Designing Our System

This is the latest in our series on energy as a tool for prepping. The rest of the series is here:


Let me repeat the following disclaimer, mostly because people keep commenting and asking me why I didn’t discuss power factor, some other brand of solar or batteries, or propane. I did research on batteries, and I don’t want to spend all of that money on propane that I will just wind up having to convert to electricity for air conditioning, anyhow. The numbers just don’t work (see the above posts as to why they don’t)

I sell propane and propane accessories. Solar is teh devil

You engineer types, this is a simplified discussion that was designed to give you all of the information that I considered and discovered in my research for a backup power source without bogging you down in details that are largely irrelevant. 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.

Also remember that each person’s situation is different. Compare my climate situation to a fictional person in Starke County, Indiana (all weather data from best places) as an example:

  • While I have mild winters, hot summers, along with lots of sun and humidity, another person living in Starke county, Indiana might have cold winters, less sun and humidity, and warm summers.
  • Indiana gets 34 inches of snow per year, I get none.
  • Indiana has an average summer high of 83 degrees. Central Florida, 94 degrees. I see 90 days per year where the temperature rises above 90 degF, Starke County Indiana sees 9.
  • Indiana has an average winter low of 16 degrees, Central Florida, 46 degrees.
  • Our guy in Indiana has 129 days where the temperature goes below freezing and 6 days spent below 0 degF, I have 6 freezing days and the temp never goes below 0 degF.
  • Indiana has an average summer humidity of 62 percent, winter of 20 percent. Central Florida has an average summer humidity of 73 percent and winter of 50 percent.
  • Northern Indiana averages 4 peak hours of sun per day. I average 5.2.
  • Where I have 232 sunny days per year, our fictional guy in Indiana has only 170. Combine that with clouds, sun angle, and other factors, and our guy in Indiana gets 30-35% less power from sunlight than I do. You can calculate your own by looking here.

For those reasons, solar makes more sense here than it does in northern Indiana. Your mileage may vary.

I don’t need to heat much in winter, but I need to do significant cooling in summer. Maybe your area is different- each of us has to do our own calculations and studies, which is why I posted so many posts about my decision. I have spent quite a bit of time looking into this, and you should, too. It’s a large investment, and not to be taken lightly.

What are We Getting & Who is Installing It?

We have decided to go with a hybrid solar system (meaning solar with batteries) and we know roughly how large of a system we need, now its time to get more details.

At this point, we will look at which system we are installing, and who will do the installing. One of the things that I noticed is that solar companies are better at selling solar than they are at anything else. They will play this sort of shell game with you- they mix in financing, tax credits, and other facts, overwhelming you with information to disguise the true cost of solar. It’s worse than buying a used car. That’s kind of what spawned this series of posts. I wanted to organize the information in my own mind, while at the same time helping others to cut through the bullshit.

In researching for this buy, I talked to a dozen different people in my area who already had solar, including three people in my neighborhood. My wife and I have a somewhat left leaning friend who bought the empty land next door to his home about a decade ago and put in a ground mounted solar array because he is worried about being green. We consulted him because, hey, a decade with solar. Yeah, he’s a lefty, but not hard core. He’s also a veteran and a nice guy. His advice was helpful.

We also looked at online customer service reviews, a ton of reference materials, and we consulted with the sales people of half a dozen solar companies. Manufacturer’s websites were also referenced. This article is a summary of what I have found out after two months of research.

The Batteries

We know that we want system rated between 9 and 10kw, but how many and what kind of batteries do we need? The 900 pound gorilla in the mix is Tesla. The Powerwall 3 just came out, and it has some impressive numbers. It stores 13.5 kwh of power, and can deliver 11kw continuously, which would drain the entire battery within slightly more than an hour. The company is claiming a brief surge capacity of up to 30kw, which is pretty outstanding. Still, that amount of power isn’t going to be enough to run the house in a grid failure without cutting to essential loads only. This means that we will likely need two of them. Batteries aren’t cheap, but we will get to that in a bit. Two batteries will mean we can deliver up to 22 kw continuously, and will have a total storage capacity of 27 kwh.

