Want To Build Small Inexpensive System

[danrclem]

Hi, new guy here.

I'm wanting to build a small system to get by if we have a power outage. I'm wanting something that I can put up and take down as needed. I've already bought two lead acid deep cycle batteries and a 700 watt, Renogy inverter. In hindsight I probably should have joined a forum such as this before I bought anything.

It depends on the cost but I'm wanting to buy two to four 100 watts panels. From reading some and watching YouTube videos I think that I want an MPPT charge controller. I've looked at some kits by Renogy and some of them seem to be decently priced. I'm really not sure what amp size charge controller that I need. I'm not necessarily buying Renogy but I'd like some suggestions from people in the know. Do any of you have any suggestions as to kits, brands or any other information that would be useful to me? Any help will be appreciated.

 

[MisterSandals]

I've already bought two lead acid deep cycle batteries and a 700 watt, Renogy inverter.

If you're locked into these, lets see what we can do. What batteries and inverter?

I'm wanting to buy two to four 100 watts panels.

Likely not the best option.

Do any of you have any suggestions as to kits,

Avoid them.

 

[OffGridForGood]

Hi, new guy here.

I'm wanting to build a small system to get by if we have a power outage. I'm wanting something that I can put up and take down as needed. I've already bought two lead acid deep cycle batteries and a 700 watt, Renogy inverter. In hindsight I probably should have joined a forum such as this before I bought anything.

It depends on the cost but I'm wanting to buy two to four 100 watts panels. From reading some and watching YouTube videos I think that I want an MPPT charge controller. I've looked at some kits by Renogy and some of them seem to be decently priced. I'm really not sure what amp size charge controller that I need. I'm not necessarily buying Renogy but I'd like some suggestions from people in the know. Do any of you have any suggestions as to kits, brands or any other information that would be useful to me? Any help will be appreciated.

Welcome to the Forum @danrclem glad you joined and made your first post!
Now that you are a member, you can search the forum for key words and read past postings and discussions on exactly this topic. I would suggest (if you haven't already) check out Will Prowse (owner of this forum) on his YouTube channel where you will see many small systems Will set up and tested using low cost parts and pieces. You're here and we are all glad to help out.

 

[danrclem]

If you're locked into these, lets see what we can do. What batteries and inverter?


Likely not the best option.

Avoid them.

I'll post links to the inverter and batteries. The reason I was thinking kits is because they seem to have better prices and I would think they would have matched parts. I was wanting something that I could maybe build on down the road. Batteries will have to be replaced later on so maybe I can get better ones then. Cost is a concern but I want to have reliable parts.

For a charge controller I was thinking that maybe this one would work.

https://www.amazon.com/Controller-Regulator-Negative-Temperature-Communication/dp/B07B9NFHS3

This is what I already have.

700W 12V Pure Sine Wave Inverter

The Renogy 1000W Inverter transforms the DC electricity stored in batteries into standard household AC power. Free delivery! Order now!

www.renogy.com

Rural King Deep Cycle Marine/RV Battery - DC31HDT | Rural King

Rural King Deep Cycle Marine/RV Battery - DC31HDT

www.ruralking.com

 

[danrclem]

Welcome to the Forum @danrclem glad you joined and made your first post!
Now that you are a member, you can search the forum for key words and read past postings and discussions on exactly this topic. I would suggest (if you haven't already) check out Will Prowse (owner of this forum) on his YouTube channel where you will see many small systems Will set up and tested using low cost parts and pieces. You're here and we are all glad to help out.

I had already found and watched some of the videos by Will Prowse and it seems like he's very knowledgeable on solar energy. I've done some searching but a lot of it doesn't pertain to my specific case. I guess the more I learn the more things will start to make more sense to me.

Thanks for the replies.

 

[SeaGal]

I had already found and watched some of the videos by Will Prowse and it seems like he's very knowledgeable on solar energy.

... there's no uncertainty

 

[MisterSandals]

I'm wanting to build a small system to get by if we have a power outage.

Lets start at the beginning. What do you expect to power and for how long? Getting your goal figured out will help us get there.

Your batteries appear to be 100Ah each and 50% dischargeable without damage:

2x 100Ah x 12.8V nominal x .5 usable = 1280Wh

A typical refrigerator will need about 2000Wh per day as an example.

