Components of a solar system
The components and technologies used to construct a solar system can be confusing to the newcomer. Not everybody is from a technical background nor do many people have an interest in the subject. When considering an investment in a solar system, basic understating of some of the technologies, components and systems could be very helpful to avoid costly mistakes. Below follows a short discussion on the basic technologies that one would encounter. It is written in as non-technical language as possible in order that as many people as possible can benefit from the summary.
Solar panels are one of the major building blocks of any solar system. Simply put, a solar panel works by allowing photons, or particles of light, to knock electrons free from atoms, generating a flow of electricity. Solar panels actually comprise many, smaller units called photovoltaic cells. Photovoltaic simply means they convert sunlight into electricity. Many cells linked together make up a solar panel, sometimes called a PV panel.
There are hundreds if not thousands of solar panel manufacturers around the world, in the Americas, Europe, Asia and elsewhere. This has caused extreme competition and consumers are spoilt for choice as numerous manufacturers offer excellent quality products at very competitive prices.
Monocrystalline vs Polycrystalline
For typical household and commercial use there are basically two technologies to choose from. These are the so called monocrystalline and polycrystalline panels. The monocrystalline technology is slightly more expensive to produce, but it yields slightly higher efficiency than the polycrystalline alternative. From a practical point of view, a mono crystalline panel of a given output will be about 5 or 6% smaller and approximately 5 or 6% more expensive than the same output polycrystalline panel from the same manufacturer. In other words, if monocrystalline and polycrystalline panels produce the same output, one would be smaller but also more expensive than the other. So, if space is limited, the monocrystalline panels could offer better output in terms of Watt per square meter, but if space is not a limitation, why not take advantage of the lower price per Watt offered by the polycrystalline panels? Both technologies work very well and will last equally long.
Tier 1 status
The Tier 1 ranking scale is orchestrated by Bloomberg New Energy Finance Corporation and is used to rank solar panel manufacturers in terms of their bank-ability or financial stability. Only solar panel manufacturers that own their own manufacturing facility can be included for review. If a solar company outsources the manufacturing of its panels then it will not be included on the Tier 1 list. Tier 1 ranking has to do with financial stability and product quality.
Vikram Solar is India’s largest solar panel manufacturer. Vikram, based in Kolkatta, was founded in 2006 and enjoys tier 1 status. Yearly solar panel production exceeds 1,1 GW.
The lead acid battery was invented in 1859 by French physicist Gaston Planté and is the earliest, yet still most widely used, type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by automobile starter motors. Lead acid batteries are widely used in solar applications, despite some limitations. The main limitations are:
- Relatively low charging life of approximately 1000 to 1500 cycles compared to newer technology batteries with lifespan of 6000 cycles.
- Relatively low depth of discharge (DOD) ability of 20 to 50% compared to 80% DOD of newer technology batteries.
Lithium iron phosphate
The lithium iron phosphate battery, LiFePO ₄ or LFP battery, is a newer type of rechargeable battery, using LiFePO ₄ as the cathode material, and a graphitic carbon electrode with a metallic backing as the anode. Compared to lead acid batteries, lithium batteries offer significant advantages, including improved discharge efficiency, longer life span and the ability to deep cycle while maintaining performance. LiFePO ₄ batteries typically have a lifespan of 3000 to 6000 charging cycles and can accommodate depths of discharge (DoD) up to 80%. The price gap between Lead Acid and LFP batteries used to be prohibitive but this has shrunk to the point where LFP is an attractive proposition.
Depth of Discharge
A battery's depth of discharge (DoD) indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery. An unfortunate fact of life is that the lifespan of a battery can be negatively influenced by large or deep discharges. As above, Lead Acid batteries have a lower tolerance for significant discharge than LFP. The graph below illustrates the general trend. The DoD characteristics of any battery should not be taken lightly. One should weigh up the implications of a deep discharge vs more or bigger battery capacity. In some cases, deep discharge could reduce the battery life to such an extent that an investment in larger capacity could be justified.
Inverters and charge controllers
Solar panels generate direct current (DC) and the energy stored in batteries, are delivered to an electrical load in DC as well. Most if not all household-, commercial- and industrial appliances, however, utilise alternating current (AC). Therefore, two important conversions are necessary in a solar system.
are used to convert the direct current available from the batteries or solar panels to alternating current for use in alternating current appliances. Various approaches are used by different manufacturers, each offering its own value proposition in terms of price and utility. Pure sine wave solar inverters generally provide a purer form of power than modified sine wave inverters. The power from a pure sine wave solar inverter is similar to that supplied by electricity generated using rotary equipment like turbines and generators, such as in the case of Eskom. Most modern devices run quietly without distortion or disturbance on pure sine wave current. Modified sine wave solar inverters have higher efficiencies at lower cost per watt, but do not necessarily work for all applications. Modified sine wave contains harmonics which can cause problems in some equipment, and as luck would have it, the most expensive and sensitive equipment is sometimes the least compatible with modified sine wave. A kettle, hairdryer, lawnmower or any other ordinary equipment will run just fine on almost any reasonable supply, but expensive, sensitive and high performance analytical equipment, fast and high capacity computers etc will probably best served by a harmonic free pure sine wave supply.
The second conversion (actually the first in a solar system) is not always so obvious to newcomers. Solar panels generate electricity , or power, in a certain combination of voltage and current. This voltage – current combination is not always suited to charging a battery. Charge controllers are used to convert the DC output from the solar panel to DC of a different combination of Volts and Amps, to optimally charge the battery. Various technologies exist like for example Pulse Width Modulation (PWM) etc, but the most efficient way to accomplish this conversion is called Maximum Power Point Tracking (MPPT). By utilising MPPT technology the combination of Volts and Amps can be varied during the charging cycle to optimise matters even further. The charge controller can reduce the solar panel output if no load exists to dissipate the generated power. The “M” in MPPT is actually a bit of a misnomer as in some cases, the Power Point is manipulated to a point other than the Maximum, but this is getting far to technical for this discussion. Some manufacturers offer MPPT charge controllers as separate units and some manufacturers integrate this functionality in their inverters. Advantages and disadvantaged both ways, separate units tend to be more expensive but in combination units, failure of one part of a system could necessitate replacing the whole unit.