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Case History: Solar Power
The SML House - so called because it is a flexible, modular design that can
be built in Small, Medium or Large configurations
was the entry of the Cardinal Herrera University, Valencia,
in the Solar Decathlon competition.
The Solar Decathlon Europe is a solar power competition for
houses that are self-sufficient or minimal consumption.
The design of these houses incorporates photovoltaic panels on both roof and walls.
In our case we have chosen to develop three main arrays, on the roof and two facades,
east and west, as well as photovoltaic paving.
That way, at any time, when there is energy production, we can either choose
to use that energy or store that energy. Surplus energy can be fed into the mains network.
We sell that energy to the grid, so that, over the year, our balance is as close as possible
to zero, or that we are producers more than consumers.
In order to generate enough power for the SML House to be self-sufficient
or even a net producer of energy, each module has an array
of photo-voltaic panels on the roof. These panels can be tilted to maximise solar gain.
At the same time there are photo-voltaic panels on the walls that face the sun.
Since the whole concept is modular, if the house is extended in the future,
the new modules will come with their own solar panels,
thus increasing the generating capacity to match the increased demand.
The management system is linked directly to the battery pack and operates
through charge controllers which are found on each facade and on the roof.
These are linked to an inverter, connected to the grid. The inverter generates
alternating current from the batteries. Surplus power is fed directly to the mains.
Finally, the XW mains management system in the power manager, is a hybrid inverter.
which allows you to take power from the batteries or manage the batteries
to balance the the consumption from the mains network.
Meanwhile, solar thermal panels provide water heating.
Also we have the hot water system. This system is connected to the roof.
On the roof we have high efficiency solar panels, vacuum-based panels,
and a reflecting mirror which allows to have hot water even when there’s
little sunshine and even in the winter.
As with any solar system, the main circuit brings hot water from the roof
it passes through the heat exchanger and then back up to the roof.
In the heat exchanger we produce hot water at 60, 70 even 80 degrees in summer.
The hot water comes from here into the house, and we take the precaution of
having a mixing valve so that the supply is never above 60 degrees
otherwise people could be scalded if they use it.
In a hot country like Spain, which may enjoy 3000 hours of sunshine a year,
air conditioning is a major energy demand. Cooling in the SML house is provided
by circulating cold water through pipes in ducts in the floor.
Fans blow air through these ducts.
What we did was use a heat pump, which we see here.
This is a heat pump that’s commonly used in geothermal energy.
In the competition on the site we couldn’t make a hole in the ground
that the equipment needs in order to dissipate heat.
What we did was change the way it worked and use a reservoir tank to behave
in exactly the same way as would a well, a well bored into the ground.
To make it behave like that we filled the tank with “phase change” material.
This material changes phase at 27 degrees.
The effect of this is that the water tank, with all these slabs inside it,
will always be at 27 degrees.
We operate just as if the installation was in the ground.
We dump heat into this tank, but it’s always going to stay at 27 degrees.
The excess heat is going into the tank all day
then the equipment can release the heat at night, because the outside temperature
is always certainly below 27 degrees.
Then we use a heat exchanger, very much like the radiator on a car
to dissipate the heat at night, letting it out into the environment.
This is the phase change material. You can specify the temperature ...
This particular one is 8 degrees which we have in the cold tank.
At the other end we have 27 degrees. You can specify the temperature exactly.
Weather is variable, so balancing generation and use, and matching these
to the householder’s energy needs is key to the success of a solar house.
The important part, or the heart of the house is the brain, the control system.
We are using a KNX bus, which is a domotic standard.
We connected various KNX elements and programmed them and also
fed information into a computer. That way we use the power of a computer to
control the operation of the air conditioning as well as the other functions of the house.
This computer includes a neural network, which allows you to do more advanced
analysis of weather forecasts, predict how the house is going to be used
and control domestic appliances. The house collects this data through the KNX bus and
sends this to the computer, which is then able to reflect and understand
the normal habits of the householder.
We added some additional equipment, purely for the purpose of the competition.
We also need to add a lot of household electrical equipment.