Do you have a solar array? And a home battery? What's your experience?
October 14, 2021 12:36 PM Subscribe
I'm having a PV array installed on my home in the spring, and am debating whether to also install a battery system. I have a bunch of usage questions for people who have such a system, or know about them, or are preppers worried about being stranded/uncomfortable following a natural disaster.
In my area (San Juan Islands, Western Washington) we're in the rain shadow of Vancouver Island but hardly rain-free. Still, my roof is big enough that the proposed array will cover ~100% of my current electrical usage. We do not currently have TOU pricing, but the local electric coop is considering implementing it. I'll have a bidirectional meter and will sell back to the utility at wholesale price.
We're somewhat vulnerable to power losses due to having all of our power come via a trunk cable from the mainland. Also we get hella winter storms. I've heard the powers that be have made us less vulnerable overall, but being on an island makes me seek redundancy and I've gone a wee bit prepper since moving here. For that reason, I'm planning to buy a plug-in hybrid when the right one goes on the market, so I'll have two sources of fuel for getting around.
My home's heat is propane fueled and I'll need a new system soon, as it's 22 years old now.
With all that in the background, a few questions about batteries.
1. Assuming TOU pricing is implemented, or that I choose to program the battery based on TOU as a favor to my local utility cooperative:
(a) Does that put me at significant risk of having low/no charge if there's a storm and the power goes out because I've drained it during my charge/use cycle? If so, is there some way to mitigate this?
(b) Does that lower the battery's life expectancy by increasing the number of cycles it goes through?
2. If I add a plug-in hybrid to the mix, does that affect the answers to 1(a) and 1(b)?
3. I'm probably going to have the battery installed in my garage, which is a separate structure, both for fire/explosion safety and so I don't have to hear the battery cooling fan. Any comments on this, e.g. about temperature or something else?
4. I've heard that you need to keep your battery locked up, and have HIGH CAPACITY warning signs on the exterior. True? (I read this on a website from India; is that local to them, or does it apply here/everywhere?) I ask because I don't lock my garage, and half the time don't bother closing it.
5. When I replace my current propane boiler (which powers radiant floor heat), should I consider moving to a heat pump or sticking with propane? Pros of heat pump: much more efficient, cheaper. Pros of propane: fuel redundancy. I think I can't heat my house with the battery if I've got a heat pump, but I can if I've got a propane boiler because the only power I'll need is the water pump. True? Thoughts?
6. General thoughts?
In my area (San Juan Islands, Western Washington) we're in the rain shadow of Vancouver Island but hardly rain-free. Still, my roof is big enough that the proposed array will cover ~100% of my current electrical usage. We do not currently have TOU pricing, but the local electric coop is considering implementing it. I'll have a bidirectional meter and will sell back to the utility at wholesale price.
We're somewhat vulnerable to power losses due to having all of our power come via a trunk cable from the mainland. Also we get hella winter storms. I've heard the powers that be have made us less vulnerable overall, but being on an island makes me seek redundancy and I've gone a wee bit prepper since moving here. For that reason, I'm planning to buy a plug-in hybrid when the right one goes on the market, so I'll have two sources of fuel for getting around.
My home's heat is propane fueled and I'll need a new system soon, as it's 22 years old now.
With all that in the background, a few questions about batteries.
1. Assuming TOU pricing is implemented, or that I choose to program the battery based on TOU as a favor to my local utility cooperative:
(a) Does that put me at significant risk of having low/no charge if there's a storm and the power goes out because I've drained it during my charge/use cycle? If so, is there some way to mitigate this?
(b) Does that lower the battery's life expectancy by increasing the number of cycles it goes through?
2. If I add a plug-in hybrid to the mix, does that affect the answers to 1(a) and 1(b)?
3. I'm probably going to have the battery installed in my garage, which is a separate structure, both for fire/explosion safety and so I don't have to hear the battery cooling fan. Any comments on this, e.g. about temperature or something else?
4. I've heard that you need to keep your battery locked up, and have HIGH CAPACITY warning signs on the exterior. True? (I read this on a website from India; is that local to them, or does it apply here/everywhere?) I ask because I don't lock my garage, and half the time don't bother closing it.
5. When I replace my current propane boiler (which powers radiant floor heat), should I consider moving to a heat pump or sticking with propane? Pros of heat pump: much more efficient, cheaper. Pros of propane: fuel redundancy. I think I can't heat my house with the battery if I've got a heat pump, but I can if I've got a propane boiler because the only power I'll need is the water pump. True? Thoughts?
