Why do private solar arrays hook up to public utility electric lines?
January 20, 2025 6:43 PM Subscribe
Everyone I know who has installed solar panels on their personal property has them feeding into the grid, so they get paid (or money off) on their electric bill. Why don't they just route it to their house and use the electricity themselves?
Does the utility own the conversion equipment to make it usable? Or does the utility have some type of financial stake in the array even though as far as I can tell it is privately owned? Or am I wrong in my whole premise?
Does the utility own the conversion equipment to make it usable? Or does the utility have some type of financial stake in the array even though as far as I can tell it is privately owned? Or am I wrong in my whole premise?
It’s usually MUCH easier to feed into the grid and have grid-level guarantee of power 24/7 than it is to have enough panels, enough batteries, or enough switches to use up all your local solar power.
posted by clew at 6:51 PM on January 20 [14 favorites]
posted by clew at 6:51 PM on January 20 [14 favorites]
Response by poster: So can you have the battery as a back up, and kind of flip a switch back and forth between using your own and buying in? I guess I would have thought more people were using solar as a "in case everything goes wrong" option, in which case off-and-on electricity would still be pretty useful.
posted by Emmy Rae at 6:53 PM on January 20
posted by Emmy Rae at 6:53 PM on January 20
We just got a solar array installed this summer, and this is how I understand it: We live in New England, and lose 4+ hours of sunlight for a portion of the year; our average usage of 25[watts? whatever the measurement is] of electricity per day might not be met on an overcast, gloomy December/January/February/March day, and so the feed from Eversource kicks in and literally keeps the lights on.
Installing solar panels is a pricey undertaking to begin with; adding the battery would have added +50% to the cost and just wasn't doable for us. So on those long, lovely summer days we'll have, we'll be missing out on the full potential of our array.
There's also probably some kind of regulatory (maybe safety-/consistency-based?) thing that dictates all power, whether from the grid or the solar panels, needs to be delivered to the house via one source.
ETA: We'll get a check from Eversource for any power we generate but do not use. We also have the option of donating that "extra energy" to a non-profit, like our local, independant radio station.
posted by feistycakes at 6:56 PM on January 20 [3 favorites]
Installing solar panels is a pricey undertaking to begin with; adding the battery would have added +50% to the cost and just wasn't doable for us. So on those long, lovely summer days we'll have, we'll be missing out on the full potential of our array.
There's also probably some kind of regulatory (maybe safety-/consistency-based?) thing that dictates all power, whether from the grid or the solar panels, needs to be delivered to the house via one source.
ETA: We'll get a check from Eversource for any power we generate but do not use. We also have the option of donating that "extra energy" to a non-profit, like our local, independant radio station.
posted by feistycakes at 6:56 PM on January 20 [3 favorites]
The panels on the roof do provide power to the house. But the chances of the output of the panels at any moment exactly matching the power needs of the house are basically zero. So there will always be either excess power from the panels or not enough at any point in time. Batteries are one way to absorb the excess and to provide extra power when the panels are at a deficit. But tying to the grid is sort of like a giant battery: it will always accept your excess (and often pay you for it!), and it will always be able to make up for any deficit. Tying to the grid is cheaper than buying your own batteries, so most people do that.
Usually, any absorbing of excess or filling in of a deficit happens fully automatically with either batteries or a grid-tied system. Energy just flows in whichever direction is needed to balance things out. If you're tied to the grid, then your energy provider will bill you based on the amount you take in and the amount you send back. There are various different schemes for how to account for the in and the out amount, with different pricing for each, caps, roll-over, etc. all potentially in play.
The "equipment to make [the power] usable" is part of the equipment installed in/on the house, and it's owned by the homeowner. It's called an "inverter." It's necessary whether you're sending power back to the grid or not, as it converts from the DC voltage that the panels produce to the AC voltage that both homes and the grid use.
posted by whatnotever at 7:01 PM on January 20 [29 favorites]
Usually, any absorbing of excess or filling in of a deficit happens fully automatically with either batteries or a grid-tied system. Energy just flows in whichever direction is needed to balance things out. If you're tied to the grid, then your energy provider will bill you based on the amount you take in and the amount you send back. There are various different schemes for how to account for the in and the out amount, with different pricing for each, caps, roll-over, etc. all potentially in play.
The "equipment to make [the power] usable" is part of the equipment installed in/on the house, and it's owned by the homeowner. It's called an "inverter." It's necessary whether you're sending power back to the grid or not, as it converts from the DC voltage that the panels produce to the AC voltage that both homes and the grid use.
posted by whatnotever at 7:01 PM on January 20 [29 favorites]
Most electrical codes prevent that kind of switch: indeed, the kind of inverter used for grid-connected solar cannot work unless there is grid frequency present. This is to prevent small solar installations backfeeding during a blackout, a major safety issue for anyone working on the line.
