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# An Electrification Essential: Electrical Circuit Mapping

Let’s say you have an older house.  Maybe the laundry room used to be in the basement but got moved to the main floor later.  Then someone added a bunch of can lights in the kitchen and family room.  Over time, various owners enclosed the porch, converted two bedrooms to a primary suite, and made a bunch of smaller changes, too.  For a house with a few decades of such changes, the electrical system can become a mess.  If you have an older house, are the breakers in your electrical panel all labeled completely and accurately?

I basically described my house above.  Built in 1961, it’s gone through a lot of changes over the years.  I can see the remnants of these changes in the different kinds of electrical cable used, the open junction boxes in the basement and attic, and the mess that is my electrical system.  The photo below shows at least three different kinds of cable entering this junction box.

An electrician who looked at my house early on told me the whole thing needed to be rewired.  Yikes!  That sounds expensive…because it is!  I’ll redo the basement wiring when I remodel it.  I’ll do what I can with the rest later.

But my first step has been just to figure out which breakers control what loads.

#### Electrical safety

Messing with the 110 or 220 volt electricity in your house can be dangerous.  You shouldn’t need to open any junction boxes or take the cover off the electrical panel just to map out your circuits.  But if for some reason you do find yourself face-to-face with bare copper, don’t trust the breaker.  It’s a good practice always to test and make sure the electricity really is off before you start touching the conductors.

These days, you can find many different devices that can tell you whether your wiring is hot (energized).  The photo above shows the simplest type and is one I got  from my grandfather.   It’s just two leads you use touch to the wires.  If the tip lights up, as it is in the photo, the wires are hot.  Always test.  And then test again to be sure.  Above all, call a pro when you need to.

#### Calming the chaos

Last summer I spent a whole weekend mapping out all of the circuits in my house.  I did it myself and got a whole lot of steps going from the electrical panel to every part of the house, flipping breakers and switches.

So, where should you start if you want to do this in your house?  That’s easy.  First look at the panel to assess what you’re starting with.  If it’s labeled, you may have a head start.  But don’t automatically trust what’s written there.  Use the labels only as a guide.

Second, identify the two kinds of breakers in the panel.  Some are big double breakers, two separate breakers that switch—and trip—together.  Others are single breakers, usually 15 or 20 amps.  In the photo of my panel below, there are four double breakers.  On the top left is a double 15 amp breaker (two 15 amp breakers ).  Right below that is a single 20 amp breaker, then a double 40 amp breaker.  The left-side breakers, top to bottom, are for a Mitsubishi ductless heat pump in the sunroom, the now-removed whole-house fan replaced by my attic exhaust fan, and the larger Mitsubishi heat pump that heats and cools most of the main floor.

On the right side is a double 30 amp breaker at the top, another double 30 amp breaker in the middle, and then a single 20 amp breaker at the bottom.  They protect the heat pump water heater, the electric cooktop in the basement, and lights and outlets on the back side of the house.

When you start mapping out the circuits, begin with the big, double breakers.  They’re the ones most likely to be labeled correctly to begin with.  The big ones usually protect:

• Air conditioners or heat pumps
• Water heater
• Range and oven
• Clothes dryer
• Electric vehicle charger

There could be other big loads, and you may not have all of the ones above.  If you use gas for heating water, cooking, and drying clothes, you won’t have double breakers for those.

The harder ones to map out are the many small electrical loads:  lights, outlets, fans, dishwasher, built-in radio (above), garbage disposal, and anything else hard-wired into the house.

#### Matching loads to breakers

The easy version of the old-fashioned way to do it would be to have two people talking to each other from different parts of the house.  One will stay at the panel, turning breakers on and off.  The other person will go to each room in the house as well as looking at exterior lights as the panel person switches breakers.

If you’re doing it alone, you can save some steps when testing outlets by plugging in a radio turned up loud enough to hear at the panel.  (Hat tip to Jeffrey Chalmers of Ontario for posting that idea on LinkedIn.)  For lights and other loads, you’re going to get a lot of steps doing it the old-fashioned way by yourself.

