12V DIY solar power station

[Bacchus]

A short while back I started my current project, building a 12V DIY solar station that would 1) power my refrigerator every day 24 hours a day as long as the sun was shining, on occasions when we have a power outage; and 2) be cheaper than commercial units with similar power (W) and energy (Wh) outputs; and 3) provide an education to prepare me for a followup power station that can keep my air conditioner running.

My current status is that at $338.91 (excluding solar panel) I have a system that is 2000W power and a nominal 2400Wh energy capacity. And since I am using lead acid batteries the energy capacity is closer to 1200Wh, compared to the commercial systems that are using LFP batteries. My system has two car batteries, an inverter, a controller, a battery state monitor, a power input monitor, and an AC charger. Most comparable reputable brands seem to cost about $600 for that power and capacity.

But, the name brands include more, such as LFP batteries that will last at least triple the number of power cycles; much nicer and more informative power status displays; maybe an app to control thru Wi-Fi; more connectors, including USB support, and more. Since I don't expect to use this more than about once a year (not many power outages in my neighborhood), the cheap lead acid batteries are fine.

And, neither my system in its present state nor the $600 commercial systems meet my refrigerator criteria: not enough capacity to run my refrigerator for 24 hours.

During my last test (with two batteries and one solar panel) my station ran for 16 hours and 44 minutes and delivered 1370 Wh of energy (my refrigerator needs about 1750 Wh in 24 hours). My one solar panel contributed 353 Wh from 9am to 1:30pm (sunny hours) before the sky clouded up.

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[Bacchus]

So I think I can get to 24 hours with another 1 or 2 batteries. I almost bought a pair of used batteries this week but they were sold before I got paid (I needed cash and the seller didn't take Goldbacks). And 1750 Wh / 350 Wh = 5 total solar panels, so I'll need four more of them, to recharge the batteries in the 5 hours of sunshine in one day, which I have seen very little of this winter.

A few things I learned. I had 1.5vdc voltage drop between my battery output to my inverter input. I reduced it to 0.5vdc by cleaning the battery terminals. I further reduced it to nearly zero (tens of millivolts) by connecting the battery cable directly to my inverter inputs instead of connecting those two devices through a bus bar. 1.5 vdc lower is a big deal at the inverter inputs.

The first time I ran the test with two batteries and a solar panel I produced 391 Wh with the panel, but the station only delivered 860 Wh to the refrigerator. The difference was I ran that test with my station (and batteries) in my garage instead of inside my house, and my garage was 28F that day. I investigated online and learned that lead acid batteries will lose half their capacity at freezing temperatures, on top of the 50% they lose just for being lead acid. So a nominal 1200Wh battery will only deliver about 300Wh in freezing weather. OTOH, LFP batteries are not supposed to even be charged in freezing weather.

There are such things as battery wraps and even battery heaters (powered by the battery's power) to keep them warmer. I wonder if a picnic cooler would contain enough of the heat the battery generates.

There seems to be a difference of opinion on the advisability of using a lead acid battery inside the house, if the battery is not sealed.

 

[dangerranger60]

The experts in 12v systems are on the RV sites. they are also experts on which appliances will do the job on the least power. You will probably find frost free appliances are the most power hungry. Also most have ditched the lead acid batteries. The low end systems are using AGM batteries and the most are converting to Li or Ti batteries. DR

 

[Koda]

Nothing wrong with DIY but Goal Zero and Jackery sell complete solar systems that will run your freezer for up to 3 days, complete kits.

Emergency Preparedness Kits for National Preparedness Month: Goal Zero

National Preparedness Month is here—stay ready with Goal Zero’s emergency preparedness kits and backup power solutions. Ensure your safety with our reliable and portable products.

goalzero.com

 

[OrPackrat]

Nothing wrong with DIY but Goal Zero and Jackery sell complete solar systems that will run your freezer for up to 3 days, complete kits.

Emergency Preparedness Kits for National Preparedness Month: Goal Zero

National Preparedness Month is here—stay ready with Goal Zero’s emergency preparedness kits and backup power solutions. Ensure your safety with our reliable and portable products.

goalzero.com

Those are spendy units and I can do the same for alot less.

I can get about just over 24hrs for every $400 in batteries to power a full size refrigerator...

