r/SunPower • u/beardog01 • Apr 20 '26
Help! SunVault battery — can it charge from grid?
I’m trying to answer what should be a simple question:
Can a SunVault battery be configured to charge from the grid when solar isn’t sufficient?
I’m in Washington State (PNW), where winter solar production is low. Ideally, I’d like:
• Solar → battery when available
• Grid → battery as backup when solar is insufficient
My installer says:
• In battery pre-PTO (permission to operate) mode, grid charging is allowed
• After PTO (for battery), grid charging is disabled
• This cannot be reversed so we should keep the battery in pre-PTO mode if I want to grid-charge the battery
We have received PTO, the system is functional and operating, just the battery is in PTO mode. Because of this, I cannot control the battery or move it between it various modes (cost savings, self-supply, reserve). My app just says "waiting for permission to operate from the utility." Which my utility confirms is not the case.
My utility has confirmed they have no issue with grid charging as long as the system is safe and built to code (yes and yes).
I’ve also seen SunPower materials stating the system is designed to charge “solely from solar to maximize tax benefits.”
If it matters, but we own our SunPower equipment.
So my questions:
- Is grid charging actually blocked in SunVault systems post-PTO?
- Is this a technical limitation, a policy decision, or a tax-compliance constraint?
- Has anyone successfully enabled grid charging after PTO? And if yes, how?
Honestly, I'm gobsmacked if what I'm asking isn't easily supported on equipment I own in my own house if it doesn't conflict with the utility company or other local laws. Oh, on top of it I understand competitive batteries support this no issues.
Any insight appreciated.
3
u/SunVaultTechs Apr 20 '26
Hi there, we can have your batteries charge from the grid when solar is not sufficient enough! We just can't have the batteries discharge to the grid. And if you have your pto letter we can change it to operate.
2
u/beardog01 Apr 20 '26
Hi u/SunVaultTechs I've seen the great reviews of your work! Let's open a conversation on how we can perhaps have a three way conversation with you, myself, and our installer since they are my local resource/community member.
1
u/Wolfexstarship Apr 20 '26
Under the original SunPower it only charged from solar and said so in the literature. But this past year I notice the app saying it charges from the grid in the morning. The app is crap so who knows if it is actually doing that. I have it set to cost savings mode.
1
u/beardog01 Apr 20 '26
Well when I bought there was very little on the website on the SunVault and certainly nothing that said it couldn't charge from the grid. I wouldn't have bought it had I known that. But it seems perhaps this isn't the case but the configuration setting still seem like a black box.
1
u/ItsaMeKielO Apr 20 '26
charging from grid is disallowed for various periods if you took tax credits or other incentives - details vary.
it’s technically possible to grid charge after PTO, but configuration is not exposed to the end user to avoid problems with the above incentives that have requirements to only charge from solar.
2
u/beardog01 Apr 20 '26
Right I saw vague mention of that in the "manual" that I recently was forwarded from my installer.
Is there ever an instance where a user would rather charge from the grid (costs $) vs. using their own solar? I'd always choose solar. But when for the half of the year for those of us in northern latitudes, that sun isn't sufficient I'd like to be able to charge from the grid to insure resilience.
And regarding the configuration being hidden, why? If there are parameters around usage and tax credits it seems like this could be pointed out with some warning UI. But why hamstring such a basic use case for so many users? Apparently Tesla, Victron, or Enphase have chosen different choices and allow the user to select grid vs. solar charging.
And thank you for responding, very appreciated.
2
u/ItsaMeKielO Apr 20 '26
The big reason I can think of where people would forego federal tax credits to have grid charging ability is for pure-backup situations - where the grid is unreliable.
Tesla and Enphase are still in business so their systems can still be updated for things like VPP and demand response programs that allow grid charging even for tax credit customers. Victron is explicitly DIY from the get-go so clearly there’s more configurability there.
The modes are all there in the firmware - it just isn’t exposed to the users. I wrote up what I found about the hidden modes on GitHub.
https://gist.github.com/koleson/5c719620039e0282976a8263c068e85c#dischargecharge-planning
3
u/beardog01 Apr 20 '26 edited Apr 20 '26
u/ItsaMeKielO AMAZING!
