Suggestions for Renogy 400W System Emergency/Backup Power

[tamichels]

My husband and I recently purchased about 2/3 of the equipment we need for solar power backup, for our fridge/freezer/portable ceramic or radiant heater, in the event of a grid power outage, and would love if there was a realistic and budget-friendly way to have the backup power come into effect automatically when grid power shuts off (if this is possible). So far, we have (4) 100W Renogy Panels and the 40A Renogy MPPT Charge Controller, as well as a Renogy 12V AGM 200ah battery.

We would like advice on where to go from here to try and achieve our goal above.
1) Best equipment to act as a generator - A power station? A pure sine wave inverter? Other?
2) Do we need any additional monitoring device or devices (ie; low voltage auto shutoff) for the system?
3) We planned to connect the solar panels in parallel - is that the best choice?

Sorry if I haven't provided enough information here. I am a newbie, so am not sure what you need in order to offer some advice.

Thanks in advance!

 

[Rednecktek]

Have you done a power audit yet to figure out your needs? I'm guessing right out the gate that radiant heater is going to kill your system real fast.
The power audit will tell you how many watts everything draws under full load (gives you the inverter size) and how many hours you'll need to feed those watts (battery bank capacity) and you really can't do much without that.

Also, AGM batteries are only good for about 50% capacity, so that 200Ah battery will only get you about 100Ah, or 1200Wh of usable power. If you were to plug in a 1500w radiant heater it would drain your battery dry in about 45 minutes and take 4 hours of direct sun to recharge.

All you should need is an inverter to change the 12v battery DC into appliance friendly AC and a good battery charger so you can top up the batteries from the grid when there isn't enough solar.

Most of the time your inverter will low-voltage shutoff itself, so just listen to the alarm. Getting a shunt involved will let you monitor how much you've got left and more early warning time, but isn't necessary.

The panels will probably be best connected in a 2s/2p setup with a pair of panels facing SE for morning sun and a pair facing SW for afternoon sun. This nets you the longest power production time with the limited capacity you have panel-wise.

Hopefully that gets you on paper, figure out the power audit and we can help fine-tune from there.

Also, Welcome!

 

[12VoltInstalls]

recently purchased about 2/3 of the equipment we need for solar power backup, for our fridge/freezer/portable ceramic or radiant heater, in the event of a grid power outage

400W might configure to handle the fridge fine, maybe some basic lights or a 600W coffeemaker as well.
The ceramic heater is impractical and not useful in a 400W system. That won’t work to any useful extent

 

[tamichels]

Have you done a power audit yet to figure out your needs? I'm guessing right out the gate that radiant heater is going to kill your system real fast.
The power audit will tell you how many watts everything draws under full load (gives you the inverter size) and how many hours you'll need to feed those watts (battery bank capacity) and you really can't do much without that.

Also, AGM batteries are only good for about 50% capacity, so that 200Ah battery will only get you about 100Ah, or 1200Wh of usable power. If you were to plug in a 1500w radiant heater it would drain your battery dry in about 45 minutes and take 4 hours of direct sun to recharge.

All you should need is an inverter to change the 12v battery DC into appliance friendly AC and a good battery charger so you can top up the batteries from the grid when there isn't enough solar.

Most of the time your inverter will low-voltage shutoff itself, so just listen to the alarm. Getting a shunt involved will let you monitor how much you've got left and more early warning time, but isn't necessary.

The panels will probably be best connected in a 2s/2p setup with a pair of panels facing SE for morning sun and a pair facing SW for afternoon sun. This nets you the longest power production time with the limited capacity you have panel-wise.

Hopefully that gets you on paper, figure out the power audit and we can help fine-tune from there.

Also, Welcome!