6. General thoughts?
You might consider getting an F-150 lightning and using that as a backup power source. It can power your house for a week! As someone pointed out on the internet, it’s kind of like buying four Tesla power walls wrapped in a free pickup truck.
posted by rockindata at 1:11 PM on October 14, 2021 [7 favorites]
posted by rockindata at 1:11 PM on October 14, 2021 [7 favorites]
Batteries are expensive and are best used for critical loads. The F-150 solution seems sound, but do a lot of research first. Supply issues have hit a few manufacturers and some systems are not compatible with generators, which would be the cheapest solution.
posted by black8 at 2:02 PM on October 14, 2021
posted by black8 at 2:02 PM on October 14, 2021
An electric heat pump will be much cheaper than propane heat in your climate. Probably about half the operating cost or less. You might want to consider installing one or more mini-split heat pump units and keeping your propane as a back up, if that's something you need.
(a) Does that put me at significant risk of having low/no charge if there's a storm and the power goes out because I've drained it during my charge/use cycle? If so, is there some way to mitigate this?
The bigger your battery, the more you can hold in reserve, but the higher your upfront cost. What are the terms of selling back to the grid? Is it selling your net excess power over some time period? The details here will make a big difference if battery storage makes sense for you and how you'll want to control it.
(b) Does that lower the battery's life expectancy by increasing the number of cycles it goes through?
Yes, but the depth of discharge is more important. Lots of deep cycles will wear batteries out faster than shallow cycles. This is also different for lead acid versus lithium batteries.
posted by ssg at 2:17 PM on October 14, 2021
(a) Does that put me at significant risk of having low/no charge if there's a storm and the power goes out because I've drained it during my charge/use cycle? If so, is there some way to mitigate this?
The bigger your battery, the more you can hold in reserve, but the higher your upfront cost. What are the terms of selling back to the grid? Is it selling your net excess power over some time period? The details here will make a big difference if battery storage makes sense for you and how you'll want to control it.
(b) Does that lower the battery's life expectancy by increasing the number of cycles it goes through?
Yes, but the depth of discharge is more important. Lots of deep cycles will wear batteries out faster than shallow cycles. This is also different for lead acid versus lithium batteries.
posted by ssg at 2:17 PM on October 14, 2021
My experience is with lead-acid, but I believe applicable to LiON too. Deep discharge affects battery lifespan more than 'float' charging, so you're burning 1/1000th (or so) of its capital cost every time you drain to 20% and recharge. Selling excess PV power is a good idea, but playing time-shifting games is likely to be a net negative.
I think hybrid PV/battery systems make more sense for off-grid systems where you have low loads, or something specific to power like medical devices. A reliable gas generator would let you ride out weeks of downtime as long as you have fuel.
posted by RobotVoodooPower at 2:28 PM on October 14, 2021
I think hybrid PV/battery systems make more sense for off-grid systems where you have low loads, or something specific to power like medical devices. A reliable gas generator would let you ride out weeks of downtime as long as you have fuel.
posted by RobotVoodooPower at 2:28 PM on October 14, 2021
Roughly $1K will get you a "portable" dual or tri-fuel 10,000W generator, which will be a better bet for long-term house supply during outages and offers fuel diversity.
...I mean, I have a PV array on my roof and am considering a battery system to cover short-term (sub-4hr) outages, but for serious outages I own a generator, installed a transfer switch (to connect the generator to my electrical panel) and a few tanks of propane. I'd have installed a permanent generator, but they're hard to get permitted where I live and they cost more as well (so I didn't want to "go rogue" with an illegal install with that much money)
posted by aramaic at 3:05 PM on October 14, 2021
...I mean, I have a PV array on my roof and am considering a battery system to cover short-term (sub-4hr) outages, but for serious outages I own a generator, installed a transfer switch (to connect the generator to my electrical panel) and a few tanks of propane. I'd have installed a permanent generator, but they're hard to get permitted where I live and they cost more as well (so I didn't want to "go rogue" with an illegal install with that much money)
posted by aramaic at 3:05 PM on October 14, 2021
Response by poster: A few answers:
The hybrid can be plugged in day or night; I'm flexible. I won't be buying a vehicle as a rolling battery because that compromises my ability to drive/power my house at the same time, and means there's no battery coverage if, e.g., I'm out of town. This would leave my freezer and water pipes vulnerable. And my cats and house plants. (I have some electric heat in addition to my boiler.)
