solar batteries inside a home

Hi all,

I havent posted on any forum in a while. Usually I can find any answer I need with Google or by searching forums but this one is more difficult. And since it has to do with my safety and the safety of my parents home, I want to get as much input about it as possible before maybe doing something careless.

I want to setup my first solar panel to see if it can power my chest freezer. It's 100 watts and I also bought 2 marine batteries from Costco, a Sunforce 30 amp charge controller and a Whisteler 1600 watt inverter.

My question is, do you all think just 2 batteries in a 20' x 10' x 8' room being charged with (1) 100 watt solar panel need to be ventilated to the outside? There would always be at least a little bit of ventilation from the 2 windows in the room that dont close air-tight and with the rest of the house. But even hypothetically, if the room was sealed, would the 2 batteries be able to produce enough hydrogen to be dangerous in such a large space? I have plans to build a box outside and will probably do that anyway but just wanted to get some thoughts on the alternative. May be useful to someone else someday. Thanks for your input!

David

I would still like to hear anything you guys have to say about this, although I have decided to build the outdoor box regardless. There are other benefits besides safety in doing it that way, and it will just be a little work to build the box.

I have 18 panels (250 watts each) powering batteries that weigh a total of 3600 pounds.
They are covered by some plastic that captures the rising hydrogen and vents them out a 1/2 inch hole to the outside.

1). I don't think you'll be making enough hydrogen to worry about, but don't light matches around the batteries, try to vent them as best you can and please don't blame me if you blow up.
2). Sealed batteries would produce much less gass.
3). I fear you won't be able to power a freezer on what you have. Lights....yes. Freezer....you will want a much bigger system.
Call Isaac at wholesale solar and ask him what he thinks. He never steers me wrong.

Best of luck.

Sealed gel batteries could be put in a living space, but not lead-acid batteries. In my opinion, you're just asking for an accident. And although its not apt to happen, a battery could explode. I've never had it happen but a good friend of ours had one explode in the middle of the night. Scared the bejeezes out of him.

Is your chest freezer a Steca or Sundanzer? If not, then your 100 watt solar panel won't be enough. You need to check the panel on the freezer and determine how many watts it needs in a 24 hour period. Then determine how much good sunlight you get per day and thus how many watts you can generate.

Do you plan to plug your freezer into your normal house if you get a stretch of cloudy weather or have you considered needing a generator to top up the batteries as needed? Batteries aren't like a gas tank. You just can't draw power until they die, then plan to simply recharge/refill them the next sunny day.

We started out with solar 10 years ago. Killed our first set of batteries within a year. Finally learned enough about solar to get the next battery bank to last 6 years before starting to fail. Replaced the bank and salvaged 6 batteries in good enough shape to bring back online. Should get about 3-4 more years out of them, but using them in a different system, of course. Can't mix old batteries with new ones.

...Su Ba
www.kaufarmer.blogspot.com

Thanks Mark and Su Ba for the replies. I'm going to store them outside after all. In an effort to be more active on forums again, I will try to post some pics of the box when it's done, as well as the entire setup and let you all know how my experiments go. I'm aware that I may not be able to power the chest freezer with only 1 panel, however I am not about to rule it out. I've been measuring it's power consumption with a kill-a-watt for the past 35 hours and it's at 1.38 kilowatt hours. If I get .1 KWH from the panel every hour of sunlight, and even if I get just 8 hours of full sun per day, that is about .033 KWH per hour the entire day. That's just under what the chest freezer is drawing. So I will watch the charge controller and battery levels closely while Im experimenting. If it doesnt work I'll just power something else with it or buy another panel. Thanks again and I'll keep you posted.

David

So the first and last hour of sunlight during the day will not provide you with much power since the sun will be at such a low angle. This is why solar planners use 6 hours as the standard in their calculations. And you will get less than that during the winter. You also should assume that 10-20% of the power will be lost due to inefficiencies of the battery charger and another 10% if you are going through an inverter to power 120VAC devices. You will want ot increase your PV panel capacity to compensate.

Thanks Tom, I had forgotten about the loss in the charge controller and inverter. And did not know about only getting 6 hours due to the angle of the sun at morning and night. Looks like Ill be getting another panel. Had planned on it anyway, just need to do it sooner now =)

David Taylor wrote:Thanks Tom, I had forgotten about the loss in the charge controller and inverter. And did not know about only getting 6 hours due to the angle of the sun at morning and night. Looks like Ill be getting another panel. Had planned on it anyway, just need to do it sooner now =)

Hi David. A 200 watt off grid system is not nearly enough for 1.4 KWh per day. Also, the battery may have to be larger than you think as well. Also, please note that the battery losses can be substantial. Figure battery losses on the order fo 20-30%, inverter losses at about 15%, and controller losses at least 5%. Add other losses like transmission losses and dust/debris on the panels and you're looking at overall losses of nearly 50% for an off grid solar PV system. A conservative estimate of actual production can be found by taking the product (solar insolation)(PV array wattage)(0.5).

