Post by woodyz on Mar 20, 2016 13:53:43 GMT -7
Backup Electric Power Design Considerations- Part 1, by Duliskov
This article covers a complex area, and to keep myself focused I will break it into three sections. In the following I would like to share what I learned researching and building an emergency power station. The content below assumes that the reader understands the basics of electricity (AC and DC), batteries, and solar power. I have no affiliation with any of the sellers of products I provided links to; the links are for your convenience only. I have no engineering degree and reserve the right to be completely wrong. It is possible to build the systems in many different alternative ways. My approach may not be the optimal one, but it should get you started.
General Advice
Building a flexible backup power station is an expensive proposition. Therefore, you would want to understand your power consumption and true needs, how the system is sized and configured, and how to optimize its use and build a low-maintenance system. You would benefit from building it yourself, because this will allow easy re-configuration, extension, and troubleshooting. Also in the process of acquiring equipment, materials, and skills, you will establish valuable relationships with suppliers and professionals that could benefit your other projects as well.
You will be working with strong DC currents and high voltage AC, so be very careful and thoughtful how you approach your work. Plan ahead each step. If possible have someone with you who can give you a hand or call for help if you get yourself in trouble.
The most important decision you will have to make is what type of power disruption you are planning to handle. It is unlikely that electronics in chargers and inverters will survive an EMP/solar flare event; therefore, prepping for that event with any substantial power generating capability is basically out of the question for an average person. While newer battery chemistries offer significant advantages over lead acid batteries, they are more susceptible to an EMP/solar flare event, because the battery bank requires extensive electronic monitoring/management/balancing to avoid catastrophic failures and to maximize efficiency. These regulators are either built into each individual battery or are in a central unit. The lead acid batteries do not have or need any built-in electronics.
You may wish to live off-grid, and then you need a self-sustaining system with renewable energy source. If you prepare for short duration outages, at most a few weeks, you can make compromises and rely on a single source of energy to replenish your batteries or you may not even need a battery bank and could just store enough fuel for a good quality generator. You may want to use the system only in an event, or you may wish to reduce your electrical bill by running your alternative energy producing equipment constantly. The easiest way to see how much energy you are currently using is to check your average daily consumption over a period of one year to account for AC and heating needs. I can assure you, you will not be able to generate that much energy on your own consistently! You will have to make choices. Also, do not count on the system paying for itself; emergency power backup is an insurance policy. You will be disappointed at the rate it can save you money. It may not be much, and it can be protracted over a long period of time. All those considerations are tough ones. If you have a set budget, whatever you spend on electric backup you would not be spending on food, security, et cetera. Make sure you have your priorities set right. You may also want to think about mobility, because covering your roof with solar panels or erecting a huge wind turbine will not help you if you have to abandon your compound.
Subsequently, you need to decide how much power you wish to use (power your entire house, just a fridge, or just your cell phone/radio) and what type of power (115 Volts, 240 Volts, multiple phases, et cetera). I do not think that very powerful generators are truly necessary unless you know for sure you will use their full power all of the time. They are heavy, noisy, fuel hungry, and costly. You can always add a second generator as needed, especially if they are of the variety that can synch together, a.k.a. parallel kit. You can easily plot power consumption using computerized meters, which will allow you to plan for peak power (driving your inverter decision) and how much on average each appliance uses (determining useful capacity of the battery bank).
Figure 1. Example of energy consumption of my Haier 1.5cft HLP23E Compact Pulsator Washer on Cycle 04 Quick Wash program. You could see that it only used 46 Watt/Hours, but the peak wattage was over 800 Watts.
There are on-line calculators as well, but best practice is to measure your own appliances you are actually planning to use.
The next question to answer is how automated you want to be. There are transfer switches that will instantaneously engage a battery bank, in case utility power is gone and in the meantime start your generator, and when it stabilizes, the switch will transfer the load to the generator and start charging the batteries automatically. This will ensure unattended instantaneous failover. Alternatively, if you protect your sensitive equipment individually with UPSes, then you can get away with a manual transfer switch, because beeping of UPSes will wake you up at night, and you will have at least 10-15 minutes to switch your loads to the battery bank and subsequently to the generator in the morning or let your solar panels take over as the sun rises.
