Design and Build an Off-Grid Solar Electric System

Anyone with a basic understanding of electricity and good mechanical skills can design and build a solar photovoltaic (PV) system. Here, condensed into a few easy steps, is what you need to know.

Overview

There are two basic types of solar PV systems, off-grid and grid-tied. An off-grid system uses batteries, while batteries are optional in a grid-tied system. In this article we’ll be discussing off-grid systems. An off-grid system uses solar photovoltaic (PV) panels to turn sunlight into electricity, and stores that electricity in batteries for later use. Battery charging must be done in a controlled manner to protect them from damage, and for efficiency and safety. The stored energy must be converted to AC voltage in order to power ordinary household appliances.

Building a system large enough to meet your daily needs for electricity can be an expensive project. For most people, reducing the load by improving energy efficiency will be more cost effective than building a system big enough to handle a heavy load. Replacing incandescent lights with compact fluorescent (CFL’s), and upgrading to energy-efficient appliances are a couple of things you can do that will pay off in the long run. Having done that, you’re ready to start the design phase.

Step 1. Determine your daily needs.

List the electrical requirements of each device that you plan to power with the PV system. Example:

A 13-watt bulb in use for 5 hours each day (average) uses 13 watts times 5 hours, or 65 watt/hours per day.

Enter the information for each device into a chart as shown below:


Your total energy needs are the sum of the individual requirements of all devices, or 4985 watt/hours per day in this example. You may choose to build a system to meet all of your needs, or choose instead to build a system to meet a portion of your needs.

Tip: If you don’t know the electrical requirements of a particular appliance or device, an inexpensive Kill-A-Watt meter can help you find out. Click (HERE) for more information.

Step 2. Determine the amount of PV needed.

PV panels are rated in watts. One 100-watt panel produces the same amount of power as two 50-watt panels. If you get 4 hours of sunlight each day, a 100-watt panel is capable of producing 4 times 100, or 400-watt/hours of power daily. The example above lists your needs at almost 5000 watt/hours per day. Dividing 5000 by 400 shows that you’ll need twelve and a half 100-watt panels to meet your daily needs. To make up for system losses, and because you’ll probably want all panels to be the same size, you should go at least 20% bigger, opting for 15 panels. You might want even more panels to compensate for extended periods of cloud cover.

Step 3. Planning your battery bank.

Batteries are rated in amp/hours. Begin by converting watt/hours to amp/hours by dividing watt/hours by 12 (the battery voltage). In this example, the 4985 watt/hours that you need divided by 12 equals about 415 amp/hours. Since discharging batteries beyond 50% of their capacity will shorten their life, you’ll need a battery bank rated at no less than 830 amp/hours (in this example). Additionally, you’ll have to increase the size of your battery bank by about 20% to compensate for conversion losses. Having done that, you should have enough battery capacity to get you by for one full day. Ten 100 amp/hour batteries connected in parallel will do the job in this example, but if you want to compensate for extended periods of cloud cover you’ll need more. In addition to keeping your equipment running in the event of extended cloud cover, over-sizing the battery bank helps to extend the life of the batteries as a result of less-aggressive use.

As you shop for batteries, be sure to select those designed for deep cycle applications, not automotive batteries. Batteries designed for golf-carts, floor scrubbers, and forklifts are all good choices. The most expensive batteries tend to have the longest lifespan. Your bank of batteries will be wired to provide 12, 24, or 48 volts. More about that later.

Step 4. Select an inverter.

An inverter converts the low DC voltage from your battery bank to 120-volts AC. To determine the size of the inverter needed, add up the power requirements of all of the loads that you intend to run simultaneously. The total load in Step 1 was just under 5000-watts, but it’s unlikely that you’ll ever use all of those devices at the same time. You might, however, use the microwave oven and toaster at the same time, a total of 1900 watts. You might also have a few lights on at the same time. In this example, an inverter rated at 2000-watts would just meet your needs.

There are two basic types of inverters, modified sine wave and true sine wave. Modified sine wave inverters are much less expensive, but some equipment may not work well with modified sine waves. Motors may overheat and run at the wrong speed, and sensitive electronic equipment can be damaged. For best results, I highly recommend a true sine wave inverter.

