[Photonicinduction] has an impressive battery backup installation that powers his whole house. Unlike a standalone emergency generator which would require you to hook up all of the device you want to run, this setup sits in between the power meter and the breaker box, ready to step in when needed.
But get this, he’s not just using it as a backup system. It kicks in during the day to run everything including two freezers, a refrigerator, his lights, television, and computers. That’s because the price per kilowatt-hour is quite a bit higher during the day than at night. So after 10:30pm the system patches his house back into the grid and charges the batteries for use the next day.
What you see here is just a portion of his system. The control board is not pictured but is very impressive, including a network of relays which are used as a fail-safe system so that there are no conflicts between mains and the battery system. Check out his 15-minute walk through of the system after the break.
[youtube=http://www.youtube.com/watch?v=48rStZV40Ks&w=470]
[Thanks Patrick]
Must be nice to be given differential pricing. My utility accounts peak vs non-peak, but both are billed at the same rate.
When it start to have differentiation, thepeak price will be so much more that you will miss the equal price.
yea word. i know in my area they wont do it either (east coast with PSEG) unless you use a lot more power. i’m stuck with $0.09/KW generation and $0.09/KW distribution. does anybody in the us know the process for getting separate on/off peak rates?
In AZ, there are various programs you can choose… If your power company offers them, you can ask, but make sure you will be saving money by doing in. The delivery costs don’t change, just the generation. For me, off-peak is half of what the normal kWh charge would be, on-peak is 5x normal charges and there is an 8 hour on-peak window. It saves us money, but only because no one is home for most of the on-peak time.
Here in Japan, the rates are pretty damn ridiculous, with 75kWh daytime equal to maybe 350kWh nighttime. While whole house backups are less common, electric heating and water heaters are usually a giant battery that is set to recharge only at night. At that rate, those systems pay themselves off in a matter of months. Even if you are talking about $1k/yr for 5 years, it’s going to offset the daytime electricity costs.
Definitely cool. I was thinking of something somewhat similar to this a while ago but I have no means to do it. Kudos!
I am also looking at a similar idea, but scaled down to just the overhead lights. Since I have already installed 10 led lights (more planned), the goal will be to reduce the required battery capacity. I also plan to wire the 2d floor and ground floor into seperate circuts (I rewired the house once when upgrading to 200A, so the rewiring should not be too challenging).
Photonicinduction is awesome. Recommend Subscribing.
Wow! Very cool!
the efficiency of inverters arnt all that great, coupled with the loss of charging lead acid , i wonder if this inst actually costing him money..
Exactly what I was thinking. Admittedly, I skipped ahead through the video, but I looked into the show notes too and noticed an appalling lack of efficiency calculations, return on investment calculation, how deeply he discharges his batteries (makes a huge difference in their lifespan, BTW), etc etc etc.
The whole project is cool, but don’t tell me you are saving money when there isn’t any concept of the time value of money presented.
+1
+2
I was thinking to modify my APC UPS to do the same (at least for my server) but haven’t got time to get around that…
I hooked my rack mounted ups so it does battery backup for my whole room and have breakers to bypass if needed. It is a great way to really keep all my equipment and everything going considering where I live the electricity flips off for a couple seconds every week.
Too bad that the efficiency loss from the charger, battery charging, battery discharging, and inverters means that he’s almost certainly losing money on this.
Considering that economy 7 here in the uk is less than a 1/3 the price of normal electric…. i don’T think so and if it is loosing money why would he still be using the system since he installed in 2006? and also why would he make a video about it if it ws a useless system… i suggest u subscribe to the guy and have a good watch :D
For instance looking at my energy prices its around 18p per kwh but around 5p per kwh on low rate…. so even if the system is 40% efficient he’ll save money
At least until he has to replace the battery.
I dunno the batteries like he said in the video last 10 yrs… so £200-300 every 10 yrs itll still probably pay for itself, and also he must suffer from the occasional power cut where he lives. he obviously runs an engineering buisness, and the time not lost due to being able to do nothing without electric must be worth alot to him, which im assuming os why he built it probably out of frustration. : P
People make videos about perpetual motion machines, ghosts, bigfoot, all sorts of things that aren’t real. Argumentum ad Youtubium…
I love what he’s done here, but I REALLY love his accent. Hollywood accent coaches should use this video to instruct Americans how to sound Cockney. Are you listening, Dick Van Dyke?
