I've Automated my Off-Grid PV System

Because over-discharging batteries can ruin them, I only connect loads to my photovoltaic (PV) system on weekends and evenings, and only when I’m home and awake so that I can carefully monitor battery voltage. I’ve been getting 10 to 12kwh of production out of my system each month, but knowing that it’s capable of producing 45kwh or more, I’ve been looking forward to this upgrade.

When the solar panels don’t provide enough power to satisfy the AC load, energy stored in the batteries is used instead. This will occur at night, of course, but also when it’s cloudy during the day. Under these conditions battery voltage will continue to decline, and eventually the inverter will stop working. My inverter stops functioning at about 11.6 volts. Allowing the voltage to dip that low can damage the batteries, and the risk is even greater if the batteries are not recharged quickly.

Shown below is a simplified diagram of my system before the upgrade.

This is my system after the upgrade.

I’ve programmed the voltage-controlled-switch to close a relay when battery voltage is above 13.75 volts. Closing the relay switches the DC to AC inverter on. The AC transfer switch is wired to use AC from the inverter as the default, only switching to grid-supplied AC when the inverter is switched off. The voltage-controlled-switch opens the relay when battery voltage drops to 11.95 volts. When the relay opens, the inverter is switched off and the AC transfer switch connects the load to grid-supplied AC. Once the load is removed, battery voltage will gradually rise. However, the voltage-controlled-switch will not close the relay until battery voltage once again reaches 13.75 volts.

I currently have a data logger connected to measure battery voltage. If I find that the battery does not fully recharge during the day, I’ll reprogram the voltage-controlled-switch. Likewise, I may need to reprogram the low-voltage threshold for better efficiency or battery protection. I’ll determine the appropriate settings after reviewing a few days worth of data logger readings.

Shown below is the complete system, with the new components.

The voltage-controlled-switch is the device at the top-left of the picture. It’s called a “Relay Driver”, and it can be programmed for four independent functions. It gets its information (battery voltage in this case), from the TriStar Charge Controller. Mounted just to the right of the relay driver is the automatic AC transfer switch. AC from the inverter, and AC from the power grid feed in to this device, and the selected AC source is applied to the AC outlet just below the transfer switch.

The off-white aluminum box mounted just below the relay driver contains the relay. For convenience, relay inputs and outputs are wired to the terminal blocks. A relay-override switch is mounted near the bottom of the relay box. To facilitate future expansion, I’ve installed two additional relays, and an LED (barely visible on the top of the box). I’ve wired one of the relays for AC. I have some expansion ideas that I’m kicking around, and I have some ideas to improve efficiency.

I’ll post additional details after I’ve had a chance to see how the system performs. Check back for an update.

John

Dealing with the Energy Crisis

Alternative energy research tends to produce interesting, but useless information. Do you really care how much of the sun’s energy falls on one square meter of land on any given day? Do you benefit by knowing how much electricity is needed to power Chicago? David MacKay, University of Cambridge Physics Professor, is one source of information of this nature. For the most part it’s interesting, but not really helpful. David did get my attention with a couple of statements: “…the people of the developed world are living immorally, and a huge crisis is upon us, unless we change our lifestyle.” I don’t know if we’re living immorally, but it’s hard to deny that an energy crisis exists, and that it’s getting worse.

How did we get into this mess?

Most of the electricity produced in the United States comes from coal-fired power plants. Since coal has always been plentiful and inexpensive, electric rates have been reasonable. Most people spend less than 2% of their household income on electricity, and as a result of its low cost, we tend to waste a lot of it. We use electric doorbells when we could be using mechanical ones. We have electric can openers, hand-lotion warmers, air-fresheners, and many other unnecessary items. In addition to the wasteful items we use by choice, many wasteful items are forced upon us because of a lack of availability of energy-efficient alternatives. Many of our electrical devices use energy even when they’re turned off. These are known as “phantom loads”, and they’re more wasteful than most people realize. Because a device appears to be off, we’re not always aware that it is wasting energy.

How do we correct the problem?

