Direct Power and Virtual Net Metering Possible together?

[Ken9research]

We are adjacent homeowners planning on getting solar installed on site. We're planning on enrolling in our utility company's Virtual Net Metering program. They call it NEMV, which is really just a financial accounting program because all home power still comes from the grid and solar power goes directly back to the grid. The virtual metering monitors the offset, whether net gain or loss.

Question is, are there equipment and controls that allow some direct solar benefits, like during the utility company's blackout? In other words, must ALL solar power go back to the grid? What type of equipment or components are involved? I've already called many contractors. They don't know. Utility company only explains their NEMV program, not alternative designs.

For example, during a utility company blackout, it would be great to still be able to charge electric vehicles from solar that we have newly installed on site.

[Ampster]

I presume you are talking about a Grid Tie inverter? Regardless of the type of Net Metering you have a grid tie inverter is unable to produce power when the grid is down. As a clarification a grid tie inverters output serves the house load then sends any excess to the grid. The other household under a NEMV arrangement gets a financial credit for the net power sent to the grid by the first household. It is not optimal if the rate plans are not exactly the same.

There are several options that would give you the ability to produce power when the grid is down. SolarEdge has a StoreEdge inverter that connects to a LG Chem battery and can run when the grid is down. What you want to ask for is a hybrid or bimodal inverter. Outback, SMA, Schneider and others make them. Alternately you could pair a grid tie inverter with a Tesla PowerWall or some others that can AC couple.
At one of my locations I have a NEM agreement similar to NEMV and there is no restriction in that arrangement about the type of inverter that you install as long as it meets the UL and local jurisdiction requirements for Grid Tie. Most hybrid or bimodal inverters meet those specs. Are you in California? Are your inverters already installed?

[Ken9research]

... StoreEdge inverter that connects to a LG Chem battery and can run when the grid is down. What you want to ask for is a hybrid or bimodal inverter. Outback, SMA, Schneider and others make them...

Interesting ideas and suggestions on the StorEdge inverter w/ LG Chem battery, which, in reading your words, is one type of hybrid or bimodal inverter. And the Tesla PowerWall idea. Thank you!

Yes, this is in California.

We're actually many many homeowners. Not sure how many of us would truly need emergency power during blackouts, but potentially 77 households in total may want to participate in the NEMV program. Many have EVs that they charge from inside their private garages.

Now, NEMV, being virtual as opposed to regular net metering, can be physically unconnected. It can even be a solar farm sitting on the other side of town. This is my understanding. And so again, NEMV is really just a financial accounting program.

This being clarified, would the solution for emergency power during blackouts come ONLY from battery backup of some kind? And so, can the batteries be separate purchases, installed by each homeowner on his/her own, even in their private garages, connected to the grid, maybe with no inverter needed? This is the confusing part to me.

Then for solar panels that actually sit on site — a few feet away from the homes in our case — would a hybrid or bimodal inverter be possible only at one location because there's only one connection to grid? No way to distribute power to all homes during a blackout? This is the other confusing part.

Any recommendation on who can help in such a custom design?

[Ampster]

Interesting ideas and suggestions on the StorEdge inverter w/ LG Chem battery, which, in reading your words, is one type of hybrid or bimodal inverter. And the Tesla PowerWall idea. Thank you!

I used the term loosely. They each have their unique strengths and weakness but all fit within a grouping that have more capabilities that simple grid tie inverters.

We're actually many many homeowners. Not sure how many of us would truly need emergency power during blackouts, but potentially 77 households in total may want to participate in the NEMV program. Many have EVs that they charge from inside their private garages.

Now, NEMV, being virtual as opposed to regular net metering, can be physically unconnected. It can even be a solar farm sitting on the other side of town. This is my understanding. And so again, NEMV is really just a financial accounting program.

Ninety percent of the time NEMV sounds like it would meet your needs for aggregating solar from on site or off site.

This being clarified, would the solution for emergency power during blackouts come ONLY from battery backup of some kind? And so, can the batteries be separate purchases, installed by each homeowner on his/her own, even in their private garages, connected to the grid, maybe with no inverter needed? This is the confusing part to me.

