Divemedic

There have been people who are saying that solar is unsafe because the batteries present a safety hazard. I was trying to keep the discussion here a simple one and not get bogged down in minutiae, but there are always people who want to make a simplified discussion more involved and complicated than it needed to be. Remember when I said that there was a lot of misinformation and outright bullshit out there?

If you don’t want to read this long post, you can refer to the CPSC page on solar system fires. Or you can read my lengthy research on the subject:

A little bit on my background. First, I was a Navy Electrician’s mate. I spent six years being professionally trained on high voltage electrical systems. I didn’t work with batteries, but I did work with a lot of electricl stuff. No, I am not an engineer, but I still have the basics.

Second, I spent decades as a firefighter. I have Bachelor’s degrees in Fire Science, in Public Safety Administration, (even though it doesn’t apply here, Nursing), and am a couple of classes shy of a degree in Chemistry. I am also certified in HAZMAT to the operations level as a result of my time as a firefighter. Yeah, I was trying to become a Battalion Chief, and I was actively working towards that, so I took a lot of college.

Let’s take a look at fire incidents involving batteries. Fire departments in the United States track fires throughout the US using the National Fire Incident Reporting System (NFIRS). Every time a fire department responds to any incident, they file a report that sends data to this system. Every kind of fire is tracked, including those by batteries. This has created a huge database. The National Fire Protection Association (NFPA) is the industry group that publishes fire protection information. The NFPA sets the standards that battery manufacturers in the US must follow, and that standard is NFPA 855.

Lithium battery fires are caused by a phenomenon called thermal runaway. In these situations, the increased temperature in the battery triggers it to raise temperatures even higher. As a result, the battery may become too hot to touch, smoke, catch fire, eject gas, or explode. As with any battery, a solar battery could potentially cause a fire if it overheats. But the top brands have strict quality control and are very quick to do a recall if something is found to go wrong, which is incredibly rare.

The type of lithium-ion battery can make a difference, too. There are different chemistries that are used in lithium-ion batteries, for example lithium cobalt oxide or lithium iron phosphate, and some are better than others when it comes to the risk of overheating. The safest in this regard and least likely to experience thermal runaway, is lithium iron phosphate. LiFePO4 batteries are also the most durable.

The other key to ensuring safety is to make sure everything is installed correctly and that the various components of your solar system are compatible. In particular, the charge controller that manages the power flowing from your solar panels into the battery: an incorrectly sized charge controller won’t protect your battery from overcharging properly and could potentially lead to problems.

To ensure the safety of your solar power system and property you should only invest in dependable and tested solar lithium-ion batteries from a reputable company that are properly installed by an experienced installer in accordance with the manufacturer’s recommendations. Always research battery brands before purchasing, including their product reliability, testing processes, and reviews.

That is one of the reasons why I decided to go with Tesla Powerwalls and why I won’t install it myself. I don’t have the experience with battery systems to the point where I trust myself to avoid a redneck engineering situation where I put together a system that works, but creates a fire hazard.

The Risk

What are the odds of an installed lithium battery catching fire? While the NFIRS system doesn’t track fires in lithium batteries versus other kinds of batteries, it does have pretty good statistics involving battery fires in general. Nearly every fire that I could find involving a lithium battery was in a cell phone, e-bike, or e-cigarette. These sorts of small batteries present fire hazards because they are small batteries where space is at a premium, and they are not properly vented due to those size constraints. Different type of issue than the larger batteries seen in EVs and large scale storage batteries.

Factors in battery fires are easy to track. Overcharging these smaller lithium batteries is the cause of these fires. According to the CPSC, approximately 54% of residential fires involving batteries resulted from overcharging or charging with incompatible chargers. In other words, people charging their e-cigarette, e-scooter, or e-bike with a cheap Chinese charger that they bought at Dollar General.

The CPSC reported that 18% of battery-related residential fires were caused by physical damage to the device. Not going to be an issue with a battery that is in a sturdy enclosure that is bolted to the wall. The NFPA states that approximately 20% of battery-related home fires resulted from improper storage conditions.

That’s 92 percent of all battery related fires being caused by improper charging, improper handling, or improper storage. This simply isn’t going to be an issue with a professionally installed home battery system.

Outside of that there are a few EV fires, and one other incident in a town called Surprise, Arizona. I searched every database that I could, and found a very few fires involving large storage batteries.

