PowerWall 2 for time of use applicaiton

[Grifon]

I live in one of the most regressive states (Alabama) in the US when it comes to solar power. The net metering is only at the wholesale price which is about 1/3 the residential rate of ~ $ .095 kWh. There is also a fee of $5 per installed solar kWh per month to be connected to the grid as a backup. Here is the link to the rate rider document if you care to read it: http://www.alabamapower.com/content/dam/alabamapower/Rates/RGB.pdf

As bad as the solar situation is, I'm wondering if I could take advantage of my power company's Time of Use (TOU) rate. I can get a steep discount on my typical kWh rate of $.095 down to $.055 for most of the year. The kicker is I would pay $.255 per kWh during the months of June - September from the hours of 1pm - 7pm. These are the prime hours when we need to run our heat pump for cooling. Here'e the link to the rate document:
http://www.alabamapower.com/content/dam/alabamapower/Rates/RTA_Energy.pdf

When the PowerWall is used as a TOU only system, is there a configuration where it could be the sole source to the house until the power is depleted, to stay off the $.255 rate as long as possible during that June to September period? Then power switches back to the power company?

Thanks in advance for the feedback.

 

[hmmm]

Yes, you can do load shifting...I looked into it and the math didn't work for me without solar, but it's doable. See a reference to it at the bottom here:

Tesla Powerwall

 

[jsmay311]

You'll want to research what the utility allows. My understanding is that it's common for utilities to prohibit residential net metering customers from using battery storage in combination with TOU plans.

Although this restriction is mostly geared towards customers who get paid 1:1 retail rates and therefore could be in a position to abuse that benefit. So it might not apply in your case.

 

[Ampster]

Although this restriction is mostly geared towards customers who get paid 1:1 retail rates and therefore could be in a position to abuse that benefit. So it might not apply in your case

My guess is the restriction applies to feeding the grid from batteries. I can't see a way that the utility could prevent someone from powering equipment behind the meter by batteries behind the meter. The utilities have influence but that kind of influence gets very close to inhibiting personal freedom. Load shifting with the help of batteries is part of that freedom.

As to the OP idea there are other strategies that could reduce the demand on the Powerwall to be able to get through that six hour window. One would be to precool the house and then run the temp a little higher during the critical time. Some large building chillers are making ice during low rate periods and using that heat absorbsion to reduce load on chillers during peak rates.

 

[Grifon]

I may have found a more favorable option. It looks like there are actually 2 options that could be utilized documented in the solar rate rider. The first option is the $5 per installed kWh of capacity per month. For a 10 kWh system that would be $600 each year for the Capacity Reservation Charge as laid out in option 1. However, the second options states:

2. In lieu of the Capacity Reservation Charge in 1. above, qualifying customers may take service under Rate RTA with the following modification. During the months of June through September, the energy charge shall be 70¢/kWh during the weekday hours of 3:00 pm – 5:00 pm, excluding holidays as outlined in Rate RTA. All other terms and conditions of Rate RTA shall continue to apply.

So, I could install a solar system and then utilize a PowerWall to ensure I would not pay the $.70 rate for those 2 hours during peak demand in the summer.

Hmmmmm......

 

[ecarfan]

So, I could install a solar system and then utilize a PowerWall to ensure I would not pay the $.70 rate for those 2 hours during peak demand in the summer.

That sounds like a good plan. Sorry to read about such punitive laws in Alabama in regards to solar. Clearly the fossil fuel industries have the state legislature doing their bidding.

 

[Ampster]

A two hour window sounds a lot more feasible for the load of a heat pump. If your historical consumption is available perhaps your installer can run some rate scenerios. That is often available in California.

 

[ChadFeldheimer]

For time of use applications, does powerwall know how much power is being consumed and therefore know exactly how much power to output to offset consumption in real time? Or does it not react to real-time power consumption and simply rely on (traditional) net metering?

