Solar power tips

Updated: Oct 2, 2019

solarpower #energy #chargebattery #solarpanel #altenergy

This will tell you the things that are more hard to find out about solar power. These tips will help you create an effective photovoltaic system for your needs. For more tips and help see http://diysolarforum.com/ by Will Prowse.

Terms

1. Amps: the amount of current a solar panel can provide, at max.
2. Amp hours (Ah): the amount of current produced in one hour, also the capacity of a battery. If a solar panel provides 1 amp per hour, and you have a completely discharged 10 amp hour battery, it will take 10 hours to charge the battery if sun conditions remain exactly the same and the sun doesn't move.
3. Volts: The amount of voltage a solar panel can provide.
4. Solar panel rating: an artificial number indicating the power, in watts, the panel can provide, which will generally never happen in real life conditions in a temperate zone. It MIGHT happen if the solar panels are on the equator on a perfectly sunny day.
5. Watts: this is called "power" and is calculated by volts * amps. Watts produced is watts produced per hour.

Solar panel ratings

For best efficiency, panels must be angled towards the sun so the sun's rays hit the panel at 90 degrees. This normally does not happen with fixed panels. So for a house at 44 latitude, the angle of the panel with the ground should be 44 degrees. Panels on the equator can point straight up to the sun.

The solar panels are rated based on how they perform in laboratory tests, and real life is generally nowhere near what the laboratory tests are like. So take the rated volts and amps, and multiply by 0.80, and that will give you the power rating for the panel on the sunniest day of the year, with the panel at the perfect angle to the sun. Do not look at the rated watts for the panel, look at the rated volts and max amps and multiply both of those by 0.80. So a panel rated at 18v 2amps max will only produce 14.4vdc on the perfectly sunny day at the perfect angle, and only 1.6 amps. So the the total watts it will produce is 14.4 * 1.6 = 23 watts.

For the average output while the panel is fixed and the sun moves around the sky during the day, take the rated volts and amps and multiply by 0.6. (Do not multiply by 0.8 also, that is not needed here.) So a panel rated for 18v at 2 amps will output, on an average sunny day, throughout the day, an average 10.8vdc and 1.2 amps, which is 10.8 * 1.2 = 12.96 watts. Keep in mind that clouds moving across the sun will further drop this power, so it's best to get more powerful photovoltaic panels than you need.

Also remember the panels will not product power at night, and will produce little, or zero power in shade. If the panel does not produce enough voltage the battery will not get charged at all. A minimum voltage is required before battery charging occurs. If your lead acid battery is at 12vdc, then the minimum voltage to charge it is more than 12vdc.

Solar power stands can be used to move with the sun automatically (called "trackers"), thus increasing the total power (watts) the solar panel will put out.

Solar power must be captured in batteries so it that power can be used when sun conditions are not very good.

Little or no power is generated in the winter in northern latitudes, but this all depends on your latitude. I'm at 44 N latitude and my solar panels produce, at most, on the sunniest winter days, 10% of their rated power, so they are mostly useless to me. The sun that reaches the earth has a larger distance to travel to the ground as it travels through more atmosphere and there is generally more clouds in the winter, so power is reduced both by the amount of distance it travels through the atmosphere, and the cloud cover blocking the sun's rays.

More tips

1. For the most power from the panels, do not let shade cover the panels at any time during the day.
2. If you have a light solar panel, attach it to a frame and weight it down somehow so the wind does not knock it over.

Charging USB devices with a solar panel

Let's say you have a solar panel in the sun, and you use your multimeter to determine the voltage coming out of it is 13vdc. But you want to charge your USB device, like a power bank or cell phone or tablet. Do you just slap on a USB port to the solar panel terminals? No! It will blow some circuitry in your device. You have to bring down the voltage to 5vdc for the device to be charged.

Buck convertor

There are devices on Ebay, Aliexpress, and Amazon called "buck convertors" which bring down the voltage. Some even have a USB port built in, along with wire terminals. Just wire the solar panel wires to the item, and charge away. But be aware that the voltage going into the buck convertor must be at least 6vdc before it will turn on the 5vdc for you.

When you convert the voltage down you will get more amps. In effect voltage is converted to amps as watts in = watts out. Thus if you want to use 2 USB ports on the buck convertor board make sure the voltage is above 12vdc. In many boards the amps will be shared between 2 ports about equally.

Boost convertor

To boost the voltage you need a "voltage booster" or "boost convertor", they are the same thing. Also since power must be conserved, if you boost volts you will lose amps in the output.

Buck boost convertor

And the combo board that keeps the voltage the same whether the input voltage is too high or low (which often happens with a solar panel) is called a "buck boost convertor". It does both!