Some of the inverters I mentioned have to be paired with solar. The Tesla Powerwall can be standalone since it has an integral battery pack. The hybrid inverters need a separate battery pack and some may be able to function without a direct connection to solar panels.

Then for solar panels that actually sit on site — a few feet away from the homes in our case — would a hybrid or bimodal inverter be possible only at one location because there's only one connection to grid? No way to distribute power to all homes during a blackout? This is the other confusing part.

Not only is it confusing but it is complicated when you start distributing power to a bunch of homes. That concept is often called a microgrid and can be a combination of solar, batteries and generators. Google it for more information.

Any recommendation on who can help in such a custom design?

There are a number of consultants in that space because the California Energy Commission was issuing grants for demonstration microgrids.
After the recent safety related blackouts in Northern California I heard a report of a city that had a microgrid for their downtown. I will try to get more information. In the meantime here is a general article about microgrids:
https://www.govtech.com/fs/infrastru...alifornia.html

[Ampster]

The report of a city may have been Healdsburg and it may have been because this company is located in Healdsburg.
https://www.prnewswire.com/in/news-r...601249945.html

[Ken9research]

Thanks again for more info. I've read the articles. They're interesting.

Microgrid was mentioned by a few in my research. Definitely seems the ultimate solution. But likely also top dollar — a special component on top of the already expensive package of conventional solar.

In the meantime, what's the next lower tier of a solution?

In other words, what's the least we can give up from having the ultimate convenience?

For example, why not physically connect all homes and just have giant throw switches clustered in a central lockable closet — for times of grid blackout? Enjoy NEMV in normal times. Can cut-off switches be designed and built in full compliance with codes and authorities?

Or would inverters have to be redundant?

[Ampster]

...............

In the meantime, what's the next lower tier of a solution?

In other words, what's the least we can give up from having the ultimate convenience?

For example, why not physically connect all homes and just have giant throw switches clustered in a central lockable closet — for times of grid blackout? Enjoy NEMV in normal times. Can cut-off switches be designed and built in full compliance with codes and authorities?

Or would inverters have to be redundant?

It is hard to answer those questions until you nail down some details about load. It would also depend on the infrastructure of your complex. I think your questions are beyond the capabilities of anyone on this Forum. At least I have not seen anyone with knowledge of microgrids posting here. My knowledge is very superficial and high level only because I was a volunteer reviewing a CEC grant request prepared by a group of consultants for the City of Hermosa Beach for a micro grid demonstration project several years ago.

There are several layers of complexity here. The primary layer is the individual homeowner. The next layer is the HOA, which may or may not include who owns the roofs. The final layer is the Power Company (POCO) owned infrastructure within your complex.

NEMV is easy to do because the POCO does the accounting. The complexity is in the formula to allocate generation amongst participants some of whom might own generation and others that only have load on the system. IF the HOA owns the roofs then the concept would be much simpler since the HOA could own the generation and the NEMV agreement would allocate percentage of generation to the participants. I think that is one of the possibilities in NEMV. I actually looked into it for some rental property I owned, The tenant, in my case, or the homeowner in your case would receive a percentage of the generation allocated to his bill and he would be responsible for the difference in net consumption.
The above is similar to a concept called Community Solar where a solar panel complex would be built somewhere and people buy into participations of the power generated. They become owners of the generating assets and share in the maintenence. NEMV accounting may be the billing vehicle but the main difference is the ownership of the assets in the latter case.

None of the above involve the POCO infrastructure but they also do not deal with the concept of back up generation. To do that for the entire complex the HOA would have to deal with the POCO infrastructure that probably includes transformers and possibly switchgear. That is an analysis in which you should probably engage a professional with experience in micro grids. There may be economies of scale with this approach but the bottom line would be if the cost to the individual home owners exceeds what they can do individually then there would not likely be much buy in and then the economy of scale starts falling apart.

That is about all I can offer at this time with the available information. I can't answer your specific questions without more information about your complex. The concept of simple throw switches depends on the POCO infrastructure.

