Question for Glenn:

Glenn, does your Bergey dump directly to the diversion load when the controller says the batteries are full? That is the power is NOT fed to the batteries and then bled off. The excess power goes directly to the diversion load, a pump in your case IIRC. twin 12 volt ford starter relays.

Glenn's answer....

I did the above question originally via IM, then realized maybe someone else might be interested in his response. So here it is....


It dumps to the relays in my case

But now that you mention it... making me think here - The red light comes on - I assume it is dumping the power generated directly to a heater etc - or my relays, but the wind generator cannot stop producing and it is hooked to the batteries so I don't exactly know how it is done.  My pump bleeds the load off of the batteries but not sure what the bergey does with the gen power.

The manual is available from the Bergey site I think for free download - XL1 wind generator.

The answer to this seems to be that the common diversion method is to charge the batteries but bleed or skim the excess off the batteries.

As the battery bank voltage approaches the battery
regulation voltage, the PowerCenter controller
will first try to restrain this voltage by applying the
5
optional Extra Load (or "dump load"). The Extra
Load function diverts current from the battery to
an air or water heater.

I've also found references to dump loads that indicate similar operation. It seems there is a reason for this method. Dump loads are made to operate within specific voltage ranges, such as 24 volts with a range of maybe 24 to 30 volts. A 24 volt wind gen could be putting out 80 volts at higher wind speeds. Without having a battery to even or smooth out the voltage the heater would burn out.

Similarly, and thanks to NM_Shooter for this, things like heater elements can behave strangely at voltages far from their design specs. The design impedance, resistance in other words is reached when the coils or nichrome wire reach operating temperature. At lower temperatures they may be quite different from their design point values. I verified this on two different electric heater elements. This can make it difficult to use a heater coil designed for one voltage at another that is significantly different. The calculated ohms at the design voltage can be very different at lower volatges where the element will not be able to reach design temperature.

Why am I bothering with this?   I was looking into using the excess, the un-used power from my PV modules as they sit there in the mountains with the cabin vacant. I wanted to use the power for heat; perhaps an air heater, perhaps a water heater. I also thought it preferable to divert the power before it was processed by the charge controller. It seems more efficient to use it right away, rather than feed it through batteries. But that seems to have problems or issues.

Maybe this'll be of interest to some other tinkerer.

We probably have covered this already, but a reason for the dump load to be applied for a wind generator is that if the generator is not allowed to continue charging, ie: is disconnected from the batteries, it will or may  increase in rpm's until it possibly destroys itself.  

It must not be unloaded during overcharge conditions but rather furled or the load burned off in one way or another.

Keep in mind that anything you run off of your AC inverter will pull the battery power down also.  Relays can be hooked to the dump load to run a water pump, heater or many other things also indirectly.

Can anyone recommend a good thorough book on residential solar systems.  In particular I'm interested in the pro's and con's of grid tie versus off grid systems. I *think* I have a decent understanding of the wiring required for a off grid system. I haven't been able to find a decent schematic for a grid-tie system or the extra components required.

Is it worth it economically for a grid tie system? (spinning the meter backwards to reduce electric bills or even get a rebate?)
By grid tying is there any extra tax or fees from the power company or local gov't?

I live in N.W. Indiana and we get plenty of sun year round, except for a few short day stretches in the winter.

Thanks,
Shawn

After more research I don't think I would want a grid-tie system.

according to the below site a grid-tie system won't operate when the "grid" is down   What the heck, why buy a expensive PV system then be in the dark like everyone else during power outages? This does answer the question in the back of my mind, " What prevents the system from back feeding and possibly injuring a lineman when the grid is down?" Now I know....it doesn't produce voltage at all. I was thinking that there would be a auto-transfer switch disconnecting the grid from the house

http://solar.smps.us/grid-tied.html

Most grid tie systems do not have batteries. That's why they go down when the grid goes down.

Automatic switches prevent feedback, the same sort of thing is required if one has a generator backup with a normal grid only home.

It is possible to have a grid tie system with batteries for backup. Also possible to do grid tie with a generator for automatic backup if the grid goes down. Frequency of outage would be one factor to consider.

Sorry, I can't recommend any books.

Not all power companies offer the same payback deals for grid tie. NM's major supplier has an excellent payback. No guarantee they will always offer the same deal though.

