Small system to power small freezer

[Sonnyboy]

Hi, I watched a video by Survival Lilly who learned from watching Will Prowse videos. I intned to have a similar system to the one she designs so I followed it nearly exactly. I have 4 100w Rich solar panels and two 100ah weize LIthium batteries all in parellel.
The freezer uses 240kwh/ year and I read somewhere, though not in the manual that it used 65w on start up. I think either I did something wrong or I need to add some more panels or battery. I am in the Northeast and it has been cloudy for days. Yesterday I went in the shed and the inverter was beeping signaling that the batteries were being overdrawn. I looked on the mt50 and saw that the batteries were at 10v. Is it possible such a small draw could deplete two new batteries in a few days. There is SOME voltage coming in from the panels even in overcast conditions. Is it maybe a setup issue in the controller?

Thanks

 

[Mattb4]

Yes the batteries can be depleted in a few days of minimal PV power coming in. Not knowing your daily draw just the annual 240kWh taht means ~ 675wh per day. There is also the watts being consumed by your inverter setup. As a guess let's say it is 25w or 600wh per day So the total would be 1275wh of power consumed. That is about 1 - 12v 100ah battery worth of power.

Now on the PV side you only have 400w. On a good day if you get 5 hours that is 2000wh. That amount not only has to recharge a depleted battery but it also is tasked to keep your refrigerator running.

I would say at the very least you would need to double your solar panels. Even than you will find after a couple of days of low production that your batteries will be depleted.

 

[DThames]

Have you looked at getting larger, residential home size, panels. Like in the 250w to 450w range? 300w size used are often available locally in large city areas. Shipping rates on a few large panels is often high but if you can drive to pick up used ones, that might be an option.

 

[Hogheavenfarm]

My smallest chest freezer uses 70 watts when running, but startup surge is 650 watts. I was running 6 185w panels into it (2s3p) and I could go for a few days, but 1 rainy day (and then night) and it would be at a point where I had to shut it down (12.3v) at the batteries. This was two 200Ah SLA batteries in parallel. Another battery would have helped in this case, but then is the 1100 watts going to be quickly charging the three batteries? Still experimenting with this setup now, but at 1510 watts of panels and batteries in series for 24v, (but my amp capacity is reduced this way to 100Ah). So same issue again, if I add TWO more batteries (2s2p) I will regain my 200 ah reserve, but can my 1510 watts charge all four? The SCC is 60 amps output, sound low for 4 batteries.

 

[DThames]

My smallest chest freezer uses 70 watts when running, but startup surge is 650 watts. I was running 6 185w panels into it (2s3p) and I could go for a few days, but 1 rainy day (and then night) and it would be at a point where I had to shut it down (12.3v) at the batteries. This was two 200Ah SLA batteries in parallel. Another battery would have helped in this case, but then is the 1100 watts going to be quickly charging the three batteries? Still experimenting with this setup now, but at 1510 watts of panels and batteries in series for 24v, (but my amp capacity is reduced this way to 100Ah). So same issue again, if I add TWO more batteries (2s2p) I will regain my 200 ah reserve, but can my 1510 watts charge all four? The SCC is 60 amps output, sound low for 4 batteries.

The sad truth is that for a series of bad solar days, you need lots of batteries and lots of panels. A secondary charging source, grid power or generator will greatly reduce what is needed because you can fall back to secondary charging if X bad solar days pass.

 

[MichaelK]

I've kept close attention to power consumption on cloudy/rainy days, and what I've measured is ~0.5 sunhours per day. Matt's consumption numbers look about right, so if you want this system to stay charged in cloudy NE weather, then you'd need 1275Wh/0.5sh = 2550W of panels. And that's starting with a fully charged battery. That's the reality of solar in a cloudy climate. My numbers might actually be somewhat optimistic?

Stop buying little 100W panels. As DT mentions, go with larger grid-ties, which will offer you more W/$. The best deals are on Craigslist with cash and carry purchases.

 

[Hogheavenfarm]

I agree, but used panels are rare in the northeast, many people did not start solar until about 6 years ago, (when Google earth started showing them up in red on houses) so not alot of aged out systems. Shipping was prohibitive from Santan, even from the Georgia warehouse. 100w panels are the easiest to acquire and are shipped with minimal expense, so thats the default option around here. I have running alerts on Craigslist for used panels, and in the past 8 months it has been running, only 2 panels (100w) have appeared there, and they were gone instantly. Not sure where the OP is, but thats the case in my area.

