solar power course ware

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This work, Solar Mak Solar Pedia by John Prim,is licensed under the Creative Commons Attribution 3.0 Unported License.

To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ or send a letterto Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.

TM

THE

A Solar Power Primer

For anyone interested in the ABCs of practical solar energy!

Solar Mak has released their Solar Pedia under a Creative Commons license - aperfect addition for open courseware or self study. Also great for Educators to usein their classrooms as a student handout. Includes:

Basic Electricity

How Solar Power Works

Solar Power Planning

Solar Mak vs Gasoline Generator
http://www.solarmak.com/http://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/http://www.solarmak.com/


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IntroductionSince the Industrial Revolution, man has been consuming finite energy sources, and finding ways todistribute or transmit it great distances over large areas.

As these sources become more difficult to find and safely extract, the price goes up. With costscontinuing to rise, its now up to us to start using renewable energy sources, such as solar power.

This section is for gaining knowledge in basic electricity and apply it to solar energy.

Electric CurrentElectric current is a controlled and continuous flow of electrons. It requires a conductor, usuallycopper, allowing electrons to easily flow through it. A copper wire can be thought of as a pipe whichelectrons flow through.

Electron flow in a copper wire is measured in Amperes, orAmps. An Amp is a large number ofelectrons flowing by each second.

Continuous current of electron flow requires that a difference in potential is maintained. To pushelectrons through a copper wire, there must be more electrons at one end while having fewerelectrons at the other end.

Ohms LawVoltage is the difference in electrical charge between two points. There must be more electrons atone point and fewer at the other point to maintain voltage.

Electrons carry a negative charge. When a wire is connected between the two points, electronsflow from the negative to the positive terminal.

Insulators are used to safely contain electricity. Plastic is an insulator, because it has highresistance to electron movement. Resistance is measured in Ohms.

Basic Electricity 1.1


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The relationship between voltage, current and resistance is explained by Ohms law.

OHMS LAW: E = I x R

E = VoltageI = Amps

R = Ohms

If the value of any two is known, then the third can be calculated. To make it easier to rememberthese relationships, one can use Ohms Triangle:

Using Ohms Law:

1) Current is directly proportional to voltage. If voltage goes up, so does current. Or if voltagegoes down, so does current.

2) Current is inversely proportional to resistance. If resistance increases, then current decreases.And if resistance decreases, then current increases.

By covering the V, the triangle shows: Voltage = Amps x Ohms

By covering the A, the triangle shows: Amps = Volts / Ohms

By covering the O, the triangle shows: Ohms = Volts / Amps

E is the electromotive force (potential difference) which ismoving electrons through the wire. Its measured in Volts.

I is the intensity of electron flow (current) moving throughthe wire. Its measured in Amps.

R is resistance of electron flow in the wire. Itsmeasured in Ohms.



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LoadsA copper wire can be thought of as a pipe which electrons flow through.

In the same way, a battery can be thought of as a tank with a pump. It maintains a constantvoltage (or pump pressure) no matter if current is flowing or not.

A load is a main circuit resistance. It can be thought of as a valve. When electrons move throughthis valve, voltage is lost because of the resistance of the load. Figure 3 shows all the voltage islost to the load.

This is known as a voltage drop. Its where the resistance of a load in a circuit causes a voltageloss equal to the source voltage.

PowerPower is the rate of energy conversion. For practicalpurposes, the rate at which an electrical charge is producedor consumed can be found two ways.

One way is to determine amp-hours (Ah), and the other wayis to determine watt-hours (Wh). Well explore each.

Amp-HoursTo find Amp-hours multiply Amps by hours.

The storage capacity of a deep cycle battery isexpressed in Amp-hours.

For most batteries, the standard means to comparethis capacity is by using a 20 hour rate.

Looking at Figure 4, the batterys capacity is 100Amp-hours.

To determine the standard load, divide 100 amp-hours by 20 hours. 100 Ah / 20 hours = 5 amps



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This battery can maintain a 5 amp load for 20 hours before being completely discharged.

Tip: Never discharge a battery more than 50%, as it shortens the life of the battery.

For this circuit, loads shouldnt exceed 5 amps total. A batteries capacity decreases as the loadincreases. The light bulb has a resistance of 6 Ohms. It consumes 2 amps of power.

