Here's when solar panel owners (and everyone else) should charge

[prius2pony]

Since I have had solar panels for a year, and my new MME will be charged primarily at home (I’m a low-milage retiree), I thought I’d share what I learned about the “greenest/cleanest” time to charge. I live outside Chicago and my solar system is on a Net Metering arrangement with ComEd. This means that at any given moment in time, if my panels are producing more than the house is using, the excess is sent up to contribute to the energy in the grid. When my bill is computed for a month, my actual usage is subtracted from my generation, and the excess I contributed is credited and “rolled over” to the next month. It continues like this monthly, until each April when any excess credits I have are zeroed out, and the annual cycle begins again. My system went live in February 2020. Since then, I have always out-produced consumption (measured by month), so my electric bill has been about $16 each month (the amount ComEd collects just for fees associated with my being part of the grid–no expense at all for Kwh used.) Since the cloudy weather last month had my production behind my consumption, I will likely be running down my rolled-over credits near to zero by the time April’s zeroing-out occurs. That’s just right!


While many of you have electricity plans that make overnight energy use rates lower than daytime, you choose night time charging to save money. For me, the money is the same no matter when I charge. I asked my son, who works in the energy industry–specifically with generation & transmission–if he could research and tell me when I should charge in order to have the most green/clean impact. The answer is a bit counterintuitive, and surprised me abit, but the explanation makes sense; it goes like this:

There is a quickly growing number of wind and solar contributors to our grid (including my rooftop system). All that clean/green energy is creating a lower demand for Kw’s from the coal/gas/nuclear plants. The grid, in fact, uses those clean sources first, then draws the needed difference from the coal & gas-fired and nuclear plants. These fueled generation plants actually have to use more fuel for each additional Kw produced.

Here’s the key: If I charge my car during the day (when my solar panels are generating Kw’s), I am lessening the clean/green solar contribution I make to the grid, and ensure that those dirty plants need to produce more during the day, when their additional production requires more fuel burned per Kw. If I charge at night, I’m tapping into power from those plants, but at a time they are using less fuel per Kw generated. (That point is, in fact, true for all of you who pay the same rate no matter the time of day you choose to charge. So night charging is more eco-friendly for you, too!) My solar panels are actually having a greater positive impact on the environment by replacing dirty daytime energy production than they would if I first tapped them for my EV charging. So, the cleanest/greenest time for someone in my situation is to charge at night–even though that’s not the time my panels are generating power. And for those who pay the same rates night-or-day, you should also charge at night when each Kw you need is being created with less fuel than during the daytime.

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[Kamuelaflyer]

There are no longer any net metering spots available in my area. Or any variations of net metering. There is simply a huge overabundance of power from solar here. Lowest cost time? 9am to 5pm as that's when all the solar panels are generating the most. That would be the cheapest and greenest times to charge here.

Because of the lack of slots we're on "Customer-Self Supply." We're connected to the grid but it powers/recharges our 2 batteries (16 kWh each) as needed when the panels can't. Our system doesn't send power off to the grid either.

So for us, the best time to charge will be after 11 am when the batteries are pretty full, until around 3 pm. It'll vary upon location and circumstances of course, but your point is well taken.

 

[prius2pony]

There are no longer any net metering spots available in my area. Or any variations of net metering. There is simply a huge overabundance of power from solar here. Lowest cost time? 9am to 5pm as that's when all the solar panels are generating the most. That would be the cheapest and greenest times to charge here.

Because of the lack of slots we're on "Customer-Self Supply." We're connected to the grid but it powers/recharges our 2 batteries (16 kWh each) as needed when the panels can't. Our system doesn't send power off to the grid either.

So for us, the best time to charge will be after 11 am when the batteries are pretty full, until around 3 pm. It'll vary upon location and circumstances of course, but your point is well taken.

Thanks for this info. I find it encouraging that your have "an overabundance of power from solar"!

 

[Maric]

Thanks for this. Also full solar and thought charging mid day at peak energy production was the best time. This makes sense though.

 

[louibluey]

Same system of Net Metering here in upstate, NY (National Grid). I have a few different kinds of Delonghi heater (ceramic panel on the bedroom wall, oil-electric in the office, convection in the living room) around the home, and enjoy a warm room now and then to burn off my excess. My annual anniversary reading is coming up around March 20. Not sure how much excess I will have next year, now with LouieBluey in the stable.