If the former, how does it know - is it connected in serial with the loads (so it can directly measure demand) or does it rely on an external device, or ???

If the latter, then Griffon's scenario is not as compatible with powerwall.

I have sort of a similar situation Griffon's. I have commercial electric service that charges by kWh (generation + transmission) as well as by maximum kW during peak hours (demand). The per kW charge is approximately $10/kW/month, and I'm interested in avoiding these charges by having powerwall supply power during peak hours. Each $5500 powerwall can output 5-7kW, potentially offsetting $50-$70/month in demand charges - but only if powerwall can offset consumption in real time. With installation, the payback period is about 10 years - far from a slam dunk, but starting to become feasible.

 

[miimura]

Tesla definitely knows how to do demand shaving since that is one of the big selling points of the PowerPack systems. The question is whether they incorporate that function into the PowerWall product. In @Grifon's case, he would want to completely zero the usage for any metering period during the 2 hour long peak window. My SmartMeter issued by PG&E in California accumulates kWh in 15 minute intervals, so you would want any battery system to either disconnect from the utility during that period and supply the loads directly from battery, or sum the consumption during those intervals and drive them to zero. If the heat pump load is greater than the output of the inverter, then you could continue to push energy into the grid after the heat pump cycles off until the net consumption is zeroed. The controller could either measure the consumption directly with its own Current Transformers or it could leverage Zigbee to get the data directly from a SmartMeter.

 

[MP3Mike]

Also, remember that one Powerwall 2 may not be enough to power your house on it's own. It can provide 7kW peak output, with 5kW continuous. I would need 3-4 of them to be able to run my house without making sure to restrict usage to stay within the 5kW limit.

 

[doubleohwhat]

So, I could install a solar system and then utilize a PowerWall to ensure I would not pay the $.70 rate for those 2 hours during peak demand in the summer.

Hmmmmm......

Have you gotten any further with this? I'm in the Birmingham/Hoover area and am dealing with this same situation. Currently, my rate plan from Alabama Power is the PEV + TOU plans stacked together which they call RTA-PEV. What I'd *like* to do is:

1) Install a solar system just large enough to cover our average ~2.75kWh usage during peak sun hours
2) Install a powerall that would charge overnight at the PEV rate and be used to:
A) In the winter, cover the TOU 5-9AM peak hours - we average 11kWh during this period
B) In the summer, takeover from the solar system during the evening (until 7pm) TOU peak hours

Basically, I'm not at all trying to go "off-grid". I just want to take the sting out of the TOU peak periods. I figured it was a pretty good plan until I realized our lovely power company has the $5 per installed solar kWh fee.

 

[brucet999]

I may have found a more favorable option. It looks like there are actually 2 options that could be utilized documented in the solar rate rider. The first option is the $5 per installed kWh of capacity per month. For a 10 kWh system that would be $600 each year for the Capacity Reservation Charge as laid out in option 1. However, the second options states:

2. In lieu of the Capacity Reservation Charge in 1. above, qualifying customers may take service under Rate RTA with the following modification. During the months of June through September, the energy charge shall be 70¢/kWh during the weekday hours of 3:00 pm – 5:00 pm, excluding holidays as outlined in Rate RTA. All other terms and conditions of Rate RTA shall continue to apply.

So, I could install a solar system and then utilize a PowerWall to ensure I would not pay the $.70 rate for those 2 hours during peak demand in the summer.

Hmmmmm......

You need to contact Tesla Energy for the exact capabilities of Power Wall. What I have read says that it can accomplish load shifting using either PV input or off-peak Grid input to the battery and out-putting AC power to the house circuits during peak rate times.

BTW, that fee is $5 per month per kW of nameplate PV capacity, not per kWh. The former is maximum rate of generation, the latter is a measure of energy stored or of Grid energy consumed during a billing period.

