I've Installed Off-Grid Solar - Why Didn't my Electric Bill go Down?

It’s interesting to talk about alternative electricity with those who live in areas where electric rates are high. They tend to know all about energy-efficient lighting and appliances. They know how to conserve, and they understand the benefits of energy efficiency-related home improvements. They’ve either installed a small photovoltaic (PV) system, or they’re planning to install one in the near future. They understand how PV systems work, and they’re tired of articles telling them to keep the panels clean and avoid shading. Those things are intuitive. What they’re really looking for is a way to reduce their electric bill.

My approach is simple; I use as much free energy from the sun as my system can supply, and switch to grid-supplied electricity only when necessary. This strategy may seem odd to those who are conditioned to think of a battery-based system as a backup to the grid. It’s counterintuitive. The first step is to get comfortable with the concept of using the power grid as a backup system.

When both sources of electricity are available, make sure that no one in the house uses grid power. Design the system to switch automatically, with battery power as the default. Switch to grid power ONLY when batteries are depleted. Many inverters have this capability built-in, but you can purchase an Automatic Transfer Switch if yours does not. By transferring all lights and electrical outlets in your home to battery power, no one has access to grid power, and therefore no one will be running up your electric bill by accident or without your knowledge. If your PV system is small, high-power items will have to be excluded. Your central air conditioner, for example, will probably not be switched to battery power. Once your batteries become discharged, late at night perhaps, lights and outlets in your home will be switched to grid power. Fortunately, this is the time when electricity use will be at its lowest level for most households.

Inverters draw energy from the batteries until battery voltage drops to a point where the inverter can no longer function. Typically, the cut-off point is about 10.5 volts (for a 12 volt inverter). Unfortunately, allowing batteries to discharge that much can be harmful to them. You’ll need another way to switch your inverter off. And, once the batteries are drained to that level, they should be recharged fully before reconnecting loads. Reconnecting batteries to the load too soon could result in chronic undercharging, which would shorten the life of the batteries. Some charge controllers allow you to configure disconnect and reconnect set points, or they have that functionality available as an option. Look for that feature in the equipment you’ll purchase. With these things in mind, let’s review system functionality:

The sun rises in the morning, and batteries become fully charged.

Selected AC loads are switched to battery power via the inverter.

The sun sets in the evening and battery voltage declines.

When battery voltage falls to a preset level, AC loads are switched to grid power.

The cycle repeats each day.

The concept I’ve described here is simple, but effective. It eliminates the waste that would occur if you were to switch manually. After all, you’re not setting at the controls 24/7 watching for the ideal time to switch, are you? By switching automatically you might save hundreds of dollars each year on your electric bill. If your PV system is small, start with one or two rooms and add rooms as you add solar panels and batteries to your system. An electrician can easily wire in additional circuits as your system grows.

I use this strategy in my home, with a chest freezer and refrigerator as the only loads. Instead of tying into my existing house wiring, I’ve added separate wiring to those appliances. Because I didn’t tie in to the existing house wiring, I saved myself the cost of having an electrician do the wiring. I’ve observed that my system switches to battery power on sunny days at about 10:30am. It switches back to grid-supplied AC at about midnight. It’s easy to see that I could use more batteries and solar panels. I plan to expand, and I hope that by the end of next year I’ll be able to add to the existing loads. By making sure that the size of the load exceeds the capacity of the PV system I know that I’m getting as much power as the system is capable of producing.

The system as described should cut your electric bill considerably, but you can cut it even more if you watch for opportunities. A properly designed system should include enough PV capacity to fully charge your battery bank each day, and excess energy is often wasted. Watch for opportunities to use that otherwise wasted energy. For maximum efficiency, use appliances mid-day with power coming directly from the solar panels.

The way to get the most from any Off-Grid PV system is not to let any solar-generated electricity go to waste.


An automatic transfer switch should be installed by a properly trained and licensed electrician.

