I have a solar-powered fan installed on my roof. It blows out the hot
air from the attic, which cools the house. The problem is that when
the sun sets, the fan stops working...but that's when we need it most.

Can I use an artificial light source (like a lightbulb) to power the solar fan?

Hello mah60-ga,

The following pages indicate that an artificial light source such as a
lightbulb can be used to power a solar fan.  However, one page
indicates that the wattage of the bulb is relevant, while another
describes a solar fan which requires a push to set it spinning
(conceivably because the wattage is insufficient).  So, if you decide
you want to try using a lightbulb to power the fan, you might want to
test it first, rather than assume it will work from the first time the
sun sets.

"H-20 - 'Solar Fan Cube'"
Purdue University - Physics Department
http://www.physics.purdue.edu/reports/demo/heat/Ht-20.html

"Simple Solar Cell Demonstration"
New Mexico Solar Energy Association 
http://www.nmsea.org/Curriculum/4_6/PV/simple_pv_project.htm

"Scientific Toys"
Bull Electrical
http://www.bullnet.co.uk/shops/live/scientif.htm

While tutuzdad-ga makes a good point in his comment, I suppose that
there may be a reason for using a lightbulb to power a solar fan at
night: namely, the cost of obtaining, rigging up, or running a
battery-powered or assisted fan.  Perhaps there is a way to place a
bulb near the solar fan in such a way that it does not generate too
much or any heat inside the house (and in such a way that it is safe
to keep lighted every night).  You might want to check with someone
who is skilled with electrical devices as to whether the benefits will
outweigh the disadvantages in your situation.

I hope that this information is helpful.

- justaskscott-ga


Search terms used on Google:

artificial "solar fan"
"light bulb" "solar fan"
"incandescent light" "solar fan"

[I tried other search terms as well, but the terms I have mentioned
led me to the pages I have cited.]

Excellent responses. You have given me some very good options to consider. Thanks!

Wouldn't that defeat the purpose? I mean, if you have a lightbulb
which burns quite a bit more energy than a normal electric ventilation
fan, and to make matters worse, generates even more heat that will
need ventilating, wouldn't it be more efficient to add a battery
powered or battery cell assist to your fan so it can take over during
hours of darkness or on cloudy days?

Seriously, think about this for a minute...you'd be adding a heat
producing electrical light to fuel a solar powered cooling unit.

tutuzdad-ga

Both tutuzdad-ga and justaskscott-ga are entirely right, but if I may
add my zero-cents worth: it all depends on whose solution to choose. 
Depends on what?

(1) How much solar energy your fan needs:  Solar cells are notoriously
inefficient and you might need a big array of spotlights to match the
power of the blazing sun and make enough electricity to power an
extractor fan.  If it's a very light fan, maybe you'll get away with
it.

(2) Complexity.  Solar fans are designed to work when the weather's
hot and lay idle when the sun sets or the sky is overcast.  Your idea
would probably drain so much power that it requires some kind of
complicated control system to save electricity.  That's up to you. 
Also, does the technical solution make sense to you and can you
implement it yourself or do you need a electrician's help?

(3) Money: Will the long-term cost of supplemental power outweigh
getting an electrician to rig you a more professional solution?

If it were my house, I'd probably just install an additional
mains-driven extractor that is turns itself on and off according to
the attic temperature.  The solar fan will contribute to cooling when
the weather's hot and reduce the efforts (and running cost) of the
other, conventionally powered fan.

If you cannot install another fan, ask your electrician to disconnect
the solar panel and run it off the mains controlled by a thermostat.

If you are determined to make use of your solar panel, ask your
electrician if it's feasible to "install a DC power supply, of the
same or lower voltage and wattage as the solar panel in parallel with
the solar panel, but with diode protection on both the panel and the
power supply.".  Also ask for a timer switch on the DC power supply so
that the fan only runs all the time during the hottest period of the
day.

Finally, make sure you have a qualified electrician set up and check
it for safety.