Going solar can be a big decision. If the system is being financed, it will take many, years to pay off.
On top of that, it seems like everyone has a different opinion on what are the best panels. As soon as a person does enough research to feel like they know which solar panels to buy, someone mentions batteries. What???? Do I need batteries also?
Oh great, just when I thought I was getting things figured out. Now I think I might need the batteries! Batteries have been gaining popularity for a while now, and after the big freeze in TX last year, they are starting to make more and more sense!
But, to be fair, the best battery available to you, might be your very own utility company! That’s right, if you live in an area that allows Net Metering, you can use the grid as a giant battery! Sounds too good to be true because it is. The utility companies are constantly pushing back against Net Meter programs because it really does affect their bottom line. They feel like they are losing millions of dollars in revenue, due to consumers using their precious grid as a battery!
Find out more about Net Metering here Xcelenergy
Not all jurisdictions allow net metering and all Net Meter programs are not equal.
You will want to check your local jurisdiction or check the Solar Reviews site to see if your area offers a decent program. It certainly makes the most sense to start your battery backup research, with your very own utility company. It really is a great program when available, and it is much cheaper than buying your own batteries.
Unfortunately, a blackout will take you back to square one, if you’re using the grid as your backup. No chance to have any power during a blackout, because it would be impossible to keep the folks safe, who are working to repair the power outage. Each section of the grid must be completely free of power, to prevent the power from back-feeding into the grid and preventing repairs.
NET METER pros-
- Easy to set up
- No maintenance
NET METER CON’s-
- No power when the grid goes down
- Still relying on the utilities to keep things on
- Regulations can change, and you might not get a true1:1 net metering
So, let’s break down the pros and cons of Battery backup for your solar system! We might have to start by just identifying the most popular types of batteries available to add storage to your Solar system.
- Lithium Iron Phosphate
- Lithium-Ion NMC
- Nickel Batteries
However, Lead-acid and Lithium-ion batteries are the most common. Keep in mind the warranties vary greatly and are often associated with discharges. Do you plan to discharge every day? Or only when the power is out? The number of expected uses will likely determine which type of battery you choose.
After you have looked at the different options available and found the type of battery that makes sense for your needs, you will need to figure out how many batteries you will need. This is simply a calculation of how many appliances you will be running, and for how long. A quick description of the best way to calculate this can be found at SolarTown.com
Remember the supply chains have been hit very hard by the current economic situation. Be sure to check with your local solar contractor or battery supplier before you make any decisions. Batteries are in high demand and are therefore often on backorder.
Now… Let’s break down the math! This is where things get fun!
I must point out though, that power outages in the first world are extremely rare. I have an off-grid home in Central America and if the batteries don’t work, we have nothing. They are used daily. Zero margins of error. What I realized about setting up the system is this:
You likely think you need more than you do. We live in a consumer society and more is always better! We tend to oversize everything. In actuality, once you start looking at which appliances use what amount of power, you immediately realize about 50 percent of the power we use is not exactly, um… necessary.
I have to mention that before we start because I want you to think in terms of absolute necessity to start. We can always adjust up later. Do you really need 6 TVs? Maybe, maybe not but if the power is out, you probably won’t need options, at least when it comes to watching TV.
Another important distinction that must be addressed is why is the power out?
I realize this seems trivial but go with me on this. Are we talking about how PG & E didn’t trim some trees? Did an ice storm knock out some power lines and take out TXU for a couple of hours? Or, are we talking about nuclear fallout? If the sun comes out tomorrow, you will likely need minimal backup storage. If we’re all wondering how we actually got to WW3, and the sun is not coming back for months, you might have bigger problems than deciding which hairdryer to use.
OK, I had to say it. Please think this through cause it will completely change the way you design the system.
- Lights 1? Or 10? (LED’s hopefully)
- Electric heat in cold climates, or minimal power requirements to run the blower on your gas heater. AC if you’re in the south
- Refrigerator (find the wattage than assume 8 hrs of use per day)
- Deep freeze (Meats)
- Computer or phone charger, maybe 2?
- Medical needs?
- 100 light bulbs (Christmas can wait!)
- 6 TV’s
- 18 devices
- Your kids new VR setup
- Jacuzzi/pool pumps
- Karaoke machine (Really?)
With this in mind, I’m confident you can run through in your mind what you will really need. If you want to have full access to every appliance you would typically use, that’s fine too. Just remember, the power will most likely be right back on.
According to Popular Science–
“In a 2017 report, the American Society of Civil Engineers reported that there were 3,571 total outages in 2015, lasting 49 minutes on average.”
With all that in mind, you now will want to start adding up your appliances.
Many online calculators can help, but just figure out the basics for now. Maybe think about a minimalist battery package, and then you can run the math again, but this time throw every possible luxury you can think of. The difference in price for both setups will be dramatic. I think this mental exercise can ultimately help you make the best choice for your needs. Additionally, many inverter/battery setups allow you to add more battery storage later. This might be a fun long-term project that just has to keep the lights on in the beginning, but you fully intend to be living in luxury completely off-grid by the time you retire!
You will want to find the energy the home uses in a day. Figure out how long each electronic device will be running in hours per day. Multiply the wattage of each device by its run-time to get the energy in watt-hours per day. Add up all the watt-hour values to get a total for your home. This estimate is likely too low as there will be efficiency losses. To get a rough idea of the value with system losses, multiply by 1.25. This will help account for any decrease in performance due to temperature fluctuations.
Example: Light bulbs run for 5 hours a day. Computer runs for 2 hours a day. 120 x 5 + 300 x 2 = 1200 watt-hours. 1200 x 1.5 = 1500 watt-hours
Days of autonomy
Now decide how many days’ worth of energy you want to store in your battery bank. Generally, this is anywhere from two to five. You might also check how many sunny days you can expect in your area. Hawaii? or Seattle?
Battery bank capacity
Finally, we can calculate the minimum battery AH capacity. Take the watt-hours per day and multiply them by the number you decided upon in step 3. This should represent a 50% depth of discharge on your batteries. Therefore multiply by 2 and convert the kWh result into amp hours (AH). This is done by dividing by the battery voltage. Rainbow Power Company has a nice summary of the Watts/Amps/Volts relationship.
Example: You want the battery bank to last three days without recharging and you use 1.4 kWh per day on average. As 1.4 x 3 x 2 = 8.4kwh, this is the capacity we need from the batteries. Converting this to AH we have to divide by the voltage of your system. This can be 12, 24, or 48 Volt. Most systems will be 24 or 48 with a 230V AC inverter. If you choose to use 48V, the minimum AH capacity is then 10 800/48 = 225 AH. Now if you divide by your battery’s rating you find the number of batteries you will need.
Now, you should have a general idea of how much battery backup you might need. With that in mind, you can start comparing different set-ups. Remember that with your new battery set up, you will likely be using the app that comes with the particular battery/inverter setup you choose on a daily basis. You might want to download and try out each app as this should be considered. Additionally, the technology is changing very quickly and many of these manufacturers have packages that allow you to add more batteries over time! That way you can start slow, but still, build out the perfect setup!
For a battery quote or more info, go to Blue Sky Solar and Roofing.
To learn more about what contributes to the relatively high cost of solar in the US, go to Why does solar cost more in the US?