I get into a lot of discussions over power storage. What you need, what you want, what works and doesn’t work, and everything else. After my last discussion where somebody showed me this “awesome” power bank that I would never have bought for myself, I decided I should put some thoughts down on paper (a white screen counts as paper, no?) So anyways, if you are worried about a storm knocking out power to your house and leaving you stranded, this is for you. If you go camping and want all the comforts of home from a tent in the woods, I think I can help you there as well.
First off, you need to ask yourself “What do I want to power, and how long does it need to run?” These are the two more important questions, but before you can answer these, you need to know a little bit about electricity and how it works. Most electronic devices work off of Direct Current, or DC power, while most houses are supplied with Alternating Current, or AC power. This is because AC power is easier to transform and can be sent long distances with minimal loss. The loss of power in DC systems over similar distances is greater, so this is typically only used locally and not transported over power lines.
How much do you need? Well, power usage is measured two ways – actual rate of consumption is measured in watts (W) (or kilowatts (kW) in larger instances, like your house), but overall usage is measured in Watt-Hours (Wh) or kilowatt-hours (kWh). The difference here is that a light bulb may use 60 watts of power when turned on (rate of consumption), but the actual amount of power will vary based on how long it is on. For every hour, a 60W incandescent light bulb will use 60Wh of electricity. So if the light is on for a half hour before bed, it only uses 30Wh. If you leave the porch light on outdoors for 10 hours, from 8 PM to 6 AM, then that uses 600 Wh, or 0.6 kWh in a day, and 18kWh over a 30-day month. If you replace the light bulk with a newer LED bulb that produces the same amount of light but only uses 8W of power, your monthly usage for the porch light drops from 18kWh down to 2.4kWh, a significant savings. Your electricity bill shows monthly usage in kWh, so this calculation is handy for helping determine your electric bill and how you can reduce it.
Power storage is measured in amp-hours (Ah) (or milliamp-hours (mAh) in smaller units) for capacity, and is rated in Amps (A) for the speed in which is can discharge that power to your device. Since our power usage is measured in Watts and our storage is measured in Amps, need to do some simple conversions to see what we need. The formula we use to do this is Watts = Volts times Amps (W=V*A). If you recall from high school Algebra, as long as we have two of those values, we can determine the third.
For this example, I am going to use the latest Samsung phone, the Galaxy S24 5G. According to the specifications, this phone has a 4,000 mAh battery and has an input of 25W wired charging and 15W wireless charging, using USB-C PD3.0 technology. PD3.0 technology is rated at 5V/3A, 9V/2.77A, or 12V/2.08A. This allows the device to choose its charging voltage. For the S24 phone, it will use the 12V/2.08A option if this is available, as it charges faster. So our formula from above works out to 25W = 12V times 2.08A. If the charger was a straight linear equation, we could then determine that if we are putting 25 Watts into the phone, it will take just under 2 hours to charge. This is because the watts is static at 25, the volts are static at 12, so to get 4,000 mAh from a charger that provides 2080 mA (2.08A), we can do the opposite of our light bulb calculation and say 4,000 mAh divided by 2080 mA = 1.92 hours. That said, charging isn’t linear and this phone says it will charge to 50% within 30 minutes, so there are other variables in play inside the phone, most likely as part of those variable volt/watt numbers in the PD3.0 technology so the phone doesn’t overheat while charging.
When we think of bringing power with us, we think of batteries, right? So are we charging our phone? That’s easy because we are comparing battery storage in the phone to battery storage in a well… battery. Our phone has a battery size of 4,000mAh. Our power supply battery can be as big or as small as you can afford, but I personally won’t buy anything smaller than 20,000mAh. All things considered, that should charge our phone approximately 5 times. Now, if you are using the phone while charging, the battery will be going down while it’s going up – or more accurately, will go either up or down slower, depending on if you are using more or less than you are providing. So the only way to get a full 5 charges is to run the phone until it dies, then recharge it fully before you turn it on again. In reality, we won’t be doing this, so assume we get a little less charge. Going from 25% to 100% while making phone calls and using a lot of power, that 75% charge may require the full 4,000mAh over the 2 hours it takes to charge it. This is why I find a basic 5000mAh battery pack to be pretty useless, as it only provides a single charge. If you are out of power for a long time, you’ll need to buy a LOT of those small one-time charge boxes to get you through until you can recharge them all for the next time.
