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Thread: Inefficient solar systems

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    Inefficient solar systems

    Current solar systems both water heating and current generating systems are very inefficient.
    The solar water heaters on the roof generate lots of hot water during the day when nobody is using it. Most people take a bath or shower in the evening or early morning. If its taken in the morning then all that hot water that was generated the previous day was a waste because the mains electric element would have to be activated to keep the water hot during the night for the next morning. If you use the hot water for washing in the evenings then you will use the solar hot water that was generated provided that everyone washes in a limited time frame because cold water will be added to the hot water tank as the hot water gets used and when that happens the mains electrical element will come on to heat up the water again. So you can see the amount of saving on your electrical bill with these solar water products are limited.
    Electrical current solar systems are too expensive and inefficient. Most small units vary in price from R50, 000 to a R100, 000 with limited solar capabilities. Even for a small system they use massive solar panels just to discard most of that power via a regulator when the batteries are fully charged. The solar panels available are all 12V DC so are most of the batteries for them. All current solar systems convert this low voltage battery power in to 220V AC via a very inefficient inverter that requires huge amounts of input power and only give out a small output power. A small R100.000 solar system is sold, as a product to save on a electric bill it cannot replace the mains power. These inverter systems are not capable of heating a geyser or running an electric stove .Its only capable of running things like fridges, TVís and sound equipment that are not big consumers of electricity.
    I donít believe in using regulators and inverters when I buy an 80W solar panel I want to use that entire 80W of power to reduce my electrical bill. The product that consumes the most power in a house is the geyser and switching it of at times to save on electricity is not the solution because you will have to heat up an entire cold geyser for hot water and that requires lots of power. As solar panels and batteries are already low voltage DC itís cheaper and more economical to stay with that power source. I have developed some LED 12v houselights that wouldnít cost anything to run as they are running directly from the batteries that get charged from the solar panels. I have now developed a system that when the batteries are fully charged I take all the available power from the solar panels and feed it in to the geyser element this power is not enough to heat up a geyser but it is enough to keep the geyser at temperature during the day. I have used this system on the 2kw geyser at work and the water remained hot all day without the mains. I am now doing the same tests but with batteries at nigh.

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    I don't know what inverters you are using, but most inverters today work at efficiencies higher than 90% making them efficient. What you should rather say is that using batteries to heat up water is inefficient.

    The best water heater is an in line gas water heater, as they only consume energy when you require hot water. The larger types, will heat up 20 liters of water a minute to 40degrees centigrade. Slowing the flow rate will increase the temperature of the water.

    Solar panels are only about 18% efficient, but they are about the next best thing for the supply of limited energy. Using a solar panel, with a MPPT controller, you can extract the maximum amount of energy out your panel, but like any piece of equipment, there are losses, and with solar panels, heat cause losses in the junctions of the panel, and on a hot midday sun, can lose up to 10% capacity due to the heating of the cells from the sunlight, and the generation of electricity through the cells. Another important aspect of solar panels, is to maintain them clean, some bird excrement could cost you 20 to 30% of the panel capacity. There are also large variations in solar luminance from summer to winter, and you can expect to lose approximately 40% of your panel capacity in winter.

    However they can still be useful to charge batteries and power efficient LED lighting. I have done many experiments, and will soon be launching some new lighting products, that will blow your socks off. With a single 1W LED, I can light up a room 3 by 3 meters very comfortably. The LEDs I use are 120Lumens per watt, so 2W leds will light up a lounge quite comfortably. So if you feel that 2W or 240 Lumens is too little you can use 3Watts. By the way you can not compare my 3Watt LED to the ones you buy in the shop, mine would produce 360Lumens as opposed to the ones you buy in store which range from 180 to 260Lumens for the more expensive ones.

    Lets just say that you have a 5 room house, and each room uses 3Watts of lights, this equates to 15Watts of electrical power. If you wish to run for 6 hours, equates to 90 watts of electrical energy. A 35Watt panel with an MPPT controller would suffice to charge up and maintain a 25Amp battery even in winter and with overcast days. Not a bad and very cost effective solution, which would require a battery replacement every 4 to 5 years. The LEDs would last some 30 or more years.

    We are just accustomed to wasting energy, and in reality just do not realize how much we waste.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    Quote Originally Posted by Justloadit View Post
    I don't know what inverters you are using, but most inverters today work at efficiencies higher than 90% making them efficient. What you should rather say is that using batteries to heat up water is inefficient.

    The best water heater is an in line gas water heater, as they only consume energy when you require hot water. The larger types, will heat up 20 liters of water a minute to 40degrees centigrade. Slowing the flow rate will increase the temperature of the water.

    Solar panels are only about 18% efficient, but they are about the next best thing for the supply of limited energy. Using a solar panel, with a MPPT controller, you can extract the maximum amount of energy out your panel, but like any piece of equipment, there are losses, and with solar panels, heat cause losses in the junctions of the panel, and on a hot midday sun, can lose up to 10% capacity due to the heating of the cells from the sunlight, and the generation of electricity through the cells. Another important aspect of solar panels, is to maintain them clean, some bird excrement could cost you 20 to 30% of the panel capacity. There are also large variations in solar luminance from summer to winter, and you can expect to lose approximately 40% of your panel capacity in winter.