12 Volts / 6 Ohms = 2 Amps

Over 20 hours, the load will consume 40 Amp-hours of power.

2 Amps x 20 hours = 40 Ah

The battery shouldnt be discharged more than half its capacity.

100 Ah x .5 = 50 Ah

The light bulb consumes less than 50 Ah over 20 hours. 40 Ah < 50 Ah

Watt-hoursTo find watts, multiply volts by amps. Looking at Figure 4, we can find the wattage of the light bulb:12 Volts x 2 Amps = 24 Watts

To determine watt-hours, multiply watts by hours. 24 Watts x 20 Hours = 480 watt hours

A more common unit is kilowatt hours, which is 1000 watts multiplied by time. Utility companies use

kilowatt hours to determine what to charge customers on their electric bill.

If the light bulb is on almost 42 hours, then it consumes 1 Kwh. 1,000 Wh / 24 Watts = 41.6 hours

Which One to Use?In general, which measure to use is determined by the application, and the load size.

For example, most electronic circuits use milliamps (thousandths of an amp). The electroniccircuits in your smart phone use milliamps.

Individual appliances, from coffee makers and vacuum cleaners to refrigerators and televisions,use Amps.

Kilowatts are used as an easier means to compare the consumption of combined appliance loads.

Its used by electric utilities to help them better match their production and obtain a standard pricerate.

With portable solar generators, were mainly concerned with individual appliance use, so well focuson Amps and Amp-hours.



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Looking at Figure 4 again, we can plug the numbers into Ohms triangle.

6 Ohms = 12 Volts / 2 Amps

2 Amps = 12 volts / 6 Ohms

12 Volts = 2 Amps x 6 Ohms

Weve determined that the light bulb uses 24 Watts, or 2 Amps. It consumes 40 Ah in 20 hours.

24 Watts = 2 Amps x 12 volts

2 Ah = 2 amps x 1 hour

40 Ah = 2 Amps x 20 hours

So far, weve only looked at Direct Current circuits. But many appliances use Alternating Current.



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Alternating Current produces a voltage that reverses regularly. The polarity of the voltagealternates and the current changes direction. It has a very rapid cycle of increase, decrease, andreversal, creating a sine wave.

Alternating Current can be produced electronically with an inverter, which converts DC to AC. Allsolar generators make use of an inverter for AC loads.

.DC & ACFigure 5 is a diagram of a Solar Mak iPower Station. Notice most of the wiring is Direct Current.

Direct Current is where electrons flow in only one direction. The polarity of the battery is always thesame where one terminal is always negative and the other terminal is always positive. Think of itas a pump that only flows in one direction.



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If the value of any two are known, then one can find the other two. Examples:

P = V x I24 watts = 12 volts x 2 amps

2 amps = 24 watts / 12 volts

P = I 2 x R24 watts = (2 x 2) x R24 watts = 4 x RR = 6 Ohms

E = I x R

12 volts = 2 amps x 6 ohms

P = V 2 / R24 watts = (12 x 12) / RR = 144 / 24R = 6 Ohms

The values inside Ohms Triangle apply only to source voltage - whereas the formulas outside thetriangle apply to both source and load voltage.

Knowing basic electricity is important for using solar energy. Lets discover how Solar Power works.



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Solar Power PathwayMost solar photovoltaic (PV) systems have the following components:

Solar Panel: Produce direct current and the electricity passes through a charge controller. Charge Controller: It regulates the flow of electricity from the solar panel. Battery: Most batteries for solar power systems are 12 volts. Inverter: Converts DC power from the battery to AC power for use with household appliances. Power Pack: Contains a battery and inverter with DC and AC outlets all in one unit.

As electricity is converted at each point in the power pathway, the available electricity is reduced.In other words, some electricity is lost with each power conversion. Such losses can be minimizedby careful use of components.

Component ChallengesThere are many solar technology solutions available today. And each technology has itsproponents that tend to be a bit too optimistic at times. Luckily, there is a great tool to find howwell any given solar technology works in the real world. The tool is calledprice to performance -and we use it for every Solar Mak.

Solar Panel

The three most common types of solar panels on the market are amorphous, monocrystalline, andpolycrystalline.

Amorphous are also known as thin-film panels. While their efficiency varies from 6 to 12 percent,they require a larger area than crystalline panels for the same amount of electric output. In mostcases, thin films tend to lose up to 20% of their power production capability after the first year inuse.

