Small system to power small freezer

[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).

 

[Sonnyboy]

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.

Thanks Michael. The specs of my Epever SCC state 520w max for solar input at 12v and 1040w on a 24v system. I only have a single pitch roof to mount on but the trees make it so I only get direct Sun on the whole roof for about four hours max.

 

[Leeds]

Before you add solar panels to your system have you considered making your current setup run more efficiently?

Your design appears to keep the inverter on all the time. Spend the $15 on an inkbird style 12vdc digital thermostat and wire it's cooling relay output it in series with the go signal in your inverter.

This $15 should just about cut your battery drain in half.

 

[Sonnyboy]

Before you add solar panels to your system have you considered making your current setup run more efficiently?

Your design appears to keep the inverter on all the time. Spend the $15 on an inkbird style 12vdc digital thermostat and wire it's cooling relay output it in series with the go signal in your inverter.

This $15 should just about cut your battery drain in half.

Whoa, really? Thanks, I wasn’t aware of that. I will check that out.

 

[Sonnyboy]

Before you add solar panels to your system have you considered making your current setup run more efficiently?

Your design appears to keep the inverter on all the time. Spend the $15 on an inkbird style 12vdc digital thermostat and wire it's cooling relay output it in series with the go signal in your inverter.

This $15 should just about cut your battery drain in half.

Would you mind being more specific with your wiring suggestion? I am going to try this.

 

[Leeds]

Would you mind being more specific with your wiring suggestion? I am going to try this.

Sure thing. This is what I'm describing:

 

[Leeds]

To be clear- you'll now be in charge of the temp in the freezer.
Before you take over that control (before wiring the relay in the back of the stat to the inverter switch) I would suggest that you power up the thermostat and watch what it does for a few days.
If you drape the temp sensor in the freezer the internal temp will be displayed. Note how high and how low the temperature goes when you have the freezer set at your preferred temp.
Then set the inkbird to come on a degree or two higher than the freezer comes on and set it to go off a degree or two higher than the freezer goes off. Then cut into the circuit and you're done.

 

[MichaelK]

Thanks Michael. The specs of my Epever SCC state 520w max for solar input at 12v and 1040w on a 24v system.

Keep in mind that these are the "pen and paper" design specifications. The real-world is somewhat different. You need to remember that the panel specifications are determined in a special test chamber held at a specific temperature (25C) with an artificial light source producing exactly 1000W/square meter.

In the real-world though, panels will rarely, if ever produce their rated output. That's because the sun at the earth's surface is not exactly 1000W/square meter, and the panels are hotter than 25C. From empirical testing, I've routinely used 85% as a "de-rating" for the label specifications. If you go through any of my other posts where I do solar production calculations, you will see that 85% value popping up over and over.

So, what will give you an honest 40A while charging at 13V, the math is..... (40A X 13V)/85% = 612W. Call that two 300W panels.

 

[Sonnyboy]

Someone should invent a box that turns on additional panels in overcast conditions and deactivates them when the sun is shining again.

 

[pollenface]

Someone should invent a box that turns on additional panels in overcast conditions and deactivates them when the sun is shining again.

someone has already done that here, I read it about 6 months ago

 

[efficientPV]

Why disconnect them? Find a use for the power. I use diverters to heat water and all energy is used every day.

 

[Sonnyboy]

Why disconnect them? Find a use for the power. I use diverters to heat water and all energy is used every day.

It’s a matter of planning really. At the moment, the solar and power is located away from any other possible use cases. But in the future that might change, so until then, if I add more panels with my current setup, it’d be great to be able to easily(automatically) engage them when needed and disengage them when they would throw too much wattage to my controller.

What if I wired them to a manual cut off switch and activated them manually when the days were overcast?

 

[Sonnyboy]

Keep in mind that these are the "pen and paper" design specifications. The real-world is somewhat different. You need to remember that the panel specifications are determined in a special test chamber held at a specific temperature (25C) with an artificial light source producing exactly 1000W/square meter.

In the real-world though, panels will rarely, if ever produce their rated output. That's because the sun at the earth's surface is not exactly 1000W/square meter, and the panels are hotter than 25C. From empirical testing, I've routinely used 85% as a "de-rating" for the label specifications. If you go through any of my other posts where I do solar production calculations, you will see that 85% value popping up over and over.

So, what will give you an honest 40A while charging at 13V, the math is..... (40A X 13V)/85% = 612W. Call that two 300W panels.

So if I add say 600 or 1200 additional watts of panels to my system on overcast days will that fry my controller? When you say you are overpaneled, are you over your limit for what your controller can handle but because of placement it works? I would like to not have to upgrade to 24v at this time.

 

[SamDeleted]

but my amp capacity is reduced this way to 100Ah

Yes but you've got the same amount of watts, two batteries wired either way around , they still have the same capacity

Two 100ah 12v batteries in parallel:

12v X 200ah = 2400w



Two 100ah 12v batteries in series (to make 24v):

24v X 100ah = 2400w

 

[SamDeleted]

I run a whole house, dishwasher, hot water, laundry, etc, besides refrigeration on a single car battery

I'd have to see it to believe it!

How does that work then, do you only use appliances when the panels are making ?

 

[12VoltInstalls]

located away from any other possible use cases

Not being mean and nothing personal but “use case” is too many letters to say “use” or “purpose.” Just say what you mean and leave the pseudo jargon buzz phrases to die and rot away. There’s nothing clinically advantageous to be gained by using extra words.

do you only use appliances when the panels are making

That seems the only logical possibility. The battery is just an in-the-moment capacitor with a long discharge characteristic.

When you say you are overpaneled, are you over your limit for what your controller can handle but because of placement it works? I would like to not have to upgrade to 24v at this time

If your demand is under 2200W or so and you already have adequate panel wattage on sunny days, adding panels to perhaps have enough harvest on cloudy days does not require moving to 24V. You just will have a lot of wattage unused. It’s the ‘cost of doing business’ in northern latitudes. While I don’t want to confuse a tank of gas as a metaphor for a battery, I’m going to use it as a metaphor for extra panel wattage. It’s like having a full gas tank versus putting $2 of gas in every time you drive 10 miles. The full tank of gas (having extra panels for cloudy-day solar) doesn’t waste the remainder of the tank of gas but it is available the next time you need to drive 60 or 100 miles. There is no real ‘waste’ with solar. They will still last 20 years whether you daily use 100% of panel capacity or 20% of panel capacity.