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My New Favorite Pastime

I am fascinated by the solar power monitor. As soon as the sun comes up, the solar panels start to make electricity. As the sun moves through the sky, the amount of electricity goes up. As clouds pass between the panels and the sun, you can see the watts go down and then back up. Our sky is partly cloudy right now, so the watts are going up and down as the sun peeks out and then goes behind the clouds. (If you look closely at the pictures on the right, you can see the batteries charged to 29.9 volts, sunrise at 07:03, and 2.9 kWH generated.)

I have not seen the watts go to zero when the sun is up and the clouds are thick. At a sunny 10:00 a.m, there are about 400 watts generated. If a hazy cloud goes by, the watts drop to 250 (see kW in second pirture). With a thicker cloud, the watts dip to 100 or so. At noon the system makes about 1000 watts if there are no clouds.

The solar panels made by REC are rated at 210 watts. With six panels, we theoretically should get up to 1260 watts. The installers told me the overall wattage could be as high as 1700. I’m not sure why there is a difference between the rating and the actual, but so far our system has gone as high as 1630 watts (see firs picture).

As you learned earlier, the refrigerator and freezer, according to the specifications, should be using 3 KWh each day. To measure what they are using, I found (with the help of a friend) this really cool gadget called a Kill a Watt. It is about the size of a wall plug and costs about $29. When you plug it into an outlet and then plug something into it, the Kill a Watt tells you how much electricity the device is using. After plugging both appliances into the Kill a Watt, I learned that they use 4 watts when the motors aren’t running, about 120 watts when one motor is running, and about 240 watts when both appliances are chugging away. In a 24 hour period, they together use about 3.5 kilowatt hours. I’m wondering if the ratings are inaccurate, or if the appliances have to work harder in a warm garage. Perhaps they will use less energy in the winter in a cold garage.

Overall the monitor reports that the system generates 5-6 KWh each day. I think that suggests the batteries need about 2 KWh per day to stay fully charged. Usually by noon or so, the system has already generated enough electricity to have to start discarding electricity. By 1:00 p.m. the system is making only 700 watts even though it could make 1200 watts. The system gets to 1500 only if the morning is very cloudy, and then the maximum wattage occurs about 2:00 p.m. Normally by 3:00 p.m. the system is keeping only 200 watts, even though there is plenty of solar potential.

If we spent a few thousand dollars more to hook the solar system into the power company, we could make use of all the energy generated in the panels. We could sell the extra KWh to the power company for 2 cents each. Like many things solar, it is just not worth it. I am hoping we can find other ways to use more of the energy without spending more money.

We are Live!


The city inspector came this morning and signed off, so we flipped the switch and started generating electricity.

Right away the system monitor displayed all kinds of information, showing the electricity coming in from the solar panels, going out to the batteries, and the total KWh generated for the day. With the sun barely up over the mountains, the panels delivered 500 watts. As the sun got higher at 11:30 a.m., the panels delivered 1200 watts (1.2 KW). The panels are rated at 1700 watts, but the panels never got a chance to reach their limit. By the time the sun was at its height, the batteries were fully charged (they came charged) and the monitor cut back on the energy that went to the batteries. The system monitor acts like a traffic cop, preventing the panels from overcharging the batteries.

The freezer and the refrigerator are plugged into the system and are running well. When their motors are not running, the monitor allows 170 watts go to the batteries. When I can hear the refrigerator motor running, the monitor allows 300 watts to go to the batteries. When I can hear both motors running, the monitor allows 430 watts to go to the batteries.

I wish I could have measured the solar panel output when the sun was shining most directly on the panels. So far today, the solar panels have sent 4.7 KWh to the batteries, worth about 47 cents. The refrigerator and freezer are unlikely to use enough energy overnight to force the system to work at its maximum tomorrow. I might turn the system off tonight, so I can turn it on again at 1:00 p.m. tomorrow to see just how fast the panels can go on a summer day. On a sunny winter day, they should do even better.

The system came in a little under budget at $18,280. That includes 6 solar panels rated at 1.7 KW, an inverter/monitor rated at 2.5 KW, and 8 huge 6 volt batteries. In another message I will break down the costs and let you know how much we will get back from the government.

Batteries are Complicated


When I started I thought it would be easy to figure out how many batteries I would need for the system. I wanted 20 KWh to cover the possibility of 4 cloudy days in a row. As it turns out, batteries are not rated in KWh, so you have to do some math. Batteries are rated in AH or Amp Hours, and the number of AH available depends on how quickly the energy is used and the temperature. If energy is used quickly, less electricity is available. When the temperature surrounding the batteries goes above 77 degrees, the capacity of the battery goes down. At 95 degrees, the batteries are only half as effective.

In our case, the installers suggested using 8 Trojan L16H-AC 6 volt batteries. These are big deep cycle batteries—11 5/8” long by 7” wide by 16 3/4” high, and they are heavy—125 pounds each. Deep cycle batteries are designed for putting out low amounts of electricity for a long time, while car batteries are made for putting out a lot of energy in a short time. Each are rated to produce 25 amps for 935 minutes, or 75 amps for 245 minutes, or 357 AH (amp hour) if drained over 5 hours, or 435 AH if used over a 20 hour period of time.

Since we are hoping the batteries would last for four cloudy days, the 20 hour rating is the most likely to apply to our situation. In theory, using the power over 96 hours would give us a little more electricity than the rated amount, assuming the garage doesn’t get too hot. So, if we multiply 435 AH by 8 (the number of batteries), we should have 3,480 AH. If you multiply amp hours by the number of volts in the battery (6 in our case), you get watt hours. 3,480 AH multiplied by 6 volts is 20,880 watt hours or 20.88 KWh. In theory then, we should have four days of reserve power.