The Tesla battery has some nice features. The battery itself comes with an inverter, the gateway, and the backup relay that will isolate the system from the grid in the event of a power failure, so we won’t need to purchase any of that separately. Each Tesla Powerwall 3 can support up to 3 expansion battery packs. The expansion has the same capacity as the main one, meaning that a Powerwall 3 and and expansion pack gives you 27 KWh of storage, while two expansion packs would give you over 40 KWh of storage.

The system also has a nice app that allows you to monitor and control the system remotely. This software also watches the weather in your area and will make sure that, when inclement weather is approaching, your battery is charged to 100% to prepare for a power outage.

I have looked at other batteries, but none of them had the power specifications that were as good as the Tesla, and the ones that did come close were in the same price range or were even more expensive, so I have decided to go with the Tesla Powerwall 3.

Florida Law and Solar

Florida has laws classifying the size of a solar installation.

  • Type 1 systems are solar systems that produce 10kw or less.
  • Type 2 systems produce more than 10kw up to 100kw. If you have a type 2 system, you are required to carry a $1 million liability policy. We already carry this much insurance, so it doesn’t affect us, but just be aware that the requirement is there.
  • Type 3 systems are those that produce more than 100kw. I don’t know what the restrictions are, and didn’t bother to look them up because 100kw would take more space than I have on my roof.

*Note: The sizing tiers established by Florida are measured in alternating current (AC) wattage, whereas solar companies measure the size of solar systems in direct current (DC) wattage. For comparison purposes: 10kW (AC) system = 11.7kW (DC) system. The difference is caused by technical reasons that we won’t get into here.

Summing Up Our Specifications

  • These quotes are for a system with 24 PV panels for a total of 9.6 to 10 kw unless otherwise noted.
  • 2 Tesla Powerwall 3’s for batteries are included, unless otherwise noted.
  • We also priced a Powerwall expansion, but it isn’t part of the quote.

This will give us an average capacity of 35 kwh per day in the winter and 52 kwh per day in the summer, with 27 kwh of storage and the possibility of more, if we later decide to add expansion batteries. (One neighbor has four Powerwalls, and tells me that this is far too much. He said he let the salesman sucker him into spending $40,000 on batteries.)

This should enable us to power the house without input from the grid, especially if we turn off loads that aren’t essential. Things like the clothes dryer, a potential pool pump (if we get a pool) and other luxuries can be shut off if the grid is down and the PV system isn’t generating enough power. We are planning on putting the pool pump, if there should be one, on the non-backup power bus.

Fortunately, we have a pitched roof with a rather large, unshaded southern exposure and a great pitch angle, which will ensure that the panels will get the maximum amount of sunlight. There is plenty of room there for the 200 square feet of PV panels we will be installing.

Power companies in Florida won’t allow you to install a system that produces in excess of 10% more than your average annual electric consumption. The good news is that they can’t tell me what my annual consumption is, because no one knows that yet.

The batteries will be mounted to the inside wall of the garage, next to the breaker box (load center). The remainder of the electrical equipment will be installed on the outside wall of the house, next to the utility meter. The PV panels will of course be on the roof.

Tax Credits

As I have mentioned before, the IRS has a non-refundable tax credit of 30% of the cost of a solar system. This gives you sort of a rebate on next year’s taxes that subsidizes nearly a third of the cost of the system. Many companies use this to make it appear that the system is cheaper. Make sure that you get the bottom line cost before this tax credit is applied, so you know what it will cost you without confusing the issue.

In Florida, solar systems are exempt from sales taxes, and any value that the solar system adds to your home is not subject to property taxes.

None of the above tax credits are available to fuel powered generators, and was a big reason for me not going in that direction. The tax advantage gives installing solar more than a 37% pricing advantage over a standby generator.