To recharge your battery from empty in a day, assuming 3 hours winter, 5 hours summer:

1280Wh / 3h = 427W of solar operating at 100%, so maybe 600W+ of panels. More if you are running loads while charging.

600W of solar / 14V charging = 43A solar charger
The Rich solar charger is sized about right for this. But a value priced SCC operating at 100% may not have good longevity.

How much will you be relying on this system as a source of power?

 

[danrclem]

Lets start at the beginning. What do you expect to power and for how long? Getting your goal figured out will help us get there.

Your batteries appear to be 100Ah each and 50% dischargeable without damage:

2x 100Ah x 12.8V nominal x .5 usable = 1280Wh

A typical refrigerator will need about 2000Wh per day as an example.

To recharge your battery from empty in a day, assuming 3 hours winter, 5 hours summer:

1280Wh / 3h = 427W of solar operating at 100%, so maybe 600W+ of panels. More if you are running loads while charging.

600W of solar / 14V charging = 43A solar charger
The Rich solar charger is sized about right for this. But a value priced SCC operating at 100% may not have good longevity.

How much will you be relying on this system as a source of power?

Powering lights, maybe a tv from time to time and a radio. I have a gas cook stove and heat with wood so those things won't be included in the power drain. I can do without AC and hot water if need be. I believe it should cover most of what I want to do except for the refrigerator.

On Rural King's site in the questions section a few people said these batteries are good for up to 200Ah. This could very well not be accurate because it could be people like me answering those questions. It says it has a RC of 210 hrs. but I realize that isn't the same thing as Ah.

Earlier this year we had an outage for three days but that is unusual. The longest outage that I can remember was for almost two weeks after an ice storm but that's been many years ago. If the grid went down, then it's hard to say how long I would be needing it.

What would it take for me to be able to run a refrigerator reliably?

 

[MisterSandals]

What would it take for me to be able to run a refrigerator reliably?

Do you have any info specs on your refrigerator?

The 2000Wh number is bandied around here quite a bit for a standard residential refrigerator.

So you'd need to harvest and store at least this much each day.



Thats 2.57h in december of solar on a sunny day (maybe 5% when cloudy).

2000Wh / 2.57h = 778W of solar so about 1000W array.
1000W / 14V charging = 72A charger (thats a lot for a 12V battery)

3 of these 325W panels ($100 each) a far far better choice that 10x 100W panels

Used GCL GCL-P6/72 325W 72 Cell 325 Watt Polycrystalline Solar Panels - electronics - by dealer - sale - craigslist

"I have recertified GCL-Poly (Suzhou) Energy 325W solar panels available for a limited time. These were recently decommissioned from a working system, processed by Solar Steals technicians,...

louisville.craigslist.org

 

[danrclem]

I looked the specs up on my refrigerator. The energy guide said that it used 702kWh per year which would be 702,000Wh per year. I divided that by 365 days and came up with 1923.28Wh per day so the 2000Wh per day is really close.

So if I went with 975 Watts of solar panels then I'd need at least a 72A charge controller? That would have to be an MPPT controller, correct?
Is that a lot for a 12V battery no matter how many batteries are hooked up?

I'll check into those panels that you gave a link to. Sounds like a good deal.

If I should ever decide to make this system bigger would I be able to keep all parts and then just add to them? If I'm reading right charge controllers can be added if needed.

I'm thinking that I can maybe put the panels on my garage and later on feed them into the house system but that's a whole other discussion. The worst part about that is that the panels won't be facing south. The garage electricity is coming from the house.

I really appreciate your help and if I'm wrong about anything don't hesitate to tell me.

 

[HOU_Castle]

I looked the specs up on my refrigerator. The energy guide said that it used 702kWh per year which would be 702,000Wh per year. I divided that by 365 days and came up with 1923.28Wh per day so the 2000Wh per day is really close.

So if I went with 975 Watts of solar panels then I'd need at least a 72A charge controller? That would have to be an MPPT controller, correct?
Is that a lot for a 12V battery no matter how many batteries are hooked up?

I'll check into those panels that you gave a link to. Sounds like a good deal.

If I should ever decide to make this system bigger would I be able to keep all parts and then just add to them? If I'm reading right charge controllers can be added if needed.