Batteries are very expensive, and seldom make great financial sense for the grid-connected user. They're also not very efficient.
posted by scruss at 7:02 PM on January 20 [11 favorites]
Batteries are very expensive, and seldom make great financial sense for the grid-connected user. They're also not very efficient.
posted by scruss at 7:02 PM on January 20 [11 favorites]
MetaFilter’s own joeyh has an off-grid solar + battery powered house, which he recently upgraded.
posted by mbrubeck at 7:41 PM on January 20 [3 favorites]
posted by mbrubeck at 7:41 PM on January 20 [3 favorites]
So can you have the battery as a back up, and kind of flip a switch back and forth between using your own and buying in?
Your electricity service is normally a one-way street. Use a kilowatt-hour of electricity, and your meter ticks up by 1. But when you’re making electricity at home, if you are making more that you use your meter “runs backwards”. There’s no “switch” per se (other than the aforementioned safety switch so you don’t kill linemen when there’s a utility outage on a sunny day), you’re just another power supplier like any power plant also connected to the grid.
posted by Huggiesbear at 7:43 PM on January 20 [2 favorites]
Your electricity service is normally a one-way street. Use a kilowatt-hour of electricity, and your meter ticks up by 1. But when you’re making electricity at home, if you are making more that you use your meter “runs backwards”. There’s no “switch” per se (other than the aforementioned safety switch so you don’t kill linemen when there’s a utility outage on a sunny day), you’re just another power supplier like any power plant also connected to the grid.
posted by Huggiesbear at 7:43 PM on January 20 [2 favorites]
Most states have a different, more difficult permitting process if you want off-grid solar. If it's on-grid, the fire department and utility want the ability to turn you off and not have surprise live wires on the property. From this perspective, it doesn't make a difference if you have a battery.
posted by michaelh at 7:44 PM on January 20 [1 favorite]
posted by michaelh at 7:44 PM on January 20 [1 favorite]
My solar array, which is small, cost me on the order of $14K, before tax incentives.
…a battery system of usable size for my house would run $9-15K.
Using the grid as my battery (effectively) has saved me a fortune. Now that I have more money I’m considering batteries but in the meantime using the grid cut my payback period in half.
With my current system I have free electricity for 4-6 months of the year, so getting batteries at the outset was a hard sell.
posted by aramaic at 8:48 PM on January 20 [7 favorites]
…a battery system of usable size for my house would run $9-15K.
Using the grid as my battery (effectively) has saved me a fortune. Now that I have more money I’m considering batteries but in the meantime using the grid cut my payback period in half.
With my current system I have free electricity for 4-6 months of the year, so getting batteries at the outset was a hard sell.
posted by aramaic at 8:48 PM on January 20 [7 favorites]
I guess I would have thought more people were using solar as a "in case everything goes wrong" option, in which case off-and-on electricity would still be pretty useful.
I think you assumption is wrong. Most people are using solar because they expect the initial investment (minus subsidies) to pay off, as in they expect the cost of the solar panels will be less than the cost of power they don't have to pay for plus the amount they get for excess power generation they send back to the grid (often at a favourable rate). People are generally doing it for economic and often also environmental reasons, not generally for resiliency.
posted by ssg at 8:50 PM on January 20 [11 favorites]
I think you assumption is wrong. Most people are using solar because they expect the initial investment (minus subsidies) to pay off, as in they expect the cost of the solar panels will be less than the cost of power they don't have to pay for plus the amount they get for excess power generation they send back to the grid (often at a favourable rate). People are generally doing it for economic and often also environmental reasons, not generally for resiliency.
posted by ssg at 8:50 PM on January 20 [11 favorites]
I'm someone living totally off-grid, with solar, batteries and multiple inverters. But in Aotearoa NZ.
The initial setup cost was high (and no subsidies). But it was all significantly cheaper than paying to run new powerlines to the property from the nearest grid lines, multiple km away.
In Aotearoa NZ, according to the various solar forums I'm on, the 'buy back' rates from power companies have continued to decrease over the last few months particularly.
We also saw just before moving off-grid, that our power charges were just about to increase by 40% per kWh, with only a few week's notice.
Most domestic households here seem to have a cap of 5kW as a maximum the power companies will buy back from you per day, and that's if they set it up correctly. So many people have been sharing that their meter was wrongly installed and so power companies were charging them for both power received from the grid, and solar generated back into the grid.