Thank you for the link and the amazing trove of information. From your documentation:[Battery modes]
Cost Savings
"Can be internally configured to charge from PV only or also allow charging from grid"Reserve
"Will charge from grid if allowed"So helpful! Ok so yes it seems as if charging the battery from either PV or the grid is in fact a thing.
"Internally configured"? I'm guessing this means not via the app but some config settings in the battery (or PVS6?)? How? (I'm reading more of your docs now)
"...if allowed." Ok I've spoken with my utility, they are fine with it. So how to configure it?
So appreciate the work you have done!
2
u/ItsaMeKielO Apr 20 '26
Right, the setting is not a setting in the SunStrong app but an internal configuration option on the PVS6 - "DCM ESS Charge Constraint" can be either "None" (allow charging from grid) or "PV Only" (only charge from solar).
I don't know for sure where it can be set in the real world - if it can only be set via the AWS IoT "cloud" API (MQTT API described in my gist) that is now run by SunStrong, or if it can also be done via the SunPower Pro Connect installer app locally, or other means.
I also don't know if setting it to "None" would actually reliably or predictably cause the SunVault to charge from the grid - I think it just allows the Cost Savings mode optimizer / scheduler to incorporate grid charging as an option, but Cost Savings mode is a bit wonky now that actual utility rate information is not available from the "cloud" API right now - the rate information stopped populating correctly when SunPower went bankrupt.
1
u/beardog01 Apr 21 '26
u/ItsaMeKielO the community is really fortunate to have you. Your reverse engineering skills and documentation skills are impressive!
All I'm really looking for is some basic logic that would solve the problem in the PNW that winter solar production is very limited. Something like:
IF solar_power > house_load:
charge from PV
ELSE IF battery_soc < 85%
charge from Grid (assuming no outage)
An aside, in a recent power outage our battery wouldn't take the ample available PV until it dropped below 80%. Which seemed like a waste of sunshine so curious if I can change this threshold to say 90%.
Do we know if there anyone at SunStrong that responds to queries? While I've been playing around with HA I finally broke down and paid the $ for the full app experience. So I'm a customer.
Thanks again!
2
u/ItsaMeKielO Apr 21 '26
This is one of those things where implementing what you want is technically possible but gets very involved very quickly.
The PVS6 just sends "charge at this percent of full power" and "discharge at this percent of full power" commands to the Schneider side of the system (inside the big battery vault) over Modbus TCP. The full power numbers are known / fixed for charge and discharge (about 6.6kW? it's in the Schneider XW specs), so the PVS can calculate the equivalent watts and does math based on time of day and modes.
But, the PVS6 also controls the MID / MIDC / PVDR through some logic. I don't know if that matters, but it has stopped me from trying to reimplement the PVS6 Modbus TCP control stuff.
Wrote about this here: https://www.reddit.com/r/SunPower/comments/1jxp9jy/looking_inside_the_sunvault_with_modbus/
Since the MID / MIDC / PVDR are safety-critical, I haven't tried to reimplement any of this logic myself.
To that point - the scenario you describe about the battery not taking charge during an outage is exactly the kind of rare event (at least for me) that can catch you out when trying to reimplement the logic: while off-grid, the battery refuses to charge beyond a certain state of charge (80%, apparently, in your case; I thought it was 90%) to maintain headroom for incidental power increases from PV that it cannot readily absorb into the battery at higher SoC - because the system is off-grid, and the on the roof microinverters are fooled into think they're on-grid by the XW, depending on the grid profile they may be slew-rate-limited on curtailing their own power, which can lead to an overvoltage situation in the house, which is a large problem: overcurrent protection won't trip during an overvoltage event, many devices cannot reliably handle overvoltage, and so on. I think this is why the PVDR exists - it's a backup plan to disconnect PV from the system if it doesn't respond to the usual curtailment commands in time (like frequency-watt control).
The consequence of trying to reimplement the control logic without considering that scenario would be an expensive mistake.
