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Rocky Mountain Solar & Wind's Introduction To Remote Power Systems

1.     The Cost Of A Remote Power System:

The cost of a remote power system depends primarily on how much electricity you need.  The amount of electricity you need is called your load.  If your remote power system has a back up generator, the size of your load and the size of your solar and/or wind system determine how much of the time your generator runs.  Asking how much a remote power system costs is similar to asking how much a car costs.  The cost of a remote power system varies all over the place from a few hundred dollars to $50 - $60,000 and more. Most remote power systems cost $35,000 to $60,000.

A.     Generator Only:  Cheapest initially, but this option costs the most by far in the long run.  One light bulb will require the generator to be on and to be very inefficient.  Generators require frequent maintenance  (oil and filter change, check water, etc.) and eventually have high repair costs like a car.  Generators are also very noisy, polluting -- and they eventually die.  Solar modules will probably last 50 to 100 years!!!!

B.     Genverter System:  A generator with inverter and battery bank.  The next least expensive option, but more expensive in the long run than a mostly, or all, solar and/or wind system.

C.    Generator mostly with some solar or wind: More expensive initially, but less expensive in the long run than option's A and B.

D.    Primarily solar and/or wind with generator back up: Even more expensive initially, but less expensive in the long run.

E.    Solar and/or wind only: The most expensive initially, but the least expensive in the long run.

2.     Comparing The Cost Of Line Electricity With The Cost Of A Remote Power System:

When comparing the cost of line electricity to the cost of a remote power system, remember to include not only the cost of bringing in line electricity but also the cost of monthly electric bills over several years.  When comparing the cost of mostly generator systems with a solar only system, remember to include the cost of fuel, maintenance and eventually a new generator.  In contrast to generators, solar electric modules are warranted for 20-25 years, they will probably last at least 40-50 years and possibly far longer.  They require no fuel, little maintenance, do not pollute our air or result in nuclear waste, and they make no noise. 

3.     Reliability And Owning Your Own Utility:

Remote power systems, especially solar only systems, have become so reliable that they very seldom are down.  Often owners of remote power systems have electricity while electric utility customers do not.  The owner of a remote power system owns their own electrical power plant.  A, for example, 15 year economic comparison should consider the fact that after 15 years you will not only save on electric costs, but you will own your own (if solar/wind) very clean power plant.

4.     Get Some Solar Now and Add Later?

A.      You can add more modules later as long as the wiring, disconnects, charge controller, inverter and related system items are sized to accommodate more modules later.

B.      Batteries can be added to later, but the entire bank will only function as well as the worst battery in the bank.  So adding batteries later is not a good idea.

C.      Try to buy an inverter that will meet your needs several years from now.  Generally speaking it costs a lot more to add an inverter, or inverter modules, later.

5.     High Efficiency Appliances vs Larger Solar and, or Wind Electric System:

      Frequently thousands of dollars can be saved by spending more money on high efficiency appliances and less on your inverter, solar modules, wind generator, batteries, and by reducing the size, wear, and run time on your generator, if one is used.   Load Change Suggestions:

A.   Fill out a load sheet in order to determine your load size. (Available from RMSI.)  It is very common for purchasers of solar electric systems to go back to their load sheets after finding out the cost of a solar system large enough to supply the electricity demand on their first load sheet.  Solar electricity is still initially much more expensive than utility line electricity.  However, solar and wind electricity not only enable us to live remotely, but to generate our own electricity without polluting the air or creating nuclear wastes.

B.   Use a solar or propane hot water heater, propane or high efficiency electric refrigerator, and a gas range (without an electric glow plug in the oven) in order to reduce the size of your electrical load.

C.      Eliminate phantom loads (all nonbattery clocks, VCR, TV, garage door opener, answer machine, furnace transformer...).  Switched outlets can be used to eliminate most phantom loads.  Furnace thermostats can be changed to line voltage, or a relay can be used to keep the furnace transformer from being on all of the time.  If the furnace transformer is on all of the time, this will cause most inverters to be on all of the time, which uses a lot more electricity in many cases. 

