New system thoughts

System · August 2011

Hi. New here and new to solar. I've been wanting to do a system for quite a while and reading as much as I can including a bunch on this site over the last few days.

Basically I want a system that I can wheel out of the garage and setup to run a limited number of items during a power loss. In the future perhaps a permanent system but I don't have that option where I am at now. No grid tie necessary.

From various calculators on assorted sites I came up with a total daily need of 1750 watt hours.
Assuming power could be off up to 3 days, 5250.
Keeping batteries from going below 50% = 10,500 watt hours.
On a 12 volt system 875 amp hours.
About 450 on a 24 or 225 on a 48.

I'm the most lost on how to best configure the batteries. So far I've come up with a whole range of configurations including:

12 volt, 100amp hour batteries, 2 chains of 4 in parallel for 800 hours.
or 3 chains of 4 in parallel for 1200 hours.

Or with 200 amp hour, 1 chain of 4 for 800.

If I switch to a 24 volt system and go with 200ah batteries I could do 3 chains of 2 in series for 600 AH.

Or... etc. I just don't know what is the best approach here.

I'm leaning towards AGM batteries if that matters.

Also this system will start small with 1 panel, minimal batteries and slowly grow as I have funds to add more. I can allocate enough for the initial setup to support where I would like it to grow to but not much more.

So with the growth target of those amp hours and having 8 or 9 60W panels (keep in mind I want this to be mobile, maybe to fold up, etc. so I can't go with large panels) I am considering a Morningstar 45 MPPT Charger and True Sine Wave inverter (Xantrex 2500, Powerbright 3000, haven't decided yet) One of the items to be powered will be a fridge which from what I have read, the cycling motor needs a high initial surge even though it settles much lower so the inverter needs to be large enough to accomodate this.

Finally I would need some way to trickle charge the batteries to keep them topped up as I couldn't haul this out after say a storm and expect to use it unless they were to begin with. Would a small panel... 15 watt or something permanently mounted (I could get away with this) feeding this charge controller work?

OK. Let the dashing of my dreams and folly of my thinking begin...

Cariboocoot · August 2011

Re: New system thoughts

Welcome to the forum.

Something like what you want could be mike90045's solar monolith: http://www.mike-burgess.org/PVinfo_1.html

What you've got working against you: you want a cracking ton of off-grid power: 5250 Watt hours
What you've got working for you: this forum.

First problem: that much stored power begs for 48 Volts. Why? Because on 12 Volts it's 437.5 Amp hours, requiring a monster-sized current bank. High current is the enemy, as it becomes heat not actual work done. Same Watt hours on 48 VDC = 109 Amp hours, or 218 Amp hours of battery minimum. That's an easily done 48 Volt bank with standard "golf cart" batteries. All battery connections in series = no problem with current sharing between the batteries. And there are other advantages. To wit:

12VDC = 900 Amp hour battery bank; four parallel banks of two in series. Eight batteries, twelve interconnecting wires, two charge controllers or one very expensive one, 1730 Watts of panel to recharge it.

24VDC = 450 Amp hour battery bank; two parallel banks of four in series. Eight batteries, eight interconnecting wires, one charge controller, 1730 Watts of panel to recharge it.

48VDC = 225 Amp hour battery bank; one string of eight batteries, seven interconnecting wires, one charge controller, 1730 Watts of panel to recharge it, no problems keeping current flow even through all batteries, least amount of current flow for the Watts delivered.

AGM's are an expensive per Amp hour way to start. Reconsider this.

One small panel will not recharge that much battery no matter how it's configured or how long it sits in the sun. It might keep it trickle charged between uses, even then you'd need 120+ Watts (and at the higher system Voltage that is difficult to do because most panels are "12V" or "24V"). You would need a charger run off the mains to properly replenish the power.

On the whole I'm against the "3 days stored power" concept. It's a long enough discharge without recharge time to lead to sulphation and shortened battery life. I prefer to size the bank for 25% DOD, knowing you've got another 25% to go if needed, then start the generator on day 3 if necessary. That plan, btw, would simplify your design and save a lot of money on batteries and panel.

Over-all, solar electric for occasional back-up use i not very practical in economic terms.