The choice of an inverter will also influence another important design decision. Inverters typically accept an input voltage of 12, 24, or 48 volts. Generally speaking, a 12-volt inverter would be the best choice for a small system, while a 24 or 48 volt inverter would be better for a large system.

Step 5. Select a Charge Controller.

A charge controller efficiently controls the battery charging voltage and current, and keeps the batteries from overcharging. If you choose to build a small system, you need not get an expensive charge controller. A single PV panel can produce no more than 5 to 10 amps of current, and just about any charge controller will be able to handle that. A large PV system may require you to use more than one charge controller, splitting the PV panels into two or more sections. Your charge controller should include a battery temperature probe. The charge controller cannot efficiently charge batteries unless it has a way to compensate for battery temperature.

Unless you have a separate device for monitoring system parameters, you should opt for a charge controller with a digital meter. Most importantly, you’ll want to monitor battery voltage. The ability to monitor PV panel voltage and current is also helpful. Reduced output may alert you to the need to clean the panels, for instance.

The best available charge controllers (suitable for large systems), are able to convert voltage to lower or higher levels. Your PV array, for example, could be wired to provide 48 volts to the charge controller, which is converted to 24 volts in order to match the voltage requirements of the inverter. Operating at voltages greater than 12-volts can cut system losses due to the resistance of the wiring. By increasing voltage you can use thinner, less expensive wire, and cut costs.

Choose a charge controller that best matches the size of your system. For small systems, the charge controller should consume very little current for its operation. Typically, these are PWM (Pulse Width Modulation) controllers. PWM types provide pulses, instead of a steady DC voltage, to the batteries. For large systems the charge controller should have the ability to track PV panel output and adjust to provide the most efficient charging. This is called MPPT, or Maximum Power Point Tracking.

Step 6. Mounting the Solar Panels.

Keep in mind that cool panels operate much more efficiently than hot panels. Mount the panels in a way that allows good air circulation under them. Check my blog of 2/15/2007 for mounting ideas, and information you’ll need to determine the ideal panel orientation for your geographical location. If panels are to be mounted on a pole or roof, a lightning protection device is a good idea. Install that in accordance with the manufacturer’s instructions.

Step 7. Wiring and Safety Considerations.

Be sure to use wire that is large enough to handle the maximum current that will flow through it. Typically, a set of wires from each solar panel terminates in a combiner box or breaker box, and a thicker wire connects the solar panel array to the charge controller. Since the output of each solar panel is usually less than 10 amps, 10 gauge wires can be used from each panel to the combiner box. Battery interconnections and battery-to-inverter wires will need to be much thicker, since the current flow there can be very high. Fuses, breakers, and disconnect switches should be included in your design for safety.

Check with an electrician for the correct type and size of wiring if you’re not sure, and to make sure everything gets done according to code.

The drawing below is a typical wiring scheme for a small off-grid system. Be sure to include safety devices (not shown here):



Adding Functionality

Perhaps you’ve decided to build a system to lower your electric bills, or to serve as an emergency supply of electricity. The system described here will certainly do those things, but it also has its limitations. You may want your system to kick-in automatically in the event of a power failure, perhaps to prevent frozen food from spoiling when you’re not home. The addition of an “Automatic Transfer Switch” will provide that functionality.

You might want to automatically disconnect batteries from the load, perhaps switching to another source of power, when batteries reach a predetermined state of discharge. Check out my blog entry of 2/25/2008 for more information on that topic.

Be sure to consult with a licensed electrician before connecting to your house wiring.

Conclusion

Don’t let a lack of technical training or experience discourage you from building your own PV system. It’s not that complicated. You can build a safe, efficient system with off-the-shelf equipment from numerous sources. Learn as much as you can before you begin, to avoid altering your plans after you’ve purchased equipment. Be especially careful to take good care of your batteries, as they can be easily damaged by abuse. If you plan to start small and add to your system over time, develop a plan that will allow you to do that with as little waste as possible. Since this post has been primarily an overview, check other websites for in-depth information as needed.

Don’t let the cost of system components discourage you from building your own PV system. Start small if you must, but start. The world is changing, and we cannot continue to burn fossil fuels as we currently do. Future generations deserve more from us, and it seems that we cannot rely on politicians to do the right thing. In the words of Charles Darwin:

“It is not the strongest of the species that survives, not the most intelligent, but the one most responsive to change.”

