Tesla Solar, Home Battery & Backup Power – Part 2

I had actually been planning a post talking more about the Tesla Powerwall, but with current events I wanted to make it broader and put in some information about backup power. As we mentioned in Part 1, we opted not to get a Tesla Powerwall for our home mostly due to economics with the current offerings, but I wanted to talk more about one of the benefits which is backup power. This isn’t meant to be a technical report, this post could have easily been a lot longer. This is more of an introduction to different options.

Our Tesla Solar Roof Tiles will not provide backup power in the event of a power outage, if we had purchased Powerwalls we would be able to use the home batteries as backup power. With net metering your solar system will shut down if the utility power goes out, this is because they don’t want your solar system sending electricity to the grid if there is a potential issue with the grid creating a dangerous situation. If you want to use your Tesla solar system during a power outage, you need to have a home battery. This concept is referred to as “islanding” meaning your home is an island from the grid. Your solar will charge your home battery with any excess power during the day and you can use it at night or you can set it to store electricity for backup purposes. Tesla doesn’t offer true islanding or off grid installation, meaning you are completely independent from the power grid. Some other solar installers may offer true off grid installs, but Tesla doesn’t offer this at the time of writing.

A single Tesla Powerwall (Version 2) can store 12.2 kWh (see part 1 for more background on kWh) and output a maximum of 21 amps for output of 5 kW on a continuous basis and 7 kW of peak power. I’ll dive deeper into Powerwall here, but for now we are talking about it as a backup power option. Peak power is for certain appliances that may use more power to start up and then drop down to a lower usage level once they are running or just general flutuations in your power usage, but know that it cannot sustain that output long term.

An Automatic Standby Generator is another option, these are usually connected to your natural gas line (can also be used with the home propane tanks), here is an example of such a system. In commercial or institutional settings these automatic backup generators may be powered by large diesel tanks, which require professional maintenance and upkeep. Think of places like the fire department, hospitals, server farms, cell phone towers, traffic lights, etc.

These are great because you can set them to turn on after a certain amount of time without power and they can produce a lot of power. For example, it can be set to automatically turn on 30 seconds after a power loss. Depending on your generator size it can produce enough to run an AC unit during a hot summer brownout. The downside to these is that they are expensive, large, loud, require pretty involved installation and if you lose your natural gas service (for example, in a large earthquake) then your system will stop working. In theory though as long as you have natural gas this can power your home for days on end.

During install of a backup power system you may need to identify your critical loads, the circuits in your home that will need backup power. What we have done is setup a critical load panel as a subpanel in our home, so the entire panel can be setup for a future Powerwall or setup with a Generator Transfer Switch which will allow us to connect a portable gas generator to a plug on the side of the house to provide power to that panel. Make sure you get the proper permits and install with a generator transfer switch and solar as they may not be compatible, if your solar thinks your grid power is on and starts sending power downstream you could damange equipment or create a hazard.

Here are some suggestions for a critical load panel:

  • Refrigerator
  • Medical Devices
  • Broadband Modem/Router & Security System
  • Garage/Gate Openers
  • Water Heater (Tankless gas won’t work without power)
  • Select Kitchen Outlets
  • Select Lighting
  • Select Outlets in bedrooms
  • If you have a large enough generator you can also have your AC unit on backup power, this may also be needed if you have people in your home who are medically temperature sensitive.
  • Depending on the size of your generator it may be necessary to ration your power, for my purposes I may only be able to turn on one appliance at a time in addition to the refrigerator.

For some of these items I also recommend using an Uninterruptible Power Supply (UPS) like this to help power these devices for short power outages. I have my modem and router connected to one and it can keep it on for about 30-45 minutes for quick power outages.

What I have is a portable gas generator. These come in many shapes and sizes, one thing to note is that if you are using this for electrics you should look for an inverter model that is suitable for sensitive electronics. These are usually more expensive and produce less wattage than the traditional portable gas generators. The simplest way to use this is with power cords, but make sure you do not operate the generator in a confined space. This may be challenging if you are using this during extreme weather as the generator needs to be protected against the elements, but also need to be able to exhaust as it uses an internal combustion engine. You can also connect this to a generator transfer switch as I mentioned above.