He says in the video that Off-Peak is about 1/3 of the cost of Peak. so maybe it is viable.
Glad this got featured….. and glad photonic got on the front page again his videos are funny and sometimes like this very informative, this guy aswell as having a decent sense of humor i think has alot to give in the hacking department.
He might get a knock on his door. Don’t some police departments identify illegal grow houses using off-peak electricity usage?
In a video about lasers he noticed a police helicopter scanning his house with some kind of imaging sensor pointed right at his house. Probably also the custom ducting he has installed.
in one off the last video you se him blast a laser beam over the hole neberhood.
you can read in it hy live neer a armybase
It wouldn’t surprise if the local law enforcement is used to it. I think he is the CEO of a electrical contracting company so he may be well known locally. In another video he sees his neighbors lights flickering as he does some high voltage something. I believe he had wired directly to the distribution box for that.
If you haven’t subscribed to PhotonicInduction’s Videos yet, DO! Saw this one earlier this week, and I am very impressed. Photonic should get his own hackaday site tab, he certainly does enough =P
Since it is just a video at the moment (which I can not access). Does it actually cover the costs and savings? (Are there any savings?) What is the payback time on this?
(i.e. how much electricity does the house normally use/say, how much additional overhead is involved in the charging/battery losses/inverters/etc.
How much difference in electricity cost (day vs. evening). How much does it save per day?
How much did the system cost? How much does upkeep cost (battery replacement, etc.)
Finally, how long will it take to pay back the investment.
He says about 600 UK pounds was the original cost.
He claims pay back is within 2 years.
Honestly, I sort of doubt it for a few reasons:
– Inverters are not 100% efficient
– Chargers are not 100% efficient
– Batteries do not last for 10 years with daily deep cycle discharging
He says he’s got 4.5kW of power available in his batteries, I’m guessing that’s a theorical amount of power probably based on battery capacity and the inverter output capability, it doesn’t account for inefficiency in the charging or inverting process.
He doesn’t mention the price delta between his day and night rates, but assuming he feels that he’s saving 4.5kW/day, and that it will pay for itself in 2 years and has an initial cost of 600 UK pounds … he needs to save 18.5 UK pence for each kW… that seems awfully high for savings, but I have to admit I have no idea what power costs there… I pay $0.145/kW here in New England, and that’s my actual cost based on dividing usage by the actual billed amount.
The price difference is enormous, 5p vs 18p
Thanks.
Since the system is used to power two freezers and a refrigerator, it seems like using thermal power storage might improve system efficiency. (Might be able to get much of benefit at much lower cost.) A well insulated freezer can keep its contents frozen for one to two days.
http://www.ext.colostate.edu/pubs/foodnut/09357.html
Why not use a programmable thermostat for the freezer – set to achieve a lower than usual temperature just before the utility rates go up in the morning (say -10 to -20). During the daytime it should let temperature rise to 0.
A crude approximation might be achieved with a regular outlet timer (to turn off freezer during day) and setting the temperature to -10.
Likewise the thermal storage could be used to help maintain the temperature of the refrigerator. Use the freezer to freeze water jugs at night, keep frozen jugs in the refrigerator to help maintain its temperature during the day. (See for instance the comment “Turn your fridge off” on
http://michaelbluejay.com/electricity/refrigerators.html
Along with well insulated refrigerators/freezers this might help take advantage of the rate differential with less expense than the battery system.
(What effect daily cycling between -20 and 0 might have on the freezer or contents I don’t know. But this is about the first instance I have come across of a potentially rational way to make use of variable rate electricity.)
Interesting setup… it looks like a 1500W inverter which is 6.25A @ 240V, he mentions it’s protected by a 6A fuse…
For we US (and other 120V) users that’s roughly 12A or less which is about the same as a typical domestic circuit…
That’s not what I’d consider to be “whole house”, although in this case I think the term is simply referring to the fact that he could potentially power anything in the house from it.
It seems like what he’s really done is built a home brew automatic transfer switch (the control board) which is connected to a home brew UPS.