John

Sizing Your Off-Grid Solar Electric System

The average US home consumes about 940kwh of electricity each month. For many, electricity use could be cut in half with a serious conservation effort. But if you had to rely on a small photovoltaic (PV) system could you get by on 120kwh per month?

To get by on less you’ll first need to make sure you’re using electricity as efficiently as possible. Replacing incandescent light bulbs with compact fluorescent (CFL’s) is a good start. You’ll also benefit by eliminating phantom loads and replacing inefficient appliances. I’ve listed many more things you can do in previous posts, so I won’t repeat them here. Check this blog’s archives for that information.

Living (comfortably) off-grid on less than 120kwh of electricity per month (about 4kwh per day) may sound impossible, but you just might be able to do it. Here’s how:

Of the 20 or so 13 watt CFL lights in your home, you might use each (on the average) 1 hour per day. So, 13 times 20 times 1 = 260 watt/hours. Shown below is the total for lights, and a list of other ways you might use this limited supply of electricity.

Lights: 13 watts X 20 hours = 260 watt/hours
Refrigerator: 50 watts (average) X 24 hours = 1200 watt/hours
TV and Cable box: 125 watts X 3 hours = 375 watt/hours
Radio: 5 watts X 6 hours = 30 watt/hours
Fans: 35 watts X 16 hours = 560 watt/hours
Computer and monitor: 120 watts X 2 hours = 240 watt/hours
Microwave oven: 1000 watts X 0.5 hours = 500 watt/hours
Toaster: 900 watts X 0.1 hours = 90 watt/hours
Vacuum Cleaner: 750 watts X .2 hours = 150 watt/hours
Cell Phone Battery Charger: 25 watts X 2 hours = 50 watt/hours
Washing Machine: 500 watts X .25 hours = 125 watt/hours
Iron: 1000 watts X .25 hours = 250 watt/hours

Total: 3930 watt/hours per day

How you use the available electricity will not exactly match my list of course. This is simply an example to show how you might get by on much less electricity than you’re currently using. Off-grid doesn’t have to mean living like a caveman. A small PV system can meet most of your electrical needs, including a limited amount of cooking and climate control. As long as you have other systems in place for heating, cooling, and other high-energy devices, you could live quite comfortably on much less than you currently use.

Why is this important?

Most of us purchase electricity from our local utility company for less than 2% of our household income. Because grid-supplied electricity is inexpensive and convenient, few people have any interest in alternatives at this time. But just as gasoline prices have skyrocketed in the last two years, we’ll soon see the cost of electricity increase dramatically. Most consumers will deal with this by cutting back, but some will choose to disconnect from the grid. A PV system large enough to meet your current electricity requirements may cost 25 to 35 thousand dollars. For most, reducing usage and installing a smaller PV system will be easier and less costly than installing a system big enough to meet current demands for electricity.

What would this smaller PV system cost?

First of all it’s important to understand that a system capable of providing 4kwh of electricity a day will not provide 4kwh on a cloudy/rainy day. Typically, a lack of sunshine prompts the user to either cut back on electricity use that day, or to use another source of electricity during those times, typically a generator. It is also important to understand that we’re discussing an off-grid system, not a grid-tied system. An off-grid system includes the extra expense of batteries, and is not as efficient as a grid-tied system. Your system design might include a battery bank large enough to compensate for a day or two of cloudy conditions.

PV panels produce electricity when the sun strikes them, but are most productive during hours of peak-sunlight, or stated another way, when the sun is almost directly overhead. We’ll do our calculations based on an average of 4 hours of sunlight each day. A 100 watt solar panel can produce 400 watts/hours (100 watts times 4 hours) of power each day. It follows then that to get 4000 watt/hours (4kwh)from the panels each day, you’ll need 1000 watts of PV panels. To make up for system inefficiencies, you should shoot for at least 1200 watts of PV. That would be 12 one hundred watt panels for example. If you shop around, you’ll find solar panels for less than $4.50 per watt, so you’ll spend about $5400.00 for PV panels alone. You’ll also need a charge controller, batteries, an inverter, panel mounting hardware, wire, and safety components. These items can be bought for $2600.00 if you shop around. If you’re not able to do the installation yourself, you might spend another $3000.00 for that, making your total cost about $11,000.00. If this sounds expensive, don’t forget that it eliminates your electric bill. The system could pay for itself in 5 years, or less as electricity prices increase. And since solar panels can be expected to last in excess of 20 years, you’ll be getting many years of low-cost electricity after that.

