What would a standard for plugging solar panels directly into our homes look like?

[zanydroid]

You have a 15A breaker (1800W at 120V), and you plug in this inverter for 700W (6A more).
You now have 21A available to power a coffee maker and hair dryer on the same circuit. But the wire can't handle it.

Would work if PV backfed from far end of a wire, just like how we land the PV breaker at far end of breaker panel busbar.
But you likely have no idea how the various outlets and lights in your house are daisy-chained together.

That keeps the wire from overloading but the receptacle and appliance can still exceed. Imagine a power strip in the middle of the circuit, or even just a regular duplex receptacle. Easily sink 30A out of that.

In places like the UK with receptacle fusing it would be safer, possibly eliminating this issue. This OCPD essentially acts like the load breakers in the middle of the panel.

TBH this discussion needs to address how to safely backfeed to arbitrary branch circuits, there has only been 10% of the discussion spent on this…

 

[JoelE]

You have a 15A breaker (1800W at 120V), and you plug in this inverter for 700W (6A more).
You now have 21A available to power a coffee maker and hair dryer on the same circuit. But the wire can't handle it.

Would work if PV backfed from far end of a wire, just like how we land the PV breaker at far end of breaker panel busbar.
But you likely have no idea how the various outlets and lights in your house are daisy-chained together.

Are you saying if I have 15a at the end receptacles and I plug this into the first near the MSP, the overall load on the branch will hit 21a, but the 15a breaker will not flip? I thought once the current hit the breaker would flip, reminding me to go unplug the hairdryer I left running?

No I reread it - you are saying available current would be 21a. So current across breaker would still be under 15a… I see your point. But assuming your current use cases never trip your breakers and you don’t go crazy, seems like more benefit than risk?

 

[Hedges]

If you only have one 15A load, not a problem. But if you plug in excessive loads, say two 10A loads for 20A total, ordinarily it would trip the breaker. If you inject additional current from PV through an outlet, the circuit could supply 21A to loads without any breaker tripping (14A coming from grid + 6A from inverter.)

As Zany said, a power strip plugged into an outlet could also be overloaded even if PV was put at far end if circuit, so house wiring wasn't overloaded. Some power strips are rated at high as 15A, but many extension cords are not. It would be easy to overload an extension cord even with just the 15A grid breaker and no PV. As he said, if the strip had its on breaker then it would be protected. Some do.

 

[zanydroid]

I strongly suspect there is some part of Article 705 that prohibits combination of additional power source and loads on a branch circuit. And if there isn’t, there should be one, since it’s pretty easy to construct a bad situation.

 

[JoelE]

If you only have one 15A load, not a problem. But if you plug in excessive loads, say two 10A loads for 20A total, ordinarily it would trip the breaker. If you inject additional current from PV through an outlet, the circuit could supply 21A to loads without any breaker tripping (14A coming from grid + 6A from inverter.)

As Zany said, a power strip plugged into an outlet could also be overloaded even if PV was put at far end if circuit, so house wiring wasn't overloaded. Some power strips are rated at high as 15A, but many extension cords are not. It would be easy to overload an extension cord even with just the 15A grid breaker and no PV. As he said, if the strip had its on breaker then it would be protected. Some do.

It’s true that you could mess things up with this setup, but it’s also true that you can pretty easily figure out which breakers control which outlets and make a plan to not be dumb about it.

 

[zanydroid]

It’s true that you could mess things up with this setup, but it’s also true that you can pretty easily figure out which breakers control which outlets and make a plan to not be dumb about it.

But the inherent safety level without remembering a bunch of random stuff is significantly lower than the typical level for a code compliant setup. Surprising deviations = annoying and unsafe. Seems unnecessarily unprofessional and janky when you can just add a dedicated branch circuit on a subpanel and obviate the risk. Installing the correct backfeed is a one time investment.

 

[JoelE]

I strongly suspect there is some part of Article 705 that prohibits combination of additional power source and loads on a branch circuit. And if there isn’t, there should be one, since it’s pretty easy to construct a bad situation.

Some states have laws against backfeeding generators to the grid, but that’s because people were feeding downed power lines and putting folks in danger and then refusing to unplug their generators. Only danger with a small home standalone solar setup is to your own house and self, assuming it’s got islanding and isn’t in the way of emergency access.

 

[DIYrich]

The rules are designed to protect the person who knows nothing. "I plugged it in to save money. I had no idea I was overloading the wire - by the way, what wire? I don't see any wire", or "one is good, two is better."

 

[svfalkor]

Hm, not sure about the US but in Germany these devices can be bought and used legally. They are called Balkonkraftwerk (balcony power plant).
They consist of a solar panel, inverter and plug. They are limited in max power and you need to register them. See for example on Amazon (just to showcase, no recommendation):

Amazon.de : balkonkraftwerk

 

[Hogheavenfarm]

deleted

 

[DIYrich]

Hm, not sure about the US but in Germany these devices can be bought and used legally. They are called Balkonkraftwerk (balcony power plant).
They consist of a solar panel, inverter and plug. They are limited in max power and you need to register them. See for example on Amazon (just to showcase, no recommendation):

Amazon.de : balkonkraftwerk

Wow, you can plug 30kW into the wall.