 

[MichaelK]

I guess I forget that I'm in a blessed area for solar. I grumbled when the price of a grid-tie ratcheted up to 65$ from 52$.
Sorry the situation is so much more challenging for you guys!

 

[efficientPV]

Solar panels are a commodity. Check with local installers. They buy pallets of the month, whatever is cheap and they always have leftovers. Next month's panels often don't match in color, physical size or power. They are always looking to get rid of leftovers or add to next order to get a better deal. There are lots of small independent installers. I've bought new and used for years in NE. More panels are better than more battery.

 

[Sonnyboy]

Have you looked at getting larger, residential home size, panels. Like in the 250w to 450w range? 300w size used are often available locally in large city areas. Shipping rates on a few large panels is often high but if you can drive to pick up used ones, that might be an option.

I do s e used 300w panels for sale. Can you mix and match those with other wattages?

 

[Sonnyboy]

Yes the batteries can be depleted in a few days of minimal PV power coming in. Not knowing your daily draw just the annual 240kWh taht means ~ 675wh per day. There is also the watts being consumed by your inverter setup. As a guess let's say it is 25w or 600wh per day So the total would be 1275wh of power consumed. That is about 1 - 12v 100ah battery worth of power.

Now on the PV side you only have 400w. On a good day if you get 5 hours that is 2000wh. That amount not only has to recharge a depleted battery but it also is tasked to keep your refrigerator running.

I would say at the very least you would need to double your solar panels. Even than you will find after a couple of days of low production that your batteries will be depleted.

Awesome easy to understand breakdown, thanks. Is there some parameter in my MT50 monitor that tells me how many wh I have been producing over the week or so I have had them up? Maybe that way I could calculate that amount of additional panels I would need. Also, can you mix and match different size panels without a problem?

 

[12VoltInstalls]

but my amp capacity is reduced this way to 100Ah

The same Watt hours are available

used panels are rare in the northeast, many people did not start solar until about 6 years ago, (when Google earth started showing them up in red on houses)

I am in northern vermont
I planned a trip to my sister’s in southern NH to coordinate with picking up panels an hour south of her in Massachusetts and bought six 315W panels for $800 which is ~30cents/watt. These were NOS usa-made not used panels. You can find stuff.

100w panels are the easiest to acquire and are shipped with minimal expense

I have eight 100W panels in two 400W arrays. About $1/watt which is expensive-ish. Feeds 8 marine deep cycle walmartha batteries. Started with just two panels and scaled up over time.
These are plenty of power to run the furnace, fridge, coffeemaker on sunny days, or 8 months of the year where the furnace is not constant.

In your case

it has been cloudy for days. Yesterday I went in the shed

i wonder -

• are the batteries protected from going below 32*F?

That’s one side issue to pay attention to.
I know you neither have enough batteries nor enough panels- from experience the last 4/5 years. Off grid.
Adding batteries helps- with lithium you don’t have to fully charge them every day, so you ‘can’ go with a strategy that lets you go several days at partial charge without going off on low voltage. So I would add a couple batteries.

However, even adding panels: the last week I have not even made 1kWh; today I’m charged up good already. So I had to supplement probably or at least 10+ kWh.
You will need to either charge by grid periodically or use a generator this time of year.

Those are the realities.

want this system to stay charged in cloudy NE weather, then you'd need 1275Wh/0.5sh = 2550W of panels. And that's starting with a fully charged battery. That's the reality of solar in a cloudy climate. My numbers might actually be somewhat optimistic?

No! Pretty good actually.
I have had other fish to fry so I’m not online yet with the new panels (~1900W). Working from experience (started out with just 200W of panels off-grid, now 800W) I used my observations of my various ‘experiments’ to wildhat guess that 300Ah of lithium batteries and 1600-2000W of panels might yield just enough to get by over the bulk of winter (other than the 8 cloudy days in a row) without supplementing much- if ever.
So it’s very interesting to me to note that my existing system is 800W of panels plus the ~1900W is nominal 2700W- and that is pretty stinkin’ close to your calcs.

However, it might be more rectangular dollar efficient to add two batteries (over-batteried vs overpaneled) and a $350 harbor freight generator with a 60A battery charger plugged in to scrape through the winter.
Nevertheless and if it’s affordable, buying more panels and a $185 Epever 40A SCC may still require supplemental occasionally. Yet with lithium batteries w/ 12V system you could even idle a car or truck an hour and put nearly a kW in if you were desperate.

My thoughts from The Northeast Kingdom where high-cloud filtered sun is still only making less than half the watts I’d expect at the moment from vertically mounted panels this time of day

 

[12VoltInstalls]

Craigslist for used panels

Facebook marketplace

BTW - where exactly are you located?

