Need help in designing DIY Emergency Solar System for small apartment

Re: Need DIY Off-Grid for Small Apartment

Stop! Don't spend one dime yet--Those emergency power packs are not going to fulfill your expectations at all (not even 1% of your expectations).

The "weak point" in any off grid power system is the battery bank/energy storage. For example, a pair of Golf Cart batteries (6 volts @ 220 AH)--which are about 2x as large as the average car battery:

• 2 batteries * 6 volts * 220 AH = 2,640 Watt*Hours of energy storage (to dead)
• 2,640 WH * 0.85 inverter eff * 80% of battery (don't take battery dead) = 1,795 Watt*Hours of "useful power"

Forgetting that heavy loads on batteries make them "appear to have less storage"--The best you can expect run from such a battery (just one appliance in examples below):

• 75watt bulb: 1,795 WH / 75 Watt = 23.9 hours
• heater: 1,795 WH / 1,200 Watt = 1.5 hours
• 600 watt microwave: 1,795 WH / 600 Watt = 3.0 hours
• Mr. Coffee: 1,795 WH / ~800 Watt = 2.24 hours
• Hair blower: 1,795 WH / 1,800 Watt = 1.0 hours
• recharge computer (laptop): 1,795 WH / 40 Watt = 44.9 hours
• smartphone: 1,795 Watts / 5 watts = 359 hours of charging
• refrigerator: 1,795 Watts / ~60 watts = 29.9 hours

The Xantrex portable power back only has a ~51 AH @ 12 volt battery. And compared to the above two * golf cart batteries (12 volts @ 220 AH) is:

• 51 AH / 220 AH = 0.23

Or only about 1/4 of the numbers I used above (in reality, neither battery bank will be able to supply much more than 600 Watts continuously without permanently damaging the battery bank.

So--Your expectations are way to high to expect these small systems to supply anywhere near the amount of energy you are requesting.

If you have a place to store a small generator (Honda eu2000i is ~50 lbs at 1,600 watts max, and eu1000i is ~30 lbs and 900 watts max), plus a few gallons of fuel will run much of what you are asking in an emergency (and you need ~1-2 gallons of fuel per day for at least 12 hours of AC power per day). And you need a place you can safely run the genset (these Honda generators are pretty quiet and can be run during the day without bothering folks--assuming you have an open area and an extension cord you can use to have it far enough from the apartment and not get Carbon Monoxide poisoning)

In summary, people over estimate how much a battery/generator/solar power system can generate and under estimate how much power they use.

You can get a Kill-a-Watt meter pretty cheaply (Home Depot, Lowes, online, etc.) and start measuring your loads.

For emergency power, you need to plan on the minimum amount of power you will need. Think of camping. Use a propane or Coleman Fuel stove for cooking--Canned goods, water filter/purifier/pills, dry goods, etc. for a minimum of 3 days of autonomy before expecting outside help. To be honest, a few good LED flash lights are going to be more helpful vs generator/battery bank/solar power for anything more than charging a radio+smart phone+laptop+some LED lighting. You can build a small battery+solar+AC backup charger to keep the phones/small laptop running--But that is probably about it.

The Kill-a-Watt meter will really be a good education in electrical power usage.

Questions?

-Bill

PS: You only need to start one thread... I have merged the two threads into one. -BB

Re: Need DIY Off-Grid for Small Apartment

Lioness29 wrote: »

Thanks so much for the reply Bill. Getting an outside generator isn't an option. I want something inside. I've already made some of the preparations you mentioned. I guess I want some creature comforts if power is ever off for more than 3 days.

And this is the problem... For folks that live in cities/apartment, there is very little that you can do safely/legally in the way of larger amounts of power that we have all become accustom to.

Short answer, is pretend you are camping. Sleeping bag, perhaps even a small tent to try and keep warm (depends on what your local climate conditions). Some LED flashlights/"laterns", and a few 1 lb propane bottles and a camp stove.

Water can be a big problem too... In a house (and many apartments), you may have a 30-60 gallon water heater that you can drain... But otherwise, the city may shut off water (to stop sewers from flooding), or if you are in a taller building, they may lose pumps to get water to the upper floors/elevator access (past 4-6 stories, things become very difficult without utility power). You can get ~40 gallon plastic bags to fill in a bathtub and use a small pump to get fresh water. If you can plan ahead before the water fails. Otherwise, you are going to want around 1 gallon of water per person per day.