You could re-create the same thing using typical off the shelf components, I don’t know that it would necessarily be that much more expensive, you’re looking at three major costs:
– UPS (the inverter and charger)
– Battery
– Transfer Switch
Used UPS from a data center w/ a dead battery can be surprisingly cheap. A large unit capable of having extended battery packs connected is what I’d be looking for. There are also inverters that have chargers built in–look at ones meant to use on board ambulances, etc–they might be a bit more expensive, but they replace the charging components in his setup.
Batteries are costly and heavy. His setup which allows the two dissimilar batteries to be electrically connected to each other is probably not a good idea for typical use (i.e. better to only briefly have them interconnected while switching between banks). If you leave them connected the stronger will discharge into the weaker and ultimately can damage the batteries–look into battery isolators like those used in RV’s or 12V diesel vehicles in the US
Transfer Switch, if it were me I’d go with a 4 or 6 switch manual transfer switch. Here in the US you can get them with an L14-30p (30A plug) on the panel, that’s the input. Under normal circumstances you keep the output of your UPS plugged in that, however having the plug allows you to also optionally connect a traditional generator for extended outages.
BTW, I don’t mean to sound like I’m dumping on what he’s done… I love it, and I’ll probably spend the rest of the night watching whatever else he has in his youtube channel… :)
The other important thing… if you’re not using sealed (no spillable) batteries you need to be worried about VENTING the battery during charging… they produce hydrogen and that can be an explosion risk.
let’s do a quick math:
Efficiency (common values?)
Charger (90%)–> Battery (80%)–> inverter (90%)
0.9 * 0.8 * 0.9 = 0.65 near (65%)
Only if the difference in electricity prices is greater than 35% your saving (not counting installation costs and battery replacement from time to time)
– As a means of save money? hummm maybe
– As an altertanive to power cuts, excelent!
If you read the previous comments, you’ll see that the economy is indeed higher than 35%.
This guys an artist, I’m surprised he hasn’t figured out how to make a rain powered system.
Actually, I am on similar project for a year. Made lots of research on it and realized that most of brain forget the “battery cost”. SLA batteries doesn’t like too much cycles.So they degrade with time. Also there is efficiency problems.
Charging circuit %95
Charging & pulling from battery %85 (Scales from %50 to %92)
Inverting to Main AC %85(or lower ?)
Know that, those are high values for normal UPSes.
0.95*0.85*0.85 = 0.686 means ~%69
So ~1/3 energy loss at conversion.
Also there is battery replacement fee for every year. SLA batteries doesn’t live more than 250-300 deep cycles.
You can use 2x battery to avoid full discharge, but then battery life became 450-500 cycle. But for 2x money of battery.
So it’s not so economic. You will decrease power bill, but instead pay for battery shop! :)
What is the disparity between night/day $/kWhr? Where is the disparity the highest in the world?
Your not far out, however the difference between day and night rates are significant, deffo on a winner if you can get big bateries cheap.
I will have to purchase more batteries in 5 years, but that must be better than spending on a large solar array, noisy gen set and diesel.
Bonus bit is, the savings made will always buy you new batteries.
So actual cost £0 lol
There is one comment he made in the middle of it all that sounds like a passing remark, but it’s the key to making this work without blowing it up.
The key is the delay between the shutdown of the utility power and the activation of the inverter circuit. He said it was for good measure or something like that, but it’s actually critical to the design.
The way many folks would duplicate this setup is with a DPDT contactor with the coil tied to the grid, one set of contacts on the grid, one on the inverter, and the contacts on the load. When the power drops, the relay opens and the NC contacts close applying inverter output. This would probably work fine for lights… but as soon as a reactive load, such as a motor, etc exists on the line, unless the frequency of the inverter and the grid are in sync (almost never the case), the kick will blow the output stage of the inverter to bits.
… so anyone trying to duplicate this, it’s doable, but there needs to be a delay of 1+ seconds between disconnection of utility and connection of inverter, using two separate contactors. Obviously that’s what he’s done… so it’s worth noting that a backup supply it is, but a UPS it is NOT.
I really do like the workmanship on his control panel, and the use of batteries to take advantage of off peak rates is a neat idea. I can see this type of system scaling up easily to handle much bigger loads or longer run times…
That would violate every electrical code imaginable in the US state I live in. It looks like he’s used Romex for everything, and uses sockets on the inverter as a permanent supply. Running every day for six years, I’m amazed he’s had no fires. It looks awesome as a backup, but like everyone else I do question it’s efficiency and efficacy for powering an entire house.
