5kW System - One Powerwall or Two?

[glide]

I am planning to have a solar system installed and after my on-site visit, my design was adjusted from a medium-size 8kW system down to 5kW due to my roof design.

I am now left wondering g if I should go with one powerwall or two for the system. I live in the Northeast where sun coverage can be spotty and we are most subject to power outages in the winter months.

My original plan was to be able to run the house off the two powerwalls. Now I’m not sure, based on the smaller size of the system, whether that is truly feasible. Or financially viable.

Anyone else with a “small” sized system able to comment on your experiences?

 

[BrettS]

Exactly what do you mean by “run the house” off the powerwalls? If you mean you want to be self powered then that’s also going to be a function of how much solar power you can generate. If your system is small enough now that you can’t produce enough solar power during the day to cover your daily power demand then more powerwalls won’t help here.

However, if you want the powerwalls to provide backup power in the event of an outage, then two powerwalls could be helpful, especially with a minimal amount of solar. Having two powerwalls will allow you to have more power available for an extended outage.

Additionally going from one to two powerwalls will likely allow you to do a whole home backup instead of just backing up critical loads with one powerwall.

 

[BrettS]

Also, it’s worth noting that depending on how much sun you get with a small system like that you may not be able to fully charge both powerwalls in one day if they were completely drained. However, I don’t necessarily see that as a problem.

Obviously this means that you can’t rely on using the full capacity of the powerwalls every night if you were trying to be self powered, but that capacity would still be there to help get you through an extended outage if that’s important to you.

 

[glide]

Exactly what do you mean by “run the house” off the powerwalls? If you mean you want to be self powered then that’s also going to be a function of how much solar power you can generate. If your system is small enough now that you can’t produce enough solar power during the day to cover your daily power demand then more powerwalls won’t help here.

However, if you want the powerwalls to provide backup power in the event of an outage, then two powerwalls could be helpful, especially with a minimal amount of solar. Having two powerwalls will allow you to have more power available for an extended outage.

Additionally going from one to two powerwalls will likely allow you to do a whole home backup instead of just backing up critical loads with one powerwall.

I was thinking in terms of whole-house backup in the event of an outage.

 

[BrettS]

I was thinking in terms of whole-house backup in the event of an outage.

Yeah, you pretty much need a minimum of two powerwalls to do whole house backup and depending on how much power your house and appliances draw might even need to go up to three or four.

 

[wjgjr]

Yeah, you pretty much need a minimum of two powerwalls to do whole house backup and depending on how much power your house and appliances draw might even need to go up to three or four.

I would agree, noting the narrow possibility for one since OP mentioned being in the northeast. If OP doesn't have/need A/C and has all gas appliances (including heat, hot water, dryer, oven/stove) it might be possible to get away with one from a load perspective. But even then, having two would increase the length of time OP could be without power.

 

[aesculus]

I have a 5kW solar and have two PWs. Would not consider anything less. During the peak solar production my 5 kW system will just about fill up the two PWs but as stated above, you will find some appliances demanding more energy than one PW can deliver.

 

[dancudds]

My home averages 12kWh/day (2000 sqft, gas heating, no AC). 1 PW will get me through AT LEAST 1 day and subsequent days can be topped-off with whatever solar I'm able to get. Making power-saving decisions (no dishwasher, unplug landscaping lights) should save me another 1-2 kWh during a prolonged outage.

Check your current power bill for your average usage. In the winter you might 1-3 kWh from a winter day which is enough to top-up some emergency usage but not much else.

 

[hurjio]

I have a 5kW solar and have two PWs. Would not consider anything less. During the peak solar production my 5 kW system will just about fill up the two PWs but as stated above, you will find some appliances demanding more energy than one PW can deliver.

Fill up your 2 PW from what state? Near zero? I imagine most of your solar production has to go to your PW to fill them up. 5kW solar system can get your 25-30kWh on a good day? What setting do you run your PWs on?

 

[aesculus]

Fill up your 2 PW from what state? Near zero? I imagine most of your solar production has to go to your PW to fill them up. 5kW solar system can get your 25-30kWh on a good day? What setting do you run your PWs on?

Exactly. Since the tw PWs can hold that much max, this is essentially my target. I roughly consume around 22 kWh/day without AC so with the solar running at peak (best ever around 26 kWh) that is my max ability.

So I drain from about 7pm until around 10am, rinse and repeat.

 

[hurjio]

Exactly. Since the tw PWs can hold that much max, this is essentially my target. I roughly consume around 22 kWh/day without AC so with the solar running at peak (best ever around 26 kWh) that is my max ability.

So I drain from about 7pm until around 10am, rinse and repeat.

So then you pull mostly from the grid for your electrical needs from 10am to 7pm? Aren't you on TOU though? Isn't that the most expensive time?

 

[aesculus]

So then you pull mostly from the grid for your electrical needs from 10am to 7pm? Aren't you on TOU though? Isn't that the most expensive time?

I was talking about when the grid is down. So if I am very conservative and have good solar, ideally my output about meets my daily consumption.

I am an energy hog when the grid is connected and only use the PW to offset peak usage from 2 to 9pm. In that scenario with AC I can use 50% of the PWs during a day. In this mode I am running Cost Savings with reserve at 50%.

Note I cannot really run my AC during grid outage anyway because the start power is greater than two PWs can handle.I tried it once and it worked and another time I had some funky things go on so I disabled them.

I come nowhere close being energy efficient normally. The PWs just offset cost and are my backup for PSPS and other grid disruptions.