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 single properly 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.