Selecting the Installer

One of the problems that we had when we first bought the house is the number of door to door salesmen who came around, trying to sell us solar. Then there were the phone calls and attempted over the phone sales. I have a policy of not doing business with anyone who calls me without me contacting them first. I have found it to be a great way to prevent scam artists from making you into their next mark. Let’s begin with the technical specifications, then see what the costs will be.

I am not comfortable cutting holes in my roof, so this system is going to be installed by a professional. In my case, I contacted a few installers to get some rough quotes. Each quote includes two Tesla Powerwall 3 batteries unless otherwise noted:

  • One quote was directly from Tesla. They subcontract out the actual work, and only use Tesla products. Their quote for a system delivering 9.7kw was right at $42,180.
  • The second quote was from SunPower, another national provider. The salesman missed our first telephone conference, but called several days later to reschedule. They also subcontract out the actual installation. They do not use Tesla batteries, but use their own in house brand of battery that has similar but slightly less powerful specifications. Their quote was $52,880 for a 9.2kw system. They pushed hard for me to get a system with no batteries at all to cut costs, but that would make the system useless for power failures- the entire reason why I want this. The attempted hard sale of something that I told them I didn’t want and the high price were turnoffs.
  • SunVena is a large Florida solar company. They quoted us $48,700 for an 8.8kw system.
  • We got a quote from a local electrical contractor who has been doing solar for about 20 years. They came recommended by a neighbor who had solar installed by them. Their quote to install a 10.1 kw system was for $43,147.
  • We tried to get a phone interview and a quote from a mid sized Central Florida solar installer. He was supposed to call at 12:30 in the afternoon. His secretary called at 1:00 and told us he was running late, and would call in about 15 minutes. The didn’t call until after 2pm. When he did call, he asked a few questions then promised to send over a quote with the promise: “I am going to make your choice an easy one.” The quote still hadn’t arrived a week later. He sure did make it easy to not choose his company, so that’s a promise kept.
  • One more regional solar company was contacted. Let’s call them Bidder 6. They are not a Tesla dealer, but instead wanted to sell us another brand of battery. He tried telling us that we needed 4 of the batteries he was selling. His batteries were Enphase batteries that store 5kwh each with a peak of 3.7KW of surge. That means these batteries are roughly 1/3 as powerful as the Powerwall 3 and I can get more storage with a pair of Powerwalls than from 5 of his batteries. When I insisted on Powerwalls, we were quoted a pair of Powerwall 2’s at a cost of $14,250 each. He also said that we need a minimum of 30 to 45 PV panels because our home was going to use an average of 30KWH per day in the winter and 60 to 75 KWH per day in the summer. When I pointed out that this house was only using 23KWH per day this past winter, he replied that it had been a mild winter this year. At the end of it, his quote was three days later than promised and was for an 11.2KW system with two Powerwall 2’s, and the quote was for $59,900.

So now that we have contacted seven different installers and gotten quotes from five of them, we know that the quotes ranged from $39,000 from Tesla, all the way up to $59,900 for Bidder 6. With the 30% tax rebate factored in, the quotes look like this (from least to most expensive):

  • Tesla $29,526
  • Local Electrician $30,203
  • SunVena $34,062
  • SunPower $37,016
  • Bidder 6 $41,934

Each of the installers offered a written warranty that was substantially similar:

  • 25 years parts and labor that the PV panels will still produce at least 92% of their rated power.
  • For the Tesla batteries: 10 years parts and labor that the batteries will store 70% of their rating
  • For the other brands: 10 years or 8,000 charge/discharge cycles for parts and labor that the battery will store 80% of their rating specifications
  • The big exception to the above warranty was Bidder 6. Their warranty was for 50 years parts and labor that the PV’s will still deliver 75% of their rated power.

Our experience

The Tesla guy consulted with us by TEAMS video call. He didn’t know anything about solar that was outside of Tesla’s product line. Their quote was nearly identical to the electrician, especially when you consider that the local electrician is offering a system with 400w more capacity.