John

Smart Transportation

Finding a car that is gentle on the environment, and fuel-efficient may be easy in Southern California, but choices are limited here in Southern Illinois. Ask about an electric car here, and dealers are likely to point to the golf-cart they use to transport customers around the lot. The 2005 Smart-ForTwo shown here seems to be way over priced at a local dealership.

They tell me there's a waiting list for these cars. I think I'll wait instead for a plug-in-electric. GM, Ford, and Toyota plan to offer plug-in-hybrid cars by 2010.

Can't wait for an electric car? You could buy a Prius now, and spend another $10,000 to have it converted to plug-in, but that seems a bit pricey to me. No, I think I'll wait instead to choose from the available 2010 models.

System Automation for a Spare Battery Bank

Having recently replaced my PV system’s battery bank, I had to decide what to do with the still-good older batteries. Connecting batteries of different types and ages together is not a good idea; it shortens the life of the newer batteries. My choice was to install a switch, allowing me to add and remove the old bank from the charge controller/inverter circuit. When I want to charge the old bank, I can simply switch it in. I can also switch it in when I need extra amp-hours, during a grid power failure for example. I can switch it out the rest of the time, keeping it from dragging down the new battery bank.

My plan worked fine for awhile, but then I neglected to check the batteries for a few days. To my horror, I found that the battery voltage dropped below 10 volts. Allowing batteries to deeply discharge, and remain in that state for an extended period of time, can ruin them. I knew I had to do something else. I wanted to use energy from the sun to keep both battery banks charged, but I wanted the main battery bank to have top priority. Here’s what I did:

The problem was easily solved by adding a relay to an unused channel of my Morningstar Relay Driver. I’ve programmed the relay driver to monitor the main battery bank voltage. When the main battery bank is nearly fully charged, I divert excess current to the older battery bank. Programming voltage thresholds is done by temporarily connecting a computer to the relay driver and running a simple configuration program. Here are my settings for the spare battery bank relay:

Turn on relay when main battery voltage > 14.40 volts.

This establishes the main battery bank as the top charging priority. Power will be diverted to the spare battery bank ONLY when the main battery bank is nearly fully charged.

Turn off relay when main battery voltage < 14.00 volts.

Turning off the relay disconnects the spare battery bank from the inverter and charge controller, preventing it from discharging through the load.

The main battery bank provides power to the loads day and night, cutting my electric bill. I’ve programmed the relay driver to remove the load from the main bank when its state-of-charge (SOC) drops below 80%. This happens at night, or when it’s cloudy, leaving me with little surplus power to use in the event of a grid power failure. However, by keeping the spare battery bank fully charged I now have the best of both worlds, lower electric bills and reserve energy to serve in the event of an emergency. A simplified diagram of my system is shown below. Relay 1 switches the inverter on and off, while relay 2 switches the spare battery bank in and out of the circuit.



John

Big Performance from a Small Off-Grid System

Gasoline prices have soared over the past couple of years, and some believe that electricity rates will soon follow. When that happens, alternatives like PV (photovoltaic) systems will become an attractive option. The surge in demand for solar panels will result in higher prices, and only the well-to-do will be able to install systems large enough to meet the needs of an entire household. The average home owner will be forced to pay the high utility rates, or to learn to get by with a small PV system. The good news is that you can get by with a smaller PV system than you might have imagined, but it’s going to take some “out-of-the-box” thinking.

Much has been written about the benefits of home improvements such as adding insulation, replacing windows and doors, efficient lighting and appliances, the elimination of phantom loads, and passive solar improvements. Alternatives to electric heating and cooling are also important. These are logical, and often necessary, prerequisites to PV system implementation, and especially important to anyone wanting to get by with a small system. Since those topics have been discussed at length elsewhere, this discussion will be limited to getting the most from a small PV system.


