I found these scribbles included in another post I have been working on. It was obvious they did not fit there, but then I thought about discussions (and at times arguments) I have had with many people about their solar, electrification, and electric transportation aspirations. Since I have had the same basic discussion multiple times, I considered that rather than throw all these scribbles away into the digital trash, I might structure them and see if they provide value to folks less immersed in the topics.
First Dabblings
In 1998 my family returned to Sunnyvale from a year in Spain, where all three of us focused on learning the language, experiencing a different lifestyle, and hanging out. We disposed of a lot of things when we left for the year. On returning part of our reintroduction into our California life was obtaining a new car. That was our first electric vehicle, a 1998 Honda EVPlus. (You can see them being crushed in the film Who Killed the Electric Car?)
The experience with that car left us with the conviction that whenever another mass produced EV was available, we would be buying it. Other than few months leasing from Hertz a Ford iThink, it took 7 years after losing our Honda to buy our first Nissan Leaf and since then we have bought only electric vehicles.
I can’t remember what prompted us to consider solar in 2006. Perhaps it was a home energy tour in Silicon Valley that got us thinking about it. Our home in Sunnyvale was not all-electric, but rather state of the art for 1959. So, heating and hot water were still gas. And from 2004 and 2011, other than an eMoto scooter, we have no option to rely on electricity for transportation. Our electric demand in 2006 was pretty modest. So, the solar system we installed was just 2.5kW with no storage system. (Residential rechargeable storage systems in 2006 were basically stacks of 12V lead acid batteries. If used regularly they had short lives and required regular maintenance.)
Maybe it was because this was early in the home solar installation history, but installation was not without its hiccups. First, in installing the mounting brackets on the roof there were bolt ends penetrating into our living room ceiling. The early systems all had a single inverter. This meant DC current was traveling through the wires from the panels to the inverter. This required conduit for the cable even when it was going through a wall. And I received a call from my wife saving I needed to head home from work. The installers had started a fire in the wall behind our refrigerator by shorting two wires.
But the system did work finally as advertised. At the end of the first year of solar, based on those year’s utility tariffs for residential solar customers (E9), we had no electric utility cost. In fact, during the true up bill, PG&E sent us a check for $80. This resulted from the timing of the tariff tiers. Midday, when our solar panels were yielding the highest output energy, was designated in the E9 schedule as being the peak cost period. In the evening, when we consumed most of our energy, was designated in the tariff as off-peak. After midnight the rate dropped to 4.5 cent/kWh while during the time our panels were running the meter backwards, the cost was 32.5 cents/kWh.
With the experience from that first year, I had a hard time understanding a business model that could sustain delivering free energy. If this was going to continue, it would be great if the benefits to be offered to others, including renters. In my community, more than 50% of households were renters. How could we make it possible for them to participate and benefit?
I also considered that the cost of my installation was not sustainable. Construction costs of a 2.5 kW array per kilowatt were outrageous. What if instead the array was 500 kW? I wondered how the installation cost might scale. It seemed obvious that the BOS (balance of system) installation costs would be much less per kW. Clearly that was not going to fit on residential roofs and it would be good to have neighborhood energy available. So, I contacted the Planning Department in my city and asked how many square feet in the city was covered with public and commercial parking. A fast calculation using the results of what my 2.5kW array delivered and assuming other homes’ consumption was comparable to ours, it was obvious that just covering parking spaces with solar arrays would power every home in the city.
I questioned how we might make the advantages I had with my array available to others by building offsite systems in which they could be part owners.
So, in 2006 I bought the domain that I use for these current posts, scalablepower, and began working with a few friends to see if we could build a business offering this option. Like many of my ideas, the time was not right. There was no financial method available at the time to create Community Solar let alone Offsite Solar.
However, in working this problem, my education began in how we actually get our electricity. It is a complex system with a number of players, all trying to be profitable while providing a service that has less than two outages a year for any customer and consistently provides power 99.9998% of the time.
Expanded Dabbling
In 2016 we moved to our current home in the North Bay that was built in 1954. Though the house had been modified a number of times, it still was relying on 1959’s technology and design requirements. (The original electric panel, hidden behind a shelf in the laundry room still used screw-in fuses.)
After a year we began an extensive renovation to make it as safe and energy efficient as possible. Besides earthquake and fire proofing the structure, we also followed the soon-to-be passed Title 24 code upgrades that specify that the external surfaces must be thermally separated from the building interior. No structural part should touch both the interior and exterior surfaces. As well we rewired the entire electrical layout in the home so that a subpanel of critical (protected) loads designed to function during utility power outages was created. And we started to electrify all the appliances of the home. This included installing our first 2 heat pumps. (More were to follow over the years.)
Shortly afterwards we had a 4 kW array installed and paired it with a 12.5 kWh energy storage system. As I mentioned above, storage was something I had dismissed as practical when we put the solar on the Sunnyvale home. However, by 2018 practical, no maintenance battery storage systems were commercially available. (We used Shell’s Sonnen system.) Some rewiring was required to place the Sonnen system in front of the critical loads subpanel we created during the renovation. As well, because the system was not IP65 rated, an external shed was built to house the battery system and the equipment to interface the solar system.