SunVena sent a guy out who was the most knowledgeable of all of the solar company people that I talked to. I really liked the company. It’s too bad that his quote was $3000 more than the local electrician and $7000 more than Tesla.

The local electrician had the least polished of the presentations. The guy who came out knew about solar, he just wasn’t a salesman. However, he knew what he was talking about and had competitive prices.

SunPower was the one that frankly rubbed me the wrong way. He tried to push me into products I didn’t want. Like Tesla, the company only sold their own products an no others, and he seemed more interested in making the sale than he did in pleasing the customer. His price being $7,000 more than the electrician was the nail in the coffin.

Bidder 6 tried telling us that we needed at least 11kw and two Powerwalls, with the possibility that we would need 17kw and three Powerwalls. Now we are getting into a price point that I just don’t want to pay. His quote of $60,000 was simply way too high to be considered.

My Choice

So for the above reasons, the choice is between Tesla and the local electrician, with the electrician being ahead. I will ask them for more specific plans to see more details. This will require a more thorough engineering inspection of my house by them. Tesla is refusing to do a more in depth study unless we contract with them, so we are probably going with the electrician.

Since a standby generator would cost us in the neighborhood of $16,000, this system is slightly less than double the cost. We do get the benefit of vastly lower utility bills, though. Our bill will go from a winter $150 and an estimated $250 in the summer, all the way to the minimum $35 electric bill year round. That will save us about $2400 a year in utility bills, so the difference between this and a genny will be paid in about 5 years (counting the fuel that we won’t have to buy and the fact that long term maintenance for the genny is higher).

The timeline is tricky. We are trying to sell our old house, and will be using the proceeds to install our solar power system. The remainder of the proceeds from the sale will pay down the mortgage on the new place, then we will refinance to a 15 year mortgage, which will cut our house payment by about 70%. So we are waiting for the sale of the old house before we move forward.

We need some time to see what our hot weather electrical needs are going to be, and the delay for the sale of the old house will hopefully give us a better idea as to how much our summer bills will be.

For the time being, that means we are waiting until May or possibly even later before we are ready to sign a contract. That gives us time for engineering inspections, final proposals, and for us to get a better idea of what power we will need for summer air conditioning. Once we move forward, I will update this with any new information that we have. I will also do other updates to answer questions.

Load Shedding

One of the things that we talked about in our energy posts was load shedding. That is, it’s perhaps cheaper and easier to shed loads than it is to buy a larger backup power system. That’s especially true if we are going to use a portable backup generator. Those units, having only 10 kilowatts or so of available power, require that we only power the most essential of loads: a refrigerator, a freezer, some battery chargers, and the like.

In my case, when we have had power failures in the past, I fill the refrigerator with bottles of water to increase the thermal mass and slow the rate of warming. Then we use the generator to power the refrigerator, the freezer, and a few other loads like battery chargers, TV, and a small air conditioner.

Like I said before, I feel like a prepper should be able to do better than that, so we are looking at entire home power sources, but it’s far cheaper to power fewer loads than it is to buy more power capability, and that is what we are going to look at today.

One way to do this is simply to go out to the garage and flip the breakers on the loads I want to get rid of. Or simply not turn them on. Or we could get a SPAN panel. After taking a careful look at my budget, my needs, and the panel itself, I don’t think that we are going to get one. The reason is that, at $5,000 installed, it is the most expensive way of shedding loads. Let me explain:

I have been analyzing my electrical loads for the past several weeks so I could get an idea of just how much power I will need. My loads break down like this:

  • General household loads are about 3 kwh per day. That includes lighting, television, ceiling fans, and all of the vampire loads like clocks, cell phone chargers, and the like.
  • My refrigerator in the kitchen is another 1.5 kwh per day
  • The deep freezer in the garage is 1.1 kwh per day
  • The clothes dryer uses 3 kwh for each load
  • The water heater uses 7800 watts, and even with no hot water being used it sucks down about 4 kwh per day. That number goes up if you are using more hot water.
  • The oven uses 3,000 watts.
  • The cooktop uses 6,700 watts with all elements on
  • The main air conditioner uses 6 kw, the upstairs air conditioner uses 3 kw. The big question is how often they run in the summer.