For me, I definately fit into the resliance catagory. The system should be good as is for more than 15-20 years. I won't have any increase in power bills during that time. Hopefully not even any significant further costs after the initial outlay. So no more power bills for a while at least, and I can use as much power as my system can generate.
We had to design the capacity of the system to supply our minimum needs during the winter days (based on our historical usage of about 8kWh per day for two people). So during the summer there's certainly an excess of power that could be further utilised.
At the moment though, I'm just enjoying our options of doing things like running the oven for longer without worrying about the bill, and loving seeing our batteries fully charged before midday.
I could use it for a heatpump to cool things down if needed, but natural summer shading and good insulation, plus some open windows here and there, is more than enough to keep things comfortable.
And then in the winter we'll be using wood burners to heat the spaces with as needed (free local wood too)..
A lot of people in NZ, seem to use an automatic switch that starts heating water cylinders when the batteries are full. Others charger their electric cars when they have a surplus. This seems to be more effective than selling back to the grid these days.
For me, an excess of avaialble energy is not a waste if I don't use it. For me it just means solar rays are falling on essentially a roof panel (if I had a solar panel there or not).
So in my case, I won't be linking up to the grid.
It'd still be cheaper to more than triple the size of our solar system, and add hydro backups, etc. than to run lines to the grid from where we now live.
I know that's a slight deviation from your question, but I hope it still gives you the info you were looking for.
posted by many-things at 10:22 PM on January 20 [17 favorites]
The initial setup cost was high (and no subsidies). But it was all significantly cheaper than paying to run new powerlines to the property from the nearest grid lines, multiple km away.
In Aotearoa NZ, according to the various solar forums I'm on, the 'buy back' rates from power companies have continued to decrease over the last few months particularly.
We also saw just before moving off-grid, that our power charges were just about to increase by 40% per kWh, with only a few week's notice.
Most domestic households here seem to have a cap of 5kW as a maximum the power companies will buy back from you per day, and that's if they set it up correctly. So many people have been sharing that their meter was wrongly installed and so power companies were charging them for both power received from the grid, and solar generated back into the grid.
For me, I definately fit into the resliance catagory. The system should be good as is for more than 15-20 years. I won't have any increase in power bills during that time. Hopefully not even any significant further costs after the initial outlay. So no more power bills for a while at least, and I can use as much power as my system can generate.
We had to design the capacity of the system to supply our minimum needs during the winter days (based on our historical usage of about 8kWh per day for two people). So during the summer there's certainly an excess of power that could be further utilised.
At the moment though, I'm just enjoying our options of doing things like running the oven for longer without worrying about the bill, and loving seeing our batteries fully charged before midday.
I could use it for a heatpump to cool things down if needed, but natural summer shading and good insulation, plus some open windows here and there, is more than enough to keep things comfortable.
And then in the winter we'll be using wood burners to heat the spaces with as needed (free local wood too)..
A lot of people in NZ, seem to use an automatic switch that starts heating water cylinders when the batteries are full. Others charger their electric cars when they have a surplus. This seems to be more effective than selling back to the grid these days.
For me, an excess of avaialble energy is not a waste if I don't use it. For me it just means solar rays are falling on essentially a roof panel (if I had a solar panel there or not).
So in my case, I won't be linking up to the grid.
It'd still be cheaper to more than triple the size of our solar system, and add hydro backups, etc. than to run lines to the grid from where we now live.
I know that's a slight deviation from your question, but I hope it still gives you the info you were looking for.
posted by many-things at 10:22 PM on January 20 [17 favorites]
Why don't they just route it to their house and use the electricity themselves?
That's exactly what we do. The electricity that flows out from the house to the grid, which we may or may not get paid for, is just the amount that the panels are making in excess of whatever the house is using at any given moment.
In Australia, we now have so much rooftop solar installed that when the sun is highest in the sky and everybody's panels are making the most power that they ever do during the day, there is more rooftop solar power being exported to the grid than the grid can use and we actually get charged rather than paid for each kWh exported. The financial incentives here, then, are pretty rapidly shifting in favour of installing house batteries so that instead of directly exporting excess power to the grid it charges batteries first, to be exported later when grid demand is high and solar production is low.
Obviously from the household's point of view it would be best if the house could disconnect itself from the grid and keep running off its own battery any time the grid fails, but the control equipment required to do all of that is still considered somewhat niche. Most grid-tied inverters in use in this country were designed before batteries were a thing, and they just shut down all the in-house power supplies whenever the grid fails so as to protect the above-mentioned line maintenance people.
