| Whenever something technical becomes popular, | | | | which is typical). The second number is even |
| junk science appears. Solar energy is one of | | | | easier to obtain because it is a well established |
| those subjects littered with junk science. Junk | | | | number for the amount solar power that strikes |
| science is often behind the specifications given for | | | | the surface of the earth. That number is 1,000 |
| solar energy systems, such as the key figure of | | | | watts per square meter of direct normal solar |
| efficiency. Sales people are very creative in how | | | | insulation at sea level. The number varies |
| they specify the efficiency of the system they | | | | somewhat depending on your altitude and |
| are trying to sell you. They may talk about the | | | | weather conditions. And depending on the type of |
| conversion efficiency of their solar cells in a | | | | collector the solar energy system uses there may |
| photovoltaic (PV) system, or the efficiency of the | | | | be some other contributors to the total energy |
| power inverter that converts the DC output from | | | | collected. But this standard number is sufficiently |
| solar cells or batteries to AC for use in the home, | | | | accurate for use in evaluating solar energy |
| or the optical efficiency of the mirrors in a | | | | systems. |
| concentrating solar power system. Those are | | | | So how might this knowledge be useful to you? |
| important numbers for the system designer, but | | | | Here is a real example. At the time of this writing |
| not for the end user. So ignore all that and look at | | | | there is a company demonstrating a solar panel |
| the basic measure of efficiency. | | | | with a claimed output power of 3,000 watts. The |
| The basic measure of efficiency of any energy | | | | company claims they have breakthrough |
| conversion system such as solar is simply the | | | | technology that makes it many times more |
| output power divided by the input power, a simple | | | | efficient than existing solar panels available from |
| ratio that must always be less than 1. Simple. You | | | | other companies. They are seeking investors to |
| just need to know those two numbers. Normally | | | | help them build a factory and ramp up production. |
| the output power is readily available. It's usually | | | | Sounds like a hot investment, doesn't it? Let's |
| the first spec given by the data sheet for the | | | | look at the basics of their product. |
| system or by the salesman. But what about the | | | | The solar panel being demonstrated measures 3 |
| input power? Although the marketing types might | | | | feet by 5 feet. That is 15 square feet or 1.39 |
| make it sound complicated and mysterious, | | | | square meters. So the maximum input power |
| determining the input power is very simple. | | | | available, based on that standard number of 1,000 |
| The input power is the amount of solar power | | | | watts per square meter at the earth's surface, is |
| striking the collection area. There are two | | | | 1.39 X 1,000 = 1,390 watts. The claimed output |
| numbers you need to know to figure that out, | | | | power is 3,000 watts. So the efficiency is 3000 |
| the size of the collection area, and the amount of | | | | 1390 = 2.16 or 216%. That's impossible. Efficiency |
| solar power per unit area striking the earth's | | | | can never be greater than 1. You cannot get |
| surface. The size of the collection area is easy to | | | | more power out than you put into an energy |
| calculate. It's the size of the solar panel, that is, | | | | conversion system. I just saved my self from |
| length times width (for a rectangular solar panel | | | | making a very bad investment! |