Thomas Anderson's posts

I don't think there is a problem with it.  In fact, I think it is a fair way to extend the life of older, weaker batteries by giving them a strong buddy to prevent from over-draining.  I don't think the type of load is particularly important.  As long as they are in parallel and not in series, the newer, stronger battery will charge the older, weaker one if its voltage drops quicker.  Overall, your capacity will be bigger than if you throw away the old one and only use the new one, so there's no use doing that.  Your loads shouldn't notice any difference. 

I've been using a 550 Ah bank of Rolls Surrette batteries for five years, and added a second identical bank three years after I bought the first one.  These are the core of my off-grid house electrical system.  The older bank does tend to hold slightly less charge, and the newer one keeps it from draining as fast as it otherwise would.  These batteries are expected to last 15-20 years and I imagine I will probably add a third identical bank in the next few years and eventually start rotating them out as the first one nears its life expectancy.  Assuming of course we haven't converted to hydrogen or something by then.

Cavitation (air) could def cause noise.

The pumps make some amount of noise.  It's hard to say if your rattle is normal operation noise or not.  It sounds like you oriented it correctly.  The electronics head should be facing out and the pipes can be in any position within that plane.  Lower output might be expected if you have a large vertical lift distance.  3 gal/min is probably with no vertical lift.  Mine only push 0.5-1 gal/min through my floors.

My intent with my system was also to get off of fossil fuels and be totally self-sufficient, but only in the sense that I wouldn't *depend on* outside sources.  For convenience, however, I am using propane for several applications.  Each of them I could do without propane, but it would be more of a hassle.  E.g. I have a wood stove I can cook on, but my propane range is the primary cooking appliance so long as my tank is full.  I also have a gas dryer, although I could hang clothes on the line.  And I have gas backup to my heat and electric, so we don't have to skimp and be uncomfortable when renewable resources are low, although rationing is also possible if necessary.  Also, since we have trillions of cubic feet of natural gas under our feet here in Pennsylvania, and gas burns very cleanly, I feel pretty good about propane being my only utility bill other than cell phone/internet.  I fill my 100 gallon tank about twice a year, and it'll probably be once a year when I get my solar thermal system hooked up.

That said, I am always on the lookout for an alternative to propane when it is convenient.  E.g. for my refrigeration, I decided against a propane fridge and am instead using a combination of root cellar principles combined with a very efficient DC compressor. And in the back of my mind, I'm looking forward to a day when I replace my on-demand electric backup from a propane generator to a biomass generator of some kind.  I have a dozen acres of switchgrass and another two dozen of woods, so would love to use these to either produce wood gas or to burn in an external combustion generator, either steam or Stirling.  I would then push the waste heat into my solar thermal storage tank.  But that is a future project, and for now, I am glad to have the propane backup, which I only use once or twice a year.

Like most people probably, I'm doing all of this in stages as time and money allows.  Propane is a great intermediate solution between dependence on the grid and foreign oil to complete and total self-sufficiency.

No offense intended.  An on-demand power source could include non-fossil fuels such as wood gas, steam engine, Stirling engine, etc.  My point was merely that given the unpredictability of wind and solar and the potential need for additional supply during special times, an on-demand source would be a more efficient use of limited resources than redundant turbine mounting and wiring.  While it's true (as I qualified originally) that this is dependent upon your individual resources (wind and monetary), as a general rule for your average case, the more different kinds of power source, the better the redundancy will be because of the law of diminishing returns.  E.g. if you have little to no wind at all during a particular period, it doesn't matter if you have 1 or 100 wind turbines.  I'm not prescribing a particular solution, but just recommending to consider all of the potential scenarios down the road.

I'm not sure about the logic of having multiple turbines for redundancy unless you have exceptional wind all the time and very little sunlight.  Otherwise, I would use solar for redundancy and a gas or propane generator for emergency.  In my off-grid setup, I have the 1kW Bergey and 1.5kW of solar along with a small 1kW propane generator (only for battery charging, not house loads). 

Usually, when it's sunny there's little wind and vice versa, so this tends to provide a predictable output across seasons and between day and night.  E.g. on a sunny day, it is dead calm at noon, but a breeze picks up in the evening.  And summers (other than storms) tend to be calm, but winds roll in with autumn and last the winter.