Thin film technology is common in many low end 45 and 60 watt kits with 3 to 4 panels. But thesepanels only carry a 5 year warranty. Few people want to buy another kit after 5 years. On a priceto performance basis, these panels should be considered only as a last resort.

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Monocrystalline panels are the most efficient, but also the most expensive to manufacture. On aper panel basis, polycrystalline are only slightly less efficient.

On a price to performance basis, mono panels are best utilized for very large stationary arrays.

The slight increase in efficiency per panel can add up to a significant increase in general powerproduction. However, the return on investment will take longer due to the increased cost of thepanel.

This leaves polycrystalline panels, which also happens to be the panel of choice for all Solar Makportable generators. Like many mono panels, they carry a 25 year power warranty. They are al-most as efficient as mono panels, but at a much lower cost resulting in a faster return on invest-

ment. Last, polycrystalline panels tend to produce decent power even in low light conditions.

Between the three panel choices, polycrystalline panels tend to offer the best price to performanceall around.



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Charge Controllers

Charge controllers are necessary to safely charge a battery with a solar panel. There are twotypes of charge controllers available, multipoint power tracking (MPPT) and pulse width modula-

tion (PWM).

MPPT controllers are claimed to increase production 30 percent. Here, we need to step back fromutopia and examine real world use. Generally, they can increase power production up to 20 or 25percent, as long as the solar panel remains cool.

As the panel warms up from the sun, the MPPT advantage quickly disappears. MPPT controllerstend to cost more than pulse width controllers. On a price to performance basis, they are bestused on larger solar arrays in areas that have cooler fall and winter seasons.

PWM controllers have been the standard for a long time in solar power. They offer bullet proof

operation at a reasonable price with consistent power production.

Solar Mak Work Pods use a PWM controller with a 99 percent efficiency, backed by a 10 year pow-er warranty. It even provides limited lightening protection, which is rarely seen in most controllers.

Battery

Three technologies are currently used for power storage of solar energy. They are Flooded Cell,Lithium, and Absorbed Glass Matt.

Flooded Cell has been around for over a century and used in many applications, from automobilesto industrial tow motors and more. This lead acid technologys best feature is its almost 100 per-cent recyclable. However, constant maintenance is necessary, from topping off the acid bath todesulfating the internal grid plates.

Lithium has become common in electronics and portable power tools. Its more expensive thanlead acid and its recycling infrastructure barely exists. While it has been used in very small solarapplications, it becomes much more difficult to manage and control as power storage increases.

Absorbed Glass Matt is also a lead acid technology, but state of the art. It was originally developedfor military use. Its spill proof, freeze proof, and maintenance free. Like its flooded cell cousin, itscompletely recyclable.

AGM batteries are more expensive than flooded cell. But AGM has none of the disadvantages offlooded cell. For solar power storage, AGMs offer the best price to performance.



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Component Placement

How components are placed in a solar power system is just as important as the components them-selves. Component placement is known as balance of system (BOS) in stationary solar arrays.

Weve seen some odd component configurations in portable solar, which well briefly review:

The Long Cord. There are some portable systems that use a very long power cord from thesolar panel to the power pack. Such cords are oversized in an attempt to limit DC voltage dropover such a longdistance. Voltage drop can greatly reduce solar charging. In a truly portable solar generator,such long power cords are unnecessary.

The Lock Box. Some portable systems have the charge controller permanently attached to apower pack. The result is a portable solar generator which is unable to charge any other power

pack. In another case, a solar generator has propriety power cords that fit only one single pow-er pack. Such Lock Box strategies tend to greatly diminish the flexibility and usefulness of aportable solar power system.

The Blanket. This is where thin film cells are sewn into a fabric, such as a tent or tarp and foldinto a compact square. Theyre very expensive and produce much less power than crystallinepanels covering the same amount of area. Its mainly used in military applications. And itsabsolutely fantastic if one is a Navy Seal jumping out of a high altitude plane to parachute intoenemy territory.

Its highly unlikely anyone else is going to jump out of a perfectly good plane with a solar generator

strapped to their back. For price to performance, its a poor choice for most homeowners andbusinesses.

