Switch between grid and off grid system in same house

[Elik]

i am thinking about installing a small off grid system in the same house as we have a grid, and then have a switch where I can choose to draw from solar or from grid.

 

I see an automatic switch on Lazard’s (ATS Automatic Dual Power Transfer Switch 2P ) that will automatically switch when the batteries turn off.

 

Amorn solar has a battery kit for 19000 THB, get a second panel your out 22 k, and earning 2 kWh pr day, so you looking at a pay back time of about 2000 days. Not too bad, and you have a little emergency power in case of power out.

 

I do have a couple of questions I hope the forum can answer

 

I rent the house and don’t want to deal with MEA, and I don’t want to break the law or electrocute a lineman for 10 THB pr day. Does the switch legally and assuredly works as a off-grid system??

 

I have a small UPS so I won’t get interrupted during the switch, but can a UPS handle if the sinus waves from the grid don’t match with the ups sinus.??

 

[patman30]

you want an "on-grid" solar inverter

the inverter takes care of switching between power sources

you can also choose to feed power back to the grid or not with most inverters
(not, in your case)

as not your property and speaking in terms of savings
you can skip the battery saving you money
and just have the solar during daylight hours
batteries are expensive, you also have to oversize the battery if you want it to last longer

[Elik]

For a grid tie system I need an installed package, and that is way more expensive.

[Crossy]

2 hours ago, Elik said:

For a grid tie system I need an installed package, and that is way more expensive.

 

For tiny systems many don't bother and just DIY.

 

Just ensure that you never go into net-export and that the meter man doesn't see the meter going backwards (assuming you have a conventional disc type meter, electronic meters are a different animal).

[Elik]

I could DIY by simply plugging an inverter into a wall socket, but I don’t to want break the law to save 10 thb pr day, and how certain can I be that those cheap inverters will disconnect in case of power out.

 

The only way I see where can get decent pay off and backup power is with the one I first discribe. I am just not sure if it legal and safe.

[Crossy]

If you want backup power then your original idea will do the trick.

 

If your inverter has no grid connection at all then using an ATS as you describe is the way to go, installing an ATS does not require any approval from PEA etc. and if done correctly you can never (try to) power the grid from your inverter.

 

Many "off grid" inverters do have a mains input so they can charge the batteries or power the load from the mains if there's no sun and the batteries are dead. These units cannot export. To the outside world they look like a battery charger, again perfectly legal to install. There is an advantage with going this way as the inverter itself provides the ATS facility.

 

 

On grid-tie inverters. I've never come across a domestic grid-tie inverter that does not implement island-protection to prevent back-feeding into a dead grid. It's easy enough to verify that your unit behaves as expected. Connect your inverter (with panels of course) to an outlet via a power strip and plug a small lamp into another outlet on the power strip. Pull the plug from the wall outlet. The lamp should extinguish. Easy ???? 

[MJCM]

8 hours ago, Elik said:

I could DIY by simply plugging an inverter into a wall socket, but I don’t to want break the law to save 10 thb pr day, and how certain can I be that those cheap inverters will disconnect in case of power out.

I guess 90% of the people who are using ON-Grid inverters are Feeding back into the Grid and thus spinning their PEA meter backwards.

 

One member forgot to turn off his Export and the Meter Guy showed up to read the meter and saw the meter spinning backwards and the only consequence for the member was that PEA replaced his meter to a NON Back spinning Meter.

 

I have a GTI that is connected to the grid and it's spinning back my meter, and I did the test which @Crossy described in his previous post and the GTI stopped "producing" and showing 0 V from the Grid, in which it normally shows what the grid is delivering.

 

Note, what I am doing is only to cover our DAY-Time use, but some days the GTI produces so much (and we are not using a lot of energy during the day) that I am using approx 1 Unit only from the PEA from 17:30-6:30am (<- time when the GTI isn't producing)

 

Edit: 2 tips when starting with GTI's

 

1- Don't let the Meter reader see that the Meter is spinning backwards

 

2- VERY important as well, don't go into negative territory, what I mean by that, suppose this month the bill says under "Current reading" 8505 units (example), don't let it go under that reading the following month. I am aiming (read told to by SWMBO) that we must use approx 130-140 units per month from PEA , which means at a certain point in time in the month I have to turn the GTI off.

[JAS21]

4 hours ago, MJCM said:

I guess 90% of the people who are using ON-Grid inverters are Feeding back into the Grid and thus spinning their PEA meter backwards.

 

One member forgot to turn off his Export and the Meter Guy showed up to read the meter and saw the meter spinning backwards and the only consequence for the member was that PEA replaced his meter to a NON Back spinning Meter.

 

I have a GTI that is connected to the grid and it's spinning back my meter, and I did the test which @Crossy described in his previous post and the GTI stopped "producing" and showing 0 V from the Grid, in which it normally shows what the grid is delivering.

 

Note, what I am doing is only to cover our DAY-Time use, but some days the GTI produces so much (and we are not using a lot of energy during the day) that I am using approx 1 Unit only from the PEA from 17:30-6:30am (<- time when the GTI isn't producing)

 

Edit: 2 tips when starting with GTI's

 

1- Don't let the Meter reader see that the Meter is spinning backwards

 

2- VERY important as well, don't go into negative territory, what I mean by that, suppose this month the bill says under "Current reading" 8505 units (example), don't let it go under that reading the following month. I am aiming (read told to by SWMBO) that we must use approx 130-140 units per month from PEA , which means at a certain point in time in the month I have to turn the GTI off.

