Solarenergy and cooling for houses by Tapani Hakonen

Diagram* Principles* Heat collection1* Heat collection2* Heat delivery and greenhouses* Appendix* Greenhouses

1000 kWh/square meter in one year

Fact: In 50 degrees latitude a horizontal square meter
recieves ca.1000 kWh direct solar radiation per year.


In theory we should move to solar energy, use solar photons, because it is eternal and free.

Build your new house in view of solar energy!
- the rooftop well short of direction east-west
- the best roof declination maybe 45 degrees
- to get sunshine at least at noon in the summer
- the place for warmth and coldness near in the soil
- the deposit of the electricity (domestic battery, car battery, electricity network etc.) ~~>

The term 'solar house' refers to a house that gets energy for heating and providing domestic warm water from the heat of the sun throughout the year. The fact that there will be enough solar energy for the winter and early spring, too, demands a large heat storage, since at that time of the year the solar radiation is not sufficient enough for any kind of heating.

The sufficiency of solar energy is good. In 50 degrees latitude a horizontal square meter recieves 1000 kWh per year of sunlight. Even in 60 degrees latitude recieves 900 kWh/m2 per year of sunlight ( H. Lunelund 1927...33) during about four - five months in summer. It varies somewhat yearly, but the collection of solar energy today is a very profitable form of heat or electricity annually, and there is more solar heat and electricity further south.

For example: In a house with 100 square meters' living space the sunny side of the roof (ca. 80 m2 including the eaves) recieves annually at least 80 000 kWh, or even more (ca. 20%) depending on the inclination. That means that there is enough thermal energy (4x) even though the efficiency of the system were not that good. Warmth will be worth collect only at hot weather midday in degrees of northern latitudes.

The solar house presented here is also inexpensive and extremely reliable, which means a highly considered reduction. The building expences connected with the energy of this solar house are in the same class as those in the modern houses with a second type of heating. Its reliability is good, since the availability of sun shine throughout the year is better than with other forms of energy, which are easily affected by crisis conditions, nor does solar heat necessarily need electricity. It should be mentioned that the production of the electric energy with the solar energy begins to be economically profitable.

The storing of solar energy has been tried before, but the previous attempts have been based on rather heavy and complicated ornanising, which then has raised the price, and the leakage of energy has been disproportionately high.

In this system the building expences are low and the energy is free. The drawback is that the system binds the city planning and the hands of the architect to plan similar houses. Even so, I believe that the plurality and the exuberance of planning will be preserved. Building this kind of solar heating system into an old house can be expensive or not always so beautifull, but all the new houses should already at the building stage be built into solar houses for merely ecological reasons. Solar houses should be made compulsory or they should at least be favoured by taxation for the reason that the ecology, national economy and private economy all favour the sun. The lobbying of the oil, gas, coal and electricity industries for these competitive forms of energy will make it difficult to move into solar energy.


Block of flats

The main principals:

1. Solar energy has often been stored into water, but water has some disadvantages like the expensive structure of the tanks, the leakages and the fact that water does not support the construction. When soilworks as the heat storage no profound building of the storage is needed. In the simplest form the storage consists of c. 3 m deep ditches, dug with a trench cutter, and the heat insulation is attached to the sides. E.g. 10 cm thick flexible aluminium, iron or plastic air conditioning pipes for heat delivery are installed in the tracks dug in the center. It is better to make two sets of pipes; the other ones for bringing heat with air as the heat-transfer medium, and the other ones, filled with air (or water), for delivering heat into the living space and cooling pipes too.

Sometimes the heat storage has to be made more profoundly. The ground is removed from the heat storage - c. 10 cm thick layer of heat insulation is installed on the bottom as well as on the side walls. Water insulation may also be needed, depending on the circumstances. The storage is filled preferably with sand and the pipage is installed inside. Different sized rocks can be mixed with the sand to increase the density of the starage and thus the heat capacity, too. The sand is rolled so that it becomes dense and does not sink any more. Finally a heat insulation is installed on top of the storage. Stones should not be placed near the sides of the storage since, due to their higher thermal conductivity, that could increase the loss of heat. The distribution of heat in the storage should be such that the hottest spot is in the middle, which reduces the loss of heat. Heat for the domestic hot water is also taken from the middle, the heat of the earth being 50 - 70 degrees there. The best way to get hot water is to let hot air circulate through the boiler in pipes, or to install the hot water tank in the hot ground.

