Simple system but I need help with it.

[Whats-n-Watts]

Hello everyone. Probably currently the newest newbie here. I could use you professionals help with a small system. I have electrical experience with both AC and DC. My DC knowledge is basic and auto repair related. AC knowledge is a little better having been an electrician field in the past. Standard every day stuff. So at least I'm not totally green lol
I have a shed with 2 very freezers and one old refrigerator. They are getting replaced since they are energy hogs. 5 amp, 6 amp and 6.5 amp. New units are .98 amp x 2 chest freezers and one 1.2 amp refrigerator. By my calculations and estimates around 400 running watts combined.
I plan to power the shed (which it's sole purpose is housing these appliances) with solar. I live in South Georgia, USA and sunlight isn't an issue as the shed gets full sun 90 percent of the day.
I only want a system large enough to keep these running on solar during the day and battery overnight for one night.
using the 8 hr per day average run time I am figuring a bank to cover 4 of those hours of darkness on somewhat of a budget as in the most inexpensive safe way is what I want. I have a generator and have grid power if needed for rain days or low performance days.
At about 1,500wh to keep these appliances going 4 hours. I'm a tight wad or I wouldn't be looking to go solar in the first place lol Having said that I don't mind spending money to save money down the road.
I have beat my brain to pieces over the last two weeks with calculations and I'm tired Boss.
i came up with 2 x 195w 24v panels in parallel and a 24v 75ah battery fed by a 30a MPPT controller with a 600w pure sign inverter . Stop laughing ?
I am very frugal but my inner nerd (Dexter) (I have D.I.D. ?) keeps telling me I am better off going with a 12v 150ah battery for such a small system and because it's usually warmer here than cold it may perform better? I trust him but only so far as he is a novice solar enthusiast. I am sure someone in here can tell me the best way to make this happen safely and the most economical way. Thank each of you in advance for your precious time (and I mean that) to help us out.

Ron

 

[Zapper77]

600 watt inverter won't cover the refrigerator defrost nor will it cover the compressor startup surge.

Check my math
Get a 2000 watt inverter, 8-10 kWh of battery (16-20 hours of backup), 800-1000 watts of solar (80% of rated times 5 hours)

*Ambient temperature will cause extra power consumption.

Edit: numbers used below

Energy audit needed but...
Max Hourly consumption: 3.5 amps x 120v = 420watts

Daily Consumption: 420 x 24 hours (assumes 100% duty cycle) = 10,000 Wh x 1.15 (conversion loss) = 11 kWh of battery (can be reduced to 16 hours vs 24)

Solar Required: 800 watts x 80% x 5-7 hours = 3-5 kWh

1000 x 80% x 5-7 = 4-6 kWh

 

[Q-Dog]

Size the battery for the power (Watt Hours) needed, size the inverter to handle max amp/startup load (what if all 3 try to start at the same time), size the solar to refill the battery. ProTip: Use the EnergyStar sticker on the freezer of fridge to estimate how much kWh you will likely need for each appliance.

My first setup was 5kWh of battery, 400 watts of panels. It could run 1 refrigerator and some security camers full time as long as there was sun. Loads could deplete 50% of the battery in 24 hours and just one partly cloudy day meant I had to recharge the battery from grid/generator. I soon doubled the battery and added a little more solar.

So, now I have 10kWh battery bank and am up to 1600 watts of panels. My refrigerator and cameras run on this setup full time, even when cloudy. The battery does not always charge to 100% but I have enough extra battery to cover the shortfall for a couple of days. Partly cloudy days can still charge the batteries to full. 1600 watts of panels can recharge a little more than 50% of our battery capacity on a sunny day with all regular loads running. With 2 or 3 sunny days in a row we have enough extra panel capacity to run a 12k window air conditioner for about 6 - 8 hours a day.

 

[Whats-n-Watts]

600 watt inverter won't cover the refrigerator defrost nor will it cover the compressor startup surge.

Check my math
Get a 2000 watt inverter, 8-10 kWh of battery (16-20 hours of backup), 800-1000 watts of solar (80% of rated times 5 hours)

*Ambient temperature will cause extra power consumption.

