Grid charging update

[RKCRLR]

In theory that's what it does now. It's using solar forecasts, which should account for weather. It still does seem to optimize for self-consuming solar rather than storing it in the battery, though. As a result, my Powerwalls often seem to fill up before the afternoon shoulder/peak period starts. For discharging it uses the shoulder and peak rates to determine the timing. If there is enough of a difference between buy and sell rates, it will make sure not to draw from the grid during those times.

Well, for me it doesn't seem to take NBCs into account and it knows my history from last year. And I had to manually enter different buy/sell rates. And I'm not convinced it takes round trip efficiency losses into account. Tesla should at least publish the details of what it takes into account so we know what we need to manually account for.

 

[BGbreeder]

Well, for me it doesn't seem to take NBCs into account and it knows my history from last year. And I had to manually enter different buy/sell rates. And I'm not convinced it takes round trip efficiency losses into account. Tesla should at least publish the details of what it takes into account so we know what we need to manually account for.

For our system, it didn't appear to, so I repriced the buy/sell difference to include NBC, and inefficiencies, and it has behaved as I would like since then. YMMV...

All the best,

BG

 

[swedge]

Well, for me it doesn't seem to take NBCs into account and it knows my history from last year. And I had to manually enter different buy/sell rates. And I'm not convinced it takes round trip efficiency losses into account. Tesla should at least publish the details of what it takes into account so we know what we need to manually account for.

Yeah! For sure better documentation would be very helpful.

I set my sell 3¢ lower than the retail buy price to account for NBCs. But for net exporters or NEM3 customers that still won't give accurate net costs, and perhaps incorrect behavior, sigh.

On the round trip efficiency, even the app and downloaded data bury the PW's losses. One can calculate that by netting out all the supplied kWh numbers, or by starting and ending a day with the same SOC, and comparing the charge and discharge totals. If it was my design, I would consider adding the lost charge to the "house" consumption number, perhaps just a fixed percentage of the charge power.

Still, I am pretty happy with how the PW works. All my friends want one, except for the price, and a few friend did follow my lead and got CPUC's SGIP "equity resiliency" program pay for them, back before that little gold rush exhausted that budget.

 

[BGbreeder]

Ah, yes! That is a different deal. We expect to owe some at true-up, so all of our exports are compensated at retail.

I must say that the NBC affect on the true-up calculation is weird enough that I don't know exactly how it will come out. But it is surprising that PG&E's pricing would encourage you to export solar during off peak when their own generation is cheap, rather than during peak when their costs (both generation and transmission capacity needs/costs) are highest. PG&E should want you to, and should compensate you to cycle your PW as much as you can to help level their daily demand curve and reduce their costs.

I wouldn't say that the pricing encourages one to export solar when generation is cheap. Both the buy and sell price is cheap off peak. From PG&E's perspective, for the cost of the NBC, they get you to provide them with peak power capacity at zero capital cost to them. By providing power close to the point of consumption (your neighbors), PG&E doesn't incur transmission costs. Win/win for PG&E, at least as far as I can tell.

I think that the trend toward real-time hourly TOU will bring the price of the kWh toward open market, but I suspect it will be awhile before the lack of transmission costs makes it back to producers like you. (Or me.) Long term should have much flatter demand curves in my view.

All the best,

BG

 

[RKCRLR]

For our system, it didn't appear to, so I repriced the buy/sell difference to include NBC, and inefficiencies, and it has behaved as I would like since then. YMMV...

All the best,

BG

I priced in NBCs for my buy/sell but it still grid charged to nearly 100% during off-peak even though I'm a net producer instead of waiting until the the sun came up the next morning. I'm hoping for an algorithm that recognizes that incurs unnecessary NBCs.

 

[swedge]

I priced in NBCs for my buy/sell but it still grid charged to nearly 100% during off-peak even though I'm a net producer instead of waiting until the the sun came up the next morning. I'm hoping for an algorithm that recognizes that incurs unnecessary NBCs.

Perhaps you should set your sell price at the compensation rate for your net excess production. Retail minus NBC only applies to those of us who are net consumers. Once you have exported more than your typical annual consumption, your export credit is effectively reduced. So perhaps you should then inform your PW of the reduced credit rate and see what it does...

It would be nice if it understood the utility rules, but nation wide there are many variations, and each installation has different solar production and consumption, both of which vary over the seasons and weather. So our job is to figure out how to best communicate with PW to get it to serve us well. This is not easy when we don't know how PW makes it's decisions, or understand even the utility rules, which, while published, are shrouded in obfuscation. So we have to pay attention, fiddle around, and figure it out. Sort of like life.

 

[swedge]

I wouldn't say that the pricing encourages one to export solar when generation is cheap.

BGb,

I think you and I are on the same page. My comment was in response to the poster finding that Exporting Everything was not beneficial for net exporters like himself. I am not sure of the net export compensation rates, but if memory serves, it is not dependent on the time of export . If this is true, then there is no incentive for a net exporter to use his PW to shift export from off peak to peak times, as Export Everything does.

