A Tiny Tiny Solar Project

    

Solar energy is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture, molten salt power plants and artificial photosynthesis. - Wikipedia

Overview

    It is the best source of renewable energy that we can harness. There are two type of solar energy systems on grid and off grid. On grid is the one which is connected to your electrical company and off grid will store energy directly to battery. I have built off grid system. As with all type of energy generation systems, initially it requires some invest but you can start with very small project to understand all the components/process. That's what I did.  Let's have a look at some of the advantages and disadvantages first and then I'll describe all the components.

Advantages

• Pollution free renewable energy source
• Virtually no maintenance as solar panel last over 30 years
• Excess power can be sold to electrical company for on grid system
• Safer than traditional electrical current

    

Disadvantages

• High initial cost
• Needs lot of space for big systems
• Cloudy days will generate less power

    For solar energy generation there are 4 main components solar panel, solar charge controller, battery and inverter. Let's get right into introduction of each components.

Solar Panel

    Solar panel also known as photovoltaics (PV) is a magical(at least that's what I feel 😃) component that converts solar energy to watts. It is usually rated by watts(W). You can buy solar panel anywhere ranging from 10W to 300W or even higher! It also has different voltage ratings which are mostly 12 volts(V) or 24 volts(V). Solar panel has two wires for output positive(+) and negative(-).

    Let's learn some basics regarding volts, amperes and watts. It's rather simple volts multiplied by amperes equals to watts ( V * A = W ). So for an example a 12V panel with 1A rating will generate 12W of energy. Well not quite, you see when it comes to solar panels a 12V panel can generate up-to 18V on fine sunny day !!!

    I have bought 20W 12V panel. As per it's specifications it has max voltage (Vmp) 17.7, max current/ampere (Imp) 1.13 and rated power (W) 20 +/- 3%. So as per our formula 17.7 V * 1.13 A = 20.001 W. There are many companies which create solar panel and there rating may vary.

    You can also connect multiple solar panels to increase volts or amperes. In serial connection where the voltage increases, you connect negative of one panel to positive of other panel and rest connections to charge controller. One thing to note here is, it is highly recommended for both solar panel to have equal ampere ratings. So panels with same company is safe bet. In parallel connection where the amperes increases, you connect positive wires together and negative wires together. For this type of connection voltage ratings of both panel should be equal.

Solar Charge Controller

    The power generated by solar panel is not consistent and obviously it can't get generate energy at night. So we need to store the energy in battery. Battery requires proper charging, a charger which provide power in incremental form till it fully charges. This is where charge controller comes into picture.

    Solar charge controller is special type of charger, it uses power generated from solar panel and stores it into battery. A solar charge controller generally have 6 connections. It consists 2 connection (positive and negative) each for solar panel, battery and load. Solar panel and battery are self explanatory, load is where you connect inverter etc.

    We need to connect battery first so that charge controller powers up and initial setup can be done. In advance charge controllers we can set various settings like max voltage of battery, load on voltage, load off voltage etc. Charge controller also has voltage and amperes ratings. There are two types of charge controllers PWM (Pulse width modulation) and MPPT (Maximum power point tracking). I won't get into more details about this but MPPT is more efficient algorithm and are also considerable more expensive than PWM.

    I have bought 12V 10A PWM charge controller. This means it can handle n number of 12V panels as long as it's total ampere rating is not more than 10A. Since my solar panel has 1.13A rating it is more than capable. In fact I can add approx 8 more of these panels. To be on safer side always stay 1 or 2 amperes blow the charge controller rating. Solar and Load LEDs indicate that charge controller is getting power from solar panel and load is active. 2 LEDs in between indicate status of battery.

    There are 3 stages for charging a battery bulk, absorb and float. When battery is less than 80% charge bulk mode is used where maximum amount of amperes are stored in battery. In 80% to 100% the absorb mode is used where amperes decrease as the voltage increase. The float mode is activated once battery is 100% charged, this mode will trickle charge the battery to keep battery at max level.