The daily capacity of a PV system can be calculated by multiplying the capacity of the PV array, in watts, by the number of hours of peak sunlight. A PV panel array consisting of five one hundred watt panels, for example, can produce 2000 watt-hours in a four-hour period. That’s 500 watts times 4 hours. It is widely accepted as fact that an off-grid PV system with batteries will be 65% efficient, lowering the expected daily production in this case from 2000 watt-hours to just 1300 watt-hours. Now that you know the basics, let’s explore some ideas for getting most from a small PV system:

1. Load shifting

An off-grid system is least efficient when it is used to charge batteries. The inefficiencies associated with converting energy, storing it, and converting the stored energy back to electricity results in a huge energy loss. The obvious solution therefore is to use electricity directly from the solar panels as it is produced, instead of storing it in batteries for use at a later time. Doing the laundry, running a vacuum cleaner, and cooking are some of the obvious tasks you can do in the daytime, but other strategies are not so obvious.


A well-insulated chest freezer will keep things frozen for many hours in the event of a power loss. Consider putting your chest freezer on a timer, limiting its operating hours to daytime. This will require a little experimentation, as you don’t want food to partially thaw each night.

To improve its efficiency, move your chest freezer to the coolest part of the house, perhaps the basement. Allow plenty of room for air circulation near the condenser to improve operating efficiency, don't limit it to the two or three inches that the manual suggests.

2. Eliminate unnecessary appliances

Could you get by without a refrigerator? You certainly could if you had to, and you’ll reduce the load on your PV system by 1000 to 3000 watt-hours each day. You’ll be able to eliminate a dozen or more solar panels from your array, saving a small fortune. I spoke to a friend recently who, after his refrigerator failed, continued to use it to keep items cold by using ice from his chest freezer. He used his chest freezer to produce ice, and placed that ice in his refrigerator. Milk jugs provided a convenient way to do it, and he cycled three, one gallon jugs, from his freezer to his refrigerator each day.


Perhaps you’re not quite ready to shut down your refrigerator full-time. Instead, why not put it on a timer? Shutting it down for a few hours each night will reduce the system load significantly.

Converting a chest freezer to a super-efficient refrigerator is another strategy you might consider. A thermostat mounted inside the freezer switches AC power to the freezer on and off as needed. No significant modifications to the chest freezer are necessary.

3. Add diversion load control to your PV system


If you monitor your PV system during the day you probably find that once the batteries are fully charged, you have a lot of excess energy available that doesn’t get used. Putting this previously wasted energy to use can significantly increase the usefulness of a small PV system. Adding diversion load control to your system is one way to tap into that extra energy. Some charge controllers can be used as diversion load controllers, but you can also use a PLC (Programmable Logic Controller) for the task. I use a Morningstar Relay Driver, a much less expensive option.

Often, systems are designed to use the extra energy to pre-heat water, but that’s probably the least-efficient way to use it. Using the sun to heat water directly makes more sense. If your home uses a cistern for its water supply, using this excess energy to pump water is a much better idea. It is far better to use excess energy for this task than to have to pump water at night, due to demand, using energy from batteries.

You could also use the excess energy to charge a spare battery bank. The spare battery bank might be used to power some DC loads, 12-volt dc lights for example. Using this surplus power for DC loads eliminates the conversion loss that you would otherwise experience by running a DC to AC inverter. This might allow you to turn off your inverter, perhaps all night long, saving yourself the power it consumes when idling.

4. Make Peukert’s Law work to your advantage

According to Peukert, a lightly loaded battery bank operates at higher efficiency than a heavily loaded battery bank. Looking at this another way; if you increase the size of the battery bank, without increasing the load, efficiency improves. Take advantage of this phenomenon by making your battery bank larger than necessary. As a bonus, your batteries will last longer because they’ll be stressed less.

Avoid using two or more high-power appliances at the same time. Making toast, while using the microwave oven, is an example of this. Heavy current from the battery bank results in lower efficiency, according to Peukert.

Conclusion

Anyone who’s ever struggled to get through an extended grid power failure knows that electricity is more than simply a matter of comfort and convenience. While it’s a necessity for some, it would be hard for any of us to get by without it. Imagine doing without lights on a long winter evening, or not having the ability to keep food refrigerated. Imagine doing without air conditioning, and not even having an electric fan to circulate fresh air.