I have a gas generator and appropriate panel setup, but have never been able to get it to run. Other people have been able to, but not me. It's huge and scary and a pull start and I am simply not strong enough to start it. I hate it. Also, it lives where my spider collection is. I'll leave it where it is in case there's a very long term outage, but I've never been able to use it, so it's not a great option to rely on.
With net metering, I sell back to the utility at 50% of retail. I get credits during the year, which I use to pay for excess use, and they settle up at the end of the year if they owe me. Maybe I should not use the battery except as a backup unless they switch to TOU pricing?
So I think y'all've answered 1 and 2 and 5 for me, leaving 3 and 4. Thanks so far :)
posted by Capri at 3:29 PM on October 14, 2021
The hybrid can be plugged in day or night; I'm flexible. I won't be buying a vehicle as a rolling battery because that compromises my ability to drive/power my house at the same time, and means there's no battery coverage if, e.g., I'm out of town. This would leave my freezer and water pipes vulnerable. And my cats and house plants. (I have some electric heat in addition to my boiler.)
I have a gas generator and appropriate panel setup, but have never been able to get it to run. Other people have been able to, but not me. It's huge and scary and a pull start and I am simply not strong enough to start it. I hate it. Also, it lives where my spider collection is. I'll leave it where it is in case there's a very long term outage, but I've never been able to use it, so it's not a great option to rely on.
With net metering, I sell back to the utility at 50% of retail. I get credits during the year, which I use to pay for excess use, and they settle up at the end of the year if they owe me. Maybe I should not use the battery except as a backup unless they switch to TOU pricing?
So I think y'all've answered 1 and 2 and 5 for me, leaving 3 and 4. Thanks so far :)
posted by Capri at 3:29 PM on October 14, 2021
What matters with net metering is what time-scale the net metering happens in. If it's monthly (i.e. you get a credit at the end of the month for your net generation or pay for your net use) and you install solar that will cover about 100% of your energy use, then you won't benefit at all from TOU rates in any months when you are producing more than you use. So if net metering is your aim and you want to generate most of your energy, then you should probably just ignore TOU. Sure, there would be some potential small benefit in the winter months, but with the cost of batteries, the complexity, and the loss of energy with battery storage, this is really not going to be worthwhile.
If your utility does set up TOU, then you can certainly look into using more electricity at night (charging an EV at night, running your dishwasher at night, heating water at night, running a heat pump before 6am or whatever time is the cut-off, etc.).
posted by ssg at 4:33 PM on October 14, 2021
If your utility does set up TOU, then you can certainly look into using more electricity at night (charging an EV at night, running your dishwasher at night, heating water at night, running a heat pump before 6am or whatever time is the cut-off, etc.).
posted by ssg at 4:33 PM on October 14, 2021
Lithium batteries are much less badly affected by being run down to empty, as long as they do not fall below their minimum voltage. But limiting full cycles will improve longevity. The faster a lithium battery is charged, the worse its longevity will be. Keeping a lithium battery always fully charged (eg in "float") is also not ideal for longevity. But without such babying it will probably still last for 10 years.
As far as TOU metering and storms, some systems can check weather forecasts. Tesla Powerwall "Storm Watch" for example. Adds complexity and risk though.
Unless you do a full energy audit of your house, and determine what loads you can avoid running in an outage, and size the battery and PV appropriately for the unavoidable loads, you're likely to find out in an emergency that it's not adequate. Or perhaps that you overspent. This is the most important thing in my view, as an offgrid person, which I think people neglect. You say your PV array will cover 100% of your usage.. But consider December, when the array will be producing 1/3rd of its nominal rating on a good day.
posted by joeyh at 6:34 PM on October 14, 2021
As far as TOU metering and storms, some systems can check weather forecasts. Tesla Powerwall "Storm Watch" for example. Adds complexity and risk though.
Unless you do a full energy audit of your house, and determine what loads you can avoid running in an outage, and size the battery and PV appropriately for the unavoidable loads, you're likely to find out in an emergency that it's not adequate. Or perhaps that you overspent. This is the most important thing in my view, as an offgrid person, which I think people neglect. You say your PV array will cover 100% of your usage.. But consider December, when the array will be producing 1/3rd of its nominal rating on a good day.
posted by joeyh at 6:34 PM on October 14, 2021
6. General thoughts?
I'm about as far from a battery expert as possible, but some years back I became responsible for two marine type lead acid batteries that were used to occasionally power an old RV permanently placed on country lot. I had thought it would be a simple task, but then they couldn't be left on site because of the difficulty in charging them there and their susceptibility to freezing weather, and when I transported them home they needed to be monitored for occasional recharging to prevent damage, plus needed a supply of distilled water to top up their internal reservoir.