But advanced controllers capable of safe grid-isolating islanding, as well as optimizing the power flows in and out of local batteries, are slowly becoming available even though they still tend to cost almost as much as the batteries themselves do.
posted by flabdablet at 10:29 PM on January 20 [7 favorites]
That's exactly what we do. The electricity that flows out from the house to the grid, which we may or may not get paid for, is just the amount that the panels are making in excess of whatever the house is using at any given moment.
In Australia, we now have so much rooftop solar installed that when the sun is highest in the sky and everybody's panels are making the most power that they ever do during the day, there is more rooftop solar power being exported to the grid than the grid can use and we actually get charged rather than paid for each kWh exported. The financial incentives here, then, are pretty rapidly shifting in favour of installing house batteries so that instead of directly exporting excess power to the grid it charges batteries first, to be exported later when grid demand is high and solar production is low.
Obviously from the household's point of view it would be best if the house could disconnect itself from the grid and keep running off its own battery any time the grid fails, but the control equipment required to do all of that is still considered somewhat niche. Most grid-tied inverters in use in this country were designed before batteries were a thing, and they just shut down all the in-house power supplies whenever the grid fails so as to protect the above-mentioned line maintenance people.
But advanced controllers capable of safe grid-isolating islanding, as well as optimizing the power flows in and out of local batteries, are slowly becoming available even though they still tend to cost almost as much as the batteries themselves do.
posted by flabdablet at 10:29 PM on January 20 [7 favorites]
The how and why has been explained above, but what I'm going to do to use what would be excess solar power ourselves first (yes, buyback and offsetting is still a thing here but will get scrapped in the not too distant future) without installing batteries is by powering a bank of electric hot water heaters, and charging our EV.
Of course the EV can (and will) be charged from the grid during the dreary seasons, but for the days that we expect to have excess power charging will be set to kick in when there would be power outflow. Of course there will be an override in case we need the battery to be full the next morning, but that's pretty rare, on average.
Hot water, which you tend to need year-round, is another way to store energy, and I figured that with a bit of DIY I can switch back to the gas-powered boiler when the water leaving the electro boiler bank drops below legionella-safe temps. The reasoning behind using a bank of comparatively small storage heaters is that where you would need 18.7kWh to heat 200l of water from 10⁰C to 90⁰C and you expect you're going to get just 5-ish kWh excess you can at least get one 50l boiler piping hot, where a single 200l one would only go from 10⁰C to about 30⁰C. And once the first 50l one is done power gets switched to the next.
posted by Stoneshop at 1:45 AM on January 21 [4 favorites]
Of course the EV can (and will) be charged from the grid during the dreary seasons, but for the days that we expect to have excess power charging will be set to kick in when there would be power outflow. Of course there will be an override in case we need the battery to be full the next morning, but that's pretty rare, on average.
Hot water, which you tend to need year-round, is another way to store energy, and I figured that with a bit of DIY I can switch back to the gas-powered boiler when the water leaving the electro boiler bank drops below legionella-safe temps. The reasoning behind using a bank of comparatively small storage heaters is that where you would need 18.7kWh to heat 200l of water from 10⁰C to 90⁰C and you expect you're going to get just 5-ish kWh excess you can at least get one 50l boiler piping hot, where a single 200l one would only go from 10⁰C to about 30⁰C. And once the first 50l one is done power gets switched to the next.
posted by Stoneshop at 1:45 AM on January 21 [4 favorites]
One thing that changes the financial equation in the US is what state you live in.
I live in Massachusetts, and state law dictates that the utility company has to buy back electricity at the same rate that I pay. Conceptually, as a consumer, this makes complete sense, but from the utilities point-of-view, my roof-top solar installation is more like a power plant that they don’t own, and so they want to pay “wholesale” rates.
In Massachusetts, OTHER THAN EMERGENCY POWER, it makes zero financial sense to have a battery— we’ve considered getting a small one for emergency power uses, but we don’t lose power enough to make it worth it.
On the other hand, my dad lives in Florida and in Florida, the power company not only doesn’t buy back power at the retail rate, they also buy back power at a greatly reduced wholesale rate, AND they only do this one a year, AND they only give you credits you can use to reduce your bill.
So, in Florida, it makes complete sense to get a battery. On sunny days, my dad is *basically* off-grid. He charges up the battery during the day and uses that power at night, and generally ends up with a small credit, even with an electric car.
posted by gregvr at 4:58 AM on January 21 [4 favorites]
I live in Massachusetts, and state law dictates that the utility company has to buy back electricity at the same rate that I pay. Conceptually, as a consumer, this makes complete sense, but from the utilities point-of-view, my roof-top solar installation is more like a power plant that they don’t own, and so they want to pay “wholesale” rates.