Maybe to flush out the available options you could think about the answers to a few questions:

What area of California is this project located.
What are the loads in aggregate or on average per unit?
Does the complex have natural gas serving the units?
Does the HOA have adequate reserves for deferred maintenance?
Who owns the roofs, the HOA or the individual homeowners?
Is there a community space with a large roof area or other area where solar panels could be mounted and generators or batteries?
Does the HOA Board have the project management skills for such a project?
Are the demographics of the homeowners such that a large capital assessment would be possible if it resulted in long term savings and resiliency of the supply of power to the complex?

[Ken9research]

Thank you again for the detailed reply. Please note that the ownership and location aspects have already been narrowed down for research purposes. The concept, if only for planning purposes, is already simple.

Namely, it will a limited canopy structure in the guest parking area, not roof top. The structure itself will be designed, engineered and built only for solar collector panels. Installation of panels itself is already easy. A third-party non profit LLC will be formed or contracted to own/operate/maintain the new facility. The limited nature is both for trial purposes and for partial buy-in, not to fully match the loads of entire community. Hoping to be modular though. These are the assumptions for research purposes. This is the premise, and only to gain a better understanding of what's possible.

There will also be space made available for equipment, but how much space? What type of equipment is involved? How large an outdoors closet? Or an underground vault? Is equipment even possible for manual switching during a blackout?

These are the questions. We're not trying to create or re-invent a microgrid.

For example, if a tie into the main POCO junction on site is necessary for a pseudo microgrid, then forget microgrid altogether. How about bypassing POCO for emergency blackout purposes? How about a privately built physical network of cables to each building's electrical closet? We are 14 buildings. This means private switchgear at the base of the canopy. But kind of switchgear? Is that necessary? This is just from my imagination to illustrate the endeavor. POCO would not meddle in private direct solar. Would they? And if they do, can the switchgear be added afterwards? Well, I actually don't mean that. Just trying to learn what equipment is necessary.

I don't know what kind of switching equipment is needed to simply throw the connection to and from the grid. To grid as normal. Off grid for limited home power during blackout.

As another example, if we can't have any of the above — if we can't have any solar power to homes during blackout, then how about fast-charging EV stations at the canopy? This would mean that the only direct solar benefit would be the ability to charge our electric vehicles during a blackout. Is that common enough? In conjunction with NEMV?

Or not even that?

[Mike90250]

The big failing with a community micro-grid, is the "It's communal power, i can sneak the microwave in, blowdryer, one more load of wash......." And very shortly, the batteries are flat, and nobody 'fesses up. With fancy metering, you can bust them next week, but that doesn't matter tonight when the power is off and all the ice cream is melting.

The nighttime battery usage is the daunting problem. And if it's bad weather, and no solar charge, who's the generator person; oil changes, spare parts, fixing the beast......

[peakbagger]

I think you are going to be running into interconnect standards that will make it uneconomical. The utility has to protect its system and workers. Grid tied is easy as the inverters are set up to not send power into a dead grid. Once you introduce the capability to have local generation then the utility has to worry about backfeeding into the grid. They definitely do not want anyone using their local distribution to send power to other homes so you end up needing each house equipped with break before make transfer switches and a separate distribution system. If you were designing the system from scratch its possible but essentially some entity is going to have to step in to maintain the electrical distribution, private metering and billing.

[Ampster]

Yes, @Mike90250 hit the nail on the head as far as the human behavior aspect. Many years ago an Economics professor once said the easiest way to turn a scarce commodity into a rare commodity is to make it free. The simplest way to address that is to let each homeowner do their own backup battery. I presume there is space in a garage or in a utility space where the power to the building comes in. That way they can size it to meet their needs. The only issue will be how to charge those batteries when the grid is down. I will try to comment on that and the rest of your post in more detail later.
@peakbagger has flushed out the issue with interfacing with the POCO and that may be what you were concerned about. Is your POCO PG & E by chance?

There are some other resources here that may be able to shed some light on some of the issues you mention now that I have a better sense of the scope of the project.
@jflorey2 has knowledge of grid issues and has seen the latest from SPI.
@ButchDeal has design and troubleshooting experience and may have some input about the design of the solar inverter/backup on the guest parking canopy.