Using your system:

Your small system may not always keep up with your needs, but you’ll learn techniques to maximize efficiency. Using energy from the sun as it’s generated (instead of storing it in batteries for later use), increases system efficiency greatly. By using the vacuum cleaner, washing machine, and other appliances during peak-sunlight hours you eliminate losses associated with converting, storing, and retrieving energy. Your goal should be to use electricity wisely, ensuring a surplus. That surplus will come in handy when it’s cloudy.

Conclusion:

Having your own power plant means that you’ll not be affected by outages and brown-outs that grid-connected customers often experience. News reports about rate increases will no longer concern you. You’ll feel good knowing that by disconnecting from the grid you’re not contributing to the environmental problems associated with mining and burning coal to produce electricity. By installing your own PV system you’ll be taking an important step toward personal electric transportation, or as a politician might say eliminating your “addiction to oil”. Declining oil supplies will soon usher in the age of electric cars, and it’s not unreasonable to think that someday you’ll be able to drive on free energy from the sun. That’s something to get excited about!

John

Hollywood Green vs. Real Green

Although alternative technologies are often mentioned in the media, the details remain esoteric. Hollywood gives us a vague overview with programs that attempt to show what green living is all about, but they’re obviously trying harder to entertain than to teach. I’m somewhat impressed by “Living With Ed”, a program that attempts to teach and entertain at the same time, but the trend seems to be to move away from substance. Les (Survivorman) Stroud’s journal of his off-grid living project was interesting, but woefully short on details. Les admits that photovoltaic (PV) technology is not his strong point, and as a casual viewer I spotted several mistakes.

The worst I’ve seen so far is the Tommy Lee vs. Ludicris competition called Battleground Earth on the Science Channel. Here we have two people who don’t have a clue, competing with each other to see who can be more green. What a joke! The contestants and their teams compete to solve riddles and to assemble pre-fabricated projects. It’s like watching someone put together a small jigsaw puzzle, and with the same educational value. This so-called “reality” program is laughable, and the Science Channel should be embarrassed for showing it. The producers believe that these two “big stars” will inspire others to go green. I doubt it. The goal of the first challenge was to see who could be the first to use solar power to illuminate a large sign with their name on it. Someone should remind the Science Channel that solar power can also help reduce our dependence on oil, while helping to clean up the environment. There are so many things wrong with this program that I won’t even begin to list them here.

Programs like those listed above may have some entertainment value, but you’ll need details if you want to accomplish anything. I suggest that you:

Subscribe to Home Power Magazine: www.homepower.com

Visit discussion sites, like: www.wind-sun.com/ForumVB

And keep reading this blog.

John

PV System Performance Update

People sometimes ask me how much I save on my electric bill since installing solar panels. I have some difficulty answering that question. While my grid-supplied electricity usage is about 50% less than it was two years ago, much of that is due to energy efficiency improvements I’ve made. Replacing my refrigerator and switching to CFL lights contributed in a big way to cutting electricity usage. Still, my PV system has made a significant contribution and it’s good to evaluate performance now and then.

About my system:

My system can be considered small. If this were my only source of electricity I would be quite limited in the appliances I could use. Although some folks rely on PV systems much smaller than mine to meet all of their needs for electricity, my family prefers not to live with such limitations. I’ll continue to use electricity from the power grid, and continue to enlarge my system as my budget allows. I plan to add 1 or 2 more solar panels before the end of this year, and perhaps 2 more next year. I would like to be able to use wind or hydro, but those options are not practical for my location. Solar fits nicely into my budget, unlike more elaborate solutions such as hydrogen generation.

System specifications and capabilities:

I have 425-watts of PV panels on my roof.
My main battery bank is rated at 630ah.
My spare battery bank is rated at 420ah.
The typical load is a chest freezer, and a refrigerator.
When neither compressor is running, the load can be as low as 5 watts.
The maximum load sometimes exceeds 525 watts.
The system is automated. The load switches to grid-supplied power when batteries are low.

With about 4 hours of sunlight per day, I expect 1700 watt/hours of electricity production.

