SOLAR ELECTRIC SYSTEMS - OFF-GRID

The following information may help you with your off-grid system design...

Off-grid systems are electric systems where you are your own electric supplier. In the past, such systems relied on the use of noisy generators to supply the electric. Today however, we are fortunate to have other options such as Solar Panels, Wind Turbines, and Micro Hydroelectric Turbines. This means that you can have a good source of electrical energy even if there is no utility to get it from. So now you can produce electric with the help of our planets natural resources. All three of these methods are producers of DC electric and therefore require solar storage batteries to store the electric you produce. Even though Micro Hydroelectric runs 24 hours a day, you will still have to have batteries plus a load diversion in your design. All of these energy generators are relying on energy sources whose energy output varies. For example the Sun Rays hitting your Solar Panels will increase and decrease because of clouds and the time of day, Wind speeds are also variable causing the electric output to vary as well. So the batteries not only store the electric but also provide a more consistent supply.

Should you wire your electrical system for AC, DC or Both?

To design your system output you need to decide which type of voltage you will use, ie. AC, DC, or a combination of both. Most off grid homes, and some RV's and boats use a combination of both.

I will use our Off-Grid Solar Ranch as an example of a working off-grid independent system.

We have a 15 acre parcel of land in northern New Mexico, which contains our home, office and studio, and our motor home (a converted bus that resembles a boat from inside).

Our motor home and house both use AC and DC, while the woodcarving studio runs strictly on 120 volts AC. The house operates primarily on 120 volts AC with the exception of our hot water Circulating Pump and Booster Pump (12VDC) that provides us with water from our cistern. These two pumps run from a separate self contained system which is made up of our 12vdc panels and batteries which I gave a second life to when I up-graded our solar system from 12vdc to 48vdc. Our well (which is 480 feet deep) uses a 48 Volt DC Lorantz ETA Pump and runs directly off our 48 Volt battery bank. And this Blog and my websites are all generated on computers that are powered by sun and wind power which is stored in Solar Storage Batteries. This stored energy is than transformed into 120vac by an inverter. We started with a 12 Volt input system but once we installed our well, we had to convert to a 48 Volt system. So from my example, you can see how a system can evolve over the decades. I hope this may help you in figuring out your own system.

What about PV System Voltage Input?

Before I go any further on your system's output, I need to mention a little something about your Systems DC input voltage. Today there are three main voltages you can choose from, 12, 24, and 48vdc. 12vdc had been the standard in the US for years before solar became popular. The main reason for 12vdc is that is what vehicles and boats used. As solar use in homes increased the manufactures started looking into more efficient options thus the creation of 24 and48vdc systems. Early on PV Panels were only available in 12vdc but this has now changed.

So which one of these input voltages should you choose?

• The 48vdc systems are the most efficient and also using smaller connection wires. However, you need to take into consideration that you will need to purchase four times as many batteries as a 12vdc system. With this system you can take advantage of the larger wattage of the 24vdc PV Panels. So if you can afford the extra cost of the batteries I would recommend the 48vdc system. Also you might take this into consideration, if there is a possibility that some day in the future you may have access to selling your extra energy to the grid, with the 48vdc system you can just swap out your Off-Grid Inverter for a Grid-Interactive Inverter.
  

• The 24vdc systems are the most common as it uses half the number of batteries as that of the 48vdc system and half the wire size of a 12vdc system. With the 24vdc system you can also use the larger 24vdc PV Panels as with the 48vdc systems.
  
  
• The 12vdc systems are being used less these days mainly because of the limitation in 12vdc PV Panel wattage output (basically from 5 to 140 watts per panel while the 24vdc panels put out 160 to over 200 watts). Also your wiring sizes on these systems is much larger and should be taken into consideration. If your system is going to be strictly DC, a system in say an RV or boat I would recommend the 12vdc system

Back to your systems voltage output

If you have a small system or if cost is a consideration, then you might consider a DC only. DC is simpler and is a less expensive way to go because you will not require having an inverter. I see DC systems used a lot in remote cabins, on small boats, and in under developed countries. However, if you plan to run appliances that you already own (Stereo, TV, Power Tools, Toaster, etc.) you will need an Inverter (an inverter is an electronic piece of equipment which turns DC electric power into AC electric power). Since AC products are more readily available and generally less expensive you may want to run AC. Remember, that if you go 100% AC, you are relying on an inverter. If the inverter goes down there goes your electric. The good news is that today's inverters are very sturdy and long lasting. At the Solar Ranch we run redundant inverters with a backup generator just to be on the safe side. In the near 30 years that I have been living with solar I have only had two minor problems, one was a relay on my original Trace square wave inverter and the other was a faulty temperature sensor.

