Looking to run home office off grid

[greenHouse]

Then you do not know about Rolls Surrette batteries Here is a sample spec from their RE line. Rolls/Surrette RE line products are the real deal and come with 10 year warranties (5000 series) where the first three years is 100% and the last 7 pro-rated..

No, I know all about Surrette and the rest of the major brands, not all of which are spelled "Surrette".

I also know that battery life is very connected to maintenance, and that replacing a $10K bank (you've yet to show the math on that one) every 5 years (or the statistics on that) means one isn't maintaining their batteries at all or undersized the bank in the first place.

[greenHouse]

As far as the technical "he said, she said" stuff here, I would say that there is one substantial thing that I would disagree with. With temperature controlled deep-cycle batteries you can expect 90% in/out efficiency as long as you keep them between 40 and 85% state of charge. This is according to Sandia National Laboratories who have done extensive research on the matter.

If you have a cite, I'd be willing to read it. However, the basics of battery charging and discharging make that impossible.

[Jonathan Cole]

If you have a cite, I'd be willing to read it. However, the basics of battery charging and discharging make that impossible.

Sandia National Labs does not agree with you.

http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf

Here is their conclusion:

"CONCLUSIONS
A test procedure has been developed to allow the
examination of battery charge efficiency as a function of
battery state of charge. Preliminary results agree well
with established general understanding that the charge
efficiency of flooded lead-antimony batteries declines with
increasing state-of-charge, and that charge efficiency is a
non-linear function of battery state-of-charge. These
tests indicate that from zero SOC to 84% SOC the
average overall battery charging efficiency is 91%, and
that the incremental battery charging efficiency from 79%
to 84% is only 55%. This is particularly significant in PV
systems where the designer expects the batteries to
normally operate at SOC above 80%, with deeper
discharge only occurring during periods of extended bad
weather. In such systems, the low charge efficiency at
high SOC may result in a substantial reduction in actual
available stored energy because nearly half the available
energy is serving losses rather than charging the battery.
Low charging efficiency can then result in the battery
operating at an average SOC significantly lower than the
system designer would anticipate without a detailed
understanding of charge efficiency as a function of SOC.
During normal weather, capacity degradation will not be
evident, but it will manifest itself when the battery is
called on to provide the full purchased capacity, which
will be found to be unavailable. Extended operation in a
low SOC environment can also result in permanent loss
of capacity from sulfation if the battery is operated for
long periods of time."

[Jonathan Cole]

If you have a cite, I'd be willing to read it. However, the basics of battery charging and discharging make that impossible.

The in/out efficiency is, of course, (in addition to the charging efficiency), connected to the discharging of the battery which is very complicated to calculate because it is related to battery temperature, discharge rate, battery internal resistance (gets greater with age), and quality of manufacture. That's why we keep the batteries at the proper temperature (room temperature is fine), we size the batteries to avoid excessive discharge rates (the faster you discharge the battery, the less of its energy comes out - a c-20 or slower rate is good)), and we get batteries from quality manufacturers who's own in-house testing allows them to give a substantial warranty indicating that their quality of manufacture will yield a battery with very uniform characteristics across the cells.

[russ]

Please carefully reread the document and you will see it says what everyone is trying to tell you.

[SpaceOddacy]

You cannot use your average insolation sun hours on a battery system, you have to use winter worse case or you go dark in winter. Further battery systems at best are only 65% efficient unlike 77% of a grid tied system. Realistically battery systems are 50% or less efficient over all.

seems like this whole off grid idea is bad for a house unless you live in a desert or only listen to the radio =(.

[Jonathan Cole]

Please carefully reread the document and you will see it says what everyone is trying to tell you.

