Solar Thermal

At home we need Hot water for bathing and washing.
Industries require hot water for various processes including space heating and climate control.

Solar Hot water systems are the best choice for domestic as well as industrial use.  They are more efficient when compared with Solar PV in converting the suns energy into useable energy.

A typical Domestic hot water system consists of a Solar Thermal Panel (1, 2, 3 or even 4 panels are used for a single system).  The other important component is the Solar Tank.  This is where hot water is stored.  It is thermally insulated and is the equivalent of a Battery in a PV system.

Although there are two basic types of Panels - Evacuated tube type & Flat Plate type - the Flat Plate Collector is more commonly used.

Each Panel is approximately 2 square Metres.
It generates the equivalent of 5 KWh of electricity on a typical Sunny day in most parts of India.  (The generation will vary by geography & season).
If we compare this with a 2 square metres of Solar PV panel; a PV panel generates about 1 KWh of electricity.

My first 'to be' crowdfunded project

Low Voltage DC Lighting

12V DC & 24V DC LED lights

LED Lights that can work off a Standard Car battery is an attractive proposition.  We have created a few designs on 12V as well as 24V DC.

It is important that LEDs are driven with a constant current.  An LED is a current driven device. That is it will light up to its given intensity when the rated current flows through it.  Its colour rendition will also be specified at that current.

Anything above or below the rated current two things will happen.
  1. The intensity will change, as will be the efficacy i.e. lumens/watt
  2. The Colour temperature will shift and you may not get the white light that you expect.
What is the role of voltage?
Once you ensure a constant current (we will see how we can achieve that later), we can then measure the voltage across the terminals of the LED.  This voltage should be in a range specified by the manufacturer.  For White LEDs it is usually in the range of 2.9 to 3.5 Volts.  Whatever the current you deliver this voltage will remain more or less close to these values.

That is precisely the reason that you should not directly apply a voltage source to an LED.  Let us assume your LED voltage (Called the forward voltage) is 3,2 Volts, and you apply say 13.2 Volts (a normal lead acid battery voltage) to it.  What will happen?
As noted the voltage across the LED terminals cannot increase significantly.  Let us assume it remains at 3.2 volts.

Now 13.2 - 3.2 =10.5 is the voltage that should be dropped somewhere else in the loop.
This is what will be dropped by the internal resistance of the battery.  Since the value of such a resistance is very small the resultant current which is 10.2/R will be huge.  This will burn out the LED.
Of course, this is an extreme case.  However, in reality for even a 4 volts put directly across an LED, excess current will flow through the LED and shorten its life.

Hence: The requirement of a constant current source for the LEDs

Below is a simple circuit which achieves this in a DC circuit.
And here is the board if you want to fabricate this PCB

Rail Stations to be LED lit

Virgin Trains: LED lighting at stations is as much about customer satisfaction as it is about energy

.............Virgin is refraining from installing high levels of intelligent lighting system in which, for example platform lights would remain off when not needed, and turn on when sensors detect people on the platform, because such systems could confuse train drivers........Click the link to read more.

Solar Lighting for Rural & off-grid use

Tata Power has started selling its PV products through snapdeal.
Here is the link to a product I have known for a while.

It is a robust system and should last years.  The light is of the CFL type. The lamp is actually a 4 Pin PL lamp which is more efficient than the traditional 2 pin variety.

A 4-Pin lamp uses a pre-heat technology for firing the lamp, and hence has a much longer life.  It also prevents blackening of the lamp at the electrode ends.

Tata Solar Venus 200 C - Home Lighting System