I thought I had this whole Solar power thing down

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  #1  
Old 12-05-13, 06:16 PM
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I thought I had this whole Solar power thing down

I have been doing all kinds of research, and I have a notebook full of formulas. However, I just don't know how to figure out what solar panels I need. Husband and I are planning on having an underground storm shelter that runs on solar energy, and I already know I will need the panels, charge controller, batteries and an inverter. Check. But past that? Dumbfounded.


Basic plans call for

4 overhead fluorescent light fixtures (max 8 hours a day)
3 ventilation fans (12 to 24 hours per day)
Possibly an electric stove, we might go wood (max 2 hours per day)
Possibly a mini fridge (24 hours)
Having excess production for charging devices, etc would be great.

If you have any idea how to figure out what I would need, please let me know!

Specifics:
I know I want Monocrystalline panels. (more expensive, but take up less space)
The location for the panels will be fixed facing South (non-rotating), and gets 5.5 hours a day direct sun (This is for Winter, and only includes time where it is not obstructed by any shade. During summer, will get a little over 3 hours extra sun).
I plan on using 6 volt deep cycle batteries.

I am finding panels for as low as about $2.50 US a watt, but not knowing what I need, I don't know how many total watts I should get. I would like to have extra to allow for reserves, unexpected devices, and to account for loss from the charge controller/inverter. (Ex, if I needed 300 watt hours a day, I would want a battery bank that would support at least 600 watt hours of capacity, but I would actually want extra to offset the 80 to 90% efficiency of the inverter, and of course the correct solar panels to support the system.)

I know I have a lot of info here, but I have TONS of research, but not enough knowledge to apply any of it. I appreciate the help.
 
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  #2  
Old 12-05-13, 06:46 PM
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Welcome to the forums!

How much power you need is purely a question of the load. To do the calculation, you have to start with the total load. It's done in watts, and watts are really watt-hours. You add up the watts for a day, divide by 24, and, I'd say, double that for a safety margin.

4 overhead fluorescent light fixtures (max 8 hours a day)
3 ventilation fans (12 to 24 hours per day)
Possibly an electric stove, we might go wood (max 2 hours per day)
Possibly a mini fridge (24 hours)
Having excess production for charging devices, etc would be great.
How many watts will each of these draw?
 
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Old 12-05-13, 06:52 PM
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May I ask an off topic question? If this is for a storm shelter what keeps the solar cells from blowing away or struck (buried) by flying debris?
 
  #4  
Old 12-05-13, 07:15 PM
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Thanks for your replies! Ray, The reason why the panels are fixed is so they can be stored in the shelter until we need them. Basically, A metal frame stand with wheels and the panels mounted to it. ETA; I meant "fixed" as in not on a solar tracking rig that would turn the panels with the sun.

Nashkat, That's what I kind of need some help with. We haven't purchased any of the individual items. I have yet to find any listings for specific OR general wattage for these items.

Sigh. Grand plans, laid low by little details.
 
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Old 12-05-13, 07:20 PM
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I would recommend LED lighting instead of fluorescent lighting. Draws even less than fluorescent and quite a few even run on 12 volt DC.
 
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Old 12-05-13, 07:30 PM
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4 overhead fluorescent light fixtures (max 8 hours a day)
3 ventilation fans (12 to 24 hours per day)
Possibly an electric stove, we might go wood (max 2 hours per day)
Possibly a mini fridge (24 hours)
Having excess production for charging devices, etc would be great.
With the exception of the stove, you can run all of these on 12 or 24 volts directly. You don't need an inverter or the associated losses. You can use auto adapters to charge most of your cordless devices, cell phones, etc.

A small inverter could be used to power miscellaneous 120 volt loads.

The electric stove is the problem. A single stove top element can draw up to 1500 watts. Gas might be a better option here.
 
  #7  
Old 12-05-13, 07:41 PM
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Solar Power

The link below may be of some help. As mentioned you can run most of your items with 12-volts however, regardless of the voltage you will need the capacity in your batteries and solar panels to handle the load. The use of a propane stove could be a good idea except if you have to use it in an enclosed space without proper ventilation. If it's a single burner you could cook outside.

How Large Does Your Solar Power System Need to Be? - For Dummies
 
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Old 12-05-13, 07:52 PM
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Aanpdan, We are looking into the option of a wood stove for the reason that stoves DO draw so much energy. We just have to figure out if we can provide adequate airflow. Tolyn, LED lights are a good idea too, since they last for a long time too. All of the panels I am finding are listed in Wattage, not voltage, and I have no idea how much amperage to figure out.