Wiring your home for both AC and DC is another option. By doing this, you can run both AC appliances, some DC appliance and lights. When you are running your wires to your outlets use 12 gauge wire and if you think you may want to have some DC outlets, run a set of wires for each outlet you want. You can run 10 or 12 gauge wire for your lighting. Run all your AC outlet wires to your main AC Load Center, all your DC outlets to a DC Load Center, and all your lighting wires to a third Load Center. By doing this, you can use either AC or DC lighting depending on which of the other two Load Centers you connect to. This also allows you to change your mind at a later date.

Terry R. Wolff

WHAT IS SOLAR (ELECTRIC) ENERGY?

Solar energy is the energy that can be collected from our Sun. It is the ultimate renewable energy and as long as we have the Sun we have energy. Unlike the electric energy plants, it is clean, plentiful and easy to harvest. Every day enough solar energy strikes earth to meet the world's energy needs for at least four years. As we come to see just what sort of a mess we have created during this era of industrialization. Things such as global warming and CO2 buildup are of critical concern and solar energy along with wind energy can become an incredibly valuable solution for helping us to protect our planet.

Solar energy systems are often classified into two categories, passive and active...

• A passive solar system uses the light and heat from the sun directly for both heating, cooling and lighting. The best potential for passive solar approaches are if you're building a new home and can design your home from the beginning to leverage the power of the sun. However, even existing homes can be retrofitted to better leverage passive heating and cooling.

• Active solar systems are those that involve the active use of technology to harvest the energy of the sun. This includes the use of both photovoltaic panels to capture the sun (PV) as well as home solar hot water systems. There have been extraordinary strides in solar panels in the last 10 years. Solar cells have become more efficient and less costly to produce which makes them an even greater value than they were a few years ago. There have also been great strides in our ability to install and implement PV technology as contractors and builders have begun to treat PV as a mainstream building technology. Originally solar energy was used by those who did not have access to electric from a utility company. Today solar electric is being used around the world in both the mainstream (Grid-Tie Applications) and in remote areas of the world such as Africa, Asia and the Americas. With today's solar technology these remote areas can replace their gas generators with quite and clean Solar Energy Systems.
  

The economics of solar energy are compelling, particularly as the costs of conventional oil and gas continue to climb. Most PV systems are warranted for at least 25 years and usually pay for themselves in much less time, even assuming that gas and oil costs don't rise.

Because of federal legislation, every state is required to allow homeowners to feed electricity into the electric grid. With grid-tied solar energy systems the meter on sunny days can actually run backwards which means the energy companies have to pay you rather than the other way around. Now isn't that a nice change! Moreover, grid-tied solar electric systems avoid the need for batteries to store the electricity making the overall system even more cost effective.

Thanks to the 2005 Energy Policy Act homeowners get a 30% tax credit for money they invest in home Solar Energy Systems.

In addition, nearly every state has begun to get on the solar bandwagon. Many states now offer additional financial incentives for home solar systems.

With the combination of federal and state financial incentives, and the improved efficiency of modern solar technology, solar energy has become an extremely sensible option for nearly every homeowner.

So more than any other time, now is one of the best times to look into how you can incorporate Solar Energy into your plans and also what you can do with your existing house to make it more passive solar friendly.

For more information about solar and solar energy products, please visit my website at Solar-Catalog.com. Yea, yea, I know I am promoting my solar business but it is part of the deal about getting this kind of information.

I would like to thank everyone who feels that they may have contributed to the making of this article. In closing I want to add this following solar thought from John Schaeffer...

It is possible to fit 1,858,560 solar modules in a square mile.
An area of solar panels 102 miles to a side would be sufficient to generate
4,000,000,000,000 kWh of electricity or enough to power the entire US.

--Source The Solar Living Source Book by John Schaeffer

Thank you for your interest in Solar Energy!!!

Terry R. Wolff

ELECTRIC 101

Many of you may have just enough exposure to electricity to maybe confuse you or to even frighten you. With this in mind, I am hoping the below information may be of some value to you who may have questions about what electricity is. I will make electrical comparisons to that of water to help you have a better understanding since most of you are familiar with water. I will not attempt to be technical. Keep in mind, that this is just an brief overview and for a better understanding of electricity you will need to acquire and read additional resources.

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You may find the following helpful in converting the value of these terms into another value...