 

[Koda]

Those are spendy units and I can do the same for alot less.

I can get about just over 24hrs for every $400 in batteries to power a full size refrigerator...

yes, they are expensive. Im curious what you come up with, the idea of keeping a fridge running is worth. Keep us posted.

 

[OrPackrat]

yes, they are expensive. Im curious what you come up with, the idea of keeping a fridge running is worth. Keep us posted.

Duel 100ah Lifepo4 batteries, under 200 for each battery with roughly 1000w usable each.

Given the OP stated a bit under 1800w for 24hrs of a refrigerator.

Given what Oregon gets for weather when power is lost, solar will be rather ineffective unless you have a massive solar panel system which would be expensive...

 

[arakboss]

Fridges are great but they suck up lots of power. I am listening to ours running right now. Honestly it feels like it runs more than it doesn't.

 

[OrPackrat]

Fridges are great but they suck up lots of power. I am listening to ours running right now. Honestly it feels like it runs more than it doesn't.

A Modem and router running, at 10w each, will draw almost 500w in 24hrs

1800w for a large refrigerator does not sound too bad.

A larger TV can draw a couple hundred watts so 5hrs is about 1000w...

 

[arakboss]

A Modem and router running, at 10w each, will draw almost 500w in 24hrs

1800w for a large refrigerator does not sound too bad.

A larger TV can draw a couple hundred watts so 5hrs is about 1000w...

Maybe he has one of those mini fridges.

 

[OrPackrat]

Maybe he has one of those mini fridges.


View attachment 2036951

I dont believe that calculator is correct...

My refrigerator does not run 24hrs a day. It shuts off and only kicks on to maintain temperature...

But to be on the safe side, I'll measure the draw on mine when the meter arrives.

Some math on the goal zero puts they calculate a full size refrigerator at just under 1900w a day

 

[Bacchus]

When I was testing my system I took hourly measurements of several operating values, including the instantaneous power draw from the refrigerator. I used a Kill-A-Watt meter on the solar station inverter output. Almost every time I made a power measurement, it was either 2.8W (compressor off) or 122W (compressor on). When I divided the total accumulated energy usage at the end of the test and divided by the number of hours the test ran, it showed the average power usage was 73W.

I did see a power draw of 600W for several minutes at a time about once a test, usually right after power on. I thought it was startup power (not to be confused with the much shorter lasting surge current), but it didn't happen every time and then later I witnessed it happening ten hours into a test. The only thing I can think of to explain that last occurrence is maybe a defrost cycle? I dunno. But! Measurements of the accumulated energy use just before the 600W and just after the 600W showed that the accumulated energy had increased by 50Wh. Since my average energy usage is 73Wh (average power 73W) for an hour, those 600W events are consuming most of a battery energy hour.

My refrigerator is about 15 years old, and I believe it qualified for "Energy Star" compliant at the time. I don't know how much more efficient refrigerators are these days.

Speaking of defrost cycles ... where does the water go?

 

[Nwcid]

The experts in 12v systems are on the RV sites.. The low end systems are using AGM batteries and the most are converting to Li or Ti batteries.

That is for sure. This is a daily topic and there are sites dedicated to it also. Even in the last 12-24 months, there is almost no reason to buy anything other than lithium unless you have a special application. The initial price of the battery is about the same now but you get 2x the usable power and easily 2x the life.

Commenting about the pre-built kits, they are nice and convenient all in one set ups, but they are easy 2x the cost of building your own system like the OP is. The biggest factor is to do an energy audit to understand how much power you will actually need to store based on your usage for the battery bank and how fast and under what conditions you will be using for solar charging to get the right amount of panels.

Here is the front bay of my RV which has 4 x 230 AH batteries, a 3000 watt inverter wired into the whole house (no sub panel). I have a 100 amp charge controller for the 1400 watts of solar on the roof, and a 30 amp charge controller for the 570 watts of ground panels we use in the winter months since they can be aimed at the sun.

We are able to run pretty independent of shore/generator power indefinitely. I can run large items like 1 air conditioner, electric heater, air fryer, etc for a little over 4 hours if needed/wanted even with no solar input. Pretty much the only time we run the generator is when we need both AC running for long periods. EDITD to add, we rarely stay anywhere with hook ups, we prefer boondocking for lots of reasons. Most of the time if we have access to power it is typically just 15 amps.

