![]() ![]() 12V is not considered a shock hazard, but FIRE is your enemy with low voltage power systems because of the high currents involved. A grid-connected solar PV system does not give you resilience against power cuts, because the anti-islanding systems in the grid tie inverter shut the system down if the main power fails, so that a PV system does not send power back into the grid when it may harm power workers trying to repair faults.ġ2V systems have different safety issues from 240VAC mains circuits. That sort of thing is on a different scale from this project, and capital costs are usually in the order of several thousand pounds, but the energy savings are much, much greater. For that it is best to get a grid-connected solar power installation which will allow you to save energy and get renewable feed-in tariff payments. If you want to primarily save energy or reduce your carbon footprint using solar power, this is not the solution. That is because in the summer you get far more solar energy and you’ll probably use the lighting less. In the summer you can also run a laptop computer power supply independently of the main for a couple of hours (these run typically 40W). The system as described lets you run one or two 12V 1.8W LED lights through the year – my system was able to run mine through the winter and the shortest day where the light would be on from about 6pm to 11pm. Although I have used lighting as an application, such a system can run an electric fence for much of the year if suitable solar panels and battery are used. It can be used at home to keep lighting during power cuts, but the same principle can be used to provide power to sheds on allotments, outbuildings or island sites without mains power. This project lets you run lighting off of solar power, effectively storing sunlight for later use. This was originally published on TI’s website, which is no more. It had to be targeted at a competent DIYer, and is for small scale lighting. The idea for the project came from the Transition Ipswich Energy group in 2011. Total costs should be in the order of £100, but there are ways to reduce that by getting some items from Ebay. the food looks good ) some LEDs make your fresh steak look like roadkill from a month ago.This project is about resilience more than energy saving, though it can also be used to save energy. Some have very high efficiency, but they look nasty! (like: greenish, bluish, make people look like aliens, make your blue veins stand out, etc). Make sure you get a sample of the LEDs first before buying the whole lot, and make really sure they look good to you. Remember efficiency is not the only criteria, color rendition is also very important for comfort, and good color rendition increases cost and decreases efficiency. My guess: the winner will be determined by the efficiency of the 12V LEDs you find. Now add the inverter losses to the 240V case, looking at the inverter datasheet, and compute how much current each case will use from the 12V battery. So you get the 12V current, and thus the cable losses. You should of course compare two installations with equal light output. Compute how many watts/bulbs you need for your target lumens. Draw your installation with number of bulbs and wire lengths.Ĭompare the lumen/watt efficiency of 12V and 230V bulbs. A wire that is twice as expensive (2x the amount of copper) will not halve the losses! It will only reduce them by 30%. Again not too bad, but remember losses are in RI^2 so they are proportional to the square of the number of bulbs.Īlso losses are in RI^2 but R is inversely proportional to the copper cross section which determines the cost of the wire. Thus let's neglect the cable losses for 230V.įor 12V the same bulb would draw 0.83A DC which amounts to 76 mW per 10m of wire. However cable losses will still be rather tiny, let's consider a 10W bulb, on 230V this would draw 50mA RMS (rounding up), let's fudge this to 150mA peaks with a duty cycle of 1/3, this gives 2mW losses on a 10m wire, which is negligible. If it's a square or modified sine, the cable losses will be different. This also depends on the waveform at the output of the inverter. Thus the 12V case is more about using the same 1.5mm2 versus thicker wire.Īnother complication is that 230V LED lights do not have power factor correction, so the current they draw will not be a sine, they would draw high current peaks of unknown amplitude and duration. For example here, 1.5mm2 wire is the standard for lights, so that would be used in the 240V case. One could say that higher voltage allows using a thinner cheaper wire, however building code and economy interferes with the calculation. I'll use metric, so 1.5mm2 wire is 11 mOhm/m. Calculating wire loss is simple, here's a US version with AWG. ![]()
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