"Product description
... You confirm upon conclusion of the contract that either the gross installed capacity of the photovoltaic system is or will not exceed 30 kilowatts (peak) according to the market master data register"

 

[webbbn]

Wow, you can plug 30kW into the wall.

"Product description
... You confirm upon conclusion of the contract that either the gross installed capacity of the photovoltaic system is or will not exceed 30 kilowatts (peak) according to the market master data register"

I guess the balconies in Germany are bigger than in the US!

It looks like the limit is actually 600W, and there might be restrictions on the circuit used. The potential registration requirements are also not clear from a quick search, but there are many ways you can take advantage of a small amount of solar without feeding back into the grid. Backfeeding kWs should, IMO, be coordinated with the provider.

 

[sunshine_eggo]

Don't know of anyone actually trying something like this -

I have one. Been using it for over 6 years now. Works great for its intended use (not as intended - I simply use it to bleed a 12V battery down for a specific reason). In my application, it never produces more than about 300W due to operating below the MPPT voltage.

This guy gave it a shot too:

Probably very non-UL ...

Very, but it does anti-islanding.

Seems interesting, as maybe this is the first step in getting to plug & play, and possibly to UL listing ...

I personally doubt it.

I'm amazed that "over 900" of these have been sold ...

Likely FAR more. Doesn't take much searching on Youtube to find several folks using them.

From an engineering standpoint, it must be that these get solar panel output, sync it to the grid, and "push" electrical pressure to the house wiring, feeding appliances before the grid side pushes power "into the house".

Yep. Same principle as whole-house grid tie. It just feeds onto a single leg of 120.

If grid goes down, then this thing goes down as well?

Yep.

 

[SeaGal]

You have a 15A breaker (1800W at 120V), and you plug in this inverter for 700W (6A more).
You now have 21A available to power a coffee maker and hair dryer on the same circuit. But the wire can't handle it.

Would work if PV backfed from far end of a wire, just like how we land the PV breaker at far end of breaker panel busbar.
But you likely have no idea how the various outlets and lights in your house are daisy-chained together.

That keeps the wire from overloading but the receptacle and appliance can still exceed. Imagine a power strip in the middle of the circuit, or even just a regular duplex receptacle. Easily sink 30A out of that.

In places like the UK with receptacle fusing it would be safer, possibly eliminating this issue. This OCPD essentially acts like the load breakers in the middle of the panel.

TBH this discussion needs to address how to safely backfeed to arbitrary branch circuits, there has only been 10% of the discussion spent on this…

Absolutely not... the same issue @Hedges identified applies to plugging generating equipment into a ring mains circuit - you could draw more power (through usage or fault) than the wires can carry.

We have BS7671 regulation 712.411.3.2.1.1 (yes, really!!)... it states "The PV Supply cable (on the AC side) shall be connected to the supply side of the protective device for automatic disconnection of circuits supplying current-using equipment."

See also my posting where I discuss that in more detail..

UK Off-grid DNO advice

He does not need to inform with an off-grid with grid backup. Grid backup essentially takes power from the grid on AC-IN but does not connect to feed back to the grid providing he has not connected the AC-OUT to a panel that is connected directly to the grid. If he has connected is distribution...

diysolarforum.com

 

[Tony_AH]

What would you imagine needs to happen to allow people to utilize solar safely with the grid without having to deal with all of the current regulatory challenges with permitting - lowering the bar so much that someone who is not technical could walk into a home improvement store, buy a solar panel and plug it into their house and start generating power.

Why isn't there a standard & regulations for plugging in ~ 1500w of power to the grid today? What would this standard & regulations need to look like?

My guess is

1. Specialized outlet designed for plugging in renewable energy limited to 1500w of 120AC - so it carries the same risks as using an extension cord with a 1500w AC heater.
2. The solar panel/inverter combo, since it generates energy needs to have its own breaker integrated into it, and ground wire to provide safety.
3. The electric company has to provide a net metering capable meter
4. I think this needs to be a dedicated circuit with a single plug for generating energy, so the supply side can't overload it.

I'm just trying to imagine a world where we had outlets you could plug stuff into to feed back into the grid, to really democratize energy generation, so everyone could partake.

The closest thing I've found is the ConnectDER, which is a meter you can easily plug solar into, but it's not something someone non-technical could just plug stuff into safely.