Hi again,

Thank you for your reply and information. We don't expect that the 400w of solar we installed will supply power during that time. We are just hoping to use it a a back-up to (even slowly) recharge our battery. We are mostly concerned with using the following items during a power outage:

Refrigerator - 780 watts / 6.5 amps
Small Freezer - 138 watts / 1.15 amps
Radiant Heater (on the low setting) - 750 watts / 6.25 amps
- OR -
Ceramic Heater - 400 watts / 3.33 amps

TOTAL WATTS (w/radiant heater) = 1668 TOTAL AMPS (w/radiant heater) = 13.9
TOTAL WATTS (w/ceramic heater) = 1318 TOTAL AMPS (w/ceramic heater) = 9.98

Just enough to keep our birds warm if placed in a small room during the winter (they are extremely sensitive to temperature), and to keep our food cold/frozen. We can bundle up in layers or blankets, and so can our dogs. We have a small 600w power station - and a Renogy 100W solar suitcase - for our electronics. We have other ways to cook, and even if we need to use our washer (and hang clothes to dry), the washer is 720 watts / 1.15 amps.

So, if you can help me determine what would be our next step (inverter? another battery? another pair of panels? all of these?) I would very much appreciate it. We know the current 400w of solar we have will generate very low wattage during the cloudy days of winter, and so will take forever to charge the battery (once depleted to 50% - if I understand you correctly), but we also have a 5000w propane/gas generator, which we can use to recharge the battery/batteries if needed. At least until we run out of fuel, lol!

Theresa

 

[joeExotic]

If I were you I would go with LiFePO4 batteries and go BIG like 600AH or bigger if you can afford it like 1,080AH with EVE cells. I spent $1,000 for 360AH LFP batteries and I wish I had gotten more batteries. I would also add two more 100w panels. your 40a CC can handle up to 520w at 12v but with 600w array you'll probably be getting 360-400w into the CC. As far as the inverter go get at least a 2,000 w pure sine inverter or even a 3,000w pure sine inverter. Also get a battery monitor, a shunt to show the percentage of the battery life.

Right now I have kind of the same set up as you. 400W panels 12V system, 40A CC mppt, 1,000w inverter pure sine with 360AH LiFePO4 battery. Yes, I am charging my fridge 24/7. I am going to install another two 100w panels soon. hope this helps.

 

[tamichels]

Thanks joeExotic,

I can't afford to do ALL those things, unfortunately, so I have to know what will get me the biggest bang for the buck.
The cheapest (with a reasonable delivery time) is a 100ah LiFePO4 for $300. I can get 100w Renogy panels for $94/ea or a 200w Renogy panel for $222. Do you have to mount them in pairs, or does the 200w work just as well to parallel with the (4) 100w panels I have? It looks like I can get a 3000w inverter for around $300. So, what is the most important if I don't want to spend more than $1200? I'd prefer to spend $1000 because I already spent $700 on the AGM battery and a power station (not a good one) that I will have to pay a lot to ship back. It will take time to recoup those funds.

 

[joeExotic]

If my budget was $1,200 I would spend 400 on panels, 600 on LifePO4 batteries, 200 on inverter and add an extra $100 for wires fuses bolts etc. That way the setup will last you 20+ years without any problems. That's what I would do. You'll have 200AH that you can drain down to 20%. Instead of your AGM that you should only drain down to 50%. But the life cycle is short with AGM. I had one AGM 120ah and it lasted 4 years but by the third year it probably only held 30ah for me to use. So no longer a good experience. With the LifePO4 you'll be happy for min 15 years or even more if you treat them right. Does your CC support lithium?

 

[Rednecktek]

As much as I'm an AGM fan, I gotta agree with @joeExotic for the most part. Going to a LiFeP04 battery will gain you more for your needs than any other individual change to the system. As for the panels, your SCC will probably only take about 60-80v of input for a 12v system, so getting 2 more panels would let you (most likely) do a 3s/2p solar setup using the 4 you already have. That'll free you up about $200 to spend on the battery bank for more run time.

For the inverter you're looking at at LEAST a 2kw Pure Sine inverter to handle all that load without pushing it to its raggedy edge. Spending the money for a 3Kw isn't going to net you any appreciable gains for the money. Likewise going to a 24v system to feed a larger inverter isn't going to net you any real gains for the money.