At 65% efficiency, I should get 1100 watt/hours from the system each sunny day.

My refrigerator and freezer need about 3.6 kilowatt/hours per day for their operation, much more than the PV system can generate. I could have provided a smaller load, but by connecting a load greater than the system can handle I’m not wasting any of the power that the system is capable of producing.

Measured results:

For the month of June, my solar panels delivered 42kwh to the batteries and load, an average of 1.4kwh per day.

My data also shows that I’m sending about 2kwh to the loads each day, more than the solar panels produce. The apparent discrepancy is due to the fact that I top off the charge on my batteries at night with a battery charger. My utility-provided electricity has been very inexpensive at night, and I take advantage of that by storing the low-cost energy for use during the day when rates are higher. This opportunity will end in the fall, when daytime rates go down, and nighttime rates increase. You can learn more about this plan at www.powersmartpricing.org.

When the grid fails:

My day-to-day strategy is to use as much of the solar-generated power as I can for household use, cutting my electric bill. My strategy changes dramatically when grid power fails. Since I don’t have enough capacity to keep my big refrigerator running, I unplug it. I place all of my frozen food in the chest freezer. I place items from my refrigerator in ice-chests, and use ice that I’ve previously stored in the chest freezer. My PV system can keep the chest freezer running continuously, as long as I have plenty of sunshine. I use CFL’s for light, watch TV and listen to the radio, use the microwave oven, charge the cell phone battery, and do most of the other things I would normally do with grid-supplied power. I just have to use this limited supply of power more conservatively.

Winter is the worst possible time to suffer from an extended grid power outage. To conserve electricity, I heat only a portion of my home using my corn-burning stove. Eventually I’ll have a solar PV system big enough to keep the stove running 24/7, but I’m not quite there yet. My system is big enough to meet my summertime needs, but using central air-conditioning is not possible. I have plenty of energy during mild weather grid-power outages, and I’m very comfortable in my home when that happens. It’s a joy to have plenty of light, to be able to use a TV and appliances, and to prepare food while many of my neighbors are using candles. I must admit that I still have a small gasoline-powered generator, but I’ll phase it out as my PV system grows.

Conclusion:

I’ll soon be installing another solar panel, and I have a couple of system modifications in mind that I expect will improve overall system efficiency. Starting small has been a rewarding experience for me, and I would highly recommend it to others. You might be surprised by how much you can benefit by implementing a small PV system, and you’ll certainly learn a lot. Each system upgrade makes you more independent, and improves your comfort level in the event of a grid power failure. Producing your own electricity will lead to using less gasoline. By using less gasoline you’ll be sending less money to those who want to kill you or convert you to Islam against your will. For each kwh of grid-supplied power that you don’t use, about 2.2 pounds of carbon dioxide is kept out of the atmosphere, not to mention other pollutants emitted from coal-fired power plants. If many of us do a little, it will help a lot.

John

Future USA

George W has a horrible environmental record as president, but his Texas ranch is off-grid with a variety of renewable energy systems. Although he’s done little to prepare the country for the effects of declining fossil fuel, he hasn’t neglected his own needs. Does he know something about the future that the rest of us don’t? We see skyrocketing gasoline and food prices, but we tend to plan for the future as if we expect things to be pretty much the same as they are today. Are we in a state of denial about our future?

Perhaps we’re all in a state of denial, even large corporations. GM spends an enormous amount of money promoting big cars and trucks, while closing several of its assembly plants due to lack of sales. Shouldn’t they have seen this coming? Why did they let Toyota and Honda take the lead with their fuel-efficient vehicles? GM continues to push it's gas-guzzlers by offering discounts and rebates, even offering to pay a portion of your gas bill. They use slogans like “Let’s Refuel America”. It seems that they’re determined to use up all of the remaining fossil fuel as quickly as possible!

Banks are in trouble, and I wonder why so many of them have been willing to make loans to people who probably won’t be able to keep up with the payments. Again, shouldn’t they have seen this coming? We shouldn’t be shocked when we find ourselves in a society that is much different than the one we live in today. Unlike some car manufacturers and banks, we should see this coming and prepare for it. We already drive less today because of the high cost of gasoline, but we still drive. We’re learning to economize as food prices go up, but we still buy food of course. Today most of us can compensate for rising food and gasoline prices by cutting back here and there, but what will we do if things get worse?

