting out details for the event this past Friday through both my own account and my friends at Teslarati’s as well.  The guys at Teslarati had family commitments to attend to during the event and I was approached to see if I could possibly cover their Twitter feed for them, so I embed those tweets that I sent out here.  Hope those of you that follow Teslarati and my Twitter accounts enjoyed the coverage.

 

 

 

 

 

 

 

 

 

 

 

 

Since I committed to cover the event for Teslarati, I figured that we should arrive a little early.  No press pass for me, but covering it as an owner was fine for them.

The valet at this event provided sent us a text with a mobile website to handle the request and retrieval of our vehicle, it’s a lot more greeen than handing us a paper voucher.  I don’t remember whether they had this system at the last event we drove in for. It’s been a while that we valet parked a vehicle at a Tesla EVent since the last Tesla event for us was the Gigafactory Party that was the subject of our Long Way Round Round trip.  However, we took a loaner to the event. So, I photographed the vehicle and key to ensure that I know what I’m looking for.  Just in case this SMS ticket method were to fail.

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We were among the first ten cars through the valet and had been asked to wait in a lounge area to the right of the check in desk until they opened the “neighborhood” area.

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I think that the folks were unprepared for the number of people forced to wait in this area. It was standing room only.

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Luckily, the wait was not too long before the “neighborhood” was opened for us to enjoy. Fans of the old “Desperate Housewives” set will recognize the set as “Wisteria Lane.”

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Tesla’s catering services were the best that we’ve had in the various parties that we’ve attended. The neighborhood setting had enough seating, the food and drink was plentiful and did not run out as they have in the past.  There was a mix of self-serve sections as well as server provided locations.

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The bar lines were manageable and had a good selection of wine and other drinks.

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A few panoramics of the first neighborhood, before the section with the four remodeled houses was opened for the presentation.

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And right around 5:30pm, they let us into the neighborhood with the new Solar Tiles.

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Here’s the stage with the sun shining brightly on it.

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I was able to take one panoramic shot of the stage and the two closest houses to it.  On the left side of the stage is the house that the Model 3 prototype will emerge from later in the presentation.  I didn’t actually notice it emerge as I was closer to the right side of the stage.

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Here’s a closer shot of the house with the Model 3 in the garage before it emerged during Elon’s presentation.

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The house on the right’s shingles was more obviously solar shingles.  However, aesthetically they were quite pleasing.

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While waiting for the event to start, we were looking at the two houses on our left and were wondering whether they were solar shingles.  Something that Elon revealed as fact during the presentation.  The Tuscan Solar Tile, as this model was revealed later, is ideal for many homes in Southern California.

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I even tweeted my suspicions just prior to Elon’s talk.

 

The Presentation

Since the presentation was a joint Solar City/Tesla Event, it started off with a few minutes with Lyndon Rive, Solar City’s CEO and Elon Musk’s first cousin.

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Afterwards, Elon spoke.

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Here’s Tesla’s official YouTube video of the event:

Needless to say… The Solar Tiles are impressive. However, as I previously mentioned, we recently re-roofed when we installed our Solar Panels four years ago. So, that’s just not going to happen. We paid less than $20 for last year’s power and have recently hit our break-even point for our solar panels.

We did take a few good close ups, but a lot of the pictures can be seen on our Flickr Album of the event.

Tesla Solar Roof

Here are some of the pictures on the album above.

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Even though we’re probably not going with the cool solar tiles, the whole house backup thing though is VERY tempting. So tempting that we put in a deposit for a few of them.

How many you may ask? Probably more than we needed… But here’s a hint.

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Especially since the new version can be more efficiently mounted and stacked this way.

The original PowerWall had to be installed side by side and mounted on the wall.

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Looks really cool, but I think it’s probably more efficient to install it stacked.

One other thing about that Powerwall… It’s capacity is doubled in the same amount of space at less than double the price, considering the fact that the AC-DC Inverters are included. I also did the iPhone 4 width test that I did with PowerWall 1 with PowerWall 2.

PowerWall 1 compared to an iPhone 4.

The Home solution is slightly wider than an iPhone 4s #TEatTesla

PowerWall 2 compared to an iPhone 4.