Battery

    Do NOT use car batteries !!! There are two reasons for that. One, Car batteries have higher CCA (Cold Cranking Amps) which are required to start a car we don't need that and Two, it should not be discharged below 90%. We can use batteries which are specifically built for inverters.

    There are 4 types of inverter batteries:

• Lead-acid
• Sealed lead-acid(SLA)
• Sealed lead-acid(SLA) gel
• Sealed lead-acid(SLA) AGM

1. Lead-acid batteries are cheapest and they are similar to old car batteries where you have to add battery specific purified water. Also as it contains liquid it should be mounted in upright position.
2. SLA batteries are also known as maintenance free as it is sealed and does not require hassle of adding water etc.
3. The gel type is also SLA type of battery which has sulphuric acid in gel form. It is shock and vibration resistant and can be mounted any any direction.
4. The SLA AGM battery is most expensive comparing to others, but has it's advantages also. It has longer life and can be deep cycled meaning can be discharged at significantly lower level.

    I have bought 12V 12AH SLA battery as it's safer then flooded type and cheaper than other batteries. AH stands for Ampere per hour. Simply put a 12AH battery can last 12 hours if the consumption is 1AH, but yes there is but here too, if you fully discharge battery before charging it will greatly reduce it's life cycle. It is recommended to not use battery below 50% of it's capacity. So we should consider 12AH battery as only 6AH battery.

    How do you measure battery charge level you may ponder ? Well, a typical SLA battery is full at 12.70V. Gel and AGM batteries have different levels. Battery is at 50% when it reads 12.20V, 25% at 12.00V and dangerously low 10% at 11.51V. You can easily check the voltage level with multimeter. So you should not discharge or stop using battery beyond 12.20V to get best possible life cycle.

    Battery charging is whole different story and it can be confusing at first, but solar charge controller takes care of it easily. SLA battery charges from current state of voltage to 14.4V !!! This is normal, when it is on stand by mode it will gradually be back to approximately 12.7V. Again to maximise life cycle if there is setting available in charge controller you should limit max voltage limit to 14.1V.

    You can also connect multiple batteries just like solar panels. Serial connection will increase total voltage and parallel connection will increase amperes. Again it is recommended to connect batteries of same type and company.

Inverter

    We get Alternating Current(AC) from wall plugs, which are converted to Direct Current (DC) via appliances’ converter. Batteries store in DC form, but we can't directly use it as appliances require AC. Inverters are used to convert DC to AC. Inverter either convert to 220V(European/Asian etc countries) or 110V(U.S. etc countries). DC flows in linear format while AC flow in wave format.

    There are two types of inverters:

• Modified sine
• Pure sine

1. Modified sine inverter converts to AC in block type wave format which means it’s not perfect conversion. Small appliances which are not sensitive for perfect wave format will not have any issue but some heavy and sensitive appliance for example sound system might not work properly. This type of inverters are cheaper and widely available.
2. Pure sine inverter as you might have guessed it, it has proper wave format. As you can expect they are expensive, big and heavy in size.

    I have bought 300W 220V modified sine inverter. You can connect it to load on charge controller of directly to battery via proper battery terminal connectors. Inverter has lot of components which are used to convert DC to AC, so it will use lot of power in conversion process.

Tools

    Additional tools required are wires, soldering iron, soldering wire, soldering paste, wire spade connectors and crimping tool. Optional tools are multimeter and small digital voltage LED screen.

Future Upgrade

    In future I will add additional battery for more storage and solar panel for faster charging. I would also change solar charge controller to one with small LCD screen which will display various parameters and has few buttons so that I can change some settings. I would also purchase USB buck converter which will decrease 12V to 5V and has USB port so I can charge small devices like mobiles, tablets etc.

Conclusion

    I have learnt a lot while building and monitoring this system. If you have read this far then give a pat on your back 😎 and I really hope you got some inspiration to build solar energy system. Leave your feedback, queries and suggestions in the comment section below. I will be more than happy to help you out. Thank you.

Update #1: This setup costed me 6,000 to 7,000 INR. Also this can be easily setup in rural area since it does not require to be connected with grid.

    In the end I will only say one thing that I keep telling my friends and family:

“Keep Learning”