Complete energy autonomy or how to survive with solar panels in the outback (part 2. practical)

The real solar autonomy for the end user consists of money spent, sampling, mounting devices and teaching households to use electricity economically. Moreover, it is worth paying particular attention to the last point, since autonomous system implies a completely special approach to energy consumption and even restructuring of usual actions.


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Since solar panels are the most visible part of the system, and even convert the sun's energy into electrical energy, it is worth starting with them. There are two ways to get a solar battery: do it yourself or buy one. At once I will say that the final cost of the final product in the manufacture of several panels and without experience will cost about the same amount as the finished panel of the same capacity, but produced at the factory. But it's interesting to do it yourself.
Here we must again add a little theory. There are three affordable buyers, for sane money, solar cell technology, consisting of different cells: single crystal, polycrystalline and amorphous silicon. They differ in structure and it is even visible by eye. I will try to tell as simple as possible, and those who wish to plunge into the difference of chemical compositions can see the information themselves - you should not overload the article.
Amorphous silicon is the most promising manufacturing technology. It allows you to make bending panels and produce current in diffused light, that is, in cloudy weather, but rather quickly degrade, which is reflected in a decrease in efficiency.
Monocrystal - pure cells of primary silicon. As a rule, black plates without impregnations, almost square shape with rounded edges. Sometimes sawn in half to increase the voltage of the line elements.
Polycrystal - cells of secondary silicon or not very clean. Probably used single crystal scrap.

Battery types are arranged in descending order of cost. And if the second and third options are still close, then the first is noticeably breaking out in cost, and over time reduces the production of energy. For the manufacture of its own Solar Panel (hereinafter the joint venture or Sat - Solar Battery) in China, a batch of Grade B solar cells was ordered (you can find HERE for the number of SS elements). It is necessary to check that the box includes junction boxes, tires for connecting the cells to each other and at least a couple of meters of cable. There were also ordered connectors MC4 for connecting batteries. In Russia, it was ordered to manufacture enlightened tempered glass 4 mm thick. This thickness is due to the need to protect against all kinds of icicles (hail) and other weather conditions (a targeted blow with a stone is unlikely to survive), and the coated glass is needed to increase the efficiency of the elements. For framing glass, protection against chipping and ease of installation, an aluminum corner 30x30 and the necessary hardware to it were purchased. To connect the solar panels to the system, a multicore copper cable was chosen with a cross section of 6 mm square. A PWM controller was ordered for charging in the same China, and a simple car inverter with a power of 100 Chinese watts was used to power 220V devices. Later I will explain the difference between ordinary and Chinese watts.

Energy system №1. Budget

Self-production of solar panels

So, the assembly. The modules came in a box and some of them were broken, as in the first photo. For this, in stock, as a rule, there are about 10 pieces. I complained to the Chinese in a letter and he sent me 10 more cells for free. Each cell gave 0.5 V and 4 A, according to Chinese merchants. That is, each module is 2 watts. To charge the battery, you must have a voltage above 14.4 Volts, that is, you must combine the cells in series. Looking at the factory panels and taking advantage of the practice of many home-builders, it was decided to combine two chains of 36 elements on one glass, getting 18 volts and 8A in peak. That is, one panel could bring up to 144 watts of energy, which never happened. The reasons will be discussed later, but for now making.
The procedure is simple. Solder shank:


Cooking glass with frame:



We put, we solder, we pull out the tires and we solder the wires, and then we fill in with a special compound to seal all the plates. The people flooded with sealant, various mastics, I liked the finished compound produced by the company in St. Petersburg. It's nice that the production is Russian, so it was not a pity to give the money, and the result was pleasantly pleased. It would be good to fit a sealed box with a diode to the terminals of the contacts, which will prevent a drop in the system's power when connected in series if one of the batteries turns out to be dark. The box was complete with cells.



In the end, I received two solar panels with an estimated power of 288 watts.



But there is a lot of convention. When the solar panel is heated, its efficiency drops even from the calculated percentage by 20. In addition, it affects non-solder elements and microcracks, which inevitably arise during soldering. As a result of measurements on the summer sun, I received 40 watts from each panel, that is, the result is three times smaller than expected. The price of such a panel was about 6000-6500 rubles, while the factory panels with delivery cost 7000-7500 rubles. So I finished the initiative and in the future I bought only factory panels.

Base Voltage Selection
Perhaps this is one of the first decisions to be made when designing solar panels. The fact is that solar systems are created with a voltage that is a multiple of 12 - because most batteries have just such a voltage. Even capacious batteries assembled from 2V cells are often collected at 12, 24, 36, or 48 volts. Here we must recall the physics and the formula of electric power: P = U * I. From it follows that at equal power, increasing the voltage, we will reduce the current. It is quite natural that a decrease in current will entail a decrease in the load on the element base and a decrease in the cross section of the wires, but it is impossible to infinitely increase the voltage. Here there is the following problem: DC, in contrast to AC, when the voltage rises above 36 Volts is much more dangerous to humans. If you do not go deep into the theory, then you can often tear off the arm from alternating current with a voltage of 220V, but almost never from a constant one. In addition to this, it is possible to vote for low voltages, if only because 12V is a typical voltage of a car battery, which means there is a mass of various devices designed for this voltage. In addition, increasing the battery capacity is possible simply by adding ordinary batteries to parallel, while with high voltage you would have to buy batteries in pairs, triples or quadruples. There is one more unpleasant moment in the series connection of batteries: unbalance of cells, which leads to the failure of a single cell, then a whole battery and the whole chain, if the problem is not tracked in time.

