Energy conservation or avoidance vs bigger systems

There are advantages and disadvantages to every battery chemistry, but the best form of chemical battery storage for an off grid home is none at all.  That sounds a bit ridiculous, but let me walk through it a bit.

First, take an honest assessment of what you might need continuous power for, and determine if there are any practical alternatives for that need.  For example, most of us know that food refrigeration is a power hog that typically requires continuous power available to regulate the controlled airspace inside a standard refrigerator.  One common method of avoiding both the demand and the battery storage necessary for a standard refrigerator is to buy a propane powered RV fridge instead, and applying the cost savings for the solar array and battery storage towards the increased cost of a propane refrigerator.  Another would be to buy a 24 volt DC chest refrigerator designed to run directly off of solar panels, which do exist but are still rather expensive.

Of course, even an RV fridge will need some amount of continuous DC power to run the electronics, but a single deep-cycle battery would suffice, or even a 12 volt alkaline lantern battery wired to only be needed when a small, dedicated solar panel (like the kind used by hunters to control an automatic feeder) can't provide enough.  So completely removing a rechargeable battery from your off-grid system is likely unrealistic, but nic-iron are huge units and tend not to be ideal for small power systems, which has a lot to do with why lead-acid dominates this category.

However, if the idea of using propane offends you, due to the non-renewable nature of the resource or the carbon footprint, then any lithium based battery chemstry capable of doing the job should be off the table as well.  Not only is lithium a relatively rare element, it's mining and refinement processes are energy intensive and create some nasty by-products.

A third option, if you have either access to a micro-hydro site or a decent wind-power site, would be to build your own "direct-driven" compression system using marine components.  This solution would be both expensive and site specific, but by directly driving a compressor from either a wind turbine or a water turbine you will elimiate conversion losses completely.  This would require the use of "holding plates" to store the cold energy from peak times to peak needs.

But, honestly, is there any other appliance that you must be able to keep powered overnight, every night?  Sure, it'd be nice to be able to use a computer or watch a DVD after dark occasionally, but is that a critical power need that should be considered during your battery storage sizing?  I say probably not.  If you size your battery storage so that it could take your little, DC fridge thorough 3 overcast days and nights; and you've had a sunny day and the outlook for the next day is sunny, you could watch a DVD with the kids without risk.

Oh, and a fourth option would be to directly drive an ice-maker from your solar array, and have the ice dump into a well insulated cooler that you use as a chest fridge.  You'd have to make it a daily chore to take the top off the cooler in the morning, and put it back on in the evening; but in this case your energy storage is the ice itself.

I am hearing alot of good ideas

1) Use High efficiency electronics/Appliance (chest fridge vs regular fridge)
2) Use electronics/Appliance when energy is being produced not at "night" for the battery bank
3) Avoid using electronics/appliance and instead use alternative (earth cool root cellar vs fridge)
4) Unplug appliances/electronics when not in use
5) Get electronics with their own battery pack (laptop vs PC)
7) Limit your dept of discharge to no more than 80% aka oversize battery bank, deeply reduced electrical demand

If I was thinking about minimizing my cost or a zombie apocalypse, I would do lead acid batteries and then go to junk yards/garages and get some older batteries.

Creighton Samuiels wrote:There are advantages and disadvantages to every battery chemistry, but the best form of chemical battery storage for an off grid home is none at all.  That sounds a bit ridiculous, but let me walk through it a bit.

First, take an honest assessment of what you might need continuous power for, and determine if there are any practical alternatives for that need.  For example, most of us know that food refrigeration is a power hog that typically requires continuous power available to regulate the controlled airspace inside a standard refrigerator.  One common method of avoiding both the demand and the battery storage necessary for a standard refrigerator is to buy a propane powered RV fridge instead, and applying the cost savings for the solar array and battery storage towards the increased cost of a propane refrigerator.  Another would be to buy a 24 volt DC chest refrigerator designed to run directly off of solar panels, which do exist but are still rather expensive.

Of course, even an RV fridge will need some amount of continuous DC power to run the electronics, but a single deep-cycle battery would suffice, or even a 12 volt alkaline lantern battery wired to only be needed when a small, dedicated solar panel (like the kind used by hunters to control an automatic feeder) can't provide enough.  So completely removing a rechargeable battery from your off-grid system is likely unrealistic, but nic-iron are huge units and tend not to be ideal for small power systems, which has a lot to do with why lead-acid dominates this category.

I disagree.

Propane has a reoccurring cost that is higher than the cost of PV and batteries, and the cost of propane will only increase in the future.  PV panels are ridiculously cheap right now and battery cost will likely fall in the near future (20 years)

I switched all the propane appliances in my house over to solar electric and the savings in propane costs paid for the new equipment in less than 5 years, and that was back when solar panels cost 5 times as much as they do today.

