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Archive for the ‘Off-grid’ Category
Thursday, June 18th, 2009
We’re from Alaska and thinking about buying 20 acres where electricity is nowhere to be seen.
And since the sun is scarce in the winter, we’re wondering what kind of a generator-battery-inverter system would be advisable and what’s the approximate cost of setting it all up?
Wind power is not an option either, as the data shows less than 5 mph, year round.
Any advice would be greatly appreciated.
You guys are in a tough place. I have talked with many folks from there and your choices are limited.
The first thing you need to do is really limit your electrical usage. I assume you will be using a wood, oil, or propane cook stove, space heater, and water heater. I would not have any heating system that requires operating a central fan or air handing unit as these require lots of power.
I would use only a few low wattage compact fluorescent and mostly LED lights for lighting, and buy only very energy efficient short wave radio, flat screen TV, computer, and video equipment. You must lower your energy needs first, and it’s worth paying extra for the higher efficiency devices.
Batteries do not like the cold, so they need to be above freezing. Diesel generators do not start when it drops below freezing unless you use crankcase and carburetor heaters, and you cannot run these high energy loads 24/7 on battery power. This means you need to find ways to keep the generator area above freezing.
Solar systems can work that far north for the periods of the year when the sun shines, but a generator-battery system will be needed the rest of the year.
I would check with neighbors to see how they deal with this.
Monday, March 2nd, 2009
Putting together an off-grid system, I am inquiring as to how best choose/purchase the solar panels for optimal efficiency in relation to their voltage output. There are panels that put out similar wattage, however the vp/imp can vary greatly.
Let’s imagine for example the system objective is approximately 2kw using a 24v to 110v inverter with battery back-up.
Which would be the best solar panels to use for maximum efficiency?
* 12 – 160w panels @ 24vp/6.80imp
* 10 – 190w panels @ 26.7vp/7.12imp
* 10 – 190w panels @ 17.8vp/10.96imp
* 10 – 200w panels @ 53.8vp/3.16imp
As we say on the web site, we cannot answer specific design questions because there are too many variables we would not know about your specific application, and we are trying to keep this a free service. However, I can provide some general answers that should help you narrow down your choices.
First, there are many things that go into the design process and the first is inverter input limits if grid tie, and solar charge controller input limits if battery based. In other words, if your solar charge controller has a limit of 75 volts DC input, this will require the number of solar modules wired in series to be well below this high limit. The NEC Article 690 provides more specific design guidelines related to safety multipliers that you must use.
The maximum input amp rating of the solar charge controller (or inverter if grid tie) will determine the maximum number of parallel strings and total amps from the array after the required NEC design multipliers are added.
Once you know the maximum voltage and maximum current your system can safely handle, this will define the solar array that your system can handle. Once you know this maximum total array wattage, you want to select the highest quality module you can buy that has the lowest cost per watt.
Take the total delivered price of a specific module and divide by nameplate wattage to get the $cost/watt.
If this process does not give you the solar array you want, then you will need to make changes to the inverter if grid tied, or the solar charge controller if a battery based system. Normally I first select the exact solar array wattage and physical size I want for a specific budget, then I select the inverter if grid tie, or the solar charge controller if battery based, but it sounds like you are working backwards and trying to base you design on comparing output voltages and amp ratings of the modules to fit a specific requirement.
In other words, its like taking a car and trying to replace the engine with a bigger engine to get more power. However, if you do not also upgrade the transmission, tires, drive shaft, fuel system, exhaust system, and brake system, then the vehicle cannot take advantage of the higher horsepower.
Hope this helps,
Monday, January 19th, 2009
I need to power a 12 volt DC pump with solar power and I’m not sure how to do it.
I need to feed water into an irrigation system in a remote location where there is no water or electricity on-site (it’s for a native habitat restoration project). The water was trucked in and put into a water pillow. I need to place a timer on the system, but the water pressure is too low for the valve to work. So I’m going to install a surface pump to push water through the valve and I need to power it with solar power. And I’m on a very limited budget.
I have spent a good deal of time searching the Internet, but I can’t figure out if I can hook the solar panel directly into the pump (I don’t need to water at night). I would like to avoid using batteries, if possible. It seems that I need a pump controller, but the ones I have found cost several hundred dollars and don’t look anything like the one in your article on solar water pumps.
I guess you already considered the obvious, move the water pillow to higher ground and you won’t need the pump! Assuming that has been considered, it’s not a problem to install a solar panel, DC pump, DC timer, and DC valve. However, it is a problem to do this “on a limited budget”. Like they say, you can have any 2 of 3 order choices - fast delivery, quality construction, cheap price, pick two!
You did not mention if this is a drip system not requiring very much water pressure, or some type of spray heads that require higher pressure. The water pressure and flow rate will determine the size of the pump. Once that has been determined you can select the solar array size that will provide this amount of power per day. You must have a solar controller wired between the solar array and pump, and several safety devices like a low water cut off to protect the pump if the water bladder runs out of water.