D.      Consider replacing your blower motor with a high efficiency blower motor if you have a forced air furnace.  For example, GE makes the ECM Programmable Motor that can improve your blower efficiency by 1/3 or more. 

6.     Mounting Methods For Solar Electric Modules:

A.      Stationary ground mount on a pole, ground rack, or on a roof:  A roof mount is generally the least expensive, however it is important that the roof faces generally South. The entire array will need to be removed and replaced when the roof is re-roofed so it is recommended to install over relatively new roofing.  Stationary top of pole mounting should include manual adjusting of modules (2 times per year).  Modules should be mounted on theft resistant racks.

7.     Wire Sizing And Choosing A 12, 24 or 48 Volt System:

A.     The more voltage drop in a wire due to the resistance of the wire, the more power lost.  We recommend that the wires in a solar or wind electric system be sized large enough so that the voltage drop of the wires is 2% or less, and so that the over all voltage drop of the entire system is less than 5%. 

B.     Changing from a system voltage of 12 volts to 24 volts, or 24 volts to 48 volts, reduces voltage drop in wires by 50%., and reduces the power loss in wires by a factor of 4.

C.     RMSI recommends using the following to choose a system voltage size:

If your long term system total watts is less than 1500 watts, then use a 12 volt system.

If your long term system total watts is less than 1500 - 3000 watts, then use a 24 volt system.

If your long term system total watts is less than 3000 + watts, then use a 48 volt system.

8.    Solar vs Wind Economics:

A.      Solar modules are warranted for 20-25 years and will last far longer, although with some loss in output.  Wind turbines need some maintenance.  Most residential wind turbines are lightweight, and are likely to last 5-10 years before they will need new bearings.  The heavier built, more expensive wind generators (which are far less common), are likely to last at least 20 years before needing to be overhauled and given new life.  One older heavy weight wind generator lasted 60 years.  (See Home Power Magazine, #90, p 64.)

B.      Which is more economical solar electric, or wind electric, depends on the climate, on the local wind and sun conditions, the amount of turbulence and the size and quality of the wind generator.  In sunny climates such as the Southwestern US, solar is generally more economical than small scale wind.  Further North in say Montana or Canada, wind is likely to be more economical than solar.  Wind is also more likely economical if the electrical need is large. Generally the larger the wind turbine the lower the cost per watt.

C.      In considering a wind system it is important to de-rate for elevation, turbulence, properly analyze wind speed, adjust the wind speed for the height of the tower, and then calculate the actual electrical output per year. The rated output at an arbitrary and high wind is not a good method by which to compare wind turbines. Use the watts produced per year at the estimated average wind speed of your site from wind maps and local conditions. Wind systems have the disadvantage of having more maintenance and repairs than solar; and wind systems are less modular, making it more difficult to exactly size your system.  The labor to install most wind systems is also likely to be more than for an equivalent solar system.

D.      A hybrid solar/wind system can take advantage of both the wind and the sun, so that when you are short on one, the other is likely to be present.  Thus a hybrid system can be sized a little smaller than a non-hybrid system.  But a hybrid system may cost more to purchase and install than either a comparable solar only, or wind only, system.  It may cost less to purchase a few more batteries to get you through the times when there is too little sun or wind.  But batteries have to be replaced.  Each situation has to be analyzed in order to determine whether a solar only, a wind only, or a hybrid system is most economical.

9.     Choosing An Inverter: Modified Sign Wave vs Full Sine Wave:

A.     Sine wave inverters provide electricity that is basically the same as utility supplied electricity.  Sine wave inverters therefore supply electricity that is compatible with virtually any appliance or electrical device. Sine wave inverters do cost more than modified sine wave inverters.  Modified sine wave inverters are becoming less and less popular.  The following is a list of the electrical devices that can have difficulty running on electricity produced by modified sine wave inverters:

1)    Laser printers

2)    Some fluorescent lights (Phillips and electronically ballasted lights like the Osram EL-15 seem to work best.)

