Take charge of your power needs, Part 1: Solar Energy as an alternative to centralized energy systems

How to design a solar system

Currently, in South Africa the centralized electrical grid is unstable and has led to the current reality of regular power outages; subsequently many people are considering solar as an alternative. We are blessed with abundant sunny days making solar very reliable without the need for a lot of backup storage in the form of batteries. These equations shift depending on where you live, however even countries like Germany which is not as blessed with as much sunshine, place a large emphasis on solar technology as part of their energy solution. Whether you live connected to the electrical services grid, or off-the-grid, there are compelling reasons to use alternative sources of energy.

This post will give you a basic understanding of how solar energy works and the components of the system. If you have no experience in electrical energy at all it may seem a little daunting, however the math is really simple and with a little practice it’s as easy as ABC.

Consider these four reasons for going off-the-grid:

  1. Solar is no longer more expensive: While the costs of grid electricity continue to rise, the cost of solar continues to fall.

When I began using solar 16 years ago a 75 watt panel cost R 3000. Now the same panel is less than R 1000 and that is not even accounting for inflation. This is a trend that is set to continue and in South Africa the cost of energy from the sun and the cost from the power utility have reached the same level. As costs of centralized large-generation capacity gets ever more expensive, be it from nuclear, coal or gas, the costs of alternative energy continues to fall. This is partly due to the fact that conventional powerstations rely on energy that is finite and as the resource gets depleted so the costs rise. Alternative energy relies on a source that is infinite and not linked to commodity prices. There is no cost for the energy from the sun, or wind or flowing water, the power of waves, geothermal energy and numerous others. As our technology develops and improves so does our ability to take advantage of this abundant sun-driven energy.

  1. Alternative energy pollutes less.

While it is true that there is no form of energy that produces no pollution, because the components of alternative systems need to be manufactured often from industries such as mining, or require heavy energy inputs in their production phase, they generally require little input later. Compare this to a coal fired power station which continues to pump black smog into the air for its entire life; or a nuclear power plant that produces toxic waste for which we have no realistic solution. Currently a solar panel produces five times less pollution over its lifespan than conventionally produced energy.

As an aside, the term ‘green’ has become very trendy these days and is often used to describe how an appliance or technology performs energy-wise. However, what these manufacturers fail to take into account is the energy required to manufacture and run these appliances and technologies, which are often not very sustainable.

  1. We can play our part.

While many of us try to do our bit by recycling, using the car less or growing veggies in the garden, the larger issues of global warming seem out of our grasp. Providing your own cleaner power is a powerful way to create change.

  1. You become less reliant on systems that seem to be becoming increasingly fragile.

The classic idiom of don’t put all your eggs in one basket is never more true than when referring to power. Being dependent on a central power source is not very powerful at all, decentralizing your power supply and potentially producing some of it at home is the way forward. Power outages are becoming more frequent and at the same time we are becoming ever more reliant on energy. A war with Russia would cut off gas to Europe, or conflict over oil will push up prices further. These conflicts will continue as there is a rush to grab what is left and companies try and leverage large profits from consumers, often manufacturing a crisis to drive up prices. Unfortunately fossil fuels have become a political tool in an increasingly manipulated market.

A basic overview of how electricity in a solar system works

This short section will give you a basic understanding of commonly used terms and will help you to understand the components of a solar system.

First, keep in mind this simple equation and these three definitions: Volts x Amps = Watts

Watts is what does the work and is a measurement of the work done in one hour.

Volts is the force field.

Amps is the flow of current.

Let us say a kettle uses 1000 watts. If you are using a 12 volt solar system, using the equation volts x amps = watts / 12v x 84 amp = 1000 watts, you would need 84 amps.

If you are using 220 volts which is what our power utility provides then you would need 4.5 amps to do the same work (220v X 4.5 amp = 1000 watts). Your power utility needs fewer amps to do the same work, but this is made up for by the higher volts and the energy consumed is the same.

Voltages vary depending on how far they need to travel and the equipment used to generate them. Your power utility needs to use higher voltages to overcome transmission loss over distance, 220 volts locally and as high as 30 000 volts to move electricity long distance to minimize power loss. 12 volts don’t travel far at all without the voltage dropping. People often opt for 24 or 48 volts at home for solar to overcome the loss associated with 12 volts.

Below are more in-depth descriptions of ‘Resistance’, ‘AC-DC’ current and ‘Storage’, as well as the various components of a solar system, following which I discuss my own solar system as an example.

Resistance

All materials, from chalk to the air around us, have resistance to the flow of electric current. Materials either have greater or lesser resistance and resistance can always be overcome. Even materials that are seen as good insulators will allow current (amps) to flow given a high enough force field (voltage). Lightning moves through air because the volts are super high and is thus able to overcome the resistance to its transmission through it. Copper is generally used for electricity because it has a low resistance; it can be drawn into a thread and is easily available, although at a cost to the environment.

