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Solar power is currently the fastest growing source of electricity in the world. As the amount of solar installed has risen, costs have come down dramatically and solar systems are becoming affordable to more and more people.
But before you dive into getting your own solar PV system, it is important to first understand some of the basics of how they operate. This is obviously necessary if you want to design and install your own system, but is also very important if you are paying someone else to install it for you so you can better understand if the system is right for you.
If you are completely new to solar, this article is a great starting point, it will introduce you to the main components in a system, and how they all work together. It will also provide links to other useful articles to continue your solar education.
The core of a solar PV system is the solar panels themselves. When exposed to sunlight, the panels produce direct current (DC) electricity.
The panels are connected together via cables into what are called “strings” before being connected to an inverter. The inverter converts the DC electricity to alternating current (AC) electricity which is the type used in homes and the electricity grid. The inverter is then connected to the AC board of your house, supplying the house with electricity.
Solar PV systems may be grid-tied or off-grid. As the name suggests, in grid-tied systems the house is still connected to the electricity grid and draws electricity from the grid when the PV system produces less electricity than the house is using. If the PV system produces more electricity than is needed by the house, then it may also feed the excess electricity back into the local grid, or charge a battery for use after the sun goes down. Whether or not it is possible to feed electricity back to the grid depends on the rules of the utility, state, or country.
Off-grid systems on the other hand are not connected to any external grid, and must supply all of the power required by the house (or RV etc), that it is connected to. In order to continue to supply electricity at night or during cloudy periods, these systems include batteries to store the electricity generated by the panels. They also require a charge controller, which as the name suggests, controls the charging of the batteries. The setup of an off-grid system is therefore slightly different. Typically they will look something like the following simplified diagram, however this will vary depending on the setup. For example, systems using hybrid inverters, or DC only systems will have different arrangements.
Solar systems are sized based on the electricity requirements of the house, the amount of available roof space, whether or not power can or should be exported to the grid, and many other factors.
First it is necessary to determine the expected electricity usage of your home, off-grid dwelling, or RV etc. Either through past electricity bills, or by adding up all your electrical devices and estimating how long you use each one (there are online calculators to help you do this).
The next step is to calculate the size of solar PV system which matches your electricity usage, while also considering what will provide you with the best return on your investment. How this is done will depend on the type of system you have:
Grid-tied systems sizing is heavily affected by whether it is possible to export electricity back to the grid, and how much the utility pays you for this electricity. When net metering is available (which is when utilities credit you for any electricity you export to the grid) you will typically size the system so that the yearly expected generation matches your yearly usage.
When you receive little or no compensation for electricity exported back to the grid on the other hand it usually makes sense to size the system so that as little is exported as possible. You therefore need to consider how your expected daily, weekly, and yearly load profile matches the generation profile of your PV system, to determine what size system will give you the best return for your investment. This can be done using online calculators specifically designed for the task.
Off-grid systems, including their batteries, are sized based on expected electricity usage, as well as how many cloudy days the system should be able to keep running through (days of autonomy). This can become quite complicated, but luckily there are many online calculators designed for this purpose, which make it quite easy.
It is possible to calculate how much electricity a solar PV system is expected to generate in an average year, although the actual output will vary from year to year depending on weather conditions. Rough calculations can be done by hand, or more accurate calculations can be done by using any one of the various solar calculators that are available to help you size your system.
Solar Panels (sometimes called solar modules) are made up of a number of smaller silicon solar cells that convert sunlight into electricity.
These are typically protected between a glass front sheet, and a polymer back sheet, with everything being held together by an aluminum frame. They usually come pre-assembled with cables so that they can easily be connected together and to an inverter.
Solar panels come in a variety of different technology types, colors, and sizes. Different solar panel types have varying efficiencies, which changes the amount of power that can be generated by a given area of rooftop.
As you can see, not all solar panels look the same, and some have been designed to be more visually appealing to others. The trade-off is that these typically cost more than standard solar panels.
For more information on selecting the solar panel that is right for your project, check out our Solar Panel Selection for Grid-tied Residential Systems.
