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Posts Tagged battery

Air Conditioning On Solar Power

Today I wanted to share some info about air conditioning on a solar panel system.  Charlotte’s heat really came full force this week.  I know for many their climate doesn’t get as humid as it does here, for us here, AC is pretty key.  Without AC I can’t really sleep, even with a fan and my house being passive cooled.  While the humidity is still pretty comfortable, it’s HOT and the humidity is coming.  It has been in the high 80’s and low 90’s outside, which made my house in the mid 90’s inside.

I thought I’d do a post today because I’ve been able to run some real world experiments with my tiny house, the AC and solar.  I haven’t seen any real world into practice reports on this stuff, so I figured it would be helpful for you all.

I have yet to hook up my mini split system because it has taken me a long time to find a HVAC installer that would install my mini split, the reason being they all want to sell you the equipment if they are going to install it.  This was an unknown factor to me when I ordered my unit, but these are the bumps in the road you experience when you live The Tiny Life.


For heating and cooling I opted for the Fujitsu 9RLS2 which is a 9,000 btu unit with a seer rating of 27.  To give you an idea, older systems have a SEER of around 8 to 10, modern systems that are labeled highly efficient have a rating of 15 or so, but most today are around 12-13.  This is very important because me being on solar, my system simply couldn’t handle the less efficient systems.  Read about my tiny house solar panel system by clicking here.  The SEER rating is simply a function of BTUs (British Thermal Units) to Watts.  The higher the number, the better.

The other big reason I choose this unit versus a window unit was that my air handler is wall mounted, out of the way and above eye level.  This does a few things:  keeps my limited square footage clear of stuff, it keeps my windows looking nice because I don’t have a window unit blighting a good design, and keeping it above eye level also makes you forget about it because as humans we don’t often look up.

el_pac_08e9_unit_picWhile I’m trying to get an installer lined up I’m using a Portable Air Conditioner which has worked pretty well.  The downside to it is it takes up a lot of space and it’s not as efficient; it has a SEER rating of 12, which makes my mini split system 225% more efficient than this.

I decided to “stress test” my system by turning the Portable AC unit on high and setting the thermostat to 60 degrees and see how long it was going to take for my batteries of my solar panel system to bottom out (50% discharge).  The charge controller on my system automatically turns off the power to my house if the power in that batteries discharges down to 50%, this allows me to not damage the batteries by discharging too deep.

batter tiny house discharge

As you can see by the chart above, keeping discharge at 50% or above gives me a little shy of 2,000 cycles or 5.4 years.  I plan to add another set of four batteries to the system pretty soon, which will give me a good capacity and keep my discharge rate much higher than 50% (though I don’t often get that low)  In about 5 years we should start seeing some really interesting battery technologies hit market, so I plan to hop on that as soon as my batteries begin to fade.

My stress test turned out pretty good.  With the much less efficient portable air conditioner I ran it solid for 3 days starting with a very warm house.  At the end of the three days I was very close to hitting 50%, but it didn’t ever dip below.  I decided that the test went on long enough to be pretty happy, so I decided to stop.  I typically turn off the AC when I’m gone.

The past few days have been a bit trickier because since my system was so low from the stress test, I needed it to build back up, but we have had a series of cloudy days.   I’ve had plenty of power to run the AC over night, but it’s lower than I’d like.  To give you an idea, on a normal sunny day I make about 8,000 watts, on a cloudy day I get between 2,000 and 4,000 watts when the clouds are very thick with no gaps.

The really great thing is when it’s hottest, during the day, I can make lots of power.  This allows me to run the AC full blast and I can make enough power to run the AC and still be dumping 1000 watts into the batteries.  Compare this to heating, you most often need the heat at night the most, which is when the sun isn’t out, so its a major drain on your batteries.  To compound the issue of heating, heaters are often more energy intensive than cooling.

The other night I tried an experiment.  I got my house very cold and turned off the AC at midnight (when I usually go to bed).  Outside it was pretty cool, about 65 degrees and about 45% humidity, so not bad.  I left all the windows closed to see how much my body heat would heat up the house and because in the summer, opening the windows doesn’t help even if it is cooler outside because the humidity increase the “feels like” temperature.

As it turns out in just three hours my body heat warmed the loft of my tiny house up to the point that I woke up from being so uncomfortable from the heat.   Around 3:30 am I woke up and it was very hot in my loft.  I checked the time and was surprised how little time it took.  I should note that I’m one that when I fall asleep, I stay asleep all night, even if I get warm, so the fact that I was woken up goes to show how uncomfortable I must have been, because it takes a lot.

I had prepared for this and all I did was crank open my sky light (the highest point in my house) and the loft end window and switched on a fan to draw in cool air.  Within 5 minutes the whole place dropped about 5 degrees and I was back asleep.

So that has been some of my real world experiences with the tiny house, AC and solar.  I know I had always been frustrated by not enough stories on this stuff, so hopefully I can help others.

Some key resources for those wanting more technical stuff


Future Of Batteries

With many Tiny Houses wanting to live off the grid, many of us dream of all electric cars charged by green energy sources, we get frustrated when our devices only last a scant few hours.  What does all this have in common?  Batteries.  Technology has allowed us to do so many interesting things in today’s world, but batteries are still from the stone age, or so they seem.  They are inefficient, heave, expensive, and have a low mass/volume to power ratio.  I have said to friends many times, want to make millions, make a better battery.