FWIW I have a large french door fridge and it uses about 1.2kwh per day (on average).  One solar panel (and not a particularly large one) and a couple golf cart batteries could power this fridge for me.   A suitably sized panel would cost about $100, batteries about $200-$300, I wouldn't buy an inverter just for my fridge, but the inverter I would buy  costs about $0.50 per watt, the fridge draws 120 watts, so about $60 worth of inverter.  There is also the cost of the battery charge controller.  Worse case you're looking at maybe $500 total.

A similar size propane powered fridge would use about $1 worth of propane a day, that's about $365 a year worth of propane.  The typical propane fridge is about 1/2 the size of mine and costs three times as much.  I don't think they make a propane fridge as large as mine.
Sure you can conserve propane by using a smaller fridge, you could also conserve electricity by using a smaller fridge which would require less PV, batteries, etc.
The fact is propane costs MORE, a LOT more, than solar PV.  

20-30 years ago it was a different story, but not today.

Propane is a pretty non-permie method. I've seen few treatments of this "Off-Grid dirty secret" - but one of that name (paraphrased) recognized that a pill-bottle fuel-tank that has to be refilled constantly essentially defeats the purpose of any Permaculture ideals from the get-go. PV is also a problem (how are they made? What nasty stuff goes into and out of that industry?)

Actually, PV is kinda the devil if one examines the Life Cycle Assessment (LCA - a buzzword in academic energy science). Over the service life of a PV, or a municipal-scale wind turbine, the device will not even begin to approach break-even. In short, it takes a LOT more energy to make a PV or muni-wind turbine than the device will EVER output - but we'll neglect that for the moment.

Propane as a fuel is a tether, a leash, a chain (depending upon perspective) and will continually increase in price, and has to be forever paid. BUT!!!

Every propane appliance (including tanks, valves, hoses, etc...) can be easily converted to Nat-Gas (known as Methane in the permie world. It's also called Swamp Gas in some circles). One can make Nat-Gas. (technically you can make propane too, but... no.)

Propane appliances can be converted to permaculture by changing valves, and digesting organic-goo. It is good to examine that when making comparisons. Use a fuel that you accidentally make anyways (the essence of permaculture is, hehehehe, farting.)

Also, like fusion power, mars colonies, and flying cars, battery technology has been in a perpetual "In 20 years!" cycle. Still, to this day, the best overall intersection of price, durability, maintenance, density, and LCA, is LEAD ACID - more than a century old tech. LiPo, NiCd, NiFe, ad infinitum, all have SOME advantages, but at the end of the day, the old Pb is still the "tried-and-true" work horse.

Maybe someday batteries will be better than Pb. Maybe someday I'll have a deuterium reactor the size of a trash-can.

My perspective is of what will work today. When I was a boy, I wanted to build fusion reactors and go to mars - in three decades we have gotten not-one-iota closer to those goals. I am a bit disappointed, and it shows, but the lesson is quite clear: All future predictions for technology timeframes are little better than propaganda - and I can't power a refrigerator on propaganda.

I CAN make Methane to run a converted propane appliance. I CAN use Pb batts if I need. I CAN make a salt-water battery.

No desire to be harsh - but banking on ANYTHING that is "20 years out" does absolutely nothing for me today - it's why I abhor suburban mortgages, and it's one of the main reasons I am interested in permaculture technology.

At the end of the day, PV and acid-metal batteries totally defeat the purpose of it all anyways - I intend to use solar-thermal and poo-gas because I can build them with realistically acquired tools and materials, and I can make use of their waste products (burning methane makes algae - algae makes fuel/food/fertilizer....)  

Spencer Miles wrote:
Actually, PV is kinda the devil if one examines the Life Cycle Assessment (LCA - a buzzword in academic energy science). Over the service life of a PV, or a municipal-scale wind turbine, the device will not even begin to approach break-even. In short, it takes a LOT more energy to make a PV or muni-wind turbine than the device will EVER output - but we'll neglect that for the moment.

This is a myth that doesn't seem to die.  It may have been true back when they invented PV panels, but it hasn't been true for decades.  The energy required to make PV panels has been dropping steadily since the seventies. Currently the energy break even point on solar panels made today is about 2 years and dropping.

This is kind of obvious.  Energy costs money.  If it took more energy (and therefor more money) to make a panel than they produced, then they'd be a WHOLE lot more expensive.  The current wholesale cost for solar panels is less than 30 cents per watt, which means the manufacturing costs is maybe 15-20 cents per watt (possibly less).
Over it's average lifespan each watt of a solar panel will produce about 45,000 watt hours of energy.

I'm not saying they are totally green, nothing is perfect, but currently solar panels are probably the greenest option available for producing energy.

Spencer Miles wrote:
Every propane appliance (including tanks, valves, hoses, etc...) can be easily converted to Nat-Gas (known as Methane in the permie world. It's also called Swamp Gas in some circles). One can make Nat-Gas. (technically you can make propane too, but... no.)
Propane appliances can be converted to permaculture by changing valves, and digesting organic-goo. It is good to examine that when making comparisons. Use a fuel that you accidentally make anyways (the essence of permaculture is, hehehehe, farting.)

