Self-Consumption of PV power: grid tied, no net metering, no batteries

[evolknuj]

Austin Energy is my provider and they do not use net metering. Instead they use VOST to pay solar owners 9.7c/kWh of generated PV while still charging for my total consumption using tiers (it's hot in texas, we often hit the top tier unfortunately). E.g.: https://news.energysage.com/austins-...g-solar-power/

Quote [emphasis added]:
Under a VOST program, a solar power system user still pays for all electricity from the grid, consumed in their home as they did before. Then the utility gives the user a credit for each unit of electricity (expressed in terms of Kilowatt Hours or kWh) produced by the solar energy system whether used onsite or pushed back to the grid.


I'm getting two different answers from installers as to what that means, so I came up with a simple scenario to ask:

It's the last day of August and I've consumed enough already to get into Austin Energy's Tier 5 rate (lets say 15c/kWh after all the extras). It's clear and sunny and my PV is generating 7000w constantly between 9am and 3pm, and my AC is running constantly consuming 5000w for the same 9am-3pm interval. What is the end result for those 6 hours?

A: Austin Energy's meter registers 42kWh of PV (7kW*6h) and I get a $4.07 credit (42kWh*9.7c/kWh). Austin Energy's meter also registers 30kWh of consumption (5kW*6h) and I get a $4.50 charge (30kWh*15c/kWh). In the end, I need to pay AustinEnergy $0.43c for those six hours, even though I was pushing 12kWh more electricity to the grid than I consumed. Boo for the tariff difference and VOST scheme!

B: My AC self-consumes the PV electricity available without it even touching Austin Energy's meter. Austin Energy's meter sees 12kWh of PV ((7kW-5kW)*6h) and I get a $1.16 credit (12kWh*9.7c/kWh). Austin Energy's meter sees zero draw from the grid in those 6 hours, so I get a zero charge. In the end, I get the $1.16 credit for those six hours. Yay for self-consumption!


Lots of simplifying assumptions in there of course, but it's a valid question I think. I think Hawaii is another market that has similar issues, except their prices are often high enough to justify battery storage so even more of their generated power could be self-consumed in the evenings. What's the answer? (I'm double-asking the installers too, and prodding them to ask Austin Energy reps as well).

I don't think it makes any difference to the answer, but I'm looking at either Enphase IQ7 microinverters or SolarEdge string inverters with DC optimizers, panasonic HIT panels, and about 12-15kW roof mounted if/when I pull the trigger.

Thanks!

[Ampster]

I am sure someone else will chime in with a similar answer, but the most accurate answer you get will be from a published tariff or rate scheduled approved by the Utilities Commission. No matter the answer you understand from the explanation from your vendor or POCO it is best to verify in writing.

[ButchDeal]

IT is going to depend on how they are measuring the production.

Your comparison to Hawaii is not accurate. They do NOT have a similar schedule at all. Hawaii restricts new applications to ZERO feed in. That means they can not produce ANY more power than they are consuming at any moment. They do get to self consume and basically because of that they get full retail value for the power they generate.

[evolknuj]

I haven't seen an actual wiring diagram, but I've heard back from the installers and they are now agreeing that it's "A". Austin Energy says:

On a wall near your existing utility meter and electric service panel, you will have an additional meter called a PV meter. This measures how much energy your solar system is producing.

I'm guessing that means that the PV system will be just connected to this meter which measures total production before any of that electricity can be consumed or fed onto the grid. The the existing utility meter still measures total consumption regardless of what the PV system is doing. This is unfortunate and seems unreasonable (see prior example where I would end up paying austin energy for putting 12kWh onto their grid for them) but is the way it is. Boo.

I was hoping it was "A, unless you use a special type of inverter like StorEdge (even without a battery) in which case it would be B" or something.

[ButchDeal]

I haven't seen an actual wiring diagram, but I've heard back from the installers and they are now agreeing that it's "A". Austin Energy says:

I'm guessing that means that the PV system will be just connected to this meter which measures total production before any of that electricity can be consumed or fed onto the grid. The the existing utility meter still measures total consumption regardless of what the PV system is doing. This is unfortunate and seems unreasonable (see prior example where I would end up paying austin energy for putting 12kWh onto their grid for them) but is the way it is. Boo.

I was hoping it was "A, unless you use a special type of inverter like StorEdge (even without a battery) in which case it would be B" or something.

This would seem to be illegal as they are charging you for using your own energy that would be self consumed without touching their grid.

Your best bet is to not do an interconnect and just work with a grid zero system. You would ONLY ever get self consumption though.

[Ampster]

This would seem to be illegal as they are charging you for using your own energy that would be self consumed without touching their grid.

Your best bet is to not do an interconnect and just work with a grid zero system. You would ONLY ever get self consumption though.

And that would only require a building permit if no interconnection was requested. Just to be clear that also assumes UL approved equipment in order to comply with codes. No permission needed from the POCO since everything is behind the meter. I think that is the workaround that people have used in Hawaii when the POCO was stonewalling them on approvals. I don't know if that is still the case in Hawaii. I do know that is possible in California according to my County Building Department.

