Myth of Photo-Voltaic Solar Power?
I felt that this part of a previous post deserved promotion to its own post:
The Myth of Photo-Voltaic Solar Power?
Solar power provides about 1,000W (1kW) per square meter at the equator's sea level. However, typical photo-voltaic (PV) solar panels are only 15% efficient so a square meter of solar panels provides only 150W. Further, even compact fluorescent lights (CFL) are only 20% efficient so 150W of CFLs provide only 30W of light. Incandescent light bulbs are only 5% efficient so 150W of incandescent light bulbs provide about 8w of light—less than 1% of the solar power that hit the solar panels.
So, the expensive “solar” system is 97-99% inefficient at providing electric light.
(For a similar reason, PV solar-electric water-heating is less efficient than passive solar water-heating which puts the water tank in direct sunlight.)
Then consider that the sky is not always clear and sunny. Solar panels will generate less in winter and more energy in summer because of the number of daylight hours. However, even a seemingly clear day might have particles that reduce available power to 80%, moderate clouds can reduce available power to 33% and heavy clouds can reduce it to 5% (a 45W panel would provide about 2W).
What do you get at the end of the day? The Southwest USA accumulates the equivalent of about 5 full sun hours per day. However, much of the US population should expect only about 3 hours or less of full sun equivalent per day (at 3 hours, a 45W solar panel would provide 135Wh per day, which might power a medium TV for 1 hour per day) . Northern Michigan should expect only 1 full sun hour per day (a 45W panel would provide 45Wh per day, which might power a 60W light bulb for about a half-hour per day after accounting for system inefficiencies).
Backup power should be independent of what it is replacing, or have an inverse relationship to it. The obvious disadvantage of solar-electric lighting as a backup to natural solar lighting is that you are trying to squeeze more energy from the very thing that is disappearing on you.