Use these strategies to the extent that you can. You might start by adding the ability to log system data. The ability to log data will help you determine if system improvements and modifications are beneficial. Adding automation to your system is the logical next step. This allows you to shift loads and divert power when it is beneficial to do so. And most importantly, be on the lookout for other ways to lighten the load and improve system performance. Please share your ideas with the rest of us, in the form of a comment, so that we can all learn from each other.

John

Off-grid Systems and Off-grid People

“To acquire knowledge, one must study; but to acquire wisdom, one must observe”. Marilyn vos Savant

Some off-grid systems and the people who use them:

I have an off-grid photovoltaic (PV) system, but since I’m connected to the electrical grid I can’t honestly say that I know what off-grid living is like. My system powers some loads on a daily basis, and serves as an emergency backup system, but I rely on the power grid for most of my everyday electricity needs. The closest I’ve come to real off-grid living has been during those times when my grid power failed. To understand what off-grid living is really like it’s helpful to peek into the lives of those who actually live off-grid on a full-time basis.

An off-grid lifestyle can range from primitive to luxurious, depending upon the size of the system. While some are happy with a minimalist lifestyle, it’s common to find others who after attempting to live off-grid, have become disillusioned upon realizing just how much work is involved. Some give up, and others enlarge their systems until they achieve an acceptable comfort level. On the other end of the spectrum are off-gridders who want all of the conveniences that their well-connected counterparts in the city enjoy. This group includes the well-to-do who choose to live in an area where utility services are unavailable. Most off-gridders, I suppose, fall somewhere in-between primitive and luxurious.

With these things in mind, let’s look into the lives of some off-grid people and their systems:

#1. Can you guess which country has the most residential solar PV systems installed? It’s Kenya. PV systems are replacing kerosene lamps in remote villages, greatly improving the quality of life of the residents. Typically, these small systems are only able to provide a few hours of light each night, but the importance of the elimination of fire hazards and indoor air quality improvements cannot be overstated. Because children can study longer into the evening with the extra light, these small systems also have an educational benefit.

#2. Here in the United States, Ward’s solar PV system was built for less than $700.00. It provides all of the electrical needs of this bachelor in his remote cabin, including lights, TV, VCR, and a boombox. Ward uses a wood-burning stove for heat, and a propane refrigerator. He has no indoor plumbing. His system includes a 75-watt solar panel, four batteries, a charge controller, and a 350-watt inverter.

#3. It would be a disservice to Karen to limit this discussion to her PV system. Karen transformed a 5-acre site in the Mojave desert to a comfortable homestead. Among her accomplishments Karen installed a septic system and a 4000 gallon water tank. She renovated an old cabin, including a passive solar system of her own design. Karen uses a wood stove for heat, and propane for cooking and refrigeration. And yes, she put in a solar PV system. Her system includes 400-watts of PV, 880ah of battery capacity, a charge controller, and a 3500-watt inverter. A system of this size can be built for less than $3000.00. Because Karen’s system is larger than Wards, she can do much more. Her capabilities include pumping water, running a vacuum cleaner, and using kitchen appliances.

Although Ward and Karen may be satisfied with what they have, a typical family would probably struggle to get by with such limitations. Some might opt for the prepackaged 2000 watt off-grid PV system described below. The cost of the entire system, including batteries and wiring, is in the neighborhood of $20,000.00. A system of this size will allow the use of a washer and dryer, and almost any electrical device imaginable. In spite of the size of this system, the average family of four may experience shortages of electricity from time to time. Energy efficient construction, efficient heating and cooling systems and efficient appliances will help, but some homeowners will opt for a generator to make up for periods of extended cloud cover.

System Specifications:

PV: 2000 Watts
Batteries: 6000ah
Pre-Wired Power Center with 4,400 Watts 120/240VAC

Need even more electricity? Obviously you can have as much as your budget and space will allow. Your decision to live off-grid means that you’ll have to maintain your own power systems, but it’s really not that difficult. You’ll have sophisticated equipment that automates some of the maintenance tasks and alerts you to small problems before they become big ones. You’ll know the status of your batteries, and the amount of stored power at a glance. If you choose to install a generator as a backup, it can be set to start up automatically in the event that it’s needed.