In the UK you can buy plug in solar kits, see link below. You can't just plug another mains source into the grid. For a start you will probably blow the device up and secondly the alternating cycles will be out of phase with the mains grid. Solar inverters are designed so that they won't operate unless they detect a mains voltage so you won't kill anyone working on the grid if the mains goes down. They must also synchronise their phase with the mains and they are designed so the load from the mains doesn't damage them. You can use micro inverters like the kit below in the link and they can be connected directly to a mains supply via a fused switch. Any energy you don't use goes into the grid for someone else to use.

Plug-In Solar 1.62kW (1620W) DIY Solar Power Kit with Fastensol Trays (for Ground or Flat Roof) | Plug In Solar

Plug-In Solar 1.62kW (1620W) DIY Solar Power Kit with Fastensol Trays (for Ground or Flat Roof)

www.pluginsolar.co.uk

 

[pvgirl]

In the UK you can buy plug in solar kits, see link below. You can't just plug another mains source into the grid. For a start you will probably blow the device up and secondly the alternating cycles will be out of phase with the mains grid. Solar inverters are designed so that they won't operate unless they detect a mains voltage so you won't kill anyone working on the grid if the mains goes down. They must also synchronise their phase with the mains and they are designed so the load from the mains doesn't damage them. You can use micro inverters like the kit below in the link and they can be connected directly to a mains supply via a fused switch. Any energy you don't use goes into the grid for someone else to use.

Plug-In Solar 1.62kW (1620W) DIY Solar Power Kit with Fastensol Trays (for Ground or Flat Roof) | Plug In Solar

Plug-In Solar 1.62kW (1620W) DIY Solar Power Kit with Fastensol Trays (for Ground or Flat Roof)

www.pluginsolar.co.uk

It's a bit misleading they call it plug in solar, but you don't just pulg it in, you have to get an electrician to do the connection.

 

[solar8484]

What would you imagine needs to happen to allow people to utilize solar safely with the grid without having to deal with all of the current regulatory challenges with permitting - lowering the bar so much that someone who is not technical could walk into a home improvement store, buy a solar panel and plug it into their house and start generating power.

EU already allows up to 800W grid-tied inverter to be plugged into outlets without any permit or approval. The last time I checked Germans are pretty good about electrical safety so the US just needs to follow.

 

[SeaGal]

In the UK you can buy plug in solar kits, see link below.

It's not plug in. The name of the company is historic from when they illegally sold kits that were not BS7671 compliant.

 

[zanydroid]

Only danger with a small home standalone solar setup is to your own house and self, assuming it’s got islanding and isn’t in the way of emergency access.

Sure, it's not a risk to the grid, only to whoever's in the house.

I don't think it's responsible to sell a plug-in product though with all these caveats about needing to know the layout of the branch circuit to use it safely. What % of customers will know how to do this correctly? I bet some fraction of licensed electricians will get the design wrong.

The generator case is actually simpler since there is only a single power source (due to the required interlock against grid power), so you don't have the same overload issue. Theoretically you could have loads on the same branch circuit as a generator, if the loads are compatible with the output OCPD of the generator.

EU already allows up to 800W grid-tied inverter to be plugged into outlets without any permit or approval. The last time I checked Germans are pretty good about electrical safety so the US just needs to follow.

What is the theory behind making this safe enough?

Also in the US if you allow 120V plug in at scale you are forcing a lot of extra balancing work on the utility transformer secondary. Not a problem with 240v but you will have very limited consumer uptake of a 240v solution.

 

[Supervstech]

What would you imagine needs to happen to allow people to utilize solar safely with the grid without having to deal with all of the current regulatory challenges with permitting - lowering the bar so much that someone who is not technical could walk into a home improvement store, buy a solar panel and plug it into their house and start generating power.

Why isn't there a standard & regulations for plugging in ~ 1500w of power to the grid today? What would this standard & regulations need to look like?

My guess is

1. Specialized outlet designed for plugging in renewable energy limited to 1500w of 120AC - so it carries the same risks as using an extension cord with a 1500w AC heater.
2. The solar panel/inverter combo, since it generates energy needs to have its own breaker integrated into it, and ground wire to provide safety.
3. The electric company has to provide a net metering capable meter
4. I think this needs to be a dedicated circuit with a single plug for generating energy, so the supply side can't overload it.

I'm just trying to imagine a world where we had outlets you could plug stuff into to feed back into the grid, to really democratize energy generation, so everyone could partake.

The closest thing I've found is the ConnectDER, which is a meter you can easily plug solar into, but it's not something someone non-technical could just plug stuff into safely.

Ok.
I can actually see how this could be implemented.
It would have to be installed by the electrician ahead of time.
Like the current requirement for home surge protection is.
The inlet would be a DC connection for the solar panel.
A micro inverter would be wired to the home panel, and specific wattage dc inlets would be mounted on the house, or off the meter base of the house.
So, the home gets built with the back feed meter, the micro inverters, and the ability to just plug in a specific range of solar panels...
Easy.
I can see them advertised as parasitic loss equalizing system or similar.
Say, 300W each inlet... so a bank of as many as your square footage allows...