Is it worth grid tieing? That depends on personal needs and wants. No batteries means money saved and less bother. Not everyone wants to tend the system. Of course some folks pay guys like Dave to do that.

Not quite right Don, but thanks for the plug! We only go where the power lines don't!  I would be go bonkers otherwise! 

Quote from: MountainDon on September 20, 2010, 06:54:36 PM

Is it worth grid tieing?  That depends on personal needs and wants.  No batteries means money saved and less bother.  Not everyone wants to tend the system. Of course some folks pay guys like Dave to do that.

I am thinking about tieing in some solar or maybe wind to our next phase in our 'moving to the ranch' build.  We are on the grid, and at this time have no intentions clipping the power cord.  However it would be nice to have back up.  Talking to some of the ranchers and a store owner up there, it seems as if there is a major outage there are three places at this time they have to come and reset manually.  Summer time this takes about a hour to an hour and a half.  They are close to the road and easy to get to.  In the winter  .  Hey it is Idaho winter.

That said how much time is involved in tending to a system that is large enough to tend to the basic needs of a home in the winter time?  Very easily heated with wood but would have some propane back up if need be so there would be a fan there.  We would need to run a well pump, few lights, refrigerator and a couple computers up and going and what else am I missing?  We have a wood cook stove for the winter time, electric or propane in the summer.

Any ideas?        





   

Time; once everything is up and running. With quality hardware (inverter, charge controller, panels, etc.) there should be no real maintenance there. Keep the dust off.  Wet cell lead-acid batteries require maintaining the electrolyte level. I have not had a lot of experience other than our own system. Our batteries use very little water. I've only added water about every 6 months. Batteries that are used more, discharged more deeply and then recharged more than ours probably use more water. BTW, water should only be added to batteries that are fully charged if at all possible. That's because the fluid level falls as the charge is depleted. If the plates are not covered they should have water added to just cover them and then charged. As batteries age they may need more frequent watering.

I take and record hydrometer readings every month or so. Mainly just to keep an eye on things, look for low cells. So far it has simply been an exercise in record keeping.


I bought golf cart batteries as a trial. I was worried I might do something stupid and ruin my first set.   I don't know what, but there it is. If I was doing this again for a cabin I'd give more thought to maybe buying L-16 batteries instead. If I was setting up a primary off grid residence I would like to have Surrette batteries.


As to whether or not to grid tie...    As with all solar generated power, the place to start is with an honest evaluation of power needs, not power wants.  At present many power companies offer great buy pricing on user generated excess power. Who knows how that will play out in the future. Here in NM the main reason, as I see it, for the high buy prices on PV or wind power is that the state government has mandated that certain percentages of a power companies power must come from renewable sources. A grid tied home counts towards that figure. So they gain without having to spend any money for equipment. In fact they charge the home owner a hookup fee before giving anything in return.

In a similar vein, the local water utility has pushed water conservation heavily for years. Many people use less water today than a few years ago. The water company revenue has fallen and they have increased rates because we've saved water. OK, maybe the price would have gone up even more if we had not conserved. My point is, that if too many people installed grid tie systems would the incentive be reduced when they reach a point of too little demand from them?   


One nice thing about looking at this early in the design stage is it would be relatively easy to divide the wiring up into "mission critical" things that one would like to have on some sort of a backed up power system, plus all the other stuff. Properly planned it could be fairly painless to switch circuits around down the road.

Watch that your grid tie system is designed to be used off grid also.  There are many up here who only bank power with the grid and do not have batteries so if the grid is down they still do not have power - no storage - pretty useless in my opinion but it does knock their bill down.

Our 'neighbor' who's been on solar power for 30 years...ya 30 years....uses, get this, caterpillar batteries now.  He says he's got almost 1000ah of batteries and his old 500ish watt solar panel array can keep the batteries charged reasonably well Monday through Friday in the summer.  They run the generator on weekends for higher demand stuff and he tells me they run way to much as it is.

Anyway, he was telling me that he's tried nearly every kind of battery imaginable over the years and for some reason settled on these caterpillar batteries and likes them.