Sparkletron · August 2011

Re: New system thoughts

If your goal is merely a backup system, no PV is required at all; simply get an appropriate charger (Iota, etc.), and use the grid.

Once you add enough PV to charge a large bank, you're going to want to use that array to offset your daily grid use and not merely for emergencies.

What voltage you configure your bank depends on how far you expect to send that DC. If you have a bunch of DC devices all over your home, then you want to avoid 12 VDC. Besides the cost of efficient wiring, you'd have to accept significant wattage limitations. Perhaps that's not an issue for you, but if you plan to power large appliances, you'll need to deal with very high amperages and all the expense and danger that entails.

Most people convert DC to AC at the source so they can use cheap off-the-shelf AC wiring, switches, etc.

mike95490 · August 2011

Re: New system thoughts

Cariboocoot wrote: »

Welcome to the forum.

Something like what you want could be mike90045's solar monolith: http://www.mike-burgess.org/PVinfo_1.html....

That is a 64 watt flexible amorphous panel (unisolar), and 200Ah of 12V battery. Not perfect but, good for emergency light and a radio and cell phone charging.

for your request, you will need a lot of them !

System2 · August 2011

Re: New system thoughts

Thanks for the feedback. It definitely gives me something to thing about.

I think the best part to start with is getting that usage number down first. The worst item is the refrigerator, after that it's mostly small stuff LED lights, cell phone charger, etc. I'm not trying to run a home entertainment system or anything like that.

I would consider grid to batteries and no panels however if the grid goes down for more than a few days then I have no way to charge it back up, with solar I do. Generator would be an option however for the same reasons I'm not doing a permanent solar installation I don't want a permanent generator and don't think a portable would hang around long enough in an emergency... if you get my drift. While you might not think it would go down for that long, and until recently I didn't either, storms we've had this year here and other areas have knocked it out for about a week and these were just "normal" storms, not the tornados that others had.

I guess the first question... is that Inverter and Charger OK to use with a small numebr of panels and batteries? and then I can add more as funds permit? Or do I need to start with a lower end option for each and then buy bigger ones as my system grows?

Cariboocoot · August 2011

Re: New system thoughts

CulexPipiens wrote: »

I guess the first question... is that Inverter and Charger OK to use with a small numebr of panels and batteries? and then I can add more as funds permit? Or do I need to start with a lower end option for each and then buy bigger ones as my system grows?

Inverter limits: A). you have to have the right Voltage;

. you have take the inverter's own power consumption into account (against a smaller battery bank it could be a problem of running out of power too soon just to tare losses); C). if you try to use a very large amount of current at one time the batteries may not be able to supply it (deep cycles are not good with the sudden current jumps, although AGM's are better) V-drop could cause the inverter to shut down from low Voltage.

The biggest problem is "fueling" a 2.5 kW inverter to provide <300 Watts, which is typically what happens on whole-house systems. Some of the large inverters have a low power draw "search" mode where it uses much less until a load is present to trigger it to full power, but that is not without failing.

Yes; refrigerators are big power users. I've just tested a few: http://forum.solar-electric.com/showthread.php?t=12272

Sparkletron · August 2011

Re: New system thoughts

Running a fridge for days or even a week off batteries is actually pretty easy--if you have the right fridge. There are a bunch of threads on this subject. I own a Sundanzer that uses 300 watt-hours a day at its coldest setting in a hot garage. It automatically switches to my battery bank if there's a loss of power. A single 250 Ah battery could keep it going for over a week (and if your outage lasts that long then you'll have other things to worry about besides refrigeration).

As for sulphation, I don't see that as a problem if you don't plan on having too many week-long outages. What you're really buying here is insurance, only it's in the form of a battery, because you don't intend on using that battery unless there's some kind of disaster, at which point the battery has served its purpose and paid for itself. And if you happen to swindle more than one emergency out of the same battery, well, even better. The 50% SOC rule doesn't apply to your scenario because that's for people who plan to deep cycle their batteries over and over, day after day. Indeed, you don't even need a deep cycle battery at all. But you will need enough CCA to get the compressor started.

