230v/50hz off grid?

no it is not

Nowhere near enough information provided.

Well I'm in the U.S. and I'm thinking of using an off grid system. I know European appliances are very very efficient, and I might be using a 230v/50hz system.

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In addition to not enough information-
there are problems in using 240V 50Hz equipment at 120V 60Hz. If one wants to use European appliances, then many are available for 60Hz, 120 or 240V operation. If it is properly designed for the voltage and frequency that it is used at- then efficiency differences are minor or negligable. It is also now sometimes difficult to determine just where a given appliance is designed or made as manufacturers are international. In some cases a "European" brand is made in the US while "American" brands are made in Europe and some damn good appliances are designed and made in New Zealand. Europeans had to face high energy (and water) costs long before North America so efficiency at a higher capital cost was worth while. Now North America is waking up to the same problem.

you mean appliances like refrigerators, washing machines, hot water heaters, and furnaces?
i think you should consider carefully some of the many pitfalls in your proposed course of action:
cost of importing appliances and parts.
cost of resizing/replacing all circuit breakers and rewiring as needed. cost of replacing outlets.
astronomical repair costs and unbelievably long repair times.
nil resale value of non-standard power plant and appliances. low resale value of the property in the event you decide to sell and move.
non-ability to reconnect to grid in the event of generator failure or lack of whatever fuel or power source you go with.
possible fire hazard if someone unwittingly plugs in the wrong thing.
possible electric code infraction depending on state/local.
a major PITA having to remember to check EVERY electrical device that comes into your house for compatibility.
i'd recommend you have a little talk with a local electrician and an appliance store. next fire up the little calculator program on the computer and see what your "savings" of the next 5 years might be.

Regarding "more"efficient 240 V. appliances...
While in Europe, I observed that something as simple as a small incandescent light bulb operating on 240 volts was not so efficient. In fact, just to touch it was to feel that it was as hot as hell. I don't remember what the wattage was, but it gave about the equivalent amount of light as a 40 watt bulb in the US.
Edison knew what he was doing when he designed his system. He came up with voltages of 100, 110 (and later 120) volts as the optimum for carbon filament incandescent lighting.
I think the Euro definition of "more efficient" means smaller, cheaper conductors, longer runs for appliance circuits and possibly less voltage drop, etc.
Many Euro hot water heaters are point-of-use. There is something of a myth that these are more "efficient" than the American practice of having large tanks of heated water in their basements and garages on "standby". Factoring the increased capital cost and more complex maintenance for these "point-of-use" systems tends to show that, in many cases, the actual cost is higher.
Beachcomber

Well, it would still help if you said what appliances you are thinking of.
US-style fridge/freezers have become popular in UK at least in last few years, and some US manufacturers have started making them to EU efficiency standards. You could try asking a US manufacturer for one. Note that their identical US models are still completely off the bottom of the EU energy efficiency scale (as people who try buying in the US and importing to the EU rapidly discover), so you would have to specifically ask for one to EU energy efficiency standards. If more people did this, they might make them available in the US too.
For washing machines, which is another item where energy efficiency very is widely different between US and EU, the problem you are going to find is obtaining the European advanced cloths washing detergents which EU machines use. They just don't exist in the US, as they won't work in US machines.
So as I said, some idea of what appliances you are thinking of would be useful.

Actually European washing machines do exist in North America. Some are bloody expensive. As for the detergents- they are now readily available. A few years ago, what you say would be quite true and many washers are still the top load agitator units which are initially cheaper. However, as happened in the 1950's with circuit breakers , European designs are taking over more and more of the market- some are made in Europe and others are made in the US or Canada. Europeans have long been more concerned with energy and water savings than North Americans.

Most "appliances" (e.g.: dishwashers, uWave, washing maches) which now run on 120 would likely be "better" were they to be operated on 240. Personally, I think anything that draws more than10 amps at 120 should be re-designed to operate on 240.
Amen. BUT in US and europe, most "utility" (as compared to "effect") lighting is flourescent. To a good approximation, efficienty doesn't change with supply voltage. With the US system, 240 volt stuff would usually require two pole switches and two pole breakers. These might offset the savings in copper ahd I^2*R losses.
"Decorative" lights are moving toward low voltage systems with built in transformers. Again, the supply voltage isn't much of a factor.
But incadescent lighting may soon be considered obsolete.
Maybe so; maybe no. In an "all electric" home, it may start to make sense to replace the hot water tank with a 5 kW heater with, say, 12kW demand based systems. It also may make sense to move the heaters closer to the point of use.
In the case of a dishwasher, a case can be made to plumb the machine with COLD water and let it heat the water with a 240 volt heater. It would have the further advantage of starting each cycle with COLD water. This will permit some washing before the food is "baked" on. Ditto for a clothes washer: it might make sense for a 240 volt powered appliance to just take in COLD water and heat it locally to whatever temperature suits the application.
Oil is becoming relatively "cheap" again but everytime oil peaks the nuke power plants start looking more acceptable.
I have seen the demand type electric water heaters on display. At present they are very expensive. Since there is so little to them, I see no reason why the can't eventually be sold for something on the order of $50 for a 10KW demand heater. At that price, any failure would result in a replacement of the entire unit rather than sending out someone to figure out the controls and safety interlocks.
Cheap demand heaters would be placed near the point of use. A bathroom might have separate heaters for the sink and bath. It might even have a "tempering" heater for the water to the toilet tank. A truly integrated system would just adjust the water heater set point rather than "mix" separate hot and cold supplies. There would be some interesting safety problems as a person in a tub would be "adjusting" a 10kW electrical appliance.