A transfer switch is a must to protect utility workers working on the lines. The transfer switch ensures that your generator cannot be fed back into the line, thereby hurting anyone. Please never ever plug the generator/inverter into your home electrical outlets bypassing a transfer switch. This is very dangerous. Even if you know what you are doing, you may not be around when someone else makes a mistake costing a life!
Manual transfer switchesare relatively inexpensive, and the outside power inlet box will let you connect your split phase generator to feed your critical loads safely with a singleproperly rated cable.
Lastly, the budget will restrict what you can do. I suggest going slow on a tight budget but buying quality parts and tools. Start with the component you will see a return on immediately. For example, if you plan to lower your electric bill, start with solar panels, wind turbine, or hydro-power and an inverter self-synchronizing to the grid. If you are primarily concerned about functional sump pumps and fridge, start with a battery bank and inverter that has a built in transfer switch and add ability to generate power later. If you want to survive a short outage but don’t have the skill to build a complex electric system, just buy a good inverter generator, focus on storing fuel, and invest in a transfer switch. Don’t forget to rotate gasoline and stabilize it. Propane can be stored indefinitely, and there are tri-fuel generators that will run on any fuel. Never store flammable fuel in a garage or basement; always store it in an outside shed, away from your living quarters.
If you are just now planning to build a retreat location from scratch, consider adding DC wiring in addition to AC wiring. This will afford flexibility to run your DC appliances without any intermediate conversion of energy.
Not all energy must be centralized. For example, having small motion-activated battery-powered lights throughout your house or headlamps will save you from running wires in each room. Battery-powered tools will allow you to work as long as you have the ability to recharge them. Make sure you have enough chargers to charge all your batteries simultaneously, if you go that route, because it makes little sense to run a generator for eight hours just to charge several sets of AA batteries. Also, make sure your chargers like the quality of the power from your generator. (There’s more on this later.)
Before you invest in alternative energy, check availability of U.S. Department of Energy incentives and other local programs that may help offset the cost.
Electric Energy Generation
The four basic forms of electrical energy generation are solar, wind, hydro, and thermal (internal combustion, not geothermal, which is not covered here). All of them utilize at least one transformation of energy, for example chemical into thermal, thermal into mechanical and then mechanical into electric energy. Solar converts photon energy directly into electrical power. There is loss of energy starting with capturing the initial energy fully and subsequently at each transformation, and lastly in the electrical wires connecting the source to the load. If the energy is stored and retrieved later, there is an additional loss. The electrical power is typically converted in the end into mechanical motion, light, and heat also with less than 100% efficiency. As you can imagine, 90% of the wind power hitting the turbine or solar energy falling onto solar panels may be lost in the process.
From the perspective of preparedness, solar and hydro generation are the most “concealable”, while wind turbines are visible landmarks and gas/propane/diesel generators attract attention with noise.
Wind, solar, and hydro are renewable but not available 24/7. Generators can run day and night as long there is fuel. If you chose to use a gas-powered generator, make sure you store ethanol-free gas (find stations selling it using “Pure Gas” iPhone or Android app) and add a stabilizer or similar. Store fuel away from the house, and rotate it at least annually. Note the fuel components differ in the summer and winter version of the same grade of fuel. I don’t know which is better from a long-term storage perspective store, and I store fuel that I buy in autumn, so I don’t have to deal with cold cans in the winter.
Operationally and to extend the use of stored fuel, it is best to have multiple energy sources. For example, solar can power utilities and charge batteries during the mid-day, and a generator can supplement that and charge batteries when there is less sun. Larger generators, above 3KW can simultaneously charge a large battery bank and supply energy to utilities. Generators run most efficiently near full capacity; they consume a bit more fuel, but the energy produced will require less fuel per kWh. Therefore, it is best to run them for a short period of time, at most a few hours, but load them with charging batteries, powering fridge/freezer, water heaters, lights, washer, power tools, etc. to full capacity. Then switch to battery power and only use the minimal load to last through next generator cycle or solar/wind opportunity.
