In looking at the power requirements for a home computing system I decided it needs to be as compact and unobtrusive as possible - don't want to upset the neighbors (grin). The alternate power source or sources must be safe to service and maintain. Since I am looking at different alternate power sources and the system is not connected to the local power grid it goes without saying there will need to be some form or forms of power storage. These methods of power storage will need to be safe methods, which goes without saying (grin).
Alternate forms of practical energy:
The following describes a couple of the practical alternate energy sources I have found to date. It is by no means an exhaustive list or comparison of potential energy sources but does describe some of the information that I have collected over the course of the last several months in researching an off-grid power source for this project.
Currently there is a great push to move some of the world's power source to Solar. In the research I have been doing lately there are some very interesting progress being made in this field - specifically in the types of materials used for solar power generation. There is even some talk of solar paint with the capability of generating electrical power from a "paint". If course these types of power sources are still "on the horizon" so I am not looking at them directly. I am keeping more with existing commercially available hardware which limits the list to just the normal silicon-based solar panels or thin-film technologies solar panels. Both types of solar panels available to the home experimenter I think it is the best method to approach solar power applications at the present time. I found a source of thin-film solar panels with a 20-watt rating - but - that is at an output (in direct sunlight) of around 18-Volts. Since normal lead-acid storage cells (batteries) run around 12.8-Volts the actual output from the solar panel will be more along the lines of 13 or so watts. I am trying to keep the cost of this project down to something reasonable so given this solar panel is around $80 I may go this route. As you keep reading you will see why shortly.
Hydrogen/Oxygen Fuel Cell:
Fuel Cell technologies are a "hot" topic, not only in fixed power systems but also mobile power systems. The military and the automotive industry have a vested interest in mobile power sources for reasons I won't go into here since neither have anything to do with my project - I just wanted to mention them in passing as some of the technologies they are looking at also are directly applicable to my project.
Hydrogen/Oxygen Fuel Cells: Ahhh yes - the staple of the space program! Hydrogen/Oxygen fuel cells have been around for a good while and the method of operation is pretty well understood. Place hydrogen gas on one side of a ion-conductive membrane and Oxygen gas on the other side, add a catalyst and a method to conduct electrons from one side of the membrane to the other you get electrical current (the definition of current is electrons moving in one direction through a conductor). Sounds simple enough - but there is a little more to it than that.
First, you need a source of Hydrogen gas as fuel for the fuel cell. There are numerous ways to obtain Hydrogen gas but in my case the only viable method would be electrolysis - the other methods are way to complex for a home system and commercial sized systems usually don't scale down to home-sized systems very well. Secondly, you need platinum for the catalyst material in a fuel cell. While the requirement for platinum as the the catalyst material is not large (requires a very small amount) it is still rather expensive. Third - you need a ion-conductive membrane material that will conduct Hydrogen ions (an Ion is nothing more than a atom with an electron stripped off of it giving it a net positive charge) and handle the heat levels generated within the fuel cell. The membrane material needs to be rather thin to allow rapid transfer of the Hydrogen ions through the membrane but think enough not to break due to pressure differentials across the membrane - usually the membrane is around 10 - 20 mils think. Again - there is a cost factor involved not to mention the construction factor in fabricating a working membrane with the catalyst material coated on both sides of the active areas of the membrane. From some if my research there are sites on the Internet where you can learn to "build" a Hydrogen/Oxygen fuel cell and they don't look too difficult to construct. But - buying the materials to build a fuel cell then actually building one with a fair amount of efficiency are two distinctly different things! Not only are they not so easy to construct you will need to construct multiple fuel cells as they normally only have about 0.5-Volt output - you actually need a fuel cell stack to get enough voltage to be useful. If you are looking to produce around 5-volts, the voltage needed for my project, you will need to either buy or fabricate 10 to 12 fuel cells.
While I am not trying to dissuade anyone from attempting to build their own fuel cell stack it is not something I care to tackle myself - I will leave it to the companies that do that sort of thing best as they have the expertise and required skills to produce viable fuel cells. Besides, I don't have the time nor inclination to go through all of the steps to design and build an efficient fuel cell stack.
A second thing that turns me away from fuel cell technologies for this application is the fact they are still expensive! An average Hydrogen/Oxygen fuel cell stack that produces around 6-volts @ 20 Watts (around 3-Amperes of current) will set you back about $500.00 USD (that is my budget for the whole project!). If you have some interest in PEM (Polymer Electrolyte Membrane) Fuel Cells a good source for them, at a reasonable price, is The Fuel Cell Store for the 20-watt version (pictured to the right). Of course you will still need a method of storing the Hydrogen gas and a way to produce it as well! This fuel cell requires Dry Hydrogen gas at around 3-PSIG @ 280ml/minute to produce 20-watts of electrical power (6.6-VDC @ 3.3-Amps) so you will need at least some method to pressurize the Hydrogen gas and store at least 400+ liters of gas for a 24-hour operational period at full rated power. This does not sound like a simple method to me for achieving a cost effective power system for my project.
