Setup an off grid while on grid.

Yogie

Thank you for this great resource on Solar/Off Grid/Batteries. I have read here extensively and learnt how much i need to learn !!

The Situation;

Have a cabin on my acreage in a remote location. Grid connected but grid is not good - very dirty power supply (been like it many years and shows no sign of improving anytime soon) (220v mains). Power cuts occur every day - duration is variable. On a good day the grid is off for 6 hours or so and this is mostly during the day. Gird usually goes very low voltage at around 6.30am, then goes off completely at around 9.00am, comes back briefly at around 12 - 1.00pm for maybe 2 hours, goes off till around 17.00 then comes on at low voltage till around 20:00Hrs then is mostly reliable through the night till around 06:00 when voltage goes very low and then we go through the cycle again. Seems to be ample high voltage power all through the night. Since i dont sit up all night and watch the power i cant be sure, but every time i am up for some reason late at night or in the early hours the power is on with good voltage.

This drives me nuts ! I cant live in a way i would like. Things like be able to watch TV through the day if i want too, listen to my Hi-Fi, make a cup of tea without making a fire to boil water (fire boiled water tastes terrible to me so want to boil water in kettle) etc. Its also very hot where i live so keeping the refrigerator running all day so cold drinks are available would be nice (currently use ICE in an ice box but supply of ICE is very erratic so this is annoying).

So that is the background to why i would like to go to an off grid setup but with grid support. I do not wish to export anything to the grid (not able to here anyway but even if i could i have no interest in this).

Therefore i need to figure out the inverter/batteries/generator and panels. So many variables and different suppliers.

So far i am thinking, 48v inverter system, battery bank, generator and some panels.

Loads are usual house hold stuff - fridge, freezer x 2, LCD 50" TV, Hi-Fi system (small system) 2 x laptops, phone, cell phone chargers etc. If we have no power at night then security lights are vital - would consist of 6 x 20w LED floods.

other loads to be run one way or another are 2 x 2Kw motors - continuous 24/7. Water pump - 15Kw motor 3 phase - need this for about 4 hours per day but can be run at night to pump water for live stock. As far as i know i need at least a 50Kva genset to start the pump set up ( star delta starter )

I figure a generator will be a major part of this in order to run the big pump when grid is down. I dont know if its practical to have so many panels that i could run that big pump off solar during the day? (highly doubtful but what do i know?) So i see that the genset will be running quite a bit unless we only pump at night when the grid is usually on. Not impossible to work that way just inconvenient.

I am wondering if the 2 x 2Kw motors can be run from panels during the day?

I would like to use LiFePo4 batteries so need to figure how to integrate those into a system. Is the BMS separate to all the other stuff or can /does it need to be part of the inverter set up (that is, under inverter control?).

Any pointers gratefully received.

CALLD

Re: Setup an off grid while on grid.

I may be a new guy here but from what I can tell since starting my own off-grid setup is its very expensive to be able to run anything that requires a lot of kw/h per day off PV. I got mine mostly to keep vital systems like lights and alarm systems going in the event of a power outage, neither of which requires much capacity. If you do have access to grid power however unreliable it is then use it for as much as possible. It's much cheaper to make and store large quantities of ice to keep fridges cool than to store the necessary power in batteries. A generator can be used to power large loads like motors and arc welders for short durations when needed. A UPS style inverter with surge protection can be used to protect your sensitive equipment from large voltage fluctuations and still charge batteries in leu of PV panels.

If I can help you learn from my mistakes then the biggest one is DO NOT expect to save money from an off-grid PV system when you have grid access. If its money you want to save go for grid-tied if you can and your grid allows it and use the smallest possible UPS system to power vital stuff during outages.

Wish I knew that before I started out....

CALLD

Re: Setup an off grid while on grid.

Did a very rough calculation based on your load requirements, and if it's true what you say about those motors you need to run then your daily power consumption including all the other stuff you mentioned must be between 120 to 160kwh per day?

If you wanted to run all of that of PV and you lived in a very sunny location you would need about 30kW of panels, and if your battery system was 48V you would need 7500-15000AH of capacity just to make sure you don't cycle them too deeply and that you have enough autonomy. This alone is going to cost you hundreds of thousands of dollars.

