Your solar installation is finished and all your neighbors are jealous. Your electric bills are going down. Then you have a storm come through and you lose power from your local utility company. Your grid tie solar doesn’t work when you lose utility power. Now what? There are options. Once your solar is installed, should you install a battery backup system on your home? A battery backup to your solar is a great idea. If solar is not available to back you up then a generator will work. These are 2 different backups – a generator backup or your home and a generator backup for your solar powered system. I want to focus on the backup for a solar powered system. A generator partially backups the solar in case there is no sunshine for a week or two. If there are dim days without a lot of sunlight or not enough to recharge your batteries. That is where it becomes critical. Your inverter will automatically switch over to battery when needed.
If you have a grid tied system, you would need some kind of backup for the battery system. That means recharging the batteries once they get below 50% which is a standard recharging level. The generator starts and runs for a period of time like 3 to 4 hours just to charge the batteries back up to their level. You don’t need a whole house generator like a 20 KW or higher to do this. You can use a very small generator that is very efficient. The idea is to get to the point that you only need to run a charge controller for a certain amount of time. That’s why a 7 KW diesel is perfect for those applications. I suggest 1800 RPM that would sip fuel, one that wouldn’t pull a lot of energy over a period of time it needs to recharge the batteries. Diesel is best because you are not relying on any other outside fuel sources.
Diesel is a fuel, yes. You do need additives to it, yes. You need to keep it up. You need to run it every so often and do things every so often to make sure it stays in operating order. But that’s with anything with mechanical parts.
When you lose utility power on a grid tie system, you have no power to your house for critical loads such as a refrigerator, water pump, sump pump, lights, or whatever you chose. This battery system will recharge so that you can run a small emergency panel. That emergency panel will run loads that you chose such as the refrigerator, lights, and maybe a window air conditioning unit – but not your whole house – only emergency necessary need loads such as a refrigerator, lights, or a window unit. At this time, it is not affordable to back up your entire house. You would be looking into hundreds of thousands of dollars to back up a whole house in batteries. You want to keep the cost of those batteries to a minimum. The batteries that are available today have a lot more power and do last longer but they still have limitations.
If you batteries fall below a certain level, the generator will automatically kick on to recharge them. But it won’t come on automatically for a weekly exercise. It only comes on when it’s needed. You could go for months without a charge. You may not need to if you have sunshine every day for months. In that case, you would need to go out there and make sure the generator runs, make sure the fuel is stirred around, make sure you go through the fuel at least once a year. You need to make sure the generator is properly running and ready to go for when you need it.
To recap, solar power has 3 different sources of charging. The main source of charging would be the photovoltaic (by sunlight). The 2nd source of charging is utility. The 3rd source is a generator. You have 3 sources to charge batteries in case you have no power from the grid which are controlled through a charge controller. A loss of power from the grid does not cause the generator to come on but a transfer on the inverter from grid tie to battery backup. That would cause the inverter to transfer to battery backup for your emergency panel. Once that occurs, then you are strictly on batteries and whatever photovoltaic is charging with that amount. If the photovoltaic is not enough to keep this up then the generator comes on, recharges it for 3 to 4 hours, shuts off and then it’s back on the solar. And if the solar is still not able to keep it up, the generator comes on every so often to back up the battery backup system.
Are you ready for a battery backup system? Post your comments below. I want to know what you think about a solar powered battery backup system.