Off grid wind power for rv

[Tommy Gillespie]

I am contemplating investing in wind power for my rv. I am not to familiar with all the components involved. My ultimate goal is to run my rv 100% off grid power. My question is how do I get from the wind generator itself to my 50 amp plug in on the side of my camper? Also about how much would the average cost be for such an endeavor? Any help or advice would be greatly appreciated

[Dave Schwartz]

That's a very tall order there. Are you looking to replace the A/C power and be able to run everything in your RV just like you are plugged it? Seems so if you're talking about connecting to the shore power inlet. If so, give up now.

First, at 50A per leg on your shore power connection you are looking at over 11kW of power. That's a pretty large and heavy turbine (plus balance-of-system) to make that, not to mention the 50 or 60 foot (or more) guyed tower to support it. I don't think you'd be able to transport it and the RV at the same time. Would also take you a few days to set up and take down.

Secondly, for that kind of wind power in a turbine you could move you'd need to go hunting very windy locations... so windy you'd probably not want to camp there. Forget about putting out your awning and the RV would be rocking and rolling pretty good.

Thirdly, you'd need lots of 12V battery storage between the turbine and inverter. The turbine alone would not be good at load-following and you'd be getting wild swings, brownouts and dropouts if it even worked at all. So add in a couple thousand dollars and some very heavy batteries. The battery buffer will reduce the size of the turbine but you're still talking about a pretty beefy inverter to make 11kW.

Most off-grid RV'ers use solar. I've not heard of any that uses wind in a serious way. Pound for pound, solar panels will give more power in a smaller footprint and be way easier to set up and transport than a wind turbine of similar power. Plus, the locations in which solar will work will be a lot easier to live with that the turbine.

I can't see any way you could have a portable system capable of running air conditioners (you probably have two). If you eliminate those (or plan to run them off the backup generator you'll have to have anyway) you might be able to run everything else off the 12V system (propane for furnace, fridge, water heater and most cooking) and an inverter for the TV and microwave used as required.

P.S. Although the forum is a bit brand-specific, there's lots of discussion about what you want to do (called 'boondocking') here (http://www.forestriverforums.com/forums/f212/).

[Tommy Gillespie]

Thank you Dave for the info. The rv will not be moving it is a permanent location I am interested in getting power to. I have only just started exploring options for off grid power. I am trying to figure out what will be the most economical and east to set up. Really the only reason I would need the 50 amp service is for the air conditioning and for the electric heaters. Would solar panels and a large battery bank be better if I plugged everything in to its own individual power inverters. Also any idea about the cost of such a setup would be.

[Joe Blake]

Tommy,

I think using individual inverters would be pretty inefficient as each inverter would have losses, so maybe one big inverter powering everything might be a better way to go.

Maybe this link might give you some food for thought.

http://www.solar-facts.com/inverters/inverter-efficiency.php

[Dave Schwartz]

Okay, if its a permanent location then its more of an 'off-grid house/cabin' than it is an RV except that the RV may give you a few more options for propane to substitute for electric if you have a convenient source of propane.

Your biggest issue is going to be the A/C or electric heat - those are heavy power draws and really going to drive up the size and expense of the system.

I'm not the expert here (Rob is... its his site, and there are a few here that are partially or completely off-grid and have the war stories to tell) but there are a few basic steps...

First thing you need to do is to calculate your maximum simultaneous power draw when everything you may want to be able to run at the same time is running (and allow for the startup surge from those A/Cs). That's going to tell you how big an inverter you need. Those A/Cs or electric heat are going to tell you it needs to be spelled B-I-G, at least 5 or 6 kW big.

Then add up all the power usage, in kilowatt-hours, for those things for the average day. Multiply by about 1.5 to account for system inefficiencies (and the fact that you never want to go lower than about 80% depth of discharge for the health of your deep-cycle batteries). Convert to amp-hours at the DC side and you'll come up with the amount of battery you need to get through a day (whether its 12, 24 or 48 volts is immaterial to that until it comes to selecting charge controllers and inverters).

Then multiply by the number of days of reserve you want in order not to have to run your backup generator because the sun hasn't shone or the wind hasn't blown for a while. This will drive the required battery bank size.