Backup Electric Power Design Considerations- Part 2, by Duliskov
Solar Energy Generation
For any significant solar power generation, plan to cover your entire roof with panels. Consider installing a few panels on the roof of your trailer, if you have one; this will give you mobile power and better concealment. If you make the panels tilt or slide out from under each other, you can significantly increase the total surface exposed to the sun while stationary. Alternatively, install the panels on a ground support for easy access and scalability. Make sure that the selected location does not have structures or trees casting a shadow over, and take photos in different times of the day and all seasons. Power generation capability of slightly shaded solar panels drops dramatically, even if the shadow covers only 5% of their surface. If you don’t have the luxury of time, you can use an application to simulate where the shadows of each object will be at any given moment in time, summer or winter. (For example, you can use “Light Trac” iPhone app.)
The distance between the panels and the battery bank is essential, especially in case of low voltage, 12-24 Volt transfer to battery charger. The cable will dissipate part of the current as heat, wasting it, and the cables will be extremely expensive. A better option is to use a higher voltage, for example 96 Volts, or installing an inverter at the panels and sending an AC current down the line to the battery bank. Another option is to install individual self-synchronizing inverters for each panel. They will synchronize frequency with each other and the utility power, so you can simply plug them into your house grid via a special switch and feed your house simultaneously from the solar panels and utility power at the same time. The battery bank will be charged from any outlet in your house. This will make solar contribute to your energy bill without re-arranging your incoming utility lines and will be transparent to your utility company. Alternatively, it is possible to isolate few circuits on a separate panel to be only fed by solar and the battery bank.
Wind Energy Generation
Wind power is noisy. If you install wind turbines on a mast connected to the frame of your house, you will hear the grinding noise throughout your house, especially with larger turbines. Smaller turbines are not going to satisfy your power needs of a larger bank, but they can supplement a solar array or generator. Specialists in wind energy say “go big or forget about it”, because wind energy is extremely inefficient in the case of small scale generators. I never installed a wind turbine, but I read many books and distilled for myself the following: don’t do wind under 5 KW; for the cost of installation and maintenance, you could buy a larger solar system and have less trouble over time.
Hydro Energy Generation
If you are lucky enough to have a creek or river flowing through your property, you can tap into hydro power. Obviously, in summer the creek may dry up and in the winter it may freeze up, but otherwise it is a constantly available source of power. Be mindful of the ecosystem of the creek when deciding how much water to divert to your project. Also, make sure local regulations allow for what you are planning to do. The water/energy of the river flowing through your land may not be legally yours. Check with local authorities before you invest in hydro generation.
Generally there are two most important considerations in selecting the micro-hydro turbine. Firstly, how high is the water column. (This depends on the steepness of the terrain or the height of the dam.) Twice the height is twice the energy the water will produce. Secondarily is the volume of water you can divert to the turbine. Again, power output is proportional to volume. This will drive to either go with an impulse turbine (optimal for the high velocity low volume) or with a reaction turbine (low velocity of water but high volume). Unfortunately, I don’t have direct experience with hydro myself. Interestingly, the 5KW rule seems to apply here as well, based on literature: forget about it if you can’t go big.
Gas/Propane Generators
Gas/propane generators sometimes have a 240V split phase output. It is best to load both sides equally; otherwise you will be wasting half of the power of your generator. Be careful buying cords. The majority incorrectly only tap into one side of 240V outlet. Buy something like this to optimally use generator power. And when wiring into your house using a transfer switch, ensure that the circuits you wired to one side or another are about equal in terms of power consumption under normal conditions.
Propane has indefinite shelf life versus gasoline. Keep in mind that in winter the propane tank will have less pressure inside. If the propane is used at a high rate, the expansion cools the tank further. You may end up having access to only about half of the propane in the tank, unless you warm your tank while using it with, for instance, this blanket. The120 Volt heater with magnetic head does not make good enough contact with the convex surface of the tank to transfer enough heat to keep it warm. I tried two 400W heaters attached to a 20lb tank and they barely raised the temperature by a few degrees, which was not sufficient. They work well on flat paramagnetic surfaces though.