Home made methane tends to have lots of impurities that can often damage/destroy appliances, engines, etc.

Many people overestimate how much methane you can make.  Digesting the poo from a family of four could produce enough methane in 1 year to run the average RV refrigerator for maybe 6 months, and the digester would be either very expensive or require a lot of work to maintain, or both.

Large municipal systems are promising and if you have a large farm and raise cattle, pigs, etc. then a methane digester might make sense, but small scale (homestead)) systems don't seem practical.
However, if you've actually built and are using a small scale system I'd love to hear about it.

Spencer Miles wrote:
I CAN make Methane to run a converted propane appliance. I CAN use Pb batts if I need. I CAN make a salt-water battery.

But have you?  

The only company that was working on salt water batteries (for over a decade) went bankrupt last year without ever producing a viable battery.  Yeah you can build salt water batteries, but they just don't work very well, and homemade ones are even worse.
There is a lot of promising research into salt water batteries, but so far it's all "maybe, someday"

Spencer Miles wrote:
At the end of the day, PV and acid-metal batteries totally defeat the purpose of it all anyways - I intend to use solar-thermal and poo-gas because I can build them with realistically acquired tools and materials, and I can make use of their waste products (burning methane makes algae - algae makes fuel/food/fertilizer....)  

Please let us know how that works out, regardless of whether it's successful or not.  

FWIW I think a lot of people waste time trying to develop ideas that don't work because loads of other people who tried and failed didn't tell anyone about it.
Thomas Edison reportedly said something like “I have not failed 700 times. I’ve succeeded in proving 700 ways how not to build a lightbulb.”
If people would provide details on what doesn't work, others could spend more time on new ideas that might work.

Peter VanDerWal wrote:

I disagree.

Propane has a reoccurring cost that is higher than the cost of PV and batteries, and the cost of propane will only increase in the future.  PV panels are ridiculously cheap right now and battery cost will likely fall in the near future (20 years)

I switched all the propane appliances in my house over to solar electric and the savings in propane costs paid for the new equipment in less than 5 years, and that was back when solar panels cost 5 times as much as they do today.

The greater savings with switching the off grid refrigeration plan is in up front costs.  I don't disagree that over a long term, a well designed solar electric system would cost less at the same scale.  RV fridges tend to be smaller as well, forcing the off-grid user to economize on space as well as saving propane for later use (i.e. energy conservation).  The use of propane appliances indoors also contributes to the winter heat demand, which may be a useful trick for those who live in climates with majority heating-degree-days throughout the year.  Granted, an electric compression fridge will do a bit of this also, but a small enough cabin can often be kept above freezing by virtue of the automatic propane fridge itself.  My illustration was mostly about the need for overnight energy storage, and how much less would be necessary if alternatives are explored.  If I were off grid (I'm not) I'd mostly likely favor a blended solution, a relatively small 3-way RV fridge (120volt AC, 12 volt DC or propane; selected by user/not automatic) plus a small ice-maker that runs only when the sun is shining and the (relatively small) battery bank is "full".  Not only does the ice that the ice-maker makes on a sunny afternoon represent additional stored energy, it's portable.  I'd segregate my stored foodstuffs into three categories; 1) MUST be refrigerated below 40 degrees (most dairy, store bought eggs) 2) Should be kept under 60 degrees (butter, hard cheeses, mayonnaise...) and 3) Best if kept refrigerated as much as reasonable (ready drinks, juices, most condiments, leftovers, yogurt)

The first group would have to fit inside the little RV fridge at all times, because the risks of an unregulated environment was too costly/risky.  The other two categories could end up in the leftover space in the fridge, in the cooler with the ice, or on the pantry shelf or outside in a shaded box/zeer pot (depending upon the season)

FWIW I have a large french door fridge and it uses about 1.2kwh per day (on average).  One solar panel (and not a particularly large one) and a couple golf cart batteries could power this fridge for me.   A suitably sized panel would cost about $100, batteries about $200-$300, I wouldn't buy an inverter just for my fridge, but the inverter I would buy  costs about $0.50 per watt, the fridge draws 120 watts, so about $60 worth of inverter.  There is also the cost of the battery charge controller.  Worse case you're looking at maybe $500 total.

Any compression fridge will need a surge capacity about 3 times what it's nameplate rating is, and that over-sized inverter will consume it's own overhead 24 hours per day.  The solar panels would be the cheap part, but if you are only spending $300 on batteries, basically just enough to make the night, you will need to buy new ones in about 4 or 5 years; because you are committed to deep cycling them daily.  As another poster mentioned, lead-acid is a fine choice, but should be oversized due to the longevity factor.  Lead-acid batteries will live exponentially longer if they are not deep cycled regularly.  Keeping the battery bank the same size, but eliminating a major overnight demand (refrigeration) and that same small battery bank will last much, much longer.

