SPCC A Casa Amarela

here's how i learned to make a solar panel, and what i've been teaching at the workshops.

as for the electrical part, here's a quick overview of the laws we're working with and some rules of thumb. google is your friend, and just google most of this.

1) since the whole setup is DC (direct current), what we need are DC Volts (Voltage) and DC Amps (Ampere). voltage is the "tilt" between your points (higher voltage flows to lower voltage [yields positive current], not the other way around), current is how much charge "flows" per unit of time

2) Power is the way to measure how much any equipment uses in terms of instant energy. a cellphone charger would be around 6W average, a netbook 40W, an LED bulb about 3W, a hairdryer 2000W (not kidding). since we're dealing with DC, we can use P=V*I (Power[W]=Voltage[V]*Current[A]). this means that, for example, if your cells are 0.5V and give 3A when in the sun, you will get 0.5*3=1.5W

3) Energy is the total energy consumed over a certain period of time (usually in hours). so let's say you used your hairdryer 1 minute. the total energy is 2000[W] * 1/60 [h] = 33.(3) Wh. also, let's say you used your LED lamp (3W) for 12h, this is 3*12 = 36Wh. your LED bulb spent MORE energy than your hairdryer. so more Power doesn't mean more Energy. it always depends on how long you use it.

4) Energy stored in batteries is usually measured in Ah (Ampere hours). Depending on the voltage of the batteries, you can calculate the total power by multiplying. let's say you have a 45Ah car battery (12V). total power is 45*12=540Wh. this means you could power our LED bulb for 180 hours, or run your hairdryer for about 15 minutes. this is the total capacity of your battery. batteries actually are a bit more complicated than this, but as a model this is good enough.

5) Power used in AC (Alternate Current), which is what we have in homes, is comparable to Power in DC. meaning, let's say you have a drill, 500W, and an adapter from 12V to 250V (this is possible, it's called an inverter) that can handle 500W. you would have: 12V * 41.(6)A = 500W = 250V * 2A . this is a gross simplification, since AC has both peak (250V) and RMS (Root Mean Square), but going deeper would require extra electrical theory. so basically, if your drill is rated 250V/500W, your battery must be able to output 500W/41.(6) amps while you use your drill. depending on the battery, this might or might not be possible. the best is to consult your battery supplier

6) an inverter has a power rating, and that's the most important think you need to know. if your inverter gives 250V 150W you can never use your 500W drill. if Power needed is bigger than Power provided, usually you will fry your inverter, or cause it to go on fault protection mode. same thing with current. if your electronics are rated 10A and you feed (or pull) anything more than 10A, either you'll break a fuse or burn something. if you don't, you just got lucky.

7) when calculating how many batteries you'll need, remember that it's good for your batteries not to be completely drained. so if you have a 160Ah battery and keep it at most 80% discharged, you only have 0.2*160 = 32Ah available. this is about 384Wh of charge. if you just use a 3W bulb, you'll have 128 hours of light.

8) when calculating how many panels you'll need, first calculate how much energy you use (in Wh a day), then double that (or even triple that) for the panel power + battery bank. remember that depending on the time of year and weather conditions, you'll only have a certain fixed value of useful sun hours. if you do the math on Wh/year, you'll have a better estimate of the average, but remember that in winter, you'll need more backup energy, and in summer you'll have surplus energy.

in a D.I.Y. system, you won't be able to use government help, nor connect it to your electricity supply company. remember that for certification and what not, your panels might not get approved, and most of your cheap equipment might be considered "hazardous". our D.I.Y. system with car batteries, cheap inverters and home made panels works, but wouldn't be seen as "safe" by the government.

to find all of this stuff, use eBay, contact the industrial suppliers for panels looking for damaged cells and panels (they still work, they just look ugly and therefore can't be sold), prefer batteries that are recyclable and companies that have battery recycling guarantee (and environmental awareness whenever possible). DON'T BUY FROM CONSUMER STORES! you can build your own system for about 300€ instead of 5000€ like in some stores! it's NOT worth it! also, prefer mono crystalline silicon to poly crystalline silicon to amorphous silicon. in practice, all the shit you hear on the news about "revolutionary solar technology X" is hype. you can't buy any of those technologies, and most companies are for business only.

CHOOSE RECYCLED, USED GOODS INSTEAD OF BUYING! the energy used to make a solar panel will never be output by the panel itself in its whole lifetime. it's ironic, but unless the factory is "green" itself, buying new stuff might cause more harm than good. look up the companies first, and ask what is their manufacturing process, and whether they are green or not. silicon production gives off a lot of pollution and industrial waste. we need better technologies, so see solar as a good way of doing things for the moment, not as the ultimate green salvation. there are many other ways of generating green energy, so look up everything and you might be surprised!

godspeed starstuff ☆★☆☆★★★☆☆☆☆☆