As mentioned earlier, the inverter is the device (or devices) in a system that converts the DC electricity produced by the solar panels into the AC electricity that is typically used in homes. There are three main inverter technologies to choose from, string inverters, string inverters plus DC-to-DC optimizers, and micro-inverters. While string inverters are currently the most common option, the use of micro-inverters and DC optimizers continues to increase as costs go down.
When string inverters are used solar panels are connected in series into strings, and multiple strings are connected in parallel to each inverter, which is called an array.
String inverters tend to be the cheapest option as there is only one device to install for many solar panels, they are also typically more efficient at converting from DC to AC electricity. One problem with string inverters however is that when one solar panel in a string is shaded or has its output lowered by soiling from dust, bird poo, etc, all the other modules in the string are also affected.
DC-to-DC optimizers are used to solve the issue of shading on one solar panel affecting all modules in a string. They are smaller devices that connect to just one or two panels and optimize the output of each panel or panels individually. As they still output DC electricity they still need to be connected to a string inverter to convert to AC electricity.
Since they optimize output at a module level, DC-to-DC optimizers can increase the total output of a solar system, especially one that is subject to a lot of shading or soiling. The downside is that they increase the system cost compared to using string inverters alone.
Micro-inverters are similar to DC-to-DC converters in that they optimize the output of solar panels at the panel level. The difference is that they also perform the DC to AC conversion so that no string inverter is required at all. Micro-inverters may be mounted externally to the solar panel, or even come integrated into the module in what is called an AC module. Using micro-inverters can greatly reduce the complexity of the system and therefore the installation costs, however, due to their higher price, still typically result in a higher price for the system overall.
Within each of these different inverter types, there are many different manufacturers to choose from, each with their own benefits, features, and downsides.
As well as converting the DC electricity from the sun into AC electricity, the inverter also performs other important functions, these include:
Including batteries in a solar PV system allows the energy produced by the solar panels to be stored for use after the sun goes down. They are almost always required in an off-grid system (unless another backup such as a diesel generator is available), however, there are also several reasons you may want to include them in grid-tied systems too:
Charge controllers are used when you want to include batteries in your system (and when you are not using a hybrid inverter).
They control the power going to the batteries, and may also provide the following functions:
We hope this article has given you a solid introduction to solar PV systems and that you are now excited to dive further into the details. See below for recommended articles to read next, or check our menu if you are looking for something specific.
If you have any comments, or suggestions for additions to this article, please leave a comment below.
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Overview
Solar home systems (SHS) are stand-alone photovoltaic systems that offer a cost-effective mode of supplying amenity power for lighting and appliances to remote off-grid households. In rural areas, that are not connected to the grid, SHS can be used to meet a household's energy demand fulfilling basic electric needs. Globally SHS provide power to hundreds of thousands of households in remote locations where electrification by the grid is not feasible[1]. SHS usually operate at a rated voltage of 12 V direct current (DC) and provide power for low power DC appliances such as lights, radios and small TVs for about three to five hours a day. Furthermore they use appliances such as cables, switches, mounts, and structural parts and power conditioners / inverters, which change 12/ 24 V power to 240VAC power for larger appliances[1]. SHS are best used with efficient appliances so as to limit the size of the array.
A SHS typically includes one or more PV modules consisting of solar cells, a charge controller which distributes power and protects the batteries and appliances from damage and at least one battery to store energy for use when the sun is not shining.
They contribute to the improvement of the standard of living by:
Furthermore, SHS avoid greenhouse gas emissions by reducing the use of conventional energy resources like kerosene, gas or dry cell batteries or replacing diesel generators for electricity generation. Further impacts of renewable energies, such as SHS, can be found in the Report on Impacts.
Stand-alone photovoltaic systems can also be used to provide electricity for health stations to operate lamps during night and a refrigerator for vaccines and medicines to better serve the community.
Technical Standards for Solar Home Systems (SHS)
To assure the quality of a photovoltaic power system and its correct functioning and guarantee costumers' satisfaction, it is important that the components of the system and the system as a whole meet certain requirements.
The GIZ prepared a publication which gives an overview of different standardisation activities and existing standards that are relevant for solar home systems (SHS) and rural health power supply systems (RHS), titled Technical Standards for Solar Home Systems (SHS).
