Practical Solar Power
Description[edit | edit source]
Solar power is now available to anyone, at modest cost and provides payback benefits for years. Also it provides independence because the home owner or apartment dweller can set up a solar panel, begin saving power, and have power when the regular power gets knocked out. Yes it takes a few years to recoup the cost but meanwhile one has the independence of always having dependable power. The emphasis in these notes are to give practical and useful information.
To be found in a back yard three 100 watt panels of six panels from which the home owner states he gets 1/2 of his power and likes not only the money he saves but that he never has a power outage even when everyone else in the area have none. He states "We have lights, can watch TV and use our laptops with no problem." He says he can run on this alone for several days. The only losses are the dishwasher and big air conditioner which use too much power. He also states they do have a gas stove for cooking.
Introduction[edit | edit source]
Why is Solar Power now practical? Most people can now afford solar power. If you don't shop around you can pay thousands of dollars for a big solar system but you can also get a 100 watt solar panel for $89, a cheap charge controller for $15, a used car battery $10, an extension cord $2., a plug in light socket $1. and a 10 watt LED light bulb $3. Total around $120. Place this panel in a window, or on a balcony, or hang it from a gutter and you have roughly 100 ts per hour of sunshine and much less during dark days. Lets say you average 4 good hours of good light a day that is 400 watt hours of power saved to the battery. Yes there is some power loss but let's see the general possibilities that you can store 400 watt hours of power a day. In theory you can then run that ten watt LED bulb for 40 hours just on one day's charge or four of those bulbs one for each room used at night for 10 hours. These new 10 watt LED bulbs last for years and each one has the brightness of an old 60 watt bulb. Your notebook computer probably uses10-50 watts of power per hour so you could run that also. All this for no additional cost and therefore free power every day.
An overview of solar energy with some nice illustrations. Solar energy
The following is much more detailed. I will be covering the basics in much briefer form below these. Wikipedia Solar power
How much power do we get from the sun?[edit | edit source]
The planet Earth receives a huge amount of solar energy every day, in fact far more than humans need to run everything they are doing. Here are the details much of which is from Wikipedia's excellent article on solar energy.
The United Nations Development Program in its 2000 World Energy Assessment found that the annual potential of solar energy was 1,575–49,837 exajoules (EJ). This is several times larger than the total world energy consumption, which was 559.8 EJ in 2012.
The Earth receives 174,000 terawatts (TW) of incoming solar radiation (insolation) at the upper atmosphere
How much energy hits a square Meter or area. Smil (1991), p. 240 see Wikipedia: Solar energy
Most of the world's population live in areas with insolation levels of 150-300 watts/m², or 3.5-7.0 kWh/m² per day.
Details if you want to see them are: Irradiance is the radiant flux (power) received by a surface per unit area. The SI unit of irradiance is the watt per square metre (W/m2). The CGS unit erg per square centimetre per second (erg·cm−2·s−1) is often used in astronomy. Irradiance is often called "intensity" in branches of physics other than radiometry. The total amount of energy from the sun depends on the angle and time of year. It is about 3.3% higher than average in January and 3.3% lower in July 2013.
The direct sunlight at the earth's surface when the sun is at the zenith is about 1050 W/m2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1120 W/m2.
Direct sunlight has about 93 lumens per watt of radiant flux, higher than most artificial lighting, including fluorescent. Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98 000 lux (lumens per square meter) on a perpendicular surface at sea level. This breaks down to 42% of 1120 W/m2 =470.4 W/m2 1m²= 10.76391ft² 1ft²= 0.09290304m² 2496 sq inches. 2496 Square Inches = 17.33 Square Feet. This is your maximum. But even one cloud throws cuts this down.
What about Cloudy Days[edit | edit source]
Solar panels generate the most electricity on clear days with sunshine. On a cloudy days, depending on brightness and clouds, typical solar panels can produce 10-50% of their rated capacity. Personal experience is that we get about one half as we do on full sun days.
Solar Panels[edit | edit source]
There are several kinds of solar panels. In one kind the sun heats up water or other fluid in the panel. This becomes a solar water heater. Another kind of panel is the photovoltaic which directly converts light into electricity. The photovoltaic panel will be the most discussed here. We will limit descriptions here to just those panels which are available and practical to the average citizen. Solar modules use light energy from the sun to generate electricity. These cells are called photovoltaic because they produce electricity directly from the photons that hit them. Module performance is generally rated under standard test conditions (STC): irradiance of 1,000 W/m², solar spectrum of AM 1.5 and module temperature at 25 °C.