So it seems to me that, unless you already have these other complimentary systems in place, for the extra cost of mounting and wiring redundant turbines, your money would be much better spent on alternative sources including solar, microhydro if you have it, and some kind of on-demand (probably fossil fuel) emergency solution.  These will help you not only if your turbine is compromised at some point, but also whenever there is insufficient wind.

When my turbine was down for a week, I did not have my emergency generator yet (didn't know I needed it until then) and it was unusually overcast (usually we don't get 7 straight days of clouds).  It was also very, very cold, so my batteries struggled to hold the charge and I actually almost lost them.  Would a redundant wind turbine or two have helped here?  Perhaps a little, if there was sufficient wind.  But I'll tell you what, when you're in fear of losing $3,000 worth of batteries, praying for enough wind to make up for your out-of-commission turbine wouldn't be a good solution.  In that case, an on-demand power source to keep the batteries charged and free from risk of freezing is a life saver.

Another thing is that neither the wind nor sun care if you have a bunch of guests over, and guests generally don't appreciate conservation of resources, and even if they did, you probably didn't design your system for double the number of people in any case.  That's another reason an on-demand power source is very important.  As your batteries get overdrawn, you can run the generator for an hour or so to make up for the extra load.

This all is moot of course if you're grid connected and assume the grid will always be there for you, but in that case, having redundant wind turbines is also unnecessary.

I've been very pleased with my Bergey XL.1.  I think they're made in Oklahoma.  I've had it since 2008 and it has performed well, especially in the winter.  It is a perfect complement to my solar.  I only had one problem with it and I think that's because it was struck by lightning... a sacrificial resistor wire was fried (saving the stator).  I cranked down the tower with my portable power drill, took out the fried wires, and had warranty-covered new ones in within a week. 

I would definitely choose a single larger turbine rather than three small ones, as it will be more efficient, less noisy, need less replacement parts, and have less redundant mounting/wiring costs.  Also, you should avoid mounting wind turbines to buildings because they can generate significant vibration and noise, and damage to the structure may not be covered by home insurance.  Structures are also usually too low to the ground to avoid turbulence and may actually create turbulence themselves.  And unless you have no trees, you should get a tower at least 60-80 feet tall.  100' would be even better.  Your results will improve the higher your turbine is from the ground.

If your controller can handle it, and an MPPT one could, then you should connect them at the highest voltage (series) that is within the charge controller's specs.  This is for just the reasons you pointed out.  Matching the voltage from the panels to the batteries is not a concern with an MPPT controller... getting the most efficiency from the panels through the wiring to the controller is what's important.

That said, you also want to think about future expansion capabilities.  If you want to be able to add a single 12V nominal panel at a time, say every few months, then adding them in parallel would be the way to go.  If you connect your first two in series, then you can only expand your system in multiples of 24V nominal.  E.g. two more 12V panels in series with each other, and the pair in parallel with your other pair.  Or if you can add a third in series, then you have to expand in multiples of 36V and so on.  Any parallel strings must be at the same voltage.

My system has the strings of panels at 48V.  I started with 4 12V panels in series, added a string of two 24V panels in parallel, and then later added another string of 4 12V panels in parallel to the other two strings.  I found this to be manageable and my Outback MX60 handled each configuration fine.  My batteries are at 24V.

Yeah, the decision on material is a tough one. 

The reason you're better off with a direct water connection rather than sand is because of contact surface area for conduction -- you want your earth tube to always be the temperature of the surrounding soil, not the air passing through it.  Sand or other fill has air gaps that act as an insulator, so your tube could more likely adjust to the temperature of the air passing through it instead of the ground temperature.  Water not only moves heat through conduction, but also convection.  During the summer, hot air will pass through the tube, heating up the water around it, and the water will rise to the surface of the pond to be replaced with new, colder water around the tube. 

I think that using water as the medium instead of soil will improve performance and reduce the length and depth required.  This part will improve the economics of the project, though the earth-moving aspect will not.  But since the pond will serve multiple roles -- solar reflector, passive evaporative cooler, landscaping, extra water storage, fire mitigation reservoir, etc -- in addition to intake air moderation, it is cost-effective overall and isn't too far removed from the cost of trenching alone.