Resistance leads to heat which is why some materials will never transmit energy, because they will burn up before they can carry any current. The light bulb is a good example of this. It was only made possible when a material was found with high resistance and that generated heat as light, but did not disintegrate as a result. A very rare find. A specific type of bamboo did the job and we have modern lighting!

Because copper has a low resistance low voltages are needed to overcome the resistance that it does have, 12 volts will move through it. The lower the volts the higher the resistance of a material and the more power loss there is as a result of the generation of heat. Which is why electricity is more efficient at higher volts, there is less power loss due to heat. 12 Volt power, when moved over distance, looses more energy than 220 volt power because at lower volts there is higher resistance and therefore more heat generated. The thickness of copper wire dictates how many amps it can carry and copper wire is rated in amps. What this means is that a 10 amp rated copper wire can carry a maximum of 2 200 watts at 220 volts, but only 120 watts at 12 volts. You will need thicker higher rated copper wire to do the same work when using lower voltages otherwise the wire will exceed its rated carrying capacity in amps and burn up.

Other materials such as gold have an even lower resistance and are used in computers and headphone jacks because they do not resist the flow of current at even lower voltages. They will also generate less heat, so they are good in laptops.

So it is volts (force field) that allows the resistance of a material to be overcome and allows the electrons (current or amps) to be bumped down the wire without too much heat being generated.

AC and DC energy

Alternating current (AC) is what you find in the power mains from a power utility. AC has a positive and neutral. Direct current (DC) has a positive and negative and is the power we find in a battery. In AC, the positive and neutral alternates 50 times per second in a sine wave pattern, at 220 volts (50 megahertz). You also get a step wave and a square wave, a sine wave is the best and smoothest of the three, followed by a step wave.

Diagram

Batteries and the energy they store, series and parallel

To understand how batteries store power we need to use the example of a standard solar battery of 105 amp hours at 12 volts. The force field of the battery is 12 volts and it holds 105 amps. In practical terms this means the battery holds 1260 watts. (12 volts x 105 amps = 1260 watts.)

Remember watts is a measurement of energy used in one hour. So if you boil a 1000 watt kettle for one hour all the power will be more or less gone, you would have consumed 1000 watts. If you only boil a kettle for 15 minutes then you only consume a quarter of an hour’s worth of watts or a total of 250 watts so your battery still holds more than three quarters of its power.

A 12 volt battery’s voltage ranges from around 13.5 volts to 12 volts at which time it is considered flat. This occurs at about 60% drain so the last 40% is not available to you, certainly not without damaging the battery. So what they call a 105 amp hour battery is really a 63 amp hour battery and holds 756 watts and not 1260 watts, enough time in reality to boil a kettle for 45 minutes.

If you wire batteries together in parallel you increase the amp hours stored and the voltage remains the same.

If you wire batteries in series the voltage increases while the amp hours remain the same.

-2 x 105 amp hour batteries at 12 volt wired in parallel = 210 amp hours at 12 volts = 2520 watts

– 2 x 105 amp hour batteries at 12 volt wired in series = 105 amp hours at 24 volts = 2520 watts

-3 x 105 amp hour batteries at 12 volt wired in parallel = 313 amp hours at 12 volts = 3780 watts

-3 x 105 amp hour batteries at 12 volt wired in series = 105 amp hours at 36 volts = 3780 watts

The higher the voltage the less transmission loss over distance because there is less resistance.

Batteries wired in series, parallel, series and parallel.

Batteries wired in series, parallel, series and parallel.

Components of a solar system

Batteries: dealt with in detail above.

Solar panels: Generate current from the sun and are generally 12 volt, rated in watts, and can be wired in series or parallel.

Regulator: Takes direct current from the solar panels and ensures that the batteries are fully charged and ensure a long life. The regulator will also not allow the batteries to be discharged to the point that they will get damaged.

Inverter: Takes the power from the batteries through the regulator and inverts it from direct current (12 v, 24v, 48v DC) to alternating current 220v.

The solar system I use at home

At this stage it is perhaps best for me to explain my own solar system and the reasons for why it is how it is. It is often the case that systems evolve over time rather than implemented in one go. Unlike conventional power systems that have monthly costs solar systems need to be paid for upfront and typically costs are recovered over a five year period, although the time taken for this to occur is getting shorter. Most of us do not have the finances to implement a system in one go and so build them over time. It is only recently that I have reached the point where I am meeting all of my perceived needs. Living in an area where there was no chance of a connection to a national grid, I have had to do without or manage what energy I had very carefully.