It is best to build the heat storage so that the hottest sunshine in the middle of the summer heats the center of the storage, and the sunshine during spring and autumn heat the edges. Furthermore, the delivery of heat from the storage can be arranged so that the air curculates from the edges to the middle. This helps reduce leaks of heat and the middle of the storage stays warmer. The delivery of heat from the storage is caused by gravity - warm air raises always upward - but demands rather thick ducts. Thus no electricity is needed. Warm air circulates between the storage and the house; a thermostat can be installed at the end of the duct to regulate the interior temperature. The regulation can also be manual. Because of the reproduction of the spore-producing mould the heating duct must be vacuumed every now and then with an extension pipe installed in the vacuum cleaner. The thermal value of sand and stone is about one fifth of that of water, counted according to weight, but about half counted according to volume.

2. The heat storage is best placed under the house unless there are special reasons that prevent it (e.g. rock - the thermal conductivity of rock is ten times bigger than that of soil - in principle there should be enough soil). In some cases the heat storage can be on the yard, but it has to be close to the place where the heat is used. The heat storage has to be placed on the yard when solar heating system is installed into an old house, or when the residents insist on having a cellar in their house. Even then part of the heat (and cold) storage should be placed under the house because of the pipage.

Diagram in summer 25oC
Collecting Warmth Cool down

Diagram in winter 0oC
Warm Collecting coldnessAppendix I,J

The distances from the solar panels to the heat storage and particularly from the heat storage to the heated area
( space) must not be long, since that will only increase leaking, piping expences and flow resistance.

For the heat to rise with the force of gravitation the heated area has to be above the heat storage. The heat storage
forms the foundation of the building. That is why the floor may sometimes feel a little too warm. But generally
a warm floor is only healthy and nice, especially in cold climates, and the heat will be made good use of. Some
heat insulation may be needed under the floor.

A sufficiently large heat storage is the area of the foundation depth 3 m when the house only has one storey.
A house with 100 square meters' living space would have 300 m3 heat mass under it, numerically 650 tonnes,
but the exact amount is difficult to estimate; it could even be twice as big. The size of the heat and cold storages
depends among other things on the latitude of the house. In practice there should be heat for at least six months'
need. The capacity of the heat storage may grow many years, since the heat loss becomes less while the surrounding
ground gets warmer. Soil with pebbles and clay (50 %, closer to the middle) and sand (50 %, closer to the side) together
with pipes has good capacity.

3. Air is clearly the best heat-transfer medium when we consider a reliable, care-free heating system. A water system is, at least in winter, in danger of freesing which breaks the solar cells and the pipes. Water can leak from even the smallest holes and a complicated system almost always has minor leaks. During a hot season evaporation occurs so that water has to be added almost daily. Other fluids: salt water, glycol etc. are expensive and polluting when leaking. If they leak into the ground water they pollute large areas permanently. Their flow resistanse is high like that of water, so rather high pumping power is needed to transfer heat from one place to another. Only air is care-free and inexpensive to use. Small leaks do not harm since there is air all around us. Air flows easily with the force of gravity - no radiators are needed. The air does not necessarily have to be returned to the solar panels. The panels can take the air from the south side of the house under the eaves - where the air has already become a little warmer.

4. As has been mentioned previously, no external power is needed in withdrawing heat from the storage since the heat rises from the heat storage by itself, with the force of gravity, into the living space. For the heat to be sufficient and even the pipes have to be rather short but thick by their internal diameter. From the other end of the pipe air goes from the room to the heat storage and from the other end comes into the room from the storage. At the other end of the pipe there should be some kind of thermostat to regulete the air flow in the pipe. In the summer both ends are closed. It would be good if the air flow in the storage would be from the sides to the center as that would reduce the flow of heat to the sides and out of the storage.