Pretty much, the emergency plan is to survive for at least 3 days before you expect organized help (in a major emergency). And beyond that time, you should have a way to evacuate (and a back pack to carry food/water/warm clothes/water filter/etc.).

We are in earthquake country here--And did do that for many years. But--our bug-out pack is probably full of expired life boat ration bars, water pouches, and flashlight batteries. Plus we never update to 4 bug-out backpacks as we had kids (oldest is about turn 18--Time flies). But we do now have a shed out back with some freeze dried 20+ year food, genset and 20 gallons of gasoline (recycled to the car every December), etc...

I don't understand what a Kill-a-Watt meter is. Do you point it at an appliance and it registers how many watts are needed to run the appliance? I know my ignorance is showing but the only way to learn is to ask. :-)

Basically, it is an inexpensive meter that can measure the rate of power you use (Watts), and the quantity of power you use (Watt*Hours or kWH).

So--Time for Math (yes, there is always math on this forum).

Watts is a rate--Sort of like Miles per Gallon (or Miles per Hour).

And Watt*Hours is an amount. You drove 100 miles (or used 4 gallons of gasoline) to get there. kWH is simple 1,000x a Watt*Hour (1 kWH = 1,000 WH).

You will see people say their heater uses 1,000 Watts per Hour -- And that is wrong. It simply uses 1,000 Watts. (a rate, like miles per hour).

And if you ran that 1,000 watt heater for four hours, that would be 1,000W*4H=4,000 WH = 4 kWH of power used. (an amount of power used, like 100 miles driven).

There is more math, that that is more than enough to get you started with a Kill-a-Watt meter (you can buy one from our host, many times at local hardware stores, and some libraries will lend K-a-W meters). Somewhere around $25-$35 each. And you can plug in your refrigerator, coffee maker, TV, computer, desk lamp, etc... For items that cycle (refrigerator, computer, etc.), you can leave the meter plugged for 1-4 days and find out how many kWH you used. Then divide by the hours it was plugged in and find out the average Watts over that 1-4 day period.

For example. Say you have a refrigerator... You plug in the Kill-a-Watt and see sometimes zero watts, 60 watts, and sometimes >600 watts (when compressor is starting or defront heaters are running.

You leave it plugged in for 33 hours and read 2.15 kWH of usage:

• 2,150 WH / 33 hours = 65 Watts (average power)

If you want to run the refrigerator for 3 days, then you would use:

• 65 watts * 24 hours per day * 3 days = 4,680 Watt*Hours = 4.7 kWH for three days of backup power

You don't know it yet--But that is quite a bit of power to expect from a "portable" battery system. Just to give you an idea--A standard good sized car battery is around 12 volts @ 80 Amp*Hours. It stores:

• 12 volts * 80 Amp*Hours = 960 Watt*Hours = ~ 1 kWH
• 4,600 WH * 1/0.85 inverter losses * 1/960 WH per battery = 5.6 = 6 car batteries to run just fridge for 3 days

There are other technical reasons, but basically, you would need ~10-12 "car sized" lead acid batteries to "reliably" run your fridge for 3+ days.

Or, you would need a 50 lb generator + 1-2 gallons of gasoline. Why generators are very nice for short term power outages.

Would the list below be a more realistic expectation?
An LED light (good enough to read by) Use 4 hours per day

LED lighting is really neat. You can get quite a bit of light from a 1 watt to 10 watt LED fixture... I have a nice little 2 cell flashlight with lithium (not rechargeable) batteries that will store for 10+ years, and run from ~1 hour on very high (like a small car spot light) to >30 days on very low (enough to walk around the home without tripping, read some instructions, etc.). There are similar versions of the light that run on 2x AA cells, or even 1 cell lights (I am a guy, I can get away with carrying a nice flashlight:p).

http://www.foursevens.com/products/flashlights/Pro

You can also get some pretty decent lighting from LED lamps that are not much bigger than a AAA battery (over 5 hours of enough light to safely hike in the woods, etc.):

http://www.arcflashlight.com/arc-aaa.shtml

(I do have both--And they have lasted for many years--And usually get lost before they have had any problems).

But, back to your questions... About the largest battery bank you could use would be (for example) 2x 6 volt * 220 AH batteries (aka golf cart--around $160 to $300 per pair for flooded cell). What could you run?