Efficiency of types of panels[edit | edit source]
They vary greatly. As you can see if the Monocrystalline panel is only $20 or so more perhaps it is worth getting that one. Monocrystalline yield 15-20% Polycrystalline 13-16% Amorphous 6-8% CdTe 9-11% CIS/CIGS 10-12%
Monocrystalline Silicon Panels[edit | edit source]
It appears that the best meaning most efficient type of panel in 2016 affordable to the average worker is the Monocrystalline silicon panel. Most are laminated between plastic back and glass front and mounted in a sturdy aluminum frame.
Most of them have specifications similar to the following: Manufacturer Warranty 10 year limited product warranty on materials and workmanship. 25 year warranty on >80% power output and 10 year warranty on >90% power output. High efficiency solar cells (approx. 18%) with quality silicon material for high module conversion efficiency and long term output stability and reliability. Positive power output tolerance from 0% to +3%. Rigorous quality control to meet the highest international standards. High transmittance, low iron tempered glass with enhanced stiffness and impact resistance. Unique frame design with strong mechanical strength for greater than 50 lbs/ft2 wind load and snow load withstanding and easy installation. Advanced encapsulation material with multilayer sheet lamination to provide long-life and enhanced cell performance. Outstanding electrical performance under high temperature and weak light environments. CERTIFICATIONS ISO 9000:2000 CE
Cell Size 156mm x 156mm (6.14” x 6.14”) No. of Cells varies Weight 10-20 kg (22-44 lbs) Cable Length 900mm (43.3”) for positive (+) and negative (-) Typed of Connector MC-IV Junction Box IP65 or IP67 Rated No. of Holes in Frame 4 draining holes, 8 installation holes, 2 grounding holes, 16 air outlet holes
Electrical Specifications (STC* = 25 ºC, 1000W/m2 Irradiance and AM=1.5)
Characteristic Details Max System Voltage 1000V / 600V Max Peak Power Pmax 60-260 W (-2%, +2%) CEC PTC Listed Power 50-260 W Maximum Power Point Voltage Vmpp 19-.32 V Maximum Power Point Current Impp 4-8 A Open Circuit Voltage Voc 19-38 V Short Circuit Current Isc 6-9 A Module Efficiency (%) 16%-18% Note the Efficiency Temperature Coefficient of Voc -0.128 V/ºC (-0.34% /ºC) Temperature Coefficient of Isc 3.63x10-3 A/ºC (0.04% /ºC) Temperature Coefficient of Pmax -1.25 W/ºC (-0.48% /ºC) Power Tolerance Operating Temperature Max Series Fuse Rating NOCT* -2% / +2% -40 ºC to +85 ºC 15 A 45 ºC ±2 ºC *Normal Operating Cell Temperature
Polycrystalline Solar Panels[edit | edit source]
Most are laminated between plastic back and glass front and mounted in a sturdy aluminum frame. Polys are usually about $20 less expensive per 100 watt panel because they are a little less costly to produce. They don't last quite as long as the mono panels. Their efficiency is a few percent less than the Monocrystalline silicon panel. Remember manufactures may fudge their efficiency a little. Here are the statistics for a 100 watt Polycrystalline Solar Panel made by the same company as the Mono above. High efficiency solar cells (approx. 17.4%) with quality silicon material for high module conversion efficiency and long term output stability and reliability. Cell Size 156mm x 104mm (6.14” x 4.40” Electrical Specifications (STC* = 25 ºC, 1000W/m2 Irradiance and AM=1.5) Model GS – STAR – 100W *Standard Test Conditions Maximum Power Pmax 100 W (0%, +6%) Listed PTC Power 100 W Voltage at Maximum Power Point V mpp 18.0 V Current at Maximum Power Point I mpp 5.56 A Open Circuit Voltage V oc 21.9 V Short Circuit Current I sc 6.13 A Module Efficiency (%) 14.63% Note Efficiency Temperature Coefficient of Voc -0.32% /ºC Temperature Coefficient of Isc +0.04% /ºC Temperature Coefficient of Pmax -0.45% /ºC Power Tolerance 0%, +6% Operating Temperature 40 ºC to +85 ºC Max Series Fuse Rating 10A NOCT* 45 +/-2ºC
