Using rooftop grid-tie solar during a power outage.

[zacksc]

I have a small system that consists of eight rooftop mounted 250 Watt solar panels with individual enphase micro inverters. Generally, when the power is on, that feeds into a PG&E electrical grid. I am planning to install new iq8 micro inverters, one for each panel. I believe the connection between each panel and its micro inverter is MC4. I am thinking of putting a splitter between the panel and the micro inverter for one of the panels to provide a way for me to access some dc power directly from a single panel during a power outage. During normal operation the 2nd unused end of the splitter would be terminated in a safe way protected from moisture or contact. During a power outage I can connect to that via an XT60 or something like that and use that to charge a Jackery or a LiFePO4 battery (via a dc-dc converter or MPPT interface). What do you think? Any advice or help is most welcome. I would be very interested to hear of perils and pitfalls with what I am thinking about.

 

[harrisonpatm]

I have a small system that consists of eight rooftop mounted 250 Watt solar panels with individual enphase micro inverters. Generally, when the power is on, that feeds into a PG&E electrical grid. I am planning to install new iq8 micro inverters, one for each panel. I believe the connection between each panel and its micro inverter is MC4. I am thinking of putting a splitter between the panel and the micro inverter for one of the panels to provide a way for me to access some dc power directly from a single panel during a power outage. During normal operation the 2nd unused end of the splitter would be terminated in a safe way protected from moisture or contact. During a power outage I can connect to that via an XT60 or something like that and use that to charge a Jackery or a LiFePO4 battery (via a dc-dc converter or MPPT interface). What do you think? Any advice or help is most welcome. I would be very interested to hear of perils and pitfalls with what I am thinking about.

In addition to a splitter between the panel and inverter, you would also need some sort of a switch; you will want current to go to the inverter or your off-grid setup, but not both.

Your problem, should you choose to take it on, is that what you're planning is almost certainly not going to be "up to code." Since you have a grid-tie system, I can assume that it was inspected at one point, and if so, any modifications to make to it will be something your house insurance provider may want to know about. Or not. Up to you.

 

[offGridDownUnder]

Generally, when the power is on, that feeds into a PG&E electrical grid.

So, your system puts out mains-level power?

What is the physical connection at the output, where it is supplied to PG&E? Is there an option to physically disconnect it and then connect it for local use?

I can't speak to the legal, insurance, or practical issues - outside my jurisdiction - but that seems like an interesting avenue to explore.

 

[harrisonpatm]

So, your system puts out mains-level power?

What is the physical connection at the output, where it is supplied to PG&E? Is there an option to physically disconnect it and then connect it for local use?

I can't speak to the legal, insurance, or practical issues - outside my jurisdiction - but that seems like an interesting avenue to explore.

I believe OP is suggesting putting some sort of splitter between the panel and the inverter, before it goes to the grid. Thus, he's after the panel's DC voltage, anywhere between 30-60 volts depending on the panel.

 

[A-DamW]

Aside from insurance and regulatory inspection, you should be able to tap into the DC of one panel just fine.

About the only thing I can think of to watch out for would be when the AC power comes back on, the grid tie inverter and whatever you have hooked up to the panel DC might oscillate a bit trying to find MPPT, but once the power is on you can disconnect from DC anyway.

 

[offGridDownUnder]

Thus, he's after the panel's DC voltage, anywhere between 30-60 volts depending on the panel.

Without knowing too much myself, in case there might be some roadblock that makes direct impractical perhaps this can be an option.

 

[Chalo]

I'm setting up 24V DC solar arrays at my place, so the grid (and city code) don't interact with them at all. Also that way I don't need to put panels in series and make sure they're all unshaded.

 

[zacksc]

I believe OP is suggesting putting some sort of splitter between the panel and the inverter, before it goes to the grid. Thus, he's after the panel's DC voltage, anywhere between 30-60 volts depending on the panel.

Yes, exactly.