Cariboocoot · August 2011

Re: New system thoughts

Note: batteries drop dead over time whether or not they're used. With deep cycle batteries you will likely get a longer lifespan if they are regularly cycled than if they are just kept charged.

It is indeed insurance. But it's bloody expensive insurance, so be sure you need it and be sure you buy the right "policy" for your needs.

Sparkletron · August 2011

Re: New system thoughts

Cariboocoot wrote: »

It is indeed insurance. But it's bloody expensive insurance, so be sure you need it and be sure you buy the right "policy" for your needs.

Actually, it's the solar-panels-as-insurance that's bloody expensive--far more so than a battery. That's why I'm trying to convince the OP to avoid PV unless he plans to use them every day.

Cariboocoot · August 2011

Re: New system thoughts

Sparkletron wrote: »

Actually, it's the solar-panels-as-insurance that's bloody expensive--far more so than a battery. That's why I'm trying to convince the OP to avoid PV unless he plans to use them every day.

True indeed! Many people don't realize that a few Watts of PV won't recharge the big bank of battery needed to supply serious Watt hours.

And before anyone dismisses your suggestion of the Sundanzer 'frige, let's remember it would use less power all the time! Conservation always gives you a better return on your $ than generation. Keeping the loads down saves money all 'round.

Frankly my tests with refrigerators show most manufacturers do not care how much power they use, and the Energy Star program appears to be a joke. :roll:

Along those lines, I have often suggested the combination of generator & inverter/battery so that you can have "quiet power" at night and recharge it cheaply and easily from the gen in a couple of hours during the day.

icarus · August 2011

Re: New system thoughts

Not to be a nay sayer, but for emergency power, a small, reliable generator is way cheaper, way more reliable than a battery bass system. Unless your grid is hopelessly unstable, buy a honda eu 1000 or 2000 prof under $1000, run it once a month, keep fresh fuel in it,, and you will be way ahead!

As we have said so often before, off grid battery based systems come at twice the price with half the performance, leading to 4 times the cost per kwh.

Tony

Sparkletron · August 2011

Re: New system thoughts

icarus wrote: »

Not to be a nay sayer, but for emergency power, a small, reliable generator is way cheaper, way more reliable than a battery bass system.

Well I have both and I'll try to make the case why that's not true--or rather--why both are good for different reasons.

To use the OP's scenario, he wants emergency power to run a fridge and some small consumer electronic items like flashlights and cell phones. The problem with a generator is that it's using fuel even when there's no work to do. Yes some have "eco-modes", but use a tachometer and you will see that the RPMs are still way up there and fuel is being consumed all the time. So it's crucial to match the load to the generator. Pick the wrong generator, and you'll quickly burn through your fuel just idling, wasting it during the 10-minute intervals when your compressor's not even running.

Then there's the reliability issue; a generator with all those moving parts versus a battery. I like the Honda EU1000i too, but a week is a long time to run one without a hitch. And unlike the battery, you'll be refueling it, servicing it, dealing with it. The fuel must be stored outdoors. In an emergency, you better plan on securing that fuel as well, since it's not inconceivable that others may want your fuel. Most fuels go bad after a while and must be refreshed--another inconvenience. A sealed AGM battery system, by comparison, is basically set-and-forget.

Finally, you can't run a generator indoors, which means you'll be running it outdoors, where it will surely attract the attention of your curious neighbors and other onlookers--you know--the ones who didn't buy any "insurance policy" and now want to use your generator. And your neighbors will likely get increasingly ornery with each day that passes, each day that they have to see and hear your generator rumbling away and affording you all the benefits of electricity while they're reduced to caveman conditions. Compare that to the battery, which makes no noise and is safe and secure indoors, out of sight and out of mind.

I'm not saying a generator doesn't have its place; you're not likely to run AC off a battery bank (at least not for long). But for the OP's scenario, a battery makes more sense.

Cariboocoot · August 2011

Re: New system thoughts

I've got over 6,000 hours on my Honda EU1000i and it's still going, so I'd say longevity isn't an issue with a decent generator. The fact it can run all day, very quietly, on $2 of gas is nice too. These little inverter generators are a vast improvement over the big "lawn mower-engined" clunkers that crank 3600 RPM all the time.