I think your note about daytime charging is spot on. Even so, and even as a green leaning person, I just charge when I get home. Here are my winter peaks that got me to just about balance out to net zero (almost no lost credits to the power company, no payment to them either for excess). Blue is solar (about 60 kWh/day summer max, 20% of that winter), orange consumption (enphase). I usually get within about $15 over.

 

[timbop]

hmm, interesting

 

[prius2pony]

Same system of Net Metering here in upstate, NY (National Grid). I have a few different kinds of Delonghi heater (ceramic panel on the bedroom wall, oil-electric in the office, convection in the living room) around the home, and enjoy a warm room now and then to burn off my excess. My annual anniversary reading is coming up around March 20. Not sure how much excess I will have next year, now with LouieBluey in the stable.

I think your note about daytime charging is spot on. Even so, and even as a green leaning person, I just charge when I get home. Here are my winter peaks that got me to just about balance out to net zero (almost no lost credits to the power company, no payment to them either for excess). Blue is solar (about 60 kWh/day summer max, 20% of that winter), orange consumption (enphase). I usually get within about $15 over.

That's really a good "tuning" of your usage. You're using up your credits just right. I'm glad my system seems to be on track to do similarly.

 

[ajmartineau]

Hawaii needs more wind and tidal power. ...And maybe some geothermal. ?

 

[phidauex]

Hoo boy, this is a complex topic, and I'll start by saying that it is EXTREMELY locally dependent. Your individual state or region is likely to have very different dynamics than even other nearby states.

Setting aside cost for the moment, there are two times that are "greenest" for charging an EV:

1. When the overall load on the grid is very low, and conventional thermal generators are running at close to minimum loads, meaning additional energy is close to "free" because the units are basically idling. This is most likely to be in the middle of the night if you live in a region of the continental US with a moderate to large legacy coal or nuclear supply.

2. When renewable generation is so high that it is being curtailed (there is too much of it on the grid so they reduce the output of the plants). This is most likely to be 10am to 2pm in regions with a lot of solar, though it could be in the middle of the night again in an area with a lot of wind (TX, IA, in particular).

There are two worst times, which are when the load on the grid is rapidly increasing, and many fast, low-efficiency natural gas peakers are coming online and trying to ramp power as fast as possible. This worst time will vary a bit, but is usually 6am to 8am, and 5pm to 8pm.

The more your region depends on combined cycle/natural gas, the less the time of day will matter, because these plants ramp faster, and have lower minimum loads than older coal plants, so the variable fuel cost of night charging is not much different from day charging (the plants don't idle quite so high).

For most parts of the continental US I'd agree that middle of the night is generally best, because loads are low, and the cheapest and lowest fuel thermal generation is idling and available. This also tends to correspond to the cheapest rates if you have a time of use plan.

In CA, MA, NV, VT, HI, in particular, daytime solar production is exceeding loads in many areas. Your load zone may be curtailing solar (throwing energy away) because it isn't needed anywhere. CA, MA and HI are addressing this through huge grid energy storage systems and hybrid PV/storage power plants, but it is creeping up in many locations.

There are extreme localized examples, such as the island of Kaua'i which is now running on 100% renewables between 10am and 2pm - the resource manager there told me that he wishes everyone would charge their EVs in the middle of the day so he could relax curtailment on their solar plants.

Likewise, my PV plants in CA are having the crap curtailed out of them right now. If you are charging anywhere in the central valley, 10am to 2pm is a great time to charge from environmentally "free" solar power (PG&E will still charge you, of course!).

Over time, I think this will result in an interesting shift in charging priorities. For now, most consumers and communities are best off with middle-of-the-night charging. However, as solar penetration increases, daytime oversupply becomes a problem, and while storage can address the issue, simply moving loads from night to day can also help, and is cheaper than adding grid storage just to support night charging.

I wonder if in 5-10 years a lot more utilities will be offering businesses incentives to add chargers for employees so they can charge with plentiful solar during the middle of the day, and raising prices at night to discourage night charging.

 

[prius2pony]

Hoo boy, this is a complex topic, and I'll start by saying that it is EXTREMELY locally dependent. Your individual state or region is likely to have very different dynamics than even other nearby states.

Setting aside cost for the moment, there are two times that are "greenest" for charging an EV:

1. When the overall load on the grid is very low, and conventional thermal generators are running at close to minimum loads, meaning additional energy is close to "free" because the units are basically idling. This is most likely to be in the middle of the night if you live in a region of the continental US with a moderate to large legacy coal or nuclear supply.