 

[zacksc]

Aside from insurance and regulatory inspection, you should be able to tap into the DC of one panel just fine.

About the only thing I can think of to watch out for would be when the AC power comes back on, the grid tie inverter and whatever you have hooked up to the panel DC might oscillate a bit trying to find MPPT, but once the power is on you can disconnect from DC anyway.

Thanks. When the power goes off I can turn off the main breaker at the panel. That will prevent the microinverters from turning back on while I am tapping into dc power. (Is it a good idea to turn off each individual breaker as well when I do that and then turn them back on one by one? Is that the best practice?)

Although if the micro inverters did turn back on while I was drawing dc power from one panel, I believe that the system would just think that one panel is not working well, exhibiting low voltage. Maybe not that different from if it was in the shade or covered with leaves. I'm not sure, but that would be my guess? (Or maybe it could oscillate? I'm not sure how the MPPT aspect (of the micro inverter) would respond to this situation.

PS. I am thinking that for the dc charging I might use, for example, a Victron Phoenix dc-dc converter that accepts 20 to 40 volt input and puts out 14.2 volts during bulk charging... I will have to research that. I'm not sure what they have or what the exact voltage range of my panel is.

 

[harrisonpatm]

Thanks. When the power goes off I can turn off the main breaker at the panel. That will prevent the microinverters from turning back on while I am tapping into dc power. (Is it a good idea to turn off each individual breaker as well when I do that and then turn them back on one by one? Is that the best practice?)

Although if the micro inverters did turn back on while I was drawing dc power from one panel, I believe that the system would just think that one panel is not working well, exhibiting low voltage. Maybe not that different from if it was in the shade or covered with leaves. I'm not sure, but that would be my guess? (Or maybe it could oscillate? I'm not sure how the MPPT aspect (of the micro inverter) would respond to this situation.

PS. I am thinking that for the dc charging I might use, for example, a Victron Phoenix dc-dc converter that accepts 20 to 40 volt input and puts out 14.2 volts during bulk charging... I will have to research that. I'm not sure what they have or what the exact voltage range of my panel is.

This all sounds good and correct. If you end up going this route, please do share how you decided to switch the panels, I'd be interested to see it.

 

[harrisonpatm]

I'm setting up 24V DC solar arrays at my place, so the grid (and city code) don't interact with them at all. Also that way I don't need to put panels in series and make sure they're all unshaded.

This is the way, I've done the same with 5000w of solar at my house.

 

[d8veh]

These are pretty good if you have somewhere to put it. I have one, and it works perfectly. You can charge it from solar, a generator or the grid. It has 15kwh stored in the battery:

https://vi.aliexpress.com/item/1005007602765814.html?spm=a2g0o.order_list.order_list_main.225.63f11802IXga1U&gatewayAdapt=glo2vnm

 

[ZeroEm]

Think on this issue all the time. One thought would be to unplug a panel from the microinverter and plug it into your other inverter. This would not alter the installed setup. If you have a lot of outages then just get another panel.

I'm just now reading up on microinverters. It seems like a lot to learn but i'm sure later will be a cake walk.
Enphase has a school for more than the basic installs like backup and other setups.

Currently wanting the grid tie, microinverters like you have as our blackouts are not that many yet. Also want back up power. Thinking of a second system, back up. Few panels and some batteries and off grid inverter. for the Refrigerator, radio, cell phone charging. This would change with the times.

That would be one way to have the grid tie and stay in code. Could mess with the second system as much as I wanted.

 

[fechter]

I have the smallest Enphase backup battery system (3kwh). If the power goes out during the day, I can get the full power from all my panels in addition to what the little inverter on the battery makes. I also have their transfer switch which automatically takes selected house circuits and puts them on the backup. Expensive, but really handy when the power goes out. The 3kwh battery can run my refrigerator for about 24 hours.

