Interesting info. Practical experience with residential solar is very useful, especially as high utility bills give a new motivation to homeowners that replaces the motivation from disappearing tax credits.
Just a minor thing: There are some places toward the end where you might want to correct some (distracting) comma run-on sentences with periods.
“The mini-inverters tend to be a part on the solar panel, so if they fail and they are obsolete, chances are you are replacing the whole solar panel.”
This is not true. These are called micro-inverters and they are almost always sold as separate units. I’m not aware of a manufacturer who has successfully sold “AC modules” in any significant volume. Typically, as long as the panel has the same cell count (60-cell, 72-cell, etc.) the voltage and input ranges for micro-inverters will be similar enough for different panel make/models. Enphase is the best micro inverter product on the market in the US in my experience.
In the industry, “central inverters” are large, MW-scale equipment that usually connect to MV transformers. The larger residential-scale inverters are called “string inverters.”
>
I’ve looked into vanadium flow batteries, and I would recommend homeowners stay away from them. Performance-wise, they have a few deficiencies: Round trip efficiencies are down around 70%, whereas li-ion batteries are closer to 90%. Power output is limited to 4 hours (meaning that the fastest you can discharge fully battery energy capacity is over 4 hours). My biggest concern is that they rely on mechanical systems that are more likely to fail or need regular maintenance than li-ion batteries.
If you’re worried about li-ion fires, the NMC batteries in Tesla cars and some other brands are more prone to thermal runaway than the LFP batteries used by most other stationary energy storage manufacturers these days. If you’re afraid of fires: don’t park an EV in your garage.
In general, while there are concerns about thermal runaway in li-ion batteries, they are the best performing chemical battery technology out there by most metrics. Which is why they’ve scaled up so much.
>
“Solar roofing” products have been around since before I entered the industry almost 20 years ago, and they’ve never taken off. I don’t think they’re ever going to be cost competitive, and if your roof ever leaks, they would been nightmare to deal with for a roofer. Again, if you’re concerned about fires, the last thing you want is inaccessible, higher voltage DC wire stuffed next to your roof decking.
>
About 2/3 of states abide by the IFC for their fire code, which has a chapter on energy storage system installation and citing. The other third rely on NFPA 1, which, since 2021 (I think) points at another book, NFPA 855, to address fire safety topics dealing with energy storage systems. Both the IFC and NFPA 855 share many regulations, although NFPA 855 has a chapter dedicated to residential sites. Generally, it is better to site these systems outside. If you’re installing a battery system in a garage, make sure it has ventilation and it must be surrounded by non-flammable material (drywall, metal, concrete, plaster, etc.). NEC 706 also discusses ESS wiring regulations.
>
If you’re using a battery for backup, you want to be careful not to connect more loads to it than the power rating of the ESS inverter can supply. Generally, with generators it is easier to get a bigger unit for less money because you’re mostly paying for power, not optimizing for a power/energy ratio, where energy is expensive. Almost every conversation I’ve ever had with someone thinking about using batteries as backup power ended with me telling them they choose a generator instead or not bother with backup power in the first place. If we had regular, rolling brownouts, the value of battery backup would be higher than it is in the US where outages are not everyday occurrences.
>
Bidirectional EVs will be big in the future and may go a long ways to obviate the need for stationary energy storage. However, control system technology is just not as sophisticated or as cheap as it needs to be to extract the real value of bidirectional EVs at a residential scale. Interconnection processes and even the NEC’s approach to sizing backfed equipment is not efficient in deploying these systems to their best effect. This is something to keep an eye in the coming years.
>
One last thing to mention about batteries and PV. They can be DC-coupled, or connected to the same inverter on the DC side of the inverter, or they can be AC-coupled, where the PV system and the ESS each has its own inverter. There are advantages and disadvantages to both configurations, and if you’re not doing a tiny system, it’s good to get someone who knows the vendors out there and understands energy applications to make good engineering decisions about this.
Thanks for calling me out on the mini-inverters. My experience is with a friends install where they were attached, and then only by conversation. He is a retired IBEW lineman so he did it all himself. It's difficult to get straight information from sales sites, they don't want to let anything slip to the competition.
The fire concern actually comes more from my world in utilities. The Moss Landing fire was the last major one, but there have been consistent issues with fires in utility scale battery developments. Wiring fires and panel fires have been regular postings on LinkedIn, so they are in the news cycle.