I could only wish I had that sort of money to spend - would be an incredibly impressive system and a lot of fun to build if I had the time! It's the sort of work I'd love to get into so I can leave my civil engineering job.........

Cariboocoot

Re: Setup an off grid while on grid.

Welcome to the forum.

It seems to me what you are actually looking for is a whole-house UPS system, because you have grid even if it is unreliable. Before you can plan such a thing you've got to nail down some numbers so you know what to go for.

The first of these would be your actual usage, particularly those items which must be kept going when the grid fails (critical loads). Get a Kill-A-Watt and measure, don't guess and don't take the manufacturer's word for how much power anything uses. The coffee maker is going to be big power for a short time, whereas things like lights will be small power for a long time.

The second numbers you need will relate to the grid: how often is it up, down, and for how long? In other words is it a source that is at all usable or should you just sever the connection? With it you may be able to pull power for charging/loads whenever it chooses to be up. The good news here is that the LiFePo batteries are actually well-suited to such an irregular charging regime. Read through this thread about PNJunction's experiences with LiFePo: http://forum.solar-electric.com/showthread.php?23898-GBS-LiFePo4-20-and-40ah-batts

The big motors are another issue altogether. Two 2kW 240 VAC motors continuous duty? That is a huge power demand. One 15 kW 3-phase for 4 hours? Again major power. It can be done from solar/batteries but you'd have to be rich as creosote to do it. This is where you look at the actual mechanical needs and think about alternate ways to achieve the same end with less power. For example the livestock pump probably is a case of huge volume in a short time, whereas it may be better to pump a smaller volume over a longer time: same amount of water, same amount of energy, but the latter is easier to achieve in an off-grid situation.

And when you do all this design work and come up with a price .... it may also be cheaper to look in to improving the utility delivery even at your own expense (i.e. what is the root cause of the outages).

BB.

Re: Setup an off grid while on grid.

And break your loads into groups:

1) Loads that need power 100% of the time (UPS type system--AC Charger+Battery bank+Inverter)
2) Loads that need to run "sometime" during the day, even if there is no utility power
3) Loads you can shed if there is no utility power for a day or so

Basically, your most expensive power is going to be #1--So you want to keep only necessary loads here. You can go with an off the shelf UPS, or with an Inverer+Charger unit. These have an AC input+battery charger+AC inverter all in one. Basically a UPS with an external battery bank. Usually an Inverter+Charger has a larger DC Charging capability than a simple UPS would. UPS are generally designed to "slow charge" the battery bank after an outage (can take 10+ hours)--Sometimes designed for "GEL" type batteries (which have a C/20 charge rate).

UPS systems also tend to have "small" battery banks that can deliver high current--Great to give you 30 minutes to shut down the computers or start the backup genset. A few people here have even taken standard (larger) UPS systems and added external battery bank + AC charger + solar array + solar charger. You should design several "paper systems" to see what works best for you (based on what hardware you can purchase locally, etc.).

The #2 power system for loads--That you can get very creative with. Here are some links to folks that have make pretty large water pumping systems with Solar Panels + VFD (variable frequency drives) + 3 phase motors for agricultural pumping:

BB. wrote: »

Some discussions about VFD (Variable Frequency Drives)... Basically a variable frequency inverter with (typically) three phase output. Used to soft start motors (handy for 3 phase well pumps, or pumps with well head starting capacitor) and can also turn an AC motor into a variable speed motor (very handy for pumping applications).

WELL PUMP and Inverter QUESTION
Wind/solar for large scale pumping etc (out of my depth!)
could use knowledge - using Gould jet pump - transfering from 230vAC to ? DC (new link/thread 10/27/2012)
Help required to design off grid system (information on possibilities to connect "standard VFDs direct to solar panels) (new link 1/13/2013)

The above is not "easy"--There will be some study on your part. But it is possible. A couple of folks, after researching/building their own systems, have turned it into a business.

In the end, conservation will be your friend. It is almost always cheaper to conserve than to generate the power you need. Once you have done your "extreme conservation", then look at powering them from battery, solar, genset, etc.

-Bill

Yogie

Re: Setup an off grid while on grid.