If that’s old-fashioned, you ask, then what’s the new-fashioned way?  There are tools available now that can help.  The Klein Tools ET310 is one that I tried on my house.  Unfortunately, I kept getting false positives.  The receiver would light up indicating I had the right breaker, but then it would light up on another breaker as well.  But the transmitter (plug-in part) is useful for other things, too, like confirming that a lot of my outlets aren’t grounded.  Other people I know have had good luck with these kinds of tools, though, so it may be worth a try.

Another tool that can help is the Emporia Vue whole-house electricity monitor.*  You can turn loads on or off in the circuits you’ve set up for monitoring and see if they affect the result.  It helped me identify a mystery load, which turned out to be the cooktop in our basement.

Whichever way you map the circuits, it’s essential to keep good notes and make sure you’ve got the correct breaker number written down for each electrical load.  And then go back and check everything again.  The bigger the house and the more complicated the electrical system, the longer it will take to get the electrical circuits all mapped out.

#### Organizing the results

Once you’ve got everything mapped out, your life will be easier.  But don’t stop yet.  Organize the data you’ve collected.  First, of course, you want a numerical list of the circuits and what each breaker controls.  That’s the norm, but most panels don’t give you space to list every load on each circuit.  This is especially true for older houses.  My busiest circuit, for example, has a dozen different loads in the basement, the main floor, the attic, and even one outdoor light.

I entered all my circuit information into a spreadsheet on three different tabs.  The first tab is the by-circuit information I just described.  It’s got four columns:  circuit number, level of the house, room, and description of the load.  You can see a screenshot of the top of it below.

The second tab is the by-load data.  This one makes it easy to find the breaker number for any load in any room of the house.  It’s actually more useful than the first tab because we usually start with a particular load we need to shut off.  Again, I’ve organized my list with the same four categories as the first tab.  They’re just in a different order.

The third tab (not shown here) is basically the same info and organization as the first tab, but I’ve put it into two side-by-side sets to match what I see in the panel.

You can take this even further, too.  Jonathan Porter, an engineer in Minnesota, made a full schematic design of every circuit in his house.  It shows every load, cable, junction box, and breaker.  Joe Smith, a contractor in California, labeled not only his breakers in the panel but also the switches and receptacles in the house.  Dennis Heidner, an engineer in Seattle, drew a schematic layout of his system and labeled the cables, too.  How OCD will you be with your circuit mapping?

#### A step in the electrification process

If you, like me and many others, are going all-electric, mapping out your circuits is an essential task.  In my case, it has helped future work I’ll be doing.  My panel currently has a breaker in every available slot.  To add circuits, I’d need to get a bigger panel or a sub-panel.

Or I could find circuits I don’t need anymore, and that’s exactly what my circuit mapping efforts helped me with.  For example, we have a kitchenette in the basement with an electric cooktop.  That uses two slots in the panel for a double 30 amp breaker.  We also have a big whirlpool tub we’ll probably ditch and a few circuits with almost no load that we can combine.

In the end, labeling the panel and measuring your electrical use with something like the Emporia Vue* makes the electrification process easier in many ways.  Have you mapped your circuits yet?

Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a popular book on building science.  He also writes the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.

* This is an affiliate link. You get a 5% discount on Emporia products, and Energy Vanguard may make a small commission if you buy after using the link.

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The #1 Reason to Have an All-Electric Home

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#### This Post Has 38 Comments

1. Barry Edenbaum says:

A suggestion……….. while labeling the breakers on the panel box inside cover is a good idea (and if I’m correct, required by code), because circuits sometimes get moved around in the panel box for a variety of reasons (e.g., space, load balancing), another good idea (when initially mapping out all the loads in the house) is to tape lettered wire markers on the HOT WIRES that go to each breaker. If letter “A” corresponds to say master bedroom lighting, it will ALWAYS correspond to that no matter what breaker wire “A” is attached to. Twenty years down the road, and after many changes, you’ll be glad you did.

1. Barry: Good idea. I think you have to be careful with what you use to label the wires, though, so you don’t create a fire hazard.

2. Paul Szymkiewicz says:

Glad you’re careful, Allison. I would add two basic items to your table for each circuit: breaker size, and if you do end up opening the breaker panel cover, the conductor size and type leaving the panel for that circuit.

