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 Post subject: Re: PV Solar sizing with and without EV
PostPosted: Fri May 08, 2015 6:10 pm 
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Joined: Mon May 27, 2013 10:02 pm
Posts: 137
Location: San Francisco, CA
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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.

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 Post subject: Re: PV Solar sizing with and without EV
PostPosted: Fri May 08, 2015 6:22 pm 
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Joined: Thu Jan 17, 2013 11:13 pm
Posts: 1591
Location: Los Altos, CA
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.

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 Post subject: Re: PV Solar sizing with and without EV
PostPosted: Fri May 08, 2015 6:35 pm 
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Joined: Wed Aug 13, 2014 8:30 pm
Posts: 215
Location: San Diego Co
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?

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 Post subject: Re: PV Solar sizing with and without EV
PostPosted: Fri May 08, 2015 10:33 pm 
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Joined: Thu Jan 17, 2013 11:13 pm
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Location: Los Altos, CA
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.

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 Post subject: Re: PV Solar sizing with and without EV
PostPosted: Tue Jul 28, 2015 11:34 am 
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Joined: Tue Mar 19, 2013 8:10 am
Posts: 77
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?


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 Post subject: Re: PV Solar sizing with and without EV
PostPosted: Wed Jul 29, 2015 4:49 pm 
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Joined: Sun Mar 23, 2014 9:35 pm
Posts: 148
miimura wrote:
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.

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