All this equipment is off-the shelf, but is not cheap. I don’t know your pump size, but most small DC pressure pumps will cost over $1,000, plus about $2,000 for the solar array and another $600 for the controls, plus some type of pole support for the solar array. If you don’t spend the money to do this right, you will most likely have some dead plants when the lower cost system fails.
Sunday, January 18th, 2009
Interested in knowing the economics comparison between a grid-tie v. off-grid system.
For simplicity, let’s imagine a 2Kw grid-tie system can be installed complete for $12,000, with no battery back-up. Also an off-grid system can be installed complete for the same price of $12,000 inclusive of battery bank.
In the course of 10 years, in comparison, which system will normally provide higher dividends?
If more details are needed for the overall scenario, please ask.
You are comparing apples and oranges so this choice makes no sense. If your goal for installing a solar system is to provide the most utility cost savings for the lowest initial cost, then any grid-tie system without batteries will have the lowest cost and will provide the shortest payback. For comparison purposes, inverters designed for grid-tie sell-back without batteries are usually a little more efficient than inverters designed to charge a battery bank, but this is not the real reason you would choose one over the other.
Any solar system with batteries cost more for the inverter and switchgear, costs more for the batteries, requires battery maintenance, takes up valuable heated interior space that could be used for other purposes, the costly batteries must be replaced every few years, and as stated above, the inverters are less efficient in sell-back mode. Yet, there are lots of battery based solar systems sold each year and the reason is very simple. People buy a more expensive battery-based solar system because it provides peace of mind. If you are in an area without grid power, it provides peace of mind of having reliable power without running a generator 24 hours per day. If you on the utility grid but in an area where there are lots of power outages, it provides the peace of mind that your freezer, lights, and other appliances will continue to operate during brief power interruptions. If you live in an area that has gone weeks at a time without power due to yearly storm damage, you have the peace of mind that any future storm will have only a minor impact on your lifestyle or perhaps your home-based business.
People place a high value for this peace of mind and do not calculate this in terms of payback or return on investment, just like you would not purchase a fire extinguisher or security system based on a cash flow analysis.
Hope this helps,
Monday, December 15th, 2008
My weekend cottage is powerless at moment, but running the lines to attach it to ‘the grid’ is estimated to cost $16,000 ! I am approx. 300 yards away from nearest power box. So instead of doing grid tie solar, I am now contemplating off grid solar and looking at generators for backup.
Sounds like diesel is the way to go for reliability and low maintenance, which is my biggest goal. I am willing to pay a little more for this.
My question is, what do you think of running Biodiesel in most modern diesel generators? Is this feasible? Is this for summer time only? (I live in northern Wisconsin, and wonder if Biodiesel mixes would freeze!).
I’m trying to be as ‘earth friendly’ as possible.
Being totally off-grid is not as easy as you think unless you have lots of solar modules and batteries, and really limit the use or quantity of larger appliances. Having said that, depending on your solar exposure and location, the more solar you have the less generator run time so fuel type may not be a big issue.
Some diesel engine manufacturers will void their warranty if you use bio-diesel, although this is changing as manufacturers get more experience with bio and the quality of the fuel processing improves. However, not only bio-diesel, but regular diesel fuels can be a real problem during the winter unless you use crank case heaters, fuel pre-heaters, and other heating devices to prevent the fuel from turning into gel. If you think solar is expensive just to run a few appliances and lights in an off-grid home, wait and see what it will cost you in batteries and solar modules just to power a crank case heater on a diesel generator all winter !
This is why many backup generators are propane. The fuel does not go stale, it does not freeze, and you don’t have to worry about it turning into a semi-solid in the fuel lines. A fill up once a year to a 500 gallon underground tank should not only give you many months of backup power, but can also be used in a gas stove since you will not be able to have an electric stove in an off-grid home.
Hope this helps,
Saturday, September 6th, 2008
Having recently bought some land in Missouri that is located out the the sticks and very much at the end of the power grid. I have pretty well deduced that I will need some back up power.
Recently I have discovered the backwoodshome.com website and a number of your articles. As one who is not totally familiar with alternative power like wind and solar, everything I read seems only to confuse me more.
With interest I have read about l-16 industrial batteries for a battery bank in some articles. In an article about adding a solar cell to a truck camper a RV/marine battery is recommended. Since RV/marine batteries are easy to find and will take to repeated charging wouldn’t they be logical choice for a battery bank vice the harder to find L-16?
I have noticed too that with wind power most often suggested is a dc wind generator that requires upwards of 6 or 7 knots of wind to operate. In searching around I have found a source for a AC wind generator that begins operation in the sub 7knot range. AC generators have to best of my knowledge a big advantage over DC generators and that is in size of the cable between the transmission line from the tower to the battery bank. An ac generator can use a standard ac power cord and suffers no loss in current between the tower and batteries.
I have to admit that my understanding of the way a ac generator works is taken from the following website: http://www.tlgwindpower.com/default.htm On the opening page there is a photo of a customer using 9 ac wind generators on his farm in Wisconsin. Although wind power as such is confusing to me I believe that this ac system must be quite good or the farmer who had added to it and bought these generators would not be doing so if they weren’t efficient.