BB. wrote: »

And break your loads into groups:

1) Loads that need power 100% of the time (UPS type system--AC Charger+Battery bank+Inverter)
2) Loads that need to run "sometime" during the day, even if there is no utility power
3) Loads you can shed if there is no utility power for a day or so

-Bill

Yes agree - break loads into groups. So the house needs to be UP all the time because i am willing to pay for the comforts of life. I want to keep freezers going 24/7 because its 420 Klms to the shops to get fresh food, meat etc. So important to do a buy up every 6 weeks or so. Need to keep that stuff good while the power goes off and on. SO things like freezers and fridge must stay on. Comms gear must stay up (satellite dish/modem/wireless router/VoIP phone). Nice to have but can be switched off if it has to be, TV, HiFi etc.

the 2 x 2Kw motors run air pumps that MUST stay UP - live stock depend on these. So that's a tricky one.

The big water pump - well as i say i can run it all night. As well i can look at building a holding tank to store 600,000 liters and pump into that during the night and then take water from that during the day = prefer not too as its $$$$$ but may have no option. As has been said, may have to get creative on this one - Not sure how yet, but running that genset all day is not attractive at our fuel rates + we have to haul in from a good distance away. Fuel is crazy money here by time its on the land.

I have room to install a few hundred panels. How realistic is it to try to generate enough energy to run the 2 x 2Kw motors and house all day from that type of source?

I have read a lot about batteries and i think i get it. Flooded lead acid will be the cheapest to buy upfront and take a lot of looking after to get long life out of them, plus they cant take being left in a partial state of charge - which could easily happen here. LiFePo can take a deep discharge, not need long genset run times to charge correctly to the right levels, dont have the pueket thingy, dont suffer from voltage sag under heavy load but cost $$$$ up front but appear to have a long life if used at the correct levels, although the lifetime is not proven yet.

I goggled all over the net looking at batteries and prices. To get 1000 useable AmpHrs in Lead acid i need about 2400 Amphrs of capacity. Cost is around $25K. With LiFePo to get 1000 useable Amp Hrs i need to buy about 1500 Amp Hrs of capacity. It looks i can get 1100 Amp Hr cells for about $1000 each. If i am understanding all this battery talk ( and i am trying to absorb all this but there is so much to it i may be confused and have this wrong) i could parallel the cells then put them in series to get up to 48v at 2200 amp hours. This would cost $32K. So upfront cost higher then Lead acid and more usable capacity and longer life.

Is it possible to run inverters stacked to give 3 phase and the capacity i need to pull from panels and grid at the same time? When grid goes down (as it does everyday) a genset kick in to take up the load when the panels cant power the load? I know it would be major panel numbers involved but how many ? How bad would the $$$ damage be? What do the maths look like or is this simply ridiculous ??

How would i manage the LiFePo battery system with the inverter chargers?

This is all too complicated.

Yogie

Re: Setup an off grid while on grid.

Oh Forgot.

Cant do anything about grid quality. It is what it is and it is NOT coming good anytime soon. Well that's not strictly true. At the moment we get about 4Mw from Hydro system. Its grossly overloaded - chronic low voltage since forever. They have just upgraded the Hydro to 15Mw at a cost of 45 Million USD. So it will be slightly better i guess, but still nowhere near enough. More new consumers being connected then new supply coming online.

So i have to make do with what i have and find ways to add extra to my land for my own use. I am near the equator so plenty of Sun but also plenty of rain at certain times of the year.

A genset is going to be part of all this - i get that there is no way to avoid this. Between "some" grid and some solar, how can i stitch a system together? I have 2 kidneys so can sell one on ebay.

Aguarancher

Re: Setup an off grid while on grid.

600,000L is a huge amount of water. What type of livestock do you raise?

Cariboocoot

Re: Setup an off grid while on grid.

Let's just take a look at a portion of the big demand: one 2kW motor * 24 hours = 48 kW hours.
On a 48 Volt system that's 1000 Amp hours being used. Convert to DC and add in the inverter consumption and you're up around 1200 Amp hours consumed per day. That makes the minimum battery bank 2400 Amp hours, and you would probably want larger than that (up to 2X or 4800 Amp hours). So in batteries alone for one motor you are looking at a huge and expensive bank.

This is definitely a case where normally you'd use forklift batteries. LiFePo may be difficult to get large enough to satisfy the energy demand even with the greater SOC flexibility. I have no experience with sourcing these batteries.