Solar Mak portable generators have the optimum configuration to meet a wide variety of purposes.Its our attention to the details which matter most is why we can offer solar generators at un-matched prices with such high performance.

With Solar Mak, there is no long cord, ensuring every available electron of solar electric produc-tion is captured for ready use. Solar Mak can charge any power pack with a 12 volt outlet, whichincludes almost every portable pack on the market today. With a simple adapter, it can chargeany 12 volt battery. One is no longer tied to a single lock box. And while the blanket is a good

system to meet a very narrow purpose, its not the optimum choice to meet the power needs ofmost homeowners and businesses.

Solar Mak portable power systems are also eligible for the federal solar tax credit (limitations ap-ply). Even without the 30% savings from the tax credit, Solar Mak still delivers the best price toperformance.

All these reasons are why Solar Mak works. Now for a closer look at solar power planning.



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Solar Power PlanningThere are seven keys to solar power planning. They are:

1. Determine a main purpose the solar generator must meet.

2. Determine the power load of appliances / tools.

3. Choose a power pack that can meet the load requirement.

4. Match solar production to the power pack.

5. Consider other uses of the solar generator

6. Consider future expansion of the solar generator.

7. Estimate the return on the solar investment.

Solar power planning is all about asking the right questions in order to reach the best answer. Theseven keys listed above help in asking the right questions. Well apply the seven keys In the

example that follows.

1. Main PurposeWhat is the one main purpose for the solar generator? One answer is emergency power, andthats a good start. But it should be more specific. What do I need emergency power for? I needemergency power to run my refrigerator during a utility outage. The main purpose is to power therefrigerator.

2. Power LoadThe following tables estimate the wattage of various appliances. A refrigerator requires 600 wattsof power. Most refrigerators cycle on and off. It turns on only to maintain a set cold temperature,

then turns off. Its known as an intermittent load. On average, a refrigerator only runs 10 minutesout of every hour.

600 watts / 6 = 100 watts per hour

From the section on basic electricity, we can determine how many amps it draws:

100 watts / 110 volts = about 1 amp (.90 amps)

We need to know the amp draw as most batteries are rated in Amp hours.

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3. Power PackWhen converting AC to DC amps, there is a power factor of 10. In other words, for every 1 ampdraw of Alternating Current through an inverter, there is a 10 amp draw in Direct Current from thebattery (at 12 Volts).

The refrigerator will draw 10 Amps of Direct Current from the battery running ten minutes* everyhour. (*Note: Appliances that do not run continuously are called intermittent loads.)

The question to ask now is how long is the utility down? It averages any where from 4 to 48 hours.

At first, it appears one needs a minimum battery size of 48 Ah. (48 hours x 10 amps = 48 Amphours). But most batteries shouldnt be discharge more than 50%, so we need to double the Amphour rating to almost 100 Amp hours.

The Solar Mak power pack closest to 100 Amp hours is the iPower Station 85. It has a 1200 watt

inverter with a 75 Amp hour battery. At 50%, its only 37.5 Amp hours.

A refrigerator is designed to hold the cold in for a long period of time. In most cases, it can remaincold for up to 24 hours without power if the door is kept closed. The strategy is to plug in the refrig-erator every six hours to keep the food chilled. Over 24 hours, the fridge is plugged in 4 times.

During the day, the pack is constantly being solar charged, with an AC extension cord from theinverter to power the refrigerator. (There is very little voltage drop with an AC power cord com-pared to a DC power cord.)

Generally, the iPower Station 85 can provide emergency power to a refrigerator almost

indefinitely using this simple strategy. But we still need to determine solar power production.

Appliance Watts

LED light bulb 7 - 14

DVD Player 35

Stereo 30 - 100

Clock Radio 50

Satellite dish 30+

Vacuum cleaner 300 - 1100

Washing machine 900

25" Television 300

Video Game(X-Box)

100

Furnace Fan(1/3hp)

1200*

Appliance Watts

Coffee pot (10 cup) 1200

Toaster 800 - 1500

Coffee Grinder 100

Blender 300

Hot plate 1200Frying pan 1200

Toaster Oven 1200

Computer Laptop 75

Desktop Computer 400

Printer 75

Refrigerator/Freezer 600*



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4. Solar ProductionThe iPower Station 85 includes an 85 watt solar generator rated at about 5 amps production everyhour.