But that does make choosing a water-proof material important.  Not that it won't get wet inside from condensation anyway, but as long as a drainage path is designed in, that shouldn't be too bad.  I wouldn't want water to be constantly seeping in though, as with a porous material. 

A perfectly water-proof material does imply plastic or other oil-based material.  I guess certain metals could work, but would most likely be prohibitively expensive, particularly for a perfect seal.  I don't know what 4-6" copper, galvanized, or stainless would cost, but probably way too much.  Copper does have anti-microbial properties, which would be a plus, but not enough to offset the cost.  Dropping a few scraps of copper wire or pipe in the bottom of a pipe of another material might be enough to achieve the same effect anyway... as these scraps corrode from condensation, they'll leave a blue-green trail of copper ions as they flow toward the drain, inhibiting mold & bacteria in the wettest part of the tube.

With clay I would be worried about the long-term integrity being exposed to water, and also I'm not sure how to make water-tight seals with clay.

PVC seems like the easy way.  I would use a thin-walled variety for best conduction, but the R-value of PVC isn't too high anyway.  I am a bit concerned about off-gassing.  I know that PVC does get used for air ducts under slabs, and has for a few decades, so perhaps the off-gassing concern isn't too big of a problem.  That's most likely the path I will take, gluing the joints for a perfect air-tight seal (to keep both water and radon out). 

I read about an earth tube system in India that used a 4" metal tube, about 150' long, and 9' deep buried in sand.  It both cooled in summer and heated in winter the intake air by about 25 degrees Fahrenheit.  But it accomplished almost all of the conditioning in only half the length, so really 75' would have been effective.  I figure by using water as the medium, I can achieve similar results at about half again that length, or about 40', and only 5' depth with 4" PVC.  Even if it didn't quite perform as well, even a 10-15 degree change would still be a huge success for a relatively low cost.

Earth tubes may provide some benefit in Florida, but not as much as in the north.  The principal works primarily on passive annual heat (or coolth) storage, similar to ground source heat pumps.  Without a great deal of seasonal variation in Florida, the ground temperature won't be much lower than the average outside air temperature.  In Pennsylvania, our ground temperature is around 50 degrees because we go below zero in the winter.  In Florida, it's in the 70s.  Still, that's not too shabby on a 100 degree day, so it may still be worth it. 

Similarly, on those rare 30 degree days (like when I went to Orlando in December), a 70 degree intake air temp might be quite nice too. 

Also, another benefit is if the ground temp is below the dew point, the incoming air will be much drier than outdoor air because water will precipitate out underground in the earth tubes just like it does with a traditional air conditioner.  That alone is probably well worth the effort when you live in a swamp.  And speaking of swamps -- you could then run that dry air through a "swamp cooler", i.e. adding moisture back in, which cools the air in the process.  That gives you the choice of cool dry air or colder, wetter air.

I haven't built my earth tube system yet, because it is going to be incorporated into a larger earth works project when the first stage of my house is complete.  My plan is to build a reflecting pool directly in front of my passive solar windows to increase winter insolation, and to run my earth tubes through the bottom of that pool.  The purpose of that is to maximize the conduction from the earth into the tubes, which is accomplished much better by water than by soil.  But if your water table is high, as it is in most of Florida, you may have water at a few feet depth anyway, and so direct burial would achieve good results.  Another trick is to redirect your downspouts to let out over your earth tubes to keep the soil moist and conductive.

I've read from multiple sources that the Surrette batteries are good for 20-25 years.  If you treat them right, they should last as long as your solar panels.  Since I'm not betting on being able to replace batteries on a 5-7 year cycle, I went with the Surrettes.  Depends on what your outlook for the economy and society in general is.  I have two parallel banks of 6 and I paid about $6000 total for the dozen batteries, which just goes to show that even in the short period since I've bought them, inflation has already driven prices much higher.  Buying the longer lifespan batteries now will be a significant inflation hedge.