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Color me impressed.

Model 3

The surprise for me was the appearance of the Prototype Model 3 at such close proximity.

The album for the event has a lot more pictures of the Model 3, but here are a few more shots.

It’s bigger than I had hoped.  It is smaller than the Model S, but bigger than the Active E. We got a few great shots in before security cordoned off the vehicle from closer inspection.

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Still a great shot that the better half took of me with the Model 3 in the background.

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We didn’t get any good interior shots, but this was the best shot of the Model 3 interior… Security was starting to cordon off and was kicking us out.

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It may be bigger than what I expected, but I still like the Model 3.

A multi-Tesla neighborhood… Sounds like a nice, clean environment.

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There was also a nice, blue Roadster there.

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There were a few Xs there, but just didn’t take pictures. There’s just so many of them around now. 😉

It was a fun event. The food and drink was the best service of the ones that I’ve been to. The valet had a wait, but I think that it was better than previous events that I used valet in. Take that last sentiment with a “grain of salt” since I used the bus at the Gigafactory Party, and I found that to be the most relaxing way in and out of a Tesla Party. The party may have been free to attend, but I walked away with a very expensive deposit for some batteries for the house. We’ll have to see how long before we get these installed.

Our fourth year of Solar usage.

SCE 2016-Year 4

This is our fourth year update. Click here for the Last Year’s (3rd Year) Summary.

It’s been four years since our PTO our solar array was approved, we originally estimated our savings on driving the Active E or a vehicle like the Active E. Since then, we moved from driving one EV to two EVs to three EVs and finally back to two EVs. We’ve also driven around a lot and our mileage has grown significantly since then. Our original estimation of a break-even was calculated with a one EV household.  Since then, we believe that we’ve achieved our break-even mileage for our EVs and home use of electricity between last year’s update and this year..

In our first year of Solar use, we had a credit. Which, as we found out, we could not claim. Because, it turns out, Net Metering means that though we’re credited for the production at a specific $ rate, customers are paid out on OVERPRODUCTION of power and not on the CREDITS earned. What this means is the system produced greater kWh of energy than consumed by the end user. If this is the case, the customer is PAID OUT the power times the wholesale rate of production. As long-time readers are aware, on our second year, we paid over $200 to SCE. For our third year, coupled with our nearly a month of travel to Maine and back in our Here, There, and EVerywhere roadtrip, we were out of the house for about three weeks that year, and a little over a month for that year. So, that created about a month of overproduction. As a result, Year 3’s bill was approximately $40.  This fourth year that just ended, we had about the same number of weeks away from home, but our annual net metering statement is about HALF of last year’s total with a nearly $20 bill for Year 4.

This full fourth year of solar production is firmly with the Model S and Roadster with a about the same number of weeks on trips as Year 3. Our 2016 Road trip to the Pacific Northwest, which we will be publishing on Monday, 9/12/2016 at 10:00 AM Pacific/18:00 BST/19:00 CET (UTC), was for only two weeks, however we’ve had a lot of other trips so that our total time away from home has been about the same as Year 3.

I considered the third year as a monumental year for having the $40 annual bill, I am just flabbergasted at the $20 year that we’ve had for the fourth year. Considering our average electric bill prior to going EV and solar was closer to $200 a month, it is incredible to get most of our transportation and home energy use at so little.  Additionally, I focused on the change in tariff from TOU-D-EV to TOU-D-A in last year’s summary.

Logic tells me that I SHOULD have been paying more for electricity in Year 4 vs. Year 3.  And we didn’t even travel any more than we did in Year 3.  Our Summer roadtrip in 2016 (about our Long Way Round to the Tesla Gigafactory Party) was several days shorter than our 2015 Roadtrip.  I guess we’ve gotten better at shifting our energy use.

I wonder what we’ll be spending on energy next year?  I predicted an upward trend from Year 3 to Year 4 and was flat out wrong.  So, let me see if an upward trend will finally hit from Year 4 to Year 5.  After all, solar panels degrade and our guaranteed production on our solar agreements always step down year over year.

Interested in going solar? Get a quote from my solar vendor – Real Goods Solar.

Our third year of Solar usage.

