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This page is for all those people having questions, doubts, technical demands ext. concerning the renewable energies world.

We will answer you by e.mail and the most interesting questions and answers will be published in this page.
We invite you to continue sending us questions. Go to "Contact us". Thank you.
[Photovoltaic] How do solar cells generate electricity?
[Photovoltaic] What components do I need for a grid-tie system?
[Photovoltaic] Can I use PV to heat water or for space heating?
[Photovoltaic] Where should I mount the solar modules and what direction should I face them?
[Wind] What is wind energy?
[Wind] What is a wind turbine and how does it work?
[Hydroelectric] Does water contain energy?
[Hydroelectric] Can energy be generated through water?
[Hydroelectric] What is hydroelectric power?
[Hydroelectric] How much water and pressure do I need for a small hydro system to work?
[Hydroelectric] How is hydroelectric power produced?
[Hydroelectric] What is the difference between small-scale and large-scale hydropower projects?
[Hydroelectric] How much energy can you gain from a given amount of water falling at a certain height?
How do solar cells generate electricity?

Photovoltaics or PV for short can be thought of as a direct current (DC) generator powered by the sun. When light photons of sufficient energy strike a solar cell, they knock electrons free in the silicon crystal structure forcing them through an external circuit (battery or direct DC load), and then returning them to the other side of the solar cell to start the process all over again. The voltage output from a single crystalline solar cell is about 0.5V with an amperage output that is directly proportional to cell's surface area (approximately 7A for a 6 inch square multicrystalline solar cell). Typically 30-36 cells are wired in series (+ to -) in each solar module. This produces a solar module with a 12V nominal output (~17V at peak power) that can then be wired in series and/or parallel with other solar modules to form a complete solar array to charge a 12, 24 or 48 volt battery bank.

What components do I need for a grid-tie system?
Grid-tie systems are inherently simpler than either grid-tie with battery back-up or stand-alone solar systems. In fact, other than safety disconnects, mounting structures and wiring a grid-tie system is just solar modules and a grid-tie inverter! Today's sophisticated grid-tie inverters incorporate most of the components needed to convert the direct current form the modules to alternating current, track the maximum power point of the modules to operate the system at peak efficiencies and terminate the grid connection if grid power is interrupted form the utility.

Can I use PV to heat water or for space heating?
No. Photovoltaics converts the sun's energy into DC electricity at a relatively low efficiency level (14-16%), so trying to operate a high power electric heating element from PV would be very inefficient and expensive. Solar thermal (or passive solar) is the direct heating of air or water from the heat of the sun and is much more efficient for heating applications than photovoltaics.

Where should I mount the solar modules and what direction should I face them?
If your site is in the Northern Hemisphere you need to aim your solar modules to the true south direction (the reverse is true for locations in the Southern Hemisphere) to maximize your daily energy output. For many locations there is quite a difference between magnetic south and true south, so please consult the declination map below before you setup your mount structure. The solar modules should be tilted up from horizontal to get a better angle at the sun and help keep the modules clean by shedding rain or snow. For best year round power output with the least amount of maintenance, you should set the solar array facing true south at a tilt angle equal to your latitude with respect to the horizontal position. If you plan to adjust your solar array tilt angle seasonally, a good rule of thumb to go by is latitude minus 15° in the summer, latitude in the spring/fall and latitude plus 15° in the winter. Most mount structures provide for a seasonal adjustment of the tilt angle from horizontal to 65°. To determine if your proposed array site will be shaded at any time of the day or year you should consider using the Solar Pathfinder.

What is wind energy?
In reality, wind energy is a converted form of solar energy. The sun's radiation heats different parts of the earth at different rates-most notably during the day and night, but also when different surfaces (for example, water and land) absorb or reflect at different rates. This in turn causes portions of the atmosphere to warm differently. Hot air rises, reducing the atmospheric pressure at the earth's surface, and cooler air is drawn in to replace it. The result is wind.

What is a wind turbine and how does it work?

A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy that can be harnessed for practical use. Mechanical energy is most commonly used for pumping water in rural or remote locations- the "farm windmill" still seen in many rural areas of the U.S. is a mechanical wind pumper - but it can also be used for many other purposes (grinding grain, sawing, pushing a sailboat, etc.). Wind electric turbines generate electricity for homes and businesses and for sale to utilities. There are two basic designs of wind electric turbines: vertical-axis, or "egg-beater" style, and horizontal-axis (propeller-style) machines. Horizontal-axis wind turbines are most common today, constituting nearly all of the "utility-scale" (100 kilowatts, kW, capacity and larger) turbines in the global market.

Does water contain energy?
Water, like many substances, contains two kinds of energy. The first kind of energy is called kinetic energy. This is energy that is used during the execution of processes, such as movement. Because of kinetic energy water can flow and waves can exist.
But water can also contain potential energy. This is energy that is stored in the water. Stored, but not used. This energy can become useful when water starts to flow. It will be transferred to kinetic energy and this will cause movement

Can energy be generated through water?
When water flows or falls, energy can be generated. The generation of energy through water is usually carried out in large water power plants, with a number of process steps and the use of several devices, such as turbines and generators. The energy in water can be used to produce electricity.

What is hydroelectric power?
Hydroelectric power is electricity that is supplied by generating energy from falling or streaming water. Hydroelectric power is a so-called renewable energy source. This means that the source, which provides the energy, can be renewed. This is because, unlike non-renewable energy sources such as crude oil, we will not run out of water fully. It can be renewed after we have used it for energy generation.

How much water and pressure do I need for a small hydro system to work?
In general, the more the better. Practically, you need at least 3 feet of fall with a 12 gpm water flow. If you have higher fall (pressure), you can get by with much less water.

How is hydroelectric power produced?
Hydropower is energy that comes from the force of moving water. Water descends rapidly from the top of a dam and flows through a pipe. The water then pushes against and turns blades in a turbine to spin a generator to produce electricity.

What is the difference between small-scale and large-scale hydropower projects?
Small-scale hydropower is usually 10 MW or less in size. One of the common definitions for micro hydropower is a rated capacity of 300 kW or less. The 300 kW limit is because this is about the maximum size for most stand alone hydro systems not connected to the grid, and suitable for "run-of-the-river" installations. Small-scale hydro is normally run of the river design and is one of the most environmentally benign energy conversion options available, because it does not attempt to interfere significantly with river flows. The break point between small-scale and large-scale hydro differs from country to country ranging between 10 and 50 megawatts (MW).

How much energy can you gain from a given amount of water falling at a certain height?
The basic elements required for a potential hydropower development are streamflow and an available drop, or "head", through which the streamflow can be used to convert the potential hydraulic energy into electrical energy. The power generated is represented by the equation:
P = eHQg
P = Electric Power Output in kilowatts (kW)
e = Efficiency range 0.75 to 0.88 (75% to 88%)
H = Head, in metres (m)
Q = Design flow, in cubic metres/sec (m3/s)
g = acceleration of gravity, normally 9.81 m/s/s
For small-scale hydroelectric applications, if an Efficiency value of 81% is assumed, the following equation can be used:
P (kW) = 7.95 x H (m) x Q (m3/s)