• 2 * 6 volt * 220 AH * 80% discharge (don't take rechargeable batteries "dead") = 2,112 WH = 2.1 kWH

Take the Average Watts that you want to run, and divide it into the available Watt*Hours. Or, say you want power for ~8 hours per day * 3 days:

• 2,112 WH * 1/(30 watt computer+6 watt smart phone+10Watt LED light) = 2,112 WH / 46 watt load = 45.9 hours (roughly)
• 2,112 WH * 1/(8 hours*3 days) = 88 Watts for those three 8 hour days of emergency power

That chartI gave you earlier, is close enough to start (used 1,795 WH for battery capacity):

• 600 watt microwave: 1,795 WH / 600 Watt = 3.0 hours Use 1/4 hour per day
• recharge computer (laptop): 1,795 WH / 40 Watt = 44.9 hours Use 1 hour per day (is that long enough to recharge laptop?)
• smartphone: 1,795 Watts / 5 watts = 359 hours of charging Use 1/8 hour per day (is that long enough to recharge laptop?)
• refrigerator: 1,795 Watts / ~60 watts = 29.9 hours Use 4 hours (minimum to keep everything cool) per day

But 2x golf cart batteries may be too heavy for your needs (~134 lbs total). And, flooded cell batteries "vent" hydrogen gas and sulfuric acid mist (electrolyte) during normal usage (during recharging). Usually, not the best thing to have in your closet or under your bed (another issue, you do not want a broken bed spring to short out the top of your battery bank--Full blown Fire in 30 seconds).

So, you might instead want to look at a single 12 volt sealed AGM type battery... These batteries only vent if severely over charged (or at the end of their life). No maintenance and much cleaner (and less sulfur smell). But they are more expensive and may last a couple years less than a flooded cell battery bank. Weights about 66 lbs and also costs around $300. But is only stores 1/2 the energy of the pair of Golf Cart Batteries, so all the times are 1/2 of the previous example:

• 12 volts * 104 AH * 0.80 discharge = 998 WH = ~1 kWH

Energy usage is a highly personal set of choices--But I would suggest you figure out how to conserve, use alternative source of heat (such as propane camp stove). And figure out how much power you need to run a few lights, Laptop, radio, small tv, etc... that makes sense for you.

-Bill

Re: Need DIY Off-Grid for Small Apartment

I am the one that spoke of 3 days of emergency prep... 4-8 hour outage, I probably would not even pull out the small Honda eu2000i I have to make power (other than to exercise the system). But I live in a temperate climate and don't need heat or A/C to survive comfortably.

The 3 day is a standard disaster plan recommendation. Take care of your self to let emergency responders to take care of the hot spots (collapses, injuries, sick, etc.).

I keep coming back to the rules of "3's" (not sure if all are part of the original list, added one or two for completeness). You risk death after:

• 3 minutes without air
• 3 hours without shelter (extreme climates/weather)
• 3 days without water
• 3 weeks without food

If you are not in a collapse (no air or no shelter), water is the critical first need. 2-4 quarts (2-4 liters) minimum per day. In hot weather, during excursion, you may need more. Symptoms of dehydration can occur within hours if you do not have access to water.

Personally, other than a flashlight and a small radio with batteries, I use stored fuel (propane, gasoline) for cooking/boiling water. Have some new trash cans and a water bag to store water (and an earthquake reenforced 50 gallon water heater) for emergency water.

I do have a generator + stored fuel (and fuel in car and a siphon hose). But I treat it like camping. Electricity is a luxury (unless you need a small fan because of hot/humid climate).

You can certainly find small 7 watt solar panels + 4x AA battery charger with USB output for ~$100-$200. I got one (I love gadgets) and tried recharging my Android phone, and it worked fine in full sun. The AA batteries can be used in LED flash lights--But frankly, I just get a 40 battery pack from Costco and they will easily store for >5 years in a cool room/closet. That will give me weeks to month+ of power with good quality LED flash lights and small radio+ear buds.

Remember, if you are planning on using DSL or Cable Modem with your laptop, there is a good chance that the Internet will fail after 4-12 hours as the backup batteries/pole top generators run out of fuel. Cell phone based internet may not do much better (unless you do dial-up--and who even has the modem/account to do that anymore).

For $500... Get a $300 battery, a $100 small AC inverter, and a $100 AC battery charger. You will not be able to power heaters, but it will give you 1-3 days of reasonable amounts of AC (or DC) power. Batteries will probably need to be replaced every 3-5 years. Flooded cell batteries need distilled water every 1-2 months (in float service). So, you are looking at ~$100 per year just to keep the system working (battery replacement, distilled water, etc.).