 

[Blup85]

Reading the crazyness of different electrical rates from across the nation and the world, it only shows how much of a big deal load shifting is going to be..Once we have a better energy storage system (graphine and a lot of others) its going to change the game, and not in a good way for utilities. I can't wait!
I've got a 11.8kw solar and EV PGE rate, my peak rate is .55c/kw! I would love to just load shift during the day with powerwalls and charge them at night..we need battery storage to not degrade so badly so I can use it daily.

 

[ecarfan]

I've got a 11.8kw solar and EV PGE rate, my peak rate is .55c/kw! I would love to just load shift during the day with powerwalls and charge them at night..we need battery storage to not degrade so badly so I can use it daily.

I use my Powerwall (first version) daily to load shift. It will be interesting to see how long it lasts. Plant to add a Powerwall 2 to my system at some point in the future.

 

[jstack6]

My In Laws are in Alabama and the utility makes it very hard to go Solar. That shorted 3 hour High rate times seems the best way to go. If you have a Time Of Day Thermostat you could set it to cool more just before the high hours and then you wouldn't need much PowerWall energy to cover it. Also get all LED light that make less heat and use 90% less energy. I like USA made CREE brand. You can buy them 10 at a time on Amazon or eBay and save a lot.
In our area of Arizona where they also charge you extra if you add solar grid tied we set up a separate Off GRID system for everything except the big items like Air Cond. Then they can't add an extra charge, use it for the PowerWall and split the circuits at you main power distribution box so you have a Off GRID Solar outlet in each room. It's very flexible and you and switch things back and forth as reserve goes up and down.

 

[brucet999]

In our area of Arizona where they also charge you extra if you add solar grid tied we set up a separate Off GRID system for everything except the big items like Air Cond. Then they can't add an extra charge, use it for the PowerWall and split the circuits at you main power distribution box so you have a Off GRID Solar outlet in each room. It's very flexible and you and switch things back and forth as reserve goes up and down.

You re-wired your house so that one outlet in each room could be on a separate PW-fed circuit? Then you unplug and plug into different outlets according to battery SOC?

 

[Ampster]

re-wired your house so that one outlet in each room could be on a separate PW-fed circuit? Then you unplug and plug into different outlets according to battery SOC?

Rewiring your house sounds like a major expense. Actually intercepting the circuits that you want to use during a power outage and connecting them to a sub panel next to the Power wall is less labor intensive. That sub panel is often called a critical loads panel and can be fed from most inverters. Most of the time the power is passed through a switch in the inverter but when power goes out or you time that load to go off grid that automatic switch feeds that panel.

 

[Blup85]

Cool. I really want to do this as well, but can't really justify it, for me it makes more sense to just buy more solar panels to offset until we have better battery tech. Is there a way to know your rate of degradation?

 

[zanary]

I use my Powerwall (first version) daily to load shift. It will be interesting to see how long it lasts. Plant to add a Powerwall 2 to my system at some point in the future.

Interesting. I just got my Powerwall 2 installed two days go. I also have no solar, and want to do Time of Use Load Shifting, but right now it's not supported in the latest v1.5.1 software for the Powerwall 2.

But you're able to load shift on your Powerwall 1? Are you on EV-A plan which is a TOU plan. Areyou then charging both the Powerwall and your Model S or Model X between 11pm and 6am to get the cheapest $0.125 rate from PG&E?

 

[brucet999]

Rewiring your house sounds like a major expense. Actually intercepting the circuits that you want to use during a power outage and connecting them to a sub panel next to the Power wall is less labor intensive. That sub panel is often called a critical loads panel and can be fed from most inverters. Most of the time the power is passed through a switch in the inverter but when power goes out or you time that load to go off grid that automatic switch feeds that panel.

But @jstack said he had a solar powered outlet in every room, so that means he had to rewire in order to have at least one outlet in each room connected to solar. You can't do that by removing certain circuits from the existing service entrance panel because all outlets in a room (sometimes two or more rooms) are normally daisy chained on the same circuit.