Specs on a Mono crystalline solar Panel for comparison. Weighing in at only 16.5lbs, HQST 100 Watt Monocrystalline solar panel contains 36 highly efficient monocrystalline solar cells protected by a thin layer of tempered glass. With an ideal output of 500Wh per day, this solar panel is guaranteed to provide a great charge for all of your favorite electronics. The tempered glass and corrosion resistant aluminum frame allow each panel to withstand high wind (2400Pa) and snow loads (5400Pa), increasing durability and value. Each 100W solar panel is perfect for permanent or semi permanent installation. Monocrystalline panels come with high-efficiency solar cells (peak: 22%) that help increase space efficiency. Note Peak 22% which means it is actually around 16% most of the time. Specifications Maximum Power: 100W Maximum System Voltage: 600V DC (UL) Optimum Operating Voltage (Vmp): 18.9V Optimum Operating Current (Imp): 5.29A Open-Circuit Voltage (Voc): 22.5V Short-Circuit Current (Isc): 5.75A Dimensions: 47 X 21.3 X 1.4 In Weight: 16.5lbs
Thin Film Solar Panels[edit | edit source]
Thin film panels are made in thin laminated layers and are often semi-flexible so are much more resistant to breakage than regular crystalline cells, but can be broken by bending them into a sharp angle. These are often used for portable uses since they are more rugged and lightweight. Even though they are flexible and laminated they are really not suited for outside mounting as the holes in the corners will teat out in time. Exterior usage almost demands a rigid frame and glass covering (PET).
Here is an example with specs: ALLPOWERS 100W Bendable Solar Panel Water/ Shock/ Dust Resistant Power Sunpower Solar Charger for RV, boat, cabin, tent, or any other irregular surface SUNPOWER solar cell is made from US, up to 22%-25% efficiency, while most panel is 17%-19%, you will get greater power efficiency even though the panel is no larger than a traditional model Sunpower solar panel is far more durable than traditional glass and aluminum models; flexible material is ideal for storage in tight spaces or crowded areas The plastic back sheet can be curved to a maximum 30 degree arc and mounted on an RV, boat, cabin, tent, or any other irregular surface This solar panel packs 100W of power, but it only weighs a mere 3lbs, making it easier to transport, hang and remove; Unique frameless design and four metal reinforced mounting holes for easy installation What you get: 100W bendable solar panel, and friendly customer service Specification: Optimal power [Pmax]: 100W (Maximum Power at STC). Working voltage [Vmp]: 18V. Working current [Imp]: 5.56A. Short circuit current [Isc]: 5.8A. Open circuit voltage [Voc]: 20V. Maximum system voltage: 1000V. Dimensions: 1050*540mm*2.5mm Air resistance: 50psf (2400 pascals) Snow resistance: 113psf (5400 pascals) Hail impact: 25mm (1 inch) at 23 m/s (52mph) Color:18V100W Product Dimensions 42.2 x 24.3 x 4.3 inches Item Weight 5.5 pounds
Measurement terms and Power[edit | edit source]
Light brightness is measured in Lumens Light brightness is also measured in candle power Power is measured in Watts Voltage is measured in Volts Current is measured in Amps Resistance is measured in Ohms
See Wikipedia articles on these for further explanation Electrical characteristics include nominal power (PMAX, measured in W), open circuit voltage (VOC), short circuit current (ISC, measured in amperes), maximum power voltage (VMPP), maximum power current (IMPP), peak power, Wp, and module efficiency (%).
How much average output can you expect?[edit | edit source]
This depends on several factors. How many hours of good light at your latitude. How much clouding or direct sunlight. How much shade. Are your panels pointing at the sun or at least set at the average position. Are they covered with ice, frost, snow, dirt, leaves, bird droppings etc?
One of the most common manufacturers states that its 100 Watt Mono Solar Panel has High module conversion efficiency (approx. 15.46%) Has Ideal output of 500 watt hours per day. They state this can fully charge a 50Ah battery from 50% in 3 hours. (depends on sunlight availability).(source Renogy specifications of their 100 watt panel).
This can be augmented using solar concentration cells.
Mounting Panels[edit | edit source]
One can spend hundreds on fancy mounting hardware or mount your solar panels on a two by four frame out in the backyard, even over a patio or on a shed, fence, window or balcony.
Panels include MC4 (someones, also USB) connectors for easy mounting.
Typical 100w solar panels sizes are 1 × 0,5 meters and includes 32 (8 ×4 ) solar cells.