Other cautions

1. The USB spec specifies how much current and voltage the USB port can handle. USB 3.0 devices can handle about 2.1amps and 5.5vdc. The buck convertor will output only the amount of current the charging device asks for, so if the device asks for 3 amps, but the convertor only outputs 2.1amps, the device will get only 2.1 amps.
2. When dealing with higher amps around 2amps or so, make sure your wire is thick enough to handle the current. If the wire gets hot, it's not thick enough, get thicker wire. I prefer solid wire 18g, but some people use 18g stranded wire because it's cheaper.
3. Chinese buck or boost convertors often inflate their amp output ratings so if you want to charge a device at 2.1 amps get one rated for at least 3 amps.
4. Some older Samsung tablets from 2014 will not charge at all at 2 amps, they require a minimum of 2.1 amps. Samsung has since fixed this problem in their newer tablets (I got another one in 2019) and the device now allows "slow charging" with lower amp output to the tablet.
5. For reliable electronics don't buy from China. See other US suppliers like Mouser here: https://pastebin.com/6MG2TjpN.
6. Drok is a good brand for parts if you can find it, so is Anker. DROK parts are often on Ebay.

Here are some examples:

1. On Amazon. This has both USB outputs, AND another output and 2 different inputs. Solar panels often have male 12vdc connectors and that's the black round female part on the input side of this.
2. On Amazon, 2 USB ports. This one has 2 USB ports for charging.
3. Ebay, 10 watt 2 amp buck convertor. This probably will never output 2 amps, expect 1.2 amps at best. And there's no female USB port to charge from.
4. Ebay, Input 6-24vdc, outputs 3 amps. Probably will only output 2.1amps, but it can handle input of up to 24v and has a female USB connection to charge from. This also means it can handle 12vdc from a car as input, you just need the right input connector for your car.
5. Ebay, 2 USB ports, 3 amp.
6. Ebay, search for Drok brand buck convertors with USB. A search is a better link because it only shows active item links. Ebay search for Drok buck convertor.
7. Ebay, Drok convertor, 1 USB port, with LED voltage display.

About batteries

Battery types

1. Battery format: The physical size and shape of a battery. AA, AAA, C, D and all common US battery formats. LiPo batteries are often in "flat packs" for use in thin devices like tablets, that is another format. 18650, CR123 are other formats.
2. Alkaline batteries: one-use batteries most of us are familiar with. Nominal voltage is 1.5vdc. Back in the 1970s (energy shortage) there were chargers which would recharge alkaline batteries, but these chargers would not shut off themselves and the battery could heat up too much. Alkalines could be recharged up to 10 times.
3. Zinc batteries: one-use batteries, also called "heavy duty" batteries, these are also common. Nominal voltage is 1.5vdc.
4. Lead acid batteries: these are often used in automobiles and in Uninterruptible Power Supplies (UPS). By putting multiple cells together we can get 6vdc or 12vdc or higher batteries.
5. NiCad: Nickel cadmium, nominal 1.2vdc. These were the earlier rechargeable batteries from the 1980s. One problem they had was a memory effect so if you discharged them to 50% capacity, then recharged them, and repeated that a lot, they battery would eventually only hold half of what it was supposed to. Cadmium, when disposed of improperly, is also highly toxic to the environment.
6. NiMh: Nickel metal hydride batteries, 1.2vdc nominal. Very little memory effect, an improvement over NiCad.
7. Lithium batteries: Nominal voltage is 3.6vdc for a single cell. There are many types of lithium batteries and physical formats they come in. One is lithium polymer (LiPo) batteries, which often come in flat packs. Lithium batteries can come in AA sizes too but they will output 3.6vdc (nominal), not the 1.5vdc of alkaline batteries. There are also one-use lithium batteries. These are good because they can last in storage for up to 10 years without self-discharging.
8. Graphite batteries: these are made partially with graphite but also with other things. They are supposed to have a bit higher capacity than LiPo batteries.
9. Universal battery: This is a lithium battery with a special buck board that drops the voltage to 1.5vdc which most devices expect in the AA battery format.
10. CAUTION: Putting the wrong, higher voltage of battery into your device will likely destroy that device. Putting in a same-size battery with a low-voltage will mean the device just won't work. Do not put 3.6v lithium AA batteries into a device designed for 1.5vdc batteries (alkaline or zinc).

Notes

1. Batteries in parallel: all negative terminals share one wire, all positive ends share one wire. Voltage remains the same but amp hour capacity is added up.
2. Batteries in series: Batteries are put end to end, positive terminal of one battery connects to negative terminal of next battery, etc. Voltages are added but amp hour capacity remains the same as one battery.
3. The chemistry of the battery will determine the nominal voltage, and how many cells are connected together. A single cell Nimh battery has a nominal voltage of 1.2vdc. It can be charged to about 1.5vdc and discharged down to about 0.8vdc. Alkaline and zinc batteries have a nominal voltage of 1.5vdc. Lithium batteries (of various types) have a nominal voltage of 3.6vdc. They can be charged to about 4.2vdc and discharged down to about 2.8vdc or 3.0vdc.
4. Nominal voltage for a Nimh battery is 1.2v. These can be charged a little about 1.2v without damage but I would not go above 1.5vdc.
5. Nominal voltage for a lithium battery is 3.6vdc. These are normally charged to about 4.2vdc.
6. Charge controllers for lithium cells come in various formats for 1, 2, 3 or more lithium batteries. If you have lithium batteries in parallel get the charge controller that charges to about 4.2vdc. If you have 2 lithium batteries in series get the charge controller that charges to about 7.2-7.8vdc.

7. 3 Nimh batteries in series is 3.6vdc, and thus a lithium charge controller can be used with a series of 3 Nimh cells.

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