Solar Electric Heating

[lkruper]

I understand that solar is not cost effective for resistance heating, so lets get that out of the way I am considering building a shed at my cabin primarily to get storage space. If I design it correctly, there is a southern gap in the trees that I estimate might get good exposure about 1.5 hours before an after solar noon. I would like to have some solar emergency backup to supplement my generator. Grid-tie won't be an option, and I think I can fit about 1000w of panels (eg 4 250w panels) on the shed roof.

We do not heat the cabin when we are not there, and the only options to heat are 1500w plug-in heaters or the fireplace. We use the fireplace almost exclusively. When we get to the cabin after being away, it is cold. It takes a while to take the chill off and after a few days it seems to retain heat mass and is more comfortable.

My thought is that if I have 1000w of panels, and if I used it to keep a small battery bank for emergencies in float and to charge in an emergency, I would have a lot of excess solar. Wouldn't diverting that power to some sort of resistance heating in the cabin every day take the edge off the cold?

I have read that it is not safe to keep a resistance heater plugged in and operational when one is not present. What about an incandescent light source? (Thinking out of the box). Don't bulbs efficiently turn electricity into heat as well? And would that be a safer alternative to use unattended? Something like a 250w heat lamp?

Any better ideas?

[SunEagle]

I understand that solar is not cost effective for resistance heating, so lets get that out of the way I am considering building a shed at my cabin primarily to get storage space. If I design it correctly, there is a southern gap in the trees that I estimate might get good exposure about 1.5 hours before an after solar noon. I would like to have some solar emergency backup to supplement my generator. Grid-tie won't be an option, and I think I can fit about 1000w of panels (eg 4 250w panels) on the shed roof.

We do not heat the cabin when we are not there, and the only options to heat are 1500w plug-in heaters or the fireplace. We use the fireplace almost exclusively. When we get to the cabin after being away, it is cold. It takes a while to take the chill off and after a few days it seems to retain heat mass and is more comfortable.

My thought is that if I have 1000w of panels, and if I used it to keep a small battery bank for emergencies in float and to charge in an emergency, I would have a lot of excess solar. Wouldn't diverting that power to some sort of resistance heating in the cabin every day take the edge off the cold?

I have read that it is not safe to keep a resistance heater plugged in and operational when one is not present. What about an incandescent light source? (Thinking out of the box). Don't bulbs efficiently turn electricity into heat as well? And would that be a safer alternative to use unattended? Something like a 250w heat lamp?

Any better ideas?

The best "bulbs" that turn electricity into heat would be those infrared heat lamps used to keep food warm. But I can tell you to generate enough BTU's of infrared heat generation to get your cabin warm will drain most small batteries quicker then you can blink.

On top of that with your small window of solar charging those batteries will never get back up to 100%.

You might think about those thermal blankets to wrap in while waiting on that fire to warm things up. Or maybe you can "super insulate" the cabin to reduce the temperature drop.

[lkruper]

The best "bulbs" that turn electricity into heat would be those infrared heat lamps used to keep food warm. But I can tell you to generate enough BTU's of infrared heat generation to get your cabin warm will drain most small batteries quicker then you can blink.

On top of that with your small window of solar charging those batteries will never get back up to 100%.

You might think about those thermal blankets to wrap in while waiting on that fire to warm things up. Or maybe you can "super insulate" the cabin to reduce the temperature drop.

The cabin was build in 1929 (single pane windows cannot be changed due to historic reasons) and I have heavily insulated the ceiling and below the floor but there is not much I can do about the walls without major construction, and when the wind blows hard, it can be felt inside! The fireplace actually heats up the place pretty good, and when sitting in front of it (which is most of the cabin!) it feels pretty good. I am just thinking that even a few degrees higher might be welcome. I really don't want to use battery capacity either, so I was looking for DC powered lights and perhaps a charge controller that has a load mode, but I know very little about either of those.

[Wy_White_Wolf]

Look into dump load charge controllers. They will send the excess to a resistance load when the battery bank is fully charged.

I would not consider lights as a dump load on an unmonitored system. What happens if a light burns out? Then you excess has no place to go so you end up overcharging the batteries. A resistance heater would be better. One could build a insulated tank to hold antifreeze and use DC water heaters. Your dump load also has to be at least as big as the solar array.

WWW

[lkruper]

Look into dump load charge controllers. They will send the excess to a resistance load when the battery bank is fully charged.

I would not consider lights as a dump load on an unmonitored system. What happens if a light burns out? Then you excess has no place to go so you end up overcharging the batteries. A resistance heater would be better. One could build a insulated tank to hold antifreeze and use DC water heaters. Your dump load also has to be at least as big as the solar array.

WWW

Thanks. I was wondering why Morningstar discouraged the use of lights in favor of water heaters. That makes sense. I have also seen some air resistance heaters advertised, but do not know if they recommend them inside living quarters unattended.

I also see that there is a third mode in the Tristar Morningstar with is a diversion mode which allows for LVD for the battery as high as 75% SOC which might not have the same limitations as Dump mode and also not sacrifice the battery. That might be ok to use with heat lamps.

[asdex]

Hi, I'm using excess power once the batteries are charged to heat water via a solid state relay and it works well. I'm using a 24 volt 900 watt element. If it did burn out the charge controller wouldn't let the batteries overcharge. You only have the problem of dump load reliability when using a wind generator.
Maybe you could have the load resistor in the fire place where it would be safe. Block the chimney though.