In Massachusetts, OTHER THAN EMERGENCY POWER, it makes zero financial sense to have a battery— we’ve considered getting a small one for emergency power uses, but we don’t lose power enough to make it worth it.
On the other hand, my dad lives in Florida and in Florida, the power company not only doesn’t buy back power at the retail rate, they also buy back power at a greatly reduced wholesale rate, AND they only do this one a year, AND they only give you credits you can use to reduce your bill.
So, in Florida, it makes complete sense to get a battery. On sunny days, my dad is *basically* off-grid. He charges up the battery during the day and uses that power at night, and generally ends up with a small credit, even with an electric car.
posted by gregvr at 4:58 AM on January 21 [4 favorites]
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Thanks for the lived experience and great summary of why off-grid works for you! Home Power magazine always had reports of "We moved to rural ____ County, and the utility was going to charge us $__0,000 to hook us up, so we installed ..."
posted by scruss at 5:48 AM on January 21 [1 favorite]
it was all significantly cheaper than paying to run new powerlines to the property from the nearest grid
Thanks for the lived experience and great summary of why off-grid works for you! Home Power magazine always had reports of "We moved to rural ____ County, and the utility was going to charge us $__0,000 to hook us up, so we installed ..."
posted by scruss at 5:48 AM on January 21 [1 favorite]
Yeah, there are all sorts of state and local(?) laws and regulations that affect what you can and can't do with solar power. Sometimes for good reasons, sometimes because of energy company lobbying.
posted by Rock Steady at 6:12 AM on January 21 [2 favorites]
posted by Rock Steady at 6:12 AM on January 21 [2 favorites]
The economics of PV is basically dictated by the following:
1: What you can get for generating power (often this is dictated by level of subsidy but some places are now beyond subsidy):
Some countries subsidise per unit of energy generated (or force a supplier to do so). There may be a higher payment for units that go into the grid but this is not always true. Some places are post-subsidy but there is a system in place where you can get paid for units which go to the grid by the supplier, and you can move your business around.
Some countries net meter, which means you effectively get subsidised for any unit you put into the grid because it comes off your consumption when you are taking from the grid, and you save power from the grid for each unit you use yourself (see below).
2: How much grid power you displace:
Basically how much power you would have taken from the grid but now don't. So you basically save each unit off your bill. This mean you are saving at market value in a net metering approach. It is undermined to some extent by systems with standing charges.
So the total value of your panel operationally is the sum of any value you get from sending energy into the grid plus what you save off your bill. Since for most people the amount displaced from bills will be the higher cost per unit then how much you are at home (and how much you use when you are there) will substantially impact the final figure for value. If you are at work away from home all day then you will use a relatively small amount of power from your panels and put a lot of into the grid. If you are at home all day and have high demand you can displace a load of your personal use, and the economics of your panel will be better.
The goal of the battery is to change the amount you put into the grid if your situation is that you are putting lots in and then using a lot of grid power at non-sunny times. They are about moving the availability of the energy you generate to when you need it, thus displacing more demand from your utility bill. The economics of batteries are dictated by how much they cost and how much power you can move around and thus how much you can save off your bill on a daily and annual basis. At the moment they often cost too much to make them worthwhile, even for those who have lots of spare solar output to move around. This has improved over time as battery tech improves but has a way to go for wider adoption.
Its worth mentioning that you can also benefit from a battery on your system if you have a local utility option to access different costs of electricity at different times of day. So if you are offered a lower rate at night then you can charge up and use it at breakfast time, when the low price has ended. This will impact the overall economics of the battery and let you save a bit more each day. You can likely expect to see more use of variable tariffs like this in the future. I am not going to get into the tech of the number of cycles you will get over battery lifetime.
posted by biffa at 6:37 AM on January 21 [1 favorite]
1: What you can get for generating power (often this is dictated by level of subsidy but some places are now beyond subsidy):
Some countries subsidise per unit of energy generated (or force a supplier to do so). There may be a higher payment for units that go into the grid but this is not always true. Some places are post-subsidy but there is a system in place where you can get paid for units which go to the grid by the supplier, and you can move your business around.
Some countries net meter, which means you effectively get subsidised for any unit you put into the grid because it comes off your consumption when you are taking from the grid, and you save power from the grid for each unit you use yourself (see below).
2: How much grid power you displace:
Basically how much power you would have taken from the grid but now don't. So you basically save each unit off your bill. This mean you are saving at market value in a net metering approach. It is undermined to some extent by systems with standing charges.