3)     Some radios, especially AM

4)     All Macintosh Computers are likely to over heat the power supply (except some older models).
Note: Most computers work just fine on either a good quality modified sine wave inverter, or a full sine wave inverter.  But occasionally a computer will crash (need to be rebooted) when the source of electricity is being switched from an AC source (such as utility or electric generator) to the inverter.  A stand alone solar system sized large enough to operate year round without the need for a back up power source would, of course, never encounter this problem.

5)     Any power tool which employs solid state power or speed control.  The components of some of these tools can be destroyed if powered by electricity supplied by a modified sine wave inverter.

6)      Some washing machines with electronic timers.

7)      Some stereo and audio equipment.

8)      Some TVs.

9)      Some new furnaces because they have microprocessors (computer chips) in their controls.

10)   X 10 home automation systems.

B.     Even the Trace SW Inverters, which are a full sine wave inverter in which the sine wave is made up of very tiny steps, have problems running some appliances.  The appliances which can have a problem with the electricity produced by full sine wave Trace SW Inverters are:

1)      Some new furnaces because of the microprocessor in the furnace control.
Note: In the event that a furnace does not operate properly, on either a modified sign wave inverter or a full sign wave inverter, the electricity to the furnace controller can be modified further by installing a power conditioner (also called a constant voltage transformer) on the line to the furnace controller only. 

2)      X 10 home automation systems.

C.    Other advantages of Trace SW Inverters:
Trace SW Inverters include gen start as a standard feature.  Without gen start an additional control will be needed to auto start.  Trace SW Inverters also work with smaller generators than modified sine wave inverters, have a 60 A transfer relay, and include some metering.  There is also a remote control option.

D.    Many of the engineers who used to be with Trace Engineering (now Xantrex) have started their own company named Outback Power.  Their inverters are in many ways superior to the Trace/Xantrex inverters.  The Outback Power Inverters are, for example, more modular.  They can be stacked to create at least 14 KW.  Their inverters are generally more efficient, handle surge better, and are fairly economical.  Therefore, we recommend Outback Power Inverters. 

10.  Charge Controllers:

Charge controllers prevent the batteries from being over-charged and regulate the way in which the batteries are charged.  Wet cell lead acid batteries accumulate less sulfation and thus last longer if they are charged to 15.3 Volts in a 12 Volt system, 30.6 Volts in a 24 Volt system, and 61.2 volts in a 48 Volt system.  It may not be economical, however, to charge your batteries to this degree if you are using a generator for much of your charging.  In most situations it is best to use a charge controller that has a variable set point that can be set high enough to meet these requirements, or close to them.  (See Home Power Magazine, #89, p 120.)

Some new charge controllers such as those made by Solar Boost and Outback Power use maximum power point tracking.  This new technology converts wasted voltage to amperage increasing the output of a solar array by roughly 10-30% or more depending on the time of year.  The greater percentage savings is in the winter.  Winter is when more electrical output is generally needed.  Most charge controllers also have pulse with modulation that is also battery friendly.

Low voltage disconnect (LVD) prevents the batteries from being discharged too far.  Generally even a high quality deep cycle battery, such as an L-16, should generally only be discharged 80%. Batteries will last a lot longer if they are discharged regularly only 25% - 50%.  All solar electric systems, except possibly some small one module systems, should have both a charge controller and a low voltage disconnect.  Many charge controllers now have LVD built into them, but the voltage setting is usually too simple to be very effective at knowing what the state of charge of the batteries actually is.  Thus the manufacturer is forced to make the disconnect point far lower than is often good for the batteries.  Most good inverters have a far more sophisticated and accurate LVD than the LVD on most charge controllers.  Battery banks lose capacity at low temperatures and over time, so that should be oversized.

