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MEMPHIS91 04-24-16 11:20 AM

Randen, I am for sure looking to go the way of an lithium car battery. I'm on the edge of my seat waiting for the price to get better and more and more cars are produced/wrecked a little.
The only way I have found to be able to go the lead acid route is used cell tower batteries or forklift batteries.
For me running the HVAC system is only a must in the summer when my solar hours will be much higher. I use wood heat in the winter, but of course if I have a large enough system I should be able to use the up and coming geothermal system on the sunnier winter days saving my wood burning for only the coldest of nights.

oil pan 4 04-25-16 01:51 AM

The prices on lithium batteries are not going experience any dramatic fall in prices.
When I built my 8 cell amp20 LifePo4 battery in 2012 then expand it by 4 more cells last year the price of the cells was almost the same price I paid 3 years earlier.
I believe the price actually went up in that time.

MEMPHIS91 04-25-16 05:11 AM

I have a general question, let us assume someone is looking more toward the worse case scenario idea. And getting new batteries every decade or 2 is not possible. Which type battery would last the longest? I know the nickle iron batteries are great but their charge rate sucks. Would lithium be the next closest thing?

stevehull 04-25-16 07:03 AM

Memphis - the perfect battery is not yet on the drawing boards. What we have today are essentially elegant capacitors. They store charge for a bit, but they lose it internally. The input output inefficiencies will always be there - and even if they are each 95% (very high), you still lose double that as you must come in at 95% and they go out at 95%.

Then there is the aging issue (that you mention). There are only so many life cycles on a battery.

I maintain the best "battery" is actually available - the grid.

A self contained battery (totally off grid) will require some 30-50 kWhrs per day minimum. For those of us in the south, where air conditioning is dominant, then double that. All the chemistry I read about is interesting, but my estimate is that it will take a generation (human) or so to further develop.

Fuel cell technology will likely be a better participant in this as very rapid gains are observed - especially in the many kW situation. Is a natural gas line to your home "off grid"?

The other day I was looking at a physical situation to describe what a mega Whr was. It was hard until I was stopped at a train crossing while a train went by. Turns out that a diesel locomotive is about 1 mW at full output. So that engine, pulling a long trainload of cars for one hour is about 1 mWhr.

I mention this as 33 kWhrs per day (minimal consumption) for a month is about one mWhr. A tremendous amount of energy.

Yes, I know that many here can survive and do quite well on less than 30 kWhrs/day, but will the average Joe/Suzy and family do so? My experience is that they want their electricity sucking appliances AND they want it now at the flick of a switch.

Yes, we can scrounge packs from smashed up Volts and Bolts and that is what people on this forum love to do. I have a friend doing exactly that right now (and am helping him test each cell as it comes out). But internal losses, aging/cycling problems and input output inefficiencies make this maybe a solution for a couple years.

NOT trying to be a wet blanket, but I maintain we do already have a "battery" - and a very efficient one at that.


MEMPHIS91 04-25-16 08:30 AM

I do understand your point. I've read similar articles saying the same thing. But I will stick with my original question, in a worst case scenario what is the best battery currently available (or at least soon to be) that would provide a reasonable amount of storage. (75-100+kWh) of power with NO grid.
I am a conspiracy kind of guy. And its no secret that the grid is a mass thrown together money pit, that gets harder to maintain and even harder to power without robbing the next generation of clean air, unpolluted water, and at safe areas to live in without radiation poisoning. What we have now will not last, I hope for everyone that it last your predicted one generation to find a different means of storing or making power, but in all my research I believe we will see a mass grid down scenario long long before that.
It would be wise at least on my part (since I believe what I do) to prepare the best I can for that to happen. I could care less about cheap electric bills. I want security. And yes that might come with having to deal without a few comforts when it happens.

jeff5may 04-25-16 09:10 AM


Originally Posted by MEMPHIS91 (Post 49848)
I find that most people who are looking to go off grid either don't understand all the is involved (money, batteries, no sun for days, etc.) or that do it as a worst case scenario as in grid down. For me, I have been planning going off grid for a very long time. It is not about saving money, its because I want security that my power company is not capable of providing.

This security you speak of does not come easily or economically. To provide backup power for when the grid is down is one thing; to provide complete independence from the grid is another. It takes a well-rounded and thorough approach, as well as lifestyle changes. Whether or not your entire family (living in the home) is willing to make these changes (or not) will bear heavily on your system requirements and backup capacity.

A recent line of commercials illustrates this idea with the usual American blatant disrespect: the "settlers" being portrayed in the DirecTV ads. This attitude of making do with what is available is a mentality that many people will no longer accept. Although your family will not have to go to the extreme "homesteader/settler" methods being ridiculed in the commercials, they will need to implement some changes in that direction in order to reduce your raw energy consumption. Simple acts like hanging clothes on a line outdoors, washing them in cold water, and washing (and drying) dishes by hand really add up in savings. Make sure everyone involved is willing, or design your system larger if not.