So the total value of your panel operationally is the sum of any value you get from sending energy into the grid plus what you save off your bill. Since for most people the amount displaced from bills will be the higher cost per unit then how much you are at home (and how much you use when you are there) will substantially impact the final figure for value. If you are at work away from home all day then you will use a relatively small amount of power from your panels and put a lot of into the grid. If you are at home all day and have high demand you can displace a load of your personal use, and the economics of your panel will be better.
The goal of the battery is to change the amount you put into the grid if your situation is that you are putting lots in and then using a lot of grid power at non-sunny times. They are about moving the availability of the energy you generate to when you need it, thus displacing more demand from your utility bill. The economics of batteries are dictated by how much they cost and how much power you can move around and thus how much you can save off your bill on a daily and annual basis. At the moment they often cost too much to make them worthwhile, even for those who have lots of spare solar output to move around. This has improved over time as battery tech improves but has a way to go for wider adoption.
Its worth mentioning that you can also benefit from a battery on your system if you have a local utility option to access different costs of electricity at different times of day. So if you are offered a lower rate at night then you can charge up and use it at breakfast time, when the low price has ended. This will impact the overall economics of the battery and let you save a bit more each day. You can likely expect to see more use of variable tariffs like this in the future. I am not going to get into the tech of the number of cycles you will get over battery lifetime.
posted by biffa at 6:37 AM on January 21 [1 favorite]
I rent a house with solar and batteries. I didn’t install it, so don’t know all the details about cost and subsidies, but I’ve lived here for 3 years and can tell you a little about the day to day practicalities.
We’re in an unincorporated community in California, on the coast between LA and SF. We have grid services for water and power, but since the weather is very temperate year round (houses here don’t have AC, just heat), the power grid isn’t super resilient. It’s normal for our “big” storms to knock out power for a couple hours a few times a year.
Our battery backup tracks the weather and knows when to pull extra power from the grid to keep us running when service is interrupted. (This way we only know about area power outages when the internet goes down)
From mid-March to mid-October, we’re powered over 95% from solar+batteries, and in the winter months that drops down to the 40-60% range as we get more cloud cover and fewer hours of daylight.
posted by itesser at 7:23 AM on January 21 [2 favorites]
We’re in an unincorporated community in California, on the coast between LA and SF. We have grid services for water and power, but since the weather is very temperate year round (houses here don’t have AC, just heat), the power grid isn’t super resilient. It’s normal for our “big” storms to knock out power for a couple hours a few times a year.
Our battery backup tracks the weather and knows when to pull extra power from the grid to keep us running when service is interrupted. (This way we only know about area power outages when the internet goes down)
From mid-March to mid-October, we’re powered over 95% from solar+batteries, and in the winter months that drops down to the 40-60% range as we get more cloud cover and fewer hours of daylight.
posted by itesser at 7:23 AM on January 21 [2 favorites]
Here in Michigan, we do use the electricity from the panels ourselves, and fill a couple of large batteries(*), but sometimes there's excess electricity. We run off the panels as much as possible. If demand is outpacing supply, power is pulled from the batteries. If the batteries are below a certain level, the inverter will pull power from the grid to use. If supply is outpacing demand, the batteries get charged. If the batteries are full, excess power is sold to the utility. Some summer days, the batteries are full by 3pm. Some winter days, or rainy spring days, they never do fill although we keep up with our usage. At night, we run off the batteries until the charge drops below a certain level, then pull from the grid. The batteries get charged the next day from the panels.
Our neighbors got a small array of panels on their garage, and they did not grid-tie at all -- the electricity they get from those panels gets used by the house, fills a small battery (to keep the furnace running if the power goes out), and then the inverter stops .
There is a state mandated cutoff such that the system will not send power out to the utility company unless the power line is "live", so that we will not electrocute anybody.
[* our power goes out often enough for long enough periods, that the investment in the batteries was worth it. They were less expensive than putting in an automatic whole house generator.]
posted by jlkr at 8:09 AM on January 21 [2 favorites]
Our neighbors got a small array of panels on their garage, and they did not grid-tie at all -- the electricity they get from those panels gets used by the house, fills a small battery (to keep the furnace running if the power goes out), and then the inverter stops .
There is a state mandated cutoff such that the system will not send power out to the utility company unless the power line is "live", so that we will not electrocute anybody.
