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Wednesday, June 30, 2021

Heat Impact on Solar Production

In my last post, I quipped that our solar energy production dipped because of the recent high temperatures. Thinking more about this, I decided that I had only looked at a couple of days. This is one of the most common human fallacies. I had an idea, I looked for confirming data, found some, and assumed that means I was correct.

You overcome this, not by trying to prove yourself right, but by looking for credible data to prove youself wrong. Well, it didn't take long. 

Day   Fri   Sat   Sun   Mon   Tues 
Temp (F)   93°  108°  111°  115°  91°
Solar (kWh)   75.1   50.5   73.5   49.4   75.2 

Looking at the table, if you compare Friday and Saturday, it sure seems like the increased temp resulted in lower solar production. Saturday was 15°F hotter and it had ~25kWh lower output. 

Comparing Monday and Tuesday is a similar story. Monday was 24°F hotter and had about 25kWh lower output. 

Problem solved right? Nope. Sunday shatters this correlation. Sunday was hotter than Saturday but had solar production closer to the cooler Friday and Tuesday. Perhaps I was too quick to blame the production fluctuation on heat. 

It is well known that heat can impact solar efficiency, but the impact is not as significant as I thought. Each brand/model of solar panels is a little different, but they all publish the heat impact by listing the efficiency impact for each degree Celsius above 25°C. One reasonable example is negative 0.258% per degree C. So going from 93F to 108F is about a 7°C change. This would be about a 2% efficiency change. This alone does not account for the ~30% decrease from Friday to Saturday. Clearly, something else is happening too. 

Looking at weatherunderground and other sites, these days went from "passing clouds", to "clear", to "sunny." Meaning that, despite all of them being hot, hot days, they had varying levels of cloud coverage. Sunday had the least cloud coverage and solar production remained high later into the evening (8PM) than other days.

So there you have it, the variance can primarily be blamed on clouds, not the heat.

Tuesday, June 29, 2021

120 Hours of AC - Excessive Energy Usage

The heatwave hitting the Pacific North West seems to have finally broken. This event set new record highs for many locations in the region. British Columbia set a new record for the entire country of Canada.

Some have called this event a "once-in-a-millennium" occurrence. This would likely true if we had a stable environment, but we've added a lot of energy into the climate system and, in a perturbed system, you see many unexpected results. We've entered into an era of "global weirding." 

Roads Buckling in Heatwave - via @wsdot_north

Several roads in the region buckled and cracked due to thermal expansion. The trolley cars of Portland had to shut down due to damage to the high power cables. Similarly, the light rail passenger train, MAX, shut down due to cable expansion and sagging. Much of Oregon has had drought conditions for the last three years. Then, compounding the problem, it was hit with temperatures higher than any that have ever been recorded in the area.  

For our little home, we had a few little challenges, but overall we were rather lucky. Some of our neighbors lost power for a few hours. This is not surprising given the load that all the additional air conditioner use caused. However, these outages were in small areas and short-lived. The Western Interconnect grid held up to this stress test far better than the Texas grid has held up to their recent hot weather. Kudos to everyone in the region that helps keep the lights on (and the AC running when we needed it most). 

Speaking of AC, our AC unit is sized for a typical Oregon summer. It is, however,  significantly undersized for extreme heat like this. Even with our AC running all-out, the temperature in our home slowly continued to increase throughout the day. As I write this the AC has been running for 120 hours, non-stop. And it looks like it will be running for at least another 10 hours. The higher highs this heatwave brought were bad, but the higher overnight lows were worse; they meant no relief overnight either. On a typical hot summer day, the AC will run about 16 hours, not for days straight.

Portland weather graph via timeanddate.com

We (and much of the region) are going to have a big power bill this month. Compounding the energy problem is that despite all the sunshine, our solar energy production was reduced. Solar panels have a preferred operating temperature; when they get too hot, their efficiency is reduced. For example on June 28th (one of the hotter days), we generated 49.4kWh. On a more typical summer day, we typically generate ~80kWh. This is a notable reduction in output at a time when we most needed it. Just another reason that you should oversize your solar PV system whenever you can (even if it results in some solar clipping on good days).

