Backup Power for Your House

With an increasingly unreliable electrical grid for many reasons, and increasing reliance on electricity in most homes, having backup power is important. There are many options for backup power though

photo by Zeke Yewdall of a power pole in the Wall Street area of Four Mile Canyon after the 2013 flood

article by Zeke Yewdall

Before we start, it's important to understand a little bit of physics. We call it a “power outage”, but when we get to the actual engineering of a backup power system, we need to provide both power and energy.

What is the difference?

Power (in watts or kilowatts) is the rate at which we use electricity, and energy (in watthours or kilowatthours) is the total cumulative use of electricity. Power is like miles per hour – how fast are we going right now. Energy is like total miles at the end of the day – whether we got there with a short time of high power use, or a long time of lower power use.

When doing the engineering design for a backup power system, we need to know both the power and energy requirements of the loads in the house. Power (watts) affects the size of generator or inverter that we'll need. Energy (watthours) affects the amount of fuel, batteries, or solar panels that we'll need.

When thinking about backup power, there are three main questions: How long is the power outage? What do we want backup power for? and How automated do we want it to be?

What is the length of the power outage?

The best answer for backup power can be different for a outage of a few seconds or minutes compared to a few hours, days, or weeks. Different types of backup power – solar/battery systems, UPS's, generators of various sorts – are better suited to different length power outages.

For very short outages of seconds to minutes – the ones that blink the lights and reset all our clocks and computers – the most important thing is something automatic with fast response time. Backing up our heating or cooling system or well pump or refrigeration is not really necessary for an outage of a few minutes. UPS units on individual computers and routers or a solar or battery backup on selected circuits for lighting and office is often the best choice here.

For outages of a few hours, the big question is how often they occur and how much involvement do we want in running the backup power system. A portable generator that we plug into an extension cord and run to a few critical things can work. The fridge, the internet, the water pump, and furnace controls are common loads for this. But that requires someone to be home to drag out the generator, start it, and run extension cords. We can get into fancier generator setups with a transfer switch and even automatic start. Or we can get into solar power systems with batteries.

Generator backup systems have the advantage of high power capabilities, and the amount of energy is only dependent on the amount of fuel storage – often propane generators can connect to the same tank as the house, so extra fuel storage is not needed. Drawbacks of a generator are that they can be noisy, maintenance prone, and expensive to operate, and have to reduce their power output at high elevation sites such as in Colorado. Solar/battery systems are usually more limited in power and the amount of energy is limited by the amount of batteries, so it is more important to think about exactly how much energy is going to be required, not just the power requirements. But they are quiet, relatively maintenance-free depending on the choice of batteries, and usually have faster response time to outages. And they can have other financial benefits, which we'll cover below.

For longer outages – days to weeks – we get into questions of energy (cumulative electricity use) more than power (rate of electricity use). We either need to replenish the energy stored in a battery bank (via on-site solar panels) or we need a good store of fuel for a generator. For response to natural disasters that take out grid power for weeks, the logistics of getting fuel into a disaster area can make them a poor choice compared to solar, despite the daily energy limits of solar.

What do we want backup power for?

The first inclination of most people when thinking about backup power is to see what they have that uses electricity now, and then figure out how to back it up. But there are many reasons why we might NOT want to back up everything. The biggest reason is that backing everything up is often just too expensive. But there are different things to consider for both for short term to long term outages.

For short term outages, especially ones lasting less than a few hours, we may simply be able to do without many things. The food in the fridge won’t spoil in a few hours. We can probably survive not having TV for a few hours. But if it’s nighttime, having some light could be very handy. And if it’s a storm situation, having communications could be handy. Something as simple as rechargeable LED flashlights and lanterns and a battery powered radio and a means of recharging a cell phone for $100 or so may address the imminent needs for a short outage instead of a much higher cost larger backup system. On a little larger scale, we could add UPS's to our computer and router, and use a portable suitcase battery/solar system to handle a few more plug-in loads for short outages, while still being a lot lower cost than a permanently installed backup power system.

For medium term outages – a few days – it can be handy to have more of our “normal” electrical things working. But even for a few-day outage, there are probably things that we don’t urgently need. Do we have to run laundry every day or could we survive a week? Do we need to have all of the stuff that lets us go to work and school every day, or can we take a few days off if a snowstorm causes a few day power outage?