 

[Bacchus]

That is for sure. This is a daily topic and there are sites dedicated to it also. Even in the last 12-24 months, there is almost no reason to buy anything other than lithium unless you have a special application. The initial price of the battery is about the same now but you get 2x the usable power and easily 2x the life.

Commenting about the pre-built kits, they are nice and convenient all in one set ups, but they are easy 2x the cost of building your own system like the OP is. The biggest factor is to do an energy audit to understand how much power you will actually need to store based on your usage for the battery bank and how fast and under what conditions you will be using for solar charging to get the right amount of panels.

Here is the front bay of my RV which has 4 x 230 AH batteries, a 3000 watt inverter wired into the whole house (no sub panel). I have a 100 amp charge controller for the 1400 watts of solar on the roof, and a 30 amp charge controller for the 570 watts of ground panels we use in the winter months since they can be aimed at the sun.

We are able to run pretty independent of shore/generator power indefinitely. I can run large items like 1 air conditioner, electric heater, air fryer, etc for a little over 4 hours if needed/wanted even with no solar input. Pretty much the only time we run the generator is when we need both AC running for long periods.

View attachment 2037030

Very nice! Your system is about ten times bigger than mine. Are you saying that the 1400W of solar input is on the roof of your RV?

WRT lithium batteries, for me the lead acid batteries make sense because I don't expect to use this system more than maybe once a year, just for the infrequent power outages. That is, if we're only factoring in power cycles. If the lead acids have a much shorter battery life just sitting around doin' nothin', then you might be right, but my system is more of a stepping stone to something bigger. I expect to go the LFP route when I design my next, much bigger, system.

 

[Nwcid]

Very nice! Your system is about ten times bigger than mine. Are you saying that the 1400W of solar input is on the roof of your RV?

Yes, my system is larger, but it was build for my use, not your use. Yes, I have 1400 watts of flat mounted panels on the roof of the RV.

WRT lithium batteries, for me the lead acid batteries make sense because I don't expect to use this system more than maybe once a year, just for the infrequent power outages. That is, if we're only factoring in power cycles. If the lead acids have a much shorter battery life just sitting around doin' nothin', then you might be right, but my system is more of a stepping stone to something bigger. I expect to go the LFP route when I design my next, much bigger, system.

Right now if you needed to buy 100AH of deep cycle battery new, depending on the brand, lithium would cost the same price (or possibly less) and provide 2x the amount of usable power with 1/2 the weight. The first battery bank I put in my RV (2018) was 6 x 6v AGM for a total of 675 AH with only 1/2 of that useable, and today's cost of $1630 + tax. When I did this lithium was still about 3x the cost so AGM made sense for me, but the is still the 432lbs of weight.

The spring of 2024 the AGM bank was down to about 70% and was not meeting our needs. I looked at replacing like for like but I went with lithium. I got 920 AH of useable power, so about 2.5x the usable reserve, the weight dropped to about 60% (not that it was an issue for my situation) and the cost shipped to my door was $1596.

The 2 big downsides or really more like considerations for lithium is you need a charger that can support the profile for that and the other is cold weather. Lithium can be used below freezing, however it cannot be charged when the cell temperature is below freezing.

 

[dangerranger60]

With Li batteries not outgassing like a lead acid they can be moved into the heated living areas of the home. this negates some of the freezing problems.
My own RV has a small residential refrigerator. we have 150 watts of solar and a pair of AGM group 27 batteries. that is enough to keep the pre cooled refrigerator and freezer going about 4 days without any other draws. this is with the panels in direct sun and 85 to 90 degrees outside air temp. on the 4th day my batteries were at 11 volts going into evening.
These batteries came with the RV. when they go bad, I will change to Li and double the usable storage. I will also double the panels on the roof, and have to upgrade the charge controller.
We normally stay in RV parks that have full hookups but the solar lets us have a day and night of use without electricity when on the road. it lets us stay a night in a parking lot without hookups. 300 watts of Pannels and double the storage would let us go a little longer and let us run the TV or laptop and still have power for a furnace if it's cold at night.

