Frequently Asked Questions

Frequently Asked Questions

Q. What is the difference between "photovoltaic solar generated electricity" and "solar thermal heating"?

"Photovoltaic solar electricity generation" and "solar thermal heating" involve two fundamentally different technologies, but both rely on the conversion of energy carried by solar radiation (sun light).
On a sunny day, sun light delivers a powerful stream of energy to the tune of 1 kW per square meter.
  • "Photovoltaic solar electricity generation" involves the one step conversion of radiation energy to electrical energy. The technology required is based on the physical properties of semi-conductor materials like silicon and others.
    The conversion efficiency is approximately 17%, i.e. the amount of energy that can be "harvested" from the sun's radiation is only about 17% of the energy carried by the radiation.
  • "Solar thermal heating" on the other hand involves a one step conversion from radiation energy to thermal heat. The technologies vary from large scale thermal power plants to household sized Solar Water Heaters and Solar Stoves where radiation is collected and absorbed resulting in the generation of heat.
    The conversion efficiency here lies much higher at 70%. Hence it follows that it is extremely inefficient to heat with solar generated electricity.


Q. What does "photovoltaic (PV)" stand for?

The term "photovoltaic" comes from the Greek phos meaning "light", and the name of the Italian physicist Volta, after whom the volt (and consequently voltage) are named. It means literally of light and electricity.
Photovoltaics describes both the technology of solar cells, and also the field, discipline, and approach of creating electricity that is made possible by solar cells.
The "photovoltaic effect" is the basic physical process through which a solar cell converts sunlight into electricity.


Q. What is the difference between a) a PV (Solar) Module, and b) a solar thermal collector of a Solar Water Heater?

  • A PV (Solar) Module is made up of an array of photovoltaic (solar) cells, embedded between a multi-layer back sheet and a special high transparency glass. The PV cells form the basis of the technology that allows the conversion of radiation energy to electrical energy.
  • A solar thermal collector of a Solar Water Heater in its simplest form can be a black plastic pipe filled with water and exposed to the sun. Today sophisticated collectors however, consist of an efficient multiflow absorber containing the liquid. They are covered by special glass with a minimum radiation transmittance of 94% and are well insulated.


Q. What is the difference between an open circuit and a closed circuit solar water heating system?

Open circuit: Potable water is heated by the sun in the collector and is then stored within the tank. The water continuously circulates through the collector and the tank due to the thermosiphon principle. www.emcongroup.com
SOURCE: Code of Practice and Register of Products
for Namibian Solar Energy Technologies




closed circuitClosed Circuit: The potable water is stored in the tank which is surrounded by a jacket that is connected to the collector(s). An anti-freeze liquid is heated by the sun, and again continuous circulation through the jacket and the collector is "powered" by the thermosiphon principle. The heat is transferred from the hot liquid in the jacket to the potable water in the tank.
SOURCE: Code of Practice and Register of
Products for Namibian Solar Energy Technologies


Q. How much does a Solar Water Heater cost, what do I get and what is the break-even point?

Depending on the size of a single household system (storage tank and collectors) and the installation, a SWH will cost anything from N$14,000.00 to N$22,000. 150 Litres to 200 Litres storage are usually sufficient for 3 to 4 people. The storage tanks can also be fitted with an electric element for supplementary heating.
The break-even point between a solar water heater and an electrical geyser currently lies between 5 and 7 years under Namibian conditions. Thereafter the SWH will not cost you a cent, whereas you will still be paying for the electricity consumed by the electrical geyser.


Q. How much do Solar (PV) Systems cost, what do I get and what is the breakeven point?

Small standard home systems cost between N$5,000.00 and N$30,000. Larger farm and lodge systems are individually sized and will cost anything from N$100,000.00 upward.
The basic components of a solar system are a PV array, a battery array and a solar charge regulator.
According to the customers needs, these components vary in number and size and inverters, chargers and control electronics might be added.

  • Advantages
    A Solar Power Supply System is reliable, silent, clean and requires low maintenance. No more (or less) transport of fuel for a generator is necessary. PV panels come with a warranty of up to 25 years. 
  • Disadvantages
    Unfortunately energy has to be stored in batteries for night time use and most heating appliances, high powered tools as well as inefficient devices are not suitable for use in small and medium sized systems.


Q. How strong must my Solar Electric System be?

To answer this question we need a list of appliances and lights you want to use. This determines the power of the system. Then we need to know how many hours per day the items will be used and if they are used every day. This determines the energy required. Please note that lights and information technology require small amounts of energy, refrigeration uses medium amounts of energy while heating/cooking appliances are often beyond the capabilities of home systems.


How can I reduce my electricity consumption?

  1. Use Compact Fluorescent Lights (CFL)

  2. Use Solar Water Heaters

  3. Buy only energy efficient refrigerators (energy class A+ and A++)

  4. Place your refrigerator in a cool place, open sparsely and let goods cool down outside first

  5. Reduce Cooking/Cooling/ swimming pool cleaning

  6. Cooking and space heating by alternative means: Gas, Wood, Solar etc

  7. Cool and heat you house naturally: Roof over-hang and North-facing Windows

  8. Make use of intelligent night-time/day-time ventilation

  9. Use evaporative cooling or use fans

  10. If you want to help preventing power cuts: run your washing machine/tumbler/dish washer/swimming pool pump during night time between 22:00 and 5:00 in the morning.


Q. How can I finance my SWH, SHS, PV pump?

Affordable loan facilities are available from the ministry of mines and energy, administered by Konga Investments (konga@mweb.com.na) as well as Bank Windhoek, where you can contact Pieter van Vuuren at 061-299 0380.


Q. How long do PV modules last?

PV modules are designed to last about 30 years. They come with a warranty up to 25 years.


Q. When do I break even when I use Compact Fluorescent Lights (energy saving bulbs)?

For generating the same amount of light, a CFL requires only 20% of the electricity required by an incandescent light bulb.

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