A similar size propane powered fridge would use about $1 worth of propane a day, that's about $365 a year worth of propane.  The typical propane fridge is about 1/2 the size of mine and costs three times as much.  I don't think they make a propane fridge as large as mine.
Sure you can conserve propane by using a smaller fridge, you could also conserve electricity by using a smaller fridge which would require less PV, batteries, etc.
The fact is propane costs MORE, a LOT more, than solar PV.  

20-30 years ago it was a different story, but not today.

Full sized propane refrigerators do exist, but as I noted above, the key to success with a propane fridge is conservation.  Accepting the smaller useful fridge space of an RV fridge and then maximizing it's usefulness will go a long way.  Also, a 3-way fridge can actually use your excess solar power as an alternative heat source on very sunny days, and switch to using propane as the sun sets or clouds roll in.  Another trick is to have two RV sized fridges instead of one larger unit; with one set to 36 degrees for category #1 foodstuffs, and the second set to about 55 degrees for everything else.  And it's pretty trivial to set up one or both RV fridges to consume your excess solar power once the batter bank is "full".  For that matter, the second RV fridge could reasonably be a DC compression type RV fridge, that only runs from the solar panels.  It would be easy enough to cool that 2nd unit down far enough to keep it below 60 degrees overnight.

In short, I don't disagree with your perspective, I'm mostly pointing out that there are other ways to think about the problem, and considering a small propane fridge for the most critical of refrigeration uses is a fine solution.  It also grants the off-gridder a degree of energy diversification, as s/he isn't dependent upon the weather for critical power needs.  I would consider dependence upon only a photovoltic array for power to be a risk of it's own kind.

I understand that TFT and metal oxide PV have lower entrainment than amorphous silicon, but the requirements spread across several supply manufacturers (mill spec materials, etc) and the energy required to produce those materials are ignored in the recent research. It is a filthy trick that is done - the published numbers are selected late in the process deliberately to lower the LCA. It is not a "myth that won't die" - it is a reality that has been hidden by ignoring materials, and using subsidies to artificially depress the manufacture and materials costs. In truth, PV is great for remote sensors or calculators - not bulk energy generation. As for the wind turbines? They are primarily Aluminum. Wind turbines consume electricity over the 20 year design life - they eat more than they make. They are GOOD for SOME applications. Like every other quality of energy production. SOME. PV is an option - but it is overloaded with extremely bad politics and fudged numbers.

Had this discussion many times in academia and industry.

I did not say biogas. I said Natural Gas or Methane. Homemade biogas is the same as municipal biogas - if it is put through 3 very simple filters (ZnO, Fe, C) and then de-humidized, it becomes Methane (>95% pure). The "impurities" of biogas are representative of an incomplete process. That is NOT an issue with biogas, it is the same issue with ignoring upchain energy consumption in PV production - Propane is highly refined, Nat-gas is too. Biogas is more easily obtained and refined than either.

Criticizing homemade methane on the basis of "impurities" is rather ingenuine. You don't burn raw biogas anymore than you would raw propane.

As for quantity - the research into that is also pretty poor. Urine must be separated as the N inhibits the process (and is better used elsewhere) - most humanure based systems ignore that (except that some firms have made toilets specific to it). I did not claim that all of the feedstock is from poo, I just made a joke. However, the AVERAGE (results vary) human daily poo contains enough SCRUBBED methane to boil around 1 gallon of water (depending on altitude and starting temperature). That's dinner.

There is also pet waste, kitchen waste, and yard waste - and the solid output is very suitable "compost" (it's humus) - so there is little sacrifice from composting, just a detour. Limiting N input, most organic waste can be methane-digested.

As for the Salt-Water Battery, yes, Aquion Energy went nasty bankrupt after Bill Gates got his hands on it, but the technology itself is completely sound, and in any case, the company is restructured. The tech has nothing to do with the dishonest business practices.

I did not say to buy a salt water battery, I said to build one, and gave directions as to how. It means nothing that most companies are chasing Tesla's obsession with LiPo, saline works - just not for cars, cell phones, or drones, and on that basis it is ignored.

Funny you should mention the lightbulb. Prior to it's development, the mathematics and science claimed directly that "Electrical incandescence is impossible". Pretty much for the same reasons that folk like to criticise methane, ignore saline batteries, and promote photovoltaics. It isn't a conspiracy, it's just the influence of trends. It is fashionable to ignore variables that lead to unfashionable conclusions.

The POINT of this is DIY and Sustainability. You can build a serviceable Saline/Methane/Solar-Thermal system to provide for your needs, using mundane and readily available stuff - it is simply a matter of dedication. It is highly unlikely that you can produce a LiPo (or NimH, etc...) and produce propane, or manufacture a PV in your garage (yes, you can do those things, but not at any useable scale).

At the end of the day, if someone chooses just to buy whatever is popular off the shelf, they can go right ahead - but they might as well just have a power-pole and gas line installed.