 

[Mattb4]

Awesome easy to understand breakdown, thanks. Is there some parameter in my MT50 monitor that tells me how many wh I have been producing over the week or so I have had them up? Maybe that way I could calculate that amount of additional panels I would need. Also, can you mix and match different size panels without a problem?

I do not know what your monitor has in the way of display. You could add a DC shunt and battery monitor to your PV (negative side)wiring just before your SCC. It might need the type that has an additional power source to keep alive the recorded wh. I use one that does not have that on my system and while most of the time there is enough trickle power overnight to not lose the watt/hr number, every now and than it will reset on lack of voltage.

Mixing and matching panels requires some thought and I will suggest you review here: https://solarpanelsvenue.com/mixing-solar-panels/

 

[Hogheavenfarm]

Facebook marketplace

BTW - where exactly are you located?

No FB, not much internet here, 54k wifi speed only, good for email, not much else. No smartphones. Not able to travel much outside of town. Everything usually shipped in.

 

[12VoltInstalls]

No FB, not much internet here, 54k wifi speed only, good for email, not much else. No smartphones. Not able to travel much outside of town. Everything usually shipped in.

Sent you a pm.
There’s a Facebook link to some panels you should seriously consider.

 

[Sonnyboy]

The same Watt hours are available

I am in northern vermont
I planned a trip to my sister’s in southern NH to coordinate with picking up panels an hour south of her in Massachusetts and bought six 315W panels for $800 which is ~30cents/watt. These were NOS usa-made not used panels. You can find stuff.

I have eight 100W panels in two 400W arrays. About $1/watt which is expensive-ish. Feeds 8 marine deep cycle walmartha batteries. Started with just two panels and scaled up over time.
These are plenty of power to run the furnace, fridge, coffeemaker on sunny days, or 8 months of the year where the furnace is not constant.

In your case

i wonder -

• are the batteries protected from going below 32*F?

That’s one side issue to pay attention to.
I know you neither have enough batteries nor enough panels- from experience the last 4/5 years. Off grid.
Adding batteries helps- with lithium you don’t have to fully charge them every day, so you ‘can’ go with a strategy that lets you go several days at partial charge without going off on low voltage. So I would add a couple batteries.

However, even adding panels: the last week I have not even made 1kWh; today I’m charged up good already. So I had to supplement probably or at least 10+ kWh.
You will need to either charge by grid periodically or use a generator this time of year.

Those are the realities.


No! Pretty good actually.
I have had other fish to fry so I’m not online yet with the new panels (~1900W). Working from experience (started out with just 200W of panels off-grid, now 800W) I used my observations of my various ‘experiments’ to wildhat guess that 300Ah of lithium batteries and 1600-2000W of panels might yield just enough to get by over the bulk of winter (other than the 8 cloudy days in a row) without supplementing much- if ever.
So it’s very interesting to me to note that my existing system is 800W of panels plus the ~1900W is nominal 2700W- and that is pretty stinkin’ close to your calcs.

However, it might be more rectangular dollar efficient to add two batteries (over-batteried vs overpaneled) and a $350 harbor freight generator with a 60A battery charger plugged in to scrape through the winter.
Nevertheless and if it’s affordable, buying more panels and a $185 Epever 40A SCC may still require supplemental occasionally. Yet with lithium batteries w/ 12V system you could even idle a car or truck an hour and put nearly a kW in if you were desperate.

My thoughts from The Northeast Kingdom where high-cloud filtered sun is still only making less than half the watts I’d expect at the moment from vertically mounted panels this time of day View attachment 122735

Thanks for the ideas. So if I put a few more panels up, that would overtax my controller when the weather is not overcast. Would you get a separate scc for additional added panels in my case? I can add one more 100ah battery no problem, maybe I will try that first. I didn’t realize it would be such a big investment to power such a small appliance, but I guess the weather is a huge factor. I am in Southern VT

 

[Bluedog225]

Sounds like you are getting the right advice. Many folks end up at the same conclusion regarding the cost to run an appliance. It’s hard to compete with cheap grid electricity.

 

[MichaelK]

Thanks for the ideas. So if I put a few more panels up, that would overtax my controller when the weather is not overcast. Would you get a separate scc for additional added panels in my case? I can add one more 100ah battery no problem, maybe I will try that first. I didn’t realize it would be such a big investment to power such a small appliance, but I guess the weather is a huge factor. I am in Southern VT

My own system is very overpaneled, by ~2000W. What I do is have panels pointed in different directions. Because my panels are on rotating mounts I can position them in any direction I want. Some arrays point SE, some S, and some SW, and one array right now is pointed WNW. That last one is great for later afternoon sun around 6pm. That keeps the air-conditioner on without additional battery depletion.