AMPS = Watts / Volts
VOLTS = Watts / Amps
WATTS = Amps x Volts
Kw = 1,000 Watts

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ELECTRICITY is an electromotive force (voltage) and the flow of electrons (current) through a conductor (wire). Think of electric as water flowing through a pipe. The pressure of the water would be represented by voltage and the rate of its flow would be its current (amps). So for example, a flow of 12 pounds per square inch of water at the rate of 4 gallons per minute is similar to 12 volts (pressure) as 4 amperes (current). To increase the flow of water you need to increase the size of the pipe, with electricity you would increase the wire size, which decreasing the wire resistance allowing an increase of current. This flow is called AMPERAGE in electric or you apply more pressure to the water, in electric this pressure is called VOLTAGE.

There are two types of electricity: ALTERNATING CURRENT (AC) which you will find in your home and DIRECT CURRENT (DC) which you would find in say your flashlight or automobile. In AC the flow of electrons first flows in one direction and then they reverse and flow in the other direction. While DC the flow of electrons is in one direction from minus (-) to plus (+).

Here are the major parts which make up electricity...

Voltage (E)

Measured in VOLTS, indicates the electrical "pressure" in a system. So if you were to take the pressure at the base of two water tanks of the same diameter, one being 120 gallons and the second being 240 gallons, you would see that the larger of these two tanks has more pressure. This is the same with 120 volts compared with 240 volts. The symbol for volts is V.

Current (I)

Measured in AMPERES (AMPS), is the quantity of electricity (electrons) that is flowing in a circuit. One amp is equal to the movement of one coulomb per second or 6,280,000,000,000,000,000 electrons per second. Again using water as our example, a pipe 4 inches in diameter will supply a larger amount of water than a pipe 1 inch in diameter. This is important to remember as the size of the wires used in an electrical system will determine how much electric current can go a distance from point A to point B.

The symbol for amps is A and the amount of amps used in an hour is amp hours (AH).

Resistance (R)

Measured in OHMS, is the resistance to the flow of electricity. It is a property of all electrical devices and is present in all of our wiring. The word impedance is often used instead of resistance. Impedance is a complex form of AC resistance that can can change with frequency. For a DC system and for this short lesson we will only be using resistance. The symbol for ohms is Ω.

Power (W)

Measured in WATTS, indicates the rate at which electrical energy is being used. The symbol for watts is W.

Energy

Measured in (for our purposes) WATT HOURS (Whr) or KILOWATT HOURS (kWh). This is the amount of electric used in the time period of one hour. For example a 25 watt light bulb in service for one hour uses 25 watt hours of electrical energy. If that same bulb was left on for 100 hours your total energy usage would be 2500 Whr or 2.5 kWh. Don't confuse energy with power. Power is the rate at which energy is being used.

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Ohm's Law

This is the relationship between VOLTS, AMPS, and OHMS. This law can be explained by the chart below.

Don't let this chart scare you, it is really quite simple to work with. It graphically shows us the relationship between VOLTS, AMPERES, OHMS, and WATTS. This chart is a powerful tool because you can refer to it to change value from watts to amperes as you size your PV power systems. You can also use it to determine the size wire is needed to minimize resistance.

Current (I) is equal to E/R or A=V/Ω

Current (I) is equal to W/E or A=W/V

Current (I) is equal to √of W/R or A=√W/Ω

Ohms (Ω) is equal to E/I or Ω=V/A
Ohms (Ω) is equal to E/W or Ω=V/W
Ohms (Ω) is equal to W/I or Ω=W/A

Voltage (E) is equal to IR or V=AxΩ
Voltage (E) is equal to W/I or V=W/A
Voltage (E) is equal to √WR or V=√WxΩ

Power (W) is equal to EI or W=VxA
Power (W) is equal to IR or W=AxΩ
Power (W) is equal to E/R or W=V/Ω
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Like I said, this is just the basics, for more detailed information you will need to do an Internet search.

Terry R. Wolff

INTRODUCTION TO SOLAR BLOG

Hi I am the co-owner of Solar Taos, LLC and run an on-line Solar Product Catalog. Due to all the calls I have fielded over the years about basic solar energy questions and issues, I have started this blog.

It will take sometime to get to all the questions I have been asked but eventually I hope to have this blog as a solar resource where you will be able to come and view the topics which interest you.

Here are some of the topics which I will be covering....

• Basic electricity
  
• Solar, wind, and small hydro electric production
• Utility free electric production
  
• Solar electric production tied to your utility
• Solar electric products
  
• Solar heating products
• System design and maintenance
• Solar batteries and their maintenance
• And other topics

Here is where you can find some basic terms used with solar electric and with solar air and water heating and information on battery maintenance. I will do one post in the future that will include some important resources to help you.

If you have a question, you can email it to me and I will post it as a new topic.

Should you be interested in knowing more about me, go to TerryWolff.com.

Terry R. Wolff