In the same way that heat collector panels are virtually always promoted unrealistically, the same is true regarding the creation of electricity from solar energy. We regularly hear from people who are attempting and expecting to "become independent of the power grid.". Most have already bought a few square feet of photovoltaic panels, with the various necessary special batteries, voltage regulators, circuit breakers and inverters. Some salesman had told them that they would be able to get several hundred or thousands of watts of elextrical power, or some such figure.
I suppose that technically that is not quite a lie. At noon, on a perfectly clear day, it might be capable of creating the number of watts that was promoted during a sales pitch. In that specific situation, there can be as much as 340 Btu/hr/square foot of solar energy coming down. (Above the Earth's atmosphere, that 'solar constant' is around 429 Btu/hr/sq. ft). If there were 10 square feet of photovoltaics, they could intercept around 3412 Btu/hr, or 1,000 watts, of solar energy. But existing photovoltaic technology is not very efficient, and the quality of photovoltaics often available to the public can be around 7%. That would mean that, out of that 1,000 watts of solar energy coming down to that 10 square feet, only around 70 watts of electricity is actually produced. Could that be called a 1,000 watt system? Not really, if ethics are supposed to be involved, but salespeople tend to inflate claims of such ratings. If around $150 in purchases are involved for each square foot (photovoltaic panels, connectors, voltage regulators, inverters, storage batteries, etc), then that customer spent around $1,500 in the hopes of making electricity. If the customer was informed that for that $1,500, he would, AT BEST, create around 70 watts of electricity, not even enough for a 100 watt light bulb, do you think the customer would pay out $1,500? Probably not! (An industry expert recently quoted on the Charlie Rose Show that one watt of electricity from PV cells has now dropped to around $10. So enough electricity for ONE 100 watt light bulb is now possible for only about $1,000 worth of solar cells (plus installation, controls and batteries).
It's even worse! The problem is, at 2 pm, it is liable to be down to 800 watts of incoming solar energy, but that is still on a perfectly clear day. Chicago in winter only has around 35% clearness of skies. So, on the average, that means 330 watts of incoming solar energy at noon and 270 watts a while later. In an entire clear day, around 5 kWh might arrive as solar energy, That would only average 1.7 kWh per day considering the cloudiness of the region. Once we consider the 7% efficiency of the solar energy to electricity conversion of the photovoltaic cells, we are talking around 120 watt-hours of actual electricity created on an average day! A whole day of collecting solar energy with that $1,500 setup, to get about enough electricity to light a 100 watt light bulb for a little over an hour! Sad, isn't it?
(The salesman for those products will tell you far more attractive things, of course, so that you will spend that money. After all, he knows that you really do not know that much about solar energy and photovoltaic cells, and that he has a tremendous advantage over you. He knows that you really have no way of telling whether what he is telling you is accurate or exaggerated. And if it later doesn't work remarkably for you, exactly what options do you have? He technically didn't lie when he described how it performed in perfect laboratory conditions under intense desert sun!)
At current electric rates, that would be a savings of around one or two cents per average day, or about $7 per year. Now, does it make sense to pay $1,500 for any device that would save $7 per year? Or with a bigger, more expensive system, to pay $5,000 for a system that would save around $25 per year in electric bills?
If it lasted for 200 years, without needing any maintenance, and if you didn't consider the interest you would have earned in the bank with that $1,500 or $5,000, it might eventually pay for itself. After that 200 years, under those conditions, it might start producing actual savings. Do you see why that current photovoltaic electric systems are nowhere close to being cost effective?
In addition, the electricity is created as Direct Current, like a battery. And, without some sort of storage, it would just disappear and be wasted. So, you have to have substantial exotic batteries to save that potential of actual useful electricity that could be collected in a day. And, unless you intend to only use appliances that use direct current, you would need an Inverter to convert the electricity to 120 volts AC. These devices have losses, too, so final performance is reduced.
