It seems that my 7.6KW solar system with 1PW is installed as a whole home backup. Any idea why? I have attached my system design. I don’t realistically expect to run both of my AC units in the event of power loss. Any advice?
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Whole home backup on 1 PW?
- Thread starter DTXMME
- Start date
In my view this is the "best" configuration even if you don't have enough Powerwalls.
One reason is that install is generally easier. No circuits need be moved. No additional load center needs be installed. I suspect this is the primary reason.
The second reason is as consumer you have all the flexibility. You don't have choose which circuits to backup.
The one downside is that you can empty the battery pretty quickly if you aren't careful. You can trigger a shutdown if you over draw the battery. If you lose power while you are awake you should know (the app notifies you). The primary risk is that you are asleep and either AC or a car charging wipes out your battery. The gateway has contacts that can be wired to shutdown your AC. If your car is a Tesla it can be configured to automatically stop charging if the grid goes down. For other EVs you may need to some of your integration but as long as your EVSE (charging station) or car has a way of controlling you can almost certainly do it.
jgleigh
Member
The biggest question is what are your goals?
And as you well know, Texas can get really cold and really hot. Are you trying to help with these?
The goal is to improve grid reliability for my home and lower costs. The Uri storm in 2021 opened my eyes and never want to go through that again.
The interesting thing is with free nights electrical plans and ability to charge from grid on new installs in 2023, the battery might be more cost effective than the actual solar panels!
What systems would you need to run to be comfortable during a similar storm and for how long?
I know my family members in the Austin area were out of power for 2 or 3 days during the "Snowpocolpse". If you want to stay powered during something like that then you will likely need more than one Powerwall and the solar can recharge them each day.
My family members had to hunker down in blankets and sleep in front of the gas fireplace for that time. Their gas bill was a killer that winter. Their biggest concern was freezing pipes.
Solar panels generate direct current (DC), and an inverter has to convert that DC to AC before it can be used in your house. My older Powerwall 2 (no plus) is coupled to Enphase Microinverters.
So the rooftop solar generates DC, the Enphase micros convert to AC, these feed the Powerwall 2 as AC and then the Powerwall converts back to DC so the energy can remain at rest. This is an AC coupled system since it's DC - AC - AC - DC
But I've never seen a line diagram for a Powerwall +. It looks like the solar sends DC directly into the Powerwall +. I wonder why for line-diagram-reasons, the inverter on the Powerwall + doesn't have to be shown differently from the storage component of the ESS. Maybe for the SLD, it really is just 1 piece of equipment? Anyway, now it looks like a DC coupled system.
I am not that adept at reading line diagrams and such, but the powerwall+ has a solar inverter built into the the top of it. Its still AC coupled, the inverter is just sitting on top of the powerwall.
jgleigh
Member
I have two Powerwall 2 and two Powerwall+ and they look like this on the line drawing.
My experience with adding solar is first determine what you want out of the system. Lower your electricity costs? Resilience through hurricanes? Power outages? For me I wanted to lower my electricity bills, but in TX, electricity was pretty cheap. So the traditional 'pay back' will take a long time. But since getting solar, energy prices have increased. Also I live in hurricane territory so some resilience to long power outages like a week, was desired. In reality if the grid was down for a week I'd still have to conserve power even if the Sun was out. Normally after a hurricane there are several clear sky days, but running the A/C overnight would still drain my 2 powerwalls. Finally, I wanted to help offset powering an EV so I increased the production side of the system as much as would fit on the available roof location.
Since most people have no experience with solar I really didn't have any feel for what I needed. But reading from others experience, I did add to the number of panels from the original system and I'm glad I did that. I didn't get a third PW, but I sometimes wish I had. I have a co-worker who has a 4 PW system. When charged it can get him through the night, but of course it is harder to get them fully charged during the day. Finding that balance between production and storage is not intuitive. That is why designers have tools and data on weather etc, but the reality is that every day can be different and one day I can produce a ton, the next day I may not get even to 50% charge on the PWs. Back in 2021 during that winter storm I don't think my system would have helped much since that week was very overcast and I would not have gotten much production or storage to last the night even in the winter when my loads are light.
