PV Solar sizing with and without EV

[miimura]

With The Release of Tesla Power Wall for Just $3500 for 10 KW. Has any one calculated what will be the Total cost with Inverter and installation.

Based on the webpage http://www.pge.com/en/mybusiness/save/solar/sgip.page PG&E has a rebate of $1.46 per W. So for 10 KW installation are we going to get back a rebate of 14,600 from PG&E. Too good to be true or my calculations are wrong.

Your calculations are wrong.

SGIP is per Watt. The PowerWall is only 2kW average power, but 10kWh capacity. You would need 5 PowerWalls at $17,500 to get $14,600 from PG&E, if it is eligible for the full amount. Actually, now that I think about it, you would need to buy the 7kWh unit to be eligible for SGIP.

 

[ravisekhar]

miimura,
Thanks for the clarification. it looks like 10 KW system is better buy if it can get 3 KW average power .

If anyone is planning to get this installed in Bay Area, Let me know if we can go as a group and get better deal to get it installed.

My plan is to recharge the battery at night for 11 cents and use it during the peak times.

 

[eschatfische]

ravisekhar, the 10kW Powerwall is intended only for backup power. It uses different batteries than the Tesla traction batteries or the 7kW Powerwall, and is not designed to be discharged and recharged daily. If you're planning to be pulling power from the Powerwall daily, you'll need the 7kW or several 7kW in series.

 

[smkettner]

I don't think you can be on net metering with a battery in CA.
Battery would need to be separate so that it could not back feed into the grid.
Not sure how Powerwall could be used to supplement home power as the solar fades off in the evening.

 

[montreid]

I don't think you can be on net metering with a battery in CA.
Battery would need to be separate so that it could not back feed into the grid.
Not sure how Powerwall could be used to supplement home power as the solar fades off in the evening.

This. Back when we first had solar, PGE specifically prohibited batteries with TOU to minimize gaming of the grid (charge batteries at night and sellback during day at peak rates).

 

[miimura]

I don't think you can be on net metering with a battery in CA.
Battery would need to be separate so that it could not back feed into the grid.
Not sure how Powerwall could be used to supplement home power as the solar fades off in the evening.

This. Back when we first had solar, PGE specifically prohibited batteries with TOU to minimize gaming of the grid (charge batteries at night and sellback during day at peak rates).

You could still power your loads from battery after the sun went down, but was still in the Peak rate period. That way your household use would not eat up your Peak generated kWh. Then you could either charge the battery from the grid off-peak, or with morning sunshine. The battery cannot actually feed back into the grid, but can minimize your household usage at selective times.

 

[cossie1600]

There is an app called PG&E toolkit on IPhone, it actually shows you based on your usage from last month and see what your amount would be if you use the Powerwall.

 

[eschatfische]

This. Back when we first had solar, PGE specifically prohibited batteries with TOU to minimize gaming of the grid (charge batteries at night and sellback during day at peak rates).

I thought Musk and SolarCity successfully lobbied the CPUC to allow battery storage on NEM.

http://www.greentechmedia.com/artic...Storage-Scores-a-Regulatory-Win-in-California

 

[montreid]

This. Back when we first had solar, PGE specifically prohibited batteries with TOU to minimize gaming of the grid (charge batteries at night and sellback during day at peak rates).

I thought Musk and SolarCity successfully lobbied the CPUC to allow battery storage on NEM.

http://www.greentechmedia.com/artic...Storage-Scores-a-Regulatory-Win-in-California

Good read. Still not clear how SDGE/PGE would allow for this grid-tied with batteries. Electricity flows based on draw or feed. If you turn on the batteries during the day it'll feed the system = 'gaming' the grid and one can 'generate' simply by discharging the batteries.

http://www.bluepacificsolar.com/solar/backup-power.html looks like a whole package at 4400watts for 10kw total system.

Scenario which PGE/SDGE would probably object:
We're already net producers during day and borderline consumers on semi-pk:
-add batteries:
-charge at night
-discharge gradually between 12noon-6pm.
-netmetering wouldn't know the difference.

Only way to keep this 'honest' would be a completely secondary circuit to allow batteries to Charge one way; and discharge another route which I don't know if that's even possible---any electricians out there?

 

[smkettner]

This. Back when we first had solar, PGE specifically prohibited batteries with TOU to minimize gaming of the grid (charge batteries at night and sellback during day at peak rates).

