As a solar installer, one of the most frequently asked questions I get is: “The solar panels will give me electricity when the power goes out, right?” The questioner inevitably exhibits a disgruntled facial expression when I give them the least satisfying answer of all time… “It depends…” Whether or not to include solar battery backup into your system is determined by your particular needs and how your system will be used. Read on for all the ins and outs of solar and battery backup.
Battery Backup Basics
For those who are new to the whole solar thing, there are 3 basic ways that Photovoltaic (PV) Solar is used. The first and most simple is direct PV, in which the sun shines, the PV panel turns the sunlight into electricity, and it powers a device of some sort. This is most often used for things like pumps or exhaust fans, where the motor runs as long as there is sun. When the sun goes down, the device stops running.
Next up the line of complexity is battery charging. In a battery-based system, the electricity produced by the PV panels is stored in batteries, and can be used at any time, day or night. These systems are great for remote locations like cabins, but to run a modern American house on batteries would take A LOT of expensive batteries.
This is why grid-tied solar was developed. With a grid tied PV system, the power from the panels is sent out to the utility grid, and it displaces all or part of your usage. You don’t need batteries because when you run short, the grid supplies the rest. When you make more than you need, you get credit. Unfortunately, when the grid power goes out, your system also goes offline.
Finally, a hybrid system combines battery backup with a grid-tied system. This gives you the best of both worlds, with battery storage AND grid interactivity. It allows you to have a smaller battery bank, but it is there when you need it.
What is Your Goal? Deciding if Solar Battery Backup Right for You
To decide what type of system will work best for you, you really have to ask yourself “what do I want my solar to do?” Do you want to reduce your electric bill? Do you want to want emergency power? Do you want to go completely off the grid? Whatever your financial, environmental or political motivations might be, you still need to look at your bottom line, and how a PV system will provide the benefits you are looking for.
Direct PV really only has applications for rural, remote or very specific uses, so I’m going to set aside for future discussions. Off grid applications have nothing but battery backup, so if that is the direction you want to go, BRAVO! You are on your way (but be prepared for a fair amount of work maintaining your battery bank – your power depends on it!) Grid-tied and hybrid systems are where it gets the most confusing. Having battery backup sounds like the best of both worlds- so why not?
Grid-tie vs Hybrid Solar
Okay, we like the idea of backup power, so we are going with a hybrid system, right? Again, the world’s most annoying answer, “It depends…” The first question to ask is, “Do I need backup?” How often does the grid go down in your area? A few hours a year? A few days a year? A few hours a month? It can vary widely, even in a reasonably small area. For instance, in rural Iowa where I live, we are served by a small electric co-op and we lose power for maybe a half day at a time in the winter. It is a bummer, but not the end of the world. In the small town nearby, they are served by a large investor-owned utility company, and they often lose power for a day or even days. For our farm, I have chosen to go with a medium sized propane generator to keep the deep freeze going and the lights on during blackouts. For straight-up emergency power, I think the investment in battery backup might be hard to justify financially unless you experience a lot of blackouts.
However, developments in solar inverter technology is giving hybrid systems a new advantage. It is now possible to manage the mix of battery power and grid power you are using. As you probably know, grid electricity is more expensive during “peak” hours. This is usually those times during the day that most people are using appliances, air conditioning, etc. “Smart” inverters can save you money by using your stored energy during those expensive peak times, and buying less expensive power from the grid in the middle of the night when demand is low. This way, your batteries are not just sitting there, full, waiting for the power to go out. The inverter is actually brokering a buy/sell arrangement constantly, and this can add a lot of efficiency to your system and cost savings to your bottom line.
You really need to get with a qualified system designer to come up with the right solar PV system for you. Solar battery backup may not make sense financially for you, but it does help provide you with a sense of security that only proper emergency preparedness can bring. For a lot of folks, a small gas or propane generator makes the most sense, but remember, you need gas or propane to run them. As we have learned in recent years, gas can run short quickly in an area hit by natural disasters. It is always a good time to think about diversifying your energy plan.