So now that we discussed phones, what else will you have? If you are camping, and you’re anything like me, you hate bugs. I have a portable, rechargeable, battery operated bug zapper. Put it 20-30 feet from your tent, and the bugs go there to die and leave you alone. But this bug zapper needs power too. It will run for about 8 hours on a 4,000mAh battery, similar to our phone battery. So if we run it for 4 hours a night, from dusk until we go to bed, we can get 2 nights from a charge. If you’re camping for a week, you’ll need to recharge it 2 or 3 times, for a total of up to 12,000 mAh of additional battery power – assuming it was fully charged at home before you went into the woods. OK, I think you can handle this now. Rinse and repeat for all the battery based devices you need to power, then add all the mAh numbers up, and that’s the minimum amount of battery you need to have in total.
When it comes to power banks for phones, they are usually small, maybe the size of a phone and twice as thick. I have seen them range from 1,000 mAh for an emergency quick 25% charge up to 40,000mAh with solar panels and hand-crank charging. There are units that have wireless charging, so you can avoid the cables and just place your phone on top to charge it. Purchase whatever you can afford, but I won’t waste my money on anything under 20,000mAh. As for the solar panel, those are really just a gimmick as they are so low powered that it will take a week or longer in full sun to fully recharge the battery. Don’t expect to just sit it in the sun for a couple hours, and be able to fully recharge your phone again. The hand crank was interesting as you could sit there all day and all night cranking to generate power, where the sun is only out a few hours a day, but you are going to wear our your arm doing that. And the power bank I bought that had one, the crank handle broke off within a couple months. The wireless charging is a decent option, as long as you can put your phone down somewhere for a while. It won’t stay properly aligned if you are hiking, and if it’s out in the sun, the phone will probably end up overheating and refuse to charge. So depending on your level of activity, it might be nice to have, or you might spend a few extra bucks on something you’ll never use.
Next, let’s talk about what we need at home. For this example, we just lost power from Hurricane X. We have a bunch of “stuff” that we absolutely need to have running if the power is going to be out for a few days. You have several options, but may actually need to use a combination of them. I suggest you make a list of everything in the house that uses electricity in some form or another, if it uses AC or DC power, and if it is need to have, nice to have, or not needed. We can do without some luxuries for a few days, right? In my house, I have a bunch of lights, a couple of TVs, quite a few computers and phones, two refrigerators, a pellet stove, my heat/cooling compressors and mini-split units, and an electric stove/oven. I’m not going to worry about the stuff like the internet boxes because those lines will probably be down as well. I can live without my electric razor if the battery dies on that and I can’t recharge it.
For your phone, so you can call for help, use the math we did above for camping, and have a power bank with enough charges to keep you available for 2-3 days, minimum (my personal recommendation). You can extend this by fighting the urge to use your phone to play games to pass the time. Leave it on, but screen off, no music playing, etc. Or if you are going to be without for a long time, shut it off and only turn it on every few hours to check for messages or make an emergency call. Also, make sure the power bank is charged before the storm hits.
OK, so the rest of this stuff is essentially AC usage. The laptops do technically use DC, but they have their own power adapter that plugs into an AC outlet to get the power. Yes, there are ways to get a DC power bank to directly charge your laptop, but we’ll deal with that in another article if there is enough interest. My laptop power adapter says it has an input (AC) power rating of 100-240V, 1.4A, and provides output (DC) power of 19.5V, 2.31A (45W). The input here makes it a little complicated as it is rated for use in most countries with different inputs. So for simple purposes, we can say we need 45W at 19.5V, but our AC power is 120V. Here’s where our math skills come in. 120VAC/19.5VDC = 6.15 ratio. We can then take 2.31ADC and divide that by the 6.15 ratio, we get 0.376. Multiply that by 120 volts, and we get – 45 watts! So at 120 Volts, we are using 0.376 amps, maximum, to produce the required 45 Watts of power to our laptop.
