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Designing a DIY Solar Power System

solar power iconResidential solar photovoltaic systems supply electricity directly to a home using solar panels mounted on a roof or an open area. These types of solar systems are basically the same type of system installed by pioneering homeowners back in the early days of solar development, the difference today however, is that the solar panels are much more energy efficient, lighter and also a lot cheaper.

The type of electricity produced by solar panel is called DC, or direct current, the same type that batteries use. However, most standard household appliances and lighting fixtures operate on higher AC, or alternating current, electricity. Therefore, any photovoltaic solar system must include some form of inverter to convert the low level DC power from the solar panels into the higher level AC power for use around the home. Household appliances operate just as well on solar generated DC power as they do on mains generated AC power supplied by the utility company.

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A Simple DIY Solar Power System

Before you can start designing a diy solar power kit you need to make a few discussions first. Do I want a grid-connected or off-grid connected system?. Do I want or need storage batteries?, and what is my energy consumption, etc.

Photovoltaic (PV) systems may only cost a fraction of what they did say 25 or 30 years ago, but they are still quite expensive to buy and install, so making some discussions before you start will same you money in the long term.

Whether you choose a whole-house grid-connected system or a self contained off-grid system with battery storage, you may need an array of solar panels producing several thousand solar watts of power just to meet your current household needs (depending on your house size, its energy efficiency, teenagers and so on). So before you start designing a solar power kit, you will need to calculate the total power requirements of all of your homes electrical items.

Calculating your Energy Requirements

The actual electricity generated by a diy solar power electric system is basically a function of its panel size (either individually or as an array), its solar efficiency, positioning, amount of sun exposure plus a variety of other such factors, so it is important that when you are designing a diy solar power kit that its size will generate enough electricity to cover your average household’s electricity usage throughout the year.

The electrical power rating of a typical appliance is generally given in Watts which you can find by either looking at the appliances identification sticky label or by the products data given in the user manual. Some manufacturers give the appliances wattage value in volt-amps, for example 200VA (two hundred volt-amps). This volt-amps rating is more or less the same as that given in Watts because Watts is just voltage times current, that is volts times amps, or V*A which is shortened to just VA.

The appliances daily energy consumption is simply calculated as the VA or Wattage rating multiplied by the number of hours per day it is switched on or being used (watts times hours or W*hr). So for example if our 200VA (or Watts) appliance is used for 5 hours during a 24 hour period, then the total consumption of energy would be 200VA multiplied by 5 hours which gives 1,000 watt-hours or 1 kWhr (one kilo-watt hours), as 1,000 watts is equal to 1 kilo-watt (kW).

Likewise if you had a 60W lamp switched on at night for 3 hours, its energy consumption would be 60 multiplied by 3 which equals 180Whr (one hundred and eighty watt hours), or 0.18kWhr. The advantage of using watts is that wattage always represents the electrical power of an appliance regardless of the supply voltage. Once done, repeat the above calculations for all the electrical items you want to power from your diy solar power kit and add them up.

Note that unless you intend to have a full-house grid-connected solar system it is beneficial when designing a solar power kit to have a mixture of both low voltage components such as 12 volt or 24 volt lamps, batteries and appliances, etc as well as mains voltage connected items just in case the mains inverter or circuit becomes faulty. Finally, the important thing to remember when designing a diy solar system is to determine exactly what it will be powering.

Storing the Solar Energy in Batteries

Once you know how much electrical energy you are going to consume each day you can start thinking about ways of storing enough of it, because without storage you would only have power available when the sun was shining. Luckily for us, somebody long ago invented the battery (French scientist Georges Leclanché in 1866) which allows us to do just that, but batteries add cost to a system so choosing the right battery is also very important.

Different videos on Youtube and websites on Google shows us that it is possible to make a diy battery with just a lemon, a single copper coin and a galvanised nail, but obviously one lemon wouldn’t produce enough power to light a single LED (but apparently 4 or more will). So to power your TV, lights and appliances around the home we need something a little more advanced such as the AGM UB121000-45978 12v 100Ah deep cycle battery below.

Modern solar kit batteries are available in a variety of shapes and sizes, ranging from just a few amp-hours (Ahr) to many thousands capable of supplying huge amounts of electrical power. Solar storage batteries are not the same as regular car type batteries which should not be used when designing a diy solar power system because these types of cranking batteries cannot be fully discharged and recharged continually without suffering from internal damage. However, they can still be charged using a photovoltaic panel.

Solar storage batteries are considered to be deep cycle lead acid types with have much thicker internal plates that can withstand many deep discharging cycles, although you shouldn’t really deep cycle them very often. When used as part of an alternative energy systems, deep cycle batteries will have a reasonably long working life if maintained and looked after.

RV or Marine type deep cycle batteries are basically classed as recreational batteries used in boats, caravans and camper vans. They are suitable for most small sized diy solar power or lighting kits, and are available in 6, 12 and 24 volt sizes. Another very popular battery for small diy solar systems is the golf cart battery. These are slightly more expensive than the recreational battery but are a good choice for a small solar system on a budget.