As you explore the loads on each circuit, observe the conductor size at each point, it better be equal or greater the size at the panel. Have seen too many “smart” solutions in older homes with a 20A breaker, a 12-ga conductor leaving the panel, and suddenly a 14-ga wire showing up somewhere down the circuit.

1. Paul Hager says:

After reading quite a few comments, (20 years as a electrical technician) a lot of the homeowners should not be going anywhere near their electrical system. Best advice I could give is to get a license electrician to conduct the tasks you would like completed. Get as many estimates as you need until you find a person you feel is trustworthy, respectful and honest. The peace of mind is worth it!!

3. Reducing vampire loads is a goal & labelling is a step in that process. Emporia does a better job by circuit than Sense but Sense gives better appliance control. Sense + Kasa smart plug on Man Cave eliminates cable box, etc for days at a time. Span I/O panel would be best but there’ll always be exceptions so back to smart plug or power strip as needed.
Next is backup of heat pumps & other critical loads. Could also be load shifting if you have TOU.
At the outlet, remove cover & write circuit #.
There seems to be conflicting advice on when a breaker should be replaced. Every 20yrs? Obviously if damaged or low quality for new load like EV charger (switching from intermittent to constant load).
Next, I’d like to log low power events. If heat pump has max HP at 120V L1+L2, how many BTU are lost at 205V? Having a house battery should fix that but I don’t know if it’s a significant loss of BTU. OTOH, you need every available BTU below design temp after X hours.

4. I use a permanent marker to list the breaker number on the inside of the outlet or switch cover; also mark junction box covers with all breakers feeding to or passing through it as needed when I access them.

5. Marty R says:

Good points, all, Allison. Here are a few additional things to look at in the process of studying an existing electrical system, from the point of view of a scientist who is not an electrician but who has constantly been looking for “best practices” information that can be informative about things that might need to be changed or added in household systems of all kinds. First, the photo of the wiring in your electrical panel, although rather limited, shows numerous wires that have been bent along their length or at the connection point well beyond (i.e., a tighter bend) the allowed “bending radius,” which differs by wire gauge, which is set by the National Electric Code and may be supplemented by local code requirements. More-acute bends like these can result in overheating, and sometimes, fires. Watch for the bending in outlet and switch boxes, as well; the boxes might not actually be big enough if there are multiple wires coming and going. Secondly, modern electrical code requires virtually all circuits to be protected by GFCI/AFCI combination circuit breakers. The GFCI protects people, while the AFCI protects against the kinds of mini-arcs (and full arcs) that are said to be the cause of about 75% of all electrical fires, as it also protects the house and user against failures inside of devices like hair dryers and hair curler sets (as I’ve personally experienced). Each outlet that is covered by a GFCI/AFCI should be marked as “GFCI protected.” (Combination breakers in the large sizes seem to be unavailable as of yet, but should be coming in the near future.) Third, the use of a whole-house surge suppressor, tied into two circuit breakers that are as close as possible to the incoming feed by wires that are as short as possible (be sure that they connect to both hot lines, and not the same one!), is a fairly small investment to protect expensive devices and appliances in places like Atlanta (as well as the entire eastern half of the country, and the west coast) from power surges caused by weather-related events, and everywhere for protection against power surges caused by accidents (e.g., a truck striking a power pole along your feed pathway or a tree or branch shorting across wires). Fourth, ensure that all wire connections in the panel and at switches, outlets, etc., are tight; looseness leads to overheating. And fifth, seriously consider mitigation if you find that your wiring is aluminum, or copper-sheathed aluminum (which looks like copper along its length, but when viewed at a cut is aluminum inside). A lot of older houses have such wiring, which is only OK as major incoming or secondary (sub-panel) distribution lines. The outlets and switches in the house might not actually be suitable under current code for such wiring, and may need to be replaced with the proper fitting type, if you do not re-wire the house. Be sure to follow any instructions for proper installation, which, for all-aluminum wiring, generally includes a corrosion-inhibiting coating added to the bare wire before installing it.

1. RoyC says:

Have any of you had problems with AFCI? I know of one case where an LED light fixture kept causing it to trip and another where the refrigerator kept causing trips. In both cases, replacing the AFCI with a conventional breaker solved the problem. I doubt that the LED or refrigerator were really having a “fault” since both houses are still standing. I am just guessing that AFCI’s have problems with some electronics used in high-efficiency motors and LED’s. Perhaps the code bodies gave in to the AFCI manufacturers too easily and too soon?

