Solar Systems in Home
Going for home solar power is a wise decision as solar energy is not only natural but is free to us unlike any other source of electrical power. So you will be helping to reduce greenhouse gas emissions. However, home solar power systems need significant initial investment. So you have to be careful.
Unfortunately, for unscrupulous companies, consumer ignorance about photovoltaic (PV) solar power is often an opportunity to cheat. In fact, many vendors are in the solar business to chase your money with little interest in the technology, environmental benefits or your needs. Here is some information that will help you fortify yourself against being shortchanged.
PV solar modules convert energy from the sun into free and non-polluting DC power. Unfortunately, this power cannot be directly used due to varying light intensity of the sun over the day. You need to use a current controller to convert it into a constant voltage under all conditions of light.
The only controller type that you have to buy is the one that harvests the maximum solar energy from the sun. This is called maximum peak power tracking (MPPT) controller. MPPT helps you to harvest about 30 per cent more energy from the solar module than any other type. Solar panels are expensive and the MPPT controller costs maximum 10 per cent of the cost of the panel. Since only an MPPT controller gives 30 per cent more energy from the same panel, this investment is fully justified.
The sun shines bright during the day. In India, often there is no electricity even during the day for many hours. During daytime, the MPPT controller can directly feed DC into your inverter and you can use that AC power for feeding electric fans, television or computers. For this, you need only a smallcapacity battery. The inverter directly uses the solar panel output to give you AC supply. If you are using it for office, you need power mostly during the day, except for some time in the early morning and late evening.
A small-size battery is good enough for this. However, home users need solar power at night after the sun has set. For this, one needs to accumulate all the available solar energy during the day and then use it at night. In such a case, you need a battery with big enough capacity to accumulate all the available solar energy from the sun and deliver it to the inverter at night feeding your 230V AC loads like lights, fans, PCs and TVs.
A small-size battery is good enough for this. However, home users need solar power at night after the sun has set. For this, one needs to accumulate all the available solar energy during the day and then use it at night. In such a case, you need a battery with big enough capacity to accumulate all the available solar energy from the sun and deliver it to the inverter at night feeding your 230V AC loads like lights, fans, PCs and TVs.
Depending on your energy need at night, your supplier will recommend certain battery capacity; its voltage and ampere-hour (Ah) capacity. Small home inverters of 300-1500W rating usually work off one or two 12V lead acid batteries depending on the inverter power and its input voltage rating. Electrical power and energy often confuse people. But it is easy to understand the difference between the two.
Your CFL light, normal bulb, fan and TV are rated by their power consumption and the unit used is watt (W) or volt-ampere (VA). You can add all these to find out how much power you need to operate them. For example, your three CFL lights (16Wx3), a fan (40W) and a TV (60W) will add up to 150W. This is the minimum power rating that you need for your inverter. It is necessary to buy an inverter with at least 50 per cent or even 100 per cent more capacity in watts.
However, for finding your energy needs, you need to multiply the watt rating of the appliance by the time in hours you need to use it. For instance, in the above example, if you need to run these appliances for five hours, your energy need is 150Wx5h = 750 Wh. So your inverter could be of 225-300W (continuous) rating but your energy need is higher.
It is important to remember that your battery capacity depends on your energy need. The battery has to be large enough to accumulate from the sun and store 750 Wh of energy and not 150W power as some people often misunderstand.
Your home inverter generally needs 12V or 24V DC input depending on what you buy. This is because leadacid batteries are often rated at 12V. For 24V, you need to connect two of them in series.
Another rating of the battery is its capacity specified in Ah. A 40Ah battery means that it can deliver 8A for five hours, 2A for 20 hours, etc. In other words, its energy storage capacity is 12Vx40 Ah=480 Wh.
So if you need 750 Wh as in the example given above, you will need a 12V, 80Ah battery that can store 12x80=960Wh energy for night use. Even here, it is essential to buy a battery with 50 to 60 per cent more capacity in order to ensure a longer battery life. Selection criteria is similar to that for a water tank capacity; buy always more than what you need.
So for the most economic size of the solar power system you need, calculate how many hours you may want to use each of your appliances and find energy need of each by multiplying by its wattage rating. For example, using a 15W CFL light for four hours will require 60 Wh of energy. A 40W fan that you may use all night long-say, for ten hours-will require 400 Wh of energy. Add up energy needs of all the appliances to calculate your energy need in Wh.
Your PV solar modules are rated in peak watts. But, in practice, these, on an average, deliver only 70 to 75 per cent power (over about five hours) of the solar energy that you get to accumulate from the sun. Therefore a panel rated at, say, 100Wp, will give you 70W for five hours-that is, energy of 350 Wh (5×0.7×100). So if your energy need is 700 Wh, your PV module should be rated at 200Wp.
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