Utility priority output Vs SUB Vs Grid Shaving Vs Blending Vs AC coupling

[doc3g]

I am still trying to understand these terms and their meaning in real-world applications.

1. Utility priority output - Saw this in an ad for a SunGoldPower SPH6548P ("6.5KW 48V Split phase solar inverter). The description says: " Utility at first priority, utility and solar provide power to load at the same time when solar is available, battery will provide power to load only when utility power is not available. (Priority: Utility>Solar>Battery)"
- This sort of setup seems ideal for what I would like to do, and at around $1200, it is budget-friendly. However, the reviews for this unit and Sun Gold Power in general are not very good. Are there similar units from other companies that are more reliable? (Yes, I'm sure the EG4 18K fits the bill but at $5k it is not a viable option)

2. SUB - It seems like this setting stands for Solar-Utility-Battery and, in theory, would blend power from sources in that order to meet the load demand? I've seen this on some lesser known units in the Sub $1200 range, but most units instead seem to only offer SBU priority

3. Grid Shaving - Sounds like this operates similarly to an SUB scenario except that maybe you can limit the total draw from the grid?

4. Blending - Trying to determine if this term is an appropriate search term to help identify units that will power a load with some mix of PV/Grid as opposed to all PV or all grid.

5. AC coupling - Seems like this term may be analogous to blending?

Thanks!

 

[BentleyJ]

These are confusing issues and terminology, seemingly getting more complex as the feature sets are starting to get blended in various ways among the Brands.

I find it helpful to think of inverters being broken into 2 main categories.
1) OFF-GRID: These products operate in one mode or the other, Either Passing-Through utility power to the load (breaker panel) and can charge batteries from grid if desired. OR the Inverter disconnects from the Grid and uses available Solar and Battery to power loads until there is insufficient solar or battery then they can automatically switch back to Pass-Through.
2) GRID-INTERACTIVE: (Hybrid) These products can operate in tandem (parallel) with the Grid because they are more sophisticated and can sync to grid voltage and frequency. These can also take excess solar, and sell back to the grid under a utility agreement.

Both types can accomplish Load Shaving during peak electrical rate times of the day. However, Grid-Interactive types (UL1741SB) can make a more seamless transition between modes because they can sync then start blending power smoothly, not just make an abrupt transition.

All-In-One is a term that can apply to both types of Inverter and in simple terms just means there is 1 or more MPPT Charge Controllers built in and maybe a Gen Input as well.

AC Coupling in the past has been a feature reserved for higher priced products that allows strictly Grid-Tie inverters to sell back to the grid through the Hybrid inverter and the inverter can modulate or shut off grid-tie inverters as needed in a outage. Although now the EG4 6000XP seems to have an AC Coupling option. Not sure exact;y what that means since its an Off-Grid Inverter.

 

[zanydroid]

2. SUB - It seems like this setting stands for Solar-Utility-Battery and, in theory, would blend power from sources in that order to meet the load demand? I've seen this on some lesser known units in the Sub $1200 range, but most units instead seem to only offer SBU priority

SUB = blend grid with solar = you will get a nasty letter from your utility. That’s why SBU is preferred

Same with grid shaving

You need to either confirm that your utility does not do detection of unsanctioned parallel interconnect, or do grid shaving with double conversion. Ie putting a chargeverter between grid and inverter.

Or take the savings from not buying a hybrid legal to interconnect, and buy more batteries/off grid inverters to cover your full load

EDIT: In other words, the reason SUB and grid boost/grid assist is becoming less common, is because of increased detection and enforcement against pirate parallel setups.

5. AC coupling - Seems like this term may be analogous to blending?

This is SUPPOSED to mean that it can form a microgrid that can activate and charge from grid tie inverters. Sometimes the manufacturers are misleading about it.

 

[zanydroid]

Although now the EG4 6000XP seems to have an AC Coupling option. Not sure exact;y what that means since its an Off-Grid Inverter.

I believe it can activate GTIs when grid down. But I don’t believe it has the hardware/software to leave them activated/charge from them when the grid is up. Which kind of sucks since the Conext SW can do this.

