I am on a time of use tariff In UK, Octopus go. This gives me 5 hours at 8.2p and 19 hours at 40p. I am installing a battery without solar. This should save me £1,000 per year. Savings may be higher as this is a fixed tariff and gas prices are set to rise significantly above 8.2 pence, I intend switching to electric heating. This could require high loads. I am looking at inverters with a minimum rating of 5kW. I understand some inverters have a relay switch which directly connects AC in to AC out when there is excess demand, ie switch totally to AC supply. The problem with this is if I have a 5kW inverter, switch the kettle on during peak time and have 6kW demand I end up paying 6 x 40p, because of the 1 kW excess. Is there an inverter where battery and grid work together? The calculation would then be 5kW x 8.2p and 1kW at 40p. Case A cost for one hour £2.40, case B cost for one hour 81 pence.
Which inverters able to meet excess demand by supplementing batteries with grid, not completely switching to AC?
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timselectric
If I can do it, you can do it.
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Victron has something called "grid assist" I think.
I believe it would do what you want.
I believe it would do what you want.
Vigo
Solar Addict
I'm not trying to be snide here because i very much want to know the answer to your question as well, but i suspect one contingency answer is 'two separate inverters/devices which aren't talking to each other'.
If they are 2 inverters, you can 'divorce' your loads and inverters (rather than inverters in parallel and all loads fed by one panel) so that neither inverter ever could go into overload other than in fault conditions. This assumes you are running into inverter capacity as the limit, not lack of battery. Lack of battery would still require something to hook to the grid.
In that case, it could be one very large inverter which can handle your loads (or 2 smaller units in parallel), combined with a battery charger hooked to grid that only activates in conditions which exceed your battery's capacity to cope for any length of time, such as when battery voltage drops below a certain level, or when the AC current coming out of your inverters rises above a level which is 'sustainable' with your solar and battery setup. Or have it trigger from either/both. Low voltage means the problem already exists, high AC current out means the problem will exist in near future and you're trying to stay ahead of it. I have found voltage sensing relays with adjustable time delays built in (so as not to trigger from motor startup surges etc) and there are probably current sensors with that feature built in as well. If not, well there's another discreet device to consider adding.
Wouldn't it be nice if all this stuff was in one box (inverter)?! If you find a good answer I will be pleased to not have to build option B there.
If they are 2 inverters, you can 'divorce' your loads and inverters (rather than inverters in parallel and all loads fed by one panel) so that neither inverter ever could go into overload other than in fault conditions. This assumes you are running into inverter capacity as the limit, not lack of battery. Lack of battery would still require something to hook to the grid.
In that case, it could be one very large inverter which can handle your loads (or 2 smaller units in parallel), combined with a battery charger hooked to grid that only activates in conditions which exceed your battery's capacity to cope for any length of time, such as when battery voltage drops below a certain level, or when the AC current coming out of your inverters rises above a level which is 'sustainable' with your solar and battery setup. Or have it trigger from either/both. Low voltage means the problem already exists, high AC current out means the problem will exist in near future and you're trying to stay ahead of it. I have found voltage sensing relays with adjustable time delays built in (so as not to trigger from motor startup surges etc) and there are probably current sensors with that feature built in as well. If not, well there's another discreet device to consider adding.
Wouldn't it be nice if all this stuff was in one box (inverter)?! If you find a good answer I will be pleased to not have to build option B there.
If I can't find an inverter that supplements battery on high load, I think I will pick one big one to meet the occasional overload. I looked at an 8k Voltronic inverter, it would take up half my garage and draw 2.4kW per day in standby mode, 876 kWh per year. I currently use a total of 3600kWh in the house a year, another 3000 charging my car.I'm not trying to be snide here because i very much want to know the answer to your question as well, but i suspect one contingency answer is 'two separate inverters/devices which aren't talking to each other'.
If they are 2 inverters, you can 'divorce' your loads and inverters (rather than inverters in parallel and all loads fed by one panel) so that neither inverter ever could go into overload other than in fault conditions. This assumes you are running into inverter capacity as the limit, not lack of battery. Lack of battery would still require something to hook to the grid.