As you are detailing in your ground-source/water-source heat pump projects, these two methods (direct and water heat exchange) are a large part of retaining comfort while reducing energy demands. When used with some sort of thermal (hot and/or cold) store, your heating and cooling needs can be buffered or time-shifted to reduce or eliminate comfort control from taxing your battery storage. Again, not simple or cheap, but highly effective. Naturally, the insulating and envelope strengthening you are doing further increases the effectiveness of comfort control systems and reduces your thermal energy needs. These comfort control improvements are essentially invisible to occupants not concerned with the details of how they operate, working behind the scenes to satisfy demand.

For a completely off-grid home, using the raw voltage your PV panels produce without conversion is the most efficient way to use that power. Having some low-voltage DC lighting that runs off a panel or two is also a great indicator to those less energy-conscious occupants as to when they can use high-drain equipment without taxing your battery bank. When the lights are on, at least some portion of the consumption will come directly from the panels; when they are off, they know they are using battery power to dry their hair or whatever. This "psychological" habit change can mean the difference between a battery bank draining overnight or not.

jeff5may 04-25-16 10:43 AM


Originally Posted by MEMPHIS91 (Post 49868)
I have a general question, let us assume someone is looking more toward the worse case scenario idea. And getting new batteries every decade or 2 is not possible. Which type battery would last the longest? I know the nickle iron batteries are great but their charge rate sucks. Would lithium be the next closest thing?

Like Steve and Randy have stated, there is no such thing as a perfect storage battery. For one, they burn generated power on the way in and out, to the tune of 10 - 20 percent round-trip loss. For two, their charge rate and capacity are limited: there is a finite number of charge and discharge cycles a battery can provide before it is spent. For three, batteries have a finite shelf life: if they are not used, they will slowly discharge and lose capacity naturally with age.

Whether or not you accept the fact, any available storage battery available today will need to be replaced (regardless of usage) over the course of a decade or two. How much loss of original capacity you are willing to accept is the main factor that will determine your replacement time frame. Over time, the replacement cost is pretty constant: if you install a larger bank to account for the loss of capacity, your replacement will be less frequent, but you will have more batteries in your bank.

Like the others have said, the power utility is essentially a low-loss, infinite source and sink of generated power for a single family home (when it operates). With most modern inverter-driven systems, insertion losses are close to an order of magnitude less when feeding power into the grid compared to the losses of charging a local battery bank. The economics of grid-tying vary with the individual power company and their pricing structure, and are worsening as the general public gains the ability to generate their own solar power. Those of us who did grid ties maybe five or ten years ago got better deals than someone wishing to tie in today. Even so, the savings of needing to maintain a much smaller (backup-sized) battery bank are substantial. You will eventually have to decide whether to pony up big bucks to support your ideal to be grid independent (and the bank it requires), orto save the investment and use the grid for storage.

Kramer 04-25-16 10:43 AM

I live in the South as well, and AC accounts for about a third of my usage. I want to build an ice storage system that i think will be much cheaper more robust then any battery bank. My idea is to put a few hundred partially water filled soda bottles in a tank and then fill in the voids with a glycol mix. My thought is that this way the expanding ice will not damage the tank or any piping since the bottles will be able to move freely as they freeze. Then, I just pump the glycol from the tank, and then through indoor evap coils (now converted to glyco/air heat exchangers) as needed throughout the day or night. The only need for batteries would be to power the coolant recirc pump. The AC compressor and condenser fan can run only when the sun shines.

jeff5may 04-25-16 11:06 AM


The type of system you describe is known as phase change material (PCM) based thermal storage. It is highly effective at leveling your load for comfort control. There are PCM's available besides plain old water, and some of them even sequester more heat (or cold) than water does. More importantly, the various PCM's have been designed to absorb and release their latent heat in whatever temperature range you may require. There are a few threads on the forums where these methods are discussed at length, and some members have shared their experiences in using these materials to acieve goals such as you describe. When and if you experiment with and/or implement a PCM-based solution, be sure to detail your experiences with us. Projects like you speak of have made this site the robust source of information and inspiration that it has become.

I wish you luck in your pursuit of this method.

oil pan 4 04-25-16 03:27 PM


Originally Posted by MEMPHIS91 (Post 49868)
I have a general question, let us assume someone is looking more toward the worse case scenario idea. And getting new batteries every decade or 2 is not possible. Which type battery would last the longest? I know the nickle iron batteries are great but their charge rate sucks. Would lithium be the next closest thing?

The cheapest battery that will last the longest and has a good shelf life are lead acid AGM.
Good shelf life high mobility but at high cost are LiFePO4.
Batteries that kind of last forever are nickel iron. But they are expensive, big and have almost no mobility.

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