So similar to @joeExotic, I'd say $200 on panels for a 3s/2p setup, $200-$250 to a good quality 2000w inverter, about $100 for fuses/wire/etc, and drop the rest of your budget getting the most Ah of LiFeP04 batteries you can.

 

[joeExotic]

Hey @Rednecktek right now I have my 100w panels in 2s2p. I would love to add another 100w panel and do the 3s2p. Can you help me with a diagram and do I need to buy a different y branch connector? Also, is it possible to do 3s3p? I just want to add as much array as I can to my 40a CC which max out at 520w at 12v.

 

[MichaelK]

A bit more information needed. You state the following consumption numbers for your frig and freezer.
Refrigerator - 780 watts / 6.5 amps
Small Freezer - 138 watts / 1.15 amps

I'm going to ignore the heaters completely. I'd recommend getting a portable propane heater running off a 5 gallon tank.

Is the 780watts the real-time power consumption while running, or is 780Wh over a 24hr period. If that is real-time, which I seem to think it is, that is very large refrigerator and there is no way 400W of panels is going to keep that running. The freezer number is in line with what I would expect for real-time. Keep in mind that the starting surge of the frig's compressor is likely to be 3-5X the running current, so startup might require 2400-4000W for 1-2 seconds.

A good rule of thumb that has always worked for me is to use 2X your highest consumer to determine the number of watts you need. So, if you have a frig that needs 780W of power, I'd say you need 1600W of panels. This is not carved in stone, but it has worked well for me.

I'm finding on a typical day with lights, TV, computer, and the frig (18cuft) running I consume 3000Wh of power. In winter, with clear sunny weather you can't expect to make this much power with less than 1000W of panels. With that frig, I'd guess you'd need 4000-5000Wh, if my assumptions are correct.

I'd recommend you go to 24V with 1500-1600W of panels and a 250-500Ah of battery, depending on chemistry.

 

[joeExotic]

It sounds like a budget of $1,200 is not going to be enough to power everything you want for an extended period of time. 1,500w of panels = $1,500. 250Ah battery = $700 cheaper if you build it yourself with EVE cells.

 

[MichaelK]

It sounds like a budget of $1,200 is not going to be enough to power everything you want for an extended period of time. 1,500w of panels = $1,500. 250Ah battery = $700 cheaper if you build it yourself with EVE cells.

Go on Craigslist. Last year I was buying high quality 245W Astronergy panels for 55$ each, so that would be 1470W for 330$. I ended up buying thousands of watts both for myself, and all my neighbors that wanted panels. It was cash and carry. I still have thousands of watts that I haven't gotten around to installing yet!

It's the shipping that's the killer with solar panels. Buy locally, and pick them up yourself and save on all that shipping cost. I've even bought panels off Ebay, when local shipping was an option. I just made an arrangement with the seller before making my bid.

 

[tamichels]

As much as I'm an AGM fan, I gotta agree with @joeExotic for the most part. Going to a LiFeP04 battery will gain you more for your needs than any other individual change to the system. As for the panels, your SCC will probably only take about 60-80v of input for a 12v system, so getting 2 more panels would let you (most likely) do a 3s/2p solar setup using the 4 you already have. That'll free you up about $200 to spend on the battery bank for more run time.

For the inverter you're looking at at LEAST a 2kw Pure Sine inverter to handle all that load without pushing it to its raggedy edge. Spending the money for a 3Kw isn't going to net you any appreciable gains for the money. Likewise going to a 24v system to feed a larger inverter isn't going to net you any real gains for the money.

So similar to @joeExotic, I'd say $200 on panels for a 3s/2p setup, $200-$250 to a good quality 2000w inverter, about $100 for fuses/wire/etc, and drop the rest of your budget getting the most Ah of LiFeP04 batteries you can.

Hi again, thank you for the additional input. My MPPT SCC will take 100v and 800w of input according to the Renogy website, so I think I'm OK there, but the website also states that if I want to set up a parallel and series system, you need to have an equal number of panels in each grouping. Does that sound correct? You mentioned me getting 2 panels to add to my existing 4 (which would be 6 total), but then you said that would be a 3s/2p setup. Isn't that 5 panels? So I'm a bit confused there. What would be the benefit to the parallel/series setup? Is it speed of power from panel to MPPT CC?