Because our lifestyle includes so many wasteful gadgets, there are many corrective actions we can take. Begin with an energy audit of your home. You’re likely to find some no-cost energy-saving measures you can take that will not adversely affect the quality of your life. Do you really need that plug-in air freshener or hand-lotion warmer? You probably already have surge protectors on your TV’s and stereo equipment. If you use the switch on the surge protector, instead of the remote-control unit for on/off control of your TV, you’ll eliminate a phantom load. Check all of your AC outlets, and remove all unused wall-warts (transformers).

Next, you might want to spend a few dollars on things that will end up costing you nothing by virtue of the savings you’ll see on your electric bill. Replacing incandescent light bulbs with compact fluorescent bulbs is a good example. And why not replace your clock-radio with a wind-up alarm clock? Having done those things, it’s time to move on to larger items. Maybe it’s time to replace that old refrigerator with an energy-star-rated model. You might cut $20.00 per month off of your electric bill if you do. And isn’t it time to replace that big old TV in the den with a new 42” plasma model? In doing so you might go from 300-Watts to 100-Watts. You’ll get three hours of TV viewing for the price of one hour. The savings really add up at the end of the month.

After doing all of those things, you might consider geothermal heating and cooling, and solar hot water heating. I use a corn-burning stove to supplement my natural gas heating. Burning corn is a little more work, but it reduces my heating bill significantly. Check with a reliable contractor to see if any of these strategies will benefit you.

How much are you willing to sacrifice?

Once you’ve done all you can to reduce consumption, and perhaps made energy-efficiency improvements to your home, you then need to decide just how far you’re willing to cut back. It’s easy to say “I’ll turn my thermostat down” when the weather is mild, but will you really do it when you’re shivering in the coldest winter months? Will you also cut back significantly on air-conditioning? Be honest with yourself. If it seems like too much of a sacrifice, remind yourself of the negative effects of excessive energy consumption. Cutting back benefits you, your children, and the entire planet.

It’s unlikely that you’ll be able to make all of these changes at once. Do some research and come up with a game plan, and a consumption rate to shoot for. Check the energy-star tags on appliances you intend to buy. Look at your electric bill. If you’re currently averaging 900kwh of electricity per month, that’s a lot. Try to cut it in half. If you’re using 500kwh of electricity per month, try to cut it by at least 25%.

As you work on your plan you’re likely to discover energy-saving lifestyle changes that actually enhance the quality of your life instead of detracting from it. I’ve found it much more pleasant to turn my thermostat down and use an electric blanket in a cool bedroom. An inexpensive Kill-A-Watt meter helps me determine how much I’m saving.

Beyond conservation

After you’ve reduced consumption, the cost of a solar photovoltaic, wind, or a hybrid electric system won’t be so daunting. If you’re not ready to disconnect from the grid entirely, you can install a small system that meets a portion of your needs. If you choose to start small, employ a strategy that helps you get the most out of your system. Solar equipment that is unused, or underused, is counterproductive. Everything you’ll need to automate your system for maximum efficiency is available, and at a reasonable cost.

Expensive gasoline – The other part of the energy crisis

Having a solar electric system in place not only contributes to your independence from the power company, it’s the first step toward gasoline independence. Plug-in-hybrid-electric-vehicles (PHEV’s) will start to show up in dealer showrooms in the year 2010. By charging your car with power from your photovoltaic system, you’ll be driving on free power from the sun instead of expensive gasoline. It’s going to take a substantial system to do the charging, so now would be a good time to get started.

Renewables – No War Required

By purchasing less oil from Middle Eastern countries we not only reduce the amount of money that they have available for war, we eliminate our need to be there in the first place. Since the politicians won’t stop it, it’s up to each of us to lead the way.

When the people lead, leaders follow. Let’s roll!

John

Electricity Use - Survey Results

Good Job!

Looking over the electricity use survey, it’s good to see that so many of us are at the low-end of the scale. While we Americans are often criticized for over-consumption, it’s obvious that many of us don’t deserve it. For the most part it’s our leadership that has failed, not the American people. President Bush’s message “America is addicted to oil” strikes me as a shameful attempt to shift the blame from his inept and corrupt administration to the American people. We should expect our government to recognize problems and provide better solutions, but clearly they’ve let us down. Too much federal money supports oil and coal interests, while little goes to renewable energy projects. I’m tired of politicians who claim to care, but don’t act as if they do.