Heavier industrial type deep cycle lead acid batteries are very common in a typical off-grid system because of their physical size and power rating. Lead acid batteries exist in three main types: flooded lead acid, AGM (Absorbed Glass Mat) or sealed GEL batteries. Sealed AGM and GEL batteries have the advantage that they do not release as much gas (if any) into the room when they are charging.

All batteries store DC power as it’s not possible to store AC power in batteries. Solar storage batteries are rated in ampere-hours or Ah and generally come in multiples of 2 volt cells, so 6, 12 and 24 volt batteries are the most common.

We said previously that we use Watts (that is volts multiplied by amperes) to measure the power requirements of a solar system. Since batteries are rated in amp-hours (Ahr), we need to calculate how much electrical power in Watts this equates to. So a typical 12 volt battery rated at 80 Amp-hours would be capable of delivering 960 Watt-hours (Whr) of power.

Charging Batteries with Solar Panels

All types of rechargeable battery can be charged-up using solar panels, wind turbines or a mains connected charger. While it is possible to charge a 12 volt battery directly from a 12V solar panel without regulating or controlling the amount of charging current it isn’t the best way of doing it.

To continually charge deep cycle storage batteries in a better and controlled way you will need a some form of charge controller. Charge controllers deliver the right amount of power from the solar panel to the battery in a precise and controlled way and are an important part of any well designed diy solar power kit.

Keeping the deep cycle batteries of your solar power kit full of charge and healthy is also important because they will last a long time if you look after them giving you a return on your investment. Overcharging and/or undercharging a battery will eventually damage it, so keeping batteries healthy means charging them fully, regularly and in a controlled way.

Of course there’s a huge range of charge controllers available to choose from a few Dollars or Euro to several hundred. The more expensive models have built-in digital displays which allows you to monitor and see exactly what’s going on in your system. The charge controllers here is an excellent high quality example and would control a system well, but choose one that suits not only your system but your budget.

Choosing Your Solar Panels

Now it’s time to choose the solar panels for your diy solar power kit. Photovoltaic panels convert sunlight into DC (direct current) electricity and come in a wide range of types for different applications and power needs from different manufacturers, but it is worth mentioning here that solar panels aren’t all equal and just because it says 100 Watts on the manufacturers data sheet does not mean it will produce that. Photovoltaic solar panels are usually rated with a solar irradiance of 1,000 W/m2, at a temperature of 25oC.

As well as a PV panels variation in size, shape, wattage rating and other such specifications, standard PV panels are made of two different types of silicon based cells. The Monocrystalline cell uses a much higher and purer grade of silicon, offering the best sunlight-to-electricity conversion efficiency, and thus are more expensive to make.

Multicrystalline, or Polycrystalline cells use less pure silicon materials and are therefore easier and cheaper to make. Having said that, the solar conversion efficiency of these types of photovoltaic cell is slightly less than that of their more expensive monocrystalline cousins. So if you are on a tight budget, then multi-crystalline or polycrystalline cells will work just as well.

The solar panel size should be selected in such way that it will charge the battery fully in one sunny day. The average daily power generated by your photovoltaic panel, or panels, should be about equal if not more than the average daily amount of electrical power consumed by your home or appliances.

For example, let’s assume that during the 12 hours of sunlight throughout a typical day we can expect 5 hours of effective sunlight to generate the rated power we need to power our appliances. Note here that sunlight is not always constant and uniform, but will differ according to your location and time of the year.

Therefore if we had a 12 volt system that consumed 200Ah of electrical power we would need to generate approximately 12V x 200Ah = 2400Wh (watt-hours). So the diy solar power required to be generated per hour would be 2400Wh divide by the 5hrs of effective sunlight would equal 480W. So we would require 2 x 240W or 4 x 120W or 5 x 100W solar photovoltaic panels to supply our average daily power consumption.

Of course, in reality there will always be some losses within our diy solar power system due to the cables, solar charge controller and self-discharging of the batteries. Thus it is better to choose a single solar panel of array that can generate a daily power rating of approximately 10 to 20% higher than the daily power consumption you require, because after all, more watts equals more power.

We have seen throughout this alternative energy website that the environmental benefits of generating your own solar electricity are indisputable, self-evident and plain obvious whether you are adding a new solar system to help save the environment or reduce your energy bills, a diy solar power systems nowadays costs a fraction of what it did 20 or 30 years ago.

Nevertheless, solar systems are still quite expensive and could easily take 20 or 25 years to pay for itself in reduced energy bills. A typical off-grid diy solar system with its charge controller(s) and deep cycle batteries will cost even more. Having said that, going green and using solar panels can still be a sound investment with the potential of a high rate of return on your investment, but the key here is to plan wisely and find out what incentives and/or grants are available through your local and government sources.

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