Looking To DIY Solar + Battery System for Space Heater

[speculant]

I have a 1500VA UPS that has connectors for 12V SLA batteries. It has fans so it should be able to run for long periods without any issues (I am aware of the issues with running a fanless UPS for long periods so I'm not trying to do that). There is a local seller nearby selling some used ENERSYS 190Ah 12v batteries. I'm still waiting on a response back concerning the battery condition/how long they were used for/what environment, however the seller has high ratings on both platforms they are selling on (OfferUp and FB Marketplace), and they seem to specialize in battery sales based off their listings (so they seem at least somewhat trustworthy). Cost per Ah on these batteries is the absolute best I can find locally so I would like to get some of these batteries and connect them up to my 1500VA UPS in order to run a 1500W space heater in the winter. The winters where I live are cold at night but not below freezing so a 1500W space heater is usually enough for the entire space I'm in at the moment.

However, I'm not sure how many 190Ah batteries I'll need to run the 1500W load basically continuously for half the day (at night when it's coldest) and I'm not sure how many solar panels at what wattage I'll need to charge it during they day when it's sunny (it is not usually too cloudy in the winter where I'm at). Also, I'm not sure what the best way is to connect the solar panels to the batteries with the batteries also connected to the UPS (I would want to keep costs down so I'd like to use the UPS as the DC -> AC and just use 12V solar panels with an SLA charging controller also connected directly to the batteries if possible).

As a side note, I ran a tool on the APC website to find out what UPS products they recommend for running a 1500W 120V load for 9 hours and they recommend a system with 750Ah worth of 12V batteries. If that is accurate, than this project may be out of my price range for the moment, but I'd like to get the advice of the experts on this forum before I proceed and waste a bunch of money trying to go in the wrong direction.

 

[Ohms42pA]

I have a 1500VA UPS that has connectors for 12V SLA batteries. It has fans so it should be able to run for long periods without any issues (I am aware of the issues with running a fanless UPS for long periods so I'm not trying to do that). There is a local seller nearby selling some used ENERSYS 190Ah 12v batteries. I'm still waiting on a response back concerning the battery condition/how long they were used for/what environment, however the seller has high ratings on both platforms they are selling on (OfferUp and FB Marketplace), and they seem to specialize in battery sales based off their listings (so they seem at least somewhat trustworthy). Cost per Ah on these batteries is the absolute best I can find locally so I would like to get some of these batteries and connect them up to my 1500VA UPS in order to run a 1500W space heater in the winter. The winters where I live are cold at night but not below freezing so a 1500W space heater is usually enough for the entire space I'm in at the moment.

However, I'm not sure how many 190Ah batteries I'll need to run the 1500W load basically continuously for half the day (at night when it's coldest) and I'm not sure how many solar panels at what wattage I'll need to charge it during they day when it's sunny (it is not usually too cloudy in the winter where I'm at). Also, I'm not sure what the best way is to connect the solar panels to the batteries with the batteries also connected to the UPS (I would want to keep costs down so I'd like to use the UPS as the DC -> AC and just use 12V solar panels with an SLA charging controller also connected directly to the batteries if possible).

As a side note, I ran a tool on the APC website to find out what UPS products they recommend for running a 1500W 120V load for 9 hours and they recommend a system with 750Ah worth of 12V batteries. If that is accurate, than this project may be out of my price range for the moment, but I'd like to get the advice of the experts on this forum before I proceed and waste a bunch of money trying to go in the wrong direction.

Amps x Volts = Watts.
Add inverter effeciency to the equation than divide by load.

Edit, roughly 1 hour run time per battery.

 

[acdoctor]

So 1500 watt load x 1.2 efficiency of inverter is 1800 watts.
1800 watts x 12 hours is 21600 watt hours / 12 volts is 1800AH consumption, at 50% discharge you need 3600 AH of battery capacity. 3600 / 190 is 19 parallel 12 volt units.
The most parallel SLA units recommended by most manufactures is 3. This is because they won’t charge and discharge equally.
I doubt your ups has 150 amp 12 volt input connections.

