Implementing a Time-of-Use function while using an Outback VFX3648

joeedens

I would like to implement a Time-of-Use function for using the Outback VFX3648 Inverter/Charger's Charger. What I want to do is to be able to limit the time frame in which the built-in charger can charge my batteries. I realize that Outback doesn't have a time-of-use function implemented so I'm looking for ideas of how I can accomplish this. One obvious way would be to disable the built-in charger and use a stand alone charger plugged into a timer switch. Anyone have any ideas on how I could use the built-in charger?

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Question: what will be your AC source?
If you're using a generator and want it fully automatic the Outback's auto gen start function does have time constraints. This includes "quiet time" setting which prevents the gen from starting if it's "outside of hours". It's been a while since I last read that part because I normally just go pull the rope when needed.

Otherwise you could use the timer method on the AC In with appropriate relay to handle the load (timer controlled transfer switch).

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

My AC input will be grid power. I don't want to put a timer switch on the AC Input to the transfer switch because I will use the AC Grid Input to pass through the transfer switch to AC loads if the battery voltage hits a set point for low voltage. This would allow the grid AC to get passed through to the AC loads if the battery voltage gets too low during the "off" time of the timer. My grid power is set up for time-of-use so I would like to do all of my supplemental grid based battery charging during off-peak times. My solar panels should normally supply most of my dynamic loads during sunny days, but if there is a deficit of energy supplied by the solar panels then the battery bank would make up the difference and supply the deficit energy to my AC loads. The battery bank would then be charged during off-peak hours (nighttime) and I would then start the next day with a fully charged battery bank. None of this is implemented yet, this is what I'm trying to design for.

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Aha! "Urban load-shifting" eh? Run off batteries/solar when utility rates are high and use the grid as your back-up gen when rates are low.

Someone more clever than I could come up with a circuit that could control AC IN via the gen start function, but basically AC IN has no separation from the inverter's charge function. So without external transfer switching or a separate stand-alone charger there is no way to divorce the charge function from the loads.

You're idea, in my opinion, makes sense. Even though the common reaction here is always "if you've got grid, why use solar?" because solar is a very expensive way to generate power. I've pretty much stopped using that argument. If people want to spend their money on a political statement that's their business. But if some says "I want to install solar to save on my utility bill" I'll hit 'em with the cold, hard facts.

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

I agree with you. My first priority is not to implement a system which will save me money on my utility bill. My first priority is to have a system which can be functional in the event the grid power is down for an extended period of time, albeit with a more moderate usage of power when that happens. After achieving that goal, then trying to tweak the system to so that I utilize my available resources (grid and RE) in a way the keeps ongoing costs to a minimum. So, many people will say, why not just do Grid-Tie? The answer is that in the aggregate usage I don't want to produce enough RE to see to the power company, that wouldn't make sense economically. I would try to keep the system size so that my peak demands (known as luxury items) would be powered by the grid. So with my aggregate RE production always less than my aggregate usage, why should I interact with the power company in a complex way that supposes that I will sell to them? My power company wants many things in a Grid-Tie agreement. They want monthly administrative fees which they can change at will, they want monthly minimum purchase amounts, they want me to provide them with evidence of a million dollar umbrella insurance policy, they want 24 hour access to inspect the system any time they want. I'm supposed to agree to all of this and in the aggregate I'll never sell them anything! Its much simpler in my mind to implement a system which meets my first priority of having grid independence "when needed" and use a feature like the AC transfer switch feed through when I don't produce enough, and store it my self in my batteries when I momentarily produce more than I use. I need to have batteries anyway even with a grid-tie system to meet my primary objective - grid independence when needed. Does this make any sense?

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

I can boil the utility's position down to one sentence: they don't want grid-tie. Obviously some legislation has been passed requiring them to allow it, but they've made it unreasonably difficult.

Here's the good news: I run the whole cabin off a 3624 and 300 Amp hours of battery. This includes refrigerator, computer/satellite set-up, water pump, digester pump, lights, radio, microwave ... It's a bit tight and requires a lot of load shifting for sunny days. On the whole it wouldn't take too much expansion to make it "seamless". Right now I squeeze an average 2400 Watt hours out of it. Doubling the array size to 1400 Watts and upping the battery bank accordingly would be an improvement.