The Xantrex type portable/backup power systems, in my humble opinion, are not well balanced between the Battery Bank capacity and AC power output.

The Xantrex 1,500 watt output with a 51 AH 12 volt battery:

• 51 AH * 12 volts * 0.85 inverter eff * 0.80 max discharge = 416 WH of "useful" 120 VAC energy

Running the inverter at 1,500 watts (i.e., microwave oven) will kill the battery in ~15 minutes. A single burner propane stove on a 16 oz propane bottle will run 1+ hours per bottle.

If you still need battery powered AC--Use the kill-a-watt meter to measure your average loads and get the smallest inverter that will support those loads. Large inverters running (on average) very small loads are not too efficient (you waste energy running the inverter electronics). If you could justify it (not cheap)--This Morningstar 300 watt 12 volt / 120 AC inverter is very rugged and power efficient (and "goes to low power sleep" if there is no AC load). People here have run their homes/cabins for years on one or two of these guys (not recommended for larger homes/cabins--12 volt battery bank is too small). It will run any small AC loads you have (short of fridge, washer, A/C, etc.).

Add some sort of battery charger (like one of these smaller units with an IQ4 option). Good/heavy cabling with bolted up connections (alligator clips do not work on "real" AC inverters with significant power capabilities).

A 100 AH to 220 AH 12 volt battery bank will meet your basic needs (other than refrigerator power). Just use small energy efficient appliances (no heating). Keep plugged into AC power to keep battery bank charged. Check water levels (flooded cell batteries) once a month. You should get a small Digital Multi-Meter so you can monitor the battery voltage (below 11.5 volts, dead; 12.7 volts, charged; 13.2-13.8 volts, floating; 13.8 to 14.4 volts, charging; etc.).

-Bill

Re: Need DIY Off-Grid for Small Apartment

Lioness29 wrote: »

You said: "For $500... Get a $300 battery, a $100 small AC inverter, and a $100 AC battery charger. You will not be able to power heaters, but it will give you 1-3 days of reasonable amounts of AC (or DC) power. Batteries will probably need to be replaced every 3-5 years. Flooded cell batteries need distilled water every 1-2 months (in float service). So, you are looking at ~$100 per year just to keep the system working (battery replacement, distilled water, etc.)." If power is out how would I recharge the battery since the battery charger wouldn't work? With my car? I can handle replacing the battery every 3-5 years, but is there another kind of battery that doesn't require putting water in it every couple of months?

And that is the problem. In an apartment with poor direct sun and no place to store/run a gasoline powered genset--You are pretty much hosed (sorry for using the technical/engineering term ). If you are serious about electric power. Get a Honda eu1000i for $700 or so and a siphon to pull gasoline from your car into a 1 gallon gas can. Put the "battery+charger" on a wagon/hand truck (remember--no elevators? May need to limit to what you can drag down stairs or if you can through an extension cord out your window to an open area on the ground). About the only practical "mid-range" power option short of getting your landlord to let you install a few solar panels on apartment roof).

After 3 days of no utility power--You are going to need to do some serious planning. In California with earthquakes--Only a few blocks at a time are affected. A mile away, everything may be fine. In Hurricanes, they can wipe out 10's of miles (or more) inland and hundreds of miles of coastlines. Ice storms or North East blackout, no power at county to multiple states--Where can you go to get supplies/fuel?--What if the water and sewer pumping is shutdown? Different disasters, different needs.

Remember, if you are planning on using DSL or Cable Modem with your laptop, there is a good chance that the Internet will fail after 4-12 hours as the backup batteries/pole top generators run out of fuel. Cell phone based internet may not do much better (unless you do dial-up--and who even has the modem/account to do that anymore). Isn't that why I need a power source -- to recharge my laptop and smartphone when their internal batteries run down?

Phone calls and Texting is pretty well supported (got one, the other is there too).

Internet--Requires a whole bunch of infrastructure to function. And that infrastructure requires a lot of power. A single Cell Repeater site at our local church uses 5 kWatts 24x7 (or ~120 kWH per day). And they have two or three such repeaters at the site (AT&T, others, etc.). That is more electric power in a day that my home with 4 people uses in a week.

Similar for Cable Internet.

