Comparing Batteries to Generators

A Storm is Brewing - Hurricane

When hurricane season comes around there is always a renewed interest in solar panels and batteries. Clients wonder if they should consider solar power instead of a whole home generator. But how do batteries compare to generators?

Notice how I didn’t title this “Compare Solar Panels to Generators.” That’s because people conflate solar power and batteries. You don’t necessarily need one without the other. A generator is useless without fuel. For backup purposes, solar panels are useless without a battery. However, solar panels are not completely useless without a battery because they can use the utility grid as a “battery” when the grid is present. When talking about backup options, let’s get something straight:

Solar Panels  Fuel (similar to)

Inverter  Generator (similar to)

Solar Panels ≠ Generator (not equal to)

In short, solar panels are analogous to the fuel you store for a generator. They are what drive an inverter to put out AC power that you can use in your home. So in reality, this post should be titled “Comparing Batteries to Fuel,” but nobody would search for that!

So once more… solar panels are like fuel, not like a generator.

Why Does This Matter?

I know what you’re thinking – just give me an answer! Stick with me, because it’s important that you understand the basic differences between your options.

When you purchase a generator and fuel tank, you have some decisions to make. The choice of whether to back up a portion of your house or the whole house dictates the size of the generator, typically rated in kilowatts (kW). The time you want to run the generator dictates the size of the fuel tank. For example, if the generator runs at 50% of its capacity for 4 days you will exhaust your fuel and then you need a fuel truck to come by, and then you can run for another 4 days. That’s all pretty simple and straightforward.

With solar energy, things get a little more complicated.

When sizing equipment, the first thing you need to determine is how much instantaneous power you need. This is similar to sizing a generator. Inverters are rated in kilowatts also. This is what converts the DC battery voltage to AC voltage you can use in your home. However, inverters have a much better surge capacity than most generators, so you might get away with a lower kW rating.

The next factor is the “fuel tank.” How much energy do you need to store? This dictates the required battery capacity. You would probably not want to size your battery for 4 days of energy use for a couple of reasons. First, batteries are very expensive. And second, the “fuel truck” comes around every single day. That’s right – solar power is your fuel, or your fuel truck if you will.

But things get quite tricky when you consider how solar power works. What if you have a cloudy day or even a couple of cloudy days in a row? If you size your battery too small, you could run out of fuel, and you can’t just call in the fuel truck. On the other hand, after a storm, calling a fuel truck for a generator could be a fruitless endeavor.

Solar Power Refuels the Battery

Your solar panels will essentially refuel your tank, your battery. How fast? That depends. After a couple of cloudy days, your battery might be exhausted and the solar panels could barely keep up with your daytime needs. This could leave you with only a small amount of energy remaining to get you through the night. At some point, you need solar power generation to exceed your daytime needs to recharge the batteries. A good weather day is like seeing the fuel truck coming down your street.

So there are tradeoffs with both backup technologies.

With a generator, you might need to go outside to check on your fuel gauge. If you are running low you might consider turning off the generator. Turning off appliances in your house will do little to reduce fuel use. Even if you turn everything off inside the house, a generator will still burn fuel. In fact, generators often run at very low loads because they need to be sized very large to meet the largest “what-if” scenario.

With solar panels, inverters, and batteries, if you turn off everything in your house, the batteries sit virtually unused. There is essentially no idle fuel use. That’s a great feature because it puts you in charge.

With new battery systems on the market, you can monitor your “fuel capacity,” your battery state of charge, with an app on your phone. You can see exactly how quickly you are depleting your battery so you can adjust your habits to make it until the next fuel truck arrives. We know exactly when that truck is arriving (sunrise). You will also have a good idea how much fuel is on that truck by monitoring the weather forecast.

It’s important to note that the utility grid is also a fuel truck. Technically you could just buy a huge battery that can carry you through any anticipated outage. You don’t need solar panels at all. When the grid power returns, the batteries would simply be recharged from the grid. This would require a massive amount of battery power at a huge cost, so it’s not a practical solution, but I wanted to point out that solar power and batteries are two separate technologies that are complementary, but not reliant upon each other.

Batteries or Generators – A Tough Choice

It takes some work and diligent monitoring of your situation. But your experience will be better with both technologies if you take an active role. Understanding how the system works and what to do in the event of an outage will make your experience much better.

The choice comes down to personal preference.

Solar power with batteries will be more expensive for sure, but you will get benefits from the solar panels year-round. With solar, it’s nice to know the fuel truck is coming every day, but you never know how much fuel that truck is carrying, and you can’t exactly call another company to come to fill you up. Generators are less costly and you can get a pretty big fuel tank, but they just sit there all year waiting for a “what-if” scenario. And they require regular maintenance and might have problems when you need them most.

The truth is that we steer many people into generators for cost reasons alone. Even as newer battery technologies come onto the market, the cost is still daunting or the choice of what to backup can be disappointing. But if you have the budget and want the peace of mind of daily fuel delivery, solar with batteries might be just what you need!



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