Edit: numbers used below

Energy audit needed but...
Max Hourly consumption: 3.5 amps x 120v = 420watts

Daily Consumption: 420 x 24 hours (assumes 100% duty cycle) = 10,000 Wh x 1.15 (conversion loss) = 11 kWh of battery (can be reduced to 16 hours vs 24)

Solar Required: 800 watts x 80% x 5-7 hours = 3-5 kWh

1000 x 80% x 5-7 = 4-6 kWh

A 600 watt peak unit I am looking at claims it can withstand 80% for a maximum of 1 hour so I felt it could handle it since the running load of all 3 combined is only 3.16a at 379.2 watts. All 3 are manual defrost so no concern there. Also they run approximately 8 hours out of 24 hours. About 20ah each per day is what I came up with as a ball park. I only need to cover half of that in battery back up to get me through the night (4 cycles of 20 mins per cycle at 400 amp)? Or maybe back up 6 hours run capacity in my bank just for sake of a low pv output on any particular day? I am probably looking at it all wrong and that's why I'm here to learn from y'all.
There is that sweet spot I know, where it's just right for system. The balance where what goes in comes out and out must go back in. I was figuring for daily sun juice to cover the approximate 4h x 379.2w = 1,516.8 (theoretically) and replenish the 1,516.8 watts used from the bank over night. The panels are literally in direct sun 90 percent of the day. Out of 14 hours of daylight during summer solstice 12 hours of that the sun will hit the panels. A good 6+ hours of direct. I have 3 wide open acres of sun.
I ordered a kill a Watt meter so I can get more accurate real life numbers because it's just a shot in the dark without one really imo.
I know what I figured was bare bones lol but we have a tiny house (500) sqft and I want to go off grid one day and I'm using this shed for a guinea pig so to speak. I'm kinda afraid of the lithium batteries because I see these EV's catching fire. Not good.
I'm currently grid tied so it isn't like I am dead in the water if less isn't enough.
Is the bigger the inverter the better? Less work = less energy used? The same concept works on humans but not sure if it applies here or not but I think so or at least to a degree.
Thanks so much for taking the time to figure that for me and I am going to keep your post in my note pad.
If the appliances behave as my scenario is written what would you suggest?
Eco-worthy has a hybrid controller rated for 800 watt pv input and has 1500 watt inverter. It's a neat looking rig that's all in one for $219 bucks. https://www.eco-worthy.com/collecti...r-inverter-50a-controller-for-off-grid-system
What do you think about it? For defrost I will just run the grid for that so my inverter doesn't start hating me ?

 

[Whats-n-Watts]

Size the battery for the power (Watt Hours) needed, size the inverter to handle max amp/startup load (what if all 3 try to start at the same time), size the solar to refill the battery. ProTip: Use the EnergyStar sticker on the freezer of fridge to estimate how much kWh you will likely need for each appliance.

My first setup was 5kWh of battery, 400 watts of panels. It could run 1 refrigerator and some security camers full time as long as there was sun. Loads could deplete 50% of the battery in 24 hours and just one partly cloudy day meant I had to recharge the battery from grid/generator. I soon doubled the battery and added a little more solar.

So, now I have 10kWh battery bank and am up to 1600 watts of panels. My refrigerator and cameras run on this setup full time, even when cloudy. The battery does not always charge to 100% but I have enough extra battery to cover the shortfall for a couple of days. Partly cloudy days can still charge the batteries to full. 1600 watts of panels can recharge a little more than 50% of our battery capacity on a sunny day with all regular loads running. With 2 or 3 sunny days in a row we have enough extra panel capacity to run a 12k window air conditioner for about 6 - 8 hours a day.

Wow that's cool that you started small and built up. That's what I will have to do as well. Where are you located? I'm in South Georgia and in the summer it's 12 hours of sun with 7 or so peak hours.

 

[Q-Dog]

I have an Ecoworthy combiner box. I would not buy one of their inverters for anything that I want to keep running. Maybe something for a hobby, but not something I want to depend on.

I'm in South Louisiana.

 

[400bird]

A 600 watt peak unit I am looking at claims it can withstand 80% for a maximum of 1 hour so I felt it could handle it since the running load of all 3 combined is only 3.16a at 379.2 watts. All 3 are manual defrost so no concern there. Also they run approximately 8 hours out of 24 hours. About 20ah each per day is what I came up with as a ball park.