I actually had a chance to try out this experiment. At the time my wife ordered a new dishwasher with the internal heater element. The cycle timer would not advance until the operating temperature was reached. We tried it with the exclusively cold water (actually turned the water heater off and let it cool down for a few hours). The result was that it took something like 1 1/2 to 2 hours to do a load of dishes.
It takes a long time to heat water exclusively with this element to near boiling, which is what the dishwasher requires. The cycle timer would not advance until the operating temperature was reached. Don't forget there are something like 5 - 6 fills cycles and each requires heating a few gallons to near the boiling point.
The conclusion was that pre-heating the hot water was a good thing and there was no reason to change from current practice. If you are in a typical household that uses hot water for bathing, clothes washing, general kitchen use and dishwashing, it is more efficient to heat up the hot water in bulk and have a means of efficient, insulated storage. For a large heater in a multi-family dwelling unit, such as an apartment building, the advantages are even greater.
Beachcomber

Yes, in my house almost all the lighting is fluorescent, and the filament lighting is 12V.
In UK, for a few years now, new builds and remodels have to include lighting at 40 lumens/Watt (IIRC) or higher in proportion of the heavily used areas of the house, and the lampholders must be of a type which will not take filament lamps (which don't reach anywhere near 40 lumens/Watt efficiency).
You think wrong then.
Euro designs and customs vary widely from one country to another. The appliance regulations are all common though.
In UK, most heating and hot water is done by natural gas, although there is some oil and a little electric. Gas appliances used for heating now have to be >90% efficient (which means condensing operation). Instant on-demand gas water heaters are typically around 30kW and are now very popular. Electricity derived from fossel fuels is all under 50% efficient before it even leaves the power staion. Hence we avoid electric heating whereever possible.
That's how ours work. They don't normally have a hot fill. There are two reasons: hot water onto protein based food cooks it onto the plates and makes it harder to get off. It comes off easily when the water is cold. Secondly, the small amount of water used in an EU dishwater makes non-viable to hot fill, as you will likely not get much if any hot water run to the end of the pipe before it's finished filling, and then you just waste that energy as the water in the feed pipework goes cold.
EU washing detergents would be largely destroyed by hot fill. EU washing machines do a profiled temperature wash -- a period of washing at different temperatures which match the optimum for the various different constituents of the low temperature washing detergents. This means they have to cold fill (or temperature controlled mixed fill at around 30C/86F), and work their way up to 40C or 45C/113F slowly which is the highest needed by the detergent. Again, it's questionable if it's worth connecting up the hot inlet -- many people don't bother as the volume of hot water used by an EU washing machine is tiny, and it certainly isn't worth it unless the pipe run is short.
These exist in the UK, exactly as you describe. However, the poor efficiency of electricity generation means they aren't a sensible choice. Also, 10.5kW (highest commonly used instant electric heater in UK) doesn't generate a very good shower -- you get a much better and more efficient shower from a condensing gas heater. Even an old obsolete non-condensing gas heater is still twice as efficient as fossel fuel electricity generation.
Instant electric water heaters have historically been more common in Germany, where you can find them rated up to 25kW, but domestic 3-phase electricity supply is more common there than in the UK.

That's about what I would expect. The heater only runs on the 120 and, likely, doesn't draw more than 700 watts if that.
The "new order" of appliances would run on 240. The heater likely would be 2 kW. It would still take some extra time, however.
A marginally sized heater in this application would waste energy because during the temperature ramp up, only a portion of the energy would be increasing water termperature. The other portion would just be countering the heat loss.

The US is quite the "consumer driven" place.
What that means in practice is the we just don't care one way on the other about "thermodynamic" efficiency. Modern life DEMANDS that a house have good electrical service and the distribution costs of electricity are mostly covered by the rate base.
Thus, it might may "themal sense" to burn natural gas in a 90% furnace rather than use it in a 50% power plant but to the customer who wants a warm bathroom, it makes more sense to used electric from the 50% power plant.
Well, when we "run out" of hot water I have found that in summer we can bare stand using the "hot" water that's just run through the water heater and picks up the heat from the 4 kW element. I would "guess" that a point of use 12kW shower heater might give acceptable service with a flow restriction on the water supply. But from what you say, I suppose something like 16 kW would be needed.

You British chaps make it sound like you are taking a lot of cold and lukewarm showers.
Is that true?
Beachcomber

Checking my UK one... It takes 4-5 pints of water for the main wash cycle. The only other fill which gets heated is the last rinse, which is really just used to heat the dishes prior to the drying, and only uses about half the water of the main wash. So that's less than a gallon of water which is heated.
Well, you were hampered by the combination of an inefficient machine, compounded by it being designed to run off the limited power available from a US socket outlet -- a double wammy. Neither of these problems are an issue anywhere in EU.
Also, you need to test the cleaning effectiveness with a variety of foodtypes. Some types of protein (egg, porrage, etc) are more difficult to clean in a hot fill system, as the heat cooks the protein into longer chains, making it impossible to break down, so the cleaning of them depends mainly on mechanical agitation. Conversely, they clean easily in cold water.
Why do you want to store it? That can only add losses, and the possibility that the store runs out.
You actually completely failed to address the efficiency issue at all, even though you seem to have reached a conclusion.

I can only assume you misread who wrote which articles?

Andrew:
While the cold water may be better for getting the chunks of food off and not baking onto the dishes, and hence the dishes look clean, but they will not be sanitary. Detergents safe enough to use in the home will not kill the bacteria left on the dishes. Only heat will suffice to kill the little buggers. The typical commercial dish washer rinses the dishes then goes to town with the soap and hot water. And that hot water, at least in the US has to be up around 180 deg F otherwise the local health department starts getting upset with the restaurant owner.
Sparky