As to your initial design for a canopy that makes it easy. The available square footage will drive the size in kilo Watts. To make the canopy structure work when the grid is down you would need a backup battery inverter near the canopy but that inverter or group of inverters stacked or paralleled together might be the only ones you would need to do grid tie and when the grid is down. Economics will probably drive that configuration, especially the capacity in kWhrs of battery storage that you would want to have.

[Ampster]

I think you are going to be running into interconnect standards that will make it uneconomical. ....... If you were designing the system from scratch its possible but essentially some entity is going to have to step in to maintain the electrical distribution, private metering and billing.

Transfer switches to comply with interconnect standards would have to be implicit in any arrangement.

Your conundrum about economics raises an interesting issue. I ran into this while serving on the Board at a private institution. This institution had maybe thirty electrical meters serving both private residences and institutional buildings. There was an analysis made that it would be less expensive in the long run to purchase the infrastructure from SCE and put one meter at the high voltage entrance to the campus. The payback came from saving the expense of many meters versus one and primarily from the less expensive rate that high voltage service amounted to over time. I don't remember the payback time but it was attractive. The idea got tabled when a fire destroyed a building and capital resources had to be allocated to rebuilding. With Zigbee meters the capture of meter usage data was already done and billing the 20 or so residents would have been simple because they were already tenants of the institution. The meters could be left in place and read over the air by services that exist for billing tenants.

[Ampster]

....... Please note that the ownership and location aspects have already been narrowed down for research purposes. The concept, if only for planning purposes, is already simple.


Namely, it will a limited canopy structure in the guest parking area, not roof top. The structure itself will be designed, engineered and built only for solar collector panels. Installation of panels itself is already easy. A third-party non profit LLC will be formed or contracted to own/operate/maintain the new facility. The limited nature is both for trial purposes and for partial buy-in, not to fully match the loads of entire community. Hoping to be modular though. These are the assumptions for research purposes. This is the premise, and only to gain a better understanding of what's possible.

As I mentioned that helps. Do you have a rough sense for the square footage? I once saw an old metric that one square foot could generate 20 Watts.

There will also be space made available for equipment, but how much space? What type of equipment is involved? How large an outdoors closet? Or an underground vault? Is equipment even possible for manual switching during a blackout?

I think the space needed for equipment might be easier to estimate once the capacity of the system is figured out. As far as grid tie inverters on canopys, I have often seen them fastened to the canopy posts so no ground floor area would be needed for simple grid tie inverters.

These are the questions. We're not trying to create or re-invent a microgrid.

For example, if a tie into the main POCO junction on site is necessary for a pseudo microgrid, then forget microgrid altogether. How about bypassing POCO for emergency blackout purposes?

Where you do that will determine how involved the POCO needs to be. The simple concept is that you have more flexibility behind the meter. There it is up to the local building code to determine what the requirements would be.

How about a privately built physical network of cables to each building's electrical closet? We are 14 buildings. This means private switchgear at the base of the canopy. But kind of switchgear? Is that necessary? This is just from my imagination to illustrate the endeavor. POCO would not meddle in private direct solar. Would they?

As far as I know as long as the properties are contiguous you can run conduit and electrical connections behind the meter to anywhere in the complex. There are building code issues that would have to be addressed. The switchgear would all have to be “behind the meter”

I don't know what kind of switching equipment is needed to simply throw the connection to and from the grid. To grid as normal. Off grid for limited home power during blackout.

Most hybrid inverters contain the necessary transfer swiches to island the system during a blackout so that it is safe and essentially off grid. That takes place behind the meter. As I mentioned earlier, it is implicit that compliant interconnect devices would be required by the building code.

As another example, if we can't have any of the above — if we can't have any solar power to homes during blackout, then how about fast-charging EV stations at the canopy? This would mean that the only direct solar benefit would be the ability to charge our electric vehicles during a blackout. Is that common enough? In conjunction with NEMV?