The options that I have offered are completely viable for anyone with the chutzpah to put them into practice. The criticisms offered against them are pretty anemic most of the time.

There is a reason why my signature says "Just build the damn thing." I have watched in academia and industry how good-intentions turn to propaganda and analysis paralysis - and then that non-progress is used as rationalization for frankly psychotic regulations and pitiful half-measures.

I am in the process of constructing my apparatus but, it is me alone. At the university, most people are so lost in LiPO that they can't see past their Samsung (I'm not kidding - it is the ONLY area of research due to grants). In industry (specifically Manufacture Engineering and Tool and Die) most are struggling so badly with inflating materials and labor costs - and taxes - that they haven't the time.

Eventually I'll finish my devices - and, like the lightbulb that is nothing more than a thread in a vacuum, folk will react all mad when they see that a glass container with dilute pee and bubbling boiler-exhaust grows Chlorella algae when placed in the sun, converting that exhaust to O2.

I haven't even invented anything - I just didn't swallow the garbage excuses that everyone makes when presented with an idea... "that'll never work"

Spencer Miles wrote:
, like the lightbulb that is nothing more than a thread in a vacuum,

Actually, only the prototype used vacuum as oxygen displacement.  All mass produced incandescent bulbs used a non-reactive gas to displace oxygen, because while vacuum works, it's next to impossible to mass produce a bulb of glass that can hold a vacuum for months at a time.  Typically, it was just pure nitrogen.  You can still get incandescent bulbs with replaceable filaments for marine use, but they are more expensive these days then just upgrading to LEDs.

But I digress...

Spencer Miles wrote:Propane is a pretty non-permie method. I've seen few treatments of this "Off-Grid dirty secret" - but one of that name (paraphrased) recognized that a pill-bottle fuel-tank that has to be refilled constantly essentially defeats the purpose of any Permaculture ideals from the get-go. PV is also a problem (how are they made? What nasty stuff goes into and out of that industry?)

I have to disagree a little bit with the highlighted statement.  A propane tank is basically a long term energy storage unit, which is not true with a natural gas service.  Yes, it does use a form of fossil fuel, but if you don't use it, do you think that it won't be used?  Eventually, propane won't be available at a reasonable price, and we will all be forced into alternatives; but in the meantime it does it's intended job very well.  That said, the RV fridge can, and has, been converted to other heat sources.  I can buy an absorption fridge that runs on kerosene (or equivalent) today, which is just an RV unit with the propane burner replaced by a lantern wick.  And while kero isn't going to be any more affordable than propane in a couple decades, running a lantern wick from animal or vegetable oils is an old technology.  Nothing that we do is truly permanent, what we look for is long term solutions.  A 400 gallon propane tank that only has to run a small 3-way fridge overnight and on overcast days could reasonably last for years before a new solution wound need to be engineered or an alternative fuel acquired.  For the critical needs, what we really are looking for is a lengthy lead-time, as all such problems become trivial over a long enough time frame.

While thinking about this, I came up with another example of a continuous power demand that an off-grid household might want to consider alternatives for, and that is running water.

Living off-grid requires that we come up with an alternative to the water company, because running water service is such a labor saving technology that it doesn't seem worthwhile to do without it.  However, the typical off-grid home uses a water well and an electric well pump with a pressure switch; so that whenever someone opens a water valve, the pressure drops and the pump turns on to run as long as necessary, at any time day or night.  However, a battery-saving alternative would be to set up a 'standpipe' connected to your system, so that 30 gallons or so of water are held in storage 80 or more feet above your house.  This would be easier to achieve for those of us who live in hill country, but a tower could also  be built that could be also used for antennas.  Either way, this basically involves a tank with both a top port and bottom drain, so that the top port is connected to a float valve to fill the tank when flow is available and the drain port has a anti-reverse-flow valve (foot valve) to allow water to drain out of the tank whenever powered flow isn't available.  This represents stored energy, and you would need to have enough tank size to manage your overnight water demands, which  can vary considerably depending on your family's habits.

However, a sound water discipline could also do the same thing, such as expecting all bathing to be completed before twilight, and limiting water-flush toilet use after dark to a 'if it's pee, leave it be' rule.  This form of water borne energy conservation would also be helpful in homes that heat water via solar collectors.

This is what I believe.
Each person must do what they know and believe.
For me that is using solar with and without batteries.
with batteries for storage to run as much electrical equipment as possible. There is no ongoing cost of fuel.
solar distillation unit to extract distilled water to use in batteries.
solar pumps {without batteries} to pump house water and dam water to header tanks 81 feet above the house for house and garden use.
the house uses electrical stove and oven as well a washing machine and a fridge and two freezers.
for wet or cloudy days and during winter there is a wood stove for cooking, heating up the hot water tank and heating up the central heating in the floor if needed.
from 10am to 2am; an 8KVA welder can be used if needed on a sunny day.