1. Paul Szymkiewicz says:

Roy, several instances, both in our personal home, and in client’s homes, so far with both GE and Eaton, both dual function AFCI/GFCI. The AF function was tripping in both. GE replaced the affected breakers for us with updated firmware versions and this helped. We replaced Eaton’s breakers with newer versions at the local supplier, and that helped, too. The supplier said they had a whole bin full of finicky AFCI breakers.

As to the GFCI’s tripping on compressors, give it time and they’ll resolve that, too. Of course, we’ll pay for the R&D costs at \$70+ a pop.

Yeah, a set of breakers for a new house these days is frequently \$1000+.

1. RoyC says:

Paul, this seems to be another case of people pushing to get their products or services put into codes so that they can create new or expanded markets without appropriate vetting by the code people. Right now, there is an argument between the breaker manufacturers and the AC manufacturers over who is at “fault” and who should pay to figure it out. In the meantime, I suspect that we will all have more customers who are annoyed by nuisance tripping in the meantime.

2. RoyC says:

Another emerging issue is that the latest edition of the NEC is requiring GFCI’s on air conditioner outdoor units. This is due to an isolated case of a child getting electrocuted on a unit that was later proven to be not grounded properly. The problem with this requirement is that many of the new variable-speed compressor units cause nuisance trips on GFCI’s. Have any of you seen this problem in the field yet? It is causing the equipment manufacturers a lot of concern.

6. Allison, I know Georgia can lag a bit, but certainly they’ve moved to the 120/240V standard by now, right? 😉

Also, you indicated that your panel is full, so that you’d need a bigger panel, or a subpanel. But your panel looks like it has at least one tandem breaker in there – that can be a useful, lower cost solution for many homeowners if they’re in need of space for circuits. Not all panels will accept tandems, but most newer ones will.

1. Tray: Oh, OK. I’ll go with 120/240 V then. Regarding ways to avoid a new panel or subpanel, maybe you missed the part about the circuits I’m going to reclaim (basement cooktop, whirlpool tub) or combine. Also, I already have a couple of tandem breakers in the panel, so that’s another way to expand.

1. Allison, sorry if I wasn’t clear – I was responding to your statement in the first ‘step in the electrification process’ paragraph: “My panel currently has a breaker in every available slot. To add circuits, I’d need to get a bigger panel or a sub-panel.”

I saw that you’d subsequently mentioned you could combine/reclaim circuits, but thought you might want to let readers know about the tandem breaker option as well, as that’s sometimes the lowest-cost option. Thanks as always for the thorough content!

1. Good point, Tray. Thanks for mentioning the tandem option.

And thanks, Marty, for the advice to verify that the panel actually is made for tandems.

2. Marty R says:

Some panels, such as ours (and maybe most or all), have limitations on which positions can take tandem breakers. If information about such placement is not permanently attached inside the breaker box cover, it may be available by searching for the panel manufacturer’s model. I believe that tandems must be specifically allowed for a panel, so that they should not be used if such use is not specifically permitted by the manufacturer.

7. Terry Grace says:

Why not create a basic floor plan with outlets/fixtures symbols then update the symbols with circuit # as each is located? Then if you color code each fixture/outlet on a circuit you have a very easy to read visual of what’s on each circuit.

8. Russell Hilburn says:

While you are at it, you can also take along a laser thermometer to check outlets, switches and breakers. They will read high temperatures long before failing completely.

1. Paul: Good eye. What you’re seeing is NOT two conductors, though. It looks a bit funky because it’s a white wire with red tape wrapped around it.

9. LeeH says:

Great article and I recommend everyone do this. We are in new construction so mine was pretty easy to do. Just a quick comment, on the double pole 15amp (top left) the white wire is used as a hot wire. I usually put black tape at each terminal to remind me that’s its not a neutral anymore.

1. Lee: Yeah, not all of the many people who have touched the wires in that panel have done things like putting tape on the white wires used as hot wires. The one you pointed out was from the HVAC company that installed the ductless mini-split.