Refrigerators, freezers, water heaters, etc. get more complicated because they 1) don’t run all the time, and 2) require a large spike of energy every time they start up, for just a few seconds. My refrigerator says it uses 4.7 Amps, which we know we can convert to watts by simple multiplication. 4.7 Amps times 120 Volts equals 564 Watts. Not bad, considering my microwave clearly says it is an 1100 Watt unit, which works out to 9.17 Amps. My electric stove/oven is rated at 40 Amps, or 9600 Watts, because it doesn’t use the standard 120V power source, it combines those two lines and uses 240 Volts! But, that is all-in. That’s if I have all my burners AND the oven elements running at the same time, which I only do around the holidays, so in reality, it uses less than that on a regular basis. But, I was prepared for an emergency and can eat sandwiches or cold food for a couple of days and I don’t think I need my stove at all. If I am really craving a steak, I’ll pull out the camp stove and small propane tank from the garage, or I’ll fire up the grill in the back yard. I have a spare bottle of propane for that.
Adding up all my AC powered devices that I intend to use, the two refrigerators at 1150 Watts, but having to have a 3000 Watt capacity for that initial start-up surge, plus my laptop so I can write another one of these long, boring articles while waiting for the power to come back on, and I’ll want to have a few LED lights running so I don’t trip over a chair. Oh yea, and my pellet stove. I can use this and keep the house relatively warm, and it uses a lot less power than all of those mini splits, which I’ll consider a luxury. Keeping the house at 65 degrees is better than 35 outside, even if 72 would be nicer, right? Well that uses 600 Watts, plus bags of wood pellets that I buy in the fall and use all winter. My total power requirements appear to be somewhere around 2000 watts, but I need that extra 1800 W available for the fridges.
How do we get there? Well, I see two options. Option one, I can buy a generator that is rated for at least 3800 Watts. I’ll pick the Champion Dual Fuel (gasoline and Propane) generator rated for 4375/3500 Watt for $490. The two numbers on the rating are peak/constant, so it will run 3500 watts all day long, but can spike up to 4375 for those refrigerator starts, for a minute or two at a time before it trips the breakers. This generator will run for 14 hours at 50% load on a 4.7 gallon gas tank, or 10 hours using a 20-pound propane tank. I’ll fill up a gas can before the storm in case I need it, but if that runs out, I’ll sacrifice my grill’s spare tank to keep my food from spoiling for an extra 10 hours.
Option 2 is to try to do this all with batteries, which is a lot harder and more expensive, but the batteries will last 7-10 years and are re-usable. You don’t need to maintain them like you do the generator, you don’t need to keep buying gasoline or propane, and having them on hand – and fresh. Gasoline will break down and be unusable after about six months, and then clog up the carburetor and make the generator useless. The easiest way to do this is to look for what is called “solar generators”. These (typically) don’t come with any solar panels and can be charged from a wall outlet. If you keep these plugged in, and the devices plugged into them, they will act as a power pass-through for your equipment. In reality, they take in AC or DC power, use that to charge a large Lituim DC battery, and then uses the battery to create AC power to standard outlets.