So I'm kind of rambling... The first thing about only having one powerwall in my mind is can it even start up my AC's? I have two A/Cs and they can run at the same time. They don't normally start at the same time, but that start up current draw can be a lot. The PW+ can surge to handle the start up, but I think if I didn't have two PW's my largest AC unit would have a hard time starting.
On a day like today we had partly cloudy skies but I still produced 37kWh which ran the house and fully charged my 2 PW+. Since we are in heat mode this will easily get us through the night without using the grid. But the day before was very overcast/rainy and I didn't get any charge on the PW's and was on the grid all night. This is our first year on solar so we're still learning. Since 1 Jan we've been generating far more power than using and I've banked over 2,000 kWh with my power company. But in a few weeks we won't be power positive and will start to use the bank up to get through the summer. The question is at the end of the year will I break even or not? I might get pretty close.
Since buying an EV I can often charge it during a sunny day at the same time I'm charging the PW's. Probably as I get into summer I won't be able to do that anymore, the AC just uses so much power.
Anyway, after all this... my biggest lesson is to go bigger. If you have doubt, go bigger. Once you go through the process of getting your system installed you are not going to add to it. Just too much of a pain and may not be cost effective as going bigger from the start. If I had gotten a 3rd PW I would be able to get further into the summer nights on the PW's. But it would have added ~$8k to the cost, and take longer to pay back, but in all honesty I'm not that worried about payback. So that is maybe the one thing I would have done differently is to get a 3rd PW.
Sorry I didn't think I would type this much,
Since most people have no experience with solar I really didn't have any feel for what I needed. But reading from others experience, I did add to the number of panels from the original system and I'm glad I did that. I didn't get a third PW, but I sometimes wish I had. I have a co-worker who has a 4 PW system. When charged it can get him through the night, but of course it is harder to get them fully charged during the day. Finding that balance between production and storage is not intuitive. That is why designers have tools and data on weather etc, but the reality is that every day can be different and one day I can produce a ton, the next day I may not get even to 50% charge on the PWs. Back in 2021 during that winter storm I don't think my system would have helped much since that week was very overcast and I would not have gotten much production or storage to last the night even in the winter when my loads are light.
So I'm kind of rambling... The first thing about only having one powerwall in my mind is can it even start up my AC's? I have two A/Cs and they can run at the same time. They don't normally start at the same time, but that start up current draw can be a lot. The PW+ can surge to handle the start up, but I think if I didn't have two PW's my largest AC unit would have a hard time starting.
On a day like today we had partly cloudy skies but I still produced 37kWh which ran the house and fully charged my 2 PW+. Since we are in heat mode this will easily get us through the night without using the grid. But the day before was very overcast/rainy and I didn't get any charge on the PW's and was on the grid all night. This is our first year on solar so we're still learning. Since 1 Jan we've been generating far more power than using and I've banked over 2,000 kWh with my power company. But in a few weeks we won't be power positive and will start to use the bank up to get through the summer. The question is at the end of the year will I break even or not? I might get pretty close.
Since buying an EV I can often charge it during a sunny day at the same time I'm charging the PW's. Probably as I get into summer I won't be able to do that anymore, the AC just uses so much power.
Anyway, after all this... my biggest lesson is to go bigger. If you have doubt, go bigger. Once you go through the process of getting your system installed you are not going to add to it. Just too much of a pain and may not be cost effective as going bigger from the start. If I had gotten a 3rd PW I would be able to get further into the summer nights on the PW's. But it would have added ~$8k to the cost, and take longer to pay back, but in all honesty I'm not that worried about payback. So that is maybe the one thing I would have done differently is to get a 3rd PW.
Sorry I didn't think I would type this much,
Yep, I have never heard anyone say they wish they had not gotten so much solar, or so many batteries
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