10. Joe Smith says:

When you were getting false positives using the breaker finder, did you go through all the breakers slowly once and then go back through again to identify the correct breaker? They usually use the first trip through to “learn” the circuit and then identify better on the second round.

1. Joe: Yes, I followed the directions exactly and made multiple passes. Not sure if the problem was with me or my house.

2. Chris Ludston says:

One question about the Klein ET-310…
Did you read ALL of the instructions ?
I admit, I’ve grabbed many tools, thinking I knew how to use them.
Most of the time, without problems
Every once in a while, I’m too excited to try something, and end up blaming the “cheap” tool.
I also go a bunch of false positives with the breaker finder, and tossed it aside.
A day or 2 later, I decided to read the instructions…
Before you can get reliable results, you have to train the tester… who thought !
Once I used it like it was designed to be used, 99% of the time, it was correct.
You’ll always come across a strange reading now and then, no matter which type or brand of tester you use, or how much it costs. Electricity can do some strange things ….
Most of the time, if your getting incorrect readings, your using the tool wrong.
Always read the directions.
I don’t care how simple it may seem, tools are designed to work under certain conditions.
If you expect it to do everything for you, you’ll be misled !
That’s why Robots and AI, will never replace a technician !

Now, if anyone knows how I came across an outlet, in Chicago, IL, USA, that read 155 volts at the outlet, and at the breaker, while both legs in the panel read 110, I’ll be impressed…

PS.. took me 2 weeks of calling friends that were retired 20,30,40 year, union electricians, to make sense of it.
And he couldn’t answer to begin with
.We didn’t give up, and worked thru it together, for an hour, before we got an answer everyone agreed on.

We all finally agreed, the only 2 things that could possible cause that, are phantom electrical and magnetically fields.
Though no one has actually seen it before me.

I spent 14 hours, pulled several circuits, a lot of wire, boxes, and EMT apart….

It was caused by having 3/4 EMT, with a 220 dryer circuit, 220 A/C compressor circuit, and 3- 20amp circuits, all in the same EMT.

Along with someone tapping off one of the 20 amp, run thru BX(which is against code here now), going to single 120 outlet……
A big no-no to begin with….

Now, the root of the problem…
Someone had tapped off one leg of the 220 dryer, ran it up to the last outlet mentioned.
It had 2 circuits, hooked up to 1 outlet, without breaking the tab, to separate the outlets…
Even though they were both off the same leg in the breaker box, it was somehow feeding back, either by magnetic fields, or phanthom electrical fields, coming off the 220 circuit.

Once I disconnected that outlet, I was back to 110 volts…

Just goes to show you……
Unless you have been trained professionally, leave certain things to the technicians.
Breaking the rules can and will be dangerous, and expensive.
If you watched a bunch of YouTube videos, and think you know what your doing, please think twice.
I was an Auto/Diesel mechanic for 15 years, been rehabbing/remodeling houses for almost 20, learned everything I know, working side by side with union journeyman of every field …
I’ve seen hundreds, probably thousands, of cars, trucks, houses, etc., where someone thought they knew what they were doing, or worse yet, didn’t care.

Unless your properly trained, please don’t go messing with things like electricity, water, sewer, or structural supports…..
It may seem simple enough, but there is a lot more to most things, than you can imagine.
What if you go to remove your cover, and the guy before you pinched a wire when putting cover on. Do you know what to do, how to avoid getting hurt, or causing an electrical fire.
Just because wires are certain colors in one place, doesn’t mean they’re right.
Especially now, in the time of YouTube, and DIY TV shows, odds are, you will come across something that wasn’t done right.
Would you even know the difference ?
Sorry, I don’t mean to ramble on and on, or, put anyone down….
I’m only trying to keep you safe.
Almost everything you see on TV, or on YouTube, or on the Internet, isn’t designed to actually teach you the right, safe way….
It’s designed to make you watch, make you tell all your friends, make them money !
There is good info out there, but it’s rare.
Most real technicians don’t have the time to create this stuff. They’re busy making money and enjoying life.
A real technician won’t try to teach you in a video or in a blog…
They know how dangerous it can be.
We charge a lot for our services, because it took us years and years to learn, we’ve spent thousands on tools and testers.
We have to maintain our tools, our vans, pay insurance, pay extra income tax ( if we’re self employed or own a business), have payroll.
It’s not easy being a technician, but if you love your job, do great work, and are honest, you can have a good life.
One more thing before I end this extremely long comment….
Not all technicians are alike.
There are some of us that enjoy what we do, will go that extra mile to make things right, take pride in everything we do, and are honest.
Most of us aren’t afraid of questions, and don’t mind explaining things to you.
Just please understand, time is money to us.
We can’t stand around talking about everything, but we will try to help you understand whats going on, and why it costs so much, for things that seem simple.
Stay safe. Respect others, and If you don’t know what your doing, please call a pro.
Don’t do something that could cause your house to burn down, possibly kill someone.
Thanks…..

