Wednesday, January 24, 2007

The Economy of Burning Corn

When it comes to heating our homes nothing beats the convenience of thermostatically-controlled natural gas-burning furnaces and space heaters. While some people choose to burn wood, coal, or grains, most people avoid these fuels due to the extra work involved. It is inevitable that at some time in the future the cost benefits of alternative fuels will outweigh the inconvenience of using them. When that happens, people will begin to switch to alternative fuels in large numbers.

I’ve chosen to supplement the heat from my natural gas furnace with heat from a corn-burning stove. I chose corn because it’s clean, and is easy to transport and store. Corn-burning stoves are efficient, safe, and easy to use. To determine how profitable heating with corn is, I carefully monitor my corn use, and compare natural gas heating costs to that of last year. Since the heating season is half over, I can now do the math.

All things considered, I’ve already saved $250.00. By the end of this heating season I will have saved $400.00 to $500.00, and I will have burned 3600 lbs of corn. The work involved in burning corn can be summarized as follows:

- Purchasing, transporting, and storing corn.
- Retrieving it and filling the stove’s hopper.
- Cleaning the stove and lighting the fires.

These tasks take no more than 15 minutes per 50 lb bag of corn, or a total of 18 hours for the entire heating season. If I were paying myself to do these chores using the money I’m saving by burning corn, I would have earned almost $28.00 per hour. And, although the price of corn has gone up recently, I’ll maintain this hourly rate by streamlining my corn-handling chores.

These numbers may surprise some people. You don’t have to wait for the price of other home heating fuels to increase in order to save money. You can save money now, and probably save a great deal more in the future. My calculations were the result of substituting corn for natural gas, but your savings will be even greater if you’re currently using a more expensive heating fuel. Additionally, you’ll become more carbon-neutral by burning corn, which is beneficial to the planet. This is truly a win-win situation.

Casper inspects the corn. No mice found this time.

For more information about burning corn, visit:


Tuesday, January 16, 2007

When it Absolutely Has to Work

I attended a funeral last night and happened to be sitting directly behind the widow of the deceased. She was talking to a friend about the last few months before her husband died. Because her husband needed an oxygen-producing device of some sort, she described her panic when an ice storm knocked out power at her home. She couldn’t understand why the device didn’t include a battery backup. At that moment my wife and I looked at each other, knowing that we could have provided a solution to her problem.

When an electrically powered device is necessary to sustain life, a backup source of power is an important consideration. While a generator might be the best backup strategy for a hospital or institution, it may not be the best solution for an individual with special needs who’s living at home. For a variety of reasons, it could fail when it’s needed most.

The most reliable system is the one with the fewest moving parts, and one that doesn’t depend upon the delivery, storage, and periodic replacement of fuel. A properly designed and installed solar photovoltaic (PV) system is the ideal system in this scenario.

A well designed PV system will have enough panels and a large enough battery bank to provide the needed power even during short winter days, and when the sun doesn’t shine for a few consecutive days. This is a departure from the typical off-grid PV system. Typically, off-grid PV systems are undersized for economic reasons, and a backup generator is used as needed.

To enhance its reliability, the PV system used as a power source for a life-sustaining device should not be used to provide power to anything other than the life-sustaining device itself. Furthermore, the PV system should be protected by proper grounding, and through the use lightning-protection devices. Over-sizing the inverter is another way to improve system reliability. Regular system tests or continuous monitoring equipment are important as well.

If my life depended upon an electrically-powered device I’d want that device to be powered by my own photovoltaic system. I would test the system periodically and inspect batteries and wiring. In addition, I would maintain an inventory of spare parts for the system. In other words, I’d attend to the system as if my life depended upon it.

Solar John

Wednesday, January 10, 2007

What to Expect from a Small PV System

If you’re thinking about starting really small, perhaps just one solar panel, you might be wondering what to expect from such a system. This post will attempt to answer that question.

To simplify, I’ll assume that you’ve chosen the following equipment:

- A 85-watt solar panel ($400)
- A 110ah, 12-volt marine battery ($60)
- A 10-amp charge controller ($50)
- A 125-watt sine wave inverter ($205)

You’ll have to add wire and mounting hardware to the list, but the entire system can be built for about $800.00. To illustrate how much power you’ll be able to generate, let’s start with the solar panel.