Russ, aren't you the guy whoie in another thread said that you use solar hotwater and were not interested in a pv system with as great a capacity as 5 kwHr? I have been using this PV equipment for decades and also researching the meaning of the data and research of others, such as Sandia. I do not have to reread the document, I have studied it for a long period of time and then compared it to the actual performance of my PV system. As I have said elsewhere, when you know where the efficient SOC charging range of the battery is and then you discharge the battery in its most efficient way, you get the best battery performance, including longevity. I have had deep cycle batteries last for 12+ years this way, so my premise cannot be that far off. The key is to not charge the battery to the top except when you are ready to equalize. Then you stay in the most efficient charge/discharge range of the battery. In order to do this without a generator you need to have sufficient PV capacity. I have breaker switches for each panel located conveniently so that I can turn off panels if they are producing more than I can effectively use. Another important implication of the Sandia paper is that these inefficient charging ranges above 85% SOC cause nearly half of the energy going into the battery to be converted to thermal energy. This thermal energy in addition to being wasted, reduces the life of the batteries, because electrodes, cell interconnects, and containment matting expand and contract with heating and cooling cycles. This causes buckling of the electrode plates and interconnects and the shedding of electrode material. The only way to get long life out of these batteries is to essentially derate them to 50% of their nominal capacity, keep them in a 45-85% SOC range except when equalizing. If you charge all the way up on a regular basis, you will definitely reduce the life of the battery.

[Jonathan Cole]

This technical discussion about batteries is somewhat off the subject of the original inquiry that was made on this thread. I think what is important for the original inquiry is that the batteries must be sized to the amount of solar pv to allow for periodic equalization of the batteries unless there is a backup charger that can do the job powered by a generator or the grid. People can get into many technical discussions and arguments about what the technical facts are. For people who are not technically oriented, what is needed is to understand what parameters are controllable that will give you the greatest delivered kwHr capacity for the buck. You can control:
the type and quality of the battery that you buy.
The type and quality of solar panels that you buy
The type of balance of system electronic components that you buy,
Etc.

You can also control how you use the equipment. Certain procedures and protocols allow the equipment to remain within their design parameters for longer which means they end up putting out more power per $ over the life of the system. Staying on top of and understanding these parameters is how you get the most for your money.

If you are unable or unwilling to actually pay attention to your energy use then your system will be much more expensive per kwHr. Now I know that Sunking and greenHouse and maybe Russ understand this simple fact, but many people don't. Learning how your system works, how to monitor, troubleshoot and maintain it is necessary for economical operation. If you want to have your own power company, you have to pay attention to the system just as the power company must pay attention to theirs. Sunking says an off-grid system is not an economical proposition. But that is only if you don't include all the negatives that go with conventional energy. For instance, in 20 years I have never had a power outage, blackout or brownout. I have never burned out any electrical equipment including a light bulb (other than the backlight in my laptop). The amount that I have saved in appliances and fixtures is therefore, substantial. My energy use does not contribute to wars to protect fossil fuel sources. The contamination of the natural world is very much less than with fossil and nuclear fuels. Up to 50% of the costs of solar energy systems, including the batteries and all the electronic equipment and installation costs are subsidized by state and federal government in the U.S.

For less than the price of a late model used car I can have an energy system that will last for decades. While there will be costs to maintain, repair and upgrade the system over its life, the fact is that utility power only gets more expensive and will continue to do so. At component replacement intervals I also have the opportunity to upgrade to better technology. I can see that when my flooded lead acid batteries wear out in 6-8 years from now, I should be able to affordably get into some long-life lithium batteries with 10,000-12,000 deep cycles.

[Sunking]

I have been using this PV equipment for decades and also researching the meaning of the data and research of others, such as Sandia. I do not have to reread the document, I have studied it for a long period of time and then compared it to the actual performance of my PV system. As I have said elsewhere, when you know where the efficient SOC charging range of the battery is and then you discharge the battery in its most efficient way, you get the best battery performance, including longevity.

Jonathon with all due respect you are misinterpreting Sandia Labs report and are not cross-checking with 3rd parties like IEEE document 450, 484, 485, 1187, 1188, and 1189 which are the industry Battery Bibles, all of which Garth Corey from Sandia Labs participate along with 59 other leading physicist, engineers, and manufactures contribute to writing and development. All the standards are written by associates I have worked with for the last 25 years Bill Cantor and Dick Black.