1. Chris Ludston says:

Sorry, I didn’t see that someone already asked you about doing multiple passes with tester already.
For some reason, those comments didn’t show, until after I posted.
And I do apologize for the long comment, that seems endless.
I make my share of mistakes, and I’m not trying to degrade anyone.
I just get so many jobs, where people are ill informed, and blame me for pre existing problems.
I hope some of what I said helps others understand how dangerous it can be, to watch videos then try to repair their homes.
Please be careful.
And I’ll try to do better, if I post again.
Thank you.

1. Chris: Your point is a good one, and I tried to emphasize that early in the article with the section on electrical safety.

11. RoyC says:

I had a past house that had problems with a couple of circuits going dead. After probing around with a volt meter, I figured out that it was due to loose connections on the common bus bar in the breaker panel, which was located in the garage. I was able to give every screw on the common and ground busses an extra half turn without much effort. Evidently something “relaxed”, possibly due to the temperature swings in the garage. So you might want to check the screws on the bus bars while you are in there next time and I suggest you use a screw driver with an insulated shaft.

1. Roy: Good point. Screws can loosen over time, especially when there are big temperature swings.

Let me strengthen your suggestion and make it a caution: Experienced electricians sometimes work in panels that are hot, but it’s best to turn off the main breakers, especially if you’re sticking a screw driver in there.

1. RoyC says:

Turning the main breaker off is good advice, but I am kind of lazy in that respect. If you do turn off the main breaker for any reason, I suggest that you first turn off all of the individual breakers (at least the big ones), and then turn them back on individually after you turn the main breaker back on to minimize current surges.

12. RoyC says:

We had an all-day grid outage in the winter one time and when the power came back up everything was fine for a while, and then the main breaker (200 amp) tripped when I turned on the microwave. I wondered how I could exceed 200 amps, but when I added up the breakers for my two heat pumps, strip heat, and electric water heater, I was near the limit. Evidently the microwave put me over the top. Lesson learned here was that when you lose the grid with an all-electric house in the winter, avoid using strip heat and let the heat pumps provide the recovery if you can.

1. Chris says:

watt if you had something that told you how much you’re using now? Emporia or Sense, for example. if you could set a notice “above 80A” that might help.
you could check the house meter but why would you if it’s just the microwave?
Span panel might automatically reduce load X when load Y goes above limit but that’s \$\$\$.

13. Paul Szymkiewicz says:

A few weekend observations…

The exercise of mapping existing electrical circuits in the house is akin to an after-the-fact load calculation exercise that article 220 of the NEC prescribes for new structures. Is one done for every new house built? Oh no, of course not. Rule of thumb is often applied.

The process of electrifying homes will be long and arduous, especially existing homes. For new homes, as loads diminish in some areas (HVAC, water heating, laundry, lighting), or remain fairly flat (kitchen, plug loads), or increase (garage), article 220 will need to adapt.

Similarly to load calculation for homes, grid management will need to adapt, especially with net-zero homes coming online. And a neighborhood full of net-zero homes with grid-connected PV will have a different impact from a neighborhood full of net-zero homes with grid-connected PV and battery storage. For some homes, the grid will become an emergency energy source only. Tell your state representative, next time you contact one, to make sure your state utilities are actively working towards that adaptation.