Projected Usage 2015-09-09

This is a third year update. Click here for the 2nd Year of Net Metering.

It’s been three years since our PTO was approved, we originally estimated our savings on driving the Active E or a vehicle like the Active E. Since then, we moved from one EV to two EVs to three EVs back to two EVs. We’ve also driven around a lot and our mileage has grown significantly since then. I haven’t done the math, but estimated that we’re either at break-even this year or definitely in a few months.

In our first year of Solar use, we had a credit. Which, as we found out, we could not claim. Because, it turns out, Net Metering means that though we’re credited for the production at a $ rate, customers are paid out on OVERPRODUCTION of power and not on the CREDITS earned. What this means is the system produced greater kWh of energy than consumed by the end user. If this is the case, the customer is PAID OUT the power times the wholesale rate of production. Last year, we paid over $200 to SCE for the entire second year of Solar. This third year, coupled with our nearly a month of travel to Maine and back in our Here, There, and EVerywhere roadtrip, we’ve been out of the house for about a month. So, that created a month of overproduction. As a result, the annual net metering statement was for approximately $40 for Year 3.

This full third year of solar production is basically the Model S and Roadster. What is interesting is that our usage this past 3rd year probably would have cost us less than Year Two’s Annual bill. But the month off really helped. At less than $4 a month for power for the third year is greater than I expected. So, I chalk this third year as a monumental year. Considering our average electric bill prior to going EV and solar was closer to $200 a month, it is incredible to get most of our transportation and home energy use at so little.

Now, this current fourth year, I wonder what our bill will be. Most of the past three years our electric tariff was on TOU-D-EV. This was a special whole house rate with a discount for EV drivers. A few months ago, Southern California Edison got rid of that tariff and adjusted the Time of Use tariffs so that the times that start with Peak, Off-Peak, and Super Off-Peak.

Under TOU-D-EV, the Peak rates were from the hours of 10am-6pm M-F, the Super Off-Peak hours were from midnight-6am every day, and Off-Peak is any other time. This was great because Solar was credited during the peak times most days and helped off-set a lot of the costs.

Under TOU-D-A, the Peak rates are now from the hours of 2pm-8pm M-F, the Super Off-Peak hours are now from 10pm-8am every day, and Off-Peak is still any other time. Though the Super Off-Peak hours are longer, the effect of moving peak time to the hours between 6pm-8pm means that we’re no longer generating credits at the Peak rate between 10am-2pm. Additionally, we’re spending more between 6pm-8pm because we’re paying at Peak rates and not Off-Peak rates.

So, I’m projecting paying a little bit more for electricity next year… Unless we go on yet another LONG roadtrip.

Interested in going solar? Get a quote from my solar vendor – Real Goods Solar.

So, we got our bill for the second year of Solar usage from SCE.

Year two cumulative Solar PV Bill

It’s been two years since our PTO was approved, and, as opposed to last year, when all we had was the Active E, we pretty much used at LEAST two EVs, if not three EVs over the past year.

In our first year of Solar use, we had a credit. Which, as we found out, we could not claim. Because, it turns out, SCE’s though we’re credited for the production at a $ rate, with net metering, customers are paid out on OVERPRODUCTION and not on the CREDITS earned. What this means is the system has to produce greater kWh of energy than consumed by the end user. If this is the case, the customer is PAID OUT the power times the wholesale rate of production.

Last year, we had a lot of credit as we primarily used energy overnight (at Super Off-Peak) and produced power during the day (the Peak rate). However, we actually used more kWh of energy than we produced. So, even though we had a credit last year, we were not paid out.

This year. We got our Tesla Roadster in the beginning of September, so, when our second year of service started, we were pretty much using TWO EVs. Then we got the Model S, and we were using three EVs during that time until the Active E was turned back in at the end of February. Regardless, the Model S and Roadster consumed energy at a greater rate than the Active E, so we did use more energy than we produced AND totaled a higher amount than we had been credited. Thus, the bill. Even so, at approximately $20 a month for all the driving that we do, and the home power usage. It’s still a win!

Interested in going solar? Get a quote from my solar vendor – Real Goods Solar.