Wiring[edit | edit source]
Most photovoltaic panels put out DC current and come with the older MC3 or now the MC4 connectors. These are easy to connect and disconnect and are weatherproof for at least a couple of years. Extra wiring containing these connectors is a bit pricey so many people just go to the hardware store and get No 10 wire. This wire is difficult to work with and bend with the single stranded version being the most difficult. I recommend the multi stranded as it is a little easier to use. Use this big wire to go to from the panel to the charge controller and from that to the batteries. Then there is the issue of how to join wires. There are splices, connectors and possible soldering which is more difficult with No 10 wire.
DC vs AC solar panels[edit | edit source]
Thought I would be smart and hook up 12 / 24 volt camping extension cords and camping lights, a 12 /24 volt fan (or also a 5V USB fan). Then I discovered none of those camping lights ow shop work lights put our the amount and kind of light I wanted in the home. So I tried to get 12 volt bulbs locally. Turned out they were not to be found. So I bought regular 12 volt DC bulbs online but they were expensive. When they arrived 2 out of 4 of them were faulty and there was an as is warranty because stupid customers screwed the 12 volt bulbs in regular 120 volt sockets and they would burn up. Well I wrote them a nice e-mail and followed it up by a phone call and was lucky enough to get two replacement bulbs. Well I wanted to power my laptop and chargers and a few other things. This was not so convenient with 12 volt power. Although 12 volt power suffers virtually no loss from conversion it needs bigger stiffer wire and doesn't match most peoples appliances, lights etc.
120 / 220 volt wiring is cheaper, easier to work with, thinner, and cheaper because almost every store has 120 / 220 volt wire and bulbs at bargain prices. One can get a new 10 watt LED bulb that puts our 800 Lumens equal to a 60 watt old Tungsten bulb. You can run 6 new LED bulbs with the same power you used to use with just one 60 watt bulb. And bulbs and lamps are much less costly than their DC counterparts.
But. You need an inverter (more accurately, a microinverter) to change the DC to 120 / 220 volts AC (so the panel becomes an AC solar panel). Inverters are at all home improvement stores and most hardware stores. They range from $12-over $110. The $29 model should do you fine.
What about Power loss?[edit | edit source]
Power loss is greater with DC wire so use that just for connections to the charge controller and batteries. Ac wire we are all used to just plug in a heavy duty extension cord and start using it, Any time you convert there is a power loss. So I bought both a DC and an AC power meter and investigated. The loss was very minimal. I found my inverter uses a couple of watts to run whether or not I used its 600 watt out put or just a 10 watt bulb.
Batteries[edit | edit source]
Solar panels can be directly connected to the grid (AC solar panels, this is, solar panels with built-in microinverters) to be used with home appliances or charge any kind of battery providing the voltage matches up. Even old car batteries do work as cheap storage. Car batteries are made to put out a lot of amperage for a short time but not to be deeply discharged as running your house on it may do. They may not last long. If there is a weak spot in the solar system it is usually the battery. They are finicky, can release poisonous or explosive gas when being charged too fest. And they all require maintenance no matter what the label states. Water or battery acid may have to be added to them and they may have to be revived.
But better is to get so called Deep Discharge batteries which will last longer and give better service. AGP batteries are sealed and alleged maintenance free. Lead Acid is the good old reliable standby Golf Cart either 6 Volt or 12 Volt sometimes offer better value and ruggedness for the money. There are other types of batteries. LiIon are dry, light weight, very efficient. These are the same kind used in your phone. They have two drawback price and if they ever catch fire your u cant put them out, they sometimes explode and give out bad gas. Most of the time they are safe. All batteries should be kept outside of the living quarters. Garage, shed, utility room are fine with a little ventilation. Might I add that good batteries are not cheap. Most systems use several batteries for better efficiency and higher storage. And is should be noted that batteries in a group should be of the same age, type and condition otherwise the weakest one will be destroyed. It is best to buy a good name brand from a reputable dealer.
Charge Controllers[edit | edit source]
Solar panels can be hooked up directly to a battery. But. This can result in over charging and eventually ruining the battery. Therefore a charge controller even a cheap one is better for the battery.
There are three general types of Charge controllers Simple 1 or 2 stage controls which rely on relays or shunt transistors to control the voltage in one or two steps. These essentially just short or disconnect the solar panel when a certain voltage is reached. These are obsolete.