11.  Batteries:

A.     Car (very short life), marine (short life), golf cart (5-8 years), deep cycle L-16s  (7-10 years), industrial  (10-30 years).

B.     Batteries give off a gas and in very rare instances can explode.  Therefore, be sure to locate the batteries separate from the inverter and charge controller.  The batteries must also be vented (unless the battery box is out doors.)

C.     A battery bank with a large number of smaller batteries with small cells is more likely to have problems with a bad cell than is a battery bank with larger batteries and larger and fewer cells.

D.    Wiring from the battery bank must be from opposite most distant terminals or the end batteries will wear out sooner than the other batteries.  It is also important to tape the inverter to battery cables together where possible.

E.   Battery conditioners have a sweep pulse technology designed to dissolve sulfation in lead-acid batteries. There is some evidence that the conditioners really work.  More testing is needed, but many companies are recommending battery conditioners, especially on larger battery banks.

12.  Deep Well Pumps: (We generally recommend AC deep-well pumps since they last longer than DC pumps, plus pump installations require special equipment and skills.) 

A.     Deep well pumps in the past were a problem for solar systems.  Not only do most deep well pumps use a lot of electricity due to over-sizing and placing them deeper in the well than is needed, but deep well pumps also have an even larger need for electricity when they first start.  The latter is called the electrical surge.  Inverters frequently must be oversized in order to be able to handle the large surge of some pumps.  Most pump installers install 240 Volt AC pumps due to their efficiency and so that smaller wires can be used.  However, solar/wind inverters are generally 120 volts.  When 240 Volts are needed a step up transformer is used, or two inverters are stacked.  The stacking of inverters can be done more economically now that Outback Power produces inverters that are modular.

B.     Generally speaking high efficiency deep well solar water pumps run off of DC electricity and are in some ways more compatible with solar systems.  Since solar water pumps consume DC electricity they don't have to draw electricity through an inverter.  Thus less electricity is lost due to the inefficiency of the inverter.  Electricity is supplied directly to the pump from the batteries. This means that a smaller inverter can be used, and that if an inverter ever fails, then the water pump will still run off of the batteries, assuming the batteries are still being charged even though the inverter is not working, i.e., by the sun or a separate charger.  Solar pumps generally do cost more than standard AC pumps, but the over all system may cost less using a solar pump rather than a standard AC pump if the well is real close and a low volume producer.

C.     AC deep well pumps can also be used economically, especially if they are 120 volts and 1HP or less (Note:  Three wire AC pumps plus ground require less electrical surge than two wire plus ground.)  Larger, even 240 volt, AC pumps can be used with solar systems, however, a step up transformer or two inverters will be required, or water can be pumped into a cistern manually once a week, or so, using a generator.  A DC pump can then be used to pressurize.  (Note:  Avoid AC deep well pumps that have no control above ground.  When the control goes bad the pump will have to be pulled.)

13.  Things To Consider When Selecting A Gasoline, Propane or Diesel Driven Electric Generator: 

A.     Sizing: derate 3 ½-4% depending on manufacturer for every 1,000 ft above 500 ft in altitude.  The larger the generator the less time it will be on.  Size an air-cooled generator so that it does not run for more than roughly four hours at a time.  Liquid cooled generators can run for days without stopping at partial load, but they should only be run for a few hours continuously at full load.  Size your generator large enough to simultaneously charge your batteries and run your loads.

B.     Quality\longevity:  For example, water cooled generators usually last 2-3 times as long as air cooled, 1800 RPM generators will last much longer than 3600 RPM generators, and propane fueled generators will last far longer than gasoline fueled generators.

C.      Auto start and auto choke.

D.     Does the generator produce full or only half power when it is putting out 120V?  Most small generators and lower quality generators produce only half their power when putting out 120V.  But most inverters are charged using 120V electricity. When running a 120 V line only, can the generator be balanced.