In that case, it could be one very large inverter which can handle your loads (or 2 smaller units in parallel), combined with a battery charger hooked to grid that only activates in conditions which exceed your battery's capacity to cope for any length of time, such as when battery voltage drops below a certain level, or when the AC current coming out of your inverters rises above a level which is 'sustainable' with your solar and battery setup. Or have it trigger from either/both. Low voltage means the problem already exists, high AC current out means the problem will exist in near future and you're trying to stay ahead of it. I have found voltage sensing relays with adjustable time delays built in (so as not to trigger from motor startup surges etc) and there are probably current sensors with that feature built in as well. If not, well there's another discreet device to consider adding.
Wouldn't it be nice if all this stuff was in one box (inverter)?! If you find a good answer I will be pleased to not have to build option B there.
Vigo
Solar Addict
Can you tell us what your peak load is so we can spitball further ideas?
For example, i have 2x 5kw inverters in parallel which do the annoying full AC bypass thing you mention. I also have a small 1.5kw inverter in my RV. If my total loads were under 5kw the majority of the time I could actually put one of my 5kws as the 'ac input' to the 1.5kw, not have them communicate or be in parallel (other than hooked to the same battery), and with the 'switch from battery to grid' and 'switch from grid back to battery' settings on the 5k I could have it work so that the 5k charges battery from grid only when below certain voltage/soc, and with the 'input priority' settings in the 1.5kw I could have it ignore the 5kw inverter's AC until it overloaded.
So you would have 1.5kw inverting from a battery that would simultaneously charge from grid through the 5kw if voltage dropped to a certain point, without switching entire load over to grid. When load exceeds 1.5kw, small inverter goes into bypass and 5kw inverts from battery while charging from solar and ignoring grid IF battery voltage/soc is still high enough. But, when voltage/soc drops, it too goes into bypass and now the grid is carrying your full load. Technically my 5kw and 1.5kw would be a total of $1100 and not do the same annoying full-bypass thing as my ~$1700 pair of 5kw. Or you just get the 5kw and have its dry contacts control a grid charger circuit.
You can see i am a fan of Rube Goldberg Electrical Machines. But I only come up with them because they aren't already in one convenient box at a reasonable price, so i feel i am not to blame for the existence of these ideas.
For example, i have 2x 5kw inverters in parallel which do the annoying full AC bypass thing you mention. I also have a small 1.5kw inverter in my RV. If my total loads were under 5kw the majority of the time I could actually put one of my 5kws as the 'ac input' to the 1.5kw, not have them communicate or be in parallel (other than hooked to the same battery), and with the 'switch from battery to grid' and 'switch from grid back to battery' settings on the 5k I could have it work so that the 5k charges battery from grid only when below certain voltage/soc, and with the 'input priority' settings in the 1.5kw I could have it ignore the 5kw inverter's AC until it overloaded.
So you would have 1.5kw inverting from a battery that would simultaneously charge from grid through the 5kw if voltage dropped to a certain point, without switching entire load over to grid. When load exceeds 1.5kw, small inverter goes into bypass and 5kw inverts from battery while charging from solar and ignoring grid IF battery voltage/soc is still high enough. But, when voltage/soc drops, it too goes into bypass and now the grid is carrying your full load. Technically my 5kw and 1.5kw would be a total of $1100 and not do the same annoying full-bypass thing as my ~$1700 pair of 5kw. Or you just get the 5kw and have its dry contacts control a grid charger circuit.
You can see i am a fan of Rube Goldberg Electrical Machines. But I only come up with them because they aren't already in one convenient box at a reasonable price, so i feel i am not to blame for the existence of these ideas.
I'm new to this game so it's going to take me a bit of time to work through the details of your reply, but it does sound like a garage full of inverters. I was just out on a bike ride and spent most of the time thinking through what was needed. My thoughts were: when load exceeds capacity a relay would have to open on an AC inverter bypass circuit, at the same time a relay would open on a circuit at the load output. This circuit would have to calculate total load demand and meet it by prioritising battery and then take the excess from the AC bypass. The AC grid feed could not pass through the inverter as it would overload it. Is there any inverter that does this, Tesla Powerwall? I know grid can top up PV, but I think that is all done through the inverter and limited to the inverters capacity.
Vigo
Solar Addict
Unfortunately I don't know anything about a Powerwall..
The setup i described is not bulky OR expensive, but you might call it.. inelegant.. i'm sure some here would say worse!