Keep in mind things like solar shingles and backup power are discussed as options. I was pretty upfront that shingles are expensive. The solar backup is being pushed hard by installers like Sunrun, so it's going to be a question on people's mind.
I very much appreciate your comments and what they ad to the discussion. You bring inside experience I do not have. Thank you. There is a link to my LinkedIn profile on my Substack profile if you want to peek.
these systems are supposedly all the rage in Germany where they’re called Balkonkraftwerke (balcony solar). Last year legislation in Utah “legalized” them and this year there are bills both in the Colorado and Vermont legislatures to copy the Utah legislation.
Here’s the summary and text of the Colorado legislation:
I am sure it is, it reflects the lack of technical understanding of many supporting the green movement. Now once an operator at Smud in Sacramento did buy 25MW from a Utility in Florida for one hour and bought all the Transmission rights to get it to Sac. It was just a,stunt to show it could be done on paper. Did any of that energy actually make it, I doubt it
Some realistic thought is that the residential acquisition should be justified with savings assuming the system is standalone and not connected to the grid. And if output does not match consumption this will be via some local storage of some kind… This may even just by heating water etc.
The grid does not need the imbalance and unreliability of solar or wind or its unplanned excess so that’s why we must assume it’s a localized consumption system.
Batteries may make sense but typically grid energy is cheapest when the sun goes down so that’s another reason to have a hybrid of domestic solar and grid service.
Living off grid is a romantic idea, but usually proves much less enjoyable in reality. Suddenly you are faced with maintainence, breakdowns and system performance. What looks cheap on paper often doesn't pencil out in the real world. Sometimes it's required, but islanding when there is a power box in the front yard, go ahead, I'll watch with popcorn.
The residential unit would still be connected to the grid to provide power when the solar install is not providing output. But the solar system would not contribute to the grid as the grid does not work well with parasitic technologies such as solar. Its clear that too much grid power supported by such parasitic systems just makes the grid more expensive and unstable.
Of course, under Net Zero, there is no fossil-fueled generator and no natural gas or propane service. Then it gets really exciting.
Interesting info. Practical experience with residential solar is very useful, especially as high utility bills give a new motivation to homeowners that replaces the motivation from disappearing tax credits.
Just a minor thing: There are some places toward the end where you might want to correct some (distracting) comma run-on sentences with periods.
I think, we found it Ruth, I had to call in the "editor". You know us engineering brain types, english is a second language. 😄
On it
>
“The mini-inverters tend to be a part on the solar panel, so if they fail and they are obsolete, chances are you are replacing the whole solar panel.”
This is not true. These are called micro-inverters and they are almost always sold as separate units. I’m not aware of a manufacturer who has successfully sold “AC modules” in any significant volume. Typically, as long as the panel has the same cell count (60-cell, 72-cell, etc.) the voltage and input ranges for micro-inverters will be similar enough for different panel make/models. Enphase is the best micro inverter product on the market in the US in my experience.
In the industry, “central inverters” are large, MW-scale equipment that usually connect to MV transformers. The larger residential-scale inverters are called “string inverters.”
>
I’ve looked into vanadium flow batteries, and I would recommend homeowners stay away from them. Performance-wise, they have a few deficiencies: Round trip efficiencies are down around 70%, whereas li-ion batteries are closer to 90%. Power output is limited to 4 hours (meaning that the fastest you can discharge fully battery energy capacity is over 4 hours). My biggest concern is that they rely on mechanical systems that are more likely to fail or need regular maintenance than li-ion batteries.
If you’re worried about li-ion fires, the NMC batteries in Tesla cars and some other brands are more prone to thermal runaway than the LFP batteries used by most other stationary energy storage manufacturers these days. If you’re afraid of fires: don’t park an EV in your garage.
In general, while there are concerns about thermal runaway in li-ion batteries, they are the best performing chemical battery technology out there by most metrics. Which is why they’ve scaled up so much.
>
“Solar roofing” products have been around since before I entered the industry almost 20 years ago, and they’ve never taken off. I don’t think they’re ever going to be cost competitive, and if your roof ever leaks, they would been nightmare to deal with for a roofer. Again, if you’re concerned about fires, the last thing you want is inaccessible, higher voltage DC wire stuffed next to your roof decking.
>
About 2/3 of states abide by the IFC for their fire code, which has a chapter on energy storage system installation and citing. The other third rely on NFPA 1, which, since 2021 (I think) points at another book, NFPA 855, to address fire safety topics dealing with energy storage systems. Both the IFC and NFPA 855 share many regulations, although NFPA 855 has a chapter dedicated to residential sites. Generally, it is better to site these systems outside. If you’re installing a battery system in a garage, make sure it has ventilation and it must be surrounded by non-flammable material (drywall, metal, concrete, plaster, etc.). NEC 706 also discusses ESS wiring regulations.