Start up surge on the compressors can be 5x running current, that's why everyone is warning you that 600 watts likely isn't a large enough inverter.

I'm not following your logic on how you got to 20ah of battery each.

For round numbers, running 400 watts x 8 hours per day (you really should test this run time) = 3.2 kWh. At 12 volts that is 266 Ah. You might be ok with 200Ah of battery, but that doesn't leave much roof for cloudy days.

In the winter, your probably let 3 hours of sun per day, so I'd get enough solar to cover all 24 hours of use (3.2kWh) in about 3 hours.

You can run the production numbers here to get a good idea of solar production year round.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Plus, you've got some inefficiency in the inverter/charger and idle consumption on the inverter, so plan a bit of wiggle room.

Alternatively, go with a tiny battery, let the system shut down all night and let the frozen stuff coast through the night, but make sure you have enough solar to run the system for hours straight in the morning to cool the freezer back down.

 

[Whats-n-Watts]

I have an Ecoworthy combiner box. I would not buy one of their inverters for anything that I want to keep running. Maybe something for a hobby, but not something I want to depend on.

I'm in South Louisiana.

Cool you're in the sunny south too. Thanks for the tip on their inverter. Do you have a company you recommend?

 

[Whats-n-Watts]

I have an Ecoworthy combiner box. I would not buy one of their inverters for anything that I want to keep running. Maybe something for a hobby, but not something I want to depend on.

I'm in South Louisiana.

Cool you're in the sunny south too. Thanks for the tip on their inverter. Do you have a company you recommend?

 

[Q-Dog]

I like separate components for small systems. Right now I am all Victron.

 

[Whats-n-Watts]

Start up surge on the compressors can be 5x running current, that's why everyone is warning you that 600 watts likely isn't a large enough inverter.

I'm not following your logic on how you got to 20ah of battery each.

For round numbers, running 400 watts x 8 hours per day (you really should test this run time) = 3.2 kWh. At 12 volts that is 266 Ah. You might be ok with 200Ah of battery, but that doesn't leave much roof for cloudy days.

In the winter, your probably let 3 hours of sun per day, so I'd get enough solar to cover all 24 hours of use (3.2kWh) in about 3 hours.

You can run the production numbers here to get a good idea of solar production year round.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Plus, you've got some inefficiency in the inverter/charger and idle consumption on the inverter, so plan a bit of wiggle room.

Alternatively, go with a tiny battery, let the system shut down all night and let the frozen stuff coast through the night, but make sure you have enough solar to run the system for hours straight in the morning to cool the freezer back down.

Yes I do understand running watts are not starting watts. I was just calculating running watts and certainly any start up watts as well as idle loss etc. Calculations were just keeping it simple to get a ball park idea. Rough estimate. As far as the ah go it was ballpark as well.
1.2a x 120v = 144w x 4h = 576wh = 4.8ah is that not correct or the correct way to calculate? That would be ballpark for for that appliances to run 4 hours off of battery to get me through the night I am estimating. Again just estimating running energy only. I realized I have to get more precise numbers but do not have those yet. Kilo watt meter hasn't arrived yet. When I do have the accurate numbers I want to know if I am thinking correctly on how to use them so I don't over power the building because that's just a waste of money. I guess I'm just asking too much?
Yes in winter 4 hours (peek) sun here in South Georgia. I still have nasty juice so any weather that reduces productivity of my panels is not an issue at this time. I have a continuous 8,500 watt generator as well should the grid become offline. Again back up isn't a problem.
What I would like to do vs what I can do are two different things probably. I may not even be presenting that to the forum properly. Thank y'all for bearing with me.
My desire is to allow the appliances to power by solar panel only on ideal days and enough SP to handle that charge the required battery that's sole purpose in my book is in place to cover the estimated run time 4 to 6 hours after dark. Are this numbers realistic? I have no idea until my meter gets here but I am basing that off of the general rule. Everyone live a unique lifestyle so that number is probably not realistic in my case. Just my wife and I and we go into a freezer once a day. And usually open the refrigerator maybe 12 times a day combined between the hours of 2pm to 6 pm. And we don't leave the door standing open. In other words there are no energy sucking children around ?
Having said that I doubt very seriously either of those chest freezers will run more than one hour through the darkness.
I have tons of room for solar to point in any direction, angle. The sun worships my property in that respect. Ground mounted is the way I am going.
Two things I want maybe what I can't have. My understanding is you match your aray to your battery needs. In off-grid (which is my goal) only requiring back up for say 4 hours limits the array doesn't it? Small battery= small array? Big array = big battery? Array/Controller/battery/load all in harmony correct? Am I understanding correctly?
In my mind I am knowing they won't all be running at the same time. 2 at best and that is likely 10 mins before one shuts off the other comes on for 20 mins so. Will 2 ever run the exact say length of time at the same time? Possible I guess but when that isn't happening and the array isn't busy powering any appliances it's got plenty of power to send to the battery 100% output. More solar for battery charging in a days time than spent running the appliances. Especially since there isn't any traffic to even mention for the freezers.
If I'm damn close but no cigar how tweek-able would it be? Just throw another battery at it? Or throw a panel at it? Doing either requires a larger charge controller or is there play room?
Throwing away money sucks no matter the amount so I'd rather build a system I can add too if needed rather than subtract in other words but I don't want to have to buy a larger controller and have one laying around I can't use. Another panel? No problem, battery? No problem if that's what it takes.
I have the luxury of other power sources to jack into?
Can you recommend a flexible controller that won't drop the ball or freak out should I need another panel or battery to top the system off to suit my needs?
Thanks a million for your time! I really appreciate everyone's help.

