Solar Panels Guide
This is a small guide with basic notions to be able to camp.. We all like to know what we are doing and why without fear of it being dangerous or ruining something.. Everything written here is a compilation based on research, own experience or user comments. If you see any errors, tell us and we will modify it with everyone's contributions..
Here you will find the reason for things to fend for ourselves!
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Sometimes it is very good to use the simile of the water of a waterfall to understand electricity.. Let's see:
Energy: Amount of accumulated energy. We will use Wh or kWh (What are they 3600000 Joules). Not to be confused with Watts (W) or KiloWatts (kW), When it has the h it means that it is a unit of accumulated energy quantity., The h means the hours during which a certain amount of watts is emitted., to know how much energy you have accumulated. Putting kwh is like putting Joules or Calories, are units of quantity, not power. Sometimes, for example in batteries, you will find Ah (amperes hour) which can be used assuming we are always at the same voltage throughout the calculation, because if not it will vary, It doesn't matter if you multiply or don't. For the simile it would be the amount of water above the waterfall., ready to fall, If what we want to know is the accumulated energy (batteries) or down the waterfall, If what we want to know is the energy expended (heat dissipated or converted into mechanical stress)
Power: amount of energy that can be emitted per unit of time. That is, if we have a lot of accumulated energy (kWh) we can release them suddenly or slowly, according to the power (w) to deliver the sending equipment. We will use Watts or Kilowatts kW (What are they 1000 Joules every second). In the same way it would depend on the width of the river and the height of the waterfall..
Intensity: amount of electricity (electrons) moving through a material. (not to be confused with speed, What would be the meters that each electron advances each second and which are usually very few even though the electrical response from point to point of a cable is practically instantaneous since they push each other like a pendulum of balls). Unit Amperes. In the simile it would be the flow of water that falls through the waterfall.
Voltage: force that pushes electrons. Unit Volts. Logically, the higher the voltage, the more electrons will be pushed, so it is the same as saying that there will be more amperes.. In the simile it would be the height of the waterfall, The higher up the water falls, the stronger..
Endurance: force opposite to the voltage generated by any physical medium by friction with the movement of electrons. Ohms Unit. In the case of a waterfall, it would depend on the width of the channel through which the water moves., If it is very small, the water advances confined and pressured, so it loses forward force., In the electrical case it loses voltage and is dissipated as heat.
Note that the simile does not work in the following situation. The voltage manages to extract more electrons from the atoms of the cable material and set them in motion.. In the case of water, if we increase the height of the waterfall, no more water moves., but it just falls harder, since it is a fluid not a metal and it moves all in a block instead of going “taking off” the molecules one by one according to the pushing force.
Note that if we increase the voltage, we drag more electrons which is the same as saying that the intensity increases. If there are more electrons moving there is more friction and therefore more heat is generated and the cable can melt.. To avoid this we will use thicker cables that have more material so that the electrons can circulate comfortably without generating as much “friction”.
*Normally the values that we can manage are the voltage and the resistance, which varies according to the type of material and its section., intensity is a consequence of the combination of the two. We can't create intensity, we can only play with the other two to obtain a desired intensity.
Most common formulas:
The power (electric) in W we calculate it by multiplying the pushing force of the electrons (voltage) by the number of them that are set in motion (intensity), that is to say:
P = V · I
We can measure the accumulated electrical energy in Wh, that is, multiplying the time during which some watts have been accumulating.
Wh = P · time in hours
When we look for plate prices we have to know:
-Max power they emit in full sun according to our needs: it is given by the manufacturer.
-Maximum voltage in full sun according to our needs: it is given by the manufacturer. Usually 12v, 24v, 48v… Note that in reality the plates are cells that generate a very small voltage that are added in series and in the end they all deliver the volts that the manufacturer tells us according to the number of cells that have been placed..
-Typology and dimensions, to know if it will be useful for our requirements. Let's see below:
1- What plate power do I need??
-First we need to foresee what we are going to consume, adding the consumption powers of each device. We will find the power in kW either on the box, in the description of the article on the internet or by asking the manufacturer. When you know the power of each one, using the formula kW = P · Time, We will multiply by the time in hours that we are going to use each device. If we use it 10 minutes, we multiply by 0,1 hours. The final sum of all the devices will give us the amount of energy we consume after a day in kWh.
-Apply a 70% performance. No plate will yield 100%, we generalize with this 70%.
-Decide how many days of autonomy we want to be able to endure. That is, if it is a rainy week and the board is not going to recharge the battery., the day the sun rises, We will need to recharge what is necessary to last those days without recharging again.. So if we know the kWh that we need to recharge for a day's consumption, and establish for us that we want to be able to last two days, On a sunny day we have to recharge twice the kWh so that it can last two days without recharging. (in case we have planned to buy a battery that allows us to store them).