Have a great summer and stay cool!

Tuesday, June 22, 2021

Virtual Power Plant Performs Suboptimally During A Heatwave

UPDATE (6/27/2021): Title updated for accuracy. Details at the end.*

We had our first real virtual power plant (VPP) event and it didn't go as intended. 

The point of a pilot project is to "learn by doing" on a small scale. Lessons learned on a small scale can prevent problems in a bigger program later; so, from that perspective, this was a victory. 

Before getting too much further into this, I should explain what happened. 

On June 21st, one of the longest days of the year, we were having a heatwave here in the Northwest. In response, Portland General Electric decided to put its new VPP into action. Our batteries would be discharged to help offset the expected increase in air conditioner use. Perfect, this is why we signed up. If this helps the utility avoid using diesel generators and peaker plants, that's great.**

On the surface, this seems like a great plan. At 5PM PGE is going to take over the battery's operation. BUT two hours before, at 3PM, peak time starts. Our battery is configured to discharge during peak hours and remove our home's load from the grid. So at 3PM, the battery responds as expected and our home is off-grid (sometimes referred to as islanding). Actually, our home is better than off-grid. The battery is running our house and the solar panels are feeding the grid. 

Then at 5PM, PGE takes over operation of the battery. Up until this point, the battery had been discharging at a rate of about 7 to 10kW (adjusting up and down with our home's needs). When PGE took over, they had the battery discharging at a steady 2kW (see graph below).

Home Energy Flow: (grey is the grid, green is Powerwall, yellow is solar)

This was 5 to 8kW lower than it had been discharging. This increased the grid load, exactly the opposite of the intention of the program.

Looking at the graph, you can see that after ~9AM, when the battery was full, our home became a negative grid load. Our solar panels generated enough to run our home, air conditioning and all. In the times the AC cycled off, we were feeding the grid. Then starting at 3PM our battery took over and we continued to be a negative load. It was not until PGE took over at 5PM that we started to use energy from the grid and add to the demand. 

If our battery had been in standby/backup mode, just sitting at 100% charged up, waiting for an outage, then this VPP plan would have worked fine. However, that was not the case. 

The SmartBattery program needs to add another level of "smarts". For example, setting up the battery to discharge at least 2kW, that would have worked better. Alternatively, they could have requested that the battery discharge 2kW more than the home required, thereby guaranteeing some level of feed-in. Perhaps the simplest option would have been to have the battery discharge at a higher level, e.g., 8kW. This is well within the 15kW that our system can sustainably supply. 

It may be that such modes are not possible with the APIs available to VPP operators. Requesting 8kW works fine for our system, but if an owner only has a single Powerwall, 8kW is not an option. The VPP does not currently customize the request for each home. Tesla Powerwalls are not the only home battery system in the mix, so they may need to adhere to a lowest common denominator mode... 

It could be, that the net result was still positive, just sub-optimal. For example, say there are 500 homes in this pilot. 50 are in a state similar to mine. Each added an average of 4kW of load to the grid for a total of 200kW more load. The other 450 homes, however, added 900kW of relief to the grid. This means that the VPP added 700kW of net relief to the grid. Still a net gain, but not as good as adding 900kW or more grid relief.

It looks like it is going to be a hot one this summer, so you can expect that this will not be the last VPP call-to-arms. Perhaps they will make some improvements before the next event.


* UPDATE1: The initial title was "VPP Fails During A Heatwave". As I explained in the article, the VPP didn't perform as intended at my house, but that does not mean that the VPP as a whole failed. Some readers, rightfully so, called me out on this clickbait characterization and I've updated the title to be more accurate and less clickbaity. One other minor update: the original article referred to June 21st as solstice. June 21st is often the solstice, but this year, in N. America, the solstice occurred on June 20th.