You may not have to do without quite as much as you thought.

mike95490

Re: Implementing a Time-of-Use function while using an Outback VFX3648

re load shifting to batteries -
Cycleing your batteries, will about double your off-peak consumption, if you consume 200WH it will take 400WH to recharge. if your peak rates are not 2x the night rate, it may not pay, and your battery bank goes from "float" use, to daily cycles, which will run down it's lifetime.

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

mike90045 wrote: »

re load shifting to batteries -
Cycleing your batteries, will about double your off-peak consumption, if you consume 200WH it will take 400WH to recharge. if your peak rates are not 2x the night rate, it may not pay, and your battery bank goes from "float" use, to daily cycles, which will run down it's lifetime.

Mike, that would be true if you were relying on the grid for 100% of your battery recharging. In this case its just taking the place of the back-up gen. I think he already understands that this is not feasible from an economic standpoint. Also the principal application is emergency back-up power, rather than steady use.

BB.

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Hmmm... A couple of posts I really though I made today--but not here now... Don't know if it my computer or me that is loosing a mind.

Anyway, every way I cut it so far, using new equipment bought from the web and just used to time shift (battery bank, inverter, charger), it pretty much works out to ~$0.45 per kWH just for the hardware and battery bank (replacement batteries wearing down from cycling, new hardware every ~10 years or so, etc.).

Add the price for power on top of that (80% AC charger efficiency, 85% inverter efficiency, and 80% flooded cell battery efficiency) ~54% end to end efficiency (as Mike said, for every 1kWH you use during the day takes almost 2kW at night to recharge)... It does not make sense.

Even cycling for "free solar PV power" to run a few loads costs a bunch of money too (~$1-$2 per kWH generated for an off-grid power system).

For a nice system, a hybrid inverter system which can do both Grid Tied and Off Grid (such as the Xantrex XW hybrid inverter) can be really nice. You get the advantages of Grid Tied (utility net metering), and you have backup power when the utility fails.

I would have really like to do something like that on my home... But I could never make economic sense out of it... Our power fails for perhaps 1 hour every two years... And the last 1 week power outage was over 50 years ago (coastal storm).

A genset with your fuel of choice is usually a "better investment".

-Bill

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

On a purely cost-per-Watt basis a gen is a better investment. However, battery-based back-up power has certain advantages which may outweigh cost in some circumstances. It is silent, there's no fuel storage, and it will come on automatically (and instantly) when you're not there (expensive gen sets can do this, except for the start-up lag).

As long as people are aware of the costs involved, it's their choice. But solar sure isn't cheap!

techntrek

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Emergency battery back-up can increase the efficiency of a genset if the genset and battery systems are both sized correctly, paying for the battery backup in the process. The base load of a home is usually less than 1000 watts most of the time, so a 5000 or 10,000 watt genset wastes most of its fuel. As a double-whammy gensets operate far more efficiently when fully loaded - exactly opposite of how they usually are loaded. And a battery/inverter system can run a base load easily, and then accept a bulk charge quickly - loading a genset into its efficient band in the process. So they complement each other well. Best to only bulk charge during the power emergency and leave the final stages for utility power when it returns.

Plus as Cariboocoot said, its silent. That was a strong 2nd reason for getting mine since I was definitely not running my genset overnight during an outage (fuel cost and noise).

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Thanks for the many replies. In response to the question about whether it is worth it to charge the batteries during off-peak for use during on-peak, or just using grid during on peak, if I understood correctly it was calculated that due to losses in conversion from charging/inverting that it would be approximately 2x the off-peak rate after taking into account the inefficiencies. My off-peak rates are 2.6x less expensive than on-peak. Not much savings after all of the conversions but still worth doing since I want to have a battery bank of sufficient size which would allow grid independence for the necessities in the event of an extended grid outage.
Another question: If the VFX 3648 inverter/charger is stacked in series would the 45 amp max output of the charger be doubled to 90 amps?

BB.

Re: Implementing a Time-of-Use function while using an Outback VFX3648

But you also have to add the cost of the hardware and replacement batteries which, very roughly, adds around $0.45 per kWH (capital costs and wear & tear).

That pushes the timeshifting costs way over any savings (at least for my area):

2x($0.09 per kWH) + $0.45 per kWH hardware costs = $0.73 per kWH

My TOU plan for Summer Peak is around $0.32 to $0.58 per kWH (they just increased our rates a bit)...

Even the worst case, I still would loose $0.15 per kWH load shifting (my normal tier is $0.32 per kWH--so the true losses are even higher).

