The Vesta can be used all day everyday there is sun. By the end of this page hopefully all the ideas are in place to imagine finding uses for all that energy Vesta.
To understand what the Vesta can do we must consider 6 things:

1 - Free Energy
2 - Temperature
3 - Power
4 - Efficiency
5 - Location
6 - Uses

Free Energy

Since sunlight is free (for now), once a Vesta is built it provides free energy. So, a straight comparison to other stoves and ovens is misleading. A gas or wood stove consumes energy, a Vesta produces energy, which is a very important difference..

Made of steel a Vesta can last about 20 years with regular maintenance by the user.

At 1800 Watts if the machine is used 6 hours in one day, it would produce about 10 kilowatt hours. At a rough estimate of 10 the Kilowatt-hour that’s 1 Euro of energy generated.

If a Vesta earns about a Euro a day, that’s 365 Euros in one year and 7300 Euros in 20 years, much more than the cost of building the Vesta. If a Vesta earns or saves 25 Euros a day by creating an opportunity that wouldn’t otherwise exist, let’s say in tourism, that’s 9125 Euros in one year and 182 500 Euros over 20 years: far, far more than the initial cost of the machine.

Because the Vesta does not depend on electricity or gas, it can go where electricity and gas cannot, and so the possibilities are out there.

Moreover, where energy is rare and deforestation is high, the Vesta does not simply ’save whatever would have been spent on energy’ but would improve health, improve the environment and create new economic activity.

Lastly, the cost of carbon fuels can only go up and will only become more unreliable, and so any straight comparison between carbon fuels and solar energy should take that into account as well.

Also important to note is that there’s little damage to the machine from using it more rather than less (and no damage that can’t be repaired locally).

Temperature

Energy varies in form and intensity. The Vesta produces energy in the form of heat and at an intensity of about 300 to 400 degrees Celsius during a sunny day. This temperature range determines what sorts of things can be done:

Water boils at 100 degrees C.
Oil fries at about 150 degrees C.
Bread bakes at about 200 degrees C.
Charcoal is made at around 250 degrees C.

As can be seen, most heat needs around the home don’t ever need more than 200 C°, and the Vesta’s focal point is twice as hot. Though we’ll see under efficiency the temperature of the oven will always be less than the temperature of the oven. Twice as hot however is a good margin. The idea behind the Vesta is to reach easily reach 200 C° with a significant amount of power yet still be local and rugged.

But other applications not normally associated with the home are also possible. The important point about free energy is that it’s free! This means things can be done that wouldn’t make economic sense if we were paying for fuel. For instance, charcoal is usually made in large batches in equally large ovens, for the simple reason that wood needs to be burned to heat the oven. To save wood, especially since charcoal is made of wood, it’s more efficient to produce on a large scale. With a Vesta (or any solar concentrator) on the other hand, wood isn’t wasted in the process of making charcoal. Large oven’s and maximum efficiency are therefore of less concern, there’s little disadvantage to produce on a small solar scale for rainy days.

Power

Where temperature determines what sorts of things you can do, power determines how much you can do. For instance, a small magnifying glass can also focus the sun’s light and also reaches temperatures of over 300 C° ... but it would take a long, long time to boil a liter of water.

1800 Watts is a good power level for a stove. A commercial electric stove or small gas burner can take as much as 10 minutes to boil a liter of water, and an open wood fire even more (not counting the time it takes to collect the wood and make the fire).

And it’s important to note that 1800 watts is the effective wattage, not the potential or maximum wattage.

Calculating the maximum wattage of the Vesta, or any solar device, is easy. With clear skies the sun delivers 1000 watts of energy per meter squared (face to the sun); the Vesta uses 2.7 square mirrors of mirrors and so the “theoretical maximum” is simply 2700 watts. Though it’s handy to know that the “theoretical maximum” may be very misleading, if temperature and efficiency, is ignored; a 4m^2 sheet drying in the sun is “theoretically” a 4000 watt solar device.

Efficiency

The efficiency of a solar machine tells you how much of the incoming solar energy is actually put to use. Energy is lost in a variety of ways.

First, to reflect the sun’s energy to the focal point the Vesta’s mirrors must be lilted and so do not face to the sun. So right away the 2.7 m^2 of mirrors will capture less: at noon not much less and 20 degrees off the horizon about 70 percent (when the sun is lower than 20 degrees there’s usually too much atmosphere and trees in the way for the Vesta to fry or boil).

Second, the energy at the focal point must be converted to what we want to do. In case of boiling water we use a black bottom pan (blackened with charcoal for instance); some energy is reflected other energy is immediately radiated off the bottom of the pan. So, we raised water to 100 C° and evaporated it for one hour. 2.7 liters were evaporated. It takes about 2.5 million joules to evaporate a liter of water, which means we could capture 6.75 million joules. A watt is a power of 1 joule per second, so we need but to divide 6.75 million joules by one hour (3600 seconds) to arrive at 1875 Watts.

To “boil” a liter of water in the sense of heating it from 20 C° to 100C° 1 takes a power of 1200 watts. However, most people use boil to mean bubbles and steam, and each person will consider the watter “boiling” for different amounts of bubbles and steam, so 5 minutes to a roiling boil satisfies everyone. It takes 6 times more energy to evaporate watter than to bring it to boil, and so to arrive at a roiling boil (water evaporating on the bottom and bubbling up) will take good fraction longer than to simply bring the water to boil (water evaporating only on the surface).

Location

Clearly, the Vesta requires light in order to concentrate, so it will not work at the north pole in winter. Moreover, it needs direct sunlight, as in sunlight that casts a distinct shadow. This sort of data can usually be gotten from a national environmental or wheater agency. Though clearly to make near continuous use of the Vesta requires an arid region near the equator, even in places not associated with sunlight the Vesta can still be useful. For instance, making charcoal can be done on the days that there is a lot of sun, and the energy saving of converting wood to charcoal would make the construction worth while (so the North pole in summer is not out of the question).

Next, one must choose a spot where there’s nothing blocking the sun (the south side in the northern hemisphere, and vice versa for the southern hemisphere). However, keep in mind you’ll want shade nearby to cool off.

Use

Though a simple pot will boil and cook, there are more uses of the Vesta, however most of these would also need to be constructed.

For instance, a simple tin box can bake a few loafs of bread or create charcoal. Other uses are also imaginable.