Marcos Buenijo wrote:Hi David. A 200 watt off grid system is not nearly enough for 1.4 kWh per day. Also, the battery is going to be larger than you think as well.

Hi Marcos,

This small beginner setup is just to experiment with to see what kind of numbers I get and to help teach myself the difference between all the power terms, what they mean and how to do some calculations. Yes, I am learning already that a single 100 Watt panel, even 2, will not be enough to power my chest freezer. However I see it as a bit closer than not nearly enough. The chest freezer does not draw 1.4 kWh. I had it connected to my Kill-A-Watt meter for 368 hours and it measured 17.32 kWh over that time. So that works out to about 1.13 kWh per day.

One 100 Watt solar panel producing 80 Watts per hour (after system loss) for 6 hours a day is 480 Watts or .48 kWh per day. Right?

So (2) 100 Watt panels would be .96 and (3) would be 1.44; enough for the freezer and then some.

As far as the batteries go, I bought (2) deep cycle marine batteries from Costco that are rated at 85 Ah each. So if fully charged they should be able to provide 2040 Wh at 12 VDC or 2.04 kWh. Plenty to keep up with the chest freezer and several other devices. Granted, they are limited to the amount of power they are being charged with, so I would just have to make sure I stay below that with how much I draw. So a lot of their potential would be going unused. At least I have that buffer so I can add more panels.

The charge controller I got is a Sunforce 30 Amp so that would limit me to (4) 100 Watt panels, maybe 5. The panel I got has an Ipm rating of 5.59 and an Isc rating of 6.19. Google told me that the Ipm rating is the ideal current production level, and the Isc rating is the most current the panel will produce before it shorts out. So ideally, 5 panels would produce 27.95 Amps, but even if they each produced just a little more than 6 amps each and stayed under their Isc, they could still overload the charge controller so that tells me I should stay with no more than (4) 100 watt panels and maybe 1 more smaller one.

Does this all seem right to you?

As for the original topic of this thread, I have the outdoor battery box nearly complete and will post some pics of it soon. And I have the 1 panel on the roof. No drilling or mounting hardware necessary. More on that when I post the pics of the box. It involves the peak of the roof, some rope and a counterbalance...

Marcos Buenijo wrote:

David Taylor wrote:Thanks Tom, I had forgotten about the loss in the charge controller and inverter. And did not know about only getting 6 hours due to the angle of the sun at morning and night. Looks like Ill be getting another panel. Had planned on it anyway, just need to do it sooner now =)

Hi David. A 200 watt off grid system is not nearly enough for 1.4 KWh per day. Also, the battery may have to be larger than you think as well. Also, please note that the battery losses can be substantial. Figure battery losses on the order fo 20-30%, inverter losses at about 15%, and controller losses at least 5%. Add other losses like transmission losses and dust/debris on the panels and you're looking at overall losses of nearly 50% for an off grid solar PV system. A conservative estimate of actual production can be found by taking the product (solar insolation)(PV array wattage)(0.5).

Oh wow, you added a bit more as I wrote that reply...I will read it carefully and post my thoughts.

...

Ok, ouch! 50%? From what I had gathered from a few different sites when I was researching, including Tom OHern's post earlier in this thread, the general consensus was 15-30% loss. Looks like I will just have to finish setting it up and test the numbers. I will clean the panels regularly to maximize their efficiency.

David Taylor wrote:Ok, ouch! 50%? From what I had gathered from a few different sites when I was researching, including Tom OHern's post earlier in this thread, the general consensus was 15-30% loss. Looks like I will just have to finish setting it up and test the numbers. I will clean the panels regularly to maximize their efficiency.

Battery losses are the major loss in off grid PV systems. Furthermore, the losses in the battery vary a great deal as a function of battery state of charge. It's a catch 22. Here's how: excessive discharge kills a lead acid battery. Therefore, a reliable off grid power system requires a large battery to prevent excessive discharge. However, the battery is most inefficient at a high state of charge! (dammit Jim!). For example, when charging from 60% state of charge (and you never want to drop below this) to float you will see losses of roughly 1/3 (33%). When charging from a state of charge of about 80% to float the losses are roughly 50%. When you factor in the losses in the charger, inverter, transmission losses, and debris on the panels, then you get down to roughly 50%. Your 15-30% figure is almost certainly based on a grid-tie system. For example, if you reference the PV Watts program they use a default derate factor of 0.77 for a grid tie system which consolidates all losses. Add the battery losses seen in an off grid system and the derate factor of about 0.50 becomes reasonable (although, I would put the overall losses from 50-60% for off grid PV systems depending on how they're designed and operated. Those that use most of the electricity while the panels are producing will avoid a lot of battery losses - see discussion below).