• The Surprise, Arizona battery facility was a fire in 2019 involving a 2 MWh battery facility that resulted in the injury of 4 firefighters. A 2MWh battery is about 150 times larger than the batteries we are discussing for a home solar system. The lithium-ion battery involved in this incident was commissioned prior to release of the current standard on large storage batteries: NFPA 855.
• Back in 2021, there was a recall of LG batteries that had a manufacturer’s defect that placed the batteries at risk of catching fire, after LG received five reports of the lithium storage batteries smoking and catching on fire, resulting in property damage and one injury.

So avoiding all of the media hype, just what are the statistics involving batteries and fires?

• Each year, there are about 9,300 fires that occur in the United States.
• Tesla alone sells about a million EVs each year. There were 44 electric vehicle fires in 2023.
• In total, there were 390 fires, explosions, overheating, or incidents of venting involving batteries of all kinds in the US in 2023, but once you remove the smaller batteries as discussed above, that drops to less than 100.
• Worldwide, Underwriter’s Laboratories reports that there have been 51 injuries and 4 fatalities from large storage batteries since they began tracking them in 1995.
• Considering that there are about 2 million homes in the US with solar storage batteries in them, seeing 100 fires per year means that the risk is extremely low: about 1 in 20,000.
• The batteries in energy storage systems (ESSs) predominantly use safer lithium-iron phosphate (LFP) chemistry, compared with the nickel-manganese-cobalt (NMC) technology found in EVs.
• The failure rate of lithium batteries is about 1 in 40 million.
• LFP cell failure results in less energy release and a lower probability of fire. A LFP battery that fails is more likely to smoke than it is to catch fire.

So yes, about 1 in 100 fires in the US involves a large battery of some kind, with the majority of those being EV battery fires, and one known case of a home storage battery causing a fire in the past 5 years. The risk of a solar battery fire is exceedingly low, but it is possible.

What if A Battery Does Catch Fire?

The National Fire Sprinkler Association is an industry trade group that is responsible for tracking how fire sprinklers put out fires. This is a great resource for fires involving lithium batteries. While it is true that there have been several high profile incidents involving lithium batteries, the incidence of them is rare, as discussed above. That brings us to our next point:

A second statement was that Lithium fires are impossible to put out, so fire departments don’t even waste their time with them. That’s a surprise to me, after spending more than 30 years as a firefighter. The metal fires that gave me fits were magnesium fires. There are certain brands of cars that use magnesium in their transmissions that are hard to put out, and I hated car fires involving them.

One of the problems that I saw with vehicle fires in general is that many firefighters have trouble putting them out. The fire is usually in an area protected from water, and lobbing water on the roof or hood of a car from 30 feet away isn’t effective at putting out a fire in the engine or transmission. You need to get to the source of the fire for any sort of firefighting to be effective.

Still, let’s look at the available information. The National Fire Protection Association is the fire industry’s main source of research and information on fires and fire prevention. Here is what they have to say on the matter:

Water works just fine as a fire extinguishing medium since the lithium inside of these batteries are a lithium salt electrolyte and not pure lithium metal. Confusion on this topic stems from the fact that pure lithium (like what you see in the table of elements) is highly reactive with water, while lithium salts are non-reactive with water.

However, this is only true of small and EV batteries. I would not recommend fighting a home solar battery fire with water, because a home battery storage system will be energized with some relatively high voltages. Although there are some companies out there that are trying to sell specialized equipment for these fires, most of it looks like hogwash that is designed to steal your money. My bet will be on using dry chem and calling 911.

Conclusion

The risk of fire from solar batteries is rare, and I worry more about an ordinary electrical fire caused by the wiring in the wall or from a stove than I do from the solar or its associated battery system. The battery in my laptop is more likely to cause a fire than a solar battery.

I am not going to worry about it.

In order to have a discussion about electricity in general and solar in particular, we need to define a few terms. (You engineer types, this is simplified. I am trying to keep things easy to understand, so spare me the discussion about how holes move. I am also excluding things like power factor, vectors, and other things that needlessly complicate the discussion.) There is a glossary at the bottom of this article.

The Basics

Your house gets power from the grid as alternating current, delivered at 60 hertz. There are two current carrying lines and a “return” line that enter your home from the grid. They are referred to as 2 “hot” lines and a neutral. The voltage as measured between either hot and the neutral is about 117 volts. If measured between the 2 hot lines, it’s about 235 volts. In this way, we can power smaller loads like light fixtures or televisions with a hot and a neutral. We power larger loads like water heaters, stoves, clothes dryers, and the like with 2 hot wires.

Your typical house circuit has a breaker that is either 15 or 20 amps. Any more than that, and the breaker will trip to prevent fires. (They can trip for other reasons, too, but that is beyond the scope of this article) Large 235 volt circuits may deliver up to 50 amps before tripping. If your home is new and like most homes, the total of all of the circuits in your house will be 200 amps. That works out to a maximum power of about 47 kilowatts. For short periods of time, like when your air conditioning compressor first starts, some circuits can use even more power than that.