Personally, not being knowledgeable about these things (sure I've built cell sites in remove location but the engineers chose the batteries) I'd go with something recommend by those who do seem to know -- thanks to Don I'm using Golf Cart Batteries and see no reason why it won't work

Anyway, back to the point about power in Idaho, I don't see why you couldn't have a small system in place to provide backup.  Since running a small 60 watt system for our well I'm very impressed and having installed (ok it's not complete yet but it's a start) a 615 watt off grid system I'm realizing the hardest part is the figuring out of what you can or might run and for how long -- but once the figuring is done and the system is in I figure we'll know soon enough what 'too much' is 

I've been told by a solar installer that the golf cart batteries are best because they are designed for repeated discharges to fairly low levels followed by a nightly recharge. They have thicker plates and stand more abuse. The car and diesel batteries have plenty of amps but were designed for massive discharges over a moment or two, followed by extended periods of charging never cycling more than a few percent from full. Could Caterpillar be using heavier batteries? They may not be the run of the mill diesel engine batteries since their equipment may lay still in a field for months, then be called upon to start in frigid weather without fail. I'd love to see the specs.

I would say that gold cart batteries are better for off grid energy storage than a battery designed for engine cranking, but not best. Better than golf cart batteries would be the L-16 type. Best would be something like a Surette.  

Also remember battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD (depth of discharge). If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%.

I like golf cart batteries  for a few reasons, their weight is one. Very cost effective when bought at warehouse (Costco, Sam's Club) prices, though they will need to be replaced more frequently than other types. Great batteries to learn your off grid battery maintenance skills.

I would love to have a set of Surette 2 volt cells, but price got in the way. We'll see how that goes in maybe 5 years.


Re: CAT batteries; links to applications and specs...
http://www.cat.com/cda/files/90229/7/PEGP7801_05.pdf
http://www.cat.com/cda/components/fullArticle?m=37407&x=7&id=241185
http://www.cat.com/cda/files/1386197/7/PEHJ0073-02.pdf
Just bigger versions of good quality car and truck batteries, more than likely.  

A too-small bank of batteries has obvious drawbacks. But is there any reason not to buy and assemble an array somewhat larger than my expected needs.. sort of a "just in case", scenario?

I've been told by others that it's a bad idea to add new batteries to older. Is that to say used and unused should not be mixed, or is it the age of the battery? I was thinking to soften the outlay, I'd buy 3 or 4, then another few each month, until I had enough to set up my system. They'd be unused of course, but would the shelf life be different in this way?

Cheers,
Doc

This is timely

I am shopping for a 48 V bank

I think I have settled on the Surrette CS 6  17 PS

they are pricey (~$800 times 8  ) but of a new design that allows replacement of individual 2 V cells 

shipping is another PITA

and unloading them without a fork lift  (OK the JD end loader will help alot) they weigh in at about 220# each

the SolarBiz seems to have the best price but again shipping is uncertain .... maybe another $500

the other option is to get a pallet of 18 Surrette S-530 (older design) but at 'only' $329 a piece and free (or nearly so) shipping from (below link)
would give me 16 for the 48 V bank and 2 spares (is there a 'shelf life' on batteries that have not been filled with acid ?) for about same money maybe a bit cheaper

  https://solarconduit.com/shop/batteries/batteries-accessories-flooded-batteries?p=2t

plus they would give more capacity ~ 26500 Watt hours @ 50% discharge compared to the cs 6 17 PS at ~ 19250 Watt hours @ 50% discharge

and prices seem to going up too


Tough decisions ...

Quote from: AdironDoc on October 29, 2010, 03:48:19 PM

I've been told by others that it's a bad idea to add new batteries to older.

Depends what older is.  If they were all put into service within a few months it's no big deal. Over a year older it is not advised, but people do it.

To go a little bigger is more than likely a good idea. When you are calculating was depth of discharge are you considering as your aim point.

I am certain that if you buy dry lead acid batteries they can sit in storage for years. The lead has nothing but air to react with and I doubt anything bad will happen. The cells are closed, any O₂ will get quickly used up, and that should be that.

Seems to me I recall there being no discount for dry purchase, but shipping and handling is easier as they are not hazardous when dry. Unless you drop one on a foot.   

The handling weight sure is something to think about.

Way back when I was a lot younger service stations stocked all their batteries and added acid only when the customer bought it. It was easy to find the acid in 5 gallon collapsible plastic containers back then. Probably a little harder now.

