Tuesday, March 15, 2016

Off-Grid Solar Power in Botswana

Dumelang*. My previous post looked at the limited number of grid-connected PV systems in Botswana. There appear to be only three of noteworthy size (>10 kW) and a small number of lower power residential systems. In this post, I turn my attention to off-grid systems, of which there are many more throughout Botswana, but let’s start by reminding ourselves about the differences between grid-connected and off-grid systems.

In grid-connected systems, the electricity flow is one of three types:
  1. Outwards only, whereby power generated by the solar operation is fed into the electrical grid to supplement the power produced by other power plants, e.g., the Phakalane solar farm;
  2. Inwards only, where the grid just serves as a backup and feeds electricity into the system when insufficient solar energy is being produced, e.g., the 34 kW system at Scales Associates in Broadhurst, or
  3. Bidirectional, whereby excess power, over and above that used locally, is fed into the grid during the day, but during the night power is drawn from the grid, e.g., the University of Botswana experimental project in Mokolodi Village.
In off-grid solar systems there is no connection to the electrical grid and these installations are typically found on homes, on farms, in villages, or at tourist lodges in remote areas. Because these systems cannot use the grid for back-up electricity supply, they usually incorporate batteries so that any excess energy, produced during the day, can be stored for use during evening hours. Off-grid installations are sometimes combined with other means of electricity generation, such as diesel generators, that can provide backup power during cloudy conditions or when the batteries are depleted. These are referred to as hybrid systems.

Understanding these off-grid systems requires knowledge of the four key electrical components of the solar system: the panels, batteries, inverters, and charge controllers. In an earlier blog I provided some details on the functions of these components. The figure below shows key components in the basic layout of an off-grid solar system.

As I drive around Botswana, I see off-grid systems almost everywhere I go. They range from small single-panel systems providing a small amount of power for few lights or mobile phone charging, to multi-panel systems powering a home/ farm or a borehole pump, to large systems powering tourist lodges in the Okavango Delta. My research at the Clean Energy Research Centre at the University of Botswana is focused on these off-grid systems and particularly the battery-storage component. I am visiting these systems, chatting to the owners about the performance of the units, taking measurements, and collecting data.

As I have noted before, there has been a big push for installing solar systems in Europe, USA, and parts of Asia. These installations range from residential installations to large grid-scale systems of the order of 500 MW. Most folks in the US and Europe who are installing solar systems on their homes or business are installing grid -connected systems. The driver for the rapid rollout in these locations is purely financial. Electricity in these places is expensive and attractive subsidies for renewable energy are available. Only a small fraction of these new solar installations are off-grid systems and they tend to belong to hardy self-sufficient folks looking to live “off the grid” or owners of holiday homes and cottages located in rural areas that are far from the grid.

In the developing world, and here in Africa, off-grid solar is a whole other matter. In an isolated community where a grid connection is not possible due to distance or the cost of connection, energy options are limited. Many people live without power and rely on wood for light and cooking, or sometimes they use kerosene and candles. If they have a generator, they have to deal with the transportation and expense of diesel to keep the unit running as well as the maintenance of the engine. Off-grid solar systems are often the only viable way to bring electricity to remote homes, communities, businesses, and tourist facilities. Once solar is installed the fuel, sunshine, is free and maintenance is fairly simple and a lot less than that involved than that required for a diesel generator.

On the surface, off-grid systems appear to offer many advantages:
  1. The obvious one is that they are not grid-connected: they thus avoid long waits to get a grid connection and save on grid connection fees, which can range from as little as P5000 (~US$450) for residences located closed to the grid to hundreds of thousands of pula for locations far away from the main grid.
  2. Once the investment is made, the sunlight is free, which can significantly reduce the daily operating costs of the installation, However, as I will point out in a future blog, even though this is often a compelling reason for solar, it is a simplistic assumption. The correct analysis is to consider the upfront costs as well as the operating costs or the total lifetime costs.
  3. Solar is “green” and a more sustainable energy option and avoids the noise and pollution of a diesel generator as well as the logistics of trucking and transporting large quantities of diesel into remote areas. In fact, for many tourist camps and lodges this becomes an important part of the branding and selling point for their operations. Visitors can visit remote camps and enjoy the peace and quiet of the African bush, and still have access to their electronic devices and other modern conveniences, such as gourmet coffee, hairdryers, hot water, and air conditioning, without a noisy diesel generator puttering away and polluting the environment. I, for one, have stayed at one of these lodges and when it becomes necessary for an operator to turn on the diesel generator late at night when the batteries are depleted, the racket, after the quiet of solar power, can be quite jarring.