Energy is needed to transfer heat from the solar panels on the roof down into the heat storage. Energy is needed also to transfer the cool air from cold storage to the house in summer, and filters are needed against bacterials and mold spores - small, good efficiency compressors with power about 100 watts. (Compare: So-called ground heat needs at least ten times more energy and can pollute ground). Compressor e.g. a turbine with two vortex wheels, is needed to blow warm or hot air down to the underground heat storage with a power proportional to the sunshine. A termistor connection prevents the operation of the compressor in the winter. The compressor is best operated by at about a 1 m2 solar battery located up on the same roof. If that is too expensive the compressor can take its power from electrical network. That will also need some kind of electrical eye for power regulation. Hot air is collected from the ridge of the roof and carried down in a pipe about there where houses used to have a chimny. Somewhere in that pipe there is the compressor. A suitable diameter for the pipe is about 20 - 40 cm. A thin pipe causes not only resistanse but noises, too. On the other hand, a faint noise just tells that the system operates.

A hot water boiler has been previously mentioned, too. At its simplest it is a closed, 150 - 300 liters tank without insulation 'buried' in the heat storage. Water goes there in one pipe and comes out hot in another pipe. This water tank is placed in the hottest spot in the middle of the heat storage. The water runs on its own pressure, what ever that in different situations means.

5. It has been previously mentioned that a solar house binds the hands of the architect. This is true in two senses: a) The house has to have a ridge roof. b) The house has to be so situated that the solar side of the roof faces south. Other minor conditions are the ground quality (water free, rock free) and the fact that there should not be any big and tall obstacles nearby (forest, tall buildings).

The angle of the roof has to be at least so deep that in the middle of the summer, when most of the energy is collected, the Sun will shine perpendicularly to the roof. When the Sun shines perpendicularly to the roof the heat under the plastic can rise as high as to 100 degrees (oC.). The air circulation could make sure that the temperature will not rise above 70 degrees Celsius. In the 60th parallel the angle of the roof should be at least 37o, which is the normal inclination in modern houses. It is important to gain a great intensity of energy on the roof sometimes, since peak temperatures are needed in the middle of the heat storage. An even steeper roof can collect even more heat, especially if one wants to collect more heat during the spring and the autumn. In that case the heat storage can be smaller. If the inclination of the roof would be 45 degrees the Sun would shine perpendicularly to the roof as early as on the first of May. This angle 45 degrees is best at all latitudes when we consider solar energy and practical. Supposedly many of people do not want to live in houses that look like experimental laboratories but rather like normal traditional houses. The most important matter, the solar panel, has not been dealt with yet. The solar panel is here very much simplified, it forms part of the roof sturucture as it is the surfacing of the roof. No heat insulators are needed perhaps because the heat is mainly collected in the summer. The outer transparent layer is made of plastic that has a wave-like cross-section profile; section c. 10-20 cm (Figure profile).
Cross-section of the solar panel

It is mostly separate from its base, but the screw fastening makes sure it does not come off in a
storm. About a meter wide transparent plastic sheet, that endures heat well, or dark metal sheet,
(iron or copper) reaches from the eaves up to the ridge. Some lining compound should be added
in the holes when fastening the screws. The seams can be sealed with glue if desired. Plane sheet
is used on the ridge for air proof sealing. For reasons of appearance the sheet can have matte
finish top surface and a different shade, it could even be tile-like, without harming the efficiency.
The plastic should be environmentally safe so, that it could either be re-cycled, melt or at least
burnt safely without harmful heavy metal emissions. Under the transparent plastic there is a black
sheet, it could be a painted or even rusted sheet iron, a red sheet will also do. This underlayer
should be of iron for the reason that it protects from fires - fire must not spread from the roof easily
and especially not under the roof. The solar panel and possible skylights are placed under the plastic.
The actual supporting structure, the matching and the roof truss, are under the iron sheet. Air flows
from the eaves between the plastic and the iron sheet, raises up and is collected hot or warm from
the ridge of the roof and is led down. Minor air leaks, which occur e.g. on the ridge, do not matter.
The plastic has to endure the UV-radiation of the Sun, stay clear and endure heat and cold sufficiently.
These requirements for the plastic are hard but achievable.

The transparent plastic sheet can be replaced by black corrugated iron sheet that heats the upward flowing
air under it. The roof consists of two layers of sheet, the upper one being corrugated iron and the lower
one plain sheet metal, and air becomes hot between them, or of corrugated iron and a flat insulation layer
under it. These do not heat air as well as plastic and sheet metal under it, but in many cases, especially
in the middle of the summer, it is sufficient.