Now if you can count on the grid power for anything it may make a huge difference in recharging. But let's say you can't and you need to do, oh, 3600 Amp hours of FLA (forklift) @ 48 Volts. Looking at 360 Amps of peak charge current which means five 80 Amp MPPT controllers and about 22kW of PV. For one motor. That's roughly 100 panels right there.

I suppose you could sell both kidneys, but then you'd need even more power to run the dialysis machine.

Yes some inverters can be stacked in such a manner as to provide 3 phase AC.

The biggest problem here (other than sheer capital outlay) is the unreliable grid which may be able to contribute something but you can't be certain of what. Very difficult to plan around a variable that can't be controlled.

Yogie

Re: Setup an off grid while on grid.

Aguarancher wrote: »

600,000L is a huge amount of water. What type of livestock do you raise?

We raise fish............

Aguarancher

Re: Setup an off grid while on grid.

Ahh..that explains the air pumps.

Yogie

Re: Setup an off grid while on grid.

Yikes ...... this looks hopeless !

OK so using that night time power is going to be critical. So i will HAVE to look into storing large volumes of water. Hmmmm.......

100 panels for one 2Kw motor......... this is heavy. No way to reduce the need for this motor. Must have it. If i can run on grid from 20:00Hrs to 06:00Hrs that's 10 hours a day on grid. For the odd night we have nothing then it will be genset all night. That leaves 14 hours a day on battery and solar of which maybe 5 or 6 could be run off panels..... right ? So i am down to about 7 or 8 hours on battery or genset. Ok grid does usually come on for 1 or 2 hours during the day, so that will help a little. Low voltage though - how do i cope with that?

So i'd be looking at around, what, 300 panels?

BB.

Re: Setup an off grid while on grid.

Look at the VFD 3 phase motor threads--And if that can get you through much of the day--Then look at some more efficient way to get circulation/air into the tanks during night/power failures (battery/system needs reduced).

If power "goes away" for more than X hours, then start up the XX KWatt backup generator.

By the way, if you do not mind, roughly, where are you located? I don't recognize the Klms designation.

-Bill

Yogie

Re: Setup an off grid while on grid.

BB. wrote: »

By the way, if you do not mind, roughly, where are you located? I don't recognize the Klms designation.-Bill

Middle of the dark continent. Klms = kilometers. Its metric here. I am very close to Congo.

CALLD

Re: Setup an off grid while on grid.

Yogie wrote: »

Middle of the dark continent. Klms = kilometers. Its metric here. I am very close to Congo.

Ah a fellow African dweller! I understand your predicament a lot better now. Economics also changes considerably when you're where you are. Pretty much everything needs to be brought in from far away over impossible terrain. Unless of course you're loaded and you can just fly it in from Joburg on a big chopper! Money's probably no issue for you then as much as abundant sunshine isn't. I can recommend a few good suppliers here in South Africa. You aren't gonna get the right stuff easily from where you are that's for certain...

Cariboocoot

Re: Setup an off grid while on grid.

Okay if you only have to run from batteries 14 hours a day that reduces the Watt hours to 28 kW hours. Still pretty massive (like 10X the typical OG install). For one motor.

Short formula (because we need to get into the practical ballpark before working out the details): kW hours AC / 0.52 / hours of equivalent good sun = array size. So there you'd be looking at maybe a 10kW array. An improvement, but still huge. About forty 250 Watt panels.

Yogie

Re: Setup an off grid while on grid.

CALLD wrote: »

Pretty much everything needs to be brought in from far away over impossible terrain. .

Yes thats it. Roads have improved out of sight the last few years so cant complain too much. Africa is expensive and thats all there is to it. I dont know why i stay here with all the challenges. Life is easier in the western world for sure. Well for all that, i'm still here and have no plan to leave. The thing with Africa is, when the bug bites, it bites hard.

Everything here will come in via container - the only way to keep things semi reasonable cost wise. As well we source direct from USA. Although panel and LiFePo makes sense to come direct from China since thats where they come from anyway.

Yogie

Re: Setup an off grid while on grid.

Yes - will have to take a knife to the whole plan and slash consumption. We are going to have to use that flaky grid as much as we can.