With our new storage capability and Enphase microinverter array installed, I began reviewing the performance of the system closely to understand how to best reduce both our costs and consume our energy directly without relying on the utility to store it for us.
The utility tariffs had evolved dramatically after our first experience in 2006 to address the changing profile of energy demand. Peak cost times had moved from the midday that addressed the Air Conditioning (AC) loads to instead the evening hours. The AC load was still there, but over the past 12 years with rapidly diminishing solar panel costs, the supply of energy midday now surpassed the increased AC demand. (When the sun is out, homes heat up. But at the same time, when the sun is out, peak solar generation occurs in the same neighborhood offsetting the AC load.)
With current tariffs, in the design of a home energy system, arbitration now becomes more important than simply offsetting energy demand. In the evening hours, when costs are highest, we wanted to avoid the high utility costs. If we need to buy energy, we want to do it when the costs are lowest, during off-peak pricing period. We could no longer simply rely on solar to offset the peak costs. We need to move the availability of that solar energy to times when the sun had already set.
The new system generates detailed data about how it is functioning and how we are consuming our energy through the Sonnen system. It all seemed to be working well, but I continued to tweak the system to see if I could get the utility costs down. I found several design problems that I made.
First, I was not using enough of the battery for arbitration. In the winter when our loads were greatest during the peak cost period the battery reached its discharge limit. A simple adjustment took care of that. I increased the depth of discharge allowed to just retain 30%. (This worked fine until we had a power outage at 5 AM that lasted 24 hours due to a storm. The following day we only got 300Wh of energy back - it was dark!)
The next issue was how I had defined the protected loads. In the summer, because the system only handled the protected loads, the other loads were only serviced by utility energy even though the battery had plenty of surplus energy.
And I had undersized the battery storage capacity. Though 12.5 kWh of storage and 8kW of peak power available would cover our average electric usage, it did not capture all the energy that the solar system was generating. Throughout the year, at sometime during the day we were sending energy back to the grid even though we would need it later in the day.
More battery, more load coverage, more collection; I needed all of these especially if we continued to expand our way to an all-electric family.
Refining the System
In 2023, two things got me even deeper into thinking about solar and energy. First, we continued to expand our electrification effort. We replaced our last gas powered vehicle buying an additional EV, a 320 mile Kia EV6. Shortly before we built an all-electric studio apartment over our garage, and we finally replaced the remaining gas furnace with a second heat pump for the house. At this point our home and transportation were entirely electric.
The second thing that impacted my thinking resulted from what I learned as a number of us worked to make a pitch to PG&E. We proposed PG&E expand its business and offer a new product. If PG&E provided controllable onsite storage in front of the meter, PG&E could become the premier provider of DERM (a topic covered in a number of my other posts.) After all, PG&E primarily makes its profit from delivery of the energy, not the energy itself.
Now with the two EVs and driving 16,000 miles a year, I realized that we needed more electricity to support the growing demand from the second car. So, additional panels were scheduled for installation and my work on the proposal to PG&E gave me an idea of how I wanted my home system to function. When the utility is up, I wanted my home storage system to support not just the critical loads panel, but to discharge and reduce utility costs for any load from the house (cars, garage, dryer, stove, oven) It turned out, once I described this to my solar installer, he said Sonnen had a product to do just that. It was called the Whole Home option on my existing Sonnen system. With this option, the Sonnen system gets two sets of input. One set tells it how energy is flowing through the utility meter (how fast and in what direction). The second is monitoring the protected loads.
Once the Whole Home option was installed, I started seeing the entire load my home is experiencing every second, how much energy the panels are generating, how much energy is being supplement each instant by utility power, and how much energy is flowing back to the utility when the panels are generating more than we are consuming or can store.
After 2 full years of history with this configuration, the two EV, and basically an all-electric home, I can understand the factors that need to be considered as a home electrifies and introduces solar and storage.
I think about our electric profile like this for 2025:
we drive 15,000 miles/year and consume 4,000kWh in the cars,
Our home uses besides the cars consume about 6,100kWh /year
Our 20 solar panels collect and deliver 7,400 kWh/year
We sent 4,000 kWh to PG&E
We bought 7,400 kWh from PG&E
I think you can see part of the problem. Besides the losses of not consuming directly what we produce, we are paying for the cost of moving the 4,000 kWh energy back and forth. Lucky for us, we are under a tariff that penalizes this very little. For new solar installations, this is not the case. There is a larger penalty if you have the utility store your energy for you (even if it is just for a few minutes.)
I am not convinced it is our responsibility to collect as much energy over the year as we will consume. Clearly if you plan to go off-grid, you would need to size your system appropriately. But regardless, larger battery sizes are required than what is your average daily usage. Heck, there are days with little sunlight and curiously they seem to correspond with the times when you need your battery to support you.
Maybe the simplest axiom is design your system so that you don’t need to export energy back to the grid. That is not as simple as it sounds. Unless you drive a lot every day, try figuring out how you might consume 32 kWh a day during the summer (about 120 miles of driving). That is not hard to use in the winter, but in the summer that consumption can drop to 8 kWh.