** Sidebar1: Global warming is causing hotter summers, which increases energy demands, which (when energy is sourced from fossil fuels) increases emissions, which increases global warming... This feedback cycle can/must be broken. Summertime is when the sun shines and solar energy production scales well with AC usage. Combine this with just a few hours of energy storage and you can time-shift loads as needed to stabilize grid demand

Saturday, June 19, 2021

Tesla Charging On The Road

Summer is right around the corner. That means road trips! After a year with little to no travel, it will be nice to stretch out on the open road. 

If, like me, you drive a Tesla. You have a long-range EV with access to a vast Supercharger network. And you have access to (the less discussed) destination charging network at restaurants, hotels, and other points of interest. In addition to all of this, Tesla has adapters that allow you to charge up at CHAdeMO stations like the West Coast Electric Highway. There's even a CCS adapter (coming soon to N. America) that will allow your Tesla to charge up on the Electrify America network.

If you find yourself so far off the beaten path that none of these will work for you, you still have an option, guerilla charging.  

Guerilla Charging: what it is and what it's not

When you have wandered off into an area devoid of charging stations, you may need to charge up at a campground or from a friend's dryer outlet. When that's the case, you have just stepped into the guerilla charging zone. 

Before we get into the details, I want to clarify that by guerilla charging, I mean being resourceful and having the equipment to get the job done. I don't mean stealing electricity or cutting locks to gain access. If you'd like to charge up on someone's property, just ask; explain how much electricity you'll use and offer to pay for it. "I'll be using about 60 cents worth of electricity per hour and I'll be here for ~90 minutes. I'll gladly pay you for it and you can have a soda from my cooler if you'd like one."

You should know that charging from a 240V outlet is a lot slower than charging at a Supercharger, so plan to spend some time there: bring a book, go for a hike, make some new friends, or catch up on some sleep, there are lots of options. 

Tesla Gear You'll Need

Your Tesla came with a mobile charging connector (MCC). Older versions of the MCC included an RV outlet (NEMA 14-50) and a standard US home outlet adapter (NEMA 15-5), the current version of the MCC only includes the 15-5 adapter. This standard US household outlet is the slowest of all the options at 2-4 miles per hour, it is really only useful for overnight/multiday charging. So if your MCC didn't include the 14-50 RV outlet adapter, you'll need to buy one from Tesla here

Adapters You'll Need

Now that you have a 14-50 on the end of your portable Tesla charging connector, you'll need adapters to be able to plug it into the sea of 240V plugs that are out there. It might seem like 240V is 240V and one plug should be enough; if only it were that easy. There are 240V plugs for dryers 1994 and prior, 1995 - 2011, and 2012+, there are welder plugs, range plugs, twist locks, 2-pole 3-wire, 3-pole 4-wire... a dizzying array. The below chart summarizes the most common 240V outlets nicely. 

The good thing is that nearly all of them are a subset of the 14-50 so with an adapter, you can plug into them. When you are shopping for adapters, you want to get high-quality parts with the right gauge of wire and molded (rain-tight) connectors. You could be charging for hours and low-quality part could get hot and slow down your charge rate (or worse). 

I found adapters at the AC Works Store on Amazon that appears perfectly suited for Tesla use cases. 

They have locking adapters, air conditioner adapters, welding adapters, marina adapters, and more. 

If you will be charging at campgrounds, one of the most important adapters to have is the TT-30 to Tesla adapter. There are other TT-30 to 14-50 adapters but they do not all work with EV charging equipment. The TT-30 adapter at your local RV shop will not likely work for a Tesla (or any other EV). So make sure to one that specifically says that it is made for EV (or Tesla) charging (like the one from the AC Works Store). 

Prepare Before You Go

I made an adapter kit, I bought a bright orange backpack and filled it with various adapters. This lives in the frunk of my Tesla and I find it reassuring to know that I can plug into nearly any outlet on this continent. You might not want to go that far, but you might want to at least have at least two (14-50, the TT-30), as well as an adapter for that weird outlet in your father-in-law's garage.