Its pretty much as i thought - we are going to have be generator dependent - the pumps are just too big and heavy. I will dig into the VFD pump thing to see how that could possibly help. It may be wiser to throw out the pumps we have and start again with newer more modern pump motor designs - the wet end has not changed and probably never will.

Does it make more sense to forget panels and have a bigger battery bank then? How would i charge it? (ok , i know a charger, but what sort, which brands/makes?)

I have a 11Kv -> 380v 3 phase 50 amp transformer on the land. Will that need changing out in order to charge a big battery bank? And given the limit of around 20:00Hrs to 06:00Hrs of reasonable power at reasonable voltage (never perfect or very close to spec - ever) is that a big enough window to charge batteries? Does LiFePo shine here for this?

Its amazed me how i just didn't realise how much power we get out of the grid and how little you can get out of a battery.

CALLD

Re: Setup an off grid while on grid.

Yogie wrote: »

Yes - will have to take a knife to the whole plan and slash consumption. We are going to have to use that flaky grid as much as we can.

Its pretty much as i thought - we are going to have be generator dependent - the pumps are just too big and heavy. I will dig into the VFD pump thing to see how that could possibly help. It may be wiser to throw out the pumps we have and start again with newer more modern pump motor designs - the wet end has not changed and probably never will.

Does it make more sense to forget panels and have a bigger battery bank then? How would i charge it? (ok , i know a charger, but what sort, which brands/makes?)

I have a 11Kv -> 380v 3 phase 50 amp transformer on the land. Will that need changing out in order to charge a big battery bank? And given the limit of around 20:00Hrs to 06:00Hrs of reasonable power at reasonable voltage (never perfect or very close to spec - ever) is that a big enough window to charge batteries? Does LiFePo shine here for this?

Its amazed me how i just didn't realise how much power we get out of the grid and how little you can get out of a battery.

Yes batteries are pretty pathetic actually, that's why electric cars are still a long way off from competing with internal combustion despite electric motors being much more efficient. You just can't put enough energy into a small enough battery to make it viable. One of the largest batteries in the world is a 40MW/H lead acid battery and even this astronomically huge battery couldn't power a small town for more than a few hours. Find a way to store utility scale power quantities in a small space and watch renewable energy take off on a global scale like we can only imagine! But for now, even with the most advanced lithium battery technology we still need mechanical generators powered by fossil, nuclear or hydro to meet most of our needs. Sad but true...

stephendv

Re: Setup an off grid while on grid.

There's a new alternative on the market which is to use a hybrid approach: Rely on the generator for the main supply and then use PV to reduce the fuel costs. Here's a pdf describing the concept: http://www.sma.de/fileadmin/intersolar/Hybrid_Systems-Brochure_Fuel_Save_Solution_EN.pdf

Not a lot of technical detail, but it looks as though you can use PV + a grid tie inverter + a special control module and connect the grid tie inverter directly to the generator output without using any batteries. So when the sun's available it will provide part of the power requirement.
Alternatively you could also install batteries + battery inverters to smooth the PV supply as an option. This system has been used for MW scale industrial production in Africa and SMA have a branch in Johannesburg so might be worthwhile getting in touch with them.

Yogie

Re: Setup an off grid while on grid.

That was an interesting read. Thanks for the heads up.

http://www.sma.de/fileadmin/intersol...olution_EN.pdf

SMA looks interesting overall.

Yogie

Re: Setup an off grid while on grid.

Is it possible to have an inverter stack setup such that it pulls power from panels and if the load exceeds the power available from the panels it then draws power from batteries or grid (if its UP of course) to make up the power requirement for the load at the time?

I still cant understand how to control LiFePo batteries from an inverter as the LiFePo seems to be new and inverters dont support them yet. Any pointers on that aspect please.

CALLD

Re: Setup an off grid while on grid.

Yogie wrote: »

Is it possible to have an inverter stack setup such that it pulls power from panels and if the load exceeds the power available from the panels it then draws power from batteries or grid (if its UP of course) to make up the power requirement for the load at the time?

I still cant understand how to control LiFePo batteries from an inverter as the LiFePo seems to be new and inverters dont support them yet. Any pointers on that aspect please.