2. When renewable generation is so high that it is being curtailed (there is too much of it on the grid so they reduce the output of the plants). This is most likely to be 10am to 2pm in regions with a lot of solar, though it could be in the middle of the night again in an area with a lot of wind (TX, IA, in particular).

There are two worst times, which are when the load on the grid is rapidly increasing, and many fast, low-efficiency natural gas peakers are coming online and trying to ramp power as fast as possible. This worst time will vary a bit, but is usually 6am to 8am, and 5pm to 8pm.

The more your region depends on combined cycle/natural gas, the less the time of day will matter, because these plants ramp faster, and have lower minimum loads than older coal plants, so the variable fuel cost of night charging is not much different from day charging (the plants don't idle quite so high).

For most parts of the continental US I'd agree that middle of the night is generally best, because loads are low, and the cheapest and lowest fuel thermal generation is idling and available. This also tends to correspond to the cheapest rates if you have a time of use plan.

In CA, MA, NV, VT, HI, in particular, daytime solar production is exceeding loads in many areas. Your load zone may be curtailing solar (throwing energy away) because it isn't needed anywhere. CA, MA and HI are addressing this through huge grid energy storage systems and hybrid PV/storage power plants, but it is creeping up in many locations.

There are extreme localized examples, such as the island of Kaua'i which is now running on 100% renewables between 10am and 2pm - the resource manager there told me that he wishes everyone would charge their EVs in the middle of the day so he could relax curtailment on their solar plants.

Likewise, my PV plants in CA are having the crap curtailed out of them right now. If you are charging anywhere in the central valley, 10am to 2pm is a great time to charge from environmentally "free" solar power (PG&E will still charge you, of course!).

Over time, I think this will result in an interesting shift in charging priorities. For now, most consumers and communities are best off with middle-of-the-night charging. However, as solar penetration increases, daytime oversupply becomes a problem, and while storage can address the issue, simply moving loads from night to day can also help, and is cheaper than adding grid storage just to support night charging.

I wonder if in 5-10 years a lot more utilities will be offering businesses incentives to add chargers for employees so they can charge with plentiful solar during the middle of the day, and raising prices at night to discourage night charging.

Thank you for this very helpful expansion on the topic! I learned a lot here.

 

[woody]

Hoo boy, this is a complex topic, and I'll start by saying that it is EXTREMELY locally dependent. Your individual state or region is likely to have very different dynamics than even other nearby states.

Setting aside cost for the moment, there are two times that are "greenest" for charging an EV:

1. When the overall load on the grid is very low, and conventional thermal generators are running at close to minimum loads, meaning additional energy is close to "free" because the units are basically idling. This is most likely to be in the middle of the night if you live in a region of the continental US with a moderate to large legacy coal or nuclear supply.

2. When renewable generation is so high that it is being curtailed (there is too much of it on the grid so they reduce the output of the plants). This is most likely to be 10am to 2pm in regions with a lot of solar, though it could be in the middle of the night again in an area with a lot of wind (TX, IA, in particular).

There are two worst times, which are when the load on the grid is rapidly increasing, and many fast, low-efficiency natural gas peakers are coming online and trying to ramp power as fast as possible. This worst time will vary a bit, but is usually 6am to 8am, and 5pm to 8pm.

The more your region depends on combined cycle/natural gas, the less the time of day will matter, because these plants ramp faster, and have lower minimum loads than older coal plants, so the variable fuel cost of night charging is not much different from day charging (the plants don't idle quite so high).

For most parts of the continental US I'd agree that middle of the night is generally best, because loads are low, and the cheapest and lowest fuel thermal generation is idling and available. This also tends to correspond to the cheapest rates if you have a time of use plan.
On your journey be wary of engineers (no offense intended)

In CA, MA, NV, VT, HI, in particular, daytime solar production is exceeding loads in many areas. Your load zone may be curtailing solar (throwing energy away) because it isn't needed anywhere. CA, MA and HI are addressing this through huge grid energy storage systems and hybrid PV/storage power plants, but it is creeping up in many locations.

There are extreme localized examples, such as the island of Kaua'i which is now running on 100% renewables between 10am and 2pm - the resource manager there told me that he wishes everyone would charge their EVs in the middle of the day so he could relax curtailment on their solar plants.

Likewise, my PV plants in CA are having the crap curtailed out of them right now. If you are charging anywhere in the central valley, 10am to 2pm is a great time to charge from environmentally "free" solar power (PG&E will still charge you, of course!).

