How can I keep my PW less than 97% charged?

[Billme]

I have a single Powerwall, and an 8.2 KW system.

Up until now, I’ve had the majority of my power outages in the morning, and the result was hardly noticeable; everything in the home continued to run normallly, and the solar panels continued to generate power and run the house; all excess solar went to charge the battery. The occasional burst of home energy, for example running the water heater, simply caused the battery to discharge along with the solar. All good.

The same is true in the evening; as long as loads are less than the battery’s capacity, fail over is easy and painless, at least until the battery fully discharges.

I recently had an outage during the afternoon, when the battery was fully charged, and it was a completely different experience. Because the battery could not accept additional power, it immediately raised the frequency to 65hz, which shutoff the solar arrays. Then the house load exceeded the battery’s capacity, and it shut power off for the house. Eventually I shed the additional load and was able to get the Powerwall back online.

I’m wondering if it is possible to configure the charging schedule such that it only reaches full battery capacity at the very end of the day, which would allow the battery to keep the solar panels generating power, at least until there wasn’t enough solar energy available until the battery is the only option for home power.

In other words, can I change the timing on charging versus sending to the grid so that the majority of the day there is enough battery “buffer” to keep solar running my daytime loads? (Pool pumps, car charging)

 

[Billme]

Of course, if the Powerwall’s algorithm could be changed so that it doesn’t raise the frequency when it’s discharging, regardless of capacity, that would also solve my problem.

 

[cwied]

I'm not sure you can achieve exactly what you want, but the way the time-based control algorithm seems to work is that it only charges up enough to cover peak during partial-peak periods. If you set most of the solar-producing day to partial peak followed by an off-peak period in the late afternoon to finish charging and a peak period overnight, it might come close to what you describe.

So, try setting time-based control with partial peak 6am-4pm, off-peak 4pm-6pm, peak 6pm-6am. Make sure the rates are significantly different for the three periods (e.g., $0.10, $0.20 and $0.30).

I'm not really 100% sure that this will work, but given my experience with time-based control I think it has a reasonable chance of doing something close to what you want.

edit to add: one drawback of this is that you'll draw from the grid during the off-peak period, which may not be what you want.

 

[jjrandorin]

I have a single Powerwall, and an 8.2 KW system.

Up until now, I’ve had the majority of my power outages in the morning, and the result was hardly noticeable; everything in the home continued to run normallly, and the solar panels continued to generate power and run the house; all excess solar went to charge the battery. The occasional burst of home energy, for example running the water heater, simply caused the battery to discharge along with the solar. All good.

The same is true in the evening; as long as loads are less than the battery’s capacity, fail over is easy and painless, at least until the battery fully discharges.

I recently had an outage during the afternoon, when the battery was fully charged, and it was a completely different experience. Because the battery could not accept additional power, it immediately raised the frequency to 65hz, which shutoff the solar arrays. Then the house load exceeded the battery’s capacity, and it shut power off for the house. Eventually I shed the additional load and was able to get the Powerwall back online.

I’m wondering if it is possible to configure the charging schedule such that it only reaches full battery capacity at the very end of the day, which would allow the battery to keep the solar panels generating power, at least until there wasn’t enough solar energy available until the battery is the only option for home power.

In other words, can I change the timing on charging versus sending to the grid so that the majority of the day there is enough battery “buffer” to keep solar running my daytime loads? (Pool pumps, car charging)

My understanding (although I am not the most technical user here, for sure) is that what you are asking about is "curtailment" of the PV (solar) as the battery approaches full, and that is a function of what inverter you have. Newer ones may support that, older ones usually dont.

IF (repeat BIIGGGGG IF) your inverter supports curtailment, what would happen is "the system" (the gateway actually) would raise the frequency gradually to slow slowly turn down the Solar generation. Most older inverters only support "on / off".

 

[RKCRLR]

I used to have a similar problem when my AC attempted to start while the Powerwalls were fully charged. What I would do was wait until the solar started generating again and then start my AC. If I wanted to expedite the process I would turn on a high load device until the solar started generating again and then turn it off. Once I got my AC started I would keep the temperature setting low so it didn't stop until the house was plenty cool before I turned it off.

 

[sorka]

I'd really love a max charge level setting that I can change during the rare times when I need the full range. My powerwalls charge to 100% every day and most of the year, when I'm not running AC, I discharge to maybe half the capacity by the time peak ends. I'd rather move the 50-100% to 25-75% to extend battery life.