Check your codes. That’s not romex, which incidentally IS legal for household wiring in the US, that is SJOO or something similar, also legal.
Finally, US electrical code is meaningless in the UK.
I’m not sure why it should be surprising no fires occurred. Romex most likely permissible in more US localities than is is not. The insurance wouldn’t allow it’s use at all if their data proved it’s a fire risk. Reasonable to assume a new inverter was used, meaning the the receptacle on the inverter was unused, and in good shape. As good as shape as any switch type disconnect thrown on for the first time, meaning there shouldn’t be any unusual heating at the recep. Not to mention he ha240 V. circuit meaning less current flowing for the same amount of power we here in the US have for lighting circuit loads, and most of his load looks to be lighting circuits. Screw terminals at the inverter would be preferable, but that probably would mean purchasing a grid tie inverter, an extra expense not needed considering he has no plans to feed power to the grid. Myself I’d put the cabinet with the batteries, chargers, and inverter in a metal cabinet in the basement, that’s vented to the outdoors, but I wouldn’t say it’s necessary.
US and Canadian electrical code don’t differ all that much.
I just had my wiring passed by the ESA. I have a 3000 Watt UPS powered with a 120 volt / 30 A circuit.
The output from the UPS is four simple NEMA 5-15R outlets, each pair separately fused at 15 Amps (Duh!). I have two circuits plugged into these via SJOOW cable with the appropriate plugs, the other ends going into an octagon box (doubled as Canadian wire limits are a bit different than US — 10 wires max, each pair of marettes counts as 1 wire, and sheathed ground counts as a wire too, so I’m at 13 wires–boxes aren’t rated for stranded wire screwed directly to them, so they had to be pigtailed) with strain relief (those mesh things electricians have rude names for). That then connects to permanent NMD90 powering several outlets. There’s no handoff switch because it’s not needed in this case.
I made a point of making sure the inspector was OK with this setup along with the panel he was inspecting, since I rewired the house. He give it all the thumbs up and I got those lovely orange and black ESA stickers.
So, unless US electrical code is incredibly different on residential wiring (It is not) it is definitely going to pass inspection. Whether or not it meets code actually isn’t important if the inspector is happy with it, he is the one who actually gets the final say and after that, if you don’t touch it, it’s grandfathered.
I dont know where this guy is located but if he gets enough sun, hooking up a set of solar panels to this would be an even better way to save money (charge the batteries either when the sun is shining or when power is cheap and use the juice when the sun is not shining AND power is expensive)
Did you watch the video? Apparently not.
I believe in one of his videos he mentions he is the head (ceo?)of a electrical contracting company that does hard jobs other companies won’t. I would trust his wiring over anyone’s. Definitely worth subscribing to.
youtube.com/user/Photonicinduction
After reading all the comments, let’s point out a few things:
He isn’t stupid, and probably did his calculations with a <100% efficiency in mind regarding paying itself back.
He says in the beginning of his video he wanted a backup in case of power outages, goal obtained. He is now using it to save money on initial costs by offsetting day use with night-cost electricity.
The whole thing is a prototype, testing the waters and figuring out what needs to change.
Even at 60% total efficiency, that's still hours and hours of power for a few lights in one room and a laptop.
Also, those look like marine (possibly RV) batteries, which, while not rated for everyday complete discharge, will probably last a good few years (definitely not 10 as rated), and even then will only store less power, not be completely dead.
He's in the UK, which isn't known for its sunny days, and he shows that his area is dead as far as wind goes, either systems would be ungodly more expensive anyway, since they also need batteries and an inverter or 2.
For batteries, Absorbed Glass Mat (AGM) lead acid batteries seem to be way to go. They are sealed, support deep discharge, are more resistant to temperature cycles, and hold their charge better than other types. With recent US requirements on tractor-trailers and idling, AGM batteries have become quite common in fairly large capacities, too.
he seems to have a thing for waffles…or is that a tick?
I LoL’d.
And then I thought of that MST3K episode, with Viking Women and the Sea Serpent, where they are all obsessed with waffles, in all of the host segments and while watching the movie. :)
I wouldnt like to live in this guys neighborhood, his backyard is like a chinese landfill with all the contaminants he blew/cooked/evaporated/spilled over the years.