Real Goods Solar installation

A picture is worth a 1000 words… So,here are some pictures…

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This is what the front of the house looks like. One of the good things about our house is the fact that the south facing roof (the one with the most power generating capability) is not on the front of the house. This fact made it easier to sell Solar Power to the better half on the aesthetics of the solution.

More front of the house shots. Closer to the roof –

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My new roof looks great, but you’re here for the Solar pictures…

So, the next picture is from the backyard looking up.

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That doesn’t really give you a good shot of it, so… Even though I have a fear of the sudden stop after a fall… (i.e. it’s not really the heights that scare me or kill you.) I decided to get on the roof to take some pictures.

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Here is a nice shot of the conduit runs for the electrical cable.

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Here’s the ActiveE peeking out from the roof.

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Closer shot…

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Here’s a shot of the junction from the South Facing and the West Facing roof… The conduit still looks good.

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Better shot of the junction

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Panoramic of my most productive panels

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Panoramic by the chimney. The shading really wrecks havoc on my production for three of the panels.

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Some of the nice warning signs

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Another shot of the ActiveE from the roof…

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Meter is going backward! Success!

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One of the things you get with Real Goods Solar under this plan is TWO monitoring systems. This one is a closed system mounted by your panel and it is for the finance company to ensure that they’re producing what they committed to.

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Here’s the one from Enphase that allows the user to see what the system is producing. It connects to the panel via Ethernet over Power and then you need to have a port on your router to connect to the Internet.

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Here’s the ports on the box –

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Here is the sub-panel for the whole system –

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These are the breakers for each of the 3 sets –

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Here’s the disconnect for the whole system –

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Lastly, the installation was very clean, here is where they ran the power to the main breaker as well as the Ethernet for the monitoring.

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The conduit on the left side (on the wall of the house) is where the power comes from the solar panels to the main panel.

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I asked them to run two Ethernet runs from the monitoring to the wall so that there’s one spare in case of failure in the future. This sucker is supposed to last 20 years.

That’s it. Several THOUSAND WORDS worth of pictures.

Interested in going solar? Get a quote from my solar vendor – Real Goods Solar.

More Napkin math, OR – Real Goods Solar and BMW’s program is a REAL GOOD deal!

Saving money while saving the environment is an addictive process.  It’s crack for good Karma!  I feel like Michael Corleone in the Godfather III, I try to get away from it, but they keep dragging me back in!

As I had indicated on my Ping! post, I got “unofficial” Permission to Operate (PTO) on August 17, 2012 and finally received official PTO ten days later on August 27, 2012.

So, we’re now running our car on Solar Power…  or are we?  Unless your house is completely disconnected from the electric grid, what you are really doing is netting out generated power from the solar panels on the roof with consumed power from the electric grid.  So, if you’re overproducing power from your solar panels than what you’re consuming, you get money back, otherwise you’re really just netting out what you’ve made with what you’ve used.  As I have published previously, the rate to charge depends a lot on what tariff you’ve chosen.

In my first napkin math post, I charged on the SCE Domestic rate which effectively got me charged at $0.31 per kWh as my usage of electricity had already pushed me to Tier 5 for most of the billing periods.  In order to normalize and compare ICE vs Electric, I calculated that the cost under the first plan was 1.714¢ per mile

By my third napkin math post, I attempt to alleviate that $0.31 per kWh charge by opting for the whole house SCE Electric TOU Tiered rate structure, this pretty much reduced my rate to charge to $0.13 per kWh for my car charging needs (as well as my pool pump as I switched the time of use for that from mid-day to mid-night to 6 am).  As we noted on that post, my cost per mile dropped to about 1.412¢ per mile.

So, the big question is what is my cost per mile under the Real Goods Solar and BMW ActiveE program deal.

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Before I took advantage of this deal, I would like to tell you about my search to save our energy costs further.  Not necessarily the environment, but that’s always a fun side-effect with this accidental environmentalism that I’ve stumbled across.  After signing up for the Active E, I figured to become educated on what my solar options were.  To that end I requested quotes from three solar companies in the Los Angeles County area: Peak Power Solutions (Sunpower reseller), Solar City, and Verengo Solar.  Each solution had its strengths and weaknesses and around the third week of March (between three to four weeks of receiving my ActiveE), I decided to sign a power purchase agreement with Solar City.