-Take into account the worst conditions, What would it be in January when the sun would recharge the plate during 4 effective hours and the best conditions would be in summer for 7 effective hours. Let's use the worst situation as a starting point.
Example:
·Portable PC: 45w x 2 hours of daily use = 90Wh
·Leds: 20w durante 4h = 80Wh
Mobile charging: On the charger it says 5v and 2A. As P=V·I= 5*2= 10W and it takes one hour to charge = 10Wh
·(Fridge: be careful because it is not working 24 hours is a special case that depends on the outside temperature and good insulation)
·Etc…
TOTAL: 90 +10+80 = 180 Wh is the amount of energy we consume in a day..
We apply the performance: 180 / 0,7 = 258 Wh is the amount of energy that the plate must supply each day to supply the consumption we have..
In winter it would only work for 4 hours, that is to say: 258/4 = 64,5 W would be the necessary power that the plates must have so that in 4 hours we have enough energy accumulated in the battery to last a day..
If we want to last two days of autonomy in the rain, we need them to accumulate double the energy during the same 4 hours., Therefore we need double the power: 64,5 x 2dias = 130 W
We need plates that give us at least 130 W. (this value is low, I haven't counted the fridge here, which could add a lot more, In reality you can have many more consumptions such as the water pump, heating, music when the engine is stopped and everything you can think of connecting, Also keep in mind that the battery is not lithium., can only be downloaded up to half, but we see that in the battery section)
2 What plate voltage do I need??
I'm going to be electrocuted? I must choose the lowest possible?
The human being has the threshold of perception of electricity from the 30 volts, and you notice it clearly from the 70. This may vary with each person since it depends on the resistance of the skin and its humidity.. Since V = I · R we will need at least these 30 volts so that enough intensity begins to pass for us to notice it. This intensity is around 0.0005 Amperes. At 220v alternating current they would happen 0.005 amperes, And yes, it can cause injuries.. If more than 10 amperes through our body we would die instantly, But don't worry, a very high voltage would be necessary to be able to push and move so many electrons given the high resistance of our body..
Video experimental: https://www.youtube.com/watch?v=z6j8OBH6SRQ
That is to say to 12 o 24 volts there is no danger of electrocution. Then why 12 o 24?
Knowing that P = V · I, for the same plate power, the more voltage they have, less intensity will pass through the cable. Since we have a ceiling space limit, We have a power limit that we can install. If this power is at 24v, Less electricity will pass through the cable than if it is at 12v since instead of moving more electrons what we do is move them with more force. It is preferable that less intensity passes, because this way less resistance is created and the section of the cables can be smaller since they will not heat up as much., they will be cheaper, and they will have less transmission losses than at the end of the day what we want is not to lose those watts that the plate offers us through the cable. So for large consumptions that need a lot of power, better use 24v.
Another advantage of using 24v is that on cloudy days the board will generate less voltage., for example a 40% any less, which would be 14.4v, still enough to charge 12v batteries. On the other hand, if the plate is 12v, he 40% less is 4.8v, insufficient to charge batteries.
3.What type of plate do I need??
All plates lose effectiveness as the temperature rises
Polycrystalline: They work well in full sun even if they get hot but do not perform well in shade. Buy them if you are from the south.
Monocrystalline: They work poorly when they get very hot but absorb energy better on cloudy days. You'll be better off if you're from the north..
4. How do I place the plate?
Based on what has been said on the forum, Each ITV is different and the regulations are not very clear..
-Without approval:
·You can drill holes in the sheet to pass the cables through but you cannot make a mechanical fixation like a screw. Then you can attach the cable gland with Sikaflex glue. Another option is to run the cables directly through the door if you want to save the hole in the ceiling. (I have passed all the MOTs with the cables through the door).
Option 1: The rigid or deformable plate attached to the ceiling. In the case of the rigid plate, has a thickness, and that implies that the air between the plate and the ceiling in the space that occurs due to the height of the plate frames, contains air. If it does not ventilate, That air rises a lot in temperature and this lowers the performance of the plate., For this reason, if your roof is smooth and the air cannot escape, It is recommended to drill holes in the aluminum frame of the plate for ventilation. In the case of the deformable plate, which is much thinner and has no frames, It is all in contact with the ceiling without air, and it gets extremely hot since it only ventilates on one side, There's no way to avoid it.