I have this portable gas inverter generator, with a 3700 watt continuous output and 4500 watt peak output. It is compliant for use in California with their stricter emissions requirements. They also make Duel Fuel generators that can be connected to a propane tank as well as use gasoline. One benefit of this is that propane tanks are easier to store than gasoline cans. You can use a meter like this to see how much power your appliances use to see what size generator will work for your needs. Some of these generators offer the ability for parallel operation, which allows you to connect two together for increased output and capacity. With a generator this size, you won’t be able to run an AC unit during a summer brownout.

We talked about how to calculate watts in part 1 of these series and this size generator is enough to power a refrigerator and perhaps and a toaster oven or water kettle. Please real all manuals and follow all safety information. A couple things to note is that gasoline cannot be stored indefinitely, you must use a fuel stabilizer like this in your gas can. I would start your generator once a month to test it to make sure that is starts and once a quarter test it with a load, such as with your electric water kettle or toaster to make sure it can produce enough power. Fuel stabilizer claims it can last up to 2 years under ideal conditions, but I change out my fuel every 6 months.

You can put the gas into your car to use and then refill the gas can with fresh gasoline and fuel stabilizer. In a severe incident you may not be able to refill your gas can, so plan out how much you will need or how you will ration generator usage for a multiple day power outage. Your refrigerator should be able to stay cool for several hours as long as you minimize opening it, so will likely not need to be powered 24 hours a day depending on your climate. May be useful to have multiple gas cans, please follow all storage and safety guidelines for storing gasoline.

They also sell inverters that connect to your car battery than can provide power, but it’s a very inefficient way to produce power by letting your car idle. Unless you’re going to stay with the car it’s probably also an good way to get your car stolen. The 2021 Ford F-150 Hybrid comes with a 7.3 kWh generator built in if you are shopping for a new truck.

I would also recommend keeping a small butane/propane stove like this one with extra butane canisters around just in case all else fails and you need to boil water or prepare food. You can also buy an adapter like this to connect it to your BBQ propane tank for more supply. I don’t want to get too doomsday prepper on you, but also keep ample water, shelf stable food, medication, batteries, flashlights, radios, etc. on hand for these type of events.

It may be useful to use your BBQ (if you have one) to prepare food and boil water. I read somewhere a long time ago that the propane exchange tanks are not that well maintained and that it was better to buy your own tanks and get them refilled locally. That is what I have done for several years now, I have two propane tanks that I purchased brand new and I refill them myself at local distributors rather than use the exchanges. I know they haven’t been dropped or abused and are in good working order. Another thing you may not know is they put less propane in the exchange tanks than they do when you refill on your own, so you are paying more for less. A standard tank is 20 lbs and these exchange tanks are usually only filled with 15 lbs so you are getting 25% less propane with exchanging. Keep an extra around space permitting in case you run out of propane mid-BBQ and also for emergency preparedness.

Powerwall

Powerwall is a cool concept for home battery, here are some ways Powerwall can be used:

  • Solar will charge your Powerwall during the day and you can use it to power your home at night or augment during peak power usage, especially useful if you don’t have access to net metering.
  • To serve as a battery backup for your home, useful if you have medical devices in your home or cannot have the other power backup options I mentioned.
  • I have read about people charging their home batteries at night on Time of Use (TOU) power plans and using them to power their home during peak hours. TOU means that, for example, using power at midnight is cheaper than using power at 6pm. It would take over a decade for this to make financial sense though. This setup is not paired with a solar system.
  • If you just think this is really cool technology and want to have it and can afford it.

Downsides to Powerwall

  • It’s expensive, and for me, it was mostly for convenience as I already have a portable gas generator. Your situation may be different where this is the only/best option for you to get backup power.
  • If you want to use it with an AC unit, you will require 2 or more units.
  • This is a giant battery and batteries deteriorate with every cycle, the Tesla Powerwall warranty is that it will hold 70% of its capacity for 10 years. Just know that you are ok with up to 30% loss of capacity over 10 years if you purchase this product.

Check out your rebates:

  • California has Self-Generation Incentive Program (SGIP) allocated by installer. Tesla did not have any allotment left so if you went with a third party installed you could save thousands with this rebate.
  • Your Powerwall may also qualify for the newly extended 26% federal tax credit if paired with a solar system.
  • These rebates often dictate how you use the Powerwall, such as a requirement to use it during peak energy usage times to relieve strain on the grid and not only using it for emergency backup.

I hope this was useful information, I think many people are surprised that if the power goes out during broad daylight their solar systems will not power their home unless they have home batteries installed. If you want more information or are interested in ordering Tesla products, please use my referral link to save $500. This link can also be used to order a Tesla car and you will receive free supercharger credits.