A power purchase agreement is basically the right to buy a guaranteed amount of power from a provider for twenty years.  I don’t own the solar array on my roof, someone else does (a finance company) and I agree to pay them a fee for this.  This means at the end of twenty years I get the option to keep buying from them, buy the equipment outright, or have them remove the array from my roof.

So, how did I compare the suppliers.  Ultimately, economics.  So, at the end the Solar City deal that I had originally signed was approximately $0.10344 per kWh.  How did I calculate this?  All the suppliers with the power purchase agreements have a guaranteed rate of production for the 20 years that the system will be produced, so I divided the total guaranteed kWh by the the total prepaid lease amount, and that’s how I got to the $0.10344 per kWh.

So, I thought that was it.  I signed up with Solar City, got a rate that I felt was fair and waited to get installed.  Solar City’s installation process was methodological and professional.  They provided a website to track the progress of the installation and was quite impressive.  However, their process proved to be the opportunity for Real Goods Solar and BMW’s deal to come in and make my costs even less.  Around the beginning of May, during the design and survey process, Solar City notified me that in order to proceed with the installation of the system that I signed in the third week of March (about five to six weeks earlier) my roof would have to be replaced.  This change provided me with an out-clause from completing the agreement that I signed with Solar City.

As I was mulling through a roof quote and setting up more roofers to see what this replacement roof would cost me, Real Goods Solar and the BMW Active E program announced their program.  So, I figured, why not ask them to see what the solution would cost me.  I contacted Real Goods and they had a sales agent contact me within the day.  Their initial quote was 12% less than the Solar City quote and agreement that I went with.  However, I had to bundle in the cost of the replacement roof and needed to get the total project cost to figure out which deal I was going to take.

Figuring that both solar companies would probably be able to get a reliable, professional, licensed roofer at a lower cost than I would have on my own, I went back to both providers to find out what the roof was going to cost from them and go from there.  My assumption was not exactly correct as my independent roofer quote was actually $500 to $1000 cheaper than the lowest quote from either solar provider.  I was at an inflection point.  I was already saving quite a bit on gasoline with the TOU tariff and this would have been the time to quit or cut bait.  I approached both providers to see if there was anything they can do to their quote to make the entire project less expensive (replacement roof and solar).

The dilemma is how do I adequately calculate my cost per kWh based on the various scenarios.  I figured the most conservative thing to do would be to subtract the lowest roofing quote from my total project cost and use that figure to divide my cost per kWh over the guaranteed generation over the life of the system.  Granted, this methodology would provide me with an understatement of cost as the guaranteed rate of production is typically rather conservative of the suppliers, but it IS what they guarantee, that is why I went with that methodology.  When the system has really sunny days it will outperform this guarantee and my actual cost per kWh is less than what I calculated.

With the total system cost, I figure that my cost per kWh is $0.10250, however, if I subtract the roof cost my cost per kWh drops to $0.07970 based on guaranteed power.  Seeing that my energy cost is a 38.7% reduction, mathematically speaking, my cost per mile is approximately .8657¢ per mile ($0.008657) or 73.58 cents per day based on the 85 mile day that I had in the last post on this matter.  Not bad at all.  Of course, the system is currently overproducing and with time of use I actually am paid a rate for the energy I am sending back to the grid during the day and most of my charging occurs between midnight and 6 am, so this is, like my other estimates “napkin math”, so I am certain my actual costs are lower, but the numbers work for me.  Remember, my original calculation of a comparable vehicle costs were approximately 17 cents per mile, so my 0.8657 cents per mile cost is quite a bit less than driving my ICE 328i convertible.

So, there you have it.  My energy costs are a heck of a lot less than it has been.

Want to see what my system is producing, check out the sidebar production information courtesy of Ken Clifton‘s plugin for WordPress or directly from Enlighten’s website.

In a few days, I will follow up this Napkin Math article with pictures and my opinion on the installation from Real Goods.  Let me just say, I recommend them and if you give my name, I get a referral on your system, so contact me if you’re serious and I will recommend them.

Interested in going solar? Get a quote from my solar vendor – Real Goods Solar.

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