It's still comes down to getting the right solution for your particular circumstances. Most often for occasional power outages that is a small, efficient generator. Cheap inverter tend to be a disappointment, and good ones tend to be money. Depending on how much power you need it can be six of one/half dozen of the other. The main shortfall with batteries is that they have to be recharged. That requires a charge source and time. A generator simply needs to be refueled, and that doesn't take very long.

There's no "one-size-fits-all" solution.

icarus · August 2011

Re: New system thoughts

Spark,

You make some interesting points. I would only add that $1000 worth of Eu genny will do a hell of a lot more work in it's total life than $1000 worth of batteries. Even batteries that sit idle on float will only last a finite amount of time, even calculating in fuel costs.

Like I said, if your grid is reasonably secure, one may buy peace of mind with a small PV system, and that is fine, but in most cases it will be way cheaper to use a genny.

Tony

mike95490 · August 2011

Re: New system thoughts

Pair a genset and a charger, with batteries. Run the genset 2 hours for charging, let the batteries run another 10. repeat as needed.

System2 · August 2011

Re: New system thoughts

Sparkletron wrote: »

I own a Sundanzer that uses 300 watt-hours a day at its coldest setting in a hot garage. A single 250 Ah battery could keep it going for over a week (and if your outage lasts that long then you'll have other things to worry about besides refrigeration).

I think this or maybe 2 of these, one as a fridge, one as a freezer might be worth the investment in order to dramatically cut down the size of the rest of the system. And since these appear to run DC then the inverter can be much lower since I no longer have a motor startup surge to deal with, just the misc small items to keep charged.

Thanks

Sparkletron · August 2011

Re: New system thoughts

Here are some Sundanzer buying tips. First, there's no difference between the fridge and the freezer except for the thermostat. Second, there's no difference in compressor size between the various models. The larger ones will use more energy but the amp requirements will remain the same. If you have the space, get the largest (8.1 cubic feet) model.

You should also check out Sundanzer's principal competitor, Engel, to see what they're offering.

Slappy · August 2011

Re: New system thoughts

CulexPipiens wrote: »

I think this or maybe 2 of these, one as a fridge, one as a freezer might be worth the investment in order to dramatically cut down the size of the rest of the system. And since these appear to run DC then the inverter can be much lower since I no longer have a motor startup surge to deal with, just the misc small items to keep charged.

Thanks

the sundanzer cost more than the a/c reefers, but you will need less panels, smaller inverter(if one is needed), and less to go wrong sense it runs straight from the battery/bank. if inverter goes out, the reefer will keep running. they are quieter than a mouse when running, only hear a click when they turn off/on. some times have to put my ear on the lid to tell if it is running or not. got the danzer fridge 4 months ago, and moved the a/c fridge to the garage and not think twice about it (ready to sell it, it is now just taking up space.)

System2 · August 2011

Re: New system thoughts

Since the fridge/freezer is running direct off the batteries, what prevents it from draining the bank to zero? The inverter should kick off when the pack gets too low but since that has been eliminated (for this appliance) what then?

Cariboocoot · August 2011

Re: New system thoughts

They have their own built-in low Voltage disconnect. http://lib.store.yahoo.net/lib/wind-sun/sundanzer165-225.pdf
Although 10.4 Volts (on 12 Volt set-up) is lower than I'd care to see the batteries go. If you wanted to change this you could use a programmable Voltage controlled switch http://www.solar-electric.com/volconswit.html & relay to shut it off before it got so low. You could even set it up to sound an alarm at, say, 11.5 Volts and then turn off at 11.0 (or whatever V you think is best).

Sparkletron · August 2011

Re: New system thoughts

CulexPipiens wrote: »

Since the fridge/freezer is running direct off the batteries, what prevents it from draining the bank to zero? The inverter should kick off when the pack gets too low but since that has been eliminated (for this appliance) what then?