I'm sure if you thoroughly educate yourself on battery maintenance and gain practical experience from using them regularly at your home base, none of these chores will be insurmountable.
However, I came away from the experience believing that caring for batteries was uncomfortably close to caring for babies.
posted by fairmettle at 1:03 AM on October 15, 2021
I'm about as far from a battery expert as possible, but some years back I became responsible for two marine type lead acid batteries that were used to occasionally power an old RV permanently placed on country lot. I had thought it would be a simple task, but then they couldn't be left on site because of the difficulty in charging them there and their susceptibility to freezing weather, and when I transported them home they needed to be monitored for occasional recharging to prevent damage, plus needed a supply of distilled water to top up their internal reservoir.
I'm sure if you thoroughly educate yourself on battery maintenance and gain practical experience from using them regularly at your home base, none of these chores will be insurmountable.
However, I came away from the experience believing that caring for batteries was uncomfortably close to caring for babies.
posted by fairmettle at 1:03 AM on October 15, 2021
Best answer: I have PV + batteries at home and work. I do off-grid & grid storage systems for a living, in Australia.
As a general thing, it's worth keeping in mind that anytime you're getting paid less for the power you generate than what you're paying for theirs, you should aim to never export power. There is no value in exporting during the day and buying it back at twice the cost at a later time. And I would never alter any system setting to benefit the utility. Not because I'm selfish and mean, but because you could run it completely for their benefit and nobody but you would notice due to the vastly different scales involved. Any system you install will be inconsequential to the grid, so make sure you set it up to benefit you.
One reality of grid storage is that if you use the battery bank to store and make use of excess solar power, one of the main reasons people get batteries, then you can be left with effectively flat batteries when the grid fails. The only certain way to avoid this possibility is to have batteries that are only used if the power goes out. This is how telephone exchanges and some other critical infrastructure is done here. Sure, you could get more batteries, but storage is really expensive so people who do this (almost) never have enough capacity. There will be juggling in terms of how you set it up, and there will always be the potential for the power to go out just after you've discharged them, which would most likely be in the evening or early morning.
Based on the TOU tariffs on offer here, I don't quite see how it would materially affect any of this, other than possibly making it economical to charge your batteries from the grid if/when it's really cheap. If you could do this you would reduce your chances of getting caught short in a power outage, but still not eliminate them. My home and work systems can charge from the grid at night, when the power is cheap, and they both do so periodically in winter. We set this up when we put them in. Everything works automagically.
Unless you can afford to not care about it, you will get far better value by doing something about your generator than by adding batteries to your solar system. Specifically, replace your existing generator with something that can be either demand started or just remotely started from the house. Someone will buy your old one and whoever supplies the new one should at least be able to tell you who can install it if they can't. Decent generators are costly (but cheap compared to batteries), you won't use it much, and getting it wired into the house will have some complexities, but it will be there on the odd occasions when you need it. It's possible to get generators that use propane if you would like to stop using gasoline. This application would not warrant a diesel unless you can get a good one second hand at a low price. Whatever you install will last a long time. You don't need to spend extra on a diesel.
Happy to answer more questions. Feel free to message me if you want. Hope it goes well whatever you do!
posted by mewsic at 3:06 AM on October 15, 2021 [3 favorites]
As a general thing, it's worth keeping in mind that anytime you're getting paid less for the power you generate than what you're paying for theirs, you should aim to never export power. There is no value in exporting during the day and buying it back at twice the cost at a later time. And I would never alter any system setting to benefit the utility. Not because I'm selfish and mean, but because you could run it completely for their benefit and nobody but you would notice due to the vastly different scales involved. Any system you install will be inconsequential to the grid, so make sure you set it up to benefit you.
One reality of grid storage is that if you use the battery bank to store and make use of excess solar power, one of the main reasons people get batteries, then you can be left with effectively flat batteries when the grid fails. The only certain way to avoid this possibility is to have batteries that are only used if the power goes out. This is how telephone exchanges and some other critical infrastructure is done here. Sure, you could get more batteries, but storage is really expensive so people who do this (almost) never have enough capacity. There will be juggling in terms of how you set it up, and there will always be the potential for the power to go out just after you've discharged them, which would most likely be in the evening or early morning.
Based on the TOU tariffs on offer here, I don't quite see how it would materially affect any of this, other than possibly making it economical to charge your batteries from the grid if/when it's really cheap. If you could do this you would reduce your chances of getting caught short in a power outage, but still not eliminate them. My home and work systems can charge from the grid at night, when the power is cheap, and they both do so periodically in winter. We set this up when we put them in. Everything works automagically.