-Bill

-Bill

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

If I were doing this specifically to try to save money on my electric bill, that would be the way I would look at it. However I'm coming from the perspective that I first want a grid independent system capable of supply my need for my necessities for an extended period of time independent of grid power. That mean that the equipment and batteries costs will be sunk costs to meet that goal. Now, given that I've already sunk those costs to achieve my first priority of being able to ride out an extended period of loss of the grid, how do I use the system on those normal days when the grid is up. I'm accepting that when/if the grid goes down that I'll adjust my life style to match my RE system output, but when the grid is up running normally I can use my basic RE system and supplement it with the grid for our "normal" life style.

tallgirl

Re: Implementing a Time-of-Use function while using an Outback VFX3648

If you want fairly complete control over your OutBack system, we have product that can reprogram the inverters and chargers on the fly, as well as control other devices needed to make sure the system performs properly overall. Plus, we're working on the software needed to do both on-demand charging and selling. As soon as I can work around some patent filings I did for a former employer, we'll have load balancing. There's only one other company I know of that can dynamically reprogram OutBack inverters.

You don't want VFXen, you want a pair of GVFX 3648, or a quad stack of them if you expect to run air conditioning when the grid is down for a prolonged time. For most on-grid residential users with large enough arrays to do what you want, a quad stack is the only way to produce the power in the first place.

Finally, no clue where people come up with the numbers they quote for system costs. If you're off grid, yeah, the system will run at very low efficiency. In fact, the better designed (more robust), the lower the efficiency. But for on-grid, end-to-end efficiency is much better. Point the array south-south-west and let it run the way it was made to run.

tallgirl

Re: Implementing a Time-of-Use function while using an Outback VFX3648

joeedens wrote: »

Thanks for the many replies. In response to the question about whether it is worth it to charge the batteries during off-peak for use during on-peak, or just using grid during on peak, if I understood correctly it was calculated that due to losses in conversion from charging/inverting that it would be approximately 2x the off-peak rate after taking into account the inefficiencies. My off-peak rates are 2.6x less expensive than on-peak. Not much savings after all of the conversions but still worth doing since I want to have a battery bank of sufficient size which would allow grid independence for the necessities in the event of an extended grid outage.
Another question: If the VFX 3648 inverter/charger is stacked in series would the 45 amp max output of the charger be doubled to 90 amps?

There are ways to control the inefficiency -- don't slam the batteries with massive amounts of current.

When a battery is charged, the voltage rises in fairly direct proportion to the amount of current. Since "watts = volts * amps", it's fairly obvious that when the voltage rises because of an increase in current, the power needed per amp-hour is higher. The solution is lower rates of charge. Since you're charging from the grid, recharging for longer periods of time isn't an issue the way it is with a generator that runs better fully loaded. This curve (from my company's software, measured on my personal system) shows the relationship between volts and amps for a given state of charge --



Each volt rise is a 2% decline in efficiency (48 volt system). Recharging at 45 amps is probably a 10% decline in efficiency, if not more.

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Tallgirl, you said:

"You don't want VFXen, you want a pair of GVFX 3648, or a quad stack of them if you expect to run air conditioning when the grid is down for a prolonged time. For most on-grid residential users with large enough arrays to do what you want, a quad stack is the only way to produce the power in the first place."

If I don't want to sell back to the grid (because of many issues associated with the power company demands in the Grid Intertie Agreement such as monthly administrative fees, minimum purchase requirements, outrageous insurance requirements, etc), but I want to have a grid AC input to my inverter/charger, why is the GVFX better than the VFX for my usage?

BB.

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Tall Girl,

The equipment costs are pretty straight forward to calculate:

(capital cost of system + maintenance costs + battery replacement ever X years) / (number of kWH per year offset * 10 year life) = $$$/kWH

For example:

• GVFX 3648 runs ~$2,000
• assume 1,200 watt average load * 6 hours day * 130 days per year (6 months * 6 hours per day TOU)
• 1,200 w*6h*1/0.25 discharge * 1/0.85 inv eff * 1/48 volt batt = 705 AH @ 48 volt battery bank
• 8x$1,000 Surrette 6CS-21PS battery 6 volts 683 amp hour batteries
• $500 for misc hardware and cabling

($2,000 + 8x$1,000 + $500) / (1.2kW * 6 hours * 130 days per year * 10 years) = $1.12 per kWH @ estimated 10 year system life

Even if you assume 20 year life for hardware + battery bank (a very lucky person), you are still looking at a cost of $0.56 per kWH just for the hardware to do the load offset... Plus for every 1kWH you offset, you will need almost 2kWH in charging energy to make up for system loses...