 

[doc3g]

SUB = blend grid with solar = you will get a nasty letter from your utility. That’s why SBU is preferred

Same with grid shaving

You need to either confirm that your utility does not do detection of unsanctioned parallel interconnect, or do grid shaving with double conversion. Ie putting a chargeverter between grid and inverter.

Or take the savings from not buying a hybrid legal to interconnect, and buy more batteries/off grid inverters to cover your full load

EDIT: In other words, the reason SUB and grid boost/grid assist is becoming less common, is because of increased detection and enforcement against pirate parallel setups.


This is SUPPOSED to mean that it can form a microgrid that can activate and charge from grid tie inverters. Sometimes the manufacturers are misleading about it.

I have an Oncor FOCUS AXR platform that logs received kWh, so I'm sure they would notice. I'm honestly a little perplexed that there isn't an inverter that has an AC in connection that is one way (ie, only allows current in, but not to back feed), but perhaps that is what you are saying the chargeverter does? I looked at the EG4 chargeverter and it seemed more to do with charging the battery than preventing backfeed to the main panel.

 

[zanydroid]

I have an Oncor FOCUS AXR platform that logs received kWh, so I'm sure they would notice. I'm honestly a little perplexed that there isn't an inverter that has an AC in connection that is one way (ie, only allows current in, but not to back feed), but perhaps that is what you are saying the chargeverter does? I looked at the EG4 chargeverter and it seemed more to do with charging the battery than preventing backfeed to the main panel.

There is no such thing as an “AC diode” AFAIK. Or if there is one, it suspiciously would look a lot like a modern rectifier, which is 1/3 of the way to a charger

Current in only is more complex than you might think. AC means alternating current, so there is negative current flow combined with negative voltage to provide positive power at all times.

The Chargeverter indeed is about charging the battery. But it is strictly a utilization equipment and not a utilization+generation (as a SUB or hybrid AIO are). So you can replenish your battery/feed the inverter from grid with no chance to backfeed

So all the grid sees is a regular load.

 

[zanydroid]

What is your target load size/application/performance goals?

Maybe getting a 6000XP class AIO is good enough.

Do you have net metering with the utility?

 

[doc3g]

What is your target load size/application/performance goals?

Maybe getting a 6000XP class AIO is good enough.

Do you have net metering with the utility?

I do not have any agreement with the utility. I don't necessarily have a target load/application/performance goal, other than, I don't want to spend $20K on solar because the ROI is far too long. I live in Texas on a little 1 acre lot in a nice neighborhood with no HOA and have ~ 5kW of PV that I would like to set up. I got a decent deal on the panels ($0.25w for new panels w/ warranty) and would like to offset my power bill in a way that makes sense (an ROI of a few years instead of decades).

I was under the impression that a small unit like the EG4 3K unit would be a feasible setup with a small subpanel that had my house lights (all LED), fridge, and maybe an outlet for my fish tanks and TV/compact media PC. I was thinking that during the day, these items could be easily powered by the PV I have, and as the sun went down, the inverter would then power the subpanel by passing current through from a new circuit from the mains to the inverter. With a modest battery attached, I would have some backup for those circuits (mostly just the lights) when the grid was down, which typically is never more than a couple of hours.

However, the idea of paying for permits and inspections, a net metering agreement, and the latest UL-listed inverter seems to make the whole concept seem like just another expensive hobby rather than a sound energy investment (such as adding insulation or updating inefficient appliances). I am currently paying about 15 cents per kWh and use 80kWh per day on avg.

It appears that the closest option may be something like the 6000xp + a 48v 100AH LiFe battery, which would allow me to harvest and use most of what would be available. I get an avg of 5.43 peak sun hrs per day. Using 80% of 5k = 4kW x 5.43 --> 21.72 kWhs on avg per day. I'm honestly not sure how to factor in the crappy days when it is overcast or whatever, unless that is factored into the peak sun calculations already?.

Anyway, in an optimal year, 22 kWh per day x 365 = 8,030 kWh. 8,030 x .15 cents per kWh = ~$1200 projected savings in a year. Am I missing something here?

Otherwise, if my startup cost is:
$1450 (EG4 6000XP w/ discounts + tax)
$1350 (EG4 LL 48V 100AH w/ discounts + tax)
$1250 (Panel cost)
+ ground mount (I'll build myself)
= $4K and some change, which puts ROI at somewhere around 4 yrs.