Each person needs to choose what they are willing to do.
sealed batteries are fine if you do not want to do any maintenance work. may not last as long.
gas works if there is always gas a available.
water works if there is a flowing stream or such.
if you need to bend over all the time into the wind, then wind power can be very cheap.
or use no power like your grandparents did.

I find that there is no best way only what works for you.

about BATTERIES there are so many types.
For myself, I made a list of what I wanted to do with my Life.
Then made a list of what was required of any power system that was going to be used.
the list was 50 items long.
the list made it ease to choose the type of power system needed.
of the 28 solar installers contacted. Only one meet the requirements sent to them.
do not let them choose for you.
do not let anyone choose for you.
CHOOSE ONLY FOR YOURSELF.................

the research for the suitable system took over three years.
the solar systems installed has lasted 15 years and is still going strong.

Donald Humbler wrote:This is what I believe.

For me that is using solar with and without batteries.
with batteries for storage to run as much electrical equipment as possible. There is no ongoing cost of fuel.
solar distillation unit to extract distilled water to use in batteries.
solar pumps {without batteries} to pump house water and dam water to header tanks 81 feet above the house for house and garden use.
the house uses electrical stove and oven as well a washing machine and a fridge and two freezers.
for wet or cloudy days and during winter there is a wood stove for cooking, heating up the hot water tank and heating up the central heating in the floor if needed.
from 10am to 2am; an 8KVA welder can be used if needed on a sunny day.

I have to say, that's impressive.  But it makes me wonder, how large is your array and battery storage?  It sounds to me like you built both so large as to be able to completely replicate a grid tied power service.

EDIT: And for myself, I wouldn't even have entertained the idea of electric cooking (or water heating).

I think our power usage will be fairly nominal.

I would start with calculating an accurate & realistic power usage requirement. Then do whatever is feasible to reduce that amount. Then design a system based on that.

Anyone seen an abandoned Prius with good battery? I really want to play with one.

I heat, cool, and cook with electricity, its the ONLY energy source for my house.  

My grid tied array is rated at 2850 watts (AC), although it rarely produces that much.   Before I bought the Chevy Volt we produced about 1.8-2 MWh a year surplus.  
We bought the volt a little over a year ago and in the year since we bought it we went slightly(~250kwh)  in the hole, so I'm going to be adding another panel.
When we go off grid I'll probably add another 4-5 panels.

FWIW the Chevy Volt accounts for ~30% of our electricity use over the last year.  It will be going up quite a bit this year because my Grand daughter is living with us and we have to drive her to school right now, that is about 45 miles a day, once she gets her driver's license that will go down.

You don't need a huge array if your house is efficient.

Peter VanDerWal wrote:
You don't need a huge array if your house is efficient.

Granted, but living in Arizona probably helps in that regard.

Creighton Samuiels wrote:

Peter VanDerWal wrote:
You don't need a huge array if your house is efficient.

Granted, but living in Arizona probably helps in that regard.

Less heat needed, more cooling.   Pick your poison.

Arizona is right at the median (by state) for household energy consumption.

Peter VanDerWal wrote:

Creighton Samuiels wrote:

Peter VanDerWal wrote:
You don't need a huge array if your house is efficient.

Granted, but living in Arizona probably helps in that regard.

Less heat needed, more cooling.   Pick your poison.

It's not quite so simple, because you need less heat, but more cooling; your cooling demand can only (reasonably) be provided by electricity.  So your all solar photovoltic is reasonable for you considering your locale.   However, in regions that depend more upon heating throughout the year than forced cooling, there are many ways to provide that heat.  And typically, our supply of direct sunshine isn't nearly as reliable as yours.  Living in Kentucky, my Heating-degree-days and Cooling-degree-days are about equal; so I need as much heating as I do air conditioning.  However, our Insolence metric varies from an average high of about 5 hours daily in the summer to just under 4 hours daily in winter.  I'm sure that you'd agree that wouldn't be enough for you to do what you do with less than 3KVA of solar panels in Arizona.  It simply wouldn't be safe for me to depend entirely on electric for my heating demands in Kentucky, even while attached to the grid.  My AC unit was old when I bought this house, and I fully intend to upgrade to a heat pump when it dies.  After that I will be able to use the heat pump for 90% of my heating demand or more, and when that can't cope my current forced air propane furnace will function as the backup heat.  This will reduce my propane consumption considerably, with the downside of a portion of that carbon savings being consumed by additional use of grid-supplied electric power.  All of that backed up by my woodstove in the event of power failures, which happen about once per winter where I live.  It is my desire to, eventually, install a 2KVA east-west solar array upon my rooftop; but with the intention that it's entire function will be to power my fridge and deep freezer during bright daylight.  I actually have an early prototype of this device... http://solar-trap.com/  ...but I haven't found the funds nor the time to complete this project.