I thought Musk and SolarCity successfully lobbied the CPUC to allow battery storage on NEM.

http://www.greentechmedia.com/artic...Storage-Scores-a-Regulatory-Win-in-California

Read it again. Still cannot back feed on standard net metering plan. Second meter could be required. Power from the battery can power the home only.

 

[eschatfische]

Read it again. Still cannot back feed on standard net metering plan. Second meter could be required. Power from the battery can power the home only.

I was responding to your statement that you did not think you could have a battery on NEM in California. Per the article and ruling, you can. Indeed, as you say, you cannot use the battery as a grid-connected generator, as that would be gaming NEM for profit, and yes, larger systems may still require a secondary meter. However, the CPUC has cleared a lot of roadblocks to allow an average residence with a PV system on NEM to easily install a battery (like the Powerwall) and then use it as a backup with an interlock of some sort to keep it from generating onto the grid.

 

[miimura]

If it is physically impossible for a given setup to feed energy from the battery to the grid, then the utility should not be involved at all. The daily cycling PowerWall can feed into the grid, so it clearly needs interconnect permission.

I am considering a battery system, but I mainly want it as a UPS for most of the house. I don't want to use the battery to feed into the grid, I just want to allow all my solar to go into the grid during the peak period while I power my house from my batteries. I would have the choice of charging the batteries from the grid during off-peak times or from morning solar generation when the reimbursement is lower. This is probably still "gaming NEM", but it is not amplifying it to the degree that you could by feeding extra energy from the battery into the grid.

 

[dstjohn99]

Interesting concept.

I wonder if the circuitry is addressed by code or requirements yet: to be able to charge the batteries during excess solar production (or from the grid in non PV systems), yet only draw from the batteries when household usage is positive and not feed back into the grid.

I imagine there will be no way to actually enforce the "no feedback into the grid" requirement for PV net metering customers unless separate inverter / battery management circuitry is required to monitor household usage and only draw from batteries when there is consumption, not excess production. For non PV there should never be any negative consumption on the meter. Either way, it could be complex and add significant expense.

**Edit**

Interesting miimua - Is it [will it be] considered "gaming" if you use batteries for personal usage to increase the PV feed into the grid?

 

[miimura]

It is actually very easy to separate the loads from the grid. For example, if you take a whole sub-panel, disconnect it from the main panel and only feed those loads from the battery connected inverter, it cannot feed back into the grid and would be easily covered by existing code. Then you just use a battery charger to take energy from the grid when the batteries are too low. Alternatively, you can actively monitor your draw from the meter, and ramp the battery charger so that the meter never goes negative until the batteries are completely full. These strategies are easy to implement with off the shelf product and a little programming.

I have been thinking about these issues after I saw this thread at TMC. That setup is WAY over the top in almost every way, but it is informative. Interesting pictures here.

I would imagine that if someone at the utility noticed something unusual in your billing pattern, they could look at the characteristic of your draw from the grid and make some informed conclusions based on the parameters of the solar system that your were approved to interconnect. In theory, as long as your NEM feed in was less than or equal to your actual solar production, they would have no basis for action.

 

[dipper]

Looking into doing solar (again). This time with the wife buying in into the idea.

I am in San Jose, wondering what company might be the best price/service around.

My house has a lot of vaulted ceiling, so it has many angles. Not a lot of straight roof space. Thinking about SunPower, but they are overpriced from what others have said. PetersonDean are using 270wh panels now, maybe they can do the job?

Any good options?

 

[GlennD]

If it is physically impossible for a given setup to feed energy from the battery to the grid, then the utility should not be involved at all. The daily cycling PowerWall can feed into the grid, so it clearly needs interconnect permission.

I am considering a battery system, but I mainly want it as a UPS for most of the house. I don't want to use the battery to feed into the grid, I just want to allow all my solar to go into the grid during the peak period while I power my house from my batteries. I would have the choice of charging the batteries from the grid during off-peak times or from morning solar generation when the reimbursement is lower. This is probably still "gaming NEM", but it is not amplifying it to the degree that you could by feeding extra energy from the battery into the grid.

Many public safety sites run from a full time UPS. The Long Beach Signal Hill site runs from a 450V battery bank. It is normally charged by Edison but in the event of power failure there is a 25K generator to power it. Powered this way there will never be a power interruption or loss of communications. It would take a lot of solar cells to maintain the battery.