If you still have a land line (local phone company), that is were you will (possibly) have reliable long term internet in an outage. I would not count on much more than 4-12 hours of cable internet (or possibly phone company DSL) until it has been proven (i.e., you already had a 2 day power outage and kept Internet). My wife won't get rid of our land line--Keeping it exactly for emergency use (phone company has large battery bank+generator with week or more of emergency fuel--AT&T designed system for disaster survival)

If you limit your power use to recharging a smart phone--You do not need very much in the way of a battery bank or even solar panel. Your laptop uses about 6x as much power as the smart phone, but it probably can run OK too.

You can certainly find small 7 watt solar panels + 4x AA battery charger with USB output for ~$100-$200. I got one (I love gadgets) and tried recharging my Android phone, and it worked fine in full sun. Can you give me brand, model, etc. If all of my grandiose ideas about a backup system fail (I hope not though), I might want to just be able to recharge my electronics. I like gadgets too!

I got a 7 watt Goal Zero portable system (around $100-$140 or so--Costco sometimes sells in store). There have been a couple complaints that the Goal Zero was not very rugged--Perhaps some folks here can recommend something else.

Otherwise, you can look at these (smaller) solar panels and see if any will fit your needs for the apartment (pick the panel that will fit, then design the rest of the system around the panel and see if it will work for you). Note that most panels are thin tempered glass and are easy to shatter if hit with metal/rocks/etc. You have to treat them just like the glass on a picture frame.

I know this is a dumb question, but are you talking about a pack of 50 AA batteries or a "40 watt battery pack"?

A big pack of 40-50x AA Cell batteries from Costco. Should easily last 5 or more years in storage without losing too much power.

Trash cans are a good suggestion. What kind of water bag can be used for storing water? I'm thinking plastic garbage bags contaminate the drinking water. Are you saying the 50gallon water heater would be another source of drinking water or used for bath? I assume this would be if there was no electrical power to use the hot water heater as it is normally used.

Here is one example of a 50-100 gallon water bag for a bathtub. (don't know anything about website/product).

BTW, can't I just look on the back of the appliances/electronics and see what wattage they require? If so, why do I need a Kill-A-Watt meter?

Not really--For various reasons. First, the ratings may be worse case, average, or something else. And for something that cycles on and off (refrigerator, laptop used most of the day, etc.)--The Kill-a-Watt "totalizes" the total energy used. It just makes it much easier and more accurate than using the labels.

Sort of like your car--You can estimate how much gas you used based on your driving habits, freeway, mountain driving, etc... But pulling up to the gas pump tells you exactly how much gasoline you used in the last week.

Kill-a-Watt meters are also handy for conservation. How much power does that refrigerator/window Air Conditioner costing you every day.

Add some sort of battery charger (like one of these smaller units with an IQ4 option) I looked at the IQ4 chargers. As the amps go up, the price goes up. As the volts go up, the price goes up. This is where I start getting lost. I just don't understand the concept of amps and volts. Discouraging... I want to put together a system, but my ignorance is stunning!

Which is why we start with loads and conservation first... Looking at the hardware before you even know what size battery bank/daily load you want to support--There are too many options for the first timer--Frustrating (sorry).

But basically, those AA and C/D Cell batteries are ~1.2 volts. Your car has a 12 volt battery system. The city bus probably has a 24 volt battery system, and your home is a 120/240 Volt AC power system from the utility.

It just depends on what you loads you want to run and how big of battery bank you want to have. For a smaller system (like you are looking at), it probably will be 12 volts.

A battery charger for a deep cycle power system should be around 5% to 13% (and upwards of 20-25% can be OK) battery charger... So, if you wanted a 12 volt @ 100 AH battery bank, then the rated charging current would be around (for a 12 volt charger which outputs around 14.2 to 14.6 volts when charging a 12 volt battery bank):

• 100 AH * 0.05 rate of charge = 5 amps minimum
• 100 AH * 0.10 rate of charge = 10 amps nominal
• 100 AH * 0.13 rate of charge = 13 amps good sized charger
• 100 AH * 0.20 rate of charge = 20 amps you want "fast charging"
• 100 AH * 0.25 rate of charge = 25 amps you want "faster charging"

So--Until we know the size of your loads--Which drives the size of your battery bank--which drives the size of your solar array+AC backup battery charger, etc...

None of this is exact--Look above, I said that a 5 amp to 25 amp 12 volt charger would work well for you... That is a 5:1 range with "fuzzy edges".

Not really trying to make it so complex... If you do it a step at a time, you will get through it fine (you may need some help if you are not mechanically/electrically inclined the first time through building a system).

-Bill