In the case of the smaller loads like the refrigerator and freezer: we don’t want to shut those off. That’s the entire reason why we have backup power, to preserve the food that is being kept cold. Those loads, combined with the smaller loads, are about 5.5 kwh per day.

You can see that most of the largest loads are ones that we have direct control over: the dryer, cooktop, and oven. If we want to shed some electrical loads, all we have to do is not use them. There is no need for load shedding there. The exceptions to this are the water heater and air conditioners, all of which turn on and off without direct input from a human. If we aren’t home and our backup power kicks in, we need to shut those loads off. If we are going to have an automatic power backup system, I believe that load shedding should also be automatic.

We can have some sort of automation to turn them off automatically whenever conditions dictate. I am opting for an automatic system with a manual backup. With that being said, there are cheaper ways to accomplish this. My air conditioners are already controlled by Ecobee thermostats, meaning that they can be controlled with a smart home controller like Home Assistant or SmartThings, or even through the cloud using IFTTT. For the water heater, you can get a smart water heater controller like this one, and use IFTTT to integrate it to your backup system, or you can use a smart relay and have a smart home controller to regulate it. These methods work just as well, and won’t cost you five grand to install. Then you can use the extra cash to add capacity to your backup system. In my case, that is most of the cost of another solar battery.

To sum this up: You can install two Ecobee thermostats for $149 each, and a smart relay for $164. This will give you automated load shedding for less than one tenth of the cost of a SPAN panel- saving you more than $4,000.

Hazards of Batteries

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, 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.

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.

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.
  • 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.


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.

Basic Electricity & Solar

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.


  • 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.

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.

* 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.


The things that you need to survive and thrive in an emergency fall into broad categories:

  1. Records: Documents, photographs, and other needed items. I include a moderate amount of cash on hand ($300 or so) in this category.
  2. First Aid: Medications, drugs, bandages, disinfectants, etc. Nothing elaborate. Simple is better here.
  3. Heat and cooking: You can live on cold canned goods and MREs, but they are simply not tolerable for more than a day or two. Hot meals are best.
  4. Light: Flashlights, lanterns, fire, batteries for them, chemlights, and other ways of creating light.
  5. Tools: People are tool users. Screwdrivers, knife, hammer, hatchet, etc.
  6. Communications: There are many ways to communicate. Cell phones, radios, flags, spray paint, chalk or grease pencil markings left on buildings, signs stapled to telephone poles, etc.
  7. Food and water: Obvious. From half liter bottles of water to reverse osmosis, MREs to farming, we need to consider short and long term food and water needs.
  8. Shelter: Tents, homes, hotels, tarps, even your vehicle. Any way to get out  of the weather.
  9. Security: Weapons, cameras, sensors, rotating watches.
  10. Energy: Solar, fire, electric, generators, etc. Anything that helps us power our equipment or our selves that is not cooking or heating related.

My latest endeavor is to secure a source of backup power for the new house. I originally was looking at a standby generator. The problem is fueling it for more than a couple of days adds to the logistical complexity of preparedness. The cost of installing such a generator (including buried propane tanks) is in the neighborhood of $10,000-15,000. Then you have to fuel it, and you only benefit from it when the grid is ,down.

Then I looked into solar. An 8kw solar setup with a Tesla wall to get you through the night or cloudy days will generate about 1200 kilowatt hours a month. The system will cost about $20,000 after taking the Federal tax credit into account. There is no fuel needed, and when times are good, you sell power to the electric company which zeroes out your electric bid, thus subsidizing the cost.

So I think that solar is the way we are going to go for our backup power needs.