Perhaps you can give some insight into battery banks and DC versus AC generators in a future story. Also the battery bank issue of l-16 versus marine batteries is very confusing to a novice seeking information like myself.
Any information you can provide along these lines would be greatly appreciated.
Lots of questions! Actually you are talking about “L-16″ batteries, not “I-16″. When I suggest using an RV/Marine battery, you will find that it is for a small 12-volt DC system that does not have a large load that would fully discharge it each day. These batteries are much heavier duty than a typical car battery, and most have re-combiner caps and do not need to add water. However, they will NOT hold up to a daily deep charge/discharge cycling like a solar powered home or cabin. For these larger loads and system sizes, the lowest cost battery designed for a heavy charge/discharge cycling each day is a 6-volt golf cart battery ( T-105 size). These are less than $100, and can be found at most big box stores during the summer months. They are about the same size as a car battery, but because they are 6-volt, the plates are very thick and very heavy.
For a 12-volt system you will need two 6-volt batteries wired in series, and for larger systems you will need 4, 8, or 12. When you start getting above 8 batteries of any size, its better to switch to a larger amp-hr battery and stay less than 16, as this can cause problems with un-even charging and dis-charging when you have multiple strings of parallel batteries.
I think you are caught up in the AC or DC debate as a marketing ploy. There is no engineering difference in the amount of wind it takes to turn a wind turbine based on AC or DC output voltage. Wind energy is a “cubic” function of the area of the blades, and below around 7 MPH I think you will find most small-scale generators will not provide any real power, although the blades might turn. There are now both AC and DC wind turbines and each has its advantages, but only in wiring and additional equipment that will be required.
A 24 or 48 volt DC output wind turbine is very easy to add to an existing solar-power system, and some models have built-in charge controllers and can be hooked directly to the batteries. Yes, this will require a larger wire size since the voltage is lower, but the ease of wiring is its real advantage. Also, unless you are talking about some huge wind machine on a 150-foot tower, the difference in wire costs would most likely be less than 50 cents per foot for the larger wire caused by using a lower voltage DC model. An AC wind turbine can use a smaller wire size since the voltage is higher, and these are usually designed for grid-connect systems without batteries. There are a few other issues, but you cannot say an AC unit works better than a DC unit having the same size and blade design, and the reverse is also true.
Thursday, September 4th, 2008
I read your article on a Battery Powered Weekend Retreat.
We have some land in Western North Carolina and was thinking of a Hybrid Solar-LP Gas Generator system to power a single wide home. Our property also faces the north with tall pine trees so not the best for Sun.
Would it be possible to build the same type system for a single wide home? Would I be able to use the AC Refrigerator Energy star and TV’s?
I was thinking the Solar could keep it charged while we are gone and the Generator would come on every couple of hours to top off the Batteries.
Would one of the Kohler 7KW generator work?
Size and type home has less to do with hybrid system sizing than your estimated power needs. However, most systems will need a large battery bank which can have a total weight of almost one ton (2000 pounds) so your single wide will not be able to support this and you will need a separate storage shed or garage to install this equipment. If you install a quality inverter that is sized properly you can use almost any type appliance, but don’t forget that most well pumps are 240 VAC and most inverters are 120 VAC so you will either need two inverters or a step-up transformer if you have a well pump.
Sunday, August 24th, 2008
My cabin in Utah is almost complete. Solar equipment is on the way. (2) panels, (8) batteries, outback inverter, etc. Outside is done. Basically trim work and plumbing left on the interior. My question is what would you recommend for water heat. I am looking at tankless heaters. Do they pull a lot of electricity or should I go propane? Also, what is your opinion on composting toilets?
Don’t even think of using electricity to heat water. We rarely do this with large systems, much less a system the size you described.
You have 3 choices depending on how much you use this cabin and access.
My first choice is an instant tank-less hot water heater as some brands like a Infinion does not require any electricity and uses just propane. The problem with any tank-less water heater is there piping will quickly freeze if the home is not heated while you are away and should be drained each time.
My second choice is a solar hot water heater, which you can buy with an optional DC pump powered pump which uses very little battery power but also can freeze when away for long periods if not properly designed and installed.
If you are not lazy, several companies still make a wood fueled water heater that is an old style insulated water tank with an internal flue pipe and a fire-box below. most hold less then 30 gallons, so they heat up fairly quickly when you build a fire. However, their fire-box is small and will not hold much wood so don’t expect to have hot water all day after building one small fire. There are also hot water heating coil options for many standard wood cook stoves that can heat a separate insulated water storage tank.
I own 2 composting toilets, one in a garage and one in a trailer. They are great if you do not have a large family. For one or two people, you may be able to go many months without emptying the recycled soil and you only need to add a little compost material each time it is used. They also make larger models with a separate holding composting tank located under the floor and separate from the seat part. These usually requier an electric motor and some even have electric heaters so keep it simple.