In an off-grid system with batteries the PV panels will always supply the load first and then dump any extra power into the batteries, in the event that the PV is not generating enough to carry the load the difference in power will be drawn from the battery bank. This is evident in that the battery voltage will increase with higher PV production and lower inverter loading or decreasing voltage with higher inverter loading and lower PV production. If you are using a grid-tied inverter with a power grid or generator then any PV production will either feed back into the grid/generator or just reduce the load on the grid/generator.

stephendv

Re: Setup an off grid while on grid.

Yogie wrote: »

Is it possible to have an inverter stack setup such that it pulls power from panels and if the load exceeds the power available from the panels it then draws power from batteries or grid (if its UP of course) to make up the power requirement for the load at the time?

Yes, most inverter/chargers support this but will need an additional external relay. Firstly, if an inverter/charger detects grid power on it's AC input then it will use that power. So the trick is in installing a relay between the grid and the inverter's AC input. Then program the inverter to close that relay if the load exceeds a certain threshold, or if the batteries are below a certain voltage. Many larger inverter/chargers support this feature which is normally used to auto-start a generator. But you can equally use it to close an external relay and connect the grid.

Some inverter/chargers have 2 built in and programmable relays so you'd be able to do both auto-generator start and connect a relay to the grid, but you'll have to check the programming for the specific model to see what's possible. I'd imagine in your case you'd want to first connect to grid and if there is no grid, then start up the generator... and when the grid comes back, then shutdown generator and connect to grid. Not sure which inverters would support that specific case, maybe the Xantrex XW since it has 2 AC inputs, and maybe the Victron Quatro and SMA Sunny Island. You'd have to check the online manuals of each to see whether it can support the scenarios you need.

Yogie wrote: »

I still cant understand how to control LiFePo batteries from an inverter as the LiFePo seems to be new and inverters dont support them yet. Any pointers on that aspect please.

IMO, they're still too cutting edge and costly for the size of application you're talking about. Better to stick with plain old flooded lead acid until LiFePo prices come down and it's a more standard component. No doubt there are benefits and it's the bees knees of new battery technology, but when you're talking about power supply it's often better to stick to the wide road that's been travelled a lot rather than risk the narrower and newer path where few have travelled

Organic Farmer

Re: Setup an off grid while on grid.

We are on-grid, going off-grid.

We are rural. We normally experience power outages every month, all year-round. Our only hope for reliable power is to be off-grid.

Every home in our township has their own generators. Most homes have two generators; one big unit to run the well, and one small unit for lighting and to get online.

Three homes in our township are already off-grid, our home will be the fourth.

It is not about saving money. When power goes down, my fences turn off and my livestock get out. When power goes down my incubators go cold. We could get generators, but my wife does not want to add another monthly bill to our budget.

It is funny when urban people focus on expense. When rural folks just want reliable power.

Yogie

Re: Setup an off grid while on grid.

CALLD wrote: »

In an off-grid system with batteries the PV panels will always supply the load first and then dump any extra power into the batteries, in the event that the PV is not generating enough to carry the load the difference in power will be drawn from the battery bank. If you are using a grid-tied inverter with a power grid or generator then any PV production will either feed back into the grid/generator or just reduce the load on the grid/generator.

This sounds like the sort of thing I'd be after. If i could use the solar to give what it can ( looking at 200+ panels ) and then use a smaller generator to top up the supply that would be excellent. Then when grid does come on, if the genset could stop and the grid pick up the load and let the solar recharge the batteries that would be perfect.

Cariboocoot

Re: Setup an off grid while on grid.

CALLD wrote: »

In an off-grid system with batteries the PV panels will always supply the load first and then dump any extra power into the batteries,

This is not accurate.
PV has no way of knowing or controlling where the current it produces goes.
When power from solar is available the battery becomes another load to it, just as the utility does with grid-tie. If the other load demand is less than what the PV puts out the battery is charging. If it is greater the battery is discharging. There is no "it does this first".

If you are using a grid-tied inverter with a power grid or generator then any PV production will either feed back into the grid/generator or just reduce the load on the grid/generator.

Never try to use a GTI with a generator; there would be no regulation of the GTI's output and the generator, unlike utility power, can not sink everything that is put to it.

You can do this with an off-grid inverter, providing it is one meant to handle AC coupling. These are few.

