Your Questions About Most Efficient Solar Panels Available

Henry Dover answers:

Hi there.

Here is some useful info for you.

Solar Power, An Introduction
Solar panels or modules convert sunlight directly in to D.C. Electricity. This is a semiconductor process within the silicon cells. The light energy is transferred to electrons where it is available as electricity, from this you will see that the output is dependent on the amount of light energy falling on the panel. Temperature has an effect but is negligible in comparison. Panels are usually designed to charge a battery of 12volts, during charging a higher voltage of about 14volts is required to force a charge in to the battery. A panel will have a voltage of about 20volts with no load. When the panel is connected to the battery a charging current will flow in to the battery causing the panel voltage to drop to the battery voltage of 12-14volts. Panels can also be connected in parallel, this increases the power output by adding together current produced by each panel.

The power output depends on the weather, siting of panels and many other variables – therefore exact figures are very difficult. From experience in clear sunny weather an output peak of about 80-100% of the panels rated output power can be expected. An average of 50% over the day can be improved upon by moving the panel to track the sun. As it is difficult to define light levels without expensive equipment, a guide to when panels begin to charge the battery system is that dark and grey clouds remove the direct light that the panels require to give a useful output, white clouds allow enough direct light to pass through. Overcast days will usually produce sufficient to overcome battery self discharge.

Solar Regulator
A regulator/charge controller is required when the maximum current in to the battery exceeds 10% of battery capacity in Amp hours. Use of a regulator/charge controller will prevent over-charging of the battery, and is essential with large panels or when using small capacity batteries. If the output of a solar panel is less than 10% of the battery capacity a diode may be used instead of a regulator. When the panel is able to supply power to the battery, the diode lets it through, when the panel cannot supply power (at night or in bad weather) the diode prevents the battery discharging back through the panel. Fuses should be used as a safety measure, and fitted as close to the battery as possible.

Panels can also power equipment directly, these should be loads such as fans and pumps, not voltage sensitive equipment like televisions, radios etc. When using solar power to charge a battery, equipment can be connected and used at the same time, the battery will stabilise the voltage.

Types of Solar Cells
Essentially four solar cell technologies are available commercially:

Single Crystal Silicon (Mono-Crystalline)
Cells are sliced from a pure crystalline silicon ingot.
(~15% conversion efficiency).

CIS (Copper Indium Diselenide)
Representing the latest development in Thin film technology solar cells. Approximately 11% efficient.

Poly-Crystalline or Multi-Crystalline Silicon
Molten silicon is poured into a mould and then sliced into cells. Now the most efficient technology (~16% conversion efficiency).

Amorphous Silicon
Commonly used in toys, calculators and consumer electronics. Thin film technology, inexpensive but least efficient alternative (~8% efficient).

What size of panel do I need?Required for 12 Volt Battery Charging (ideal conditions).

This depends on the size of battery you have, the amount of power you use and the amount of light available each day. In power terms we measure the amount of energy consumed in amp hours. A 1 Amp draw over 2 hours is a total of 2 Amp hours (AHr) of current.

Determine the number of Amp hours you will use to run your electrical equipment in one day such as lights, TV, Stereo. If you divide the wattage of the equpment by 12 this will give you an approximate Amp per hour rate.

E.g A typical 15″ LCD Television rated at 36 watts uses approximately 3 Amps per hour.

The maximum current available from a solar panel is given by dividing the panel Wattage by 17.

E.g. A 75 Watt solar panel will give a maximum charging current of: 75 divided by 17 = 4.4 Amps per hour.

Where possible it is a good idea to reduce the amount of energy you consume our low power TV’s and Low energy Lights are good solutions.

Henry Dover answers:

Silica based solar cells are not the kind of thing you whomp up in you basement.
Here are a couple ideas for solar systems you can build and install yourself.

Take a 4 x 8 sheet of 1/2 inch plywood. Frame sides with 2 x 4′s. Screw tin cans in a staggered row (checker board) pattern inside frame. The more cans the more heat you get so place them nearly touching. Paint cans and entire assembly flat black. Cover top with glass, plexiglass (best) or heavy mill clear plastic (cheapest)Place on roof. Drill 3-4 inch holes in opposing sides. Run pipe or tubing into house. Attach to small low speed fan.
The black paint will absorb sunlight and heat. The air moving through box will carry heat into house. It’s a cheap efficient way to help heat your home. You can vary size and shape of box to fit your roof. If you use more than one box, hook them up in series. More boxes mean more surface area means more heat.

To heat water. Take a steel tank. A car gas tank works well. It is galvanized so it won’t rust, is cheap, and easily available at any auto salvage yard. But you will have to flush in throughly to remove gasoline odor. A steel 55 gallon drum is easier to work with but may cost more. Paint exterior of tank flat black. Weld/glue/clamp water pipes to tank. Place on ground in area that gets lots of sunlight. Attach water supply to tank and route discharge pipe to house or appliance. Black painted steel absorbs heat from sun light and heats water. In spring and fall you get warm to hot water. In summer you get scalding hot water and in winter you get cold to luke warm water.

Both of these solar powered systems are seasonal and their output varies according to location and climate, but they are very inexpensive and easy to build and provide FREE heat and/or hot water for many years with little or no maintainence.