Your Accomplishment

Your efforts to conserve electricity, and your interest in renewable energy technologies, show that you care. Because of your efforts, the world is less polluted, and what remains of the earth’s fossil fuels will last a little longer. People may notice your PV panels, or your windmill, but they probably don’t give much thought to how much your efforts contribute to the quality of their lives.

Your Reward

The decline of fossil fuels will lead to electricity shortages, which will lead to laws restricting the use of electricity. Energy use restrictions will not apply to those who generate their own. Instead of a shortage, you’re likely to have a surplus of electricity from time to time. If you’re feeding that back into the grid, you’ll be compensated financially. If not, you can use that electricity in any way you wish, and think of it as “guilt-free” electricity.

Why we’re Ignored

We use bio-fueled stoves, windmills, PV panels, solar hot water heaters, and a number of other environmentally friendly systems. We talk about our projects with those doing similar things, but seldom with others. Mostly, we’re just ignored. Some are reluctant to discuss renewable energy because they don’t understand the technology, but others shy away from the topic out of feelings of guilt. After all, they see you and I doing much more than they are doing.

Promoting Renewable Energy

While it might be tempting to flaunt a “greener-than-thou” attitude, it’s important to know that successful movements are not powered by guilt, they’re the result of confidence and passion. Be patient, and nonjudgmental, but don’t expect to convert everyone you see. There will always be those who don’t care about anyone or anything but their own selfish interests, and there will always be those who have discretionary income but no discretion.

Conclusion

Pat yourself on the back, enjoy some guilt-free consumption, and get back to work! The world needs you, and is better off because of you.

sj

Off Grid Solar PV - Measuring Progress

In a speech at the World Future Energy Summit recently, Department of Energy Secretary Samuel Bodman told the audience “the biggest source of immediately available “new” energy is the energy that we waste every day.” Those words reminded me of my own conservation efforts. My habit of turning off lights and resetting thermostats can almost be called obsessive-compulsive behavior. But my past efforts have not been particularly satisfying because I’ve never measured progress. Because of that, I had no real sense of accomplishment.

To generate interest, I’ve decided to track my electricity use over time. I was able to get records of my electricity use for the past two years from my utility company’s website. I entered that information in a spreadsheet, and could immediately see that past efforts have been worthwhile. My use of electricity was significantly lower in 2007 than it was in 2006, with the greatest reductions being in the most recent months. This was expected, since I’ve recently replaced a refrigerator and a TV with energy-star-rated models. Here is the data for November:

My electricity use in November of 2006 was 747kwh.
My electricity use in November of 2007 was 562kwh.

The 185kwh difference was a huge reduction, and perhaps somewhat of an anomaly. The October 2006 to October 2007 difference was only 22kwh. Still, I’m quite pleased with my overall progress. As my use of utility-provided electricity is going down, my use of solar- (PV)-provided electricity is increasing.

My current average monthly use of PV-generated electricity is about 12kwh. I’ll soon be applying a system upgrade, and expect my average monthly use of PV-generated electricity to be about 45kwh.

If I can continue to use less electricity, and generate more of electricity I use, I’ll eventually be able to meet all of my needs with solar panels. And while my figures seem to show that the date is many years in the future, it may be sooner than expected. In the not-to-distant future my wife and I will become empty-nesters. When the kids leave, electricity use will go way down. Unused rooms will be closed off, and we’ll seldom need to use lights or appliances in those rooms. Our laundry and dishwashing loads will decline. At the same time we’ll continue to replace worn-out appliances with energy-efficient ones. We’ll replace more of our lights with CFL’s, or perhaps with LED lighting.

I look forward to the day when I can finally flip the utility breakers off, and still live comfortably with energy from the sun. Last Sunday I used surplus PV-generated electricity to make toast. My batteries were fully charged at the time, so this was an opportunity to take advantage of solar energy that otherwise would have been wasted. I’ll be watching for more opportunities like this in the future. Energy Secretary Bodman would be pleased if he knew about my efforts, but more importantly, I feel good about what I’m doing.

Sunday Morning Toast - Courtesy of the Sun



Please take the time to answer the survey question; “How much electricity do you use each month?” Provide a monthly average if you can. Look for a line on your electric bill that states “total usage in killawatt hours (kwh).” Keep the information you’ve collected so that you’ll be able to measure progress as you take steps to reduce consumption.

John