    However they can still be useful to charge batteries and power efficient LED lighting. I have done many experiments, and will soon be launching some new lighting products, that will blow your socks off. With a single 1W LED, I can light up a room 3 by 3 meters very comfortably. The LEDs I use are 120Lumens per watt, so 2W leds will light up a lounge quite comfortably. So if you feel that 2W or 240 Lumens is too little you can use 3Watts. By the way you can not compare my 3Watt LED to the ones you buy in the shop, mine would produce 360Lumens as opposed to the ones you buy in store which range from 180 to 260Lumens for the more expensive ones.

    Lets just say that you have a 5 room house, and each room uses 3Watts of lights, this equates to 15Watts of electrical power. If you wish to run for 6 hours, equates to 90 watts of electrical energy. A 35Watt panel with an MPPT controller would suffice to charge up and maintain a 25Amp battery even in winter and with overcast days. Not a bad and very cost effective solution, which would require a battery replacement every 4 to 5 years. The LEDs would last some 30 or more years.

    We are just accustomed to wasting energy, and in reality just do not realize how much we waste.


    I agree gas heating is the best but the cost of replacing existing geysers is the problem.
    I donít want to use solar panels or batteries to heat up the water in the geyser I just want to use it to keep the hot water at temperature. Iíve been manufacturing LED lights for the last 12 years and the biggest problem I found with a single led lamp is the small area it covers even the wide angle ones. I got the best results using ledís thatís mounted in the lamp to cover 360 degree angles. How do you calculate the efficiency of your inverters? The input 12v amperage compared to the 220v output amperage.

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    Efficiency = (Power Out / Power In ) x 100

    Losses are usually attributed to power device switching, transformer mutual induction issues and rectification diodes, and ultimately land up as heat. The cooler your inverter runs, the more efficient it is.

    With respect to LED lighting, I have been very successful in achieving overall light with a single source LED. The main secret is the light fitting that you use along with the diffuser. I do not make LEDs to replace conventional lamps/globes. I replace the complete fitting, and in my case, most fittings are applied on a ceiling, or on a wall, there are no hanging chandeliers. Most of my customers use the LEDs to light up low cost homes, so total cost of the solution plays a role in the type of light fitting.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    I see you have a website I will send you info on the house lights we are making. We are busy with a light that can be changed for many applications and light outputs.

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    Perhaps this is an opportunity for the members of the TFSA to start a business by tying up an agency for the Sunbandit.
    A 120Litre tank and panels is priced at +_R30,000.oo less duty and transport.
    Apparently you can connect them to existing Geysers to reduce the cost of grid power used for water heating.
    Would this be a viable alternative to existing technology available in RSA?
    "Nobody who has succeeded has not failed along the way"
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    Read the first 10% of my books "Didymus" and "The BEAST of BIKO BRIDGE" for free
    You can also read and download 100% free my short stories "A Real Surprise" and "Pieces of Eight" at
    http://www.smashwords.com/books/view/332256

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    I am currently doing tests to see exactly how much power a geyser uses by fitting an hour meter to my one geysers element at work it’s a 100L with 2KW element.
    Test so far.
    Ambient temp was 27C in roof when the cold geyser was switched on.
    It took 2hours 18min before the thermostat switched the geyser off.
    Starting with a hot geyser the hour meter was on for 1hour 3min from 1700 yesterday till 7 this morning. I will continue with this test for 24 hours. How would one calculate these findings in to Rands?

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    Hi der. The Water Heating system you are referring to is called a pre-feed and is VERY inefficient for exactly the reasons you give, and is outdated.
    There are however EXTREMELY efficient systems available nowadays.
    The first is the Thermo siphon where the house geyser is removed and a solar geyser (With back-up element) is installed on the roof with the collector (Solar Water Heater).
    This means that the water heated by solar (Sun) is fed directly to the household as required. This is the Most effective system.
    The second is the Split-Pumped system. This uses your current geyser, and a collector on the roof. The whole system is run with a Geyserwise management device. The collector starts cold in the morning. within 10-15 minutes the water in the collector is 7deg hotter than the water in the geyser. A circulation pump is activated and pumps the hot water into the geyser, while pumping the water from the geyser to the collector. When the temperatures equalise, the pump stops circulating. The water in the collector (about 7 litres) then quickly heats to 7deg hotter than the geyser, etc, etc.... This is also VERY efficient and Either system should cut overall electricity bill by approx. 50%.
    Unfortunately, regarding solar electricity, this is cost prohibitive as you have pointed out. New technologies are being developed, and the cost will decline as more systems are being purchased and utilised.
    The place to start is by converting to a SWH as this is economical and immediately cuts your solar electricity requirements by about half.
    You are welcome to contact me directly if you would like further discussion/information.

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    I’m not in favor of solar water heating systems. Solar water systems generates hot water during the day when its not needed, you also can’t store the hot water so the element must keep it hot during the night. We tried one of those small electric units but found that it didn’t heat up the water sufficiently. What we are doing is feeding solar panel power directly in to the standard geyser element and it works very well. We are still experimenting with the best option for feeding battery power in the geyser element at night. Our system is for keeping the water at temp our tests has shown that a 2KW 100L geyser was switched on for 1hour 40min over a 24 hour period without us using any hot water. During cold winter months this on time could be much longer. Send me a mail to celgo@eject.co.za and I will send you more info.

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