Many people do not know that if you own a solar system for your house it is law that the system shuts down during a grid failure… WTF?!? Although this is the stupidest thing ever in the history of fucked up laws which have hit our books, it is true. The reason is if your solar system is producing power during a total failure of the electrical grid it can back feed electricity into the system and potentially electrocute a Lineman working on the power lines to restore electricity to your community. Makes sense right? Well no. You can actually zip on over to Costco and buy yourself a gasoline generator with a built in a switch; which when it detects the grid electricity has gone down it will turn itself on and will prevent power from back feeding into the system. When the electricity comes back on, it reverses the process, shut the generator off and reconnects your house to the grid without you ever knowing anything happened except of course if there were zombies walking around. So why are you able to do this in one application and not another? Who knows.
Anyway with this in mind I wanted to create a battery back up system for my house. The bid from my solar contractor came in at $50,000. I said all I need is a 20 amp outlet… They said you can’t do that… I said screw yourself and with the help of a buddy we came up with systems of our own. Why a battery system and not a generator? Well generators will eventually run out of fuel and can only produce power 1/20th their total output so if you need to only charge a cel phone which needs 5 watts to charge and you have a 5,000 watt generator that generator will produce at the minimum 250 watts, meaning you are wasting 245 watts of electricity and fuel consumption. A battery can produce about 1/200 it’s total power output so it will only producer what you actually need. Wasting very little energy.
Here’s my backup system:
This is a portable battery back up system for my house mounted on a hand truck. The top left of the hand truck is a 2 watt LED which comes on as soon as the inverter is turned on making it easy to see your way if trying to manuever the hand truck during the night.
The top of the rig is a Solar Charge Controller. It allows me to tap into one of my 21 – 220 watt solar panels on my roof to recharge the battery during the day. It should keep this system topped off fairly well as long as I don’t let the batteries drain too much each night.
Below the Solar Charge Controller is a Whistler 1600 Watt Inverter which will allow me to run my refrigerator, some LED lights, charge my cel phone, run a radio and power my HAM radio. On the side of the inverter is a handy volt meter I had from working as a lamp operator, it has a digital readout and allows me to make sure the voltage is good while it’s in operation.
Under the Inverter is my Shumacher Digital charger, it’s a microprocessor controlled charger which evaluates the batteries condition and maintains it properly. The days of trickle chargers are gone. If you have one on a battery throw it away, you’re doing more harm than good using it. This charger is a 80 amp charger, which means it will charge these batteries really fast and can maintain them easily. It’s completely overkill for this rig but I got it at an out of business sale and it was cheaper than the 20 amp version I was going to get, so I made out like a bandit.
The batteries are a class of battery called GC2 – which means they’re Golf Cart batteries which are 6 volt each requiring two of them to make 12 volts… get it? GC2. After a lot of research I found the Trojan T-105’s were a good model for my needs. Because they are golf cart batteries they are incredibly robust. They’re built incredibly rugged because people who use golf carts are usually very hard on them flooring the accelerator, slamming on the brakes, rolling the carts over and crashing them. The manufacturers know these batteries will be abused so they build them tough for that reason, and not just tough physically. These can be hit with sudden huge drains and then recharged easily. They are a great battery for a back up system.
A lot of my research came from battery1234.com the site has an incredible amount of information about all things batteries. On the site you will find a link to the TSP podcast, I highly recommend listening to it. With the system now complete I spent about $500 to get it operational. Because I had a lot of electrical supplies I did have a lot of wiring, and supplies. I also have the solar panels on my roof so that was an expense I avoided.
Here is my buddies back up system. He opted for one 12 volt AGM (Applied Glass Matt) Battery which can be turned upside down and won’t leak. It’s the safest battery you can buy and is great for a situation where you may be worried about kids or animals coming in contact with acid from the battery. These batteries are so safe you can take them on an airplane. As you may notice my buddy who shall remain nameless for security purposes did a very ‘Clean’ install with his system and wiring. He’s a little OCD in that regard.