Tesla Solar and Powerwall Review

With the summer months in our area getting warmer each year, we are finding that our power bill ramped up significantly as we started running the air conditioning for more hours each summer. Our power bill 7 years ago was peaking at $280 / month in August, last year it peaked at $490 in the same month.  Our electric bill for 2020 totaled about $3500 - I was able to download .csv file formatted usage data from the PG&E website to look at this data. This drove me to consider investing in solar as a way to mitigate this electrical expense, and even have a small return on that investment down the road. 

We decided to put in 2 Powerwalls Gen 2s, 10kW of solar production, plus the smart power Backup Gateway and a string inverter with power optimizers. Estimated annual production 12539 kWh, which is very close to what our usage was the previous year.

Layout on a roof of an outbuilding that is about 22' x 42':

This is not one of their standard packages, so I was surprised that they were willing to create a custom production size to match our roof, but they did. I ordered the 12kW sized system, and then asked them to fit on our outbuilding and they came back with the 10.2 kW proposal. I wanted them to get the panels closer to the ridge lines and squeeze some more production on there, but they were limited by fire and wind load code and had to leave gaps on the ridges.

I put in the order for solar on the Tesla website on Aug 31, 2020, and they projected that the installation would be done on Oct 19, 2020. 

Tesla sent out a site inspector, who took pictures of the roof for an hour or so, and then we heard nothing for a few days. Then we got a notice that we would need to pay Tesla to replace our roof or have a contractor do it. The price they quoted was for a 30 year roof, I had a contractor put a 40 year roof on for about $1500 less than Tesla's quoted price.

We had a camphor tree that would block the solar during the first half of the day, so we took that out as part of the project. Online research indicates camphor trees are more flammable than other trees, and given the current ongoing threat of wildfires we decided it was probably a wise mitigation to do anyway.

I sent an email to our project manager at Tesla as well as responded to the text messages they sent, but it wasn't clear whether we needed to be ready for a power outage on the day of the install. However, all that worry was useless, because nobody showed up on Oct 19.

 I logged into the portal they provide and there was an update there saying the installation had been moved to Oct 21. But nobody had notified me. That was a bit annoying, a big lack of communication from Tesla. 

They truly did begin work on Oct 21, putting mounting hardware up on the roof sporadically throughout the day. It turned out that contractor was having some churn in their employees, and lost some of their team and fell behind on other projects. The used a solar contractor named JMB Renewables. The employees of JMB Renewables worked for part of the day, and fiddled with their smartphones for part of the day, they mis-drilled holes in the roof several times in various areas that they then filled with black goop to seal up. The goop dripped down and got into the carpet in our outbuilding in a few spots, since the building has exposed rafters. We have gone through one semi-rainy season since the install and saw no sign of leaks, so it looks like their goop sealed up the holes ok.

They only put up the mounting cleats (what they call "roof penetrations") the first day:

The next day they put up the panels. We don't have optimal angles or placement on the roof, so we don't expect to ever have the sun shining on all of the panels at the same time. But we planned to get enough to cover our annual usage and have a bit of surplus.

We had a surprise after the panels were installed, that the existing conduit in the ground between our outbuilding where the panels were installed and our main house wasn't big enough for the power wiring. So I had to quickly hire a contractor to trench and put in conduit to provide capacity for the wiring to get the solar installers to come back the following week.

As part of the install, Tesla also planned to put in a subpanel for the entire house, that would be fed by their power gateway. Their plan was to install it outside on the wall next to our existing breaker panel, and then run jumper wires from every circuit in the house over to new breakers in this panel. 

That seemed like a lot of complexity and added a lot of potential failure points, so at the advice of a trusted electrician (who did the trenching and conduit install), we put the sub-panel inside our garage right behind the existing panel and routed the existing wiring straight in without extra jumper cables. I finally got a chance to label everything in the house correctly as we tested it all out, nice to have breaker panels fully labeled with what really connects to them!

Once we had the conduit in place, they were able to come back and install the Powerwall batteries, Gateway, and inverter.  

Living in California, we also have the rolling blackouts during fire season (a delightful experience we get courtesy of PG&E), so we decided to invest in some Powerwall batteries so we could make use of the solar panels during a power outage. 

If you don't have a battery system, modern solar technology will immediately turn off the power being generated by solar when the main power goes out, to protect people upstream from you from getting electrocuted by the power being generated by solar panels. 

So this means that for most people who have had solar installed on their roofs in the last 20 years in our area, they found themselves needing to buy a generator even though they had solar, because they had no power in an power outage ... even though they had the means to generate power sitting on their roof. I decided I didn't want to have that frustrating feeling, so we splurged for the Powerwall batteries.

Here is the setup they deployed - which looked a bit different than their data sheet. They wanted to deply a subpanel, but put the whole house in the subpanel:

Now there is a caveat that I learned after everything was installed on the Powerwall batteries that you won't see in the marketing material. If the power is out, and it's a bright sunny day, your solar panels will generate more than enough power to fully charge up your batteries AND power your house. 