My system is split into several parts, firstly lighting, this is run off one 12 volt, 80 watt panel and one 105 amp hour battery, using efficient LED lighting. The lighting itself is 12 volt DC so there is no need to invert the current, leading to a simpler system less prone to failure. If we had 10 hours of sunshine with an 80 watt panel this would translate into 960 watts. An average LED light may consume as much as 5 watts. This would mean that enough energy is generated to run one light for 192 hours or exactly 8 days. This more than meets all of my lighting requirements and is a stand-alone system. There is no chance of the power running out for lighting even if there is persistent bad weather. I consider lighting to be the most important part of a system so its stability should be guaranteed. Having long ago lived with candles and smelly paraffin lamps with poor light to read with, it was an absolute joy to free myself from that continuous cost.

Secondly, one 80 watt, 12 volt panel with a 105 amp hour battery panel running the internet and an alarm system. (Yes, unfortunately we need one if you would like to come home to your computer, shoes and furniture.) Like lighting this system needs to be as stable as possible, as both communication and security are vital as we live in an isolated unpredictable environment, with the internet our only form of communication. These systems run directly off 12 volts so there is no need to invert the power.

Thirdly, two 110 watt panels wired in series to give 24 volts stored in two 105 amp hour batteries for an efficient fridge, the latest addition to our family. There is again no need to invert the power as the fridge accepts 24 volts DC, leading to an uncomplicated system. Again there is no chance of running out of power even in persistent bad weather.

Lastly, numerous types of panels I have collected over the years wired in series and parallel to provide 36 volts and 600 watts. (This voltage is historic as at the time I began it was common so I have stuck with it. Now common voltages are 12, 24, or 48.) They are controlled with an MPPT regulator so it can make sense of the different panels. An MPPT regulator has a microprocessor that checks the peak voltages to maximise the efficiency of the charge with minimal power loss. It is particularly useful if you have many types of panels as they will give slightly different voltages and have different peaks which the MPPT regulator is able to recognise and compensate for. The energy is stored in six, 6 volt batteries wired in series and parallel (two , six volt batteries wired in series to increase the voltage to 12 volts, replicated three times and then the three twelve volt pairs wired in parallel), giving us a total of around 400 amp hours at 36 volts. This energy is inverted to 220 volts through a 1000 watt pure sinewave inverter to provide our mains electricity.

It is important to note here that we don’t rely on as many appliances as a typical household. We have a solar geyser and various ways of cooking, including a wood stove, rocket stove, gas and a solar oven. Our mains power is used for a washing machine, computers, juicer, stick blender, slow cooker and a printer. We don’t own a TV. It is those appliances like stoves, ovens, kettles, toasters, geysers and irons that generate heat that consume the most power. Over the years I have collected an assortment of tools and gadgets that work with the inverter and are of high quality so that they do not put undue stress on the inverter. Most of my tools are small so they can run directly off the mains without the need to start a generator, which is in any event itself only 1000 watts.

The generator can be used on its own or can be used to charge the systems above and the current can be drawn through the inverter or directly from the generator, depending on my energy needs at the time. For example if the batteries are low and I need the drill for a few moments here and there it does not make sense to use the generator on its own because most of the time it will be running with no draw. In this instance it is better to hook it up to the batteries and use the inverter to supply the current so that batteries can be charged as well as run the drill, making for a more efficient use of energy.

In conclusion, solar systems that evolve over time develop their own character that suits the usage patterns of the homeowner like a glove and they will, by design, all be different from one another as well as being more stable. If any one part of a system collapses it does not lead to the failure of all the other parts of the whole.

It is an empowering feeling to be in control of your energy needs and it creates an awareness around its use. We are disconnected in our everyday lives from the source of some of our basic needs such as food and water. We are mostly unaware of where our food comes from and as a result overindulge and waste this precious resource. In just the same way as we would show more respect to what we ate if we grew it ourselves, we would show more respect to other resources including energy, if we were responsible for our own needs. We will discover that we tread on the planet with a kinder footprint.

In my follow-up post on solar energy I will show you how to calculate your power needs and enable you to design a system that will suit your very individual needs.

7 thoughts on “Take charge of your power needs, Part 1: Solar Energy as an alternative to centralized energy systems

  1. Thanks Peter for this amazing information . We moved to our house on the farm a month ago(no eskom) and started to install a very small solar system. I loved your idea to put lights on DC separate . We would like to try the same, we have 125w solar panel 12v available , i’d like to know:
    1. what type and how many amps of regulator/charge controler do we need for lights system like yours(or maybe what do you use) and
    2. what type of the battery is the best for this(you use 105amps).
    blessings Julia

  2. Pingback: Take charge of your power needs, Part 2: How to design your own off-grid solar energy system |

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s