It is true lead acid batteries are most efficient operating at 50 to 90% capacity (charge efficiency), but that in no way means you should be keeping your batteries at that SOC. Doing so will cause rapid growth of lead sulfate crystals and hardening on the on the plates which is the major leading contributor to pre-mature battery failure.

Second i am curious how you determine your battery SOC. Are you using a volt meter?

[greenHouse]

Lest anyone think the Messiah is coming because I'm agreeing with Sunking, I'll point out that the Sandia report very clearly stated, in the last sentence that was quoted, that operating batteries in that manner is harmful and leads to premature death.

The solution is NOT NOT NOT cycling batteries at low levels of SOC but rather tracking the amount of power lost due to floating and using statistical methods to determine how much power will be spilled and find effective ways of utilizing it.

Even if all one does is use an electric hot water heater as a "Float" stage dump load, anything done to keep the electrons from getting dropped on the floor can make a significant improvement in overall efficiency =without= ruining batteries in the process.

[Jason]

Lest anyone think the Messiah is coming because I'm agreeing with Sunking

:becky:

[russ]

Agreed with Sunking & greenHouse! Also with Jason!

Misinterpreting a document and then insisting on sticking with that misinterpretation is not good engineering.

How long batteries last is a function of(among others I suppose)
a) DOD allowed
b) Time before returning to fully charged state
c) Charging methods
d) Maintenance

What percentage of the population is qualified to check the battery status?

How many even know what a specific gravity tester is for or how or use it?

You quoted one thing right - I personally have no interest in a small system. As I mentioned previously, other fuels are either not available at my location (natural gas) or very exğensive (LPG or diesel). Everything is electric from well pumps on. The home is quite energy efficient but comfortable (read large) with modern conveniences - I intend to use them.

I am not whatsoever against small systems - some people live off grid with minimal power consumption and are perfectly happy - more power to them. Others can well use a small system to offset a portion of their power consumption (small or large) which is great.

What I am against is spending ones money on things just because they are promoted by some parties as 'the best thing to do' for whatever reason. Salesmen will say anything to get a sale. People need a source of decent information from people that have no financial stake in the decision that the potential buyer makes. Not many have funds to just throw away on each and every solution.

If a person wants solar of some type we have to help them into decisions that best suit them. Sometimes grid connect - sometimes battery based - sometimes hybrid - sometimes solar thermal.

One thing to remember is that the efficiency solar thermal is much higher than solar PV. In my location I have not used the AC the past two summers since completing the home. Winter times we do need heat at times and as heat from PV is not one of it's strong points solar thermal seems a better fit for me.

Russ

[greenHouse]

I am not whatsoever against small systems - some people live off grid with minimal power consumption and are perfectly happy - more power to them. Others can well use a small system to offset a portion of their power consumption (small or large) which is great.

I intend to live off-grid and without a small system when I'm older and grayer than I am at present. There are a lot of solutions to the "off-grid" problem that aren't considered in most system designs. Too many systems are cookie-cutter, and not enough are made by pastry chefs ...

The key, and you make this point well, is that people shouldn't spend money just because someone says to. But you also have to be honest about all of the costs of a solution, and how to minimize those costs.

[hank2222]

I use a Apple Mac Book Pro 17.inch screen with a h.p protable printer with a Pentax DS protable scanner that runs off the laptop battery along with a wired usb mouse along with a Verizon wireless usb modem and everything can fit into a backpack and be taken any where and set up shop as it need

[dvhenry]

I use a Apple Mac Book Pro 17.inch screen with a h.p protable printer with a Pentax DS protable scanner that runs off the laptop battery along with a wired usb mouse along with a Verizon wireless usb modem and everything can fit into a backpack and be taken any where and set up shop as it need

So your point is,,, um,?

An apple a day keeps the solar away?