If you were to be given a ‘no export’ meter…how many units (kwh’s) do you think you would have to pay for in one month?

 

 

[Elik]

12 hours ago, Crossy said:

 

Many "off grid" inverters do have a mains input so they can charge the batteries or power the load from the mains if there's no sun and the batteries are dead. These units cannot export. To the outside world they look like a battery charger, again perfectly legal to install. There is an advantage with going this way as the inverter itself provides the ATS facility.

 

Yes! That’s what I want. Can you recommend a small one?

 

regarding being sure it works to cut grid power, it’s one thing to have a new one work, but how about after 15 years, or a gecko finds it’s way in there.

[MJCM]

11 hours ago, JAS21 said:

If you were to be given a ‘no export’ meter…how many units (kwh’s) do you think you would have to pay for in one month?

 

 

Oooh difficult question to answer. My guess is around 150 and when I leave the GTI on all the time definitely under the 100. Estimate now till meter reader comes middle of next month is 105.

[007 RED]

On 10/23/2022 at 7:37 PM, JAS21 said:

If you were to be given a ‘no export’ meter…how many units (kwh’s) do you think you would have to pay for in one month?

An interesting question.   I think it’s not “if”, but “when”.  That said, as TIT the “when” could be any time from tomorrow or sometime in the next millennium.  Who knows?

 

My small scale system (4 x 415 W panels connected to a 2.2kW GTI) in theory should be capable of producing 1.66kW under laboratory conditions.  However, given that we are living in the real world, the system is more likely to produce about 1.2kW under good sunshine and assuming 6 hours of decent sunshine a day, the system should be capable of producing around 7 units a day ????.

 

Although we have a range of household appliances, including a couple of air conditioning units, my wife and I are somewhat conservative electricity users.  Prior to installing the solar system, PEA billing records for the previous 2 years indicated that we were using on average 10 units/day.  So when I designed the system, I did so with the objective of the system being capable of producing a maximum of 75%, or 7 units/day, in order to avoid any risk of producing negative meter readings.

 

The graphs below for the current billing period shows that our small scale system is currently producing 65% of our needs, leaving us to purchase 35% from the local PEA.

 

 

It should be noted that weather conditions this month have been mainly overcast with the occasional heavy downpour, hence the somewhat lower than hoped for production yield ????.

 

As I type this post, the monitoring facility is showing that the solar panels are producing 1.24kW and hence my meter is merrily whizzing around backwards due to the nice blue sky and nice bright sunshine ????.  Obviously if the meter were to be replaced with an electronic type thus preventing backwards spinning, I will not be able to ‘store’ my surplus power in the grid for use when the sunshine disappears behind a cloud.

 

I have noticed from the system’s monitoring facility that on the couple of days when my system is in the NO EXPORT mode prior to the meter reader coming, the system appears to almost keep ‘pace’ with our needs, except for short periods when we are using the shower heater, water pump or washing machine.

 

I envisage that if/when the PEA install an electronic meter, because we are relatively low electrical users, we will only need to purchase a few additional units a month and I may well then consider installing an additional solar panel to compensate for the loss of 'free' storage convenience. 

 

Due to the high costs associated with hybrid systems, and our low consumption, I have no plans to go down the ESS route.

[MJCM]

1 hour ago, 007 RED said:

and I may well then consider installing an additional solar panel to compensate for the loss of 'free' storage convenience. 

+1

 

But read this from a previous post by @Crossy in another topic about digital meters and MAYBE "log exported energy as chargeable"

 

after reading that it worried me a bit, but hey if they install a Digital meter for us and they charge us for export then next MONTH Export is OFF end of story! ????

 

 

[Danderman123]

On 10/22/2022 at 4:43 PM, Elik said:

I could DIY by simply plugging an inverter into a wall socket, but I don’t to want break the law to save 10 thb pr day, and how certain can I be that those cheap inverters will disconnect in case of power out.

 

The only way I see where can get decent pay off and backup power is with the one I first discribe. I am just not sure if it legal and safe.

A standard grid tie inverter requires AC power to operate. If the AC power fails, the inverter shuts down, same as your TV.

[Danderman123]

I have a very small solar system in my condo, sized so the meter won’t run backwards. It’s intended to reduce my electric bill, not eliminate it.

 

But, I do have a battery powerbank set up that charges constantly. If my AC mains fail (which often happens when it rains), I have a manual switch which diverts solar power to my off-grid inverter.  I can then manually connected my refrigerator and lights to the off-grid inverter for basic needs.

[Crossy]

On 10/23/2022 at 7:37 PM, JAS21 said:

If you were to be given a ‘no export’ meter…how many units (kwh’s) do you think you would have to pay for in one month?

 

I just did a quick and dirty calculation for our system of 10.6kWP of panels, 11kW of inverter, 5kWh ESS (actually bigger but I'm limiting usage to maintain UPS functionality).

 

Over a week that had 4 average days, 1 really good day, 2 crumby days.

 

Average export / re-import was 12.2kWh.

 

So, over a month that would be about 366kWh or 1,650 Baht which would be lost if we got a no-export meter and did nothing.

 

Adding 12-15kWh of (DIY) storage would be around 75k Baht so ROI on the ESS would work out at just under 4 years. If you went for commercial ESS units that would at least double and potentially enter the "not really worth it" area.

 

Also, note that on the "really good day" we exported/re-imported 21kWh a fair chunk of which would have been thrown away because a 15kWh ESS was full.