The Sundanzer runs off AC just like any other appliance. If it detects a loss of AC, it automatically switches to DC (and back again when AC is restored). It's plug-and-play; there's no need for you to do anything except supply a battery and a charger. If the grid is down then the Sundanzer will draw from the battery until it's depleted. Ideally, you would also have a generator so that you could charge up the battery every day. But honestly that's not really necessary; in an emergency--go ahead and run the battery until it dies.

Cariboocoot · August 2011

Re: New system thoughts

Sparkletron wrote: »

But honestly that's not really necessary; in an emergency--go ahead and run the battery until it dies.

And then go buy new batteries.
Or plan ahead and prevent the occurrence in the first place.

Slappy · August 2011

Re: New system thoughts

Sparkletron wrote: »

The Sundanzer runs off AC just like any other appliance.

the sundazer is a DC appliance, it is battery based (12/24 volt), solar panel, charge controller, battery, fridge/freezer. now it can be run from the grid from a ups type set up.....as in "ac battery charger-> battery -> fridge."

the sundanzer does have its own low voltage disconnect built in.

Sparkletron · August 2011

Re: New system thoughts

Cariboocoot wrote: »

And then go buy new batteries.
Or plan ahead and prevent the occurrence in the first place.

Every insurance policy has an expiration date, and must be renewed from time to time.

If all goes well, the battery will never be used, and will live out its days doing absolutely nothing. That's the best-case scenario. If all goes well, he'll throw out the battery in five years or so never having used it once.

Cariboocoot · August 2011

Re: New system thoughts

They have different models, including AC powered units that have DC back-up.
Haven't seen a wiring diagram, but I suspect the AC model is simply a DC unit with a power supply added on. If so it makes no sense whatsoever to use one in an off-grid application: converting DC to AC and then back to run the 'frige would be silly. Straight DC powered would be most efficient.

Cariboocoot · August 2011

Re: New system thoughts

Sparkletron wrote: »

Every insurance policy has an expiration date, and must be renewed from time to time.

If all goes well, the battery will never be used, and will live out its days doing absolutely nothing. That's the best-case scenario. If all goes well, he'll throw out the battery in five years or so never having used it once.

Unless I've gotten confused along the way, this is an off-grid situation and all the power will be coming from batteries (except when generator is absolutely necessary). See my prior post about DC-AC-DC efficiency.

No sense in abusing batteries.

Sparkletron · August 2011

Re: New system thoughts

Slappy wrote: »

the sundazer is a DC appliance, it is battery based (12/24 volt), solar panel, charge controller, battery, fridge/freezer. now it can be run from the grid from a ups type set up.....as in "ac battery charger-> battery -> fridge."

When you order a Sundanzer, make sure it comes with the AC/DC Option. That will make it work as I described.

Sparkletron · August 2011

Re: New system thoughts

Cariboocoot wrote: »

Unless I've gotten confused along the way, this is an off-grid situation

Well the OP can correct us both, but this is from his original post...

CulexPipiens wrote: »

Basically I want a system that I can wheel out of the garage and setup to run a limited number of items during a power loss.

That describes an emergency scenario. I think you'll agree that worrying about sulfation during an emergency is an inappropriate ordering of priorities.

Cariboocoot · August 2011

Re: New system thoughts

They even have a "battery-free" model that runs directly from solar panels à la direct solar water pumps.

Cariboocoot · August 2011

Re: New system thoughts

Sparkletron wrote: »

Well the OP can correct us both, but this is from his original post...

That describes an emergency scenario. I think you'll agree that worrying about sulfation during an emergency is an inappropriate ordering of priorities.

Okay, I'm getting lost in the posts. So many asking the same kind of questions - they start to blend after a while.

You could probably by-pass the AC adapter and power the unit from your solar set-up directly as needs be. That dual current conversion will consume power. At least I've got that part right. Unless they changed the laws of physics and forgot to tell me.

Sparkletron · August 2011

Re: New system thoughts

Cariboocoot wrote: »

They even have a "battery-free" model that runs directly from solar panels à la direct solar water pumps.

I would love to read a review from someone who has that model. I know it uses the same chassis and insulation as the DC Series. So after the sun goes down, it's really counting on a cold sink and insulation to get it through the night. And if the next day is overcast? And the next? Again it would be nice to hear from someone who owns one.

New system thoughts

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