While another terrorist attack could trigger a sudden collapse of our economy, we might suffer more from a gradual decline. If your cost of living outpaces your income long enough, you’re in trouble. You may think that these gloom-and-doom scenarios are unrealistic and choose to do nothing, but if you believe that the worst is yet to come you should prepare as soon as you can. If you wait until things get worse, it will be too late. You’ll be forced to use the renewable energy systems you have in place, not the systems you planned to install someday.

Once you’ve decided to prepare, the next question is “How do I prepare?” How you prepare depends on how you want to live, and on your budget. You might choose to prepare for a total melt-down of society by considering your basic needs, or you might opt for a strategy that attempts to maintain your lifestyle as it was before the melt-down. A reasonable approach would be somewhere in between. Since everyone’s goals and budgets are different, this article is not a one-size-fits-all design guide. Instead, these are some ideas to help you formulate your own plan.

You can probably live as comfortably as you do now, and use half of the resources that you’re currently using, if you’ll simply cut waste. Start by eliminating phantom loads. Put your TV’s, and other items that continue to use power when turned off, on power strips. Get used to powering these items on and off with the power strips on/off switch. Get rid of unnecessary items like hand-lotion warmers. When possible, replace electrical items with mechanical items that serve the same purpose. Alarm clocks, can openers, and doorbells are a few examples. If you haven’t done so already, replace your incandescent light bulbs with compact fluorescents (CFL’s). Replace old and inefficient appliances, especially your refrigerator. Consider energy-saving home improvements, such as adding insulation and replacing inefficient windows and doors. These things not only help to cut your energy costs, they are a logical prerequisite to implementing alternative energy systems in your home. Having done those things you can get by with a smaller photovoltaic (PV) system, but you’re still not fully prepared to deal with a serious energy crisis. Let’s go beyond the basics.

Do you heat and cool your entire house 24/7? You could cut your heating and cooling costs dramatically if you were to heat and cool only the area’s that you’re using. Is a 14’ by 14’ bedroom really necessary? Couldn’t you sleep just as well in a climate-controlled 6’ by 9’ space? Providing climate control to a much smaller space requires less energy, making it possible to get by with a smaller photovoltaic (PV) system. If you have an unused room in your home, perhaps an unfinished basement with a window, you can easily create a living environment that requires little energy. You can be just as comfortable in a small well insulated space, perhaps with the aid of a window air conditioner or an electric blanket, as you are now in your big bedroom. If you’ll make the necessary adjustments you’ll be able to meet your energy needs with a small PV array, instead of covering your entire south-facing roof and spending $25,000.00. I’ve determined that I can meet my own basic needs with as little as 800 watts of PV panels, and a total investment of less than $6000.00. With 4 hours of sunshine, a system that size can generate 3200 watt/hours each day (not taking into account system losses and inefficiencies). A big portion of the energy I produce will be used to keep a small chest freezer running. I’ll also use cfl’s, radio and tv, cell phone charger, microwave oven, and fans. I’ll have limited use of my corn-burning stove or a window air conditioner. I can summarize my minimum needs as shown below:

Mild Weather Energy Requirements: 1220 watt/hours per day

Hot Weather Energy Requirements: 2530 watt/hours per day

Cold Weather Energy Requirements: 2990 watt/hours per day

If I build a system that barely meets my cold weather requirements, I’ll have shortages on cloudy days. I’ll need to cut back at times. But a system designed to meet my cold weather requirements will give me a surplus of electricity during mild and warm weather, allowing me to use other appliances to a greater extent. I’ve learned techniques that help me get the most from a small system. For example; if I place my chest freezer in the coolest portion of the house, it uses less energy for its operation while providing some heat to that area. I don’t run my refrigerator when the power fails; I use an ice-chest instead. My freezer, which is powered by my PV system, provides the ice.

As you make your plans, don’t neglect your basic needs. You’ll need fresh water on an ongoing basis of course. You might want to visit one of the many survivalist websites for information and ideas along those lines.

Since your need for food is an ongoing one, knowing how to grow and preserve vegetables and fruits is a skill that will serve you well. If you’re already a gardener, enlarge your garden. Tomatoes and other veggies are easy to grow, and easy to preserve. By canning your vegetables, you’ll have a supply of food that doesn’t require refrigeration. It’s a good feeling to know that an extended power failure (or a failure of your PV system), won’t ruin a big portion of your emergency food supply.