I'm thinking that I can maybe put the panels on my garage and later on feed them into the house system but that's a whole other discussion. The worst part about that is that the panels won't be facing south. The garage electricity is coming from the house.

I really appreciate your help and if I'm wrong about anything don't hesitate to tell me.

Can you supply the refrig operating voltage and current? this is also to calculate power surge.

 

[danrclem]

Can you supply the refrig operating voltage and current? this is also to calculate power surge.

I'll post it if I can find it. I might have to pull the refrigerator out and see what's on the back of it.

Edit;
On the inside of the refrigerator it says "FULL LOAD AMP 7.2." Not sure if that helps.

 

[OffGridForGood]

The FLA does not equal the in-rush starting amp upon start. A good quality multimeter with an in-rush function would capture the actual max on start up. About 3x FLA it seems from my fridge.

 

[ryankshaw]

So if I went with 975 Watts of solar panels then I'd need at least a 72A charge controller? That would have to be an MPPT controller, correct?
Is that a lot for a 12V battery no matter how many batteries are hooked up?

that is correct. that's a lot of amps at 12 volts. that's why it makes sense to up your system voltage to 48v (or at the very least 24 v) at that kind of wattage. then you don't need such beefy and large charge controllers, inverter, and wires

 

[Smeeg]

Large RV Solar Power Blueprints

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

 

[Smeeg]

 

[Smeeg]

https://www.mobile-solarpower.com/2000-watt-24v-solar-system.html

 

[AT1(AW)]

FWIW, I bought a kit from Rich and have had no problems. 3 200 watt panels, 2000 watt inverter, 40 amp SCC, and all the wiring needed, all for just over a grand. I also have 2 200 ah lifep04s. I use it to run a 20 cuft refer/freezer. Your 750 w inverter might be pushed during compressor start up. My fridge when running burns about 100 watts and runs about a daily 800 wh in the winter and 1000 to 1250 in the summer. I figure I can get 3 to 4 days of runtime with no sun, but my Batts are usually topped off by lunchtime.

 

[HOU_Castle]

I'll post it if I can find it. I might have to pull the refrigerator out and see what's on the back of it.

Edit;
On the inside of the refrigerator it says "FULL LOAD AMP 7.2." Not sure if that helps.

Again, what is the refrig operating voltage? If your battery is 12V lead acid, and your inverter is 700Watt Continuous or peak rating? And you want to run 7.2A (assuming 110V refrig) plus others. You will end up kill your batteries and inverter in the short run (if your system even can pick it up).

Again, you need to run power audit as per MisterSandal's suggestion.

 

[MichaelK]

An important point to remember in your power audit is that the inverter itself is a load, that needs to be included in the calculations. Inverter draws power just being turned on. How much depends on the brand/model. A general rule of thumb is that background idle is related to the quality of design, and the inverter size. Bigger inverters consume more power. Poorly designed inverters of a certain size consume more power then quality inverters of the same size. Most inverters publish their background idles. If they don't, that's a good reason to avoid it.

To help this thread along, I'll mention my own consumption numbers. In the winter, on days when I'm not there but the frig is on 24/7, I consume as little as 1.5kWh. In summer, when more cooling is required that's 2.5kWh. For you, to keep the frig running, some lights on, and a bit of TV, let's say you need 3.0kWh, or 3000Wh of electricity.

In Kentucky, I'd guestimate you get maybe 3sunhours in winter and maybe 5-6 sunhours in summer. Let's say your power goes off in the winter. If you need 3000Wh per day, and you get 3.0sh per day, then you need 3000Wh/3.0sh = 1000W of panels. You are better off at 24V for this much power. Charging at 25V minimum, you will max out at 40A, so a less expensive controller like an Epever Tracer 4210 will work for you. You can get 60-cell residential panels dirt-cheap. Wire four 250W panels 2S2P, and that 4210 controller will work just fine.

You could wire your existing batteries in series right now for 24V, but only 100Ah at 24V is still rather light. You might want to add a second parallel string of batteries in the near future as finances allow. If the batteries are not yet used, and they can be returned, it might be a better choice to upgrade to four 6V golf-cart batteries, such as Trojan T-105s. That would give you 250Ah of power at 24V, and a better size for 1000W of panels.