A couple things to consider:  Solar panels produce more power when they are cold than they do when they're hot. Inverters can also run at over their rated output when cold.  My system will often produce 5% over rated output during the winter and 5% less than rated during the summer.

Heat pumps also work better in heating mode than cooling.  All of the energy used to run the heat pump gets added to their hot side.  This is a bonus during the winter, but a negative during the summer.

If you have a connection to the Natural Gas grid, then that 'might' be cheaper than heating with solar PV, unless you also need cooling during the summer.  If you need cooling, then you already have to buy the equipment (AirConditioning and perhaps PV array) and its silly not to buy something that can also provide free heat.

If you're off grid and have access to lots of free wood, then that is going to be cheaper than a heat-pump...unless you need cooling.  If you need cooling then again you might as well use the heat-pump for heating, and supplement it with wood burning as needed.

If your choice is between heating with propane and heating with PV, PV is almost always going to be the winner (unless you live way up north)

You really need to do an individual analysis for your particular location.  

My point is that solar PV prices have fallen so far recently that the old assumption that you should always use propane, etc. for heating is no longer valid and in most cases these days it's wrong.
PV prices have dropped so far that even using PV to heat water is now cheaper than direct solar water heaters in most areas.

Peter VanDerWal wrote:
You really need to do an individual analysis for your particular location.  

Agreed

My point is that solar PV prices have fallen so far recently that the old assumption that you should always use propane, etc. for heating is no longer valid and in most cases these days it's wrong.
PV prices have dropped so far that even using PV to heat water is now cheaper than direct solar water heaters in most areas.

I agree with the bolded statement, and I think that we might be talking past each other here.  My original point about considering propane for refrigeration needs was to significantly reduce the need for battery storage, because I consider that the weak link in an off-grid photovoltic system.  I haven't run the numbers, but I would strongly suspect that photovoltic panels have dropped enough in price that it now makes sense to use extra panels to electrically heat water, or the 12 volt DC resistive heater on a 3-way absorption fridge.  But rechargeable chemical batteries remain a stubborn nut to crack, and would be an environmental compromise (at best) in their own right, even if propane is eliminated from the options.

I was trying to use the fridge as an example of a critical energy demand, that needed to be provided for on a continuous basis, regardless of the state of charge of the batteries.  It was simply the most universal example that I could think of.  And I was offering propane as an alternative solution.  I'm not actually recommending propane as the best alternative, just trying to nudge the OP to think beyond electricity.

Creighton Samuiels wrote:I haven't run the numbers, but I would strongly suspect that photovoltic panels have dropped enough in price that it now makes sense to use extra panels to electrically heat water,

Solar electric panels are about 20% or less efficient at converting sunlight to electricity.
Solar thermal panels are about 80% efficient at converting sunlight to heat.
It would be really hard for the solar electric panels to compete in any application that was generating heat.

I have been following this thread intently, and enjoying it thoroughly. I'm planning on building (with help) an off-grid small straw bale home, no electric heating/cooling other than a fan and interested in learning more about battery options. Thank you to everyone for your contributions.

Creighton Samuiels wrote:First, take an honest assessment of what you might need continuous power for, and determine if there are any practical alternatives for that need.  For example, most of us know that food refrigeration is a power hog that typically requires continuous power available to regulate the controlled airspace inside a standard refrigerator.  

I really enjoy living without a refrigerator. It requires that I approach food and meals with a different mindset. I eat different types of foods when I'm living without refrigeration. I prepare them in different ways. Many of the foods that I would refrigerate if I were living in my birth-culture don't really need refrigeration, etc... There is tremendous infrastructure savings available to me if I simply skip refrigeration.

Joseph Lofthouse wrote:

Creighton Samuiels wrote:I haven't run the numbers, but I would strongly suspect that photovoltic panels have dropped enough in price that it now makes sense to use extra panels to electrically heat water,

Solar electric panels are about 20% or less efficient at converting sunlight to electricity.
Solar thermal panels are about 80% efficient at converting sunlight to heat.
It would be really hard for the solar electric panels to compete in any application that was generating heat.

Thermal panels do not have a fixed efficiency, their efficiency is effected by the temperature differential between input and output, the flow rate, the outdoor temperature, solar insolation, etc.  When it's very cold out, many solar thermal systems don't produce any usable output, however when it's really cold out, PV panels produce MORE output.

However, efficiency is irrelevant to cost.  What matters to most people is the COST of the system.

If you live somewhere it never freeze you could use something like a batch heater which tend to be really cheap.  But folks that live in areas that experience freezing conditions typically use indirect systems with antifreeze, pumps, heat exchangers, etc.  Not only does this reduce the efficiency of the system, it drives up the cost, PLUS they usually require energy to run the pumps.  Even around here folks with these types of systems need a backup water heater for 3-4 weeks a year, when it's too cold to harvest thermal energy.  
The energy needed to run the back up systems and the pumps, is almost the same as I use to run my heat-pump water heater.
So the total cost is thousands more, AND it uses almost the same amount of electricity.