Ethanol/Oxygen Fuel Cells:
There exist other types of fuel cells which use a different fuel than Hydrogen. One such fuel cell is the Ethanol/Oxygen fuel cell. The basic operation is the same with one exception - the 'fuel' is Ethanol and the Ethanol Hydrogen/Carbon chain is broken down by catalytic action to release the Hydrogen ions for combination with the Oxygen to form water. Of course the Carbon has to go somewhere which is in the form of CO2 (carbon dioxide - a green house gas). While this form of fuel cell does add to the carbon footprint (releases green house gas) the fuel source is from a renewable energy source - that of fermentation of grains. Since the plants remove carbon dioxide from the atmosphere as part of the growth process you basically are just recycling the carbon dioxide instead of releasing "new" carbon dioxide into the atmosphere as is done with fossil fuels. There are some who would argue this defeats the purpose but in my mind it is not adding to the total green house gas problem. A second advantage with using an Ethanol based fuel cell system is you remove the issues of storing a highly flammable fuel - Hydrogen. To store Hydrogen in any quantity you need either a large storage tank for atmospheric pressure storage of you will need some form of compressor to pressurize the Hydrogen gas for storage under pressure. Given we are attempting to "save" energy it just does not make sense to run a compressor to store Hydrogen gas under pressure. With Ethanol all we need is a storage tank for the liquid - the Ethanol is acting as the 'storage' vessel for the Hydrogen used in the fuel cell system. Personally, I think it is a much more efficient storage system as you remove the possible Hydrogen Gas flammability issue. For those who don't know - Hydrogen Gas has a flammability ratio to air of 4% - 97% which means that anywhere within the two percent ranges Hydrogen is highly flammable - almost to the point of being explosive! The flammability range of Hydrogen is the highest of all flammable materials. Hydrogen as burns at a very fast rate - about 11000 ft/sec which makes it fairly explosive when burned (high expansion rate). Ever wonder why Hydrogen is used as the liquid fuel for the Space Shuttle main engines??? Now you know! Of course there are some current "drawbacks" to the use of Ethanol as a fuel for fuel cells. One of the drawbacks is the need for platinum as a catalyst material in the Anode and Cathode of the fuel cell. There have been strides made in the last year to find suitable, cheaper materials to use for the catalyst materials and it should be only a matter of time before a suitable material or alloy is found to replace platinum in the fuel cell's construction.
Needless to say - a fuel cell solution is not quite there yet but it is on it's way!
There also exists a fuel cell which utilizes Methanol as the fuel source - of course this is probably not the way to go as Methanol is rather toxic and is produced from fossil fuels commercially - not my preferred choice of a deep green system power source and the CO2 released is "new" greenhouse gas as apposed to the CO2 released from Ethanol, which is "recycled".
The more exotic fuel cell systems are basically out of reach for most experimenters so I will not go into them any further - if you are interesting in fuel cell technologies as a whole or are looking for information about them just use Wikipedia and do a search for "fuel cells" - there is all sorts of good, easy to understand information there along with links to more information than a person can read in a lifetime!
There is a great deal touted about the virtues of wind power. Of course you need to live in an area that has wind blowing most of the time to gain an advantage in using wind power! The part of the United States in which I currently reside normally does not have wind speeds great enough to utilize wind power as a viable solution. Needless to say this is one form of alternate energy I can not tap into easily so will not go any further into it.
My Final Solution:
From the previous information I have posted here, which is just a small fraction of the information I have been gathering for the last few months I decided my best option is to use a solar solution for my power needs. Living in Florida has the advantage of a fairly good solar supply most of the time - not as good as living out in the western part of the United States in the desert but over all it is fair. Living at a lower latitude also has the advantage of being able to place the solar array on the roof of the house and not requiring elaborate solar array mounts to raise the angle of the solar array to match the latitude (best for capturing the most amount of energy).
