energy demonstration units
Similar to farming techniques, the area of energy presents a lot of opportunities for small, efficient and cheap energy solutions that could potentially save rural residents money in the long run and reduce their exposure to dangerous indoor air pollutants while keeping their houses and chicken coops warm. Relatively cheap and easily accessible electricity has been shown to transform rural communities in other parts of the world. It's time to apply the same principles to this area in Zimbabwe.
We will focus on solar energy on our site. In its simplest form, solar energy involves using a photovoltaic solar panel to convert the sun's rays into electricity, which is then either used directly used as DC current or stored for later use as DC or AC current.
In reality, things are a little more complicated than this. For example, if one connects the battery directly to the solar panel the charge coming from the panel may damage the battery if there is no way of regulating the amount of power going to that battery. Therefore, one needs a charge controller to protect the battery (see below). Some charge controllers allow you to also get some of the energy directly from the controller to appliances (bypassing the battery, to be discussed later).
PHOTOVOLTAIC SOLAR panels
As intimated before, solar energy is the energy source that has the greatest potential to solve the energy access and security issues in rural Zimbabwe. However, before it gains even more widespread use, residents must first understand the full scale to which it can be economically used. We intend to demonstrate solar energy use and related hacks and efficiencies at our site.
A simple off-grid solar system is made up of four components
The following videos show important aspects of photovoltaic panels in the areas of:
1. Sizing your system (11 mins)
2. What one can power with a 100W solar panel (7 mins)
3. Building a portable solar generator (8 mins)
4. Guide to living off the grid (47 mins)
5. Home batteries (28 mins)
6. How to build a solar panel (28 mins)
7. Sizing your solar panel and battery requirements (30 mins)
8. 12, 24 or 48V systems? Choices, choices, choices (6 mins)
9. Sizing a battery bank and the number of solar panels (22 mins)
10. How many solar panels do I need? (6 mins)
11. Difference between 60 and 72 cell solar panels (11 mins)
12. How much does a solar system cost in the US? (9 mins)
Here is how you would size a solar system for a residence in four quick steps. We will simplify this for rural residents.
The first part of your job is to determine the possible electrical load for all the electrical appliances and gadgets that could be in use in this cabin. The total possible maximum load at any one time is important in determining the size of the charge controller to be used in your solar system. The load over a period of 24 hours [I’d use 72 hrs, in case of rainy and snowy days]) is important in determining the number of batteries to be used and how they will be connected.
Now that you have determined the possible power withdrawal at any moment and the power requirements over a period of 3 days, let us try to figure out what type of charge controller to use. There are two types of charge controllers, but we will leave that discussion to another time. In most situations, one is advised to go with a charge controller that can hold 120 to 150% of the estimated total power consumption (the max).
Setting up your batteries is the next step. Here are a few things to remember when you connect batteries. Remember, you only have as much power as what is stored in your batteries. We will assume that using 350 Amp hour batteries that can reach 100 % charge. The most commonly used batteries in the US are 6V batteries. When you wire batteries in series the current stays the same but the voltage adds up. For example, four 6V batteries in series will have the same current but their voltage is 6+6+6+ = 24 V. if you wire batteries in parallel, you add up the current but the voltage stays the same.
For example, if you have 16 batteries that are set up in two sets of 8 (in series i.e. 48V and 350AmpH) and the two sets are connected in parallel (i.e. voltage stays the same but the amperage doubles), we end up with a 48 V DC volts set up that provides 700 AmpH.
To calculate the power rating of such a set up, you use Ohms Law
Power (W) = Current (Amps) X Voltage (Volts) = 48 x 700 = 33600 Watt hours = 33.6 kWH
Now, remember that you should not drain your batteries to 0% everyday. Let’s use a very cautious ratio of 30% as the amount you should drain your batteries before they have to be recharged. Based on the wattage you calculated in 1, you should be able to calculate the number of kilowatt hours you would need to use a day. Consider that to be 30% of the power you need in your bank. How big a power bank do you need (use simple proportion)? If you factor in the rainy days you may want to consider draining only 10% of your batteries. Do calculations for both and see just how different they are.
Some of you may have seen papers or videos that discuss 6V, 12V and 24V systems and may be wondering what the difference is among those systems. I like higher voltage systems because they are easier for the inverter to convert 48V to 120 V for AC appliances. However, the majority of DC appliances use a 12V supply, hence the popularity of those systems. Which reminds me, you must account for the power loss associated with an inverter (5 to 8%).
Determining the number of solar panels to use is the next task. Remember that the most common solar panels are either 12V, 24V or 36V panels. However, when you buy them you are usually going by the wattage. Also, the number of hours that each solar panel is actually charging the battery at 100% varies by location. Let us assume that our solar panels charge at full capacity for 6 hours (taking other losses into account). Remember to factor in a loss of about 20%. Try to determine the number of solar panels that will be needed to charge our battery bank and how they should be connected to our battery bank (series, parallel or a combination).
Winter temperatures in Mashonaland province dip down to below freezing regularly in late June and early July. This is especially exacerbated by the strong wind chills in July. Zimbabwean homesteads often have very cold interior temperatures due to the lack of heating systems. The result of this is that most people burn firewood and any other fuel source (as firewood is scarce during the winter just to stay warm. These fuel sources often lead to significant indoor air pollution without even guaranteeing warm nights for the residents.
Early morning and evening temperatures are also just as challenging. The aim of our project is to develop demonstration units using local materials that locals can use to reduce their dependence on scarce non-renewable resources.
Here are a few interesting videos that we have used for research:
1. Building a solar air heater from pop cans (8 mins)
2. Building a solar air heater with soda cans and a solar powered fan (35 mins)
3. Building a solar heater from aluminum baking pans and plastic for $35 (9 mins)
The next section is still under construction