What's the easiest way to connect an incandescent bulb to a DC only solar setup?

Many car lights are incandescent and run on 12 volts DC.

I think the easiest way would be to get a couple of 12v DC rated incandescent light bulbs which would allow direct connection to the solar system.  Conventional bulbs could be used, but would require an inverter to step up the voltage to 120v and convert from ac to dc.  The latter option would be more expensive and complicated so my thought would be to go with the first.

Eric

How big is your battery?

I assume you are doing this for heat?  If so any bulb that puts out any usable amount of heat will kill a regular sized battery in minutes or hours.  And unless you have some sort of low voltage shut off circuit that light will stay connected until the battery is totally dead.  If you do that 2 or 3 times in the winter you will destroy your battery.

If I were in your shoes I would look for a way to connect a heater or light bulb to the the systems as a dump load(windmills often require dump load heaters and dump load controllers)  That way once the battery is fully charged any extra power gets dumped into the heater.  With such a system you are turning power that would have been wasted into heat.  But it only makes heat when the sun is shining.  You probably need the heat mostly when it is dark.  You can try to store that heat by burying your heating element in sand or rock or some other large heat sink mass.  That way the the mass absorbs heat any time the sun shines and radiates it when the sun isn't shining.  If you combine that with good insulation and stopping air leakage that may be enough heat to stop your pipes from freezing.

Using a battery to store energy to later make heat is often a poor use of resources.  Heat requires a LOT of energy and batteries a very costly once you start trying to store large amounts of power.

Here is a link to a cheap dump load controller
https://www.amazon.com/Controller-Generator-Waterproof-Charging-Regulator/dp/B0C66Y5FWZ
I have never used it, I don't know if it is any good or not but you would need something like this that meets your amps and volts needs.  The controller will put solar power from the panel into the battery until the battery is fully charged than dump any extra power into what ever you have connected as a dump load.  Then if the battery voltage goes down it will automatically go back to charging the battery.

Here is a link to a dump load.
https://www.amazon.com/Longzhuo-Resistor-Hybrid-Charge-Controller/dp/B0B18LV9GT/ref=asc_df_B0B18LV9GT/?tag=hyprod-20&linkCode=df0&hvadid=693458464558&hvpos=&hvnetw=g&hvrand=15747190138966782821&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019361&hvtargid=pla-2015390020938&psc=1&mcid=16dc7befe0b33bd99f5fd4d3cb570860&gad_source=1&gclid=CjwKCAjwupGyBhBBEiwA0UcqaNaE7I5urnDUYra3N0m_X9uYswssmKZtrHmlCIaewVNQYhgesPl-tRoCK4QQAvD_BwE
I have never used this either,  you would have get one that matches your volts and amps.  This could be replaced by any type of heating element or a large lightbulb

Please clarify -- is the bulb an above-ground "warning light" or a heat source?

Douglas Alpenstock wrote:Please clarify -- is the bulb an above-ground "warning light" or a heat source?

Heat source.

Tina Wolf wrote:

Douglas Alpenstock wrote:Please clarify -- is the bulb an above-ground "warning light" or a heat source?

Heat source.

Does your charge controller have a load controller option? What kind is it? They are a good way to control discharge on the battery to avoid killing it. As for temperature control there are a lot of cheap temp controllers. Manual or digital. I've used an ac electric baseboard thermostat before but they are not made for dc amperage. Usually they are derated 90 percent for running DC so about 1.5 amps. You could also use said thermostat to control a DC relay which then switches the light on and off... So first question what voltage are you operating at? Second what charge controller are you using? Third how comfy are you tinkering?

David Baillie wrote: I've used an ac electric baseboard thermostat before but they are not made for dc amperage. Usually they are derated 90 percent for running DC so about 1.5 amps.

Thanks, David. I didn't know that.

Use nichrome wire as a heating element, you can get a 50ft roll for $5. Thin wire will heat up with less power and it is malleable enough to form coils by hand or with a drill

If you do use Nichrome wire you should look up ohms law.  volts =  amps X resistance

You need to measure the voltage and amps your panels produce on a sunny day while it has a load on it to see what it produces.  From there you can figure out how many ohms of nichrome wire you need.  I would suggest buying nichrome 60 wire in 22 gauge.  It is very close to 1ohm per foot so it is easy to figure out how many feet of wire you need.  If you need 10 ohms you need 10 feet of wire.

Also, if you use nichrome wire you need a way to stop it from being a fire hazard, it will get hot and if anything falls on it it can start a fire.  I sandwich mine between slabs of marble that I got as off cuts from a countertop factory(they are the cutouts from sinks and they gave them away for free when I called them up to ask if they would sell them)   By sandwiching the wire it protects it from fire hazard but it also slowly heats up the marble and then the marble slowly releases the heat for a couple hours once the sun stops shining.

An alternative to nichrome wire is a barrel full of water with a water heater element put into it.  The element will heat the water which acts like a thermal battery that slowly lets of the heat.  You don't have nearly as many choices of ohms when it come to water heater elements but you can pick on the one that best suits your needs.  If you are connecting it to more than one panel you can run the panels in series or parallel to best match the ohms of the element you choose.

Most large solar panels are in the 300 watt range.  And they almost never put out their rated power, and they don't work at night when you the the heat the most.  A small space heater can be in the 700-1000 watt range.  So you may need to have 4 to 10 panels hooked up to get the same output as a small space heater plugged into grid power.

First question: Are you attempting to keep the well equipment from freezing? If yes,start by improving the thermal insuation around the equipment you want to protect. Consider a secondary enclosure to reduce the volume of the protected space. The enclosure needs to conserve the heat within it. Most people think only about conductive heat loss, but fail to do a good job seaing up air leaks, the last consideration is radiant IR losses. Then you can get a simple, single contact 120/240vac electric baseboard thermostat to control 12vdc from your battery. 12 volt lamps are available at any auto part store (Or Amazon). Lamps can fail. I would say get a 100 ohm, 10 watt wire wound resistor.