You could try it with Trojan 16x Trojan L16RE-B 370 AH Deep Cycle Battery for $5,000 -- But assuming a 5-8 year battery life, you will have to spend a second $5,000 for $10k total--vs $8,000 for the Surrettes which should last 10-15 years on one set...

I have used my TOU pricing plan as a model--5 days a week, noon to 6pm, summer time, my summer peak is, at least, 3.6x my off peak power costs. And I still cannot even come close to breaking even.

Efficiency, I used 80% for the flooded cell batteries, 85% for inverter, and 80% for charger for 54% overall end to end worse case generic efficiency.

I also assumed inverter running an average of 1/3rd load to support starting surges and allow for cycling loads.

Assuming a best case of 90% inverter, 90% charger, and 90% flooded cell battery efficiency = 0.73% efficiency. Better, but a bit optimistic. Still will need to buy 36% more electricity than was load shifted.

Regarding cost of power, I have tiered pricing, and as the total usage goes up, for folks with A/C, it is easy to get into the $0.58 peak vs $0.36 off peak rate tiers. Much less spread in cost of power.

Do you have some suggestions on where I may need to update my financial model? Have not even included labor, permits, cost of money, or even some money for repairs that may be needed

Again, I am not claiming my costs are the end all--Just a starting point. And that people should rough out $/kWH cost (or whatever costing measure make sense to them) to understand where best to spend their money.

For me, it was always better to spend the first dollar on conservation instead of solar or time-shifted power.

-Bill

Brock

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Joe I am in the same boat as you are so to speak. I have an MX-60 and xw6048. What I do is just use a contactor fed from a signal from the utility meter that cuts my secondary panel from the grid and the 6048 picks up all the loads when we hit on peak. Since the majority of the on peak time is during the day I use the batteries between 5% and 10% of their capacity and that usually happens in the evening as the sun starts to set right before we hit off peak. Most of the time I leave the charger off and the next day they get topped off, but if I know it's going to be cloudy I turn the inverters charger back on. It is a manual thing, I could just leave the charger on all the time but 90% of the time they get topped off the next day from solar.

As in your case my system is technically not grid tied and meant as backup more than anything else, but I take advantage of my setup by powering my loads via the system during the on peak time.

The way I understand it though you are just trying to avoid the charger kicking in on peak and waiting until off peak. So again you are not significantly dipping in to your battery reserves, just not topping them off on peak.

I do have a setting on the 6048 that you can set to not allow battery charging during certain times, I believe it is load shifting, all it does is turn the charger off during the set time, which sounds exactly like what you want to do. The problem is it sounds like the FX inverters don't have this feature?

If it doesn't I would just get a charger and connect it to the batteries and put it on a timer like you had suggested. Personally I prefer the iota chargers, but xantrex and a couple of others make nice chargers as well.

I don't think you're crazy for not wanting to charge on peak

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Brock,
Its good to hear that someone else is doing what I'm trying to do. The FX doesn't have the ability to using time frames for charging so it looks like I'll be looking for a standalone charger to use with a timer.

Ralph Day

Re: Implementing a Time-of-Use function while using an Outback VFX3648

I don't have OB products except for MX60, but I have seen someone ''use'' and ''drop'' utility power via their mate. Mate controls the FX, just not sure if it was automated or manual.

Might the Mate be cheaper than an external charger (if you don't already have one)?

Ralph

GreenerPower

Re: Implementing a Time-of-Use function while using an Outback VFX3648

joeedens wrote: »

...My first priority is not to implement a system which will save me money on my utility bill. My first priority is to have a system which can be functional in the event the grid power is down for an extended period of time, albeit with a more moderate usage of power when that happens. After achieving that goal, then trying to tweak the system to so that I utilize my available resources (grid and RE) in a way the keeps ongoing costs to a minimum.