The Next Phase
At this point, I need to take some of my own advice. Add more storage! The question is how?
I can upgrade the Sonnen system, but because of some physical constraints that could be both disruptive and costly.
I have been exploring attaching an IP65 rated battery system to outside of the studio wall. The part I don’t understand is how it would recognize when it can discharge and ideally I would want it to charge only when solar energy is being collected. This is an option I have been seeing in many of the new integrated systems. Obviously, it requires the solar to communicate with the battery system. But with the Sonnen battery how would it know they were both taxing the one system.
The other option is to leverage the 100 kWh of battery storage sitting in my garage; the EVs. That is my current investigation. It will likely be pricey, but it will be interesting to learn how a system 120 ft away from the meter can work intelligently to optimize our energy system.
Yo que tú
My lessons learned might be summarized with these points:
Figure how to reduce the costs paid to the utility. Install a solar array sized to match home needs. Too large an array is as bad as too small an array
No matter what you decide - it will not be perfect year round. In my climate zone, I will be getting too little return for the energy produced in the summer, or will be paying too much to the utility in the winter. You need to find a goldilocks solution.
Send as little of the energy back to the grid as possible. Size the storage based on the solar capacity, not the home requirements. This often means larger than the solar will typically generate, as you will want to keep some buffer for the occasions during utility power outages (that seem to occur just as your battery is discharged the most.)
Cover the entire home with the battery storage when the utility is up. This increases the benefit you get from arbitration.
Find a smart installer you can trust that takes the time to understand what you want to accomplish; and who will be there as long as the warranty on your equipment.
Be energy efficient and rely on electric appliances! Insulate and use heat pumps, modern lighting, inductive ranges. In doing this, we reduced our energy consumption by 60% and gained a much more comfortable home.
If you start on this journey and have new lessons to share, let me know.
Appendix: Arbitration thoughts
If you made it through my story and learning process and you still want to dig in and start “electrifying” your self, I am providing this section with some of the terms and explanations of how the money works out when you consider how to use your system to arbitrate costs.
If arbitration is a foreign term to you, in the financial world it means to buy low and sell high. That is what we are trying to do with our home energy system. We want to buy energy when it is cheap and avoid buying when it is expensive. We do that by filling our batteries with low cost energy from either solar or from the grid at off-peak periods and discharging it for our home loads when the utility energy is at its peak price.
This is a short section, there is obviously a lot more could be covered, but I hope this gives you a starting place.
Tariffs
If you are trying to manage your energy costs, then education on the tariffs and tariff options is important. Our local utility, PG&E, used to give day long classes on this at their Energy Center in San Francisco. You probably don’t need that much education, but you do need to understand Time-of-use (TOU) vs Tiered tariffs.
Tiered tariffs were predominant until about 10 years ago. They were designed to incentivize customers to be more efficient. As you use more energy, at certain total consumption thresholds each month, the per unit cost would go up to a more expensive tier. (Some areas with municipal utilities still use this method and natural gas is still priced this way.)
With TOU there are normally 3 periods defined; off-peak, partial-peak, peak. The per unit price is different for each. Each tariff has specific hours when these rates apply and the rates for each may change depending on the time of year and specific climate zone you are in.
I was surprised to learn recently that though the structure of the tariff (when periods are and how they are adjusted) is stable, the actual price in each period can change based on adjustments the CPUC authorizes.
In California, the regulated utilities are being forced to convert all customers to TOU by 2027. Originally it was solar and EV customers who took advantage of TOU schedules. But over the years, with changes in the tariffs you might change the word from advantage to deal with as the peak cost periods no longer align with the peak solar periods.
Battery Schedule
The system I have, Shell’s Sonnen Battery system, has three distinct modes it can run in. A fourth is being added, but my old manual does not describe how it functions.
Though other systems might have different names or slightly different behavior, you can assume any system will provide at least these options.
BACKUP - basically the battery gets fully charged and only discharges if the grid becomes disabled. Curiously, this is the mode most people use, because they think of the storage as a guarantee of energy. It is something the local CCA is trying to train people out of.
TIME OF USE - here we configure the storage so it knows the utility Tariff. It attempts to shave the cost by discharging only during the peak or partial peak periods where the cost is higher. The rest of the time it is either filling up or just lazing around. The real value of battery storage both to the consumer and the grid operators every day is when it is used to do arbitrage during peak periods.
SELF_CONSUMPTION - In this mode, the storage system is always willing to discharge in order to stop consuming grid energy. It does not know about peak expense periods, but treats all periods the same. This was the mode we were advised to NOT use since you might run out of energy when prices are expensive.
This summer since my battery was not ever discharging more than 12% and I was sending all my solar energy back to the grid, I decided to try using SELF_CONSUMPTION. and yep, my self-sufficiency went up.
Successful arbitration using the Time Of Use is one way to reduce the cost of your energy. As an example, the current tariff at my home has a peak rate of 62 cents/kWh and an off-peak rate of 32 cents/kWh. So, my goal is to avoid paying the higher rate.
When I calculate my full cost over a year’s time for the 10,000+kWh our home consumes, the average cost comes to just 16 cents/kWh.