Nowadays, we often run into electrical loads that are not just an inconvenience if they stop working, but are actually a health and safety hazard. Many people have oxygen concentrators and CPAP machines that need electricity. But there are other less obvious safety hazards when the electricity goes out. As we break new records for heat in the summer, air conditioning can become a life/safety issue. Luckily in the mountains we are not as affected by this, but every year many more people die of heat related causes around the world than hurricanes, snow storms, and floods combined. If we don't have a store of non-perishable food, lack of refrigeration can be a danger, either from running out of food or from consuming spoiled food, or from attracting bears to large amounts of spoiled food thrown out (this was a problem in many communities after the 2013 floods). And most modern heating systems will not function without electricity, even if they use propane or wood pellets as the actual fuel source. In the winter in the mountains this can be a severe problem if you don't have a backup wood stove.

For longer term outages, like several weeks or longer, we start getting into questions of lifestyle changes. Many people assume that they want to maintain their same lifestyle if the grid is down for a long time. This is where we get into questions of why is the grid down. If it is down because of a natural disaster, what else has that disaster affected? Can we get more fuel for the generator if roads are blocked or washed away or if the gas station is out of electricity too? Can we harvest any solar input if the disaster is a massive snowstorm that has also buried the solar array? If a wildfire has taken out the power lines, what else has it also disrupted? After the floods, many people moved out of the mountains for months, because the combination of lack road access and communications was just too much for them to remain there and maintain their original lifestyle with school and work, regardless of whether they had backup power. Others adjusted their lifestyle to staying home a lot more and doing with what their backup solar power system could provide for several months till the grid was rebuilt.

A common attitude that I see when designing backup power systems is trying to plan for keeping the entire house completely normal during a long term (months- or years- long) outage – the zombie apocalypse prepper. They want to run their normal lifestyle even in the event of total societal collapse. Is this realistic? First, this will be quite expensive, but say they do have enough money to back up the entire normal lifestyle house with a combination of solar and generators and fuel storage and everything technically necessary to do this. Is it a good idea to be the one conventional suburban house that still has its lights on in a dark neighborhood? Maybe a bit better to retreat to the mountain house that’s a little better tactical location, and have more limited power to be somewhat comfortable, but not attract attention. Some loads, such as the internet and TV, maybe just don't need to be backed up if you're planning for societal collapse ;)

When thinking about backup power, we also need to think about things that may use power that we don't initially think of. The first one that gets people not used to a more rural lifestyle is the well pump – in the city, running water still works even when the power goes out (sometimes relying on a very large backup generator for the city water pumps, but still independent of your home's power). But if you have your own well, powering your well pump is a very important concern. Power for heating systems is another major one. Most heating systems, even powered by natural gas or propane, require electricity for the fans/blowers/pumps/controls and even some wood heat requires power for blowers or pumps. While providing backup power to electric heat is very expensive, providing enough backup power to keep a propane boiler functioning is quite reasonable.

There are other electricity needs that are even less obvious. For example, newer septic systems require a pump to function. So if your power is out, not only do you lose running water, but you also lose the ability to flush the toilet more than a few times even with a bucket. How about garage door openers: can you get out of your garage if the automatic door opener doesn't have power?. And sprinkler pumps: if the utility shuts off power to the entire neighborhood because of a wildfire or windstorm, do you lose your sprinkler pump right when you might need it most? Even diesel trucks and tractors – will they start in the winter in the mountains if the block heater is not plugged in overnight?

How automatic do we want the backup power to be?

Do we want it to all be automatic and we never realize the power is out till it emails us a summary of use afterwards, or are we okay with dragging the generator out of the garage, fueling it up, and running and extension cord through the door and through the house to the back of the fridge? A manual setup with either a small portable generator or a small portable solar suitcase can be set up for a few hundred to two thousand dollars. But it will require us to set it up to use it and will be limited in how much backup power it can provide.

A large solar/battery backup system permanently wired into the house can run many tens of thousands of dollars and a large generator with an automatic transfer switch to safety back up the entire house can run several thousand dollars to tens of thousands of dollars.

Safety and reliability

When we are hooked to the electrical grid, the safety and reliability of our power supply is out of our control. Obviously, it is not 100% reliable (which is why we are talking about backup power) and it is also not 100% safe (power line-sparked wildfires?). When we have a backup power system, its safety and reliability is in our control. This means it's up to us exactly how safe and reliable it will be. A good quality backup power system should be more reliable than a rural power grid in a natural disaster.