Planning, Installation and Maintenance of Solar Home Systems (SHS)
Before installing a photovoltaic (PV) SHS, its size has to be calculated according to different assumptions, such as measurement of solar radiation, solar insolation and power demand. Regarding the installation process, Solar Home Systems have to be installed by a trained technician who knows how to handle its different parts. Thus, aspects of maintenance and a solar technical training manual is presented: Planning, Installation and Maintenance of SHS.
Costs
Typical systems costs in the Eastern Africa region range between US$ 170 for a 12 Wp system and up to US$ 2,000 for a 150 Wp system. For developed countries the average cost per installed watt for a residential sized system is about US$ 6.50 to US$ 7.50, including panels, inverters, mounts, and electrical items. In Eastern Africa the cost is 2-3 times higher[1].
-> For more detailed information on SHS costs click here.
Project Examples
Featured Content)How Teddy’s Tailoring Business Was Re-ignited by Solar Lighting, provided by Fosera’s partner in Zambia VITALITE
After more than two decades spent building up a loyal customer base, Teddy Hangandu, a tailor in Lusaka’s Luangwa Compound, found himself falling into a slump.
If you are living in a house without power, work comes to a standstill once the sun goes down. But Teddy’s clientele wants their clothing when they want it, sun up or sundown. With this in mind, Teddy tried using paraffin lamps at nighttime, but this wound up costing him K50 (about 2.80$) a week on fuel.
These lamps also pose serious hazards;
Aware of these dangers and unhappy about spending money on fuel instead of more valuable activities, Teddy vented his frustrations to a friend. Luckily, his friend, a VITALITE customer, introduced him to the fosera SPARK – a product that is particularly adapted to the needs of people with limited or no access to grid electricity in Zambia.
The fosera SPARK, built on a Pay-As-You-Go basis, comes with three lamps that last six to eight hours when fully charged and three years warranty. Because of these extended hours, Teddy went from serving 10 to 15 customers a week to a booming business with 20 to 30 customers a week. He no longer turns away last minute clients and has increased his turnover.
Outside the long-term positive impact on the environment, the FOSERA solar system has helped Teddy save money. The increase in sales means he can better support and provide for his two orphaned grandchildren.
His advice for small business owners still reliant on candles and paraffin lamps is to make that switch and join the VITALITE family. He is no longer pressured to turn away clients or only work in daylight hours. He no longer worries that a clumsy grandchild might knock over an oil lamp and burn the house down. More importantly, the FOSERA solar system has and will continue to save him money in the future.
In 2018, Fosera Solarsystems GmbH & Co. KGaA, together with the Zambia-based partner company Vitalite, won the German Sustainability Award in the Corporate Partnerships category. The partnership between the two companies exists since 2013. Fosera develops and produces solar systems while Vitalite takes care of sales and service in Zambia. On the one hand, Vitalite benefits from the cooperation because it receives high-quality systems, customer-specific product developments and technical support. Fosera, on the other hand, receives direct feedback from Vitalite and the end customers on site. Around 120,000 Zambians are Vitalite customers and have gained access to sustainable and economical renewable energy through Fosera. Around 7,000 people in Zambia were even able to increase their income with the help of Solar-Home-Systems.[2]
Solar Home Systems in Peru
A rural household from the Andean region of Cuzco uses a SHS.
In Peru, a series of renewable energy projects have been implemented, predominantly using hydropower and solar photovoltaics (PV). Solar energy is a reliable source because it involves no moving parts, is easily applicable to the geographic conditions of rural populations, and relevant information is readily available.
About 21% of the population of the country is without electricity and the only way for these people to access it is if existing networks are extended or renewable energy projects implemented. Thus, the General Directorate of Rural Electrification (DGER) estimates that approximately 2.48 million people in Peru could be provided with electricity through renewable energy.
Photovoltaics have become, in recent years, a viable option for rural and isolated populations, because their electric generation costs have become competitive compared to other options, such as the extension of the conventional power grid or the use of diesel generators.
In the early 90s, the number of rural electrification projects in various countries, including Peru, increased significantly. The beginning of this new era in our country coincided with the formation of several initiatives, among which were those of the GTZ (now GIZ). In conjunction with the former Tacna-Moquegua-Puno Region, they promoted various applications of PV technology, trained locals and established funding mechanisms for the purchase of photovoltaic systems.