What the OP is looking at now is gen support: a battery-based inverter that can connect to the generator and utilize its power to charge batteries and run loads but if necessary seamlessly add to the gen's capacity for loads. Not all inverters can do this either.

One of the big questions for this application which hasn't yet been asked is: how long a power outage can be tolerated? An occasional blip, several minutes down, or none at all?

Yogie

Re: Setup an off grid while on grid.

stephendv wrote: »

Yes, most inverter/chargers support this but will need an additional external relay. Firstly, if an inverter/charger detects grid power on it's AC input then it will use that power. So the trick is in installing a relay between the grid and the inverter's AC input. Then program the inverter to close that relay if the load exceeds a certain threshold, or if the batteries are below a certain voltage.

Some inverter/chargers have 2 built in and programmable relays so you'd be able to do both auto-generator start and connect a relay to the grid, but you'll have to check the programming for the specific model to see what's possible. I'd imagine in your case you'd want to first connect to grid and if there is no grid, then start up the generator... and when the grid comes back, then shutdown generator and connect to grid.

This sounds great. Good thinking there !! Is there anyway to do this with programming on an inverter rather then use external relays? (edit - what i mean by this is can it be done with all on-board relays inside the inverter so that the inverter "owns" all functionality ?)

Re the LiFePo. I am pretty much sold on this. One of the big big big issues i have is i am not always there on the place. So things get left to local workers. If things go wrong it would be ideal to say " Just leave it and I'll sort it out when i get back, for now switch to generator only". This means if batteries got left at low SOC the batteries are not going to die quickly. My biggest fear with lead acid is that i am out, something goes wrong and the batteries are run down to 50% or less and i take a month to get back to the place = dead expensive battery bank. This is the biggest single thing that attracts me to LiFePo4. Plus if i do need to charge from generator the LiFePo's can take a hard quick charge if needs be - saves $$$ in fuel. Size/weight issues are of no concern at all once on site so that bit about LiFePo has no interest to me . But hard to look past the other benefits that fit my usage pattern. Plus they last longer i believe?

Yogie

Re: Setup an off grid while on grid.

Cariboocoot wrote: »

What the OP is looking at now is gen support: a battery-based inverter that can connect to the generator and utilize its power to charge batteries and run loads but if necessary seamlessly add to the gen's capacity for loads. Not all inverters can do this either.

Yes - gen support. I was hoping that solar and batteries could cover the grid down holes but realistically its not going to work. I am now thinking that several generators are going to be needed. A genset for the 3 phase pump (although have not looked at the VFD pumps yet - about too soon), a smaller genset for sharing the loads with solar and /or batteries to everything else except the big pump set and perhaps a third much smaller to run the air pumps if the grid is down, its night time and the batteries cant cope with the load. Unless i have understood this wrong, thats how it looks to me. plus multiple gensets is no bad thing (other then my wallet!) We are in the boonies, so far from help,spares or support. Multiple gensets gives us redundancy in that area and that is comforting.

But i am here for an education, so by all means tell me why i am wrong.

Cariboocoot

Re: Setup an off grid while on grid.

I don't know about lasting longer; they have not been around in RE applications long enough to determine that.

But the LiFePo chemistry is better suited to inconsistent recharging (i.e. grid up, grid down before charging is finished, no charge available for awhile, et cetera). They can also sit at low SOC for long time without suffering permanent damage.

I'm seeing a couple of ways to go here. One is taking the loads off grid and using the grid as an "opportunity" charging/load source. The other is the reciprocal of this; running on grid and using the batteries and inverter to take up the slack if the grid goes down. Which of these would be used depends mainly on how much the grid can be counted on; the less dependable it is the more I would lean towards the first option.

Solar may not be needed at all, or perhaps not as much as it would with total off-grid with no outside charge source.

I also think you're going to need separate, dedicated systems for the high demand items and they may be different than the 'base' system.

Yogie

Re: Setup an off grid while on grid.

Cariboocoot wrote: »

One of the big questions for this application which hasn't yet been asked is: how long a power outage can be tolerated? An occasional blip, several minutes down, or none at all?

I could be down with the air pumps for an hour at most. Once we start breeding we just cant afford to lose our brood stock - it would set us back years.

I'd prefer not to lose the freezer but while that is an annoyance and expensive and means a long drive to go get more fresh food its not a deal breaker.