Yes, it's wrong.  24.7A @ 12VDC is a lot different from 24.7A @ 240VAC.  Think of it as the difference between the power contained in water gently flowing through a babbling brook versus the same volume of water shooting out of a fire hose.  You can't use the brook as your power source in order to pressurize the fire hose even if the volume of water is the same.

It is best to convert it to kilowatt-hours first and then to amps at the lower voltage.  This is what I did in the math I showed you.


That depends on a lot of factors, such as if you consider other benefits besides monetary in terms of "payback".  E.g. independence, self-sufficiency, fault tolerance, saving the planet, sticking it to the man, not having to run grid power to a remote site, inflation/hyperinflation, ability to outlive catastrophic social collapse, etc.  If you're just trying to save a few bucks, then yeah, it's probably not worth it for that kind of load to replace perfectly good grid power with solar power unless you're getting every possible rebate and incentive.  Your money would probably be much better spent making your load much more efficient.  Then at that point, it might be worth thinking about going solar again.

If you describe your load, maybe we can offer suggestions on how to make it more efficient so that you could power it with fewer panels.

Surrette Batteries have a 10 year warranty and 15 year expected lifespan

Richard, excellent scientific study!  The results are intuitive to me... the lower impedance/capacity string should be no worse off than if it was the only string.  The addition of a higher capacity string should protect the lower capacity one from discharging too far.  You could almost think of the higher capacity string as being a charging source once the lower capacity one is discharged far enough.  Meanwhile, the higher capacity string is protected from deep cycling, increasing its lifespan as well.  The addition of a desulphator should protect the higher capacity batteries from issues stemming from too shallow of discharges.

Theoretically, you could even out the charge/discharge pattern by increasing the impedance of the lower impedance string by perhaps using a longer cable or smaller gauge cable.

I'd put some Water Miser caps and a desulphator on them and leave them connected.  You don't want them to sit in a less than 100% charged state for extended periods.  Batteries will naturally leak charge over time, so after 8 months, they could be nearly completely discharged.  They will only lose water through electrolysis (hydrogen & oxygen vented) while charging, so if they're not being discharged beyond leakage, there shouldn't be much water loss.  The solar will merely top-up any leakage and keep them at 100%.  The Water Miser caps will prevent evaporation and the desulphator will prevent crystals from forming from the extremely shallow charging cycles.

This advice is purely theoretical as I've never stored deep cycle batteries for extended periods.  But I think I have a solid grasp of how they work though, and this is what I would do.  If anyone has experience otherwise, please speak up.

Here's a diagram I created when I was spec'ing out a system for my father.  Thought it might be helpful to visualize.


In this case, he already had a main utility-connected breaker panel and would be adding the off-grid stuff, transferring some of his circuits to the uninterruptible panel.  My preferred design would be to remove that panel altogether and move all of the loads to the FlexWare panel, perhaps with subpanels.  The utility grid would be directly connected to the Outback panel then.

I also prefer moving as many circuits to DC as possible.  E.g. replace the well pump, refrigerator, lighting, etc., so as to have the improved efficiency and fault-tolerance of not needing the inverters for those loads.  DC-direct also eliminates power factor losses on pumps, motors, CFL & LED lighting, etc.

I think the system design here is overkill for any residential purpose, but he wanted to do this for tax reasons without having to change any loads to make them more efficient.  With proper care to make the loads as efficient as possible, anyone should be able to eliminate 1/2 to 3/4 of the solar and 1/2 of the wind and be just fine.  This system ought to be able to power a small community, which I guess it very well might if/when the SHTF.

BTW, I would seriously recommend tapping the water resource.  Investigate that further before doing the solar even.  You may be able to power your entire load requirement just with the water.  The battery/inverter setup can be the same.  You would just need an appropriate micro water turbine, alternator, and charge controller.

Personally, I would only go with batteries designed and warrantied for long life in the intended role.  Golf cart batteries may work well, but what if, as you fear, we have a global currency crisis and you cannot find replacements in 3-5 years?  I'd rather have something I know will last at least 10 years and have been known to last 20+ years, which the Rolls-Surrette deep cycle batteries are known for.  I've also just recently added two redundant parallel banks in case one or more of the batteries fail.  If you only have a single string of batteries, e.g. 6x4V=24V or 8x6V=48V, then the loss of only one of them results in the entire string being worthless since you cannot maintain your system voltage without it.  I have two strings of 6x4V in parallel (or I will just as soon as the new ones are delivered anyway), preventing a single point of failure.  Therefore, I'm confident my batteries will see me through the current economically/politically/socially volatile times.