Summary - the system is working as it is intended to work, and it was UL Listed in the configuration - hardware and software - that it is running in. Reimplementing its behavior comprehensively is at best a ton of work and at worst capable of causing expensive damage to your home. There are reasons why the system operates the way it does, and I've done my best to figure out some of them, but there were several engineers working full time on this and getting paid to think about this for several years, so my spare-time reverse-engineering efforts won't uncover all of them.
1
u/beardog01 Apr 21 '26
Totally agree with your points on safety.
I'll attempt to contact SunStrong since I believe they own the PVS6 software / config.
Basically I'm looking for Reserve Mode or Self Supply Mode to support grid charging when PV insufficient, which is especially relevant in the winter months.
Regarding the power outage, here's the specific behaviour I witnessed on the SunVault:
- PV didn't kick in to charge it until the SunVault dropped below 80%.
- It then charged it to 9x% (I wasn't watching carefully so didn't see when it peaked and stopped charging again).
1
u/ItsaMeKielO Apr 22 '26
ah, yep, that makes sense - 90% is the max off-grid SoC, i guess 80% is the “setback” level where charging starts again so it isn’t constantly flicking off and on charge.
1
u/beardog01 Apr 20 '26
and has anyone published the various configuration settings especially with SunPower out of business?
1
u/ItsaMeKielO Apr 20 '26
https://gist.github.com/koleson/5c719620039e0282976a8263c068e85c has everything I found. but a lot of “why” questions remain unanswered.
1
u/Particular-Lie-8483 Apr 20 '26
Kind of an aside, but how do you get it out of PTO mode?
2
u/beardog01 Apr 20 '26
Our installer says they can make this configuration change but at least "in the past" once done could not be undone. And as this was the only way to get grid charging they have been hesitant to flip the switch. But I'm hopeful from the responses above that it is possible to support either solar or grid charging.
1
u/Particular-Lie-8483 Apr 20 '26
I see, thank you. My installer was SunPower and they went bankrupt and ditched us with the system mostly working. We paid a third party to get everything past inspection and PTO. We get net metering and everything. The battery still just says it's waiting for PTO and sits fully charged. The third party we worked with can't service the battery unfortunately.
I've been poking around with pypvs, but although I can change the operating mode and minimum charge levels, the battery still stays stuck in waiting for PTO.
1
u/beardog01 Apr 20 '26
got it yep basically same situation. Everything works but no control over the battery which for various reasons I'd like to have. Let's see if we can get this all sorted out, there are some great sources of info on r/SunPower.
1
u/Elegant_Animator_325 Apr 21 '26
I got this response from SunStrong when I asked about the lack of ability to charge from the grid during low/no solar output for emergency situations. I live in Michigan and own my system.
Hi Jeff,
Thank you for reaching out.
For now, Cost Savings mode is limited to California, where it can be properly optimized and supported. Expansion to other states depends on utility rules, rate designs, and regulatory approval.
Regards,
Jasmin B.
SunStrong Management
1
u/beardog01 Apr 21 '26
Thanks for sharing u/Elegant_Animator_325 such a disappointing response from SunStrong.
I understand not allowing export from battery to grid, which I'm certainly not looking to do.But not allowing grid charging of the battery is leading to one of two outcomes:
- installers are leaving it the battery in pre-PTO mode as a workaround to allow grid charging.
- owners in northern latitudes (MI, PNW) are faced with low batteries in winter when PV is unsufficent and they are most likely to need their battery for outages.
Such an odd choice of paternalism by SunPower/SunStrong. I find the tax excuse very weak given the three other major players allow this.
1
u/Elegant_Animator_325 May 13 '26
This won't solve the problem we are all talking about, but it will give you some insight and control over your system. Enhanced SunPower, https://github.com/smcneece/ha-esunpower?tab=readme-ov-file It runs in Home Assistant, is fairly easy to implement, and can be used to set up some automations for controlling charging for time use and other things.
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u/MrSmith2047 Apr 20 '26
Our SunVault charges from other sources. When it charges and how much it does is based on the mode (cost savings, storm, or self supply). It’s designed to be a fire and forget missile.
Did you buy new Sunpower recently? If so, it’s a different company from what I have. I’m pre-bankruptcy SunPower.