The most common of our blowers uses around 700 watts of electricity. The off-power-grid people expect to use their $5,000 photovoltaic setup to run all kinds of appliances and lights and the JUCA blower. However, that $5,000 electricity creation system, on a nicely sunny day, could create only around 350 watt-hours of electricity, enough electricity to run ONLY the JUCA blower for around half an hour that day/evening! So there would not even be enough electricity to run one device (the blower) through the night! If they could absolutely count on perfectly clear days, around $50,000 of photovoltaic equipment would be able to collect create around 3500 watt-hours of electricity, enough to keep the blower running for five hours of the evening. For Chicago, with its 35% clear skies, around $150,000 of photovoltaic equipment would be necessary JUST to run the blower for a few hours on the $1,400 woodstove! Seems pretty expensive, huh?
The general point being made is that salespeople of photovoltaic equipment tend to make very impressive claims for the performance of what they sell, in order to justify the rather high prices. But, since it is NOT sunny 24 hours a day, and any climate has cloudy days, and very little solar energy is collectable early or late in the day, the reality is that benefits are FAR less than the ideal scenario presented during the purchase! If you're seriously considering such equipment, ask to talk about these matters with several owners (who are NOT connected with that company!).
Next, you need to find the ACTUAL efficiency of the specific photovoltaic panel you will use. NASA has some that are better than 15% efficient, but you probably cannot afford them! And salespeople rarely admit to just what that efficiency is. They, as salespeople, will sometimes make outrageous statements, like 99% efficiency, or 70% or whatever they think you might believe. Hey, they are trying to earn a commission on whatever they might be able to sell you! The actual WRITTEN documentation on percentage efficiency is hard to get to see, but that is the number you need. As indicated above, for photovoltaic panels that are generally available to the public, they are rarely over around 7%. (So now we're down to 1,000 * 0.07 or 70 watts of electricity, at noon, when it is perfectly clear).
In winter months, the Sun drops down pretty quickly each side of noon, so there is limited benefit more than a couple hours away from noon. If you figure a daily total of about the equivalent of three hours of noon Sun, that will probably be close. You could always actually calculate the amounts, or look them up from the ASHRAE Handbooks! In summer, the Sun stays higher for longer times, so the equivalent daily total can be five hours of noon Sun. (Now we're at daily totals of 210 watt-hours in winter and 350 watt-hours in summer.)
At this point, you should call your local newspaper or weatherman, or again, look in the ASHRAE Handbooks, to find the cloudiness for your city for that month of the year. (Continuing our example, for Chicago with its 35% clearness [65% cloudiness], we then get from 70 watt-hours [winter] to 120 watt-hours [summer] of realistic electricity being created in an entire average day.) You probably pay around ten cents per kilowatt-hour of bought electricity, so these are on the order of one penny's worth of electricity saved per day.
Those numbers are REALLY different from what any salesperson describes, in trying to sell photovoltaic systems to you! You might want to print out the previous four paragraphs, so you can take them with you. You could then ask him to show you how he got the impressive numbers he claimed to you! He cannot make the Sun brighter than it is, and until tremendously better photovoltaics are invented in the future, their conversion efficiencies are hard to brag about. The logic of the above paragraphs is very straightforward, and pretty simple. You are now in a position to confirm or deny any claims he might make to you about how much electricity you will generate!
The Earth's Rotation as a Source for Energy
Waste Nuclear Power For Making Electricity And Heat?
The Physics of Efficiency In Electric Power Plants
Individual Ways of Reducing Your Energy Usage
Methods of Storing Energy for Later
How Much Energy Comes From the Sun? And Why is there Global Warming?
How does the Sun create so much energy?
Inventions Which Might Help Deal With Coming Energy Catastrophes
An Invention to Efficiently Make Electricity from Solar
Enormous Heating of the Atmosphere by the Alaska Pipeline
Air Conditioning without Huge Electric Bills and without Freon
A Method of Storing Summer Heat to (Nearly) Entirely Heat a House all Winter
An Extremely Highly-Efficient (and Fast, 200.0 mph) Transportation System for People and Products
The Sophisticated Woodstove I Invented in 1973
The Physics of Wood as a Heating Fuel
Why is the North Pole Heating Faster than the rest of the Earth?
A Possible way to greatly reduce Aerodynamic Drag of Airplanes
Solar Heating
Free A/C.