Option 2: Rigid plate raised 10cm from the ceiling. You cannot screw anything to the sheet without approval, but if you have a roof rack or want to buy one, you can fix the plate screwed to the roof rack. How do you not screw to the sheet metal but to the roof rack?, and it is considered that the vehicle provides for the bolting of a roof rack and its loading legally, no need to approve (I have passed several MOTs like this). Another option instead of a roof rack is to use corner pieces to raise the plate., they sell many on aliexpress. The plate would be screwed to the corner pieces and the corner pieces would be screwed to the sheet with high-resistance Sikaflex glue.. It is VERY dangerous because the air enters at full speed between the plate and the roof when the van is moving and would have the effect of sailing against the plate, pushing it with great force and there is a high possibility of detaching it. (I have been able to read comments from people who have been blown away in the middle of the highway). If this method is used, I don't recommend it at all, You have to put an L-shaped profile in front or something that covers the front air inlet and prevent the plate from entering directly underneath.
-Approving:
We screw the plate to the ceiling or to the corners and these to the ceiling. It is more expensive because you need a homologation project with an engineer and also drilling the roof sheet is not easy., so you can't do the same thing yourself and you will have to take it to a tinker who will charge you.
5. What section how much cable do I need for the board?
The plates generate different voltages depending on the amount of light that reaches them, which depends on the time., clouds and sun angle. A 12v plate at maximum power, It can reach 25v and a 24v can reach 50v.
There are tables to know the necessary cable section according to the amperes that are going to pass., so that the cable does not overheat.
Guide – cable section according to length and amperes
So first we need to know how many amps will pass.:
P = V · I -> I = P / V
Intensity passing through the cable = maximum power of the plate / 25v or 50v depending on the board we have purchased (remember that they are the peaks, that is, the plate 24 It can reach 50v when the midday sun shines fully without clouds)
6.Why do I need a regulator??
The regulating devices are placed between the plates and the batteries. They serve to send a stable and continuous voltage to the battery since the voltage that comes from the plate is changeable and is not good for the useful life of the batteries.. They also allow you to connect an inverter or any consumer cable that works with the output voltage they offer, such as LEDs and others.. It is advisable to connect all the van's electronics there instead of directly to the battery since this way the regulator manages the energy that goes directly from the plate to the consumption without going through the battery and extending its useful life..
To do this, we must take into account that we can only connect the maximum power generated by the amperes admitted by the regulator., otherwise we are going to burn it. That is, if the regulator is 30 amps, and converts the electricity that comes from the 24v plates to 12v for the battery or for consumption, We cannot connect devices whose powers added to those 12v generate an intensity greater than 30 amps. That is, in the case of a 30a regulator: P= 30 *12 = 360w are what the regulator could supply. If we want to plug in more things, we connect it directly to the battery. (It would also be necessary to look at the maximum power the battery and the inverter can provide, but this is at the point of batteries.).
For example, if what you want is to use the 400w generated by your 24v plate to charge the battery or whatever., you need to know in which situation it will handle more amperes, which will always be where there is less voltage, In this case it is at the regulator output at 12v, since P=V·I so 400=12·I then I= 33 amperes. You need to buy a regulator that manages 30 minimum amperes to take advantage of the 400w of your plate, since in reality you will have margin because it will be a little less due to the performance of the plates explained before. Another option is that you only decide to connect a total of 200w consumption to the regulator., then you will only need a regulator 16 cheaper amps, but of course you are wasting half the plate.
So it is advisable to use the output of the 12v regulator for lights., usb ports, laptop, water pump and low consumption things and calculate the amperes based on these consumptions. And then plug in a direct inverter to the battery for extreme consumption at 220v such as the dryer., microwave, a drill at a specific moment, air-conditioning… since the battery is usually prepared to overcome those 30 amperes (always sizing the cables correctly since more than 30 amperes is a lot and they can melt and set your van on fire).
There are two types of regulators: MPPT i PWM
PWM: They are the simplest but they cannot change the voltage. They can work at 12v or 24v, but they can't do the conversion, so to connect 24v plates we would need 24v batteries.
Always connect the battery to the device first so that it recognizes the voltage and then the plates to the device, never the other way around otherwise you can ruin them.
MPPT: They are more expensive but they make much better use of solar energy at any time since they can convert the voltage that comes from the plate to the voltage that goes to the battery, keeping the latter constant..
7. Solar panels of different voltages can be placed?
The quick answer would be NO. Although there may be some exceptional cases such as having a solar panel of 200w a 12v and a solar panel 200w a 24v, In that case they could be put in series with a regulator MPPT.
But put plates of different capacities and voltages, The only thing we would achieve is to limit the set to the power of the smallest panel.