To determine average daily production, we need to find the sun hours for our area. The followingchart shows sun hour ratings for the United States.

A large portion of the United States averages 5 sun hours. The average daily production of thesolar generator is then 25 Amps (5 sun hours x 5 amps = 25 Amps)

3 to 4

4 to 5

5 to 6

6 to 7

Average Sun Hours

5. Other UsesThe main purpose has been planned for. Other than emergency power, what else can it be usedfor?

Looking at the appliance chart again, a few options stand out. It can be used to power a smallhome office. Or it can be used to power an entertainment system in the man cave for the biggame.



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6. Future ExpansionThere are two ways to expand the iPower Station 85. On the one hand, the solar generator cancharge any power pack with a 12 volt outlet. A sound investment in one or two more smaller pow-

er packs can expand emergency power to other rooms and appliances.

On the other hand, the iPower Pack is expandable with an additional solar panel. Another 85 wattsolar generator can be added to increase power production up to 50 amps per day ( 5 sun hours x10 amps = 50 Amps).

7. ROIWhat is the return on investment for the iPower Station? How soon does it begin paying me?

The iPower Station 85 is $1,495.00. If its for home use only, then the 30% percent federal taxcredit would reduce the final price to $1,047.00

Most Americans have about $350.00 in the refrigerator every month. If power outages occur twicea year, then the solar generator saves $700.00 worth of food every year.

Based on food savings alone, the iPower Station pays for itself in about 1 and a half years. Afterwhich, its paying you with free, clean energy for 20 + years.



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This is a comparison between a 3 hp gasoline generator rated at 1400 Watts versus the iPowerStation 85 rated at 1200 Watts. Keep in mind these general rules regarding gas generators:

Most are built for intermittent use only.

Its almost guaranteed to self destruct when used forprolonged periods (even with moderate

load).

Most are optimistic in their rating. Many are over rated in both the wattage and run times theycan provide.

For example, some gas generators are marketed at their peak wattage (higher rpm) rather thanits standard wattage. There is much more wear at higher rpm, translating into a much shorterproduct life. The gas generator in this comparison is rated at 1400 watts with a peak of 2000watts.

Fuel

The gas generator consumes about 1.5 gallons of fuel in 9 hours at 50% load. Generally, if theappliance draw doesnt exceed 700 watts, then it can provide 9 hours of power. At full load fuelconsumption is increased, and run time is cut in half. This means the gas generator will be out offuel in 4.5 hours at standard wattage (1400 watts).

The biggest advantage of the solar iPower Station 85 is free fuel - the sun. There are no movingparts resulting in a very long product life. Theres no need to keep cans of gas nearby forrefueling. It can provide reliable backup power during extended electric outages. By following asimple strategy, it can provide emergency power to a refrigeratorfor 48 hours or longer.

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NoiseGas generators can reach 85 to 90 decibels (about as load as a gas lawnmower) when in operation.Prolonged exposure to noise above 90 decibels results in gradual hearing loss. There is no peaceof mind when a gas generator is making noise over a long period of time during a power outage.

Solar power is almost noiseless. Other than the whisper of a fan on the inverter, there is no noise.One will never hear the neighbors complain with an iPower Station for backup power. Its also amuch better solution for mobile office, vendors and recreation.

CostA gas generator appears to have the advantage on initial purchase price compared to a solargenerator. This advantage quickly disappears when operation and maintenance costs are takeninto account.

A gas generator will always rely on fuel purchased at the pump. Gasoline prices have beenincreasing, and will continue to increase with each passing year. Maintenance of a gas generatoris a continuous cost. From regular oil and filter changes, to replacing parts such as spark plugs,such costs can add up quickly.

A Solar Mak iPower Station has almost no operation or maintenance cost. The only regularmaintenance is wiping dust off the solar panel once in a while in order to maximize solar powerproduction. One can realize a sizable financial gain over time, as these costs have beeneliminated.

Emergency PowerKeep in mind during a power outage, theres no electricity to operate the pumps at the gas station.So if you run out of gas on hand, one will be unable to purchase more when the grid is down.

With Solar Mak, one has power when its needed the most. An iPower Station for home use or aWork Podfor industrial solar power isnt only the better choice - its the best choice.

Its also great in the classroom.Increase your energy independence with Solar Mak.

Solar Mak versus Gasoline Generator 4.2
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