Interested in alternative energy sources?
Thinking about trying solar energy?
Today our resident energy expert Robert Brenner will explain how you can get 1500 watts of AC power from solar energy. Check out the article below!
Alternative Energy: Get 1500 Watts of AC from Solar
(Based on the book: Power Out! How to Prepare for and Survive a Grid Collapse by Robert Brenner.)
A recent newspaper article described a local homeowner who uses a “trial version” of the Tesla Powerwall in his home for battery backup power if the grid goes down. Several comments in the article piqued my interest—he said his Powerwall could be used to charge cell phones and run his refrigerator. In essence, the Tesla battery bank could “keep lights on and the kitchen fridge cool for several hours.” As an engineer, whenever I see or read about innovations like this, I immediately wonder how much power is actually being generated, how many amps it can provide and for how long? I don’t need another Iphone or Ipad charging station. I want to keep my refrigerator running and my food cold until power comes back up.
So I started digging. The Tesla Powerwall is purported to provide 7 kWh for daily cycling or 10 kWh for backup. The Tesla Company claims the battery bank can generate 2,000 watts continuously and 3,300 watts for peak use. The typical house consumes about 30 kWh every day. At a Powerwall discharge rate of 2 kW per hour, a 7kWh battery driving an inverter will generate AC for this home for under 4 hours before the battery is drained. This may be acceptable at night when there is no other power source available. It’ll give you some AC to operate at minimum load, but the conversion efficiency of 0.94 during the charge and discharge cycles leaves me with more questions than answers.
An installed 7 kWh Powerwall will set you back over $7,000—the initial advertised price of $3,000 didn’t include installation and permits. How long will one of these keep the lights on and the furnace or refrigerator running? What can or cannot be operated?
It seems the Powerwall is kept charged by the grid but activates when local electricity is lost to power an entire house for a couple of hours. Then the battery in the Powerwall must be recharged to 7 kWh—currently using a 4 amp (1.6 kW) charger. That will take 5 hours assuming local electrical power was restored.
An alternative is to use a $500 gas generator but the noise may be unacceptable. Some home owners in Louisiana have had thieves sneak in early in the morning with a running gas lawn mower, set it next to their generator, then turn the generator off leaving the mower sound while they steal away with the homeowner’s emergency power source.
The article implies that solar power won’t work when local grid power goes out. This is no longer correct. After the Fukishima magnitude 9 earthquake, 49-foot tsunami, and meltdown at a large nuclear power plant, people in that country without power demanded the Japanese government to get them electricity. Many had solar systems so an inverter manufacturer in Japan was authorized to sell an inverter with a secure power feature that directly converts solar DC into grid-quality AC.
For years, Sunny Boy (SMA) had been trying to get U.S. government and utility bureaucrats to let them offer a solar-to-AC backup system that they had already designed. Based on the precedence set by Japan, the U.S. stopped stonewalling SMA and today thousands of homes are getting solar with a TL inverter that provides a socket for 1500 watts (12.3 amps) of AC directly from the solar system. Many homeowners with existing photovoltaic solar are investing about $2,400 to replace their own inverters with an SMA TL secure power product. They want that power loss insurance.
Grid goes down on a sunny day? Switch to secure power and get up to 1500 W (12.3 amps) that can easily drive a 700W 6 amp refrigerator to keep the drinks and deli meat cold. Just turn the refrigerator temp setting up to max, unplug the unit and plug it into a power strip connected to the socket on the inverter. Then slowly rotate the temp setting down to your desired temperature. You shouldn’t have a surge problem, and your refrigerator should continue to hum along nicely.
Now imagine what you could do with a 7.4 kW solar system comprised of two arrays and two identical inverters. Using two SMA TL inverters can give you 3,000 watts of power protection as long as the sun shines on the panels. Oh sunny days!
Backup power solutions are out there, and the cost of ownership continues to decrease. What a great time to be alive and enjoy technology.