My selection: 12V

Choice of solar charge controller
There are two main types of controllers: PWM or PWM controller and MPPT or Maximum Power Point Tracking - Track the Maximum Power Point.
The first type is as simple as possible and familiar with PWM is not necessary to explain, and for the rest it is as simple as possible: once the maximum charge level of the battery is reached, the controller pulsates to deliver current to the battery, preventing it from recharging. Plus this scheme: simplicity, which means low cost. Minus: you can connect the battery, the nominal voltage of which coincides with the nominal voltage of the battery.
MPPT controllers are more complicated, more expensive, but have a huge advantage: solar panels can be connected in series, thereby increasing the voltage in the circuit to the controller and reducing current, which allows the use of thinner wires and reduce the loss of energy transfer to the controller. And the efficiency of such controllers is higher, because they scan the currents at various voltages with a certain frequency and choose the maximum power point. Hence the name. Those who wish to plunge into the world of technology can go here , where quite sensibly and in detail painted.

For my own panels, I bought a Chinese PWM controller that gives a charge of up to 30A, that is, 360 W at 12V or 720 W at 24V. But since the system is selected at 12V, the limit is 30A or 3 solar panels connected in parallel.


To him was added a voltmeter and an ammeter ordered from the same place, in order to see the condition of the battery and what charge goes to the batteries. The battery was chosen the cheapest lead-acid, with a capacity of 190 Ah, because I still believed that I was about to connect the mains electricity.

Choosing an inverter
We turn to the most interesting point of our system. To begin with, the inverters, in addition to power, are easily divided into two types: with a pure sine wave at the output and a modified sine wave (also referred to as an approximated sine wave or square wave). The first give a pure sinusoidal signal, the second have a step on the graph:



For most appliances, there is no difference, and even if you connect a simple voltmeter, then its readings will be about the same. But if you compare the prices of both types of devices of the same power, it turns out that the price is different by an order of magnitude. Do I have to pay for the pure sine and what is it for? As practice has shown, most devices easily get along with a modified sinusoid, although some engines, for example, compressors of refrigerators, begin to warm up more and the risk of premature failure increases. In addition, if you connect audio equipment to a modified sine wave, a noticeable noise will be heard, which is not at all happy when you want to enjoy good sound. From my own experience, I can say that only the washing machine refused to work on the modified sinusoid — all other devices worked successfully. If there is a sum for a good inverter, then you should choose a pure sine, if other devices are sensitive to signal purity.

We select the power of the inverter
In this matter there are a lot of nuances that affect the choice of the inverter. The following rule applies: all planned power load is summed up and multiplied by two. To examples: 4 lamps of 60 watts + washing machine 800 watts + laptop 80 watts + refrigerator 100 watts + tv 50 watts. It would seem that the maximum consumption is 240 + 800 + 80 + 100 + 50 = 1270 W and it is enough to take an inverter for 1300-1500 W, but! Different loads behave differently. For example, the starting current of the refrigerator can reach ten times during start, which means it will require 1 kW of power instantly, and if the light and washing machine are turned on at that time, the inverter will simply fall into error if it does not burn. In addition, the Chinese 1500W inverters of this type were unable to start the refrigerator with a rated power of 100 watts. The experiment was conducted when the refrigerator started from the generator, and then quickly switched to the inverter using the phase switch. So it was possible to feed the refrigerator from the Chinese inverter to 600 watts - barbarism, difficult, but it worked. The trouble is one thing: this inverter is unable to start the refrigerator a second time. The deception was to set the fridge settings to maximum frost. And the refrigerator freezes until it is turned off. So you can freeze food for a light day, and turn it off at night.
So, the power of the inverter must be such as to provide a double supply of consumption of your conventional devices or tenfold to start the engines.

My choice: two Chinese inverters with power of 1000 and 600 watts.

Duplication
When choosing cheap and simple components it is better to immediately lay down on the duplication of systems. This will not remain without electricity in the event of failure of any element. Such a reinsurance will not be expensive, but will provide peace of mind and stable nutrition.

In general, the first set of autonomy looked like this:
1. Two homemade solar panels with a total power of 80 W
2. PWM- battery charge controller with maximum current up to 30A
3. Automotive lead-acid battery with a capacity of 190 Ah
4. 600 W and 100 W inverter with modified sine wave

The scheme of a working budget autonomous system looks like this:



Please note that the inverter is connected directly to the battery, even if it consumes all the power of the solar panels. In addition, it is necessary to avoid a break in the controller's power when solar batteries are connected, because this threatens to damage the controller.
For the first year, my solar autonomy existed in that form and allowed me to charge gadgets, stay in the evenings with light and work with electric tools on bright sunny days, like a drill or electric jigsaw.

The material turned out more than expected, so the second version of the solar autonomy, which cost a little more, but allowed to use powerful power tools, use the pumping station, and I’ll describe in general the gas generator for the summer in the next article. What is the difference between good china and European China? Should I buy expensive equipment through Ebay? And also I will answer the main question: was it worth it? I ask you to ask specific questions, which I will answer in the next part.