diy solar

diy solar

Space heater

Minimoose

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Joined
Jan 24, 2022
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153
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Western Pennsylvania
Was just wondering about running a little space heater on my system. On medium it is 750 watts. I have 4 100Ah AGM batteries wired in parallel and a 3000 watt inverter with 600 watts of panels.(40 amp mppt controller too) Am I thinking right that I'm going to need to up that to 1200 watts of panels to keep up? I'm just bored and the battery bank is just sitting there for emergencies any ways. On a good day I get about 30-35 amps coming in through the controller with a load on the inverter.
So if I'm pulling 750 watts plus inverter losses it would be more like 860 watts correct? 7 amps at 120 volts. So wouldn't I need about 1000 watts coming in? I was just thinking it would be free heat from things I already have even if it's only a few hours a day.
 
I have several space heaters of differing wattage. 1-200w, 1-400w, several at 1250/1500w that I use for load testing and to get out some heating from unused solar panel production in the Winter. I test each heater with a Kill-A-Watt meter since I have found rated output is not actual for these things.

Every inverter amount of loss will be different. If they display watts you can check that against your heaters tested wattage.
 
I have several space heaters of differing wattage. 1-200w, 1-400w, several at 1250/1500w that I use for load testing and to get out some heating from unused solar panel production in the Winter. I test each heater with a Kill-A-Watt meter since I have found rated output is not actual for these things.

Every inverter amount of loss will be different. If they display watts you can check that against your heaters tested wattage.
I checked them with a killawatt and one read 750. The other read 850. Both read 1500 on high.
 
So, you want to run your 'emergency' system, creating the most inefficient heat you can, making zero difference in room heat??
Running batteries down everyday??
The heat isn't really free.
The cost is simply deferred.
 
I already have everything and the battery bank is setting there unused at this point. I realize it's a trade off, but one that is already paid for. I have kerosene backup for heat. This was just an experiment and it worked fine. I have multiple backups for running things in a power outage. This is just one of them. I was just bored and wanted to try it. It would be much more effective to use the battery/inverter for other things. That one little heater would only do a small room any ways. :)
 
In my RV I normally heat it with the propane furnace. I have excess solar production, so I bought a 400 watt space heater. At the time I had a 1000 watt inverter, hence the small space heater. It worked fine as long as I kept an eye on it and didn't leave it running when the sun went down. At night, I'll use it in the closed bathroom when I take a shower so I don't freeze my keister off. Such a small heater wouldn't warm the entire RV to where I want it, but if I have excess PV, I might as well make use of it and reduce my propane bill a bit.
 
In my RV I normally heat it with the propane furnace. I have excess solar production, so I bought a 400 watt space heater. At the time I had a 1000 watt inverter, hence the small space heater. It worked fine as long as I kept an eye on it and didn't leave it running when the sun went down. At night, I'll use it in the closed bathroom when I take a shower so I don't freeze my keister off. Such a small heater wouldn't warm the entire RV to where I want it, but if I have excess PV, I might as well make use of it and reduce my propane bill a bit.
That was kind of what I was getting at. I have enough extra solar to run it on the 750 watt mode. If I hook up 1000-1200 watts of solar to my battery bank the 3000 watt inverter runs it without breaking a sweat and the batteries stay above 13 volts. I have other sources of heat. It was just an extreme emergency kind of test. It's not uncommon here for heavy snow or ice to knock out power here in Pa. We lost power for 12 hours last year. The kerosene heater took care of that though.
 
The concept is simple, even the hardware is minimal. Operate right off the PV array and when the voltage climbs above the anticipated MPP draw off just enough energy to lower the voltage of the panels down to power point. There are dozens of circuits which will accomplish this, a simple shunt regulator. Avoids the need for bigger charge controllers, inverters or batteries. Someone here ought to build a kit. heater1.JPGYou find these oil heaters out on trash day because the electronics fail. Often have two heating elements. With such a large surface area no fan is needed.
 
So, you want to run your 'emergency' system, creating the most inefficient heat you can, making zero difference in room heat??
Running batteries down everyday??
The heat isn't really free.
The cost is simply deferred.
It's a good idea to run the system regularly, but I would probably run the refrigerator.
 
Considering the cycle life of AGMs (which is not bad, but not in the thousands when you're talking about a space heater type of load on 400ah) I personally would not do it outside of an emergency unless you had solar production to break even with the load at least a good part of the time.

If it's something you just want to experiment with, you could always set over-protective voltage cutoffs so that it's basically impossible to actually 'cycle' your battery with a space heater whenever the solar drops out. This is assuming the equipment isn't also powering something else that needs to stay up 24/7.

My space heater + RV experience, since HRTKD brought up RVs, is that I once slept in a little town about 30mi south of the grand canyon in my tiny RV which is a van-based ~23' which means it really only has a ~19x8ft box on it, and even with a heavy blanket blocking off the 'cab' area and FOUR adults and a child in this tiny RV, a 1500w space heater could not keep us comfortably warm in something the size of a small bedroom. I don't remember the actual temp but it was probably in the 20s F overnight. I was actually surprised that it wasn't enough, but it wasn't. I know RVs aren't insulated like houses but i kind of assumed that with all the body heat and blankets it would be ok, and it wasn't!
 
Considering the cycle life of AGMs (which is not bad, but not in the thousands when you're talking about a space heater type of load on 400ah) I personally would not do it outside of an emergency unless you had solar production to break even with the load at least a good part of the time.

If it's something you just want to experiment with, you could always set over-protective voltage cutoffs so that it's basically impossible to actually 'cycle' your battery with a space heater whenever the solar drops out. This is assuming the equipment isn't also powering something else that needs to stay up 24/7.

My space heater + RV experience, since HRTKD brought up RVs, is that I once slept in a little town about 30mi south of the grand canyon in my tiny RV which is a van-based ~23' which means it really only has a ~19x8ft box on it, and even with a heavy blanket blocking off the 'cab' area and FOUR adults and a child in this tiny RV, a 1500w space heater could not keep us comfortably warm in something the size of a small bedroom. I don't remember the actual temp but it was probably in the 20s F overnight. I was actually surprised that it wasn't enough, but it wasn't. I know RVs aren't insulated like houses but i kind of assumed that with all the body heat and blankets it would be ok, and it wasn't!
For a situation like that I have a king size heated blanket. It draws low wattage and will keep you warm. Going to be cold when you get up though!
 
One of my projects, sometime this fall, is to connect my inverter power to run my natural gas furnace. It's a Goodman furnace and there's a good discussion in this forum's archive. I guess getting the neutral right can be tricky. I'm not certain how a major electric grid failure would affect natural gas delivery.
 
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One of my projects, sometime this fall, is to connect my inverter power to run my natural gas furnace. It's a Goodman furnace and there's a good discussion in this forum's archive. I guess getting the neutral right can be tricky. I'm not certain how a major electric grid failure would affect natural gas delivery.
My father has an oil furnace. I got him a 2500 watt champion generator that only weighs 50 lbs. It runs his furnace just fine. He can run the generator on gas or propane. At least I know he will have heat if the electric goes out in the winter. Not sure what brand his furnace is. It's a simple extension cord hook up.
 
In the northeast, some have a 120V power cord coming out of the furnace which plugs into an electrical outlet mounted on the furnace. Ready made for a quick connection to an extension cord going to a generator.
 
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