The cost for each battery with shipping and sales tax is about $500. They are sealed, so there is no maintenance, but they only last for 5 to 8 years. We should probably ignore the fact that if we do save $182.50 per year, we won’t have saved enough money to replace the batteries. At least the technology is really cool. The monitor has a lot of lights and numbers and switches.

In the picture at the top of this post, you can see the closet where the batteries are stored. If you look at the bottom of the picture, you can see a glimpse of the batteries. The batteries are mostly covered so the grandkids can’t touch them.

I’ll let you know as soon as we go live.

Almost Ready


Our solar power system is installed. Once we pass the Orem City inspection, we can flip the switch.

The system includes 6 panels on our garage roof, 8 huge deep cycle batteries, an inverter (to covert the DC energy to AC), a monitor (to keep track of the energy generated, used, and stored in the batteries), an electrical outlet inside the house, two electrical outlets in the garage, a small fan to vent the battery compartment, and some emergency lighting.

The panels are rated to produce 1.7 KWh each hour the sun is shining and in the right position in the sky (A KW is 1000 watts, and a KWh is 1000 watts for an hour. For example, 10 100 watts light bulbs would use up a KWh in an hour. A slow cooker is rated at 300 watts, so that would use 1.5 KWh if you cooked with it for 5 hours. Note: All the math makes solar power a lot more fun.). We’re hoping the solar panels give us 15 KWh on a sunny summer day and perhaps 8 KWh on a sunny winter day. Our goal is to have available at least 5 KWh per day year round, even if we have three cloudy days in a row. (The batteries provide the power when the sun isn’t shining. The “Dummy” books suggested we store enough power for 4 cloudy days, but the solar guys talked me down to about 3. I still don’t know exactly how much energy the batteries can store and produce, because getting an straight answer about batteries isn’t easy.)

Although we wanted the solar power primarily for emergencies, we decided to hook up a refrigerator and a freezer to the system so that we didn’t waste all the electricity we could produce while we wait for the power to go out. A few weeks ago we noticed RC Willey had a sale on all its Energy Star appliances (Energy Star is a government designation for energy efficient appliances), so we went looking for a refrigerator and a freezer for the garage that would work well with the solar system.

We weren’t too concerned about prices, but we did look closely at how many KWh per year each appliance would need. We found a fridge that used only 400 KWh and a freezer that used 550 KWh. Unfortunately for the environment, none of the Energy Star freezers were frost-free, so Marieta vetoed them all. We ended up buying a freezer that needed 800 KWh. We found that the efficient appliances were relatively inexpensive (and came with government rebates), but they lacked any fancy options like an ice maker or filtered water.

If we assume we will have 1,825 KWh of power to use in a year, we should have more than enough to provide 1,200 KWh for the appliances. We’ll see. We did put the appliances are on a special plug, so that regular power will take over if the batteries run out of juice.

I’m still not sure of the final price of the solar power system, but it will be about $20,000. If we generate and use 5 KWh per day, we will save 50 cents each day on our power bill. If this were an investment (and not just a project to keep me out of trouble), that’s a return of a little less than 1%. With the government rebates (by the way, I would like to thank those of you who pay taxes for contributing to our solar power system), the cost could be cut in half and the return could be as high as 2%. I will let you know the actual amounts once we know them.

In my next message, I hope to explain more about the batteries. I thought it would be a simple calculation to multiply the amount of energy one battery could hold by the number of batteries in the system to find out the total stored power in the batteries, but it’s not that simple. I wish I had paid more attention in my chemistry and physics classes.

Learning More about Electricity

After my last post about solar power, my neighbor Tom Dickson suggested I use propane instead of the sun. For a lot less money I could bury a propane tank in the backyard and run a generator whenever the power goes out. Tom is a really smart guy, and his solution makes a lot of sense.

Normally our electric company generates just enough electricity to match demand. If demand exceeds generating capacity by even 5%, we experience a brownout. If generated electricity exceeds demand, then the extra is usually lost. The power company has to have enough capacity to run all our air conditioners and appliances on the hottest day of the year and also carefully monitor customer usage to match moment-to-moment demand.

Electricity can travel only about 300 miles with our current power lines, so it is usually generated close to the place where it will be used. When you hear someone talk about powering the whole country with wind farms in the Midwest or solar farms in New Mexico, you also hear them talk about a “smart grid.” A smart grid would be one that uses new and more expensive power lines to create a grid that would allow electricity to travel across the county. It would also balance the solar and the wind energies.

Electricity doesn’t store well. You can charge a battery, compress air, or use “pumped storage” (water is pumped up into a large storage tank when there is excess electricity, and then the water is released to power a turbine on the way down when electricity is needed). These methods are very expensive, so it’s unlikely there would always be enough stored power to make up for many cloudy days or windless nights. A wind/solar, long distance transmission, and power storage system could easily cost $3 trillion. That’s about $10,000 for every man, woman, and child in the USA.

Usually a smart grid also includes putting devices in our homes that would automatically turn up the thermostats on our air conditioners whenever demand exceeded capacity. In other words, with a $3 trillion smart grid we could all experience hot flashes.

We typically pay 8-10 cents per KWh for coal, nuclear, or natural gas-based electricity. Solar or wind power costs more like 21 cents per KWh, even after federal and local governments subsidize half the cost. Even ethanol, which makes no sense at all, is cheaper than solar or wind power. As Tom Dickson suggests, propane at about 11 cents a KWh is a no-brainer.

So, why am I still interested in solar power? I guess I am trying to figure the whole thing out.