But if we didn't design it correctly, built it cheap, or didn't maintain it over the years, it may not be. Even a high quality generator requires annual maintenance and testing. Batteries can wear out over time and need replacing. All of these maintenance and upkeep items are now our responsibility as the owners, if we expect it to be a reliable source of backup power when the utility fails.

Installing a reliable backup power system requires hiring a qualified electrical or solar contractor with experience doing backup power (not all of them have this), or educating yourself enough to know how to filter the 75% of youtube videos with bad advice from the 25% with good advice.

Generators can be a major safety concern

Running a portable generator inside of a garage can cause carbon monoxide poisoning, even if the garage door is open. Almost 100 people a year die from carbon monoxide poisoning from generator fumes. Often we are needing backup power during inclement weather (storms, heavy snow), so thinking about how to run a portable generator without being exposed to the exhaust is important. Generators are also a fire hazard, both from using gasoline cans to refuel them (which should never be done while they are running or hot from previously running), and from packrats and mice building nests inside of larger permanently mounted generators.

Improperly connecting a generator to your house electrical panel without a transfer switch can cause power to go back out on fallen powerlines, potentially killing service people. This is common with DIY connections of portable generators. If you aren't using a transfer switch, the only safe way to use a generator is with an extension cord, NEVER connected to the normal house wiring.

On the solar side, most solar inverters designed for backup power include an internal transfer switch, so we are not as concerned with that problem, however, there is a wide variety of quality of equipment. There are many cheap components with poorly translated installation instructions flooding the market in the last few years, that are very attractive to the DIY backup power crowd. They typically have no UL listing and at best have poor reliability with short warranties. At worst, the actual electronics can catch on fire.

Battery banks are another big area of concern. There have been very few issues with modern UL9540 listed lithium batteries for homes, however there have been a few high profile fires from older lithium batteries, and homebrew battery banks made from cheap Chinese cells, or used EV batteries without a battery management system installed. Lithium battery fires can even worse than gasoline generator fires. If doing a solar backup power system, using UL listed components from a reputable manufacturer, and doing a complete electrical design is paramount to making a safe and reliable system.

Solar or generator for backup power?

One big choice is whether to go with a generator or with solar/batteries for backup power. There are advantages and disadvantages of each which we've talked about a little already.

Generators require fuel. If you can get and store fuel (money, logistics), then they can provide power as long as they have fuel – using more power will use more fuel, but if you can supply it, not a problem. Essentially you design for power (rate of electricity use), and the energy use (cumulative electricity use) is only a question of fuel supply. If you run out of fuel, they are useless.

There are also a wide variety of quality of generators. Some are cheap, loud, hard to start, require fueling every few hours from a gas can, and are only expected to last a few hundred hours of operation at best. On the other end are ones that aren't much louder than a truck idling in the driveway, connect to your large propane tank for fuel, start themselves if the power goes out, and can be expected to last 10,000 hours of operation. We can spend a few hundred dollars up to tens of thousands of dollars for a backup generator. The best systems can respond to a power outage in less than 15 seconds – not long enough for computers to stay online, but pretty quick. Manual systems using portable generators may take minutes or hours to get backup power online.

How about the natural gas infrastructure?

Many backup generators operate from either natural gas or propane and natural gas can be very convenient if you happen to be in one of the areas that has it available. There is no need to store fuel, which is always a big issue with generators for longer term outages. However, some larger disturbances that cause area-wide natural gas system outages can cause both the electricity to go out (from not having enough natural gas to run power plants), as well as cause the natural gas pressure to houses to go out. This happened to large areas in the state of Texas in 2018, and has happened to smaller regions many times. Events such as earthquakes or floods or even an errant backhoe could also damage the natural gas pipelines, so you may be out of both natural gas and electricity. Propane stored on site can be a better option (as long as your propane tank doesn't go wandering downstream in a flood or get burned up by a wildfire).

Solar, on the other hand, excels at fast response – most solar/battery systems will respond fast enough that the lights may barely flicker and computers and routers will stay online. This is great for short outages. And they can recharge themselves each day (if the sun's out) without need for bringing in fuel. But they can also be much more limited in what they can do, depending on how much battery storage we have and how much sun we collected that day.

For longer term outages, we have to pay close attention to the weather and adjust our loads to match what we are collecting from the sun. The benefit is that no matter how long the outage is, we will still have more sun coming – so while our energy is more limited than with a generator, we can't run completely out of fuel. Though I guess a nuclear winter or long-term climate change in the weather patterns could severely change the amount of sun we get compared to what we expected.