Living off the grid is one of the biggest benefactors of improvements in batteries.  While solar cells aren’t quite there yet, they have made some big strides in making them cheaper and more efficient.   The point is, they are on there way.  The second component to a solar array is storing that energy to have on had at night or when you are in some heavy  usage.  Better batteries will allow us to do this.  Here is a good article from Good.


For those who didn’t pay attention in class: Batteries are typically comprised of three main parts: a cathode (positive electrode), an anode (negative electrode), and an electrolyte (an ion-rich liquid that separates the electrodes). The movement of metal ions between the cathode and the anode through the electrolyte (and back) releases electrons, generating electricity

Lead-acid batteries, found in conventional automobiles, have a low ratio of energy to weight, which means it takes a lot of battery to provide just a little juice. Nickel-metal hydride batteries, the ones powering today’s hybrids like the Toyota Prius, are significantly lighter, but offer only a slight improvement in efficiency. Neither can compete with gasoline-fueled internal combustion.

Several technologies are competing to fuel the next generation of EVs. All of them, however, have serious weaknesses that researchers are still attempting to address. “People are betting on different horses at this point in time,” says Matt Keyser, a senior engineer in energy storage systems at the National Renewable Energy Laboratory in Golden, Colorado. “Which one is going to come out and win is anyone’s guess.”

Here’s a look at some of the technologies vying to corner the EV market:


lithium-ion-smallThese batteries use lithium ions as the electrolyte. A battery pack made of these cells, while more powerful than lead-acid and nickel-metal hydride batteries, is still 10 times weaker than an internal combustion engine of the same weight. Versions of these batteries are already used in in both the Tesla Roadster and Chevy Volt, as well as many electronic devices, such as laptops and cell phones. The knock on current lithium ion technology: It dispenses its stored energy slowly, so acceleration may be slow, and the batteries take several hours to charge. Also, while lithium is plentiful, it’s not extensively mined, so it’s expensive to obtain. It may take up to 10 years for supply to catch up to projected demand.


ultracapacitor-smallUltracapacitors charge quickly and dispense their charge speedily (curing the slow acceleration problem that plagues some electric cars). They also last much longer than batteries—they can be recharged over and over again, whereas batteries eventually will not recharge. That’s because ultracapacitors use electric fields, instead of slowly depleting chemicals, to get charges. They are already in use in short-run electric buses in Russia and garbage trucks in the United States. The downside: They only hold their charge for a limited time, so it’s unlikely that ultracapacitors will become a viable option for powering a car alone. “I think ultracapacitors are a technology that’s going to work with [battery] systems,” says Savinell. However, one Texas-based company called EEStor says it has solved the storage problem, claiming its ultracapacitors will enable a small car to travel 250 miles on a single charge that only takes five minutes to complete.

Fuel Cells

hydrogen-fuel-cell-2-smallLike batteries, fuel cells have cathodes and anodes and involve a chemical reaction, specifically making water and electrons (and thus electricity) by combining hydrogen with oxygen. The technology is simple enough, but the safety issues are the drag: The transport and onboard storage of highly explosive (remember the Hindenburg?) hydrogen gas could keep fuel cells from catching on. In addition, the catalysts needed to split hydrogen atoms into protons and electrons (like platinum, palladium, rhodium, nickel) are very expensive. “Fuel cells from a mobile standpoint are difficult,” says NREL’s Keyser. “Maybe in twenty five or thirty years down the road, we may be able to deal with all the storage issues, the transport issues, the infrastructure issues, the catalyst itself.” Seemingly agreeing with Keyser’s skepticism is the Obama administration, which cut $100 million from the federal hydrogen fuel cell program in 2009.

Redox Flow

vanadium-redox-flow-smallSimilar to fuel cells, redox flow batteries would require filling stations rather than plug-in capability. In this case, a charged electrolyte flows through the battery, producing electrons. After a while, the electrolyte loses its charge and needs to be pumped out and replaced. The electrolyte is typically made with vanadium, which is the 22nd most abundant element in the world. It’s also very safe. “If you were to spill this on the road and light a cigarette near it, it’s not going to go off like hydrogen,” says Keyser. “The big thing with [redox flow batteries] is: Are you going to get the energy density or power density that you need for the car itself?” Right now, even lithium ion cells are several times more powerful than redox flow cells. German researchers, however, claim they have a method to increase the distance redox flow batteries can power a car by four to five times, rendering them roughly equal to lithium ion batteries.

Metal Air

metal-air-battery-smallSavinell and Keyser both point to metal air batteries as the technology of the future. This battery uses the oxygen in the air as its cathode, which means it doesn’t need as much material and gets more energy for its weight. Depending on what material is used for the anode, metal air batteries could be anywhere from three times more powerful than lithium ion batteries of the same weight to as powerful as an internal combustion engine. IBM intends to bring these to market in five years for smaller electronics. “For lithium air, I think that’s more ten to fifteen years down the road [to power a car],” says Keyser. “We’re just starting to really look at that and understand all the benefits and the costs associated with lithium air batteries.” One major barrier remains: When the oxygen reacts with the electrolyte to form ions, it also creates a solid that can gunk up the air intake, blocking the battery’s function. Researchers are searching for an electrolyte that will produce the necessary ions but avoid the formation of this solid.