 

[ZeroEm]

I have the smallest Enphase backup battery system (3kwh). If the power goes out during the day, I can get the full power from all my panels in addition to what the little inverter on the battery makes. I also have their transfer switch which automatically takes selected house circuits and puts them on the backup. Expensive, but really handy when the power goes out. The 3kwh battery can run my refrigerator for about 24 hours.

Refrigerator is my biggest worry when power goes out. Tested my Refrigerator just over a 1kw in 24hrs with a cool house. Hot house who knows. Enphase looks to be a good microinverter. Don't like having to pay to get your data off the cloud. The DC part is of interest to me for the DC refrigerator and freezers. Then the inverter refrigerators that are costly.

 

[ZeroEm]

I'm setting up 24V DC solar arrays at my place, so the grid (and city code) don't interact with them at all. Also that way I don't need to put panels in series and make sure they're all unshaded.

Getting started learning all about solar. Not in general but the rules regulations here in SanAntonio, Bexar Co and Texas. In the next few years will pay to have solar installed on the house. In the mean time want to play with it on the Garage, that is separate from the house. So Chalo how much are you doing and what do you plan to do with it?

 

[ZeroEm]

This is the way, I've done the same with 5000w of solar at my house.

Are you at 24v or move up to 48v at 5000w. Lot of questions.

 

[harrisonpatm]

Are you at 24v or move up to 48v at 5000w. Lot of questions.

48v

 

[Chalo]

Getting started learning all about solar. Not in general but the rules regulations here in SanAntonio, Bexar Co and Texas. In the next few years will pay to have solar installed on the house. In the mean time want to play with it on the Garage, that is separate from the house. So Chalo how much are you doing and what do you plan to do with it?

This installation will be for lighting, device charging, and running small appliances and power tools. It's to serve needs on my lot in advance of building anything on it.

I'm only installing a rated 1500W of panels (roughly 10 x 10 feet) that deliver ~30V at max power, and using them with a cheapy-cheap 24V charge controller and a 24V automotive inverter. I have 3.6kWh of 24V LFP packs and all the plugs and terminals to connect them. I haven't yet built the shade structure to hold the panels, nor have I acquired the cables because I'm not sure where the components will sit yet.

 

[ZeroEm]

I'm twisting my self in knots trying to decide between 24V and 48V for every pro I find a con. Don't want more battery than useful, Just a few black out's here every year. Guess can go 24V and later double the bank size and go in series to 48V. Have a garage/pool table room in the back, would like to power it with solar. Leave it hot most of the summer as don't want to run up the electric bill. If I add batteries out there may need to heat it in the winter. No gas out there.

 

[Chalo]

I'm twisting my self in knots trying to decide between 24V and 48V for every pro I find a con. Don't want more battery than useful, Just a few black out's here every year. Guess can go 24V and later double the bank size and go in series to 48V.

I chose 24V because I got a good deal on 24V batteries whose BMS won't tolerate 48V open circuit voltage. But also, charge controllers, inverters, and DC powered devices are cheaper and more widely available for 24V, which is a common operating voltage for trucks. I'm only about $600 in, and all I have to buy now is lots of cable and MC4 connectors and an inverter.

 

[harrisonpatm]

Lots of pros and cons, but one of the biggest reasons for my choice of 48v was wire gauge. Same wattage can get by with wires/cables half as thick as what you would use on 24v. Plus, better efficiency at higher voltage when it comes to wire lengths. I do several different runs around and through my house, and 48v is better for that kind of thing than 24, so its worth it for me.

I have a 2000w inverter for a few things, but most of my solar powered stuff in my house is direct DC, via various different buck converters. 12v for phone chargers, LED lights, computer charging, modem and router. 5v for USB outlets here and there. 12v for my 18650 testing equipment. 24v for my 3d printer. I keep DC-AC-DC conversion to a minimum. Also, I like that it's so modular. No one piece of equipment gets stressed or used too much, and if something breaks or dies or needs an upgrade, I've got plenty of backups or other options. XT60 connectors for everything.