One big advantage of solar is that it can have benefits even when the power is not out – whereas a generator only has benefits us when the grid is down. There are many options that vary from using the battery bank during times of the day when the grid electricity is higher, to selling excess solar energy back to the grid during the daytime. Many backup solar power systems produce enough energy to greatly reduce the utility bill as well as providing backup power; this can make their economics compare more favorably to a generator, which usually has a lower up- front cost.

It is also possible to do a combination of solar + generator backup, where the solar quickly responds to short outages, and can recharge anytime the sun is available, but if the batteries get low at night, it will start the generator and recharge the batteries from that.

Switching loads to not using electricity.

When planning for longer term outages, it can make a lot of sense to find non-electric ways of doing many things, rather than having a large enough backup power system to run them. Switching loads off of electricity, and thus not needing backup power for them can also make your home more resilient to grid outages to begin with.

Electric heater loads are the first one to look at, especially when looking at solar backup. Anything that makes heat directly from electricity is very power intensive. Electric space heaters, electric cooking appliances, electric water heaters, and electric heat for the house are major ones that will be very expensive to run on backup power. For example, a standard portable space heater drawing 1500 watts of power all day to provide heat during a snowstorm would require a $15,000 battery bank, plus another $15,000 of solar panels to recharge that battery on an average Colorado winter day. Powering that space heater with a small generator could be done with a $1500 generator, plus $30 of gasoline every day. While this is much cheaper than the solar power system, it's not very convenient to refuel the generator 7 times a day, and store 50 gallons of gas for every week of doing this. And it still burns three times the fuel that just using an equivalent propane wall heater would. Investing in a small propane wall heater would be a much cheaper option. Even if it requires electricity for its fan and controls, these needs could be provided by a $1200 portable suitcase solar unit, or it could run an entire day on one tankful of gas in a small generator.

Providing backup power to a propane-fired boiler or furnace or a pellet stove is quite reasonable compared to backing up an electric heater of any sort. And many wood stoves can be operated without any electricity at all. Even if we have a house that is primarily electrically heated (the new heat pumps are getting better and better in weather below zero and even in higher altitudes), it could make sense to have a woodstove for snowstorm-induced power outages, compared to the cost of backing up the electrical heating system.

For short term (several-hour) outages, it can be cheaper to store pressurized water (in a larger-than-normal pressure tank) than to provide backup electrical power to the well pump. Similarly, it can be cheaper to store heated water in a tank-type water heater, than to store enough electricity to run an electric water heater (on- demand electric water heaters are especially power intensive and often cannot run even from typical permanently mounted generators used for backing up houses).

Refrigeration of food is high on the list of what many people want backup power for. A typical household has a lot of perishable food that can last a few hours to maybe a day without power. Having backup power for the fridge is good, but also having a store of non-perishable food larger than what fits in a fridge is good in the mountains. In the 2013 floods many people went the first 2 weeks without any ability to get out, so even if they'd had backup power, they may have run out of food in the fridge.

If you lose power outage during a snowstorm, you also have access to a giant refrigerator – your entire neighborhood. I always hear about people who lost the contents of their fridge and were without food due to a snowstorm taking power out. This makes no sense, as simply putting the food outside in a box would have kept it from spoiling (perhaps frozen, but not spoiled).

For many people though, it is not just the few days of food stored in the fridge, but months of food stored in deep freezers. Often this is their winter storage of home produce from their own garden or meat from hunting. Losing this can be much more impactful than just losing a week’s worth of store-bought food in a fridge. A reliable electrical system to back these up can be critical. But even there, there are other options. There are many ways of preserving food that don’t require electricity. They are not as convenient or cheap or sometimes as tasty as freezing food, but canning, drying, smoking, pickling are other ways to preserve food that will work without electricity, and can make your food storage more resilient.

Summary

There are many options for backup power, depending on your particular needs and budget. Hiring an experienced contractor to build a system or getting the necessary training to design and built it yourself will be key to having a safe and reliable backup power system. However, before buying anything or calling anyone, you will need to think about exactly why you want backup power, what your typical backup power scenario is, and what you really need to power in those situations.

About the author

Zeke Yewdall is an electrical engineer who has spent his career designing and installing battery based solar electric systems and backup power systems and lived in Ward, Colorado for 20 years. He currently lives off grid in the mountains of Washington. He is the author of a forthcoming book this summer on the basics of living off grid with solar electricity, and has another in the works about backup power system design.