Over time, I think this will result in an interesting shift in charging priorities. For now, most consumers and communities are best off with middle-of-the-night charging. However, as solar penetration increases, daytime oversupply becomes a problem, and while storage can address the issue, simply moving loads from night to day can also help, and is cheaper than adding grid storage just to support night charging.

I wonder if in 5-10 years a lot more utilities will be offering businesses incentives to add chargers for employees so they can charge with plentiful solar during the middle of the day, and raising prices at night to discourage night charging.

Hoo boy, this is a complex topic, and I'll start by saying that it is EXTREMELY locally dependent. Your individual state or region is likely to have very different dynamics than even other nearby states.
Your opening statement hits the nail on the head.
The energy provider monopoly here in Colorado is Xcel. They have fought alternative energy since the beginning. They vigorously fight and continue to fight individual residential solar at every turn. They have found a way to destroy every program the state has come up with to date.
Take a trip to Colorado and see how much residential solar there is. Perhaps as much as 10% - 310 days of sunshine. My community of 25 homes only has 3 homes with solar (12%, and they all could afford it). Then take a trip to Germany - no sunshine, solar everywhere.
Colorado only recently became a CARB state. We now are able to purchase EVs. Prior to this only Teslas, Leafs, Volts or Bolts were available.
Perhaps alternative energy will change here as well, under CARB.
I am 100% electric(had to pay Xcel to remove their gas lines off my property!). My solar array produces more energy in a year than I consume.
Excel "pays" me 5mils/kWh and charges me $.13/kWh. They recently changed their billing methods(again) and now charge me ~$5/month for 9 months (manipulated monthly) and `$200 for the remainder of the year. Under the previous billing system I would receive $5 - $20/mo for those 9 months and be charged nothing except for the other 3 months [winter]. The new billing system does no longer show my PV production. They only have a very few people who understand their billing procedures, and they do not really understand.
We charge our vehicles in the daytime at level 1 charging, using our solar production directly. Rarely using Level 2 charging. We are now both retired and therefor only occasionally operate two vehicles at the same time. We still send more energy to the grid than we consume most of the year.
Yes, EXTREMELY locally dependent.
The Coal, Oil, Gas and Utility (COGU) powers still absolutely control energy production. They control the source, the resources, the media, the politicians. There are no true consumer organizations to help the homeowner with solar.
There has been and continues to be negative press regarding solar and EVs, although this does seem to be waning.
Granted the 100 year+ old legislation which enabled the "public utilities" is outdated, but it remains. They are inept and inefficient, as are all government (subsidized) agencies. They do not have to compete or worry about profit. They are guaranteed a profit when loosing money or are criminally mismanaged (CA, TX - recent examples).
We do not have good or efficient batteries because COGU controls . The technologies for compact and efficient batteries are there but not there for you.
The utilities want to maintain their monopolies. They cannot survive competition. They know not how.
The utilities stumbling block is not production, but storage. Controlling storage will be their triumph. (I, for one, should have 4x my current battery capacity to successfully function year round and remain grid tied)
Some of the other COGU gangsters are already considering and venturing into the alternative energy world.
Mr. Musk may not be looked upon in the best light by some of us here, BUT he has been instrumental in moving EV and solar forward at a faster pace than would otherwise be there.
I have stated before, he is not a manager or a businessman, but he is a great salesman and idea promoter and has to be considered part of the formula leading to success.
On your journey into the future, be wary of engineers (no offense intended), especially electrical and renewable energy types. (talk to the electrician, not the engineer; the framer, not the architect; etc.) The big RED FLAG is if they ask or talk about solar panel efficiency(solar panels are not currently efficient, it is still a primitive technology).
The only number that has any relevancy is watts/panel.
I believe success will be best achieved cooperatively, us and them.
Collect it and use it.
Enjoy the journey

 

[engnrng]

Lots of good information and analysis here! The worst thing you can do is "plug it in and start charging when I get home". The car can be set to start charging at 10 pm or midnight. At Level 2, my Mach E is "full" by breakfast, and off I go to work. During the day, my solar has replenished my onsite batteries by noon or so, the surplus solar then helps to feed the grid when it is hungry, and my batteries supply everything I need through the evening hours when demand for fossil fuel energy is highest. If I am not charging, my batteries supply my needs throughout the night (pool filter pump is set to run from midnight to 6 am). If I am charging one of my EV's, beginning at 10 pm, my batteries reach their reserve level by 3 am or so - then I am pulling charge power from the grid for a couple of hours at a time of very low grid demand. I wish I could add 1 more battery, but codes, County, State, and Utilities prevent that. I can't imagine why... All in all, I am quite pleased with my system and my (mostly) solar powered vehicles.