Remember that you don't necessarily need to charge to 100% on these charging stops. Use the Lagom method; charge so you can safely make it to your next destination.

This article contains affiliate links 
I am long Tesla

Saturday, June 12, 2021

Portland Virtual Power Plant

Portland General Electric is starting a virtual power plant pilot program and we've signed up for it. 

 A Virtual Power Plant is like Energy in the Cloud ☺

What is a Virtual Power Plant (VPP)? 

A VPP allows your electric utility to utilize residential energy storage systems to balance the grid energy needs. You may also see this referred to as utilizing "behind the meter assets." 

If you have a Tesla Powerwall (or another home battery system), normally, that battery in your garage or on the side of your home is only going to respond to your home's demands. Unlike solar, home batteries are usually not allowed to feed energy into the grid. A VPP frees your battery from this restriction and allows it to respond to the grid's needs too. A VPP can be used to reduce or eliminate spinning reserves or peaker plants. 

VPP Example

Say it's a hot day in August at 6PM. People arrive home and turn on their air conditioners (AC), fans, and start cooking diner. This places a big demand on the grid. Let's say that you have solar and home batteries. For round numbers, let's say your solar is generating 4kW, your home is using 2kW, and your batteries are full. The extra 2kW that your solar is generating helps the grid by effectively carrying the load of one additional home in your neighborhood. This is good, but not great since the Powerwalls are not being used in this first example.

Now, let's say it is peak price time and you are on a time-of-use plan. In this situation, your home battery would be discharging to carry your home's load. This allows the full 4kW from the solar panels to feed into the grid. This would mean that your solar would be carrying the load of 2 of your neighbors. This is better than the first example, but we can do even better. 

A VPP allows the utility to dispatch your batteries for more than just your home's needs. So on this hot day, when the grid is burdened, rather than firing up a peaker plant, the utility sends a dispatch message to your batteries (and hundreds of others) to ask them to start discharging near their sustainable rate. Let's say you have 2 Powerwalls and they can continuously discharge at a rate of 10kW. Now along with the solar, you are sending 12kW of power into the grid. This is enough to run 6 homes on your block.

Scenario Solar Production Powerwall  Output Grid Feed-In Homes Supported
Solar Only 
(or Powerwall in Backup Only mode)
4kW 0 2kW 1
Powerwall with TOU 4kW 2kW 4kW 2
Powerwall with VPP 4kW 10kW 12kW 6

This example is for just one home. A virtual power plant could have hundreds or thousands of homes participating and if each of them can ease the grid of the burden of 4 to 10 other homes, then you start to see why the utilities are interested in this idea. 

How Much Of The Battery Capacity Can They Use?

You get to define the 'Power Outage Reserve.' This means you can keep whatever percentage of the battery you'd like for your own peace of mind. In the winter (when outages are more likely here), I keep the reserve at 60%. In the summer, I lower it down to 30%. Even if we have an outage during the summer, we have more energy coming from the solar panels, so I'm not worried about keeping the batteries too full. 

What's In It For Me?

Okay, this helps the grid, but it will cause extra cycling wear and tear on my battery and if there is a power outage, my battery might be lower than it would have otherwise been. Utilities don't expect you to do this out of kindness, there are incentives for participation.

VPP programs have various incentives and payments for the people that participate. Some give you several thousands of dollars of incentives to install home batteries, others even give you the batteries for free. Some pay you for every month that you are in the program, others pay you per event or per kWh.

The PGE program that I'm enrolling in will pay participants $20 per month if they have solar. Ironically, if you DON'T have solar, you get paid $40 per month. You are paid more because the utility can also charge your battery at their discretion when they have surplus power available. When you have solar, the rules are generally written such that you can only charge home energy batteries with solar. 