[ButchDeal]

And that would only require a building permit if no interconnection was requested. Just to be clear that also assumes UL approved equipment in order to comply with codes. No permission needed from the POCO since everything is behind the meter.

absolutely right.

This can be done with most grid tie inverters as well as all of them from SolarEdge and enphase. Consumption meter is required and configuration change for grid zero.
A smaller array would be set up and best if you can get east and west modules (longer production day).
A battery would allow more self consumption but at higher cost.

[evolknuj]

Yeah, with current battery costs I think it's prohibitive for the rates I'm working with -- my top tier rate is less than half of some numbers I've seen out of Hawaii. Going entirely off grid wouldn't be an option for me. I'm not sure about "illegal", but it's certainly annoying that AustinEnergy wants to prevent self-consumption, or at least wants to meter separately and have me pay for self-consumption. I would have thought they'd be fine with people actually reducing their dependence on the grid... but I'll be doing attic insulation / radiant barrier improvements to help with that too.

[ButchDeal]

Yeah, with current battery costs I think it's prohibitive for the rates I'm working with -- my top tier rate is less than half of some numbers I've seen out of Hawaii. Going entirely off grid wouldn't be an option for me. I'm not sure about "illegal", but it's certainly annoying that AustinEnergy wants to prevent self-consumption, or at least wants to meter separately and have me pay for self-consumption. I would have thought they'd be fine with people actually reducing their dependence on the grid... but I'll be doing attic insulation / radiant barrier improvements to help with that too.

They are not PREVENTING your self consumption but why I say it is illegal is that self consumption is still happening, but they are charging you for it.

as I mentioned a smaller solar system set up east/west can be configured for grid zero (no feed in) with just the addition of a consumption meter and configuration change. You then would not need an interconnect. It would not be as much savings but would also not be as much cost.

[evolknuj]

Gotcha -- I'm still learning the terminology, grid-zero not-equals off-grid. I think POCO means POwerCOmpany, but only 90% sure . I wouldn't get the Austin Energy rebate for such an install, not _sure_ if I would qualify for federal tax credit (probably would)... and of course I would prefer a larger system for personal satisfaction (carbon offset) even if it's not 100% optimal financially. But it's a good point / option for others in the same scenario.

Does that suggest that if Austin Energy changed their policies at some point in the future, whatever system I install (lets say SolarEdge HD Wave inverter) could be reconfigured, perhaps with the addition of the SolarEdge consumption meter box, to allow self-consumption before the meter, but also supplement from the grid when production is not sufficient and feed back to the grid when production is too high?

[ButchDeal]

Gotcha -- I'm still learning the terminology, grid-zero not-equals off-grid.

Grid zero just means not feeding power into the grid and is definitely not off grid.

I think POCO means POwerCOmpany, but only 90% sure .

PoCo is Power Company, yes

I wouldn't get the Austin Energy rebate for such an install, not _sure_ if I would qualify for federal tax credit (probably would)... and of course I would prefer a larger system for personal satisfaction (carbon offset) even if it's not 100% optimal financially. But it's a good point / option for others in the same scenario.

Yes you would still qualify for the Federal Tax Credit

Does that suggest that if Austin Energy changed their policies at some point in the future, whatever system I install (lets say SolarEdge HD Wave inverter) could be reconfigured, perhaps with the addition of the SolarEdge consumption meter box, to allow self-consumption before the meter, but also supplement from the grid when production is not sufficient and feed back to the grid when production is too high?

In a grid zero situation, the inverter would TRY to provide all the power that the house is using and no more. There is no physical limitation on the power just the electronics trying to regulate the inverter such that the consumption is zero. IF you are consuming more than the inverter can produce, it will come from the grid.

If the PoCo changes their policy it is just a software configuration change to the inverter to allow it to net meter as regular though it would require a net meter application (documents) with the PoCo.

[Ampster]

Does my HD Wave inverter have a setting for self consumption? I thought it only worked in Grid Tie mode? I know my Outback inverter can be configured for Grid Zero (self consumption)

[ButchDeal]

Does my HD Wave inverter have a setting for self consumption? I thought it only worked in Grid Tie mode? I know my Outback inverter can be configured for Grid Zero (self consumption)

yes if you have a consumption meter configured.

https://www.solaredge.com/sites/default/files/feed-in_limitation_application_note.pdf

[evolknuj]

yes if you have a consumption meter configured.

https://www.solaredge.com/sites/defa...ation_note.pdf

Yeah, I'd found that document before and was hoping I could do exactly what was shown in Figure 1 with my POCO -- import and export still, as needed, but self consume as much as possible with the POCO meter completely unaware (not that I'm trying to "trick" the meter or bypass it or something, I just want to be able consume what I produce without being charged extra for it). Seems Austin Energy doesn't want me to do that.

[ButchDeal]

Yeah, I'd found that document before and was hoping I could do exactly what was shown in Figure 1 with my POCO -- import and export still, as needed, but self consume as much as possible with the POCO meter completely unaware (not that I'm trying to "trick" the meter or bypass it or something, I just want to be able consume what I produce without being charged extra for it). Seems Austin Energy doesn't want me to do that.

Figure one is a general Net Meter configuration with the addition of a consumption meter.

you can do it but can not export without a net metering agreement.