As I mentioned earlier you could do that. EVs can consume a lot of power and how much you want to store will be driven by economics. A rough rule of thumb would be $1000 per kWhr of storage . It might be less expensive for several hundred kWhrs. A kWhr would give a small EV about 4 miles of range. It could be a big number. One can buy an EV with 50 kWhr battery for less than $50,000 as an example of comparative value.
You may have enough information to at least outline a Request for Proposal.
I have seen my local Kaiser Healthcare facilities in Sonoma County add solar canopies and their contractor might be a good resource. Here is a link to an article and the name of the company is Collins Electrical Company:
https://cleanpowerexchange.org/solar...te-santa-rosa/

Also, Sunworks, a solar installation company that did a 100 kW roof top solar installation for the City of Hermosa Beach, gave them a proposal for canopy structures on several city parcels. They are headquartered out of Roseville and they are the ones that figured out the contiguous parcel information that I mentioned above. In that proposal, there were a number of city sites that would be good for solar and since they were all contiguous to a long City Park they could use a form of NEMV to maximize the solar generating capability. In that case there was not enough roof space above City Hall to cover that building’s load so NEMV made sense.

[Ken9research]

The big failing with a community micro-grid, is the "It's communal power...

Thank you for the comment. Your reply seems to be directed at *non microgrid* for the lack of metering controls, yes? Not the type of intelligent microgrid that was suggested earlier? I was already trying to progress in discussion to NOT talk about microgrid. So your points are noted (continue reading below).

I think you are going to be running into interconnect standards that will make it uneconomical...

Thank you for your feedback. If the problem of interconnectivity is addressed one part at a time, wouldn't the first part simply be a disconnect feature?

For example, set up everything with proper connections to the grid for NEMV. Probably "permanent" whatever — as required by the utility company. This would be normal daily operation. Then, in rare times of blackout, there's a manual upstream switch to disconnect. Stream direction meaning power coming from solar. This is what I meant by "bypassing POCO" and hopefully what Ampster means by "behind the meter".

Wouldn't this solve (bypass) the interconnect problem?

The second part, of course, is how to privately distribute to multiple homes on the private site. But first things first, talking only about interconnectivity — simple as that?

... The simplest way to address that is to let each homeowner do their own backup battery... Is your POCO PG & E by chance? ... The available square footage will drive the size in kilo Watts... To make the canopy structure work when the grid is down you would need a backup battery inverter near the canopy but that inverter or group of inverters stacked or paralleled together might be the only ones you would need to do grid tie and when the grid is down... Most hybrid inverters contain the necessary transfer swiches to island the system during a blackout so that it is safe and essentially off grid.

Thank you again. This design where batteries are necessary at each home seems good as a design suggestion. I never suggested otherwise, so thank you for the suggestion.

Wouldn't the Tesla PowerWall in each home be an answer? Not too familiar, but PowerWall seems capable of charging from the grid. Seems in general any bimodal or hybrid inverter (from your earlier suggestion) can do same? Each home's battery would just stay charged all the time.

Then a backup battery inverter at the canopy to take the power when the disconnect switch is thrown?

As for private distribution, how about the low-tech solution of individual keyed switch boxes? I mean, let's stretch our minds and go super low for a sec. For example, and this again is only from my imagination, the switchgear is simply 77 separated cutoff switches at the canopy closet, wired to the 77 homes. Each household that buys into emergency power gets handed a physical key. Then during a blackout, they walk over with flashlight, unlock the closet, unlock their own flip switch. Even if everybody does this, the diluted power might still help for a few dim light bulbs, but still provide some power, yes? Common equipment? Or common enough components to build such a closet for cheap?

Rough area of one canopy 1,575 sq.ft. Hoping for 34 kW? Hoping modular. We can potential fit 5 of these canopies, but let's say start with one canopy. Yes PG&E jurisdiction.

It sounds like a hybrid inverter at the incoming power source (at solar canopy) would have built-in disconnect switch yet still allow for operation "as an island" ??

[Ampster]

........ I was already trying to progress in discussion to NOT talk about microgrid.

I think the term micro grid may broadly apply to what you are thinking about but I understand the goal is to keep it simple. The term "microgrid" may cause people to focus on a more complex solution. I will try to stay at the 10,000 foot level for the purposes of framing a simple outline.
Also since this seems like a brainstorming session I will try to adhere to the rules crafted by several facilitators that I had the pleasure of working with over the years. Essentially there are no bad ideas for the purposes of getting ideas out there.