There are next the Three-stage PWM such Morningstar, Xantrex, Blue Sky, Steca, etc. These are less expensive and much used.
The third type which is the most efficient uses Maximum power point tracking (MPPT), such as those made by Midnite Solar, Xantrex, Outback Power, Morningstar and others. These are the ultimate in controllers, They are very efficient. They can save considerable money on larger systems since they provide 10 to 30% more power to the battery.
Many controllers have LED lights and some have very useful screens that tell you how much power is being generated. The Outback MPPT is probably the best.
If you go to the web sites of these companies you can see more details.
Fuses and Safety[edit | edit source]
Although there are usually no dangerous voltages in photovoltaic systems hooked up in parallel. The average cell puts out about 1.3 amps maximum. A panel consists of several of these cells. The average mono 100 watt panel of 36 cells puts out around 18.9 volts at a low amperage usually around 5.2 amps. A large panel of 60 cells gives 260 watts puts out an average of 8.2 amps (a short reading of 8.6) at an average of 31 volts (37.9 open circuit). This is usually harmless to humans unless one is stupid enough to put leads across ones tongue. Panels hooked in series can attain high voltages that can cause injury or fires. It is good practice to fuse everything electrical. The cost is negligible. Think of fuses as cheap permanent insurance.
Effect of Angle of Light[edit | edit source]
Output is best when the sun is exactly perpendicular to the panel. Some people put their panels on movable swivels so they are pointing to the sun. This would require a motorized set up to move them unless one has extra helpers around who can go out and more them hourly. The problem is that motorized panels have additional purchase, instillation and maintenance costs and can freeze up in winter.
Effect of shadows[edit | edit source]
Solar Panels depending on type and the way they are set up can vary greatly in output caused by being partially shaded. All panels still put out out electricity even on cloudy and even dark days. Partial or total shading of one cell hooked up in series often reduces the entire array to the value of the shaded cell. Hooking up panels in parallel or use AC solar panels (solar panels with built-in microinverters) are the best simple way to over come the shading of one or more panels.
Effect of Temperature[edit | edit source]
Solar panels work best at cooler temperatures. The same panels in Michigan out perform those in Florida because Michigan is in general cooler.
A panel rated at 100 watts at room temperature will be an 83 watt panel at 43°C (110°F). This means it is better to have good air circulation under and around them.
Installation And Maintenance[edit | edit source]
Once installed there is very little maintenance. Some people put their panels on the roof which puts them out of the way. But there are problems with that. Even if the cells are set at around 45 degrees which is very steep, snow and ice can build up on them. Sure they are dark colored and the sun will melt that snow and ice. Sure. Well depending on the weather and temperature that melting may not happen for hours to days to weeks. Meanwhile the panel output may go down to 0. Some of us have discovered that we are not good on roofs, some of us oldsters have a balance problem. And no one should be on an ice and snow covered roof which slopes because they are dangerous. I also discovered that in my area there is so much pollution that the panels need to be cleaned occasionally. Then there our little friends the birds who don't care where they…Well some of us found out it is much safer to have our panels in the back yard on a tall rack which puts them out of the way and yet where they can easily be cleaned with a brush, squeegee or wiper safely for us on a pole. Then there is the issue of home owners insurance. Some owners with roof panels have been canceled even if they ask the insurance company to exclude the panels because the insurance company's risk department doesn't understand their safety and just doesn't want any risk. Some people get riders in their insurance. Back year installation is safer and usually not a problem for insurance companies.
Sometimes you can install your solar panels in your tiles (as Tesla solar roofs), windows or balcony. For this can be used solar PV glass or thin film solar panels, with upto 50% transparency (this is called building adapted photovoltaics, BAPV).
What Is In the Near Future[edit | edit source]
Shopping Around 100w is a Must but Buyer Beware[edit | edit source]
A 100 watt solar panel can cost from $50-5,000. Obviously one needs to shop around, read the specs and become familiar with what different companies offer and for how much. Several big name stores offer solar panels from good brands and also have warrentees and even payment plans. It is best to acquire a knowledge of the products so you know what you are buying and buy from knowledge rather from emotion. We chose to have panels delivered to my local home improvement store because first they would inspect them on receipt to make sure they were not damages and secondly I didn't want a multi hundred dollar item dropped off on my step where it could be damaged or stolen by those crooks who follow the UPS trucks around.
Bibliography[edit | edit source]
Discussion[edit | edit source]