Ward and Karen may be thought of as being on the fringe of society now, but that notion will change someday. Declining fossil fuels and an increased awareness of the harm we’re doing to our environment will someday make a change to renewable technologies a necessity, not just a good idea. Folks like Ward and Karen will be typical, not the exception. We’ll all be better off when that happens.

For more off-grid systems and people, click on this link: http://offgrid.homestead.com/OffGridersPage.html

Here’s another site that showcases off-grid systems and people: http://gallery.altenergystore.com/main.php?g2_page=1

John

Are Electric Cars More Harmful to the Environment than Gasoline-Powered Cars?

Because we’re likely to see a massive shift to personal electric transportation in the next few years, this is an important question. Ideally we should reduce our carbon footprint in the transition, not increase it, but here are the facts:

• Burning a gallon of gasoline releases 19.6 pounds of CO2 into the atmosphere.

• A gallon of gasoline has as much energy as 33kwh of electricity.

• For every kwh of electricity that a coal-fired power plant produces, 2.2 pounds of CO2 is released into the atmosphere.

These statistics seem to indicate that it is better to burn a gallon of gasoline and release 19.6 pounds of CO2 than to use an equivalent amount of electricity and release 72.6 pounds (33kwh X 2.2 pounds), into the atmosphere. It seems that driving an electric car will be much more harmful to the environment than driving a gasoline-powered car. Could this be true?

These statistics suggest that an electric car, starting with a fully charged 33kwh battery pack, would travel as far as a similarly-sized gasoline powered car could go on a single gallon of gasoline. However, the Chevy Volt is expected to be able to travel 40 miles on a fully-charged 16kwh battery pack. What gives? The discrepancy is due primarily to the fact that electric motors are 90 to 95% efficient, while gasoline engines are only 20 to 30% efficient. In reality, driving an electric car will produce about the same amount of pollution as driving a gasoline-powered car, it just moves the source of the pollution from the tailpipe to the power plant.

The net result, it seems, is that we accomplish nothing by switching to electric cars, but that’s not entirely true either. It’s easier to stop pollution at a few power plants, than it is to stop it at the tailpipes of millions of cars. Electric cars also give us the opportunity to use electricity from clean sources, such as solar PV panels or hydro-electric plants. So instead of releasing millions of tons of pollution each year, we’ll soon have an opportunity to drive our personal automobiles without releasing any CO2 into the atmosphere. That’s something we’ll never be able to do with gasoline-powered cars.

The millions of electric cars we’ll see on the road within a few years will all need to be recharged each night. It’s clear that our priority as a nation should be to clean-up or eliminate coal-fired power plants. Expensive schemes, such as carbon sequestration, are not the best use of federal funds. Promoting solar-, wind-, and hydro-power would be better. Energy from a modestly-sized solar-electric (PV) array on a single residential rooftop can offset 2000 pounds of CO2 each day, so just imagine how beneficial a million solar roofs would be. That’s 2 billion pounds of CO2 each day!

Concerned about electric car performance? Don’t be. Electric cars can be built to be both highly efficient and very quick. Tesla Motors has already proven that. Increasing the size of an electric motor improves both horsepower and efficiency. On the other hand, a big motor is needed to make a gasoline-powered car quick, but gas mileage suffers as a result.

Driving a personal automobile doesn’t have to be an environmental disaster. The switch to electric transportation can have a positive effect on the environment. All that we need now is intelligent leadership and an aggressive plan. Maybe if we can get our politicians to stop taking money from coal and oil interests, we might just get legislation that is good for the environment for a change.

John

Sources:

Carbon Dioxide Information Analysis Center:
http://cdiac.ornl.gov/pns/faq.html

Chevy Volt Site:
http://gm-volt.com/

Tesla Paper:
http://www.stanford.edu/group/greendorm/participate/cee124/TeslaReading.pdf