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

[DIYrich]

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...

Just go the route of California and require the installation of the entire system.

 

[solar8484]

What is the theory behind making this safe enough?

Theory? Probably no different than the US just a different risk/benefit tradeoff decision. The Germans probably thought 800W (lower most of the time) will most likely be consumed by household loads vast majority of the time. Even when it's not the net export would be very low. Given that Germans have a history and reputation of being conservative on electrical matters I doubt they would make decisions that would cause real world safety issues.

In general, the US codes are mostly determined based on what a panel of career code people (subject to various undisclosed influences) thinks rather than concrete data of safety incidents. It would be more scientific and sensible if significant changes have to be substantiated by actual data.

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.

The Germans require the units to be registered so POCO's know how many and where the units are. Same could be done in the US and the POCO's can make transformer changes when needed based on the data. Also, a 240V solution can potentially be implemented using 2 120V plugs that must be plugged into sockets of different phases in order to activate the units. Even having to have a 240V socket means much much less bureaucracy and redtape than the current home solar permitting process.

 

[DIYrich]

. Also, a 240V solution can potentially be implemented using 2 120V plugs that must be plugged into sockets of different phases in order to activate the units. Even having to have a 240V socket means much much less bureaucracy and redtape than the current home solar permitting process.

For 800 watts, I doubt the utility cares. Turning on the toaster creates more imbalance than that.

 

[DIYrich]

Theory? Probably no different than the US just a different risk/benefit tradeoff decision. The Germans probably thought 800W (lower most of the time) will most likely be consumed by household loads vast majority of the time. Even when it's not the net export would be very low. Given that Germans have a history and reputation of being conservative on electrical matters I doubt they would make decisions that would cause real world safety issues.

800 watts is 3.5 amps at 230 v (germany). 15 amp wire is oversized and uses wire capable of 18 amps. So, it is close to the safety margin.

800 watts is 6.7 amps at 120v (usa). That 144% of the rated capacity is well over the safety margin.

"My circuit breaker kept tripping when I used the <defective> appliance. I plugged in the balcony charger, and everything was fine. Problem solved."

 

[JoelE]

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.

Agreed dedicated is ideal but plug and

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

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...

Sounds overcomplicated. Could just derate your branch breaker to make room for whatever feed ampacity and plug it into a regular receptacle. Average homeowner could do it.

 

[zanydroid]

Theory? Probably no different than the US just a different risk/benefit tradeoff decision. The Germans probably thought 800W (lower most of the time) will most likely be consumed by household loads vast majority of the time.

As stated above in the thread, it is easy to construct a sequence of devices and sources on a wire in a branch circuit that exceed wire rating.

Consumption by household loads does not address the branch circuit risk.

 

[JoelE]

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.


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.

What if you just derate whichever branch breaker you are plugging into? You could recommend on the box that it be installed by an electrician, but include instructions for diy to replace their 20a breaker with a 15a, say based on whatever ampacity the product produces?

 

[zanydroid]

Sounds overcomplicated. Could just derate your branch breaker to make room for whatever feed ampacity and plug it into a regular receptacle. Average homeowner could do it.

This is highly optimistic on the knowledge level of humans. Have you looked at how many people are confused with 120% rule? Even professionals? And how many homeowners ask about #14 vs #12 and when they can bump breaker to 20A

Sounds like the rule you want is. Find a 20A circuit. Derate the breaker to 15A. You are now allowed 480W backfeed (5A*80%*120V). This is probably not terrible. One or two circuits should be safe enough within the busbar margin.

This will need an amendment to 705 since it actually explicitly says dedicated branch circuit.

Could also use an amendment to allow the lighting circuit breakers (10A) to give more backfeed headroom.

 

[solar8484]

Consumption by household loads does not address the branch circuit risk.

Sure but is it really any greater risk than people that plug in chain of multiple power strips into the same circuit and overload it?

 

[solar8484]

800 watts is 3.5 amps at 230 v (germany). 15 amp wire is oversized and uses wire capable of 18 amps. So, it is close to the safety margin.

800 watts is 6.7 amps at 120v (usa). That 144% of the rated capacity is well over the safety margin.

Yep, that's why I would prefer keeping the 240V grid-tie standard in the US.

 

[zanydroid]

Sure but is it really any greater risk than people that plug in chain of multiple power strips into the same circuit and overload it?

If you can analyze the branch circuit situation and show an argument that all problems are outside the walls, maybe.

There’s also a safety factor related to the max OCPD for regular household appliances. Does your proposal respect that?

 

[solar8484]

There’s also a safety factor related to the max OCPD for regular household appliances. Does your proposal respect that?

Sure. The Germans probably decided on 800W limit for similar reasons.

 

[zanydroid]

Yep, that's why I would prefer keeping the 240V grid-tie standard in the US.

I can sort of see a plausible path of adding onto EVSE branch circuits.

However there is the added complexity of no GFCI protection possible despite plugging in the solar in a garage or outdoors. Code writers will get triggered by that.

Code prohibits backfeeding into GFCI equipment not listed for backfeed.

 

[zanydroid]

Sure. The Germans probably decided on 800W limit for similar reasons.

Math and numbers >> English

I’m pretty sure we have about 3-4A to work with in the US within these rules

 

[JoelE]

This is highly optimistic on the knowledge level of humans. Have you looked at how many people are confused with 120% rule? Even professionals? And how many homeowners ask about #14 vs #12 and when they can bump breaker to 20A

Sounds like the rule you want is. Find a 20A circuit. Derate the breaker to 15A. You are now allowed 480W backfeed (5A*80%*120V). This is probably not terrible. One or two circuits should be safe enough within the busbar margin.