On the other hand, off grid-solar systems present a variety of problems:
  1. The upfront capital costs are high.  Solar systems are expensive, especially when compared with an equivalent diesel system. Moreover, the need for battery storage can often double the investment cost.
  2. Excessive heat is a problem for solar systems. In a previous blog, I noted that solar panel performance decreases as temperature rises, so the high ambient temperatures and the high panel surface temperatures can significantly decrease the expected output and even the life of solar panels. Similarly, battery lifetimes and performance are very temperature-dependent. Batteries do not like high temperatures and their lifetimes are considerably shortened in Botswana’s hot conditions.
  3. The output of a solar system is very dependent on weather conditions. The ideal conditions are cool sunny days; day after day of cloudy weather will seriously compromise the functioning of a solar system. After the sun goes down, the performance of the system is dependent on the installed battery capacity and operation of the battery bank.
  4. For large loads, large numbers of solar panels and batteries are needed, which means that a large amounts of space for their installation are required. In a space-constrained operation, say an island-based tourist camp in the Okavango Delta, this could present a problem.
  5. Unlike a diesel generator, every solar system is a custom built and the performance of the installation is very reliant on the competence and experience of the solar contractor.
  6. The lifetime costs of solar, which include the upfront investment cost, maintenance costs, and battery replacement, can be high especially when compared with grid-supplied electricity.
I have visited a good number of off- grid solar systems in Botswana, ranging from single-panel systems to large multi-panel installations with massive battery storage and have learned a great deal about the performance of these installations in general. Here are some of my findings:
  1. There are a lot of off-grid solar of different scales and sizes scattered through Botswana. These range from 50 W single-panel systems used for cell phone charging and a few lights to 100 kW multi-panel systems at lodges in the Okavango Delta.
  2. The solar portion and electronics are, for the most part, robust and work well. However, panel degradation has been seen in some cases. I have seen panels with cracks in the glass which have allowed in moisture and I have seen panels with a distinct browning of their appearance. See the photos below. The browning is due to the degradation of the organic material (ethylene vinyl acetate) that is used to encapsulate the individual solar cells in a panel. This degradation is accelerated at high temperatures and by high solar irradiation – both of which are plentiful in Botswana.
  3. I am surprised at how many non-functioning systems I have found. Often times, systems have been donated to communities that benefit initially from the installations. This is then followed by years of a lack of attention and post-installation follow up. As a result, three to five years after installation, the systems are no longer working. In some respects, this is a typical development problem – well-intentioned donors donate systems which are installed and are just left to community to run. Insufficient thought is given to developing local expertise or training nor is any provision made for follow up.  Years later, when problems occur, there is nowhere for the community to turn to for repairs and, as a result, systems, which initially provided a benefit, sit idle.
  4. There is a lack of branding with solar systems and little public knowledge as to what to constitutes quality for these installations. Solar systems are built from a number of components and purchasers are reliant on the design expertise of their solar contractor and the equipment choices those contractors make. It is unlike buying a car where, if you pay a lot of money for a Mercedes, you can be sure you are getting the benefits of great German engineering, quality components, and great after-market service. With solar power, there is no single Mercedes brand – you are reliant on your vendor making the correct design and component choices for you. I will note that many solar vendors, concerned about their reputation, will make the correct choices; however, as with cars, watches, and many other consumer goods, you get what you pay for. Buying cheap components or trying to save money by installing fewer panels or batteries will result in an inadequate solar system.
  5. Load creep is a problem. Often a system is designed for a specific load, say on a farm, to run lights, a fridge, a TV, and a borehole pump. Over the years, more electrical devices are purchased, such as a second TV, more lights, a freezer, a printer, etc. As result, the electrical load grows and, after a number of years, the system is inadequately sized for the demands placed on it.
  6. Many folks, ranging from individuals, to businesses, to high-end tourist lodges, are to varying degrees disappointed in their installed solar systems. The solar systems initially appeared to provide an elegant, sustainable, quiet, non-polluting alternative to a diesel generator. Invariably, the disappointment is associated with the inadequacy and shorter-than-expected lifetimes of the battery-storage systems.
  7. The Achilles heel of just about every system I have visited are the batteries. The battery life is generally half, or even less in some cases, of that expected. This seems to be result of:
      • Poor system design and insufficient solar panel output;
      • Lack of battery maintenance;
      • High operating temperatures;
      • Greater draw on batteries than originally planned.

Many of these problems can be overcome by the correct design, the right components, and spending oddles of money for both, which bring us to the fundamental problem that plagues solar systems: high upfront costs. In my next blog, I will take a closer look at this problem and dig into a comparison of the lifetime costs of solar vs. diesel.

Until next time, remember to turn off the lights when you leave the room. 

Tsamayang Sentle**
Mike Mooiman

(*Greetings in Setswana)

(**Go well or Goodbye in Setswana)