E.     You must have a large fuel tank (usually propane or diesel) in order for your generator to operate automatically.

F.      Quality of the electricity produced.  Does the generator produce electricity that is very close to 60 cycles and the voltage required?

G.     Noise level

H.     Fuel consumption

I.       Availability of a repair shop that will repair your unit.

14.  An Example Of The Maintenance Required On One Of The Highest Quality Generators On The Market:

A.    A Kohler 12 KW Generator (gasoline fired) needs to have the oil and oil filter changed, water checked, etc. every 50-75 hours of run time.  If the generator runs six hours per day on average, that means changing the oil, oil filter, etc. every 1 ½ - 2 weeks.  If a generator runs three hours per day on average, then the maintenance is every 2-3 weeks.  (The time between maintenance will be significantly greater if the generator is run on propane, and if the oil used is a high quality synthetic oil such as Amsoil.)

B.     Major repairs are likely to be required on this excellent quality Kohler water-cooled generator every 4,000   -5,000 hours assuming the unit is well maintained, and, of course, depending on how many hours a day the unit runs.  If the generator runs four hours per day on average, and if the unit is well maintained, then major work would need to be done on the unit every approximately three years.  (This is not guaranteed. This is just a rough average based on talking with a Kohler Service Manager.)  If this generator is not well maintained, then it could need major work in less than six months. (If the fuel used is propane, and if the oil used is a high quality synthetic, then the life of the generator will be much longer, possibly even twice as long or more.)

C.      Most generators are air-cooled and include far less quality than the above liquid cooled generator.  So most generators will require repair much sooner than the above generator.

15.    National Electrical Code:

A.     Use only listed equipment and materials (when available) and pull a permit. 

B.     If you, or your installer has questions, talk to your inspector prior to purchasing and installing equipment so as to avoid problems later.

C.    The primary reason for the electrical code and inspectors is safety.  Purchasing and installing a solar electric system that meets code has the added advantage of making it easier to get insurance with some insurance companies, and of selling the house later. 

D.      Eliminate three wire circuits from any house using an inverter system.

The first step in sizing a system, whether it is a solar system or a generator only system, is to fill out a RMSWI load sheet. 

A Rocky Mountain Remote Power Load Calculation Sheet should have accompanied this Introduction.  If you need a load sheet contact:

Rocky Mountain Solar & Wind, Inc.
1120 N. Circle Drive, Suite 120
Colorado Springs , CO 80909

Phone: 719-330-3699

Email: info@rockymtnsolar.com

and we will provide you with one.  Once you have filled out the load sheet, mail, fax, or email it to RMSWI and we will assist you with the design and pricing of your system.

Solar Basics

PV power generation Systems are made up of interconnected components, each with a specific function. One of the major strengths of PV systems is modularity. As your needs grow, individual components can be replaced or added to provide increased capacity. Although the selected components will vary depending on the applications, PV systems generally conform to the schematic shown below. What follows is a brief overview of a typical PV system.

Solar Array - The solar array consists of one or more PV modules that convert sunlight into electric energy. The modules are connected in series and/or parallel to provide the voltage and current levels to meet your needs. The array is usually mounted on a metal structure and tilted to face the sun.

Charge Controller - Although charge controllers can be purchased with many optional features, their main function is to maintain the batteries at the proper charge level, and to protect them from overcharging.

Battery Bank - The battery bank contains one or more deep-cycle batteries, connected in series and/or parallel depending on the voltage and current capacity needed. The batteries store the power produced by the solar array and discharge it when you need it.

Inverter - An inverter is required when you want to power AC devices. The inverter converts the DC power from the solar array/batteries, into AC power.

AC and DC Loads - These are the appliances (such as lights or radios), and the components (such as water pumps and microwave repeaters), which consume the power generated by your PV array.  

Balance of System - These components provide the interconnections and standard safety features required for any electrical power system. These include: array combiner box, properly sized cabling, fuses, switches, circuit breakers and meters.