Unless you can afford to not care about it, you will get far better value by doing something about your generator than by adding batteries to your solar system. Specifically, replace your existing generator with something that can be either demand started or just remotely started from the house. Someone will buy your old one and whoever supplies the new one should at least be able to tell you who can install it if they can't. Decent generators are costly (but cheap compared to batteries), you won't use it much, and getting it wired into the house will have some complexities, but it will be there on the odd occasions when you need it. It's possible to get generators that use propane if you would like to stop using gasoline. This application would not warrant a diesel unless you can get a good one second hand at a low price. Whatever you install will last a long time. You don't need to spend extra on a diesel.
Happy to answer more questions. Feel free to message me if you want. Hope it goes well whatever you do!
posted by mewsic at 3:06 AM on October 15, 2021 [3 favorites]
Best answer: You might consider getting an F-150 lightning and using that as a backup power source. It can power your house for a week! As someone pointed out on the internet, it’s kind of like buying four Tesla power walls wrapped in a free pickup truck.
OK there is a colossal amount of nonsense in this one comment so I logged in to correct. Let's go.
- The Ford F150 won't be out for a long time, at least a year
- ... and when it does launch, they'll lead with the $90k version
- ... and you will never ever see the "$40k" version that you might have heard about, because it is for fleet purchases only, and will be stripped down to nothing, and you can't buy it, and they may never actually sell it a la the $50k Model S that never happened, and did I mention you can't buy it?
- the power export is strictly via the low power AC interface (not high power DC) and in theory will power 10 kW of stuff but OMG you need so much fancy electrician work to make that happen you might as well forget it
- the best you can do is power anything you can RUN AN EXTENSION CORD to, like maybe a fridge if you pull it out from the wall
- in short, you're not "powering your house" with an F-150 for the above 5 reasons
I'm an EV expert, have solar on my roof, and work in residential energy storage.
Back to the OP, two things:
Generally you SHOULD include an energy storage system (ESS) with your solar install, because you can claim the tax credit (currently 26%) on the ESS along with the solar install. Adding ESS later doesn't necessarily qualify for the credit.
Net metering generally depresses the economic value of ESS, because the grid becomes your time-shifted virtual energy storage. But you don't get backup / resiliency. And you said you get 50% net metering, so it's kinda in between, so I guess you'd get half the time-shifting economic benefit of the ESS.
Personally, I think it's a no brainer. DO IT.
posted by intermod at 7:33 PM on October 15, 2021 [3 favorites]
OK there is a colossal amount of nonsense in this one comment so I logged in to correct. Let's go.
- The Ford F150 won't be out for a long time, at least a year
- ... and when it does launch, they'll lead with the $90k version
- ... and you will never ever see the "$40k" version that you might have heard about, because it is for fleet purchases only, and will be stripped down to nothing, and you can't buy it, and they may never actually sell it a la the $50k Model S that never happened, and did I mention you can't buy it?
- the power export is strictly via the low power AC interface (not high power DC) and in theory will power 10 kW of stuff but OMG you need so much fancy electrician work to make that happen you might as well forget it
- the best you can do is power anything you can RUN AN EXTENSION CORD to, like maybe a fridge if you pull it out from the wall
- in short, you're not "powering your house" with an F-150 for the above 5 reasons
I'm an EV expert, have solar on my roof, and work in residential energy storage.
Back to the OP, two things:
Generally you SHOULD include an energy storage system (ESS) with your solar install, because you can claim the tax credit (currently 26%) on the ESS along with the solar install. Adding ESS later doesn't necessarily qualify for the credit.
Net metering generally depresses the economic value of ESS, because the grid becomes your time-shifted virtual energy storage. But you don't get backup / resiliency. And you said you get 50% net metering, so it's kinda in between, so I guess you'd get half the time-shifting economic benefit of the ESS.
Personally, I think it's a no brainer. DO IT.
posted by intermod at 7:33 PM on October 15, 2021 [3 favorites]
This thread is closed to new comments.
For the hybrid, will it be plugged in during the daytime at this location, or will it be elsewhere? A battery might be necessary if the only time you have to charge it is at night.
Any change to a renewable system involves estimating a payback period. Heating can be the hardest to pay for in a reasonable time. And could the money be better spent on insulation or better windows to minimize your energy costs first?
posted by nickggully at 12:49 PM on October 14, 2021