[* our power goes out often enough for long enough periods, that the investment in the batteries was worth it. They were less expensive than putting in an automatic whole house generator.]
posted by jlkr at 8:09 AM on January 21 [2 favorites]
We got a solar system with a battery through the Georgia BRIGHT solar leasing program (non-profit funded solar leasing was one of the many good things to come out of the Biden administration). Georgia Power had a net metering program limited to the first 5000 customers, which was filled up years ago, so we get only wholesale value back for power we put into the grid, so the only financial motive is in being off grid as much as possible.
The battery nearly doubled the monthly charge for the lease, but we are glad to have it. Many days, we run primarily off of our panels + battery. But in the middle of the snow storm last week, of course, we were not making any solar power. As described above, our batteries charge themselves fully before storms, allowing us to be off grid when the power goes off (which is all the damn time because we're in a lower socioeconomic zip code and Georgia Power does not give a fuck about its customers).
posted by hydropsyche at 8:48 AM on January 21 [1 favorite]
The battery nearly doubled the monthly charge for the lease, but we are glad to have it. Many days, we run primarily off of our panels + battery. But in the middle of the snow storm last week, of course, we were not making any solar power. As described above, our batteries charge themselves fully before storms, allowing us to be off grid when the power goes off (which is all the damn time because we're in a lower socioeconomic zip code and Georgia Power does not give a fuck about its customers).
posted by hydropsyche at 8:48 AM on January 21 [1 favorite]
When we installed solar about 10 years ago in Olympia WA, the incentives were good enough that we added batteries to our overall system. We can power about 80% of the house off the batteries, but that doesn't include AC, our electric oven, or our pool filter. It does include all the wall outlets, so we can keep using the toaster oven, microwave, etc. My mother, living with us at the time, kicked in the extra cost of the batteries because she really wanted to not have to deal with power outages at night/in winter, if it was possible to avoid them.
We have long since earned back the cost of our system through incentives and power buy-backs and would recommend it to anyone considering doing an install today. If you can power just a few rooms with batteries, it makes sense to add them if your area is outage-prone. We have had many short term power outages in our neighborhood in the past 10 years and really not noticed any of them except for the few appliances that have to be reset afterwards. It's a very nice accommodation to have.
posted by drossdragon at 3:49 PM on January 21 [1 favorite]
We have long since earned back the cost of our system through incentives and power buy-backs and would recommend it to anyone considering doing an install today. If you can power just a few rooms with batteries, it makes sense to add them if your area is outage-prone. We have had many short term power outages in our neighborhood in the past 10 years and really not noticed any of them except for the few appliances that have to be reset afterwards. It's a very nice accommodation to have.
posted by drossdragon at 3:49 PM on January 21 [1 favorite]
When we installed our solar, batteries that could really make you totally off-grid where not really - practically and affordably - available.
Some people even then were doing completely off-grid systems. But those were usually people who didn't have a lot of options. They did it partly by generating electricity via solar, but also - just as important - by carefully planning their usage (mostly to minimize it, secondarily to make hay while the sun shines, literally, and then just do the bare minimum when running on battery) and also anticipating the possibility that they might have little or even no power for certain periods.
So it's not just installing solar & battery and off you go, but rather designing a whole system including every electricity-using item in your household, in order to fit the stringent requirements of being able to run off the battery during the very most difficult part of the year for solar.
So it's not just the cost of the solar, plus batteries (which would have doubled or maybe even tripled the cost of the system when we were looking at it), it's also the cost & complication of basically redesigning all the power usage in your entire household.
OR, you can just hook up to the grid. Problem solved, instantly and cheaply. And the grid is even happy to take your extra power when you can provide it, and even more happy to supply you with power during the >50% of the time you can't generate enough.
Also, when there is a power outage: In our system we can flip a switch, plug a cord into a special outlet, and then plug as many things into that as the system can handle.
So in a power outage it doesn't just switch over and run all the normal circuits in the house (for the reasons people have outlined above) but we can generally run like the fridge, freezer, and furnace, or air conditioner, and then charge devices and such, for as long as the sun shines.
So for example right now, the temperatures are around 0F and if we should lose electricity it would be a life threatening emergency. But with the solar panels we could run the furnace probably 8 or 10 hours a day. Not ideal, but enough - with the other measures we're able to take - to keep us from freezing.
posted by flug at 8:08 PM on January 21 [2 favorites]
Some people even then were doing completely off-grid systems. But those were usually people who didn't have a lot of options. They did it partly by generating electricity via solar, but also - just as important - by carefully planning their usage (mostly to minimize it, secondarily to make hay while the sun shines, literally, and then just do the bare minimum when running on battery) and also anticipating the possibility that they might have little or even no power for certain periods.
So it's not just installing solar & battery and off you go, but rather designing a whole system including every electricity-using item in your household, in order to fit the stringent requirements of being able to run off the battery during the very most difficult part of the year for solar.