How about this system built from parts available on AltE:

• $13,770.00 = 27 x ES-A-210-fa2 solar panels (5.67kW total)
• $ 2,606.16 = 6 x IronRidge 180" adjustable mounts
• $ 2,002.50 = 3 x Outback Flexmax 80 charge controllers
• $ 6,624.60 = 12 x 4-CS-17PS Rolls-Surrette batteries
• $ 3,637.70 = 2 x Outback 3500W grid-capable off-grid inverter
• $ 3,000.00 = assorted accessories, wires, fuses, panels, breakers, etc.
• ---------------------------------------------------
• $31,640.96 = total

Plus shipping of course, but you can probably get free shipping for an order of that size (plus some 5-10% discount probably).

That's also tax-deductible... I think it's a 30% federal rebate, so you'll get $10k back.  In fact, if you buy this or anything similar, stop paying taxes for the rest of the year if your normal tax liability is less than $10k.

That gets you almost the 6kW you were looking for, plus redundant strings of deep-cycle batteries, and redundant grid-capable inverters, for barely more than you were willing to shell out for only 4kW.  Granted, you have to install it yourself, but that's the only way you'll know it's done right, plus you'll be intimately familiar with it so that you can troubleshoot in the future. 

BTW, that list assumes that you have 30' available across your roof -- 3 strings of 9 panels; each string connected in series for 108V to one of the charge controllers.

I would build the battery boxes out of plywood.  I used 3/4" so that I could screw them on-edge.  Insert a 2" PVC pipe for a vent.

For best results, add a wind turbine or water turbine to this system.  I would recommend the Bergey XL.1 1kW turbine on an 80-100' tower.  Cost should be around $8k, tower & accessories included.  If that's too much, I would eliminate one of the strings of PV panels (plus 2 mounts and 1 charge controller) to get the wind turbine.  It's counter-cyclical to the solar, so you'll greatly improve your average production.  I have direct experience with this.

As far as being debt-free, that is a noble goal, but directly at odds with your recognition that the central bank is inflating our currency to nothing.  The most rational course right now is to take a home equity loan at 3-4% interest to purchase capital improvements such as this.  Leave your liquid assets in inflation-protected investments such as precious metals, commodities, and mining company equities.  So long as you have assets that can be liquidated to pay the debt in full at will, you are essentially debt-free.  But the leverage of cheap credit at a time when the real inflation rate is far greater than your interest rate is too good to rationally pass up!

Not yet on tech support.  I only use pex and copper in my system, so I don't know where any iron could come from.  My well water is almost perfectly pure... I had it tested for everything and all minerals were almost nonexistent.  I think I will dismantle it and have a look, but I'm not optimistic I'll find anything.  I think it is an issue with the drive head.

My 12VDC breaker panel is fed by a Samlex SDC-60 (http://www.altestore.com/store/DC-to-DC-Voltage-Converters/Samlex-SDC-60-20-35V-Input-138V-Output-60A/p6050/) which puts out 13.8V from a nominal 24V source (22-30V).  I have a 20A breaker in my panel feeding a 15' long #10 wire run to my distribution box.  There I break into 10 zones, each with a 3A fuse (each pump only requires 1.67A continuous, but I gave some leeway for start-up surge).  The distribution box switches the pumps via 12V relay, triggered by millivolt programmable thermostats.  The final run from there (3-4' long max) is #16 wire.  I doubt the voltage drop is more than 1-2% tops, but I've seen it claimed that these pumps are ok from 8-16V.


Yep, there's a filter on the input of my hot water heater.  It's possible some junk got from the pipes into the pumps prior to going through the filter on the HWH, but I wonder then why only the battery model pumps are having an issue and not the PV ones.  I'm hesitant to take apart the impeller casing because I didn't think it was a serviceable part, but I can do so and see what happens.

