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This is going to be a long post. I hope it won't be quite as dumb as the last question I asked. This is inspired by a conversation I've been having with alternative energy evangelists. Before I start, I want to say that a) I own an electric car but am absolutely no one's "EVangelist," and b) I'm intrigued by solar and have considered it for my new house, and am still thinking it over. I'm saying the foregoing in case anyone thinks that I'm somehow negative on alternatives. That's not the case. I am a facts and numbers guy. I don't do faith-based transportation or HVAC.
With that, here goes.
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Let's start with the current reality that EVs don't have the capability to send electricity anywhere but within the vehicle. That, of course, could be changed pretty easily, so for this purpose I'll postulate that we're talking about an EV that can discharge power outside of the vehicle. I will also frame the discussion, for now, in terms of the newest popularly-priced EVs now on the market or arriving soon: Chevy's Bolt, the forthcoming Tesla Model 3, and the next version of the Nissan LEAF. All of them will ship with a battery that holds approximately 60 kWh. Because of the nature of lithium-ion batteries, the intelligent EV owner will use 80% of the battery's capacity; using all of it will kill the battery life. If you use 80%, your EV battery will last for 2,000 charging cycles until it drops below 70% of original capacity.
Note to those considering a pure battery EV: Do not top it off every night. It will have a negative impact on your battery life. Instead, you should wait for your EV's battery to reach 10%-20% state of charge, then fill it up to 90%. Habitually exceed those parameters and you run the risk of turning your EV's battery into a typical cellphone battery, enjoying only a few years of life.
I'm going to use my own electricity consumption as the baseline. Yes, results will vary, but you have to start somewhere. My house, just built, is 2,700 sq ft with triple-pane windows, upgraded insulation and a hybrid heat pump, meaning one that runs on electricity to 30 degrees and a propane furnace below that. 95% of the lighting here is LED.
In the coldest month this winter (late December to late January), this house used an average of 72 kWh a day. I did some tweaking of use here, and between late January and late February it went to 53 kWh a day. Next winter will tell the real story, but for now I think 60 kWh a day at the depth of winter is a reasonable guesstimate. I've been reading the meter every day at 2 p.m., so I lack precise information on how much power is used outside of the period when panels would generate electricity.
For now, I will assume that, in winter, panels produce electricity between 10 a.m. and 4 p.m., and that the house uses more electricity before 10 a.m. and after 4 p.m. than during those hours. If it's 60 kWh a day, I'd score the "off-sun" use at 50 kWh. That would be roughly 80% of a Bolt-Model 3-new LEAF's battery, and one complete charging cycle. I'm sure these numbers aren't precise, but I think they're close enough for horseshoes for this purpose. Note: There would be losses involved in sending juice from the EV battery to the house. I figure about 15%, but maybe that's wrong? If it's roughly correct, then a 60 kW EV battery could send 40 kWh to the house net of losses, operating within manufacturer's recommendations, i.e., using 80% of battery capacity.
Also: These panels would be located at 45.75 degrees North, i.e., along the Columbia River. Unobstructed in all directions.
The foregoing raises the following issues:
1. To use the EV battery for the house will render the EV unusable for six hours a day, unless it's driven to a workplace that provides EV charging. Even then, however, the house would use all of the car's battery capacity, so you'd have to hope that your workplace was very close to your home. Otherwise, you'd have just bought yourself a $35,000 storage battery. Yep, it'd have wheels and a motor, etc., but God help you if you actually used it for that purpose in winter.
Note: Why pick winter? The answer is that winter is the most challenging, and if you're thinking that you'll go off-grid, you need to plan for the worst. Same goes for EV driving, by the way. In winter, an EV typically uses 50% more electricity per mile than it does in summer. I'd point out that EVs really don't like going uphill. You use a lot more juice going uphill than you save by going downhill. These and other things rarely get mentioned by what I like to call the EVangelists.
2. Can a typical household panel setup generate 50 kWh a day during winter, over and above what the house itself uses when the sun is up? How does that change when in rain, snow, and fog? (Between mid-December and late February, it's no day at the beach around here.)
3. Charging cycles. I think someone who uses an EV as their panel storage will devote at least 200 cycles a year, and probably more, to backing up the panels. Use it for nothing but that purpose, and the battery life will be 10 years. I suspect the reality would be harsher -- at least 300 cycles a year -- hence 6-2/3 years of battery life.
4. There can be no seasonal storage, given the relatively small capacity of the EV battery. Thus, the great summer surplus from the panels cannot carry over to winter months in an off-grid application in which your EV is your storage battery.
5. Someone who works for a living will leave his house before prime panel hours, and arrive afterwards. So, if he's truly off-grid, he's going to need another backup battery at home.
THESIS:
Forget about using your EV battery as your panel backup. If you do, you'd better heat your house entirely with wood or propane, and ditch that heat pump.