>
If you’re using a battery for backup, you want to be careful not to connect more loads to it than the power rating of the ESS inverter can supply. Generally, with generators it is easier to get a bigger unit for less money because you’re mostly paying for power, not optimizing for a power/energy ratio, where energy is expensive. Almost every conversation I’ve ever had with someone thinking about using batteries as backup power ended with me telling them they choose a generator instead or not bother with backup power in the first place. If we had regular, rolling brownouts, the value of battery backup would be higher than it is in the US where outages are not everyday occurrences.
>
Bidirectional EVs will be big in the future and may go a long ways to obviate the need for stationary energy storage. However, control system technology is just not as sophisticated or as cheap as it needs to be to extract the real value of bidirectional EVs at a residential scale. Interconnection processes and even the NEC’s approach to sizing backfed equipment is not efficient in deploying these systems to their best effect. This is something to keep an eye in the coming years.
>
One last thing to mention about batteries and PV. They can be DC-coupled, or connected to the same inverter on the DC side of the inverter, or they can be AC-coupled, where the PV system and the ESS each has its own inverter. There are advantages and disadvantages to both configurations, and if you’re not doing a tiny system, it’s good to get someone who knows the vendors out there and understands energy applications to make good engineering decisions about this.
Thanks for calling me out on the mini-inverters. My experience is with a friends install where they were attached, and then only by conversation. He is a retired IBEW lineman so he did it all himself. It's difficult to get straight information from sales sites, they don't want to let anything slip to the competition.
The fire concern actually comes more from my world in utilities. The Moss Landing fire was the last major one, but there have been consistent issues with fires in utility scale battery developments. Wiring fires and panel fires have been regular postings on LinkedIn, so they are in the news cycle.
Keep in mind things like solar shingles and backup power are discussed as options. I was pretty upfront that shingles are expensive. The solar backup is being pushed hard by installers like Sunrun, so it's going to be a question on people's mind.
I very much appreciate your comments and what they ad to the discussion. You bring inside experience I do not have. Thank you. There is a link to my LinkedIn profile on my Substack profile if you want to peek.
Quick update on these smaller “plug-in” solar systems.
Per the usual solar boosters, (example: https://www.canarymedia.com/articles/solar/balcony-panels-germany-utah)
these systems are supposedly all the rage in Germany where they’re called Balkonkraftwerke (balcony solar). Last year legislation in Utah “legalized” them and this year there are bills both in the Colorado and Vermont legislatures to copy the Utah legislation.
Here’s the summary and text of the Colorado legislation:
https://leg.colorado.gov/bills/HB26-1007
Of course the bill sponsors are selling this bill as an easy and cheap solution to the “climate crisis” and the state’s increasing electric bills.
"We once thought New York City would be powered by clean energy imported from California.."
from article you linked
is that a serious comment?
I am sure it is, it reflects the lack of technical understanding of many supporting the green movement. Now once an operator at Smud in Sacramento did buy 25MW from a Utility in Florida for one hour and bought all the Transmission rights to get it to Sac. It was just a,stunt to show it could be done on paper. Did any of that energy actually make it, I doubt it
Some realistic thought is that the residential acquisition should be justified with savings assuming the system is standalone and not connected to the grid. And if output does not match consumption this will be via some local storage of some kind… This may even just by heating water etc.
The grid does not need the imbalance and unreliability of solar or wind or its unplanned excess so that’s why we must assume it’s a localized consumption system.
Batteries may make sense but typically grid energy is cheapest when the sun goes down so that’s another reason to have a hybrid of domestic solar and grid service.
Living off grid is a romantic idea, but usually proves much less enjoyable in reality. Suddenly you are faced with maintainence, breakdowns and system performance. What looks cheap on paper often doesn't pencil out in the real world. Sometimes it's required, but islanding when there is a power box in the front yard, go ahead, I'll watch with popcorn.
No.. that’s not what I ment…
The residential unit would still be connected to the grid to provide power when the solar install is not providing output. But the solar system would not contribute to the grid as the grid does not work well with parasitic technologies such as solar. Its clear that too much grid power supported by such parasitic systems just makes the grid more expensive and unstable.
Solar is only useful off grid as suggested.