Battery Charger
When selecting the solar battery charger, make sure you pick an MPPT (maximum power point tracking) type. They will allow for fluctuation in the input voltage, while flexibly adjusting the voltage conversion ratio, so they utilize the full power of the solar panel, not wasting any energy. In other words, their peak conversion efficiency is close to 100%, no matter how much sun is hitting your panels. There is a good technical explanation of PWM vs MPPT technology online. The same is true for wind turbines. However, many wind turbines come with a built-in battery charger, so pay attention to what is built in. Not all are equal.
Sensitive Equipment and Battery Care
Lower quality generators may not operate at exactly 60 Hz (50Hz in other countries) and can cause electronics to misbehave or UPSes to switch to internal batteries due to low quality of current received. You may want to consider protecting sensitive equipment with an isolation transformer.
If your batteries have multiple types of posts, it is usually less expensive and more secure to use the ones with holes in them to connect wires. Cover the car type posts with short pieces of garden hose, just a bit longer that the post itself; this will prevent shorting if you accidentally drop a wrench onto the battery. You can also use shrink tubing on cables to reduce the risk of shorts.
Some battery manufacturers provide a max torque rating for screws attaching cables. Be careful and measure your torque wrench, because you can ruin your battery by twisting the soft lead post with excessive force.
Apply shrink wrap or terminal caps boots to cover as much of the exposed conductor as possible to prevent shorts.
Tips
It is a good idea to install a 12 volt outlet right next to your batteries, for instances, where you connect them to the inverter, so that you can power a 12 volt tool or light directly without power conversion back and forth. A 12V outlet can be used without powering an inverter.
If you have power tools, it is useful to have a car charger for the tool batteries to recharge your tools without running the inverter, which can use as much power as it deposits into the batteries.
Energy Storage
The only practical way to store electric energy is in chemical form in batteries. There is loss of energy while it is being deposited into batteries and converted into chemical energy and then also while the battery sits in storage (self-discharge). The following is applicable to 12 Volt lead acid batteries.
The output from a battery will be DC current. Batteries are built from units of 2 Volts each. For example, six of these units make a 12 Volt battery. Physically larger batteries are more susceptible to damage from rough handling (drops, vibration) because they use larger plates. Some batteries are of a sealed type of manufacturing and require no maintenance, but be aware however that the pressure regulators on sealed batteries will vent above 5 psi typically, resulting in permanent loss of electrolytes that is impossible to replenish due to their sealed nature. These batteries needs to be charged very carefully with temperature corrected charging regime, especially at high ambient temperature. Other batteries are of open type and will evaporate water while being charged, requiring a periodic refill with distilled water (manual or automatic). The open type also emit hydrogen gas, which may accumulate in the battery compartment and explode with a spark; therefore, adequate ventilation is needed. Because hydrogen is lighter than air, ventilate at the top not bottom of the compartment. They can also spill acid more easily. There is no consent amongst specialists which type is best for deep cycle energy backup systems. While sealed batteries require less attention if “ruined” by overcharging at high temps, they can’t be corrected as easily as open types.
Due to low voltages, when supplying power to pumps, microwave ovens, welding equipment, and other large loads, the current flowing through the cables from batteries to the inverter is very high, easily in the hundreds of amperes. This requires cables with very little resistance– beefy expensive ones. (There is good information on cables online.) Generally speaking, anything below 1.0AWG will be inadequate to power a 2kW or larger inverter. I suggest using welding cables or similar, because they are pure copper, not alloys, with less resistance, and are built of hundreds of thin wires, that makes them very flexible, relatively speaking of course, and easy to work with. Also their outer shell is multi-layer and much more durable. Thick cables require capablecrimping tool. If by any chance your connectors will be exposed to salt water, only use atinned copper connector, as copper “rusts” in salt water quickly and tin protects the connectors and wire. Alternatively, you can cover the surface of your connections withdielectric silicone grease, but that will make re-arranging your batteries a little messier. You can buy premade connecting cables, but I suggest developing the skill and acquiring the equipment to do this yourself.
survivalblog.com/backup-electric-power-design-considerations-part-1-by-duliskov/
survivalblog.com/backup-electric-power-design-considerations-part-1-by-duliskov/
alternative power
collect it
convert it
store it
sometimes convert it
use it