Does that sound realistic?

 

[zanydroid]

Anyway, in an optimal year, 22 kWh per day x 365 = 8,030 kWh. 8,030 x .15 cents per kWh = ~$1200 projected savings in a year. Am I missing something here?

Sun hour average is tricky because it’s more of a net metering oriented calculation. If you have net metering at 1:1, the grid effectively acts as a super battery (that can shift production across seasons), and it’s easy for permits and plans to be cheaper than batteries. I don’t think Texas guarantees that long term.

Without net metering you have to worry about when the power is generated. Use it or lose it.

Use PVwatts to calculate for different months and see if you can consume all of it. In the summer , if you have a big AC bill (which I think is possible in Texas) it is definitely possible, but it can be challenging to drive an AC with an entry level AIO.

Otherwise, if my startup cost is:
$1450 (EG4 6000XP w/ discounts + tax)
$1350 (EG4 LL 48V 100AH w/ discounts + tax)
$1250 (Panel cost)
+ ground mount (I'll build myself)
= $4K and some change, which puts ROI at somewhere around 4 yrs.

With a 5kwh battery and 22kWh daily production you need to use most of the production in real time, otherwise you will quickly saturate the battery and throw away the solar. I am not familiar with how to calculate smaller battery

Hopefully you can still get 30% tax credit, that will chop off another year.

 

[doc3g]

Sun hour average is tricky because it’s more of a net metering oriented calculation. If you have net metering at 1:1, the grid effectively acts as a super battery (that can shift production across seasons), and it’s easy for permits and plans to be cheaper than batteries. I don’t think Texas guarantees that long term.

Without net metering you have to worry about when the power is generated. Use it or lose it.

Use PVwatts to calculate for different months and see if you can consume all of it. In the summer , if you have a big AC bill (which I think is possible in Texas) it is definitely possible, but it can be challenging to drive an AC with an entry level AIO.



With a 5kwh battery and 22kWh daily production you need to use most of the production in real time, otherwise you will quickly saturate the battery and throw away the solar. I am not familiar with how to calculate smaller battery

Hopefully you can still get 30% tax credit, that will chop off another year.

Sounds like I need to nail down some hard numbers on what amount of power I'm using and when. I have a 2 ton unit (2 yrs old) and for most of the peak sun hours during 9-10 months of the year it is running. It is mid November and I've turned the heat on twice and only overnight and typically have to turn AC back on during the day. Hence, if I could parallel with the grid I could likely use everything I produce in a given day. I'm learning more about the chargeverter setup so it's something I'm considering too.

 

[zanydroid]

Sounds like I need to nail down some hard numbers on what amount of power I'm using and when. I have a 2 ton unit (2 yrs old) and for most of the peak sun hours during 9-10 months of the year it is running. It is mid November and I've turned the heat on twice and only overnight and typically have to turn AC back on during the day. Hence, if I could parallel with the grid I could likely use everything I produce in a given day. I'm learning more about the chargeverter setup so it's something I'm considering too.

Is it an inverter unit or non-inverter unit? Inverter unit is easier b/c it doesn't need soft start.

You should install an Emporia or similar energy meter and check the average power utilization. You can also get a clamp meter with surge measurement to see how hard it might be to start.

Non inverter either translates to inverter with good surge (which also requires battery that can feed without BMS shutdown), extra inverters, or adding soft start. Or using a grid assist setup so that the grid can eat the surge.

 

[doc3g]

I'm guessing it is a non-inverter because I'm looking at the manual, and one of the available accessories listed is a "compressor start assist." I was also off on the tonnage; it's 4 tons and 14 seer. Some ratings that are probably useful:

Minimum circuit amps: 25.9A
Max fuse: 40A
power supply: 208-230 VAC

Again, I think grid assist or "parallelling with the grid" would be ideal but I need to figure out what sort of red tape fiasco it would take to get an agreement with Oncor. I'd also be OK with just putting some lights into a subpanel and maybe an outlet. I'm also not 100% sure we will be living here in another 3 years, though I will likely keep this house as a rental property, so I'm trying to be mindful about either putting in something that is easy to take down or at least something that is relatively low maintenance.

I have a clamp meter but I'm going to look into the Emporia or similar.

Thanks for all the help btw!