If you are participating in the Energy Trust of Oregon's Solar Within Reach program, you may be eligible for an instant $5,000 rebate in addition to the above monthly $20. 

If you are within one of PGE's 3 Smart Grid Test Bed areas and you are one of the first 200 to sign up, you may be eligible for an instant rebate of up to $3,000 in addition to the above monthly participation funds.

How Big Is The PGE VPP?

This is a 5-year pilot program with up to 525 homes and up to 4 megawatts of dispatchable power. That's an average of ~7.6kW from each home. Our 3 Powerwalls can provide about twice that much. I guess they expect the average participant to only have 1 or 2 Powerwalls or (more likely) they will not be using the system's full potential. 

Which Home Energy Storage Battery Brands Are Supported? 

The PGE VPP currently supports home battery systems from Generac, SolarEdge, Sonnen, Sunverge, and Tesla.

If you want Tesla Powerwalls and/or Solar, you can use my referral link.

If you want to sign up for PGE's VPP pilot, here's the link

I'm Long Tesla

Monday, June 7, 2021

Product Over Advertising - How Tesla Is Different #78

Tesla does not do things the way that other automakers do things. Whether it's how they recruit talent, create mega castings, or eschewing lidar and insisting that full self-driving can (in fact must) be done via camera alone, citing lidar and (more recently) radar as a crutch to camera vision that leads to a local maximum from whence the 100% goal cannot be achieved, Tesla does things their own way.

Elon Musk's appearance on Saturday Night Live is yet another example of this unique path. Commercials for the Audi E-tron, Ford Mustang Mach-E, Volkswagen ID.4, and Lucid Air all aired within the first 30 minutes of Musk's SNL episode. Lucid Motors even used the air time to debut their first ad for the Lucid Air with 500 miles of range, due later this year.

While the other automakers are paying for this air time, paying ad agencies to make the commercials, and paying marketing companies to craft their message, their executives review and refine ad pitches, Musk is doing none of this. 

The minimum SAG scale is currently $3,488 per week. NBC would be required to pay Musk at least this much for his time preparing, rehearsing, and shooting that week. So while other automakers were paying NBC for ad space, Musk was getting paid (albeit an insignificant amount for a billionaire). Whatever impression a 30-second ad spot had on the audience (if they even saw it) was far outweighed by Musk's air-time in front of the audience. 

Other car companies are paying for ads. Tesla is making a compelling product.

Musk has been asked many times why Tesla does not spend money on PR and ads. In the Q1 2021 financial update, one of the SAY investor questions asked why Tesla didn't hire a PR staff to fight the FUD. The answer was that the truth will come out, and that time, money, effort... would all be better spent making a better, more compelling, product, rather than “trying to trick people” with perfectly crafted messages.

In 2018, Musk said, “At Tesla, the thing we focus on is we put all the money and attention into trying to make the product as compelling as possible because I think that the way to sell any product is through word of mouth. The key is to have a product that people love.” – Elon Musk

Tesla is an engineering company first and foremost.

Tuesday, June 1, 2021

Tesla Powerwall Gave Us A Negative Electricity Bill!

Our electricity bill came with a credit. This is a first for us. We've had home solar since 2007 and we've never had a negative electricity bill. 

As you can see above, for this billing cycle, we used net 87 kWh; and yet our bill is negative. There are a few things that allowed this to occur. 

  1. We are not driving our EVs as much with the new work from home program
  2. Springtime is great, we get sunshine, but don't have to run the air conditioning (graph below)
  3. We received a credit for entering our Powerwalls into our local utility's Smart Battery program
This last item on the list is how we were able to receive a credit, yet still some energy use. The 87 kWh is about $4 worth of energy. Along with the $10 connection fee and the various taxes, we owed about $15. Our partial month credit for joining the Smart Battery program was about the same. 

Next month we'll receive the entire $20 credit for the battery program, maybe that bill will be negative too.

Below, you can see as the seasonal sun comes out, our net grid use drops.