 

[speculant]

So 1500 watt load x 1.2 efficiency of inverter is 1800 watts.
1800 watts x 12 hours is 21600 watt hours / 12 volts is 1800AH consumption, at 50% discharge you need 3600 AH of battery capacity. 3600 / 190 is 19 parallel 12 volt units.
The most parallel SLA units recommended by most manufactures is 3. This is because they won’t charge and discharge equally.
I doubt your ups has 150 amp 12 volt input connections.

Dang. So powering a space heater for 9 hours at night off batteries alone is not feasible with my current budget. My UPS does not have 150 amp 12 volt inputs so on second thought I actually believe the UPS uses 24V or 48V input with the factory default battery pack. So I may need either two or four of the batteries anyways. When I get home today I will verify the input voltage for the batteries so I know the minimum amount needed. Four of the 190Ah batteries is pretty much maxing out my budget on the project so I'd need to pause for a moment after the battery purchase before getting the solar panels and DC -> DC solar charging unit.

It usually still gets cold enough during the day for at least 3-4 months to run the space heater. Then with the 2-4 190Ah batteries I could also run it at least a few hours at night too if I'm up late before shutting it off and allowing the HVAC to take over. So it wouldn't be a total waste of a project. Then I'd also have a nice hefty backup in case of a total power loss.

The next step then is I would need some help in calculating the solar panel requirement and what type of charge controller I'd need for 2-4 of the 12V 190Ah batteries in either a 24V or 48V configuration. Then I would need to make sure connecting the charging controller to the batteries at the same time that the batteries are connected to the UPS would be an "ok" config.

 

[Bluedog225]

You seem to get it. But I’ll say it plainly hoping it’s helpful.

This plan seems like a (very) bad idea. Heat from solar and batteries is rarely (never?) an efficient or cost effective option. By a long way.

And 1500 watts is a lot. If you really, really need to go this way, perhaps look at an electric blanket. Something with a much smaller power draw.

And welcome!

 

[MrThisIsME]

You could spend a lot less on a small on a small pellet stove or propane heater then the solar route. A cloudy couple of days with solar and you will change your mind fast.

 

[camelCase]

If you want to heat a space overnight with solar, you'd be much, much better off using a solar system that captures heat directly instead of electricity. These types of systems can trap solar energy much more efficiently than electricity. For example, the system could use solar hot water panels to heat a few hundred or more gallons of water to 160f or so and then use a radiator of some type to circulate the hot water for space heating. To size the system, you just need to apply a little math.

 

[acdoctor]

So 190AH x 4 x 12 volts is 9120 watts with only half of that capacity usable on a sustainable basis. This doesn’t charge with 24 or 48 volts. The capacity of 4 batteries is the capacity. They make efficient window unit heat pumps. That approach 4 times as efficient as resistance heat.

I didn’t mention 22 kWh of needed power, your area probably gets 5 hours of 100% sun like most of us. 22/5 is 4500 watts of panels.

 

[speculant]

Alright, so I've been convinced to go toward the direction of a solar water heater, pump + radiator for a much more efficient heating setup. However, I'd still like to get the required amount of 12v 190Ah batteries and solar panels for a bulky backup system in case power goes out (I currently have no backup system in place and I'd like to avoid installing and maintaining a generator). I think I got my answer on the amount of panels I'd need, so my last question is the recommend charging controller I'd need and if it's safe to connect the charging controller up to the batteries at the same time that the UPS is connected to the batteries.

 

[acdoctor]

Flooded and valve regulated Lead acid batteries required a curtain charge amperage on a regular basis in order to keep the electrolyte stirred. This varies from type and manufacture. Usually between 0.1 and 0.2 x the capacity of what ever battery assembly you decide on. Also they require a specific amount of time charging in constant voltage ( Absorption). All of those should be available from the manufacture.

Charge controller size is determined by the panel array wattage, but are rated in amperage at the battery voltage. You can charge from multiple chargers at the same time, just take in account total amperage. Or charge from controller and consume from UPS.

 

[welnat]

Flooded and valve regulated Lead acid batteries required a curtain charge amperage on a regular basis in order to keep the electrolyte stirred.

Could you quantify regular basis ? Can you clarify that in a usage vs. a storage application?