Tesla Solar Roof Tiles & Introduction to Solar – Part 1

When I first started this blog, I wanted to write more than just about coffee. Well, here is my first non-coffee post about our Tesla Solar Roof. The photos on this post are of our actual roof that was recently installed.

For those of you new to solar, I wanted to do a intro to solar power to help understand some of the terms and figures you’ll see.

Here is some electricity background that will help with solar shopping, you can skip over if you already know this. This is based off ideal conditions and simplified for our limited purposes of explaining solar.

You may own a microwave or toaster and see that it says 1000 watts, what does that mean? What are volts, amps and kilowatt hours (kWh)?

Volts x Amps = Watts

A standard U.S. household plug is 120 volts. Many homes also have a 240 volt plug for the dryer or an electric oven. A standard U.S. household plug is 15 amps, sometimes in the garage you will find a 20 amp plug. The number of amps that can be supplied to an outlet is determined by the size of the breaker and the gauge (thickness) of the wire.

If you do the math for your 1000 watt toaster, it means that 1000 watts/120 volts = 8.3 amps. You won’t see standard household appliances that use more than 1800 watts, because 120 volts x 15 amps is 1800 watts, which is the maximum amount of power a standard home outlet can deliver before the circuit breaker trips. You can use a watt meter like this to see how much power an appliance is using.

If you have an electric car you likely have a 240 volt outlet with a 60 amp breaker meaning it will deliver up to 14,400 watts or 14.4 kilowatts.

A kilowatt hour (kWh) is a measurement of energy and is the same unit you will find on your electric bill. Your 1000 watt toaster, if left on for one hour will use 1000 watt hours or 1 kilowatt hour (kWh). If let on for two hours it will use 2 kWh and so on. Tesla cars used to be badged with the kWh of the battery, such as 75 for 75 kWh, so it would take that amount of power to charge it from 0-100%.

The estimates vary, but for this example let’s say your Air Conditioning (AC) unit uses 6000 watts. Your AC will use 6 kWh for each hour it is on. If you run the unit for 5 hours, you will use 30 kWh of power.

Ok, why was all that important to explain, because solar is sold in kilowatts (kW) and you need to know the math behind the quote. Our solar system is quoted as 10.525 kilowatts and is estimated to produce about 15,800 kWh per year. If someone asks you what size your system is, they are asking what the kW size is.

Tesla used an estimate of about 4 hours of peak production a day x 365 days a year to arrive at the annual kWh (this estimate will vary by angle, orientation, region, system, installer and other factors) for our system. If we want to estimate the amount of energy our system will produce in a day we take the system size x 4 hours, for us that is 10.525 kW x 4 hours = 42.1 kWh a day, meaning we could run our AC for 5 hours a day with 12.1 kWh of energy for lights, TV, appliances, computers, etc. These are just estimates since weather, time of year, system performance and other factors will impact your production.

Your electric bill will tell you how many kWh you use on a daily average and you can use this to help estimate your solar needs and how much you want to offset. Check to see if your area has net metering (where your electric bill is based off off your net use as you will be giving any extra power you produce back to the grid). Excess power can go back to the grid under net metering and/or be stored in a home battery if you choose to have those as part of your system. We opted not to get a home battery because of the economics of current offerings. Please see Part 2 for more on backup power and Powerwall.


Our Solar Roof Project:

For 2020, the U.S. had a Federal Tax Credit of 26% for solar. In 2021, this was scheduled to go down to 22%. Fast forward to time of writing, the 26% has been extended into 2022. If you are considering solar and want to save some money, please check to see if you qualify for this credit as it may be a good reason to start sooner rather than later.

The Tesla Solar Roof Tiles were a good option for us, because we needed to install a new roof as part of our renovation process. However, if you have an existing roof in good shape, installing solar panels may be a more economical option, if you are ok with the aesthetics. South facing is the best elevation for solar in the U.S., east/west are the next best and north facing is the lowest producing. Our first solar quote had panels placed on the north facing roof, we ended up moving those to face south, east and west to optimize efficiency.

Many solar companies will not guarantee the production estimate, if they it will be over an annual basis. They can also say that was a cloudy year and there are a lot of variables they can use. Just know that it isn’t exact and that during the sales process they will say it is usually above the quoted production. I hope to talk more about this in a future post.