 

[offGridDownUnder]

Refrigerator is my biggest worry when power goes out.

May not be relevant to your situation...

• How much capacity do you actually need/use?
• Could you switch to a top-loading RV refrigerator? Avoids dumping cold air every time it's opened.
• Can you fill it half with water jugs (may be useful if you already have a large refrigerator)? Keeps "cold" in when the door is opened, and when the power goes out.
• Can you use a freezer instead? These are more likely to be top-loading and the water jug approach is very applicable.

An accommodation I'm trialing - sprouting for my greens, that is, for my vitamins and fresh enzymes. Much fruit can store at room temperature, or at least without refrigeration, as can some vegetables - potatoes, uncut squash. Beans can sprout.

If you're only designing for a "normal", first-world lifestyle, these might not be relevant questions. I'm inverting the question - I'm rather working out how to live a first-world lifestyle without first-world support.

 

[ZeroEm]

May not be relevant to your situation...

• How much capacity do you actually need/use?
• Could you switch to a top-loading RV refrigerator? Avoids dumping cold air every time it's opened.
• Can you fill it half with water jugs (may be useful if you already have a large refrigerator)? Keeps "cold" in when the door is opened, and when the power goes out.
• Can you use a freezer instead? These are more likely to be top-loading and the water jug approach is very applicable.

An accommodation I'm trialing - sprouting for my greens, that is, for my vitamins and fresh enzymes. Much fruit can store at room temperature, or at least without refrigeration, as can some vegetables - potatoes, uncut squash. Beans can sprout.

If you're only designing for a "normal", first-world lifestyle, these might not be relevant questions. I'm inverting the question - I'm rather working out how to live a first-world lifestyle without first-world support.

Know what you are talking. Started looking in to low energy usage before wanting to go green. Worked out of town for over five years during that time Gasoline in South Carolina was around $5 a Gallon. The trip home was 500 miles. Started living in my Van on weekends to avoid the cost. Living out of that van introduced me to inverters and others that live off the grid.
There is top loaded freezer/refrigerator that run on DC. Think about them, even top loaded AC unit would save on power.

Now i'm disabled and still want to keep cost down. The new tv's LCD save on cooling, not producing the heat the old style did.

 

[Papa]

one of the biggest reasons for my choice of 48v was wire gauge. Same wattage can get by with wires/cables half as thick as what you would use on 24v.

Yes, but there's more. I started collecting components 13-14 years ago, after calculating my minimum load requirements. Yes, 48v requires more batteries, but the overall efficiency of the system, as a whole, is better - especially my inverter choice. I bit the bullet and opted for a Victron Phoenix 48/1200, and at the time, the only place that had one was a marine retailer. Not 24 hrs after ordering, the salesman called me to confirm the 48v choice, because he said he need to order it and wanted to be sure it's what I wanted. Last year I also added a smaller 48/250 Victron inverter for smaller chores such as chargers for my cordless Makita's and cordless Ego weed trimmer. Nearly everything else is on DC.

I gave much consideration to my initial load requirements. I wanted a small microwave, a 1100W induction cooktop, and a 450W AC unit. No two appliances are running at the same time, of course. The Victron handles all of those, but does occasionally trip feeding the microwave if I run it too long.

I was on FLA's until last year when I replace them with lithium. I went through 3 sets of four FLA's over the course of 14 years - good riddens!!

I'm still on my original set of ten 100W Grape PV's - six in series W/two paralleled, all feeding a Victron 150/35 MPPT controller. Last year I added another series string of smaller 50W PV's which gives me around 1.2kW total. I prefer 20v nominal panels because it gives the option of pulling lower voltages (from a single PV) through a cheapy PWM controller for charging things like tractor batteries. My initial plan was to have enough solar to be able to cook lunch, and not consume any watts from the batteries.