 

[joeExotic]

Is the 800w 24v? Or 12 v?

 

[chrisski]

What you’re asking for can not be done on a budget. If this is a need, take half that money and spend it on a generator.

Refrigerator - 780 watts / 6.5 amps
Small Freezer - 138 watts / 1.15 amps
Radiant Heater (on the low setting) - 750 watts / 6.25 amps
- OR -
Ceramic Heater - 400 watts / 3.33 amps

The amps you seem to showing are 120 VAC amps, so with the amps from a solar panel to a 12 volt battery would be 10 times what you listed.

The battery is the biggest cost to each build. THe money you save with only going with 400 watts of panels wil be insignificant compared to the cost of a battery to run a 500 watt heater through a 14 hour night in the winter.

Get a kilowatt meter and plug those devices in a week at a time to see the watt hour rating. That will give you an idea of how much energy you need.

Drop the 500 watt heater and get a diesel heater or a kerosene heater, and then you may find the rest of the power requirements can be met. I think after you get your watt hours for the fridge and freezer, you’ll see they don’t come close to 900 watts per hour on average.

 

[joeExotic]

I'm using a space heater and on the lowest setting it uses 400w. Just trying to help here.

 

[Rednecktek]

You mentioned me getting 2 panels to add to my existing 4 (which would be 6 total), but then you said that would be a 3s/2p setup. Isn't that 5 panels? So I'm a bit confused there.

Nomenclature clarification: $s/$p is a term used when talking about combination series & parallel. In this example 3s/2p is 3 panels in series to form a "string", then putting 2 strings in parallel. 3series/2parallel = 6 total panels.

As another example, when I get to camp I'll be installing a 3s/3p array, so 3 panels in series per string, 3 strings in parallel for 12 panels total.

What you NEVER want to do, unless you just nailed the lotto and found the perfect panels, is mix & match numbers of panels. If you had 5 panels and did 3 in series, you wouldn't want to put the other 2 in series and parallel it up. If you're ever in the situation where you have mismatched panels, the only realistic and safe way to use them is putting the oddball panels on a separate charge controller and connecting multiple charge controllers to the battery bank. It happens all the time, not a big deal.

As for why you keep getting people saying it's impossible, it's all about the math in solar stuff. That little heater at 400w for 24 hours would eat 9,600 watt hours, which on a 12v battery is 800Amp Hours of battery power assuming perfect conversion (which isn't real). Even if you went with the cheapest flooded lead acid batteries out there, you would need 14 batteries which even using WallyWorld Specials is $1400.


Or 8 Lithium batteries (since you can use more power out of Lithiums) at about $500ea...

And that's not counting in anything else you might want to use. With your panels you'll need about 30 hours of direct-no-cloud-perfect-angle-bright sun to recharge the batteries, which again never happens. Although, if you do get 30 hours of sun in a day, PM me.

If you can replace the heater with a propane or diesel version (I use the diesel Parking Heaters you see all over YouTube at my camp, LOVE 'EM!) and get a good long run of what the fridge & freezer & lights do over the course of a week then your power needs will drop SIGNIFICANTLY and it's plausible.

As much as we all like solar here, that's kinda in the name, you would be much more cost effective to pop over to Home Depot and get a Champion 2500 Dual-Fuel for about $600 and a big propane tank to feed it for a couple hundred dollars filled and that gets you enough power to keep the birds warm AND the lights on for about half your budget.

 

[joeExotic]

I was told with my 360Ah LFP batteries that I can power my 400w space heater for 8 hours.

 

[G Hale]

I am likely not as expert as some who have posted but I was happy to read you scrapped the heaters. I don't know how many birds or the type but there are 12 volt bird warmers available that would likely not tax your system. Just food for thought your refrigeration and freezing appliances are burden for a small solar backup.