Export Everything make the SOC lower at the end of the day, which means that on the next day more solar is used to charge rather than be exported, mostly during off peak. Using EE, this difference is instead export during peak, resulting in the lower SOC for the next day. The alternative to EE means exporting more during off peak.

For net consumers, EE is incentivized by the peak price being higher than the off peak price. But since net export compensation is below off peak, this is no incentivized for net exporters, which seems perverse.

Maybe I'm missing something. But it is late, my mental off-peak time. Or maybe perverse pricing from utilities is to be expected.

 

[RKCRLR]

Perhaps you should set your sell price at the compensation rate for your net excess production. Retail minus NBC only applies to those of us who are net consumers. Once you have exported more than your typical annual consumption, your export credit is effectively reduced. So perhaps you should then inform your PW of the reduced credit rate and see what it does...

It would be nice if it understood the utility rules, but nation wide there are many variations, and each installation has different solar production and consumption, both of which vary over the seasons and weather. So our job is to figure out how to best communicate with PW to get it to serve us well. This is not easy when we don't know how PW makes it's decisions, or understand even the utility rules, which, while published, are shrouded in obfuscation. So we have to pay attention, fiddle around, and figure it out. Sort of like life.

The only time I use grid charging is when Stormwatch doesn't activate but there is a possibility of my power going out due to weather. So right now the easiest thing to do is manually activate grid charging when needed. But it would be nice if Tesla would recognize this on its own and keep a higher reserve.

 

[Redhill_qik]

It would be nice if it understood the utility rules, but nation wide there are many variations, and each installation has different solar production and consumption, both of which vary over the seasons and weather. So our job is to figure out how to best communicate with PW to get it to serve us well. This is not easy when we don't know how PW makes it's decisions, or understand even the utility rules, which, while published, are shrouded in obfuscation. So we have to pay attention, fiddle around, and figure it out. Sort of like life.

The issue is larger than understanding all the utility rules across the nation/world. This can be done, but would need a dedicated team that would review the tariffs on a monthly basis or an agreement with distributors and suppliers to communicate changes through some machine-machine portal/database/API. The larger issue is understanding the rules and forecasting for an entire year for people with annual true-ups and or for a month for people with monthly true-ups.

It can be done, but I don't think that Tesla will invest the resources to do this as the ROI is low for them.

 

[swedge]

The only time I use grid charging is when Stormwatch doesn't activate but there is a possibility of my power going out due to weather. So right now the easiest thing to do is manually activate grid charging when needed. But it would be nice if Tesla would recognize this on its own and keep a higher reserve.

Yes, I find grid charging better than Storm Watch, for several reasons. Storm watch will charge during peak price times, a behavior I am allergic to, so I usually leave it off. Also, it has been slow to respond when I do turn it on during active events, so it is hard to know if it'll do the job or not. Worse still, Storm Watch was not activated even when the TV weather folks were freaking out about Rivers of Atmospheric Cyclone Bombs or some such. So I usually leave it off, and pay attention.

Just before that last storm, I thought it best to hang on to more reserve, just in cae. So I at midnight the day before the store was forecast to hit, I grid charged by setting the reserve to 100% and I turned off Export Everything. PW still kept us from using peak that afternoon and evening, but it left us with 50% SOC at midnight, enough to get us well into daylight and make coffee the next morning even if some random tree took out our grid power. We lucked out, but we were braced for an outage.

 

[bemyax]

Here's a thing that has happened every so often after I toggled on grid charging. It seems as though the charge level sags below the set reserve. The gateway calls for grid charging for a few minutes, just enough to restore the percentage to the reserve. Is this telling me something about the battery health? (Yes, I'm glad I preserved the old app version on one of my phones. The new version doesn't adequately demonstrate this behavior.)

David

 

[swedge]

Here's a thing that has happened every so often after I toggled on grid charging. It seems as though the charge level sags below the set reserve. The gateway calls for grid charging for a few minutes, just enough to restore the percentage to the reserve. Is this telling me something about the battery health? (Yes, I'm glad I preserved the old app version on one of my phones. The new version doesn't adequately demonstrate this behavior.)

Mine also does occasional short grid charges. Always during off peak times, and generally on days when some grid charging would be reasonable, but otherwise they seem pretty random. In any case it does not strike me as indicative of any battery problem.

The battery SOC does seem to sag a bit if the temperature drops substantially, but then come back up as it warms up.

You can query your PW to see what it thinks it's capacity is. Three years after installation, mine is saying "nominal_full_pack_energy":12971, roughly 96% of it's 13.5 kWh spec when new.

I get this by connecting to PW directly with a web browser over my home network, logging is as Customer, and then entering this URL into my browser: https://powerwall/api/system_status . The full pack energy is roughly the third parameter in a long list of comma separated values.

 

[bemyax]

Yup. Mine is at 10571, also just over three years from installation. When I first started recording this a couple of years ago it was 11327. I kind of wondered if I could run it up and down 100% to 10% a few times, if it would recalibrate.

Anyway, I mainly wondered about the occasional boost thing, so knowing my experience wasn't the exception answers that.

David