Nope.  The load is always plugged into the inverter and the battery is continuously replenished by the charger while power is available.  When power goes out, the battery starts being drained.  When it comes back, the charger charges it back up again.  65W @ 12VDC is roughly 5.5A (rounding up slightly), so a 10A charger will allow you to run your pump and still charge the battery with 4.5A at the same time.  It's true that this is a little less efficient than switching between grid power and backup power, but you'll only lose about 20% in the process (assuming charger and inverter are each 90% efficient), i.e your 65W pump is now effectively 78W, but the benefit is immediate failover without any fragile electronics (which would also suck some amount of power).  And that 13W difference (the amount of a single CFL lightbulb) while the pump is running is insignificant if you're on grid power.

The alternative is a product by APC, Tripp Lite, et al., for twice or more the cost.  A 100Ah battery would run your pump for 9 hours until it is 50% discharged.  You can get a Trojan AGM (sealed) 100Ah battery for $200.  The charger should be another $100-$150.  And the inverter under $100.  So no more than $450 total.  For a commercial UPS solution, you're looking at a minimum of $1000, or perhaps much more for 9 hours of backup power.  Most computer backup systems provide no more than a few minutes of power.  Also, they're still going to be only 90-95% efficient max.

You could also eliminate the inverter inefficiency by changing your pump to a DC model that runs directly off the battery.  And you could eliminate the charger and the battery itself by converting to a PV-driven pump, as I originally suggested.  Since your solar thermal system can only overheat when the sun is shining, a pump that runs only when the sun is shining is ideal.

The water is the lubricating medium.  Computer fans have bearings, the El Sid pumps do not.  There is nothing to grease.  If you put grease in the impeller compartment, it would surely cause it to clog up and fail.  The PV head is actually weaker than the battery head because the battery version provides rated wattage at 12-13V whereas the PV version provides rated wattage at around 17V.  Being more powerful is not the answer.  Also, the pumps run very quietly until they stop functioning.

In the extremely thin documentation that I could find online, when the pump stops and one of the LEDs goes out, it means the pump is "unbalanced".  However, as I said, it is oriented according to specs.

I was hoping since the product is sold on this site, someone here would be familiar with it.

For such a small space, I would go with either passive solar if possible or a solar air heater.  No need for complex plumbing for just one room.

That seems just about right.  The nominal voltage is not the same as the charging voltage.  Something in the neighborhood of 25% higher than nominal voltage is expected.  Otherwise, you could never charge a nominally-rated battery bank if the voltage weren't higher.  There would be no pressure to send electricity into the batteries. 

I usually get 50% of the rated wattage out of my panels pointed at 60 degrees in the winter.  Pointed straight up, 25% or so wouldn't be unexpected.

In other words, everything seems to be working as it should.  If you must keep your panels at zero degrees (dead flat), then maybe putting a diffuser of some kind over top might help.  Or put them on a tiltable frame that you can move up to the appropriate angle when you're not moving.

The standard thermostats have a maximum load rating of between 0.3 and 1.3 Amps.  That's not quite enough to run a 20 Watt pump at 12 Volts.  Do you think it's OK to exceed their maximum ratings, or would I risk frying something?  The Wirsbo rep said I would need a relay for their thermostat, and they only sell line-voltage (120 VAC) relays.  I'm going to search for automotive relays.

The thermostat you linked to is rated for 10A @ 12VDC, so that might be my best bet.  I was really hoping for something programmable though.

Yes, they're seperate zone pumps, not valves.  They pull individually through a manifold from a solar storage tank (or back-up propane water heater which is triggered by flow).  There is no single system pump.

I'm using 10 guage wire for all of my 12 VDC systems to minimize voltage loss.  If I end up using relays, I'll probably go with 14 guage for the signal wire.

I've got 12VDC battery power and 12VDC "El Sid" circulator pumps for my hydronic heating.  Right now I have the pumps wired to a manual switch and they work fine, but I need to have zone thermostats.  How do I set up thermostats to drive the pumps?  All thermostats I've found which can run on 12VDC have something like 0.5A max load, so they can't run a pump directly.  Do I have to use a relay?  Has anyone built a system like this before?  I wish there was just a thermostat which I could just wire to power and to the pump and it would work.  It only needs to drive about 2A.  Any help is appreciated.