The 85-watt rating is the result of laboratory tests. Under ideal conditions the panel can generate 85-watts, but it’s unlikely that you’ll get that much power from the panel in your installation. Let’s be optimistic and assume you’ll get 80-watts from the panel. Let’s further assume that you’ll have 4-hours of sunlight each day. The daily production of your panel is 80-watts times 4 hours, or 320-watts per day.

Next, let’s consider the battery.

It’s important to note that you should never fully discharge the battery, as that will shorten its life. We’ll assume that you use only half of the energy stored in it, or no more than 55ah. An alarm will sound when your inverter senses low battery voltage, so you’ll know when to stop using stored energy.

I’ve found that a 100-Watt inverter load results in about 10-amps of current at the input to the inverter. It follows then that the battery should be able to provide power to the load for 5.5 hours. (55ah divided by 10-amps equals 5.5 hours). Considering conversion losses, we’ll drop that by about 20%, and assume that the battery can provide 100-Watts for 4.4 hours. Since 100-Watts for 4.4 hours equals 440-Watt/hours, the solar panel doesn’t quite measure up to the capacity of the battery on a day-to-day basis. There’s nothing wrong with that, it’s good in fact. I prefer to somewhat oversize the battery for a given solar array output. A little extra stored energy helps to make up for deficits caused by cloud cover.

A typical use for a system of this size is to provide emergency power, or as a primary source of power in an off-grid cabin or camper. Here is an example of how you might use the available power each day:

Radio - 5 Watts - 4 hours per day - 20 Watts per day
CF Light Bulb - 13 Watts - 5 hours per day - 65 Watts per day
Fan - 30 Watts - 2 hours per day - 60 Watts per day
Portable TV - 60 Watts - 2 hours per day - 120 Watts per day
Cell-phone charger - 25 Watts - 2 hours per day - 50 Watts per day

The total energy used is the sum of the energy used by each device, or 315-Watts per day. As long as you have plenty of sunshine, you’ll have power to spare. Unless you upgrade to a more powerful inverter, you won’t be able to operate a microwave oven, toaster, or other high-power devices.

While the system described here won’t significantly reduce your electric bill, it can really come in handy during an extended power outage. If you need more power than the solar panel can provide, you can use your automobile’s electrical system to recharge the battery. This increases the usefulness of your system, but at the expense of burning fuel.

If you live in an area that experiences frequent power outages, you’ll probably want to enlarge the system to a point where it’s able to provide refrigeration in order to keep food from spoiling. I’m in the process of enlarging mine so that I can do all of these things, and also keep the motors running on my corn-burning stove. Meanwhile, I’m producing clean, quiet, non-polluting power. This is so much better than getting up in the middle of a cold night to refuel the generator.

Please let me know what you thought about this, and other articles on this blog, by posting a comment.


Wednesday, January 03, 2007

Battery Monitoring and Charging

It seems that I’m always learning something new about batteries. Since this information is so important to the overall health of a PV system, I’ve decided to include this, my third battery-related post.

If battery voltage drops below 50%, the sulfate layer that forms on the plates as a battery discharges can harden. When this happens, the capacity and the life of the battery is reduced. If you should accidentally discharge your battery(s) below 50% of capacity, you’ll need to recharge within 24 hours in order to prevent permanent damage.

Check battery voltage daily, or use some type of automatic monitoring equipment. Automatic monitoring equipment should include an alarm, set to alert you when battery voltage falls below a preset value. Many inverters have this feature built-in, making it unnecessary to purchase a separate piece of equipment. The Tri-Metric Battery Monitor also provides this functionality.

I used to think that charging a lead-acid battery was just a matter of applying a DC-voltage, greater than the voltage rating of the battery, across the terminals. I now know that properly charging a battery is a four-step process. This is how it should be done:

1. Bulk Mode: Ramp up power until battery voltage reaches 2.43 volts per cell. Then go to Mode 2.

2. Absorption Mode: Maintain 2.43 volts per cell until the current accepted by the battery drops below 2.5 ampere, then go to Mode 3.

3. Equalization Mode: Alternately apply 2.75 volts per cell for 30 seconds and remove for 30 seconds. This mode should be done about once every 30 charging cycles, and should last for about 30 minutes each time. Go to Mode 4.

4. Float Mode: Charging is complete. If the charger stays connected, it should keep the battery voltage at 2.1 volts per cell.

Important: For sealed batteries, skip step three. If in doubt, follow the manufacturer’s instructions for charging.