"A Study of Lead-Acid Battery Efficiency Near Top-of-Charge and the Impact on PV System Design"
http://www.localenergy.org/pdfs/Document%20Library/Lead%20Acid%20Battery%20Efficiency.pdf

There is a way around this, but not without effort. It's possible to provide a thermal mass in a freezer, drop the thermostat to the lowest setting, then place the unit on a timer so that it operates only while the solar array is producing. In principle, this will allow the current from the array to mostly bypass the battery and avoid most of the battery losses (it moves straight through the inverter and compressor motor circuit). In this configuration the battery is acting primarily as a voltage regulator for the circuit rather than an energy storage device. The thermal mass takes the place of this energy storage function. A salt water solution can be used as a thermal mass by lowering the freezing point of the solution. Freezers should be kept lower than 15F. An aqueous solution of sodium chloride can have its freezing point depressed to as low as -6F. Something like 5F would be appropriate. Other salts might be used as well. This approach can also allow for greatly reducing the size of the battery, and it's also possible in principle to provide enough thermal mass to carry the freezer through several days of zero solar flux, especially with added insulation on the freezer.

ADDENDUM: Just wanted to clarify the argument in the last paragraph. The idea there is to make hay while the sun is shining. If all the electricity from the array (via the controller) is put to use at the exact rate that it is generated, then there will be zero battery losses. Of course, it's not possible to use the electricity from the array at the exact rate it's produced (at least not in an off grid system), but it's possible to reduce battery losses by taking advantage of this principle.

Thanks so much for all that great information and the ideas, Marcos. At this early point in my experiments with solar power, with sooooo much yet to learn and absorb, I just need to hook it up and start reading the numbers and see what I get. I'm glad you gave me the heads up about the much higher loss than I had been expecting. Frustrating to learn that but I'm anxious to see what I get from the components I chose. Will keep you posted.

David Taylor wrote:
One 100 Watt solar panel producing 80 Watts per hour (after system loss) for 6 hours a day is 480 Watts or .48 kWh per day. Right?

So (2) 100 Watt panels would be .96 and (3) would be 1.44; enough for the freezer and then some.

Not quite. I think you've forgot about converting 12v to 120v.

Cj Verde wrote:

David Taylor wrote:
One 100 Watt solar panel producing 80 Watts per hour (after system loss) for 6 hours a day is 480 Watts or .48 kWh per day. Right?

So (2) 100 Watt panels would be .96 and (3) would be 1.44; enough for the freezer and then some.

Not quite. I think you've forgot about converting 12v to 120v.

Actually, that's why I figured in 20% loss from the charge controller and inverter. After everything said here, I am now prepared for up to 50% loss including from the batteries. Really hoping it's not that much though!

No, that's not what I meant.

100 watts dc 12v is like 10 watts ac 120v!

I'm used to thinking in amps though. So my when my charge controller says we're getting in 40 amps on a sunny day that's great but the well pump uses 11 amps AC which is 110 amps DC! See?

Here's an important formula:
watts/volts = amps

One more thing for reference.
I have 17 panels of various wattage and the smallest chest freezer I can find. I only run it late spring/summer early fall so I'll be turning off soon. Of course, my whole house is off-grid, and I live in Vermont which I think gets an average of 4 hours over the year!

David Taylor wrote:Thanks so much for all that great information and the ideas, Marcos. At this early point in my experiments with solar power, with sooooo much yet to learn and absorb, I just need to hook it up and start reading the numbers and see what I get. I'm glad you gave me the heads up about the much higher loss than I had been expecting. Frustrating to learn that but I'm anxious to see what I get from the components I chose. Will keep you posted.

You're welcome. I look forward to your results.

Cj Verde wrote:No, that's not what I meant.

100 watts dc 12v is like 10 watts ac 120v!

I'm used to thinking in amps though. So my when my charge controller says we're getting in 40 amps on a sunny day that's great but the well pump uses 11 amps AC which is 110 amps DC! See?

Ahh ok. Thanks for the heads up about that. I definitely did not realize.

Cj Verde wrote:Here's an important formula:
watts/volts = amps

Good to know. I will write that one down.