So it's not just the cost of the solar, plus batteries (which would have doubled or maybe even tripled the cost of the system when we were looking at it), it's also the cost & complication of basically redesigning all the power usage in your entire household.
OR, you can just hook up to the grid. Problem solved, instantly and cheaply. And the grid is even happy to take your extra power when you can provide it, and even more happy to supply you with power during the >50% of the time you can't generate enough.
Also, when there is a power outage: In our system we can flip a switch, plug a cord into a special outlet, and then plug as many things into that as the system can handle.
So in a power outage it doesn't just switch over and run all the normal circuits in the house (for the reasons people have outlined above) but we can generally run like the fridge, freezer, and furnace, or air conditioner, and then charge devices and such, for as long as the sun shines.
So for example right now, the temperatures are around 0F and if we should lose electricity it would be a life threatening emergency. But with the solar panels we could run the furnace probably 8 or 10 hours a day. Not ideal, but enough - with the other measures we're able to take - to keep us from freezing.
posted by flug at 8:08 PM on January 21 [2 favorites]
Summing up from above: It is indeed primarily to reduce emissions, and save or make money over the long run.
But to your specific question: There is indeed a an emergency preparedness/survival/resilience/"in case everything goes wrong" aspect to it as well. It's probably the equivalent of a $5000 or even $10000 generator of the type a bunch of our neighbors have installed. It's worse in some ways than a generator (won't run 24 hours/day) but far, far better in others (it will run for a day or a week or a month or a year or a decade off-grid, and no stinky diesel fumes).
posted by flug at 8:16 PM on January 21 [2 favorites]
But to your specific question: There is indeed a an emergency preparedness/survival/resilience/"in case everything goes wrong" aspect to it as well. It's probably the equivalent of a $5000 or even $10000 generator of the type a bunch of our neighbors have installed. It's worse in some ways than a generator (won't run 24 hours/day) but far, far better in others (it will run for a day or a week or a month or a year or a decade off-grid, and no stinky diesel fumes).
posted by flug at 8:16 PM on January 21 [2 favorites]
In California, it's common for a full rooftop solar install to be generating AC power which feeds your whole house and also backwards through the meter to the grid. These days folks also usually get a battery for storage.
Until a couple of years ago, under the NEM 2 rate plan this was a very good deal for homeowners. PG&E would buy power from homeowners at the same rate they sold power at, sending a once-a-year "true up" bill for the net cost if you used more power for the whole year than you produced. (You could also get a modest payment if you generated excess but at a much lower rate.) This meant you didn't have to store power locally. The optimal thing was for a homeowner to install enough solar panels to net out to zero electricity used or generated for a year.
The new NEM rate plan is much more complicated and I don't understand it. But a big piece of that is an economic incentive to have a battery to smooth out your electric usage a little, to use more generated power at home before sending excess to the grid. The optimal thing now seems to be for a homeowner to install enough solar to generate about 50% of their usage for a year.
From a homeowners perspective, we're just installing panels and batteries to optimize according to the rate plan. From the grid operator's perspective they're trying to manage power generation and consumption in as even a manner as possible. A specific problem in California is during a sunny, windy day we generate significantly more power than we can use or store. They're literally turning commercial solar facilities off at peak generation times because there's nowhere to put the excess electricity.
posted by Nelson at 10:10 AM on January 22 [2 favorites]
Until a couple of years ago, under the NEM 2 rate plan this was a very good deal for homeowners. PG&E would buy power from homeowners at the same rate they sold power at, sending a once-a-year "true up" bill for the net cost if you used more power for the whole year than you produced. (You could also get a modest payment if you generated excess but at a much lower rate.) This meant you didn't have to store power locally. The optimal thing was for a homeowner to install enough solar panels to net out to zero electricity used or generated for a year.
The new NEM rate plan is much more complicated and I don't understand it. But a big piece of that is an economic incentive to have a battery to smooth out your electric usage a little, to use more generated power at home before sending excess to the grid. The optimal thing now seems to be for a homeowner to install enough solar to generate about 50% of their usage for a year.
From a homeowners perspective, we're just installing panels and batteries to optimize according to the rate plan. From the grid operator's perspective they're trying to manage power generation and consumption in as even a manner as possible. A specific problem in California is during a sunny, windy day we generate significantly more power than we can use or store. They're literally turning commercial solar facilities off at peak generation times because there's nowhere to put the excess electricity.
posted by Nelson at 10:10 AM on January 22 [2 favorites]
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posted by Rash at 6:50 PM on January 20 [6 favorites]