Then you have to determine what resource (wind or solar) you have available to recharge that battery bank. For wind, you're going to need a pretty strong, consistent wind to do that (and without a proper study, almost everyone overestimates how windy their location is). For solar, there are online government databases for the U.S. or Canada that will tell you what the solar resource is like for your location. I'm not sure there's the equivalent for wind. This is probably going to vary seasonally, as will your loads so you may have to look for the worst case on a month-by-month basis.

Once you know the resource (average wind speed, average hours of full-sun equivalent) you can size the turbine or solar panels (or a combination) plus charge controller(s) you need to give you the amp-hours you need to put back into the batteries each day (and you'll probably want to upsize that again in order recover from a few sunless or windless days, although using the generator is still probably going to be required occasionally).

So it all starts with your loads and only you can tell what those are (and what you're willing to shed when your eyes start to pop out at the expense and effort). If you go to Rob's commercial site at solacity.com you may be able to get an idea of pricing.

Not simple stuff. After all that, if you're not too far from the grid you may find its still cheaper to extend the grid to you rather than install and maintain your own micro-grid.

[Joe Blake]

Tommy,

You said in your original post that you were "contemplating" going off grid. Might I suggest that your contemplations include looking at as much 12/24 volt gear as possible. For example I've got two 12v/24v/240v AC freezers which I've been running off about 200 watts of 12 volt fold up solar panels and four 6 volt deep cycle batteries, linked in series/parallel. The older freezer is into its 8th year (I think) and they both run 24/7. When there is plenty of sunshine I can run them off a 600 watt 240 volt AC inverter, but otherwise they can run off 12 volts DC. (When running off 240 volts AC the temperature can get as low as -20 degrees C. At 12 volts, they get down to -5 degrees C.)

There are plenty of other low voltage items available today, so might be worth your while investigating a few of these.

[Dave Schwartz]

An RV already has nearly every appliance capable of running on 12V (fridge/freezer, lighting, water pump, sound system, ventilation fans) or propane (fridge, range, water heater, furnace). The only things that can't are the television (although there are some 12V TVs), the microwave and, of course, those air conditioners and resistance heaters. In most cases, if the RV built-in battery is upgraded to dual batteries, a small-ish inverter can be used to run the TV and microwave as required and a fairly simple and relatively inexpensive solar setup can recharge the batteries. Its those A/Cs and the electric heat that put this in a whole 'nuther league.

[Rob Beckers]

Dave, any time you're turning off-grid electricity into heat you're on the wrong track. Off-grid electricity is too expensive to be wasted on heating (unless you have very deep pockets!). When one runs the numbers it takes a very large amount of electricity to produce a very small amount of heat, which translates to large off-grid systems, in particular since heating is at the worst time of year for solar.

Air-conditioning is somewhat similar, with a twist: A/C units are notorious energy hogs, though more efficient than resistive heating (they're heat pumps). Since A/C is needed in summer, and for people living off-grid the system is sized for winter, there tends to be excess energy at that time of year that can be used for A/C. At the same time, because A/C units tend to be large power and energy users, it drives up the size of the system and that comes at a cost. The long and short is that depending on system size it may be possible to run a small A/C unit in summer, for the larger systems it's usually not a problem, for the small systems it may not work.

Central A/C units, such as for a whole house, are never really an option for an off-grid system (again, unless you have an unlimited budget). I realize yours is a camper so this doesn't apply, this is for anyone else that's thinking of taking a grid-tied house off-grid...

-RoB-

[Dave Schwartz]

Rob, I think you want to dissuade Tommy from using his off-grid renewable energy for heat or A/C, as am I. Tommy posted the original questions.

The difference between a system to recharge batteries with the RV running everything off 12V and propane and one capable of running enough AC into the shore power connection to live like you were plugged into the grid is probably around an order of magnitude (i.e. 10x). If you go for the smaller option, you can probably buy a nice quiet 10kW propane generator to run those A/C's on a few truly unbearable days and be miles ahead both cash and effort-wise. Plus that generator will be a kick-ass backup for recharging after more sun/wind-less days that you budgeted your batteries for.

Tommy: In case you haven't looked at Rob's site for prices, solar wins every time. A Bergey 1kW turbine w/tower is nearly $11k while you can buy twice as much solar panel with adjustable ground mounts for $3k (and the balance of the system will be about the same for either type). The wind may not blow at all for many days but the sun comes up every day so you get something every day (e.g. my 4kW roof-mount solar array is putting out 338W on a day so heavily cloudy you can't tell where the sun is).