Cj Verde wrote:One more thing for reference.
I have 17 panels of various wattage and the smallest chest freezer I can find. I only run it late spring/summer early fall so I'll be turning off soon. Of course, my whole house is off-grid, and I live in Vermont which I think gets an average of 4 hours over the year!

Cool. Sounds like you built your solar collection like I'm planning to...one panel at a time over a few years. Is that right? What other kind of devices do you run off that setup? Thanks again for the help.

Well, we run our whole house. We do have a sun frost fridge/freezer which we've had for like 20 years but the fridge part hasn't really worked work well for a few years & even new I wasn't totally thrilled for the price.

The point is reduce your energy consumption - big time! We do run our generator quite a bit during the winter especially to run our pump. A great thing we did last winter was to put the pump on a timer switch because we used to turn it on and if we forgot to turn it off it would really run down the battery if the pump kicked on.

There are things you should just do without like a frost free freezer or a toaster oven or AC or electric dryer or electric water heater....

We do have a DSL modem on all the time (sometimes I'll put a timer on it so its off for 6 hours while everyone should be sleeping - I've got 2 teenagers). I do have a small aquaponics setup and the pump runs 15 minutes / hour (15 minutes / 3 hours at night). My husband isn't thrill about that though. He thinks its a drag on the batteries.

Cj Verde wrote:Well, we run our whole house. We do have a sun frost fridge/freezer which we've had for like 20 years but the fridge part hasn't really worked work well for a few years & even new I wasn't totally thrilled for the price.

The point is reduce your energy consumption - big time! We do run our generator quite a bit during the winter especially to run our pump. A great thing we did last winter was to put the pump on a timer switch because we used to turn it on and if we forgot to turn it off it would really run down the battery if the pump kicked on.

There are things you should just do without like a frost free freezer or a toaster oven or AC or electric dryer or electric water heater....

We do have a DSL modem on all the time (sometimes I'll put a timer on it so its off for 6 hours while everyone should be sleeping - I've got 2 teenagers). I do have a small aquaponics setup and the pump runs 15 minutes / hour (15 minutes / 3 hours at night). My husband isn't thrill about that though. He thinks its a drag on the batteries.

Yes, I am already in 'reduce-big time' mode. Recently sold my 250 watt max/80 watt idle tower PC and invested in a 26 watt max/9 watt idle Fit-PC3 mini PC (also happens to run off unregulated 10-15 VDC so could run off panels directly and bypass inverter). And have started monitoring all my power devices with a Kill-a-watt meter and am thinking about how long I use them and if I even want them anymore. It is definitely a mind-set. I'm fortunate to have a buffer period to learn, adjust my habits and plan ahead while I'm living with my parents.

David Taylor wrote:Yes, I am already in 'reduce-big time' mode. Recently sold my 250 watt max/80 watt idle tower PC and invested in a 26 watt max/9 watt idle Fit-PC3 mini PC (also happens to run off unregulated 10-15 VDC so could run off panels directly and bypass inverter). And have started monitoring all my power devices with a Kill-a-watt meter and am thinking about how long I use them and if I even want them anymore. It is definitely a mind-set. I'm fortunate to have a buffer period to learn, adjust my habits and plan ahead while I'm living with my parents.

Hi David. Where can you buy the computer you mention here, and what kind of pricing are we looking at?

Marcos Buenijo wrote:

Hi David. Where can you buy the computer you mention here, and what kind of pricing are we looking at?

Hey Marcos,

I got it at Amazon here and it's currently $379 with free shipping. And here's the specs for it. That company makes several different mini low power PCs so you may want to check a few of them out. One of them uses 3 watts at idle! Unfortunately that one is Linux only and does not support Flash (youtube) so that one was out for me. So far the one I got has been working very well. Running Windows 7 and it's plenty fast for it's size and power.

Listen to podcasts available at www.battery1234.com. Also note that Steven Harris has done about 15 such podcasts on The Survival Podcast hosted by Jack Spirco. These are packed with practical alternative energy information.

Steven Harris considers the hydrogen production from batteries to be neglible, but you'll have to listen to the podcasts to get his full discussion (starts at 65:45 of part 1).

Marcos Buenijo wrote:Listen to podcasts available at www.battery1234.com. Also note that Steven Harris has done about 15 such podcasts on The Survival Podcast hosted by Jack Spirco. These are packed with practical alternative energy information.

Steven Harris considers the hydrogen production from batteries to be neglible, but you'll have to listen to the podcasts to get his full discussion (starts at 65:45 of part 1).

I will check those out, thanks.