If you are running a home freezer or refrigerator look to see if it has heat strips to defrost. if you can unplug or disconnect those it cuts the power use in half or more.
God Luck DR

 

[osprey]

I have been researching this topic quite a bit lately in order to set up a power station in my four wheel project M camper. I used a LiP04 140ah battery in kickass battery box with built in dc/dc charger with solar control. I do not have solar panels yet but 200w worth on the top is in the plans. I use this to power lights, fans, a portable 45qt fridge/freezer and a 5kw diesel heater. I have found I can go 3-4 days before needing to drive truck or plug in to wall outlet or genny to charge battery. I think in warmer weather with favorable sun conditions I could easily go a week or more with 200w of solar panels. Things I have learned on this journey:
Cost continues to come down on LiP04 batt technology and the benefit is the longevity and usable capacity is double that of lead acid or agm technology. My group 31 140ah batt was $240 and weighs 26#. I am not convinced the fire danger has been fully mitigated with this technology however. I would be hesitant to put them in a house for this reason. LiP04 batteries cannot be charged below 32 deg f without damage. Most reputable batteries have a bms (battery management system) that does not allow charging below freezing. Since mine is in a all weather rv application, I wired in a small 12vdc silicone heater pad and controller that cycles on at 35 deg and off at 40. It sits below the battery in the battery box that I lined with reflectix. Total outlay was $25 for this. Some batteries have this feature built in but were beyond my budget. If I were to have a system for the house I would have the batteries in a small outbuilding or enclosure not attached to house. I would also look into a fridge that runs on dc so as not to have the parasitic draw of running an inverter all the time. I have an inverter but only run it occasionally for ac only loads and it has a switch so I can turn it off when not in use. The solar power stations out there in most cases run the inverter full time and do not have a switch to turn the inverter off. If you do not have the technical savvy to tackle putting your own power system together, I can recommend Pecron brand power stations as they are one of the few that you can turn off the inverter portion and continue to use the dc side. Also Pecron units work in a ups mode which is also fairly uncommon in the sector. Happy off gridding!

 

[osprey]

When I was testing my system I took hourly measurements of several operating values, including the instantaneous power draw from the refrigerator. I used a Kill-A-Watt meter on the solar station inverter output. Almost every time I made a power measurement, it was either 2.8W (compressor off) or 122W (compressor on). When I divided the total accumulated energy usage at the end of the test and divided by the number of hours the test ran, it showed the average power usage was 73W.

I did see a power draw of 600W for several minutes at a time about once a test, usually right after power on. I thought it was startup power (not to be confused with the much shorter lasting surge current), but it didn't happen every time and then later I witnessed it happening ten hours into a test. The only thing I can think of to explain that last occurrence is maybe a defrost cycle? I dunno. But! Measurements of the accumulated energy use just before the 600W and just after the 600W showed that the accumulated energy had increased by 50Wh. Since my average energy usage is 73Wh (average power 73W) for an hour, those 600W events are consuming most of a battery energy hour.

My refrigerator is about 15 years old, and I believe it qualified for "Energy Star" compliant at the time. I don't know how much more efficient refrigerators are these days.

Speaking of defrost cycles ... where does the water go?

Water drains into pan down by compressor/condenser components where it evaporates with the heat and air movement.

 

[OrPackrat]

I recommend watching some videos by this guy.

DIY Solar Power with Will Prowse

Want to build an awesome off-grid solar power system? My videos will teach you everything you need, no experience necessary :)

youtube.com

Has some good stuff and tear downs to find the better quality inexpensive lifepo4 batteries...


Also, going to pickup a 50a minimum lifepo4 charger to run off AC as when the power goes out, my existing 500w of solar may as well be 50w in a storm..

As such, my 2550w inverter generator can recharge my batteries at in a few hours and given the draw off the 50a charger, say 4 hour of generator to recharge the batteries at 200ah, 40hrs run time on a 5gal gas can, 10 full recharge cycles of the battery.

5 gallons gas with no solar input will give me 10days of run time of a 200ah lifepo4 battery bank running refrigerator.

 

[OrPackrat]

One other thing, there are RV gray water heating mats you can install on a metal sheet under the batteries that can be activated in cold weather to warm the Lifepo4 batteries before charging...