This will need an amendment to 705 since it actually explicitly says dedicated branch circuit.

Could also use an amendment to allow the lighting circuit breakers (10A) to give more backfeed headroom.

Yep, good point about the lighting breakers. I think derating would be simpler for the average end user vs trying to come up with a scheme of mapping out the branch and connecting in the right spot.

You could extend similar logic to 240v branches as well to make room for larger systems. Permitting and inspection process to put in an EV level 2 outlet, let’s say, can be a lot easier and cheaper than a solar install. By adding a 240v outlet on a dedicated branch, you could charge your car at night and charge your house during the day.

 

[zanydroid]

Yep, good point about the lighting breakers. I think derating would be simpler for the average end user vs trying to come up with a scheme of mapping out the branch and connecting in the right spot.

You could extend similar logic to 240v branches as well to make room for larger systems. Permitting and inspection process to put in an EV level 2 outlet, let’s say, can be a lot easier and cheaper than a solar install. By adding a 240v outlet on a dedicated branch, you could charge your car at night and charge your house during the day.

The lighting breakers will probably have a tough time making it through a hypothetical code change. Legitimate complaints about increase in nuisance trips. If they were approved one day for receptacle circuits, sure.

I think a micro microinverter system would already be easily code compliant with the branch circuit code changes discussed above.

String inverter loses a lot of cost advantages for such small systems and have extra fixed cost and complexity to deal with RSD and DC conductors. Maybe if there were some low power exceptions added… but probably no point because microinverters are already there.

Both DC and microinverter are probably equal complexity to add some limited off grid capabilities. My thinking is it would disconnect from the backfeed and allow someone to plug in small appliances directly to it.

 

[JoelE]

The lighting breakers will probably have a tough time making it through a hypothetical code change. Legitimate complaints about increase in nuisance trips. If they were approved one day for receptacle circuits, sure.

I think a micro microinverter system would already be easily code compliant with the branch circuit code changes discussed above.

String inverter loses a lot of cost advantages for such small systems and have extra fixed cost and complexity to deal with RSD and DC conductors. Maybe if there were some low power exceptions added… but probably no point because microinverters are already there.

Both DC and microinverter are probably equal complexity to add some limited off grid capabilities. My thinking is it would disconnect from the backfeed and allow someone to plug in small appliances directly to it.

If the system is ground mount, there are not the same module level RSD requirements, right? I’m thinking a pergola or a carport where panels and inverter come with the kit and mount onto it. To your point about connecting appliances, if you could get to the right voltage and amps you could potentially do level 1 DC fast charge to an EV direct from the panels or hybrid panel/battery setup.

 

[zanydroid]

If the system is ground mount, there are not the same module level RSD requirements, right? I’m thinking a pergola or a carport where panels and inverter come with the kit and mount onto it. To your point about connecting appliances, if you could get to the right voltage and amps you could potentially do level 1 DC fast charge to an EV direct from the panels or hybrid panel/battery setup.

Probably some combination of AFCI and RSD will be waived, but not GFP. Because I would hope everyone can agree that we should try to detect or mitigate ground faults (yet there is equipment on the market that don’t do this out of the box or at a reasonable price, so maybe this is first world privilege talking).

Not sure what a level 1 DC FC is but the minimum equipment cost to do DC charging is probably massive. DC charger requires an actual charger that can communicate with car and adjust current/voltage to match the traction battery. EDIT: and this means probably boost SCC in many cases.

Very high fixed costs just to make it safe. Once the equipment cost and inherent risk crosses a threshold the chances dwindle for a viable mass market/low overhead product

On top of that low volume product currently. And what is the point if you are only talking about 1kW of solar panels. The OBC can easily handle that.

 

[cs1234]

Without the expensive permitting process to get backfeed approval for a regular full solar install, micro-inverters are without a doubt the easiest and safest way to go. Costs on them would also come WAY, WAY down with increased volume and competition. Many homes could easily replace most of their day time base load with the microinverters, reducing draw on the grid. ESS systems could easily be made for night time use as well to cover base loads by injecting into the house.

I think the current utility permitting and city/county permitting process is causing an unnecessary delay in a dramatically improving the resiliency of our energy grid. It holds back innovation and keeps costs much higher than they need to be. Even 1000 watts of solar in every yard would make a difference, especially if paired with say 3-5kwh of batteries to help with early evening draw.

 

[hyxsungold]

To enable safe and widespread utilization of solar power while reducing regulatory challenges and simplifying the process, several key changes and developments would need to occur:

1. Plug-and-Play Systems: Development of standardized plug-and-play solar systems that are user-friendly and require minimal technical expertise to install. These systems should come pre-assembled and pre-configured, allowing homeowners to simply connect them to their electrical system.
2. Pre-Approved Designs: Establish a library of pre-approved solar system designs that meet safety and grid compatibility standards. Homeowners can choose from these designs, eliminating the need for individualized engineering assessments for each installation.
3. Streamlined Permitting: Implement streamlined permitting processes that rely on simplified documentation for pre-approved designs. This reduces the administrative burden on both homeowners and regulatory authorities.
4. Smart Inverters: Require the use of smart inverters with advanced communication capabilities. These inverters can monitor and manage grid interactions in real-time, ensuring safety and grid stability.
5. Grid Compatibility Standards: Develop clear and standardized technical requirements for connecting solar systems to the grid. These standards should address voltage, frequency, and power quality to ensure seamless integration.
6. Education and Training: Provide accessible educational resources and training for homeowners to understand the basics of solar installation, safety protocols,
7. Third-Party Certification: Int
8. Consumer Protections:
9. Collaboration with Utilities: Collaboration between solar industry
10. Progressive Pilot Programs: Init