So now that we know our house can use a maximum sustained amount of power that is equal to about 47 kilowatts, we can plan for our backup power needs. Now we need to know how much power we use each day. My utility has supplied my house with a “smart” electric meter. On average, my house is using about 25 kilowatt hours per day. During the summer, when the air conditioner is running, I am guessing we will double that. Maybe more. We will wait until July comes around before we make any decision, so we have a better idea of what our cooling will cost us.

How Solar Works

How solar works is that photovoltaic (PV) panels convert the light striking them into electric current. Nowadays, each panel puts out about 400 watts when new. (Panels lose about 0.25% of their power output each year as they age. After the 25 year warranty period, they should still be producing more than 93% of their rated power.) The power produced by those cells is direct current at about 40 volts. It needs to be changed to alternating current that matches the incoming grid power, and this is accomplished by an inverter.

Your solar system can produce more power than your home is using, and that excess power can run your electric meter backwards, effectively selling that power to the utility. At night, or when it is cloudy, your solar system doesn’t produce as much, and you buy power from the grid. If you size your system correctly, you will produce at least as much as you consume, thereby making your bill as close to nothing as possible. (Sadly, the local utility won’t let you run a negative bill. In fact, the least that your bill can be is $30 per month.)

So let’s proceed with the assumption that we consume 50 KWh per day in the summer, and about 25 KWh in the winter. With Florida being as sunny as it is, we can count on 4 hours per day on average of sun year round, and 6 hours per day in the summer. (This accounts for nighttime, cloudy days, etc. Days in the winter are both shorter and cloudier.) I got the figure of average hours per day of sun from the solar companies. That’s the numbers that they use.

If we want to produce 55 KWh per day during the 6 hours of summer daylight, we need to have a system that produces around 9 KW. That means we need about 23 PV panels in our system, making it a 9KW system. That will give us the 50 KWh that we consume, plus 5KWh additional in case we need it. As you can imagine, some days will be extra sunny and we will have lots of power, and other days, not so much. More on how we deal with that later.

What about grid failures? When the grid goes down, the National Electric Code says that our solar system must disconnect from the line so as not to endanger linemen who may be working on the system. That’s where batteries come in. If your system has solar panels and a battery for storing power, you can get a relay installed that will disconnect your system from the grid, thereby allowing your system to act as its own backup power source. This sort of solar system is known as a hybrid system.

With the system disconnected from the grid, instead of running the meter backwards, it sends 100% of its excess to the batteries. Then at night, our house uses that stored power to keep the lights on. As you can imagine, the battery that does that is large and somewhat expensive. In fact, a battery is half or more of the cost of installing a solar system. Still, the system can’t be used as a whole house backup without a battery.

So our battery should be capable of doing two things: storing 11 or more KWh per day of energy, and delivering large amounts of current for short periods as our air conditioners and the like start up and use more than the PVs can deliver.

One note about battery systems: the battery is the weak spot of the system, and a major part of the expense. Batteries are only warrantied for ten years, and will need to be replaced more often than the rest of the system.

During the day when the grid is still running, your system’s inverter does something smart. It powers your house from the PV cells, then sends some energy to charge your batteries, and the rest gets sent to the grid to run the meter backwards. When the power goes out, the batteries either get charged or supply power to your house, depending on the needs of the moment.

Load Shedding

Wouldn’t it be a good idea to shut off non-essential power drains when the gird is down, so as to conserve battery power? You can do that by turning off circuit breakers to nonessential loads, or you can use a smart breaker box to do it for you. That’s where the SPAN panel comes in. This panel allows you to designate loads as being essential, nice to have, or nonessential. When the grid goes down and your PVs aren’t making enough power to supply everything, the SPAN panel will disconnect the nonessential loads from the system, sacrificing their operation to save battery power. When your batteries have less than half of their charge remaining, the SPAN panel then shuts off the “nice to have” circuits to preserve the remaining battery for things that need it, like refrigerators.

So I think that is enough to get the basics down. Ask questions in the comments.

