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“Why is it we can launch a satellite costing hundreds of millions of dollars into outer space and operate the thing 24 hours a day, seven days a week for years, using nothing but a solar panel to power it and yet have so much trouble getting a silly light bulb to burn all night long using the same solar panel?”
By Nathan Jones
There are several factors that come into play that must be considered in order to answer this question. The short answer is that it is much easier to power the satellite in outer space than it is to power a light bulb here on earth when using a solar panel. This may come as a surprise to most people, but it is true.
Space facts:
- Since the sun never sets in outer space there is no need to store electricity, eliminating the need for batteries.
- The temperature is constant in outer space so there is no fluctuation in the power production of the solar panel. In fact, the colder the solar panel, the better it performs.
- There is no such thing as a cloudy day in outer space.
All that is necessary is to determine the power requirement of the satellite, hook a solar panel to the thing that makes that much power, and get it into space. Simple! ( We do not mean to imply that the issues of launching and positioning satellites into space is in any way simple, but this article is not concerned with those issues. Rather, we are addressing only the issues of using solar panels to provide the electricity, and doing so as to provide a comparison as to space based vs. ground based systems.)
The earthly light bulb burning all night is a much more complex undertaking. Since we have night and day, the electricity must be gathered during sunny conditions and stored for darkness-- when we want the light to come on. This requires a battery. This is also the beginning of our problems.
Earth facts:
- The length of night and day on Planet Earth is constantly changing and we generate the least amount of power when we need the most.
- We have cloudy days on earth. (In the Ozarks we have cloudy weeks.)
- The angle of the earth in relation to the sun is constantly changing.
- The temperature is constantly changing.
All of these variables come together in winter, and combine forces, to overwhelm the systems’ ability to keep the light on all night. Even with all these variables, it is relatively easy to achieve a 70% success ratio. The remaining 30% is another matter altogether. This 30% is the issue. The long answer is a combination of physics and economics--with a healthy dose of Mother Nature thrown in to keep it interesting.
This elusive 30% is a result of winter. The nights get long, using larger amounts of energy to keep the light burning. The days get shorter-- limiting the amount of solar energy available to store in the battery. The battery gets cold-- limiting it’s ability to store the energy. We have clouds and overcast conditions that restrict the sunlight from reaching the solar panel. The sun dips low over the southern horizon changing the angle of the sunlight striking the panel, and reducing it’s output unless it is tilted up at a steeper angle.
Combine all these factors and you can see why one little light bulb can cause so much grief.
Now to economics. It comes down to money. The 70% success ratio can be designed into a system and marketed, enmasse, with a fairly attractive price tag. To achieve the other 30% requires the price tag to be at least doubled, and sometimes tripled. So most systems engineer up to that 70% success ratio and write off the other 30% to keep the cost down and sell their product. There are two problems with this approach. The first is the end user usually thinks he is getting a system that will work year round, when it will not. The second problem is cost of operation due to this under engineering. The weak link in any solar/battery setup is the battery, and this is always the area where engineering shortfalls manifest. Regardless of where the engineering of the system falls short, the problem manifests in constant replacement of the battery to the end user. Since the mathematical equations needed to comprehend the overall system performance are usually not understood by the end user (or anybody trying to fix the system, in most cases) the end result is the conclusion that “solar power doesn’t work.” So you pick up a telephone and call your buddy in Tokyo to inform him of your conclusion, using the solar powered communications satellite in outer space to discuss your findings.
Clearly, a solution exists. Let’s look briefly at what must be done to find that other 30%.
The Battery
Batteries are temperamental. More specifically, batteries like only one temperature, and it is 77 degrees F. Hotter than that and they begin to discharge themselves at a higher rate. Colder than that and they do not store energy as well. It is the cold that causes most problems, not the heat. (Do you carry jumper cables for your car in July, or January?) The other problem is the discharging of the battery, or rather the depth of the discharge, and the length of time it remains in that discharged state. Batteries like to be fully charged, and even though we refer to some batteries as deep cycle batteries, even they do not like to be deep cycled. A better name would be a shallow cycle battery since this is what they prefer, but we are stuck with the deep cycle name and all the confusion it creates. Let us be perfectly clear on this point- a lead acid battery has no memory and the deeper the level of discharge it is subjected to, the fewer discharge cycles it will deliver. Further, the longer it is left in a discharged state, the shorter it’s life span will be. Put a deep discharge on one and leave it in that condition for an extended period of time and it’s life will be shorter still. This leads to annual replacement of a battery that should provide five or more years of reliable service. When the labor and nuisance cost are factored in, the cumulative cost of under sizing the battery is far more costly than erring on the side of “bigger is better.”
So the first thing that needs to be done is double the original size of the battery capacity to compensate for the cold. It needs to be increased, yet again, to limit the depth it is discharged during the long nights of winter, thereby limiting the damage done to it when it is forced to remain in a discharged state due to a week or more of cloud cover. How much more it needs to be increased is somewhat site/application specific, but seldom does anyone err with too much battery capacity. Rather the opposite is true. Most applications do not have enough battery storage, yet seldom is this addressed when a solution is attempted.
The Solar Panel
This is another area that is usually undersized due to economics, but is seldom acknowledged as the culprit since a mistake here won’t shorten the life of the panel. It manifests in the battery if there is one, and limited power output if the device is hooked directly to the panel such as a water pumping application. Since the batteries need to be charged as quickly as possible, as often as possible, the size of the panel does need to be increased substantially to achieve the elusive 100% success ratio. A good rule of thumb is that it takes at least as much solar panel output to achieve the last 30% as it does to achieve the first 70%, and this is just a starting point. More may be needed but, again, this is a site/application question which needs to be addressed, and that exceeds the scope of this article.
The Charge Controller
Usually the battery charging must be controlled with a device that regulates the charging of the battery by the solar panel. Since the solar panel makes electricity whenever it is exposed to light-- the charge controller serves as a switch which opens and closes depending on whether the battery can hold any more electricity at any given time. They are rated by the amount of amperage they can handle from the solar panel and if the solar panel is up sized, the charge controller must be able to handle the higher current flow.
System Wiring
In most cases these systems are running on 12 volt DC straight off the battery. When the panel size is increased to achieve year round capability the wiring is often inadequate to handle the increased current flow to the battery and must be increased to prevent excess voltage loss, which is critical in a solar powered battery charging setup.
This is in no way an attempt to address all the factors inherent in solar lighting systems, but rather a guide to the problems that routinely occur with these types of systems. If you want a system to function year round in the Ozarks, it is probably cheaper to design and build it locally than to buy an off the shelf unit and try to make it work in our area. The reasons for this are several and we will mention a few notable ones here in passing. The battery enclosure is usually too small to handle the size of the batteries once corrective measures are taken. The mounting pole and brackets are unable to withstand the added weight of the heavier batteries, as well as the additional wind loading requirements the larger solar panels add to the equation in most cases. This alone leads to tremendous cost. Other than the solar panels themselves, there is usually very little that can be used in a system upgrade, and this results in the end user essentially paying for the system twice, not to mention the cost of however many batteries they bought in the meantime, and what labor costs they incurred to change them out.
We will be happy to provide specific data to make your foray into the wonderful world of solar a pleasant experience. While acknowledging that outer space solar power is infinitely simpler to accomplish, we at Power Source Solar prefer the added challenge of designing, engineering, installing, and servicing solar applications here on earth.