1. Marty R says:

A very good set of points, Paul. It is interesting that some utilities are now looking to tie privately-owned battery systems into their grid, under their optional control, so that they can ultimately have a highly distributed battery-backup system to supplement large-scale more-centralized battery systems. And, of course, make use of the investment that the homeowners and business owners have put in. When batteries with the necessary control systems become cheap enough and powerful enough, more people with solar or wind systems will install them, and such utility-connected control could reduce the prices of their grid connections and power consumption, as a trade-off by the utilities. Of course, the utilities will want to slant it heavily in their favor, as ours does now with relatively low payment rates for solar injection into the system, but averaging higher rates for purchased power, plus charges for the “privilege” of being connected to the grid. Nonetheless, we have been producing about 90-95% of the power that we consume (on an annual basis) with no battery system, while reducing our annual bill by 65-70%. To get to 100% coverage of our bills by adding more panels, including the extra charges for being grid-connected solar, we’d have to drop our ROI from 7-7.5% (after tax credits) to about 6.5% or maybe less, since they’ve reduced the payment rates per KWh. (I was originally aiming for 8%, without realizing the size of the extra charges and the amount of two-way power flow even when the sun is shining brightly on the panels, but I’m still happy with 7-7.5%.)

2. Paul Szymkiewicz says:

A clarification to the above: diminishing, flat, or increasing electrical loads for homes were meant in relation to similar all-electric older homes. A heat pump water heater with COP of 4 is a big one. Replacing resistance heaters in rural GA with even a simplest heat pump would be another one.

Glad to see a fellow PV watter, Marty! You might be interested to know that our local EMC (Sawnee EMC, north metro Atlanta) has just increased excess PV production rates from \$0.047/kWh to \$0.0525/kWh effective in May 2023, and we are not paying any extra “solar” charges on top of the regular base charge. The letter did not mention what, if anything, will happen to consumption rates in May ;-). With our smaller system that covers only about 53% of yearly energy needs (all electric) and net metering, this rate increase won’t make much of a difference. We’re using the grid like battery storage. In fact, a house battery in our case would make no financial sense.

But I am digressing. Allison wrote about electrification house cleaning, and like a distracted toddler, whenever I read “electric”, I navigate towards PV. Maybe, as you map your electrical circuits, sketch in a “future” PV circuit.

1. Marty R says:

When we installed our PV in the summer of 2021, Arizona Power had a “power purchase agreement” rate of \$0.1049/KWh, which is “fixed” for 10 years before changing to an undefined “market rate.” APS lowers their power purchase rate 10% per year. It is also not a “net” measurement, so any flow into the house from the grid arrives as the TOU rate, and any flow to the grid gets the fixed “power purchase” rate. In high-cost times, the TOU rate can be about \$0.23/KWh, but at wintertime super-low mid-day rates about \$0.03/KWh. Of course, the latter is when we tend to have significant “direct use” of the PV power (as measured by Sense), and the former is at the start and end of the day, when the PV is non-existent or low. A programmable thermostat helps, but a cold-sensitive wife and her sister require more of the high-cost grid use in colder weather. We’re all-electric also, but we have gas in the street, if we wanted to pay about \$10K to connect it and retrofit-plumb our slab-on-grade house, not counting changing appliances and converting HVAC to dual fuel. Not gonna happen.

1. Paul Szymkiewicz says:

Ah yes, the TOU rates can be a blessing and a curse. And believe me, if I lived just a couple blocks away, I’d be in GA Power territory, having similar PV billing structure to your APS. I appreciate having net metering. It seems to be somewhat fair. Our residential rate is about \$0.09/kWh, and we get paid \$0.047/kWh for net monthly excess. In designing the system, I did not count much on the excess, because I knew the size of the array wouldn’t produce much of it. Happens in 2-3 months per year (mostly Spring, sometimes Fall), and it’s a very small 100-200kWh each time.

The utility calls the \$0.047/kWh a “cost recovery” rate, presumably reduced by what it costs them to deliver “my” kWhs to other customers. I do not know much about electrical grid physics, but my guess is the electrical energy from my PV system probably does not “travel” very far before it is used by someone on the local grid.

For anyone thinking about it, knowing your consumption well, or in our case modeling the consumption of a new home within a reasonable margin of actual is important when deciding on a size of your PV system, given the type of PV billing structure your utility has.

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