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Glossary

• Alternating current: The electricity reverses course in a cyclic fashion. The number of cycles per second is measured in Hertz. The electricity delivered by the grid is 60 hertz alternating current.
• Current is the number of electrons moving past a fixed point. It’s measured in Amps or Amperes.
• Direct current: All of the electrons move in a fixed direction. DC is the current supplied by batteries.
• Electricity is simply a measurement of the movement of electrical charges, mostly as carried by electrons.
• Kilowatts: 1 kilowatt is equal to 1000 watts
• Kilowatt hour: A measure of how much power is being used over a period of time. 1000 watts for one hour.
• Voltage (or what is called potential) is the equivalent to water pressure. The higher the voltage, the more “pressure” there is pushing the electrons through.
• Watts: A measure of power. It is calculated by Volts times Amps= Watts.

In our prepping series, we already talked about some others, like records. One of the middle tier needs for prepping is energy, and that’s what we are going to talk about today.

Many of the other things that we rely on for survival rely upon energy. We use it for a lot of things- heating, cooling, light, communications, all sorts of the things that we use rely upon energy. In some parts of the country, heat is important. Here in Florida, not so much. What we need is energy for cooking, light, air conditioning (summer heat will kill you more than our mild winters), communications, and other things.

The most useful of these is electricity. We could use propane for cooking, but it isn’t practical for other things. Since electricity is what is most useful, that’s where we are going to look. Most of the time, we rely on the electric grid. However, anyone who has lived through something as mundane (for Florida) as a hurricane know that it isn’t unusual to lose power for several days. In fact, during the ten year period that ended in December, we had no fewer than four electrical outages. Those outages ranged in duration from two hours all the way to three days.

I want to have a redundant backup because that is what prepping is. Knowing that not being prepared for a grid failure is a violation of the 7P rule, I want to plan to ride out a grid failure. Since the stakes are high as well as the cost, I am going to research and plan the crap out of this. I will post the results of my research for others to benefit. I will also post the results once the system is installed. I report, you decide.

There are three methods of backing up our electrical needs:

• A gasoline powered portable generator that powers selected loads. The advantage is that it has a small upfront cost of around $1,000 or so. Disadvantages are that you can only power a few, small loads, and that you have to refuel the thing every few hours. The power goes out, you have to go rig the generator, which takes a bit of time. They are also noisy. The one I have now (a 9kw gasoline powered genny) goes through about one and a half gallons per hour.
• A mounted generator that powers all or most of the loads in the house. The advantages here are that it powers more than does a portable genny, and it needs to be refueled less often since the fuel supply can be buried in the yard. It’s nice- the grid drops out, and within seconds, your genny takes over and powers the house. The disadvantages are that it costs more (the quote I got for a whole house generator was just under $15,000 including the transfer switch, permits, cable trench, propane tank delivery, 240 gallons of propane, tank utility, back filling the trench and a 10 year warranty.) 240 gallons of propane will last about three to five days, which will get you through most minor to moderate outages, but after that you are in the dark.
• The third option, as I already mentioned is a solar setup. I am pricing out a 9 kw solar system with batteries. I have been doing a ton of research and have discovered that there is a lot of BS out there. Enough that the solar discussion will be its own separate post or two. The advantage over the generator system is that it doesn’t need refueling and if done correctly, it can power the entire house indefinitely. Many people who have solar systems don’t even notice when the grid fails. The disadvantage is that it isn’t cheap. A solar system can cost as much as $30,000 or more. There are ways to offset that, but that will be for the future post. The good news here is that 30% of whatever you spend on solar can be recouped in the form of a nonrefundable tax credit* that isn’t available for a fueled generator. More there on a future post.

The first thing that we did was calculate our electrical needs. Our average electrical use is about 700 kilowatt hours per month. Our highest use has been 43 kilowatt hours in a single day. Our lowest has been 10 kilowatt hours in a day, but we were out of town. The average is about 25 kWh/day. These numbers are for the new house, so we haven’t seen what it is like to run the air conditioning on a hot day, yet.

To rein the cost of air conditioning, I am installing smart thermostats for our two AC units. That will allow me to control and monitor our AC use more accurately. The smart thermostat that I have selected is the Ecobee smart thermostat. It accurately tracks your AC and heat usage and compares you to similar homes. It has a lot of added features that help maintain comfort at a minimum amount of utility cost.

So now that I know what I need, I can plan for what option will be the best. Another post coming on that.

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Someone in comments suggested pairing a Goal Zero with 10 gallons of propane and a couple of 400 watt solar cells. That is a horrible option. You only get 3.6 kw of power for more than $13,000. That is the least cost effective of the options and was one I wasn’t prepared to consider.

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* A refundable tax credit is one that can be used to reduce your taxes paid in a given year. What nonrefundable means is that, if your taxes owed are $400, and you get a credit of $500, you can’t receive the $100 as a refund. Since I always pay more than $30k a year in taxes, this isn’t going to be an issue with me.