Joseph Lofthouse wrote:

Creighton Samuiels wrote:First, take an honest assessment of what you might need continuous power for, and determine if there are any practical alternatives for that need.  For example, most of us know that food refrigeration is a power hog that typically requires continuous power available to regulate the controlled airspace inside a standard refrigerator.  

I really enjoy living without a refrigerator. It requires that I approach food and meals with a different mindset. I eat different types of foods when I'm living without refrigeration. I prepare them in different ways. Many of the foods that I would refrigerate if I were living in my birth-culture don't really need refrigeration, etc... There is tremendous infrastructure savings available to me if I simply skip refrigeration.

Yes, I know that it's possible.  I'm a "certified" sailor as well as a formerly-employed US Marine, and have experienced lengthy periods without the benefit of powered refrigeration.  Canned butter is a God-send on a sailboat anywhere near the tropics; and in my more temperate zone, a butter crock on the countertop works just fine for weeks.  Also, many items that Americans, without our larger-than-life refrigerators, typically store in the fridge don't really require it.

All that said, my wife is unwilling to adapt to a lifestyle without powered refrigeration.  And every time that I had to do live without a fridge, I knew that the condition was temporary, so I'm not sure that I'm willing to live that lifestyle permanently either.  Also, canned butter and meats are more expensive; so if you are doing that enough then a (small) fridge becomes economical.

A couple of years ago, I was experimenting with 'variable' refrigerated space.  One of the variables that we can control with respect to how much energy we require for refrigeration is the volume of refrigerated space we maintain, because over the long term the amount of cooling power required is relative to the surface area of the fridge.   Yet, even though we still buy most of our food from a grocery store on a weekly basis, our refrigeration needs vary.  We go to the grocery on day one, and we can barely make everything that (my wife believes) needs to be in the fridge fit, but by day 3 we have plenty of open space, because we are consuming food and disposing of the packaging continuously.  Most people just buy whatever fridge is large enough to accomplish their greatest needs, and then decide upon models by the features; but I was trying to convince my wife to accept the next size down and use a custom built milk cooler (top opening, holds 4 gallon jugs, internal dimensions of 28x28x28 inches, very heavily insulated, one or two of the jugs would be ice blocks that I pull out of the deep freezer on shopping day) for the first few days, until all of the extra items would fit into the fridge without issues.  She would have none of it.  Too inconvenient, too risky according to her perspectives.  When I remodel the kitchen, I might add a prep-island and include a RV small compression fridge (or perhaps I should make it propane) that could be used as needed, and turned off when not needed.

For the more savvy:

A Stirling Cycle Engine is a heat pump. A Rhomboid drive - co-axial piston arrangement becomes elegantly cryogenic when driven mechanically, as opposed to driving when exposed to a delta T.

I am certain that a dedicated Permie can contrive all sorts of ways to make a shaft turn. Wind, steam, compressed air, water-wheel, dog-treadmill....

A brine or glycol solution, running between a heat exchanger on the displacer head, and another exchanger placed in a heavily insulated box, will remove the heat from said box down to levels that are quite surprising.

Rhomboid drives are complex, but not vital - any 90 degree crank-drive will do and consists of simple bearings (ceramic skate-board bearings from Amazon are about 9 bucks each - no lubrication, long life) and an assortment of linkages.

The box can be insulated with saw-dust, vermiculite, or any other low-density/high-bubble material like fiberglass or polystyrene (if you are so inclined).

40 deg F (fridge) and 0 deg F (freezer) are really easy with this arrangement - these things can get cold enough to condense Oxygen to a liquid if you let them. Thermostat is a bypass valve for the cooling fluid. Added benefit of a cooling source to use for home AC, and the heated end of the displacer head is an available source of heat. It is a heat-pump, so it isn't like fire or anything, but use what you've got.

A centralized unit can run cooling lines to several cooling appliances if you wish - or it can be a single shaft-driven fridge (Coleman used to sell one that had a DC motor in it, but could be retrofit - haven't found one for sale as they are prized by their owners)

Rather than making electricity, then making that electricity into cold (a continuous and high-loss process) why not make a rotational shaft directly into cold - overall LCA is much better than the standard methods.

You would be surprised how easy it is to make this sort of thing - and unlike a sealed scroll compressor working on R-22, freon, isobutane, or others (normal Sears model fridge) - or an evaporative system (propane fridge works with Hydrogen - lost over time) - this is a mechanical system that can be continuously maintained, and re-charged with simple gasses as the gas only moves between the displacer and power pistons - the cooling fluid runs in a closed loop, if convective, requires no maintenance and remains sealed.

Your cold-box can be as small and inconspicuous as a cupboard under the sink, to as large and beastly as a 60 x 40 shop - depending on how strong a shaft you've got, and how many of the little units you make.

I suggest glass and graphite power-pistons. No lubrication, extreme high-cycle, low maintenance, very low friction.