 

[Q-Dog]

But if I were starting over and couldn't buy Victron I would look at other name brands with proven reputation like Morningstar, OutBack, MidNite, Magnum, and maybe Aims and a couple of others.

The MidNite DIY series looks interesting.

 

[Hogheavenfarm]

I am running a very similar setup, 2 chest freezers and one chest freezer converted to a refrigerator. Average running watts is about 110 watts, but on one of the freezers I have seen 830w on a start up surge. Assuming all are similar, thats a 2490w load for startup. Some argue thats unlikely to happen, but after a power failure thats highly likely to happen. To power these overnight I am using 4 AGM 200ah batteries, and that will get me overnight plus one 12hr (rainy) day before the voltage drops to 12.2 or so. These are supplied with 2500w of panels.
I could probably go with 2 AGM batteries, but that would be pushing it.

 

[Whats-n-Watts]

I am running a very similar setup, 2 chest freezers and one chest freezer converted to a refrigerator. Average running watts is about 110 watts, but on one of the freezers I have seen 830w on a start up surge. Assuming all are similar, thats a 2490w load for startup. Some argue thats unlikely to happen, but after a power failure thats highly likely to happen. To power these overnight I am using 4 AGM 200ah batteries, and that will get me overnight plus one 12hr (rainy) day before the voltage drops to 12.2 or so. These are supplied with 2500w of panels.
I could probably go with 2 AGM batteries, but that would be pushing it.

Oh wow that's a lot of panel but also a lot of storage. With me going with Lifepo4 batteries would that convert to 2 x 200ah batteries to get the same amount of storage? I read they are for 80% capacity. Thanks a bunch for your input!

 

[Hogheavenfarm]

LiPo would be a better choice, but for my cold temps I am using AGM, and the fact that I could not afford two LiPo's. The panels allow the freezers to run all day and still fully charge the batteries by noon, and on cloudy days they can still still do all that by 4pm, so I always start the night with the batteries around 12.9-13 volts. On a typical cycle they will be about 12.6v by the next morning, but over the last very heavy rain weekend they were at 12.3 the following morning, but the sun was up the third day and I didnt have to switch them back to grid. BTW, I am using a 24v system, batteries are 2S2P and the inverter is 3500w. Most of the time there is about a 130w load visible on the meter, sometimes as high as 325w if all units are running, sometime just 9w of idle current. The cycling helps with the loads, I doubt I could run 325w continuously 24/7, but I havent tried it.

 

[400bird]

In my mind I am knowing they won't all be running at the same time. 2 at best and that is likely 10 mins before one shuts off the other comes on for 20 mins so. Will 2 ever run the exact say length of time at the same time? Possible I guess but when that isn't happening and the array isn't busy powering any appliances it's got plenty of power to send to the battery 100% output.

Think about what happens when the battery runs flat at 2:00 am, all 3 cold boxes start getting warm, so come sun rise all 3 are warm enough to need to run. Sure does sound like not just 2 but, all 3 are guaranteed to start at once in that situation and run for a longer cycle than usual.