A 5000 Watt solar generator from Jackery, one of the leading brands, retails for about $3500 (Jackery Explorer 5000 Plus). They have additional options if you want solar panels included to recharge the battery while power is out, or with smart transfer switches, so the battery unit will only be used when the power goes out. The bigger issue here is the battery capacity. The battery capacity is 5040Wh/45Ah. We need to power our 2000W of equipment. This will not be running all the time. My refrigerators run for maybe 10 – 15 minutes per hour, and it maintains the coolness unless I open the door. I won’t be leaving the door open and shopping around for dinner. Take a quick peek inside, close the door, then think about what’s in there and go back in for it, you’ll save power. While the generator needs to be sized to run both refrigerators at the same time, because it might happen, the battery will only get used while they are actually running. My pellet stove does run non-stop however, and my laptop charger will be running as long as it’s plugged in and the laptop is on. So either I run on battery for periods, then recharge it, or I’ll give up on my future article and wander around, bored.
But we are looking at maybe 800W of continuous use, plus 1200W at 25% usage – with a bit of a spike included. So that averages out to around 1250W continuous. Our 5000W battery will run for 4 hours before the battery dies. You can add on (for an additional cost), two 500W solar panels. So during the day, while you are pulling 1250W, you are recharging UP TO 1000W. I say up to because this will depend on the time of day, cloud cover, shade from trees, etc. And you only get around 8 hours of sun per day – less in the winter, more in the summer. While this will extend your time, you are still using more than you are recharging. Solar is a whole other article (the one I’ll be writing when I lose power), but for today, let’s say that every day, you can recharge the battery once, up to 5000Wh on a good day. Odds are, you won’t get a full 100% charge each day. So you’ll be able to run your stuff for 3-4 hours per day on this solution, at a whopping $5000 expense.
Doubling that will be a much better deal for long-term outages. If you split your home equipment between two of these devices, you’ll be running 625W on each, which will extend your runtime up to 8 hours. But you’re also recharging at the same 5000Wh per day, which gives you 16 hours per day of runtime, two full charges, assuming it was fully charged at the beginning. This is still better than the one device, giving you around 6.5 – 7 hours for the first day, and 3 – 4 hours on subsequent days, if you were fully charged on Day Zero. If not, you can expect to have to power off something on the one-device system, so you are charging MORE than you are using, so the battery goes up a little. Can you live without the pellet stove and heat during the day? That 600W is half of your total usage and will give you a lot more runtime by giving the batteries time to charge during the day, so you can use it at night.
So, for emergency subsistence, you can spend $500 plus fuel ($25/day) and maintenance ($100 annually if you have to bring it to somebody for tune-ups and cleaning), plus having to empty the fuel when not in use, which takes some time and you have to remember to do that. You will also need to either buy a bunch of extension cords to plug everything in (let’s say another $100), or pay an electrician to wire it into your house (probably around $600) so you can flip a couple switches to get your important devices powered up once the generator is running. But it will run forever if you can keep feeding it fuel – if the power is out, the gas stations and propane refill locations won’t be able to refill your tanks for you because their pumps requires power, too.
Or, you can spend $5,000 to $10,000 up front for a system where you have to shut off some stuff during the day, can’t run everything all the time – and that is assuming we are getting an “average” amount of sun each day. If it’s still snowing/raining for three days, you will get very little, possibly nothing at all, and only have the first charge of 4 or 8 hours before everything shuts off. But you won’t have to buy anything else for 7 to 10 years when the batteries eventually give out.
Now, that Jackery would be a wonderful addition to my camping trip. I can charge my phone non-stop, keep that bug zapper running all night, every night, run the air compressor to inflate my air mattress, and even be able to power up some portable speakers and have music playing all day, with LED lights up around my campsite all night. And with even just one of those two solar panels, I probably won’t even go below 90% all week, and recharge before lunchtime! I’d probably buy one or two smaller units for camping though. Something I can pick up, carry around, and bring into my tent if it looks like rain. Electricity and water don’t mix, after all.
I have two 400W handheld power stations for camping, and that fed my bug zapper, air compressor, and phones for a group of 12 last summer for 7 days. I did recharge them a couple days using a $100 folding solar panel each. And I have a larger 7500W/9000W generator for the house, so I can keep my TV and DVD player powered up, more lights, and a little more heat if I need it. I’d love to hear what you have or are looking to purchase if you’d care to share.