You will hear how solar panels are more efficient than solar tiles, this is true on a per square foot basis. Due to the nature of panels versus tiles you have more square footage available to you with tiles as they cover your entire roof and panels have to be placed in open spaces in your roof.

You may have also heard that Tesla customer service is awful, this is also partially true. I think this had to do with the fact that everyone was rushing to get their system installed before 2021 due to the reducing tax credit and they were just overwhelmed. When we could get a hold of our representative they were helpful and capable, but getting a hold of them was the hard part. At one point emails, voicemails and texts appeared to be going into a black hole, to the point where we were told to call the 800 number for a live person (which was pretty easy) and ask that person to tell our rep to call us back. In the end, due to delays, Tesla was willing to offer us a discount of 4% if they could not meet the install deadline.

We started this process in April 2019 by paying $1,000 for a deposit on a solar roof, it was fully refundable and we just decided to get our name on the list. We are not normally the early adopter types, so this was a first for us. At the time they were still on Version 2 of the solar tiles.

In June 2019, we were told that as our home was a large scale renovation, they no longer had spots open for their construction pilot program. They were only focusing on projects where replacing the roof was the only work that needed to be done.

Fast forward to May 2020, we reached out again as our project was moving along and they said they would be able to include us as part of their custom home program. It is easier for Tesla to only do roof replacements, because they don’t need to coordinate with any other contractors on site. Tesla was now offering Version 3 of the solar tiles.

In October 2020, we had been waiting for months to get an install date, something they absolutely will not commit to without all permits being in hand. After trying to track down our rep for weeks, we were told they arranged an install date on December 28, 2020. With the whole tax credit thing in mind, we kindly told them that was unacceptable and the next week they brought in a crew from Phoenix, Arizona to start work. Tesla actually paid for a crew to come in from another state and put them up in a hotel to install our roof.

Dry-in Process

At the very beginning I told the Arizona crew that I wanted to make sure all the wiring was done internally since the drywall and insulation had not yet been installed. They said they would do their best and said they were working on it several times when we followed up. They started with a dry-in process to weatherproof the roof.

This is what the active solar tiles look like up close
The install is coming along
Active tiles installed

At this point I realized why Tesla doesn’t like working on projects with other contractors on site. Home renovations have a lot of moving parts and a lot of subcontractors all trying to get in to do things in a certain order. This crew wanted to install the entire roof, however we still had scaffolding up and the stucco hadn’t gone up yet and through a lot of back and forth, it was decided that the Arizona crew would only do the second floor and leave the rest of the house for another crew once all the stucco was done and scaffolding was removed. On the last day I asked about running the wires in the house (instead of having exterior conduit run from the roof to the first floor) and I was told it just couldn’t be done without compromising system performance. I was given a bunch of excuses about how having the wiring and boxes outside would make it easier to service and that the techs wouldn’t need to go into my attic if there were any issues. I asked how often would there be issues that would require techs to come service my system and they never had a good answer, in the end I think they just didn’t want to do it.

At this point Tesla already promised to give us a 4% discount on the system since it wasn’t going to be installed by the end of 2020. We got all the other work taken care of and they said they would send a second crew in January 2021 to finish the job.

May be a little hard to tell – the tiles in the foreground are active, the ones on the top right of the photo are not as they face north

Everything went pretty smooth with the second crew, one thing of note is that they said they could absolutely run the wiring behind the walls and that it wasn’t a problem. The drywall and insulation was already in at this time, but they took care of it and also had someone come to patch the stucco and drywall where they had to remove it. They also had to rearrange some tiles the Phoenix crew installed in an area prone to afternoon shade for better system optimization.

After the install was all done Tesla sent out a third crew to inspect the work and spent a few days fixing some odds and ends to make sure everything was up to standard. At this point, I am pretty satisfied with Tesla. Sure there were delays and frustrations, but doing a big renovation project this stuff happens all the time.

The inverters

I hope this provides you a good background of solar energy and Tesla solar tiles. At the time we had these installed (and at the time of writing), Tesla was the only company offering solar tiles and they only came in the one black/glass color. Hopefully there will be more offerings in the future. Our system has not been interconnected to the power grid or the house at this time as we are still finishing up the rest of the electrical system, I’ll do another post when it is up and producing power.

We also did look at solar panels, but the cost of them + a new roof would cost more than the Tesla solar tiles.

If you want more information or are interested in ordering, please use my referral link to save $500. This link can also be used to order a Tesla car and you will receive free supercharger credits.