More solar for battery charging in a days time than spent running the appliances. Especially since there isn't any traffic to even mention for the freezers.
If I'm damn close but no cigar how tweek-able would it be? Just throw another battery at it? Or throw a panel at it? Doing either requires a larger charge controller or is there play room?

If you purchase components correctly, that aren't already maxed out, yep you can add more solar. Adding more parallel batteries wouldn't require any change from the inverter or charge controller.
It's hard to add more capacity to the inverter short of putting one freezer on a dedicated inverter separate from the other 2.

 

[Vigo]

Just as an anecdote, I have a 400w travel inverter that would start my house fridge sometimes, but not others. A 600w inverter might have made it 100% reliable, but that's for ONE (probably energy hog) refrigerator.

To start 3 simultaneously the 2000w inverter is a good idea and at that, you're still in a fairly cheap price range for something that size. A 2-3kw 'all in one' inverter/charger/solar controller would be $300-500 in the cheaper brands. You could do separate inverter, optional AC charger, and solar controller but you'd need to make a lot more connections and unlike the AIO it doesn't have the built-in option of an internal transfer switch that lets you run grid power as a backup off of simple extension cords. That would let you run cords out there temporarily until you get the system truly 'self-sustaining' and then reel up those cords for good. With separate components you'd have to either implement an automatic transfer switch (more money + install complexity) OR manually go plug in an AC charger which leaves all kind of room for error (i.e. without some kind of wifi connection you're not going to know if the system is struggling unless you happen to walk out there). SO i'd suggest an AIO and some extension cords until you get the solar and battery amounts nailed down. Technically if you had an AIO and some extension cords you could run batteryless off of solar and AC power and get a feel for how much battery was necessary (by watching accumulated solar power and load power in kwh which a lot of inverters track and can display on their screens) before you ever even bought any.

 

[wme]

Having "a just enough perfect sized system" isn't big enough

 

[Whats-n-Watts]

Hi guys I went yesterday and got a killowatt meter. I also swapped out appliances. You can imagine the starting amps for a side by side 1995 refrigerator and a 1993 upright freezer. Even without solar that's going to save a great deal of electricity. Start amps on the refrigerator was a whopping 11.5 amps and 9.5 amps on the old upright freezer. I have preliminary data on starting amps which are much lower now as well as running amps / watts.
Unfortunately I do not have 24hr measurements yet. I plan to record those as well as run time for each appliance during off-peak hours only so I can get an accurate bank size needed.
I've decided to go with a 24v hybrid inverter at 2,000 watts continuous load rating. It will switch to grid should it need too. It will run with or without batteries. I have a couple of questions if anyone can answer them for me.
Number one if I have a battery bank will the battery compensate for the starting load should the panel output not be high enough to power the start load? My starting load for two freezers and a mini-fridge is currently 11.39 amps. My running amps are 2.2 amps combined and a sum of 207.8 watts. Again that's all three combined.
So in a perfect world for solar ( i.e. 4 full winter hours of peak sun with no clouds ) would 4x100w panels handle the running watts of 207.8 as well as charge the battery required to handle the starting amps "if that's how it even works. The gird will be available so reserve capacity isn't a current demand. I was thinking maybe a small 24v just to kick start a small panel array during the day and however long it runs the load is a just a bonus at this point. I'm guessing it wouldn't be impossible to add more bank later as well as panels so what do you guys think? Will it work?
Closing with wishing you all a great rest of the week and hope it's been good so far.
Dexter ?

 

[Hogheavenfarm]

Four panels is a good start, but I would plan on adding them as you go. I started my solar experience with 4 100w panels, then I bought 6 used 185w panels, then 4 more 100w panels. I kept making experiments and started from one appliance, gradually adding more. For this you also want at least a 24v system to keep those amps under control. A 48v would be better, but you can always work into that (just get LiPo batteries you can serial together). In good sun you should get 80% out of your panels. My freezers are 4.5 amps, 3.5 amps, and 4 amps, so when they all run about 12 amps at 24v, this figures out to 288w, but I have seen it up to 325w when just running, no startups. I did get a bigger inverter as I want plenty of overhead room for start surges. Summer I get great early charging, but winter is poor and I have to watch the system more closely then.