Similar solution but on much more bigger scale was done before. e.g. here http://byway.pl/UploadedImages/88076ef8-18e7-4f5c-acb3-34d73be1d6ac/451026ca-b955-4abc-bfda-cb52667566a8.jpg. During night hours water was pomped up and during pick hours electricity was produced.
I’m in the UK and was also thinking recently about doing this. Then I discovered on Economy7 the day rate is inflated to compensate for the cheap rate (which only applied ~1am-6am anyway). Got rid of E7 for am immediate saving (YMMV).
Is it just me, or did you all misunderstand this project? :)
When I watched the video, I thought he was only using the system when a power failure kicked in and NOT as a “battery powered house” during the day w/ charging at night – that would be kinda pointless wouldnt it, since he is not able to run any high power electrical devices.
Afaik he is only using the system as backup, the fact, that he is saving money by charging batteries during the night is “just” a feature, making the whole project pay itself off.
It seems that this man have a good source of free lead-acid batteries.
I use nearly same system for cutoff protection made from 3kW online UPS and 8 60Ah automotive batteries as 96V backup ($100 each). Also this system helps with voltage drops and spikes, online UPS eats 110 – 260 volts and gives stable 220V sinus.
The batteries life is 2 years maximum with permanent battery maintenace (measuring density, adding water, proper charging etc.) and perfect temperature conditions (20 degrees C). With all that boring maintenance batteries loose 80% of capacity within 2 years if system works often. If it will work every day, batteries will be completely dead in a year or even less.
I tried to find alternative batteries, with longer life, but totally failed. It’s impossible to buy something accessible and not very expencive different from automotive batteries.
May be some super-LiFePol things will work better, but they have totally inadequate price.
Every 2 years I have to pay $800 for the new batteries (didn’t do that, because 20% of capacity is still enough to have time slowly go to the garage and start generator).
So, where is economy? Or, maybe, [Photonicinduction] hide something about batteries from us.
Yes the cost of and life of lead acid batteries aka storage batteries. What about the ole times when wind chargers (out on the farm) were connected to a group battery jars, those square blue green glass jars that housed the internal parts and acid of a battery. Arent they still used to power emergency exit lights in buildings? Could these be cost eff3ctive?
On the subject of batteries,inverters and UPS
my laptop battery wont hold for more than 5 minutes, and this is going on 3 years. I don’t care because its always plugged into its AC power supply. My guestion is, is my “dead” battery functioning as inverter or kind of?
In the contract with our electricity supplier it specifically states that storing the cheap electricity at night for daytime use is prohibited. Might want to check that before putting it online.
Will be a moot point soon anyway, with all these solar panels the electricity during daytime will be cheaper than at night (in some villages with more solar power than consumption, they installed large resistor farms, watercooled sometimes, to burn off the heat as it can’t go back into the hv grid without raising voltage too much.)
For those who are interested, here’s the link to that inverter:
http://www.samlexamerica.com/products/productdescription.asp?ProductsID=18033
He shoudl look into NiFe cells. They’re heavy but you can abuse the crap out of them and they don’t degrade. Weight shouldn’t matter too much since this is a more or less fixed installation. They used to be used in telecoms to back up towers but I think they’ve been phased out in favor of more compact designs.
http://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery
Apprently they just suck at holding a charge compared to other chemistries. It’s wikipedia so caveat lector.
He should try these batteries, when they come on market.
http://www.aquionenergy.com/
The design is pretty much tailored for exactly this application, just upstream at the generation site. They’d work just as well for this application, though.
There is a different system in place in wales that makes use of the insanely huge differences in rates in the UK called “Electric mountain” – http://en.wikipedia.org/wiki/Dinorwig_Power_Station
It pumps water into a reservoir during off peak times and generates hydroelectric power during peak times to fill sudden demand on the grid. hugely effective if not entirely environmentally friendly.
Whole different scale though…
Because that I rely on a water well, I have considered building a variation of this over the years, although I don’t have the option of off peal power purchase, the inefficiencies would be an added cost for the luxury of taking a dump in a toilet that will flush it away during a power outage. An auto start power plant is something I can’t afford, if could I would get one. I don’t have the same reservations about them as this person has.