....

Wouldn't the Tesla PowerWall in each home be an answer? Not too familiar, but PowerWall seems capable of charging from the grid. Seems in general any bimodal or hybrid inverter (from your earlier suggestion) can do same? Each home's battery would just stay charged all the time.

The Tesla PowerWall has the capability of charging from the grid. If the owners wanted to take the investment tax credit then some mechanism could be worked out to facilitate that. The credit has some limitation on how often the PowerWall can be charged from the grid. The credit is intended to apply to solar installations but batteries are included if they charge from solar a certain amount of time. I have some thoughts about that but it gets complex and I will save it for later.

Then a backup battery inverter at the canopy to take the power when the disconnect switch is thrown?

Yes that is the concept. I think the disconnect would have to be automatic in order for it to comply with PG & E's NEM agreement as a grid tie inverter. That would typically be in the the hybrid inverter which would function as a grid tie inverter while the grid is up.

As for private distribution, how about the low-tech solution of individual keyed switch boxes? I mean, let's stretch our minds and go super low for a sec. For example, and this again is only from my imagination, the switchgear is simply 77 separated cutoff switches at the canopy closet, wired to the 77 homes. Each household that buys into emergency power gets handed a physical key. Then during a blackout, they walk over with flashlight, unlock the closet, unlock their own flip switch. Even if everybody does this, the diluted power might still help for a few dim light bulbs, but still provide some power, yes? Common equipment? Or common enough components to build such a closet for cheap?

Yes, and you could look at the wiring topology and run a conduit to a sub panel at each building and have the keyed switches there. The design details will figure out the most economical and convenient way to do that. A later step in the design would be how much power you would want to deliver to each home.. For starters it could be a simple socket with a 20 Amp circuit. The next level could be sub panels for essential loads.

Rough area of one canopy 1,575 sq.ft. Hoping for 34 kW? Hoping modular. We can potential fit 5 of these canopies, but let's say start with one canopy. Yes PG&E jurisdiction.

If my rule of thumb works that would be about 31kW per canopy. I think with more efficient panels it could be better. I recently saw a parking canopy at the Charles Schultz Museum in Santa Rosa that looked like these new bifacial panels that have recently come out.

It sounds like a hybrid inverter at the incoming power source (at solar canopy) would have built-in disconnect switch yet still allow for operation "as an island" ??

Yes, that is how it works. I will dive into the details to help give you a mental picture. I wish I had computer drawing skills but if you can imagine four boxes, One is the grid, one is the inverter for the panels on the canopy, one is a sub panel that could be the distribution for the homeowners and the last one is the charging stations. When the grid is up the inverter, the grid and the charging box are all connected. Power can flow from the inverter to the grid and/or support charging stations from solar that is produced when the sun shines. When the sun goes down the grid powers the charging stations. When the grid goes down the grid is disconnected to protect the linemen. If the sun is out the hybrid inverter powers the homeowners box and the charging stations. When there is not enough sun the batteries provide power to the inverter to service those two loads. That is the simplistic concept.
The final design will have to take into account the complexity of the loads, the amount of solar generation and the capacity of the batteries to serve the loads. There are a lot of details as one gets to that level. There will need to be some thought given about how to ration or restrict the off grid capacity unless you want to consider a backup generator. The generator could be sized to handle everything and would only be limited by the fuel source. It would inform your planning process if you could make some assumptions about loads because that information will be useful later on. At some point in time someone will point out the obvious economic fact that a generator will be a lot less expensive than batteries. I did not do that because it seemed like that was not something you initially wanted to consider.

Another brainstorming comment. If you are in PG & E territory you may also be in a Community Choice Aggregation program. Sonoma Clean Power, Marin Clean Energy, and many others are in the Bay area. The first two are fairly mature and have programs that may provide incentives for this kind of system you are planning. The PG & E bankruptcy may also provide opportunities that were inconceivable a few years ago. One thing is certain in my mind a least, is that rates are going to continue to go up. Your planning could bring a good value to your homeowners.