Solar PV for the Self Builder

Part 1 -The Basics

As energy prices increase and the switch from fossil fuels takes place one is left with few options to offset rising electricity costs. In this blog I am going to go through the choices that are available when using Solar PV. Solar PV systems typically generate DC (direct current) power and this is then converted to AC (alternating current) power for use around the home. These systems also synchronise with your own electricity supply grid so that you can use it. The standard system one purchases will automatically disconnect from the national grid if there is a power failure thus ensuring that you do not send power into the national grid. The abbreviation PV stands for Photovoltaics (when light is used to generate electricity from a semiconductor material).

A common-sense starting point before considering Solar PV is to try and reduce your existing electric energy use. This might be as simple as changing old fridges, washing machines, dryers, or pumps. If one uses electricity to heat one’s house then insulating the house and upgrading the hot water tank is also a good starting point. For example, one 300 litre water tank will store 20kw of energy at 60 degrees Celcius (see the previous blog on the water tank). Typical battery systems can not economically or environmentally compete with water as an energy storage system. All homes need hot water and you will not find a safer, more economical, and environmental approach for storing excess energy from Solar PV. One can also opt for reduced price electricity at night (approximately half the price of daytime electricity) which helps the national grid balance its load.

A simple starting point is to visit your home supply meter and work out how much electricity you use per minute on a typical day. This is the load one uses without using main appliances such as kettles, cookers, water heaters, etc. It typically would include fridges, ovens timers, clocks, computers plugged in, modems, etc.

Supply Meter

To do this one only needs to look at your meter and it will display a number that tells you how many revolutions or pulses it uses to record one Kw/h (kilowatt per hour) of electricity. One is billed by your electricity supplier for each kw/h you use. Above and below are examples of where you can find the numbers. In the example above the digital meter has 1000 Impules per kw/h and the old type shown below has revolutions -in this case, it is 250 revolutions per kw/h.

To calculate your typical energy use without using main electrical appliances follow this example. Set your phone/ watch to the stopwatch setting. When you see the first pulse start your timer and visually count the impulses in that minute. If you get 10 impulses in 1 minute then multiply 10×60 minutes=600 impulses in an hour. So we know that we now use 600 watts of power in one hour without using main appliances.

In the old type meter, you will notice that there is a red/black mark on the wheel when it revolves in one revolution. In the meter above we can see that it does 250 revolutions in one hour to record 1kw/h use of electricity. So if it does 125 revolutions it is 500 watts of power in one hour or 0.5kw/h. One can use the same principle above and use a two-minute count to increase the accuracy of your calculation. In Part 2 I will look at what PV systems are available to purchase and the parts that make up a good Solar PV system.

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