At the same time, the national government, through the Ministry of Energy and Mines (MEM), initiated their first pilot project in the town of San Francisco, Pucallpa, which involved the installation of 134 Solar Home Systems (SHS) of 53 Wp. This project was expanded in the following years to the point that they put into operation about 1500 SHS in various parts of the country.
Also, the MEM, with the Renewable Energy Center of the National University of Engineering (CER-UNI), promoted a pilot project, that offered credit for the purchase and installation of SHS, primarily to families living on the islands of Lake Titicaca. This included after-sales service for a year. Through this initiative about 500 SHS were installed. The MEM also implemented pilot projects to install photovoltaic and wind systems of 1 kW in community centers and health posts in eight isolated parts of the country.
The experience gained from these projects has served to improve the implementation of future PV projects, through the program “Photovoltaic Based Rural Electrification in Peru," funded by the Global Environment Facility (GEF), the MEM and in partnership with the United Nations Development Program (UNDP), which has led to the following:
The project facilitated the installation of 4200 SHS in the Amazonian regions of Cajamarca, Loreto, Ucayali and Pasco; they were later transferred to the Electrical Infrastructure Management Company (ADINELSA) for administration.
The Photovoltaic Rate:
Given the large number of SHS installed in various parts of the country, the Supervisory Agency for Investment in Energy and Mining (OSINERGMIN) established a fixed rate for photovoltaics.
This rate applies to electric generation between 50 and 320 Wp. However, about 80% of the users of this system receive state-subsidized rates, which have substantially improved the sustainability of the projects, as they are managed by governmental, non-governmental and private entities.
Finally, it is important to note that the solar energy market has generated about 14 million Peruvian Nuevos Soles (about 5.4 million dollars) between 2010 and 2011, either for the replacement of components or the implementation of new projects in both the private and public sectors.
In 2010 and 2011, public institutions, from the MEM to district municipalities, invested about 5 million Peruvian Nuevos Soles (about 1.9 million dollars) in new projects and it is expected that this year investment will continue to grow, bringing renewable energy to the forefront in rural areas, which will aid its development.[3]
Solar Home System in Rural Bangladesh
For information about the impact of solar home system in rural Bangladesh, see Impact of Solar Home System in Rural Bangladesh.pdf and Overcoming Barriers to Rural Electrification - Example of Solar Home System in Bangladesh.pdf.
Solar Home System in Nigeria
Nigeria is a sub-Saharan Africa Country. It has the highest number of people without electricity in the region. With the Solar home System, the number of people with a power supply has increased. The Federal Government of Nigeria through its Rural Electrification Agent Project has shown her commitment to the distribution of Solar Home Systems to reduce pollution and increase remote and rural electrification in the country. Partnership with solar companies in Nigeria has made the project impactful.
Solar Home System in Germany
So called "Balkonkraftwerke" (literally meaning: energy-producing systems for your own balcony) are small solar home systems producing electricity. Legal installation has been made considerably easier by a new VDE guideline in 2017[4] (which came into force in 2018). Since then, private users have been allowed to put systems into operation themselves as long as they do not generate more than 600 watts of power and register the system.
However, there are still legal grey areas that have not yet been finally clarified, e.g. whether the generated electricity has to be fed in via a special energy socket (Wieland) or whether a normal socket (Schucko) is sufficient.
Further Information
References
The article on SHS in Peru was originally published by EnDev Peru in the second issue of Amaray Magazine published in November 2012.
GTZ (2007): Eastern Africa Resource Base: GTZ Online Regional Energy Resource Base: Regional and Country Specific Energy Resource Database: I - Energy Technology
Solar Server (2018): Deutscher Nachhaltigkeitspreis für Fosera und Vitalite https://www.solarserver.de/2018/12/10/deutscher-nachhaltigkeitspreis-fuer-fosera-und-vitalite/
Peru: Amaray Magazine.
VDE (2017): Mini-PV-Anlagen: VDE|DKE bahnt Weg für sicheren Betrieb. https://www.vde.com/de/presse/pressemitteilungen/mini-pv-anlagen#
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