The main plan is to have a battery bank in the shelter, and the shelter basically wired up more or less like a house with standard outlets. Neither husband nor I are electricians, so the less adjusting we have to do, the better. We are familiar with light diagrams, and replacing light swtches and outlets, but that is about as far as our knowledge with electric systems goes. The Panel Bank would ideally be able to be mounted on more or less a dolly, so that it can be stored in the shelter until we need it.

We really would like to go for absolute worst-case scenario here, like if there IS an extended outtage due to weather (our winter storms here have left us without power for over a week, so imagine a tornado), and there are no natural gas tanks available. Renewable power sources like solar, and renewable fuel sources like wood for cooking and heating, are really our goal. We already have a rainwater reclamation system, and use some gray water for gardening (flowers, not food).

All in all, we is po folks. Neither one of us comes from wealthy families with lots of resources, and we have both spent time "roughing it" from hurricanes and other foul weather. We want better for our own family.

ETA: Bahtah, thanks for that link. You posted the same time I was responding to the thread. The link looks like it might answer some of our questions. Thanks again!
 
  #9  
Old 12-05-13, 07:59 PM
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To cook, I think I would build a masonry grill/oven outside the shelter to use wood. That would make it safer than having it in the shelter. Keep a small hot plate for cooking in the shelter during bad weather or for small items.
 
  #10  
Old 12-05-13, 08:19 PM
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The hot plate is not a bad idea. Do you know of any that would be able to boil water, and/or how much wattage those typically pull?
 
  #11  
Old 12-05-13, 09:59 PM
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Emergency Shelter

A single element cooking burner draws about 1000-watts. You mentioned you wanted to have a battery bank in your shelter. You need to be careful about having batteries charging in your enclosed space, that could be quite hazardous especially if there is any open flames. You may want to provide a separate enclosure for the batteries with ventilation. If you cook using wood you can boil drinking water in an emergency and with proper ventilation have heating. A wood stove with a water jacket can provide you with plenty of hot water. You should include a fan for ventilation for an underground enclosure.
 
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Old 12-05-13, 10:33 PM
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My emergency kit includes water purification tablets. Do you really need to boil water during an emergency?
 
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Old 12-06-13, 12:22 AM
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Emergency Shelter

Need to boil water? Only if you have a family all drinking and cooking with water and you run out of tablets.
 
  #14  
Old 12-06-13, 05:10 AM
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The big problem with solar is to size it for a few days without sun. Then you find your batteries and panels get really expensive. I think a small propane generator with large underground tank will cost less and give you more power.
 
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Old 12-06-13, 08:15 AM
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The reason why the panels are fixed is so they can be stored in the shelter until we need them. Basically, A metal frame stand with wheels and the panels mounted to it.
When a storm bad enough that a shelter is required is coming or when the tornado sirens are blowing, there probably won't be enough time to install the panels. I'd also be afraid the panels would blow away in a tornado.
 
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Old 12-06-13, 09:41 AM
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Joe, I think he meant stored till after the storm.
 
  #17  
Old 12-06-13, 12:17 PM
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I think we have gotten a bit off topic here.

The plans are to have an emergency shelter that we can live out of if necessary. Husband and I have BOTH experienced extended periods (over a week) of no power or water. I was in on the Alabama/Florida line for Opal, and was without electricity for nearly 3 weeks, and without water for a week. Husband was in New Orleans for Katrina. We all know how that went. This portion is not up for debate, as we for the most part know what our plans are. Houses are destroyed. Propane becomes inaccessible. This is our reason for wanting solar power, and that is why I am asking about solar power. I am not looking for alternatives, other than to change the electric stove to a wood stove if I can get the ventilation taken care of. That is actually on another thread where I am discussing that there.

My questions for the forum are as follows.

Other than buying items that I find on a shelf and then testing their wattage, how can I find what typical wattage uses would be? Preferably for the items I already listed, as it would be handy to compare BEFORE purchase.

Where would I be able to find more information on solar panels set up, especially "off grid" systems, since this will be for emergencies when the local lines might be down? As I said before, Hubby and I can read light and wiring diagrams, as long as they aren't extremely technical. Most of what I am finding is for building models, or for large-scale setups.

Does anyone have any suggestions for making this system more efficient, and provide enough power? Bahtah already brought up a good point about the battery bank, and we have taken that into account and changed the "power alcove" to a "power room". And yes, as it was pointed out, the panels themselves are intended to be placed on a rig that will have them stored inside the safety of the shelter except a few days to charge during good weather, for occasional inspections/cleaning of the shelter, and then during actual emergency use. With the exception of emergency use, these panels will be used at most one day a month as I rotate emergency food stores, and then only for the lights.

Thank you all for your help so far.
 
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Old 12-06-13, 05:22 PM
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Other than buying items that I find on a shelf and then testing their wattage, how can I find what typical wattage uses would be? Preferably for the items I already listed, as it would be handy to compare BEFORE purchase.
Everything that uses electricity has a label on it that tells you how much and what kind. I would think any listing on line would also state this information. If not, go to the manufacturer's web site.
 