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Folks, please shoot holes in the above if you'd like. All I ask is that people withhold their sarcasm. I can live with it, but I so much more prefer a civil and informative conversation. I have a lot of respect for this group, and hope for some guidance here. There are things I don't know, and that's why I am here asking. Thanks much.
With that, here goes.
---------------------
Let's start with the current reality that EVs don't have the capability to send electricity anywhere but within the vehicle. That, of course, could be changed pretty easily, so for this purpose I'll postulate that we're talking about an EV that can discharge power outside of the vehicle. I will also frame the discussion, for now, in terms of the newest popularly-priced EVs now on the market or arriving soon: Chevy's Bolt, the forthcoming Tesla Model 3, and the next version of the Nissan LEAF. All of them will ship with a battery that holds approximately 60 kWh. Because of the nature of lithium-ion batteries, the intelligent EV owner will use 80% of the battery's capacity; using all of it will kill the battery life. If you use 80%, your EV battery will last for 2,000 charging cycles until it drops below 70% of original capacity.
Note to those considering a pure battery EV: Do not top it off every night. It will have a negative impact on your battery life. Instead, you should wait for your EV's battery to reach 10%-20% state of charge, then fill it up to 90%. Habitually exceed those parameters and you run the risk of turning your EV's battery into a typical cellphone battery, enjoying only a few years of life.
I'm going to use my own electricity consumption as the baseline. Yes, results will vary, but you have to start somewhere. My house, just built, is 2,700 sq ft with triple-pane windows, upgraded insulation and a hybrid heat pump, meaning one that runs on electricity to 30 degrees and a propane furnace below that. 95% of the lighting here is LED.
In the coldest month this winter (late December to late January), this house used an average of 72 kWh a day. I did some tweaking of use here, and between late January and late February it went to 53 kWh a day. Next winter will tell the real story, but for now I think 60 kWh a day at the depth of winter is a reasonable guesstimate. I've been reading the meter every day at 2 p.m., so I lack precise information on how much power is used outside of the period when panels would generate electricity.
For now, I will assume that, in winter, panels produce electricity between 10 a.m. and 4 p.m., and that the house uses more electricity before 10 a.m. and after 4 p.m. than during those hours. If it's 60 kWh a day, I'd score the "off-sun" use at 50 kWh. That would be roughly 80% of a Bolt-Model 3-new LEAF's battery, and one complete charging cycle. I'm sure these numbers aren't precise, but I think they're close enough for horseshoes for this purpose. Note: There would be losses involved in sending juice from the EV battery to the house. I figure about 15%, but maybe that's wrong? If it's roughly correct, then a 60 kW EV battery could send 40 kWh to the house net of losses, operating within manufacturer's recommendations, i.e., using 80% of battery capacity.
Also: These panels would be located at 45.75 degrees North, i.e., along the Columbia River. Unobstructed in all directions.
The foregoing raises the following issues:
1. To use the EV battery for the house will render the EV unusable for six hours a day, unless it's driven to a workplace that provides EV charging. Even then, however, the house would use all of the car's battery capacity, so you'd have to hope that your workplace was very close to your home. Otherwise, you'd have just bought yourself a $35,000 storage battery. Yep, it'd have wheels and a motor, etc., but God help you if you actually used it for that purpose in winter.
Note: Why pick winter? The answer is that winter is the most challenging, and if you're thinking that you'll go off-grid, you need to plan for the worst. Same goes for EV driving, by the way. In winter, an EV typically uses 50% more electricity per mile than it does in summer. I'd point out that EVs really don't like going uphill. You use a lot more juice going uphill than you save by going downhill. These and other things rarely get mentioned by what I like to call the EVangelists.
2. Can a typical household panel setup generate 50 kWh a day during winter, over and above what the house itself uses when the sun is up? How does that change when in rain, snow, and fog? (Between mid-December and late February, it's no day at the beach around here.)
3. Charging cycles. I think someone who uses an EV as their panel storage will devote at least 200 cycles a year, and probably more, to backing up the panels. Use it for nothing but that purpose, and the battery life will be 10 years. I suspect the reality would be harsher -- at least 300 cycles a year -- hence 6-2/3 years of battery life.
4. There can be no seasonal storage, given the relatively small capacity of the EV battery. Thus, the great summer surplus from the panels cannot carry over to winter months in an off-grid application in which your EV is your storage battery.
5. Someone who works for a living will leave his house before prime panel hours, and arrive afterwards. So, if he's truly off-grid, he's going to need another backup battery at home.
THESIS:
Forget about using your EV battery as your panel backup. If you do, you'd better heat your house entirely with wood or propane, and ditch that heat pump.
------------------
Folks, please shoot holes in the above if you'd like. All I ask is that people withhold their sarcasm. I can live with it, but I so much more prefer a civil and informative conversation. I have a lot of respect for this group, and hope for some guidance here. There are things I don't know, and that's why I am here asking. Thanks much.
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