Glenn, just wanted to pass on info on the SUN SL 3024 inverter/charger. I sent it back to sunelec yesterday. It was giving constant over voltage alarms and would not reset properly without having to completely disconnect the unit from the dc bus. I contacted Tony with sunelec and he said to ship it back to his attention, should be there by Friday. I have since rolled back to a backup HF 1200 Modified Sinewave inverter for lights/gargedoor opener.
The price on the inverter/charger was great but I guess you get what you pay for. Will probably be looking for Xantrex or Outback model after final dispostion.

I notice a number of folks in this thread have opted for 120V inverters, or 24V over 12V. How long a run of wire can I use before 12V either becomes ineffective cost-wise, or loses voltage? I plan to either run 12V appliances or use an inverter to 120V if its more cost effective. My cabin will be 20 x 36 with ceiling lights and the like, maybe 2KW/day with three days reserve. Batteries would in a small shed pushed up against the wall of the house, and 500W PV on the south facing roof. I'm pondering 120V versus 12V in terms of simplicity, cost of appliances, need for inverters or other add-ons, and wire costs. Any thoughts guys?

Doc

Thoughts, yes.

1. What sort of appliances would you like to have available for use?

2. Have you done any shopping for them in 12 VDC?



More later on wiring.

Have shopped but not yet bought:
12V ShurFlo Well Pump to cistern,
12V ShurFlo classic to fill pressure tank
12V RV Microwave
12V 10cu.ft. SunFrost Refrigerator
12V LCD TV/DVD Combo.
max of 8 15W LED lightbulbs

I'll state right up front that I do not believe a 12 VDC electric system is advisable in any but the most basic situations. Basic = a few lights and that's about all. But that is me and I wanted more than a few basic lights. I recognize this is my personal bias.

Note that when designing low voltage circuits it is desirable to keep the voltage drop to 3% or less over the run of the wire when under load.
Also note that standard home 120 VAC switches will fail after a very short time when used on DC circuits.

12 VDC RV microwave. Wow! The smallest microwaves are usually around 600 watts or so. That's cooking power. Most back of the case nameplates on a 600-650 watt m-wave will indicate a draw of about 800 watts at full cooking power. 800 watts / 12 VDC = 88 amps!    That's what the math says, unless there's some kind of magic they've discovered or I don't know about.  I am amazed. I must be missing something. But if there was a draw of 66 amps, 12 VDC a person would need #4 AWG wire ti run just under 9 feet and keep the voltage drop at or less than 3%.

If it's the item I saw on a Walmart ad it draws up to 20 amps at 12 volts and the reviews I read are mostly by customers disappointed with the speed; 8 minutes to make 10 oz of cold milk hot.  Anyhow, 12 VDC, 20 amps, 3% max drop, #10 AWG wire, maximum length of wire = 7.44 feet. #10 is heavy wire. Solid Romex type is hard to work with.  


A 15 watt LED light would be drawing a theoretical 15 / 12 = 1.25 amps. For a 3% max drop that would mean...
2 lights total on circuit, #12 wire, 2.5 amps, a run of 37 feet is okay
3 lights, total on circuit, #12 wire, 3.75 amps, a run of 25 feet is okay
4 lights, total on circuit, #12 wire, 5 amps, a run of 19 feet is okay.


7 amps, like the max on the Shurflo Classic pump:
#12  3% drop  14 feet     5% drop  22 feet
#10  3% drop  22 feet     5% drop  35 feet
#8   3% drop   34 feet     5% drop  56 feet

How many lumens does the 15 watt LED put out? The 26 watt CFL's I have and like as they make it easy for me to read a book are rated about 1600.

Links for those 12 VDC items would be nice. Maybe some of them would sway my personal bias.

One of many available online voltage drop calculators.

http://www.windsun.com/Hardware/Voltage_Calc.htm

Select if you wish to solve for Distance or Conductor Size
For calculating wire runs in a cabin use the "overhead" in the Installation field.
Use "single phase"

Totally agree Don

the cost of an inverter will be paid for quickly by savings in wiring and 'special' appliances

a 12VDC system is useful for only very basic situations -- like maybe a popup camper -- and probly not even then if you are considering microwave or entertainment systems

Tesla was right Edison was wrong