“Perhaps the day will come when the United States is no longer addicted to imported oil; but that day is still many years off. For now, the reason for America's rapt attention to the security of the Persian Gulf is what it has always been. It's about the oil.” Ted Koppel

Fighting for control of every last drop of oil is the foundation of this administration’s energy policy, and it will not end well. To the extent that we can, let’s not support this policy. Mass acceptance of renewable energy systems by the general public will show our elected officials, and the rest of the world, that we want to do the right thing. We can do it. We should do it. Future generations will appreciate our efforts.

John

My Renewable Energy Projects, an Update

Solar Water Heater:

My solar swimming pool water heating project is still a work in progress. I now circulate water through 200 feet of pvc tubing mounted in the attic of my storage shed. I pump cool water from the pool, circulate it through the pvc heat exchanger, and return the heated water back into the pool.

The system heats the water nicely, but I seem to have too much pool for the small amount of hot water I’m producing. I’m using an ordinary garden hose for the water input, and it has a tendency to collapse under the vacuum that the pump creates. This restriction lowers the output of the system. I may put this project on hold, since heating the pool water is not necessary this time of year. I suppose I'll work on it again this fall, or next spring.

Home Heating with Corn:

My corn stove saw limited use last winter due to the high cost of corn. Corn was about $2.50 per bushel when I installed the stove, but it’s currently about $7.00 per bushel. The sharp increase was due to the huge demand for corn by the ethanol industry. I expect the cost of corn to decline as cellulosic ethanol plants come on line, and I’ll once again be able to economically use the stove.

If the price of corn remains high, I might try growing it myself (again). I've recently purchased my first piece of equipment to help with the process, an old corn sheller. I found the sheller at an antique store. This should be well worth the 20 dollars I paid for it.

My PV System Automation and Battery Charging:

Summer has arrived, and hot weather has resulted in an increased demand for electricity. My utility rate plan has me paying for electricity based on demand, and the rate has exceeded .17 per kwh a few times. However, my nighttime rates have been surprisingly low, sometimes below .01 per kwh. To take advantage of this large discrepancy, I sometimes charge my batteries at night and use the stored energy to run my refrigerator and freezer during the day when utility rates are high. It seems that switching to a variable electricity rate plan has paid off, and that my load shifting plan is working. Here are some statistics:

My cost for the electricity I used in June of 2008 was $65.38.
My cost for the electricity I used in June of 2007 was $116.31.

I used 625kwh of electricity in June of 2008.
I used 1127kwh of electricity in June of 2007.

Other PV System Statistics:

I currently have 5 – 85 watt PV panels on my roof. I’ve not yet adjusted the angle for the summer sun, so they’re not pointed at an optimal angle. I waited a little too long to do this, and now I want to avoid walking on the roof while the shingles are hot. Later this year I’ll add another PV panel, and I’ll adjust the angle at that time.

In addition to the inefficiency caused by a less-than-ideal angle, I’ve noticed the effect of temperature on the PV panels. I seldom see PV panel current exceed 22 amps. I’ve seen panel current exceed 25 amps during cold weather.

System output averages a little more than 2kwh per day, or about 10% of my total household usage, but that is with a boost from the battery charger. I’m pretty happy with this free, and low-cost, electricity.

Summary:

Some say that unless utility rates are exceptionally high, and renewable energy incentives are exceptionally good, the payback for a solar PV system might be in excess of 25 years. But for those of us who do most of the labor ourselves, and explore ways to improve efficiency, payback can be much quicker. At the same time we benefit from a system that shelters us from utility failures. We can stay comfortably in our homes at a time when others need to abandon theirs. We can keep our refrigerators and freezers running, protecting our food from spoiling. We can keep our communications and entertainment equipment working, and protect our property and belongings. I don’t dwell on the payback period. My system has already paid for itself as far as I’m concerned. My systems can keep me comfortable in my home regardless of outside weather, or disruptions of any of my utilities. My systems are far from complete, but are improving with time. In the not-to-distant future I’ll be able to cut my transportation expenses thanks to my PV system. Perhaps one of these days I’ll be able to pull the plug on all outside services.

John