 

[engnrng]

...Even so, and even as a green leaning person, I just charge when I get home.

Good for you as a net contributor to your grid. However, PLEASE reconsider your charge habits. Plug in when you get home, yes, but please set your Charge Time to after 10 pm. That few minutes it takes you one time to set your charge time in FordPass will truly confirm your "green leaning" commitment! Thanks in advance!

In California, one of the big problems the utilities have is the huge increase in demand after the solar tapers down in the late afternoon - as more EV's come online and begin energy draws due to the unawareness or laziness of EV owners. In the space of an hour, the grid goes from high green to higher dirty. This provides an opportunity for the anti-EV folks to claim that EV's are using dirty energy and pollute as much or more than gas/diesel. Truly a false claim, but why given them more "fuel" for their ire?

 

[HBGuy]

We're having 3 x 13.5 Kw Tesla Powerwall-2s installed, when they become available. Ours have been on backorder since Aug'20, and we expect them in 2Q or 3Q'21. For anyone resident in California, its "Self Generation Improvement Program" (SGIP) offers an incentive of up to $3k for each 13.5 kwh battery installed. There are two programs: residential (which was oversubscribed for 2020) and commercial. The latter had funds available when we placed our order, but there is a minimum order of 3 Powerwalls. Our 3 Powerwalls will cost ~ $14k after installation ($9k SGIP grant, plus 26% Federal tax credit). SGIP grants are valid for 18 months because of supply constraints.

I mention this because with the additional 3 KW of solar we recently installed (5.8KW total), we were moved to SCE's TOU-PRIME rates, which will result in us having peak rates of $0.41/kwh + 5% City of HB excise tax, or ~ $0.43/kw between 1600-2100 PT. The Powerwalls will enable us to use our excess production and keep our cost at $0.17/kwh. We were also advised the 1 Powerwall is needed for household appliances - fridge, lights, microwave, etc. - and a second for our A/C. The third is in case of a prolonged outage - earthquake, etc.

 

[Livinglavidaleggings]

We're having 3 x 13.5 Kw Tesla Powerwall-2s installed, when they become available. Ours have been on backorder since Aug'20, and we expect them in 2Q or 3Q'21. For anyone resident in California, its "Self Generation Improvement Program" (SGIP) offers an incentive of up to $3k for each 13.5 kwh battery installed. There are two programs: residential (which was oversubscribed for 2020) and commercial. The latter had funds available when we placed our order, but there is a minimum order of 3 Powerwalls. Our 3 Powerwalls will cost ~ $14k after installation ($9k SGIP grant, plus 26% Federal tax credit). SGIP grants are valid for 18 months because of supply constraints.

I mention this because with the additional 3 KW of solar we recently installed (5.8KW total), we were moved to SCE's TOU-PRIME rates, which will result in us having peak rates of $0.41/kwh + 5% City of HB excise tax, or ~ $0.43/kw between 1600-2100 PT. The Powerwalls will enable us to use our excess production and keep our cost at $0.17/kwh. We were also advised the 1 Powerwall is needed for household appliances - fridge, lights, microwave, etc. - and a second for our A/C. The third is in case of a prolonged outage - earthquake, etc.

I'm wondering if you can clear something up for me. Im in California and believe I qualify for sgip equity resiliency. I need a developer to apply for the sgip for me. Im having solar installed and want to have the company submit the sgip for me. I thought I could have the system installed and apply for sgip at the same time. Then, when I receive the reservation of funds notice, I could buy the batteries (with the expectation of being reimbursed because I received the reservation of funds). The company im installing with says I have to pay for the battery before they can even submit for the sgip. Is this true? They told me its because they need a serial number off the batteries to put on the initial application. At the same time, batteries are backordered and grants are good up to 18 months but how does this work if you don't have the serial number off the batteries because they are backordered? Is someone who is eligible for sgip just supposed to pay up front and hope everything goes right with the sgip application or they are out thousands of dollars? Its hard for me to believe that you can't start the application for sgip to see if you can get funds reserved unless you buy a battery outright before you can even know if you can get funds. Sorry for the long post. Ive asked other places but no one seems to understand what im asking. I worry im not clear. Thank you.

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