Evidently this individual experiences electrical power outages enough to cause him to look for a means of providing backup power. The differences in peak rates is what make this viable for him where he lives. At the end of the video he said his system cost less than an engine driven power plant, he has no love for,he barely mentioned renewable power, and then he said they aren’t an option now. Respectfully those alone should have overruled comments about the financial viability of the investment.
Once again, Big thanks to the administrator of the site for posting.
Just for info, a 200AH 12v SLA lasted 5 years with daily cyclic use at 70% discharge, the battery cost £100 only.
Now upgraded to 600AH flodded Rolls Solar batteries. The smaller 150AH SLA is there as a last resort ( 10 year life ) on standby.
This will not make you lots of money, but in a very resonable time gives you a back up system all paid for, I’m sure I will be looking out for good deals on batteries for when they will inevitably be required. running 6A from a 13A plug is not likly to cause a fire. It works, trust me. More than happy to help you guys with questions if required.
All the best to all you guys.
I looked at Rolls batteries, but they are too big ang too expencive. Didn’t find something with 96V at all, and minimum Rolls backup battery is 12V x 80 Ah with final price near $800. And I need eight of them to drive my 3kW UPS. Too expensive for me.
The same situation is with SLA – something like 12V x 40 Ah will cost $200 each. And it will be China junk. Good quality 12V x 40Ah SLA will have a price near $400
Seems that maximum voltage I can found for single battery is 12V. So, in any case I have to buy 8 batteries. Using backup voltage lower than 96 volts for >1kW UPS is a bad idea, because of high currents and lower COP. And it’s impossible to find a good online UPS with enough power, clean sinusoidal output and lower than 96V battery voltage.
I can’t find acceptable batteries ( at least in Russia ) at all, except automotive battries.
Also, batteries of necessary capacity are heavy and large, so ordering them by post service from other country is possible, but will cost me tons of $ for shipment and custom. :(
The electrical inefficiencies in this system will be dissipated as heat loss into a home environment precisely when heating is needed, supplanting some of the energy otherwise used for this purpose.
I wonder what influence this might have on the economic calculus? (The UK is a cold place!)
Try Useing LED Lights ?
The youtube video seems to be unavailable, because the uploader has closed his account.
Pity the video is gone. I like the concept. It would be useful in the wintertime in conjuntion with a PV system. Using €1000 a year in Ireland at 10c kwh night and 18c day, 100% efficient system would save €400.
Anyone have a copy of this video?
I found the video
https://www.youtube.com/watch?v=xcfd2Ncoeis
Yeah does anyone have a copy of the video it was a great video.
You can find his new channel here http://www.youtube.com/user/Photonvids
This is a great concept. I have a lake cabin on the border of Minnesota / USA and Ontariao / Canada that would be an ideal setting for this. I was glad to see someone else had the same idea well ahead of me and implemented it as a power back-up approach that pays for itself. I was just thinking of the savings of only being off-peak and letting the system be the primary system. Is that a practical approach — given your experiences?
If it works well I don’t see why it wouldn’t work as an approach to use off-peak electricity more effectivety.
I had this idea myself but found it to be non profitable.
I have an electric car with a 409V DC Battery, rated at 8KW. Charging is done with a single stage power factor corrected charger, with an efficiency of 94%. Same charger can also operate from raw DC (48-350VDC) from a solar array. For most of my loads at home I could just run the battery DC power back into most appliances. For example: lights, tv, computer 9all switch mode power supplies, generally rated for up to 450VDC) The fridge freezer uses very little power and all other appliances are already used at night. Efficiency wise, converting back to AC would result in far higher losses.
The problem comes when one analyzes the cost benefit. Assuming the lithium battery would be good for 1000 cycles at 80% DOD and that no significant capacity reduction would take place over time, that would be about 6KW of useful energy every day (also assuming I would not use the car, hence no reserve needed). My peak rate is 15p or 250% more expensive than the offpeak rate (6p), giving me a 9p per KW saving, or 54p per charge. After 3 years, or 1000 charge cycles, when the battery useful life was maxed out that saving would have been £711. Assuming 94% charger efficiency this would drop to £670. Notice I’m not even taking into consideration the battery losses. (convert this to your favorite currency).
At this point it’s hard to see why the savings from not using electricity at peak times would never make it cost effective. It’s an excellent idea as a portable or backup source of energy, or even to store solar energy, but not cost effective as a grid replacement.