Solar Power for dummies Part 2: Getting to know your devices

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Now that we have gotten the introduction stuff out of the way its time for you to get acquainted with some of the basics of electricity in general and solar power in particular. I won’t be introducing anything scary, I promise, just the basics you snoozed through during the Physics and Integrated Science lessons.

A typical off-the-grid solar system, which is the subject of this discussion, consists of the following components: A solar panel that converts light to electricity (eeeh not heat to electricity  as some people think, the infra red[heat] is just incidental), electric cables to link the components and devices, batteries to store the electricity for use during times when there is little or no sunlight, a charge controller to regulate the charging and discharging of the batteries and an inverter to convert DC power to AC for use with most household appliances.

solar system

A typical Solar installation

Basics of electrical power

  • A solar system primarily produces Direct Current (DC) power i.e. power that only flows in one direction as opposed to Alternating Current (AC) from ZESA which flows,in an alternating fashion, in two directions.
  • The power consumed by each household device is measured in Watts. Watts=Voltage(Volts) x Current(Amps). Given any two components of this equation we can always find the missing variable.
  • Voltage is also known as the potential difference. If you think of electrical wires as water pipes voltage represents the water pressure.
  • Current is the actual amount of electricity flowing through the wires. In the water analogy this is the equivalent of the litres of water coming in from the mouth of the pipe at any given instance.
  • I am not going to bore you with details of such things as resistance which measure the opposition to the flow of electricity, think of it as friction in the pipe.

Assumption

  • As said most Solar installations are DC systems which operate around 12V/24V. While it is both easy and possible to have 220V DC system the voltage of the system is usually limited by the voltage required by your inverter system. Most of the inverters in Harare operate on a 12V system so we are going to assume that you will be building a 12V solar system.

Getting to know your devices

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Although it is possible to use energy-hogging devices such as stoves and microwaves on a Solar system it is usually not a good idea to use these. Because they draw way too much power in a short time they are more likely to damage some of the components of your system especially the batteries whose lifespan will be significantly reduced. Besides you will need to build a serious Solar rig to use these which would cost you a good portion of Cuthbert’s yearly salary. Besides, given the fact that you can utilise other sources of energy like LP Gas, the opportunity cost of using these devices is higher than would be justifiable.

Before you proceed you need to create a list of the devices that you are going to be running on Solar Power and create a Solar Budget. This budget will be useful in determining the size of your solar system in terms of watts. This is simply a list of the total amount of power in watts that are going to be used on your system on each day e.g:

Device Watts Hours of Use Total KWH

DeviceWattsHours of Use Total KWH
Total 2451,240
32” Ecco LCD TV458360
PVR Decoder 805400
Laptop704280
ZOL Outdoor Modem 504200

I am a Dummy I need help on the budget

The good folks at Free Sun Power have created a sizing estimator that you can use to estimate how much power your devices will consume. Though it is easy to use you should bear in mind that these are estimates that may or may not correspond to the actual amount of power your devices consume. You can also use their clicking budget there; it’s just below the estimator.

Going by the above budget a 245 Watts system should, by all appearances, be adequate for your needs but nothing can be further from the truth. There will be nights when your system will not be generating any power and has to draw power from your batteries. To prevent blackouts my general rule of thumb is to double the Wattage of my system. So in this case I will install a 500 Watts system instead.

There is also the little matter of efficiency and cloud cover which affect the needed wattage. So you would do well to triple the required Wattage of your system instead, you never know when your neighbour might pop up to watch the weekend game and bring his iPad and iPhone and charge them using your system or if the game goes into extra-time and you end up using the Decoder and TV longer than usual. So going by our example you would be best advised to build a 750 Watts system.

Keep your budget at hand as it will be useful over the course of our series. In the next installment we will take an in-depth look at solar panels, their costs, solar irradiation and other such matters.

Source Credit: Free Sun Power



13 Comments

  1. Anonymous says:

    good one.thanx

  2. Kodzwa DT says:

    That is a good one. Thanx

  3. [email protected] says:

    Great article!

  4. Mr Jiang says:

    Thanks for this simplified series…..do you have the average load profile for residential consumers in Zim?

    1. Garikai Dzoma says:

      I would hazard a gues and say about 5KW most of the time.

  5. Anonymous says:

    Thanks Garikai. I’m seriously considering going off-grid instead of just complaining about the incessant power cuts thanks to our beloved ZESA. This info is quite useful. Please keep it rolling.

  6. Hungwes says:

    Garikai
    I am rural based and my Internet is erratic, I have just managed to view part 2 today after a struggle, I haven’t seen part 1 yet!
    Keloid much obliged if you could send me each part as an attachment for easier access.
    Thanking in advance

  7. Itai SolarSky says:

    Two important things to note:

    1. Solar panels available locally are rarely the sticker size. The common tendency by informal suppliers is to apply a big value sticker to small panel. Hence it appears cheaper but in actual fact you are paying a fair price. Usual trick is to sell 135W as 180W and the best price you get is $170.

    2. Best practical sizing for a battery based system is to use the amperage of the solar panel instead of wattage. I have tested many a panel type on rooftops and again the sticker amperage is rarely achieved by a large margin. Standard 135W/140W panels will give a practical output of 3A at noon against a sticker value of 5A.

    Multiplying that by 7 hours of effective sunshine (sunshine equivalent to noon time) give a daily yield of 21A maximum.

    This is the biggest battery killer as it never achieves full charge every day.

  8. WIND ENERGY says:

    CAN YOU ALSO DO THE SAME FOR WIND ENERGY

    1. Maloon says:

      hie,wind systems are basically the same with solar systems.Our company has successfully designed, manufactured and installed a 250 watt wind turbine.The Wind /solar hybrid system has been is installed in Mrehwa, Mashonaland East province of Zimbabwe.Production will commence soon for the Zimbabwean market.

      We are expects in solar system design, installation and maintanance.
      For more details contact : [email protected] call : +263 773 529 289 /+263 778228758

  9. Maloon says:

    hie,wind systems are basically the same with solar systems.Our company has successfully designed, manufactured and installed a 250 watt wind turbine.The Wind /solar hybrid system has been is installed in Mrehwa, Mashonaland East province of Zimbabwe.Production will commence soon for the Zimbabwean market.

    We are expects in solar system design, installation and maintanance.
    For more details contact : [email protected] call : +263 773 529 289 /+263 778228758

  10. drexter says:

    Good food, in the real world of energy

  11. Ignatius Saburinyu says:

    Thanx for the article

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