It flattens the noon amperage curve, but broadens the overall production curve, making more amps in the early morning, and late afternoon, when I am actually inside the cabin doing stuff.

I also have a 1000W array on a diversion breaker, and can send additional power from the workshop system, to the cabin system. I just flip an either/or breaker and send the power from the workshop, about 130' away, over to the cabin. This becomes quite important on days when I decide that I just have to run the well-pump at 7:30AM.

One the cloudy overcast days, I don't really pay much attention to orientation, because the light is so scattered.

 

[12VoltInstalls]

Thanks for the ideas. So if I put a few more panels up, that would overtax my controller when the weather is not overcast

If overwattage is not explicitly prohibited by your owner’s manual and you do not exceed VOC (adjusted for temperature) or the amp rating of the SCC it will simply just not produce amps beyond its output rating. It will not be ‘taxed’ as @sunshine_eggo or @MichaelK posted in a recent thread of mine.

 

[efficientPV]

I have 3,000W of panels on a 500W controller. That works for me because 70% of panels are shaded at any time. My east facing panels are great for recovery in the morning and it flattens production all day. I run a whole house, dishwasher, hot water, laundry, etc, besides refrigeration on a single car battery. On overcast days every panel produces some power and refrigeration can run for days in clouds with no problem. This is what can be done when you design with purpose.

 

[Sonnyboy]

I have 3,000W of panels on a 500W controller. That works for me because 70% of panels are shaded at any time. My east facing panels are great for recovery in the morning and it flattens production all day. I run a whole house, dishwasher, hot water, laundry, etc, besides refrigeration on a single car battery. On overcast days every panel produces some power and refrigeration can run for days in clouds with no problem. This is what can be done when you design with purpose.

That’s awesome. I don’t have the resources to have that elaborate of a system.

 

[Sonnyboy]

Please comment on this potential setup.

I currently have:
4 100w panels
18v 5a each
150v max 40amp Solar charge controller

I am considering adding 4x300w panels(36v 8amp)

Please analyze this wiring layout and give your thoughts.

4 300w panels wired in parallel producing 36v 32amp
2 100w panels wired in series producing 36v 5amp
2 100w panels wired in series producing 36w 5amp

Wire the two series arrays in parallel and connect them to the 300w array in parallel giving me 36v and 42amp and 1500w of solar out of a potential 1600w.

Will this work? Will the additional two amps fry my controller?

 

[MichaelK]

Please comment on this potential setup.

I currently have:
4 100w panels
18v 5a each
150v max 40amp Solar charge controller

I am considering adding 4x300w panels(36v 8amp)

Please analyze this wiring layout and give your thoughts.

4 300w panels wired in parallel producing 36v 32amp
2 100w panels wired in series producing 36v 5amp
2 100w panels wired in series producing 36w 5amp

Wire the two series arrays in parallel and connect them to the 300w array in parallel giving me 36v and 42amp and 1500w of solar out of a potential 1600w.

Will this work? Will the additional two amps fry my controller?

I myself would do this differently. You are lucky in the sense that the 100W panels can be paired up in parallel with the 300W panels. Since you have the 150V controller I see no need to have so many parallel strings. Just have three. Wire the four 100W panels as one string putting out 72V, then put the 300W panels in two parallel strings with two panels in series for 72V.

That would give you three parallel strings putting out ~ 5A + 8A +8A = 21A at 72V. Three strings will be cheaper and less complex to wire. You'll save money with fewer lengths of thinner copper wire.

Overloading your controller with too many amps though could be an issue. Your system is 12V? Even with 85% de-rating, that's (1600W/13Vcharging) X 85% = 105A. What you can do is what I mentioned in post #19, having each string pointed in a different direction. Maybe one facing East, one facing South, and one facing West. I'd put the 100W string in the middle, facing South. Then current flow will be a bit more balanced over the course of the day, but you'll be getting the most amps in the early morning and late afternoon.

Alternatively, upgrade to 24V. That will cut the amps in half for the same amount of power.

 

[Hogheavenfarm]

Similar to my setup - three strings of (2) 185w panels in series (86v, 5.5a), coupled with a string of (4) 100w panels in series (80v, 5.3a). I am getting 84v at the controller and 27amps. Seems to be working fine. These are all on the South rack as I am not near any of my limitations (150v, 60a).