Joe,
Your thoughts were exactly mine when I started my RE system (except I had grid-tie backup, PVs were added much later). You are absolutely right, with such policy against grid-tie of your ESP, you want to stick with FX, not GX, not anything associated with "grid-tie", otherwise the ESP would find reasons to force you to put in an application. Unfortunately the FX charging starts as soon as it connects back to grid and its charger has priority over the MX/FM !!! Your best bet is to turn off the FX charger (set charge current to 0, just turning charging off via Mate2 is not enough) and use external charger . The FX charger has poor power facter to load your back up gen in case of prolonged power outage (~ 3hrs when there was a blown transformer in the neighborhood, >2 weeks when Ike hit our area 3 years ago). Alternatively, you could tune the FX charging current significantly down for the main charge to be delivered by PVs the next day.
GP

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Ralph Day wrote: »

I don't have OB products except for MX60, but I have seen someone ''use'' and ''drop'' utility power via their mate. Mate controls the FX, just not sure if it was automated or manual.

Might the Mate be cheaper than an external charger (if you don't already have one)?

Ralph,
I don't have the equipment yet but as I understand it the Mate is the device you use to communicate with and program the FX. So what you saw was probably someone manually change the setting on the FX to enable the charger and then manually disable to stop the charger. This would work. I would be the timer in the circuit. Don't know how long I would want to perform this function though!

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Greenpower,
Thanks for the info on the FX charger. Automatically giving it priority to use grid power to charge the batteries over the charge controller seems counter productive. Is this a bug somehow or do you think it was designed to do this? At the very least it seems they should provide a programmable feature to set the priority.

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

joeedens;

You are correct that the MATE units are just programming interfaces for the FX units. Keep in mind the OB inverter/chargers were not designed to be used as you intend. They simply never thought there'd be a need to control time-of-use input from an AC grid! As I mentioned before there is the gen function's "quiet time" feature which probably could be adapted to this situation. And since the grid is your gen, the power factor isn't really an issue (it's not much of one for generators either, in reality).

Obviously the simplest thing is to disable the built-in charger and use a stand-alone unit on a timer. But it should be a good charger, to be sure the batteries only get what they need and you're not drawing any excess power.

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Cariboocoot,
Thanks for reminding me about the gen function. I glossed over it in the manual since I'm not using a generator. I'll check it out and see if I can use it.

GreenerPower

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Cariboocoot wrote: »

...They simply never thought there'd be a need to control time-of-use input from an AC grid!

Via the Mate, you can program the FX for time-of-use i.e. when to connect to grid but not "time-of-charging". As soon as the FX is disconnected from grid, once it is connected back it would try to charge battery. As far as charging, both FX and MX are trying to charge battery. I think the Mate should be smart to turn off charging from FX as soon as it detects charging from MX, but it's not :grr
Joe, on your other question, when you stack FXes, yes, the charging current to battery can be doubled, each FX would try to pump at the charge current setting in bulk-charge state.
GP

joeedens

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Greenpower, I don't see anything in the VFX programming manual about being able to program it for the time of when to connect to the grid. Can you point me to where I can find that info?

Cariboocoot

Re: Implementing a Time-of-Use function while using an Outback VFX3648

I think this one is also in the MATE manual.
http://www.outbackpower.com/pdf/manuals/mate.pdf

"Timers" - about page 94. :roll:

(Bloody complicated little buggers, ain't they? )

GreenerPower

Re: Implementing a Time-of-Use function while using an Outback VFX3648

Be careful, some functionalities provided by FX or MX individually i.e. they are still functioning without the Mate. Some are provided by the codes in the Mate. Those can not function without the Mate and the devices attached via the OB Hub. Time-Of-Use is such Mate's function.
Another area you might want to look into is to program the AC input as AC1 (grid) or AC2 (gen). Even when you have grid input, program it as AC2 might have some advantage. For example you can limit the total current drawn from the AC input so that the charging current would be reduced when load increases. This could allow you to charge battery minimally when the FX connects back to grid.
GP

tallgirl

Re: Implementing a Time-of-Use function while using an Outback VFX3648

BB. wrote: »

Assuming a best case of 90% inverter, 90% charger, and 90% flooded cell battery efficiency = 0.73% efficiency. Better, but a bit optimistic. Still will need to buy 36% more electricity than was load shifted.

That's not at all an optimistic figure. I run systems higher than that -- some of mine get into the 80's, and that's using devices with fairly high accuracy for measuring various currents and the like.

A lot of the inefficiencies that happen off-grid don't happen at all on-grid. And as I pointed out, if you want better battery efficiency, don't slam them with as much current as you can get your hands on. For example, instead of setting the inverter chargers at close to the limit, calculate the current needed to recharge during off-peak. ALL of "off-peak". Since you aren't running a generator to do the recharging, you gain on efficiency because Vbatt isn't being elevated as much by the high current levels.