  #19  
Old 12-06-13, 05:57 PM
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The problem is calculating the power for the mini fridge. Sure you can get the current draw when it's running but how many hours does it run in a day.
 
  #20  
Old 12-06-13, 06:41 PM
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Plunge,

Use 12 or 24 volt appliances and lighting. They function and in many cases look just like your normal household appliances. Since they don't need an inverter you've already become much more efficient - no losses there. You can get low voltage CFL's or LED's.

If you need 120vac then you'll need to run an inverter. Limit the need for it to reduce your demand on the batteries.

Seriously, reconsider what you need versus what you want. You don't need a fridge or a stove for a week or even a month. You can survive on something like MRE's, no refrigeration needed. While it might be nice to cook a burger keeping that burger refrigerated and then cooking it all takes energy, energy that you may not have to spare. Keep a portable stove you can use outside the shelter when the weather is better.

Depending upon the emergency you may have to adjust your lifestyle.
 
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Old 12-06-13, 07:10 PM
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Or use a kerosene or propane refrigerator.
 
  #22  
Old 12-07-13, 12:00 AM
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Shelter Power

Looking at your original post I did a quick calculation of the following items and used LED lighting as suggested by one of the other people trying to assist you.
(8) LED lights 16" in length with a lumen output equal or better than a 40-watt incandescent lamp. They draw 6-watts each. (1) portable radio that has battery backup which draws 5-watts. (1) Low-Voltage charging station for up to 4 devices (cell phones, Ipad etc) and draws 36-watts. (3) ENCO duct fans, 250-CFM which draw 42-watts each. I figured 16hrs a day on lighting and 24hrs a day on the other loads. I figured watts x hrs/day for each of the items and got a total of 4.776 KW x 1000= 4776 Whrs. I figured only one day of autonomy (days you cannot charge batteries). Typically on off-grid systems you figure 25% depth of discharge but since this is not for long term use I used 50% depth of discharge (amount of energy you will allow to be used from the battery). The less taken on each charge/discharge cycle the longer the battery life. 4776/.50=9552 Whr. Not knowing the temperature of your battery room, I figured 60-deg which is an adjustment factor of 1.11, so 9552 x 1.11= 1602.72 Whrs. Battery bank size: 1602.72/48volts = 220.89 Amp-hours (Ah). That would require (8) 12V 150Ah batteries. (4) set of two connected in parallel to get 300Ah capacity and the sets of two, connect in series to get 48Volts. I did not look at solar panels or the inverter(48V to 120V) I don't have any experience with those.
 
  #23  
Old 12-08-13, 12:35 PM
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Yay! Numbers! I've got this information all copied down in my notebook for future research, Thanks!

Bahtah, This is exactly the kind of information I have been trying to find. Where did you find the info for the lights and fans? I have even checked contractor supply websites, and I feel like there is something I am missing, because it's like people just KNOW the parameters of this stuff, so no one lists it. The battery room, if it stays the same as the shelter, should be about 62 year round. Will a two degree difference change the adjustment factor much?

For the battery bank, we had also planned on 6 volt golf cart batteries, since they are better suited to higher drainage. They can often be used to the 50% point without being damaged. I do have diagrams on how to wire them up for solar.

Drooplug: Yes, the appliances themselves often have ratings, but online I am not finding the information I need very often. They will have wattage, but not amperage or voltage; or voltage, but not wattage or amperage. I can figure out the third number if I have two others, but it's getting hard to solve for X, without the whole equation. In store locally, where I can actually look at things face-to-face, the selection is very limited, and I know there are better options out there, if only I can find them.
 
  #24  
Old 12-08-13, 08:14 PM
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If you are going to use 6-volt batteries you will need 8 connected in series to get the 48-volts. If your batteries are 200 Ah rated and you reduce the fans from three down to two, I calculated you would need 175 Ah so you would be ok. Batteries are connected in series to establish the voltage you need and in Parallel to increase the Ampere-Hours. Here are some links that will be of help. If you have Excel you can build a calculating spread-sheet so you can change loads and see
how that will effect your design. Information on sizing batteries: Sizing Battery Banks
Information on LED lighting: http://www.americanlighting.com/2013...ED_CONTRAX.pdf
Information on the fan:Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies
On the Enco site you can search for Fans and then Duct Fans and look for
what you need.

Solar panel usually need to be about 10% of you system demand. So if you figure 200Ah you need panels to deliver 20amps at 48-volts. And what ever
associated equipment is required. A couple of deg should not make much difference in your calculations. You will see that information of the Sizing Battery Link.
 
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