The use of a solar array also reduces the complexity of storing the collected energy for use during "dark" periods as apposed to fuel cell technologies which require storing either highly flammable Hydrogen gas or some form of liquid fuel - such as Ethanol or Methanol. The only additional components for the solar array system is a storage battery and a power regulator to control the charging of the storage battery by the solar array panel. The power regulator can be either complex or simple, depending on the bells and whistles you are looking for. Some allow remote connection by a computer to monitor the system but in my case I only need something to efficiently regulate the solar panel output so as not to overcharge the storage battery. One such regulator is produced by SunGuard and meets all of my requirements. If you are interested you can find more information here: Regulator
The solar array I finally settled on is a thin-film design - in other words the active material is deposited on a thin sheet of glass instead of being built up on a silicon wafer. I chose this design for the simple reason I found a 20-Watt rated solar array for $90 instead of the usual $160+ price you normally find for a 20-Watt solar array! My source is: Electronic Goldmine which is an electronics website for parts. Now - this is just the solar array and needs to be mounted to a support frame. I leave it to you to perform this as there are all sorts of methods to mount the solar array - just be aware it is thin glass and as such needs the proper support to keep it from breaking! By my estimate it is about 1/16th of an inch thick. When I built my mount I used a 3/4-inch X 1-Foot X 3-Foot board as the backing material and a 1/16th inch think piece of glass over the top to protect the actual solar array. The additional glass cover reduced the effective sunlight conversion by about 3% but the tradeoff in protecting the solar array was worth it in my opinion.
Since the power for the computer system will be supplied from a solar cell and the location where I live (and most people on the planet for that matter) is not in direct sunlight 24-hours I need a method to "save" the power supplied by the solar panel. We have the technology! It is called a lead-acid storage cell array (Lead-Acid Battery by any other name). Kidding aside I decided to use a deep-cycle lead-acid battery as the storage medium for several reasons:
Price - a deep-cycle lead-acid batter handles deeper discharge rates much better than the normal lead-acid battery you find in a car or truck. It is designed (uses a higher purity lead and the plates are thicker) to supply current for long durations without causing issues that would occur with a normal automotive lead-acid battery. The biggest issue is the life of the battery itself. Automotive lead-acid batteries are designed to handle the vibration generated in an automobile from such sources as the engine, potholes, out of balance tires and so on. In order to do this the lead contains some impurities to make it harder than it would be otherwise. This "hardening" of the lead allows the battery to survive much better than it would otherwise - at a price. Since there are impurities in the lead they don't add to the total storage capacity of the battery. The impurities also cause other issues when the battery is discharged close to the maximum of it's total capacity - as in the form of conductive material that accumulates in the bottom of each battery cell. Once the accumulation reaches the bottom of the lead plates within the cell they "short" out and will no longer hold a charge. This can cause all sorts of nasty things to occur - even to the point where the battery cell generates enough heat to cause a fire! Not a good thing! A second point is the actual plate construction. Automotive batteries are designed to supply high cranking current to start the engine. In order to do this they are constructed more like a sponge - to increase the total surface area of the plate. The larger the surface area the more instantaneous current can be obtained. The lead forming the "spongy" material is like a woven mesh and is small in diameter. When you deep discharge this type of battery the "spongy" lead gets consumed due to the electrochemical process of releasing the electrical current and some falls to the bottom of the cell as well.
Now - you are probably wondering why I said "price" as the heading here - that is because if you use an automotive battery you will go through around three or more of them as you would using a battery designed for this application. The total "cost" of the power storage system is actually less using the deep-discharge lead-acid battery over the life of the storage system than the total cost using automotive battery technology!
Total Usable Energy Capacity - Automotive batteries have one job to perform and that is powering the cranking system of the automobile to start the engine. They are designed to supply large currents for a short period of time and not designed for deep-cycle operation. Deep-cycle batteries are designed to allow up to 80% discharge whereas an automotive duty battery usually will not tolerate such "deep discharge cycles" without failing prematurely. Once the engine is running the Alternator takes over powering the electrical system in the car and also re-charges the battery back to it's full charge for the next cranking exercise. The automotive lead-acid battery is not designed to output current continuously for long periods of time. They are designed to supply the cranking current needed to start the automobile. This normally is around a couple of hundred amperes of current for a short amount of time. If you ever have attempted to start a flooding engine you know you can not keep on cranking without the battery getting low pretty quickly! When you try to draw low current levels for long periods of time the battery voltage drops quicker than with a deep-discharge lead-acid battery.
Total recharge cycles - An automotive battery does not handle being discharged to it's lowest usable level then recharged very well. The impurities within the lead that harden the lead is the biggest culprit of this issue as well as the actual construction of the plates with a "spongy" lead material to increase the total surface area of the plates. A deep discharge lead-acid battery does not suffer from this issue anywhere near as much as an automotive battery because of the high purity of the lead used in it's construction and thicker solid plates. An additional advantage if the high purity lead is the discharge of the battery is more consistant than in the automotive battery and the re-charge cycle tends to be shorter as well given the total surface area of a deep-cycle battery plate is less than in an automotive battery.
If you are interested in the different types of lead-acid batteries a real good website is:
Wind & Sun who have a great FAQ on the subject - a must read if you are looking to use solar technologies for alternate energy!