The capacity of the ac passthrough on an inverter is just limited by the physical size of the components in the physical circuit. Most small relays max out at 30-40A and whether a small relay or the circuit it's on is reliable at 40a just because it says 40a on the relay housing is another thing too. But from what I have seen (cant say ive looked at too many) it does seem like many inverter manuals claim that their AC passthrough is basically not any higher capacity than the inverter itself, or at least not much more, which makes you wonder how safe or reliable it would be if used very much for loads that already overloaded the inverter itself. You can always use an external transfer switch if that's a concern, it's just an added cost and bit of wiring. I guess the basic idea of the built in ones in all in one inverter/chargers is they're trying to sell the most features in the most price-sensitive end of the market and whether the end user could nail the manufacturer with proof that some kind of damage came down to the design of the pass-through circuit is.. doubtful.
I dont 100% follow the idea of the circuit you're describing but it touches on what i think is the hard part of implementing the thing we want, which is how do you determine 'load-sharing' between 2 sources. ANY inverter with ac input terminals, the inverters in parallel-capable generators, etc can all detect the incoming AC frequency and sync their output to it, so that is the easy part. But how does the inverter detect and then control how much of the total load it is contributing? I am guessing that is where all the extra hardware and programming would be required. The other aspect which might even be the bigger one, is just legalities. If something exists on a circuit that leads back to the grid, it can put effects into that grid which can damage or at least degrade the quality of service of that grid. So things that do that have to be tested and certified to some extent that i know almost nothing about (i have a vague idea what UL listing is about, that's as far as my knowledge goes on that).
So anyway until the thing we are looking for pops up and is affordable, i think the practical approach in the meantime is to design ways to automatically manage non-critical loads such that when the total load would overload the inverter, non-critical loads are automatically cut off. If that wasn't enough, you COULD use dry contacts of the inverter to control a transfer switch that would switch some of your loads onto grid, and then back to inverter when the load on inverter decreased. Simplest way to take power from the grid while still powering everything from your inverter (ie not overloading the inverter but running out of battery) would just be DC charging from the grid, which could be controlled by the inverter through dry contacts etc.
The setup i described is not bulky OR expensive, but you might call it.. inelegant.. i'm sure some here would say worse!
The capacity of the ac passthrough on an inverter is just limited by the physical size of the components in the physical circuit. Most small relays max out at 30-40A and whether a small relay or the circuit it's on is reliable at 40a just because it says 40a on the relay housing is another thing too. But from what I have seen (cant say ive looked at too many) it does seem like many inverter manuals claim that their AC passthrough is basically not any higher capacity than the inverter itself, or at least not much more, which makes you wonder how safe or reliable it would be if used very much for loads that already overloaded the inverter itself. You can always use an external transfer switch if that's a concern, it's just an added cost and bit of wiring. I guess the basic idea of the built in ones in all in one inverter/chargers is they're trying to sell the most features in the most price-sensitive end of the market and whether the end user could nail the manufacturer with proof that some kind of damage came down to the design of the pass-through circuit is.. doubtful.
I dont 100% follow the idea of the circuit you're describing but it touches on what i think is the hard part of implementing the thing we want, which is how do you determine 'load-sharing' between 2 sources. ANY inverter with ac input terminals, the inverters in parallel-capable generators, etc can all detect the incoming AC frequency and sync their output to it, so that is the easy part. But how does the inverter detect and then control how much of the total load it is contributing? I am guessing that is where all the extra hardware and programming would be required. The other aspect which might even be the bigger one, is just legalities. If something exists on a circuit that leads back to the grid, it can put effects into that grid which can damage or at least degrade the quality of service of that grid. So things that do that have to be tested and certified to some extent that i know almost nothing about (i have a vague idea what UL listing is about, that's as far as my knowledge goes on that).
So anyway until the thing we are looking for pops up and is affordable, i think the practical approach in the meantime is to design ways to automatically manage non-critical loads such that when the total load would overload the inverter, non-critical loads are automatically cut off. If that wasn't enough, you COULD use dry contacts of the inverter to control a transfer switch that would switch some of your loads onto grid, and then back to inverter when the load on inverter decreased. Simplest way to take power from the grid while still powering everything from your inverter (ie not overloading the inverter but running out of battery) would just be DC charging from the grid, which could be controlled by the inverter through dry contacts etc.
timselectric
If I can do it, you can do it.