Unfortunately, you end up with a surplus of power, and when there is no where for the surplus power to go, the system has an automatic back-off mechanism that shuts down the inverter and stops power generation. So if there is a power outage during the day, you end up actually using your battery in the middle of a bright sunny day while the panels stop putting out power, then once an hour the system checks to see if it can turn on generation again, and if there is somewhere to put that power (i.e. if your battery has drained enough to go into fast charging mode), it re-activates the panels. 

So the Tesla recommendation is on a day like that, to turn on all your lights, computers, air conditioning, etc, to consume enough power to keep the panels running so they don't go into back-off mode. Pretty strange. You can see the status in the mobile app, if your internet is still working. Here you can see the Grid power was out, the solar panels were putting out 3.8kW, our home was using 1kW, and the rest of the power was going to charge the Powerall batteries.

The back-off mechanism changes the AC power frequency of the Powerwall from 60 Hz to 66 Hz by default, and this frequency change is what signals the inverter to stop putting out power. We learned the hard way that our UPS systems in the house don't work on 66Hz, so even though our lights were still working, the server, router, etc went down after an hour or so when the UPS units ran out of juice. So we had to call Tesla soon after the installation to have them adjust that backup frequency down to 62.5Hz so our UPS systems would take that power and think AC power was restored. They should have done this by default, I don't know why they default to 66Hz, but something to keep in mind if you have UPS (Uninterruptible Power Supply) units from APC or CyberPower in your use. Other units, like from Patriot, can apparently handle these wider frequency variants. 

Below, you can see that the solar suddenly stopped working, even though our Powerwall wasn't fully charged, because there was an excess of power being produce by the panels with nowhere to go, and the house wasn't using enough power to balance out what was being generated, so the solar output shut down:

So these are just details to keep in mind when getting a system like this. It has worked remarkably well once everything was setup, but you have to know the quirks or you will be surprised at some point.

Despite the panels sitting on our roof since Oct 22, we had to wait until inspection was done to receive PTO. We received PTO (Permission to Operate) on December 10, 2020. This turned out to be a delay in Tesla's internal system -- I called multiple times to find out when the inspection was going to be scheduled, and it wasn't clear. When the installer had left he had said 2 of the 30 panels on the roof weren't coming online like expected, so they had an open ticket to fix those, but never sent anyone out to fix them. I eventually told them to cancel that repair ticket, and that's what broke the ice-jam and got us to the inspection step.

Once we had PTO, a few days laters I called Tesla support and requested SolarEdge access, so I could use the mySolarEdge app to view the output of each panel individually. The Tesla app only shows a summary of the whole system, not individual panel output. I wanted to see if those 2 panels were truly bad or if they had finally come up ok. 

However, that ticket got lost. I call again 10 days later, made the request again, and then again in January called and made the request again and finally access was provided via an email they sent me with login information. 

As it turns out, all 30 panels were working ok, so apparently those 2 panels were just misbehaving during the day the installer was there. 

One very nice bonus, the installers put in Hyper-Engineering Sure-Start soft starters on our 2 air conditioning units. These are required to deal with the start-up current of the air conditioning compressors when we are on battery backup. 

We are seeing production increase dramatically from it's low point in December when we received PTO, to 4 months later now. Here are the production numbers for December. You can see the days that were overcast and rainy, the production drops significantly. Unfortunately we are having a dry winter, so there weren't as many rainy days as we would hope for.

Here are the production numbers ramping up in Feb 2021:

A few days ago, we had a solid sunny day, you can see how the production ramps up to mid day when the sun hits the highest point in the sky and then heads back down.

What did this cost us? 

$36k for 10.2kW of solar production (30 panels), SolarEdge string inverter with power optimizers,  installation, and 2 PowerWall batteries (27 kWh). 

After the 2020 26% Federal Tax credit, this came out to: $26,640. Payoff in about 8 to 9 years with current electric bills. If we hadn't purchased the Powerwall batteries, payoff would have been more like 5 to 6 years.

However, there were some other "hidden" costs - you may have to do some of these things as well:

• Roof Replacement: $5300
• Tree Removal: $1000
• Trenching and Electrician doing the subpanel right: $2800

Total after tax credit and extras: $35,740 

This equates to $3500 per kW of generation capacity + 27 kWh of storage capacity.

So, all things to keep in mind if you are thinking about going solar. The process was a bit bumpy, but the final outcome is pretty cool. I really like the idea of the sun that is always beating down the roof actually being useful -- being used to power the air conditioning running inside the building. 

Would I recommend Tesla if I were to do it all over again? I would say mainly yes, despite the communication issues, unexpected extra costs, and the timetable, the equipment they put in was high quality and appears to be operating as expected. They projected the install originally would be done Oct 19 in their first communication, we eventually were able to use everything on Dec 10. So they didn't nail the dates - but from what I had read online about Tesla installs, I went in expecting this to take longer than the marketing would promise.

If you want a $100 discount on your Tesla solar setup, use my referral code: 

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