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I just looked up the Victron "power assist". (I had the name wrong) it actually works the opposite way I thought. It uses battery to assist the grid, if it's insufficient. Mostly for mobile shore power situations. When trying to draw 40a, when the shore power is only 30a. The battery will take the other 10a.
schmism
Solar Addict
The simple answer is 1) build enough inverter to cover your needs. or 2) split off critical loads into a separate panel that you know won't exceed the inverter supply wattage.
A smart AIO with battery bank will do what you want. inexpensive ones like Growatt/MPP lack the software features to run time based grid management however other more expensive AIO's (like solark) do have time sensitive settings. Allowing you to pull nothing from the grid durring peak hours and charge the battery durring off peak (low cost) times. (regardless if you have solar or not)
A smart AIO with battery bank will do what you want. inexpensive ones like Growatt/MPP lack the software features to run time based grid management however other more expensive AIO's (like solark) do have time sensitive settings. Allowing you to pull nothing from the grid durring peak hours and charge the battery durring off peak (low cost) times. (regardless if you have solar or not)
timselectric
If I can do it, you can do it.
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Growatt has the settings. At least the 5000ES does. Not sure about other models.
Setting #49 time of day utility charging.
Setting #50 time of day inverter powers loads.
Vigo
Solar Addict
^That is a cool feature. I have ignored their stuff because i am still in the 'break stuff while learning by doing' phase and don't want to break anything very expensive, but it does seem you get what you pay for with Victron..
100FUEGOS
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All you need is a Sunsynk inverter. Couple it with a big enough battery for your needs and it will do everything you are describing in your initial post.
P.S: I mention Sunsink because it is available to you in UK. It is basically a Deye / SolArk / Turbo Energy and many other commercial brands.
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Many thanks, Deye/Sunsynk seem to be just what I need. Found a discussion elsewhere on these inverters. The 5kW version can pull 35A 8kW with 5kw from battery and 3kW from grid. The 8kW version can pull 50A 12kW with 8kW from battery and 4kW from grid. As you say load is pulled from battery and topped up by grid, not replaced by AC bypass meeting total load. I found this photo showing the 8kW inverter meeting a load of 9.2kW (UPS) , using 8kW from the inverter and 1.2kW from grid, just what I need. I might just get a 5kW, instead of the 8kW. These are perfect for time use tariffs, my peak rate cost is five times more than off peak.
My peak load COULD theoretically be 11kW but more usually well under 5kW.
I had a quotation from a Victron dealer for a 5kW Multiplus II which the dealer said should be adequate for my specific needs.
Having looked at the MultiPlus II manual I was not at all convinced that the 32A auxiliary output would meet my needs.
Having spoken to the dealer about this function I was only more confused!
I have a reliable grid and the inverter will be connected to the grid but will not export power to the grid and I do not want to ask for permission from my utility to connect the inverter! I therefore need to use an off-grid inverter.
The choice was between the Multiplus II (preferred if everything else was equal) and a higher capacity inverter of at least 8kW.
In the end I ordered a 11kW Conversol MAX II (Axpert) as this was a considerably cheaper solution than using one or two MultiPlus II 5000VA.
I know that I could have made an external by pass switch using a current sensing circuit and contactors but in the end it was simpler to specify a larger inverter. The difference in cost between the 8kW and 11kW MAX II is relatively small.
It is possible that I have totally misinterpreted the by pass system of the MultiPlus II. Maybe it would have met my requirements.
Does anybody have any experience with this?
CrossStreet
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I confirm, if you place you high loads before the Deye inverter, but after the point where you attach the CT-clamp on the wire, the inverter will try to feed as much as it can to those loads up to its limit. I have an 8kW inverter and a 8 kW shower. As there are other consumers, the inverter can supply much of the shower consumption and augments the remaining from the grid.
My other house circuits are of a lower power ratings and are attached to the inverter "Load" output and are fully powered by it, they will be able to function even if the grid goes down. The shower won't.
My other house circuits are of a lower power ratings and are attached to the inverter "Load" output and are fully powered by it, they will be able to function even if the grid goes down. The shower won't.
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Nobodybusiness
Collecting the leftovers of the Great Sky Reactor.
Sunsynk or Deye or Sol-Ark should work.
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