Sun shine turns into Warmth
The roof profile

When the sun shines on the roof the air between the plastic sheet and the underlaying or black sheet
iron starts getting warmer. The solar cell on the same roof produces electricity for the compressor,
that pushes the heated air down to the underground heat storage. During the summer the coupler is
turned so, that adjustedthe hot air is directed to the center of the heat storage, otherwise the air
is directed more to the sides of the storage. The duct branches underground to reduce flow resistance.


Warmth, ~60 Celsius, goes to the ground

When hot water is needed and the user turns on the water tap, cold water flows into the pressure tank
heat storage in the middle of the , where it is heated. The already heated water flows from the other
side of the pressure tank for the user. Temperature in the tank must be above 47 Celsius for Legionella
pneumophila strains.

When it gets colder in the autumn the covers are removed from the ends of the pipes coming from the heat
storage, and warm air starts flowing into the rooms regulated manually or by thermostates. Air circulates
the faster the bigger the temperature between the living space and the storage is, the thicker and shorter
the pipes, the more there are pipes and the wider open the ends of the pipes are. Warmth and perhaps
coldness can rise to the house by water too, but we need pumps and eletricity.

3........................HEAT DELIVERY FROM THE HEAT STORAGE
Warmth rises to the house

Remember clean pipes every year by vacuum cleaner with spherical brush because of
mildews. Water circulation is often better and quickly ventilate the windows.

Use in constructions much pure natural materials like wood and stones.

In greenhouses construction is very simple:
In the summer greenhouse's too hot air will be led to the ground with pipes and the same but cooler air will come
back to the greenhouse. You need not ventilation, less irrigation, less energy and added carbon dioxide stays better
in the greenhouse. In the winter air circulates in same pipes and bring back the same warm to the greenhouse.

Lights are perhaps rapidly beated blue and red leds because of economize electricity. The efficiency of light will be
more than 1% of ordinary light, and production of food must be more economical.



A. A warm house and warm domestic water are part of our basic security. Of course that is not all, we need lighting and energy for houshold appliances. The amount of the extra energy needed can vary a lot - normally in the West it forms one third of the energy used at home, but it can be much smaller. For example the filament bulbs must be switced, and Your following computer could be a portable, "laptop". I already have.

P.S. The unnecessary traffic can be reduced by favouring telecommuting at home. The telecommuting can be improved by developing equipment and by changing attitudes. Society takes care of that many trench must be inserted in the optical cable, and every mobile mast and many satellites serve as the link of the broadband. Schools will ensure that surfing is used for data acquisition and processing. I think that the community programs such as wikipedia will bring added value especially in childen and replace traffic congestions. Only pictures and data are transferred, no matter.


B. It should be mentioned that even the sauna can be heated with solar energy. There are big covered holes on the floor of the solar sauna situated in the middle of the house. When the covers are removed the sauna warms up to 50-70 degrees. Water is thrown in the hole, where it evaporates slowly. The water has to be thrown on larger surfaces to make evaporation quick (finnish sauna).

C. In order to optimize the heat collection the system could include a small intelligent processor to regulate the compressor and the valve with the help of temperature sensors.

D. This solar heat system has been developed for a house with a one and a half floors. Heat can be led upstairs from the underground storage through a pipe; no return pipe is needed.

E. When the solar batteries become cheaper more of them could be installed on the roof, which would increase the amount of electricity recieved for lighting and domestic appliances. The energy production would be so organised, that lowest on the roof would be the solar batteries with their electricity production of c. 10% efficiency, and above that would be the plastic sheet and the air space with heat production of 50% efficiency. The voltage of the solar batteries would be a little higher than the general line voltage (230 V), and join together with an elektric car, or a special transformer would transform the electricity into alternating voltage, and the extra would be fed into the general network. The transformer would contain thyristors, voltage transforming filters and syncronizers. Since it creates some heat it should be placed appropriately. There would be two electrical meters: one for buying, the other one for selling electricity.- The meter is inspected by the same person who reads it: it must not cause electromagnetic disorders, for example. The system is much less expensive than storing much power in accumulators. Some of the electric power can in this system be used for charging a accumulator in house or electric car, when needed and when warm is not enough to store (holiday cottages).

F. Large halls, e.g. sports -, railway -, exhibition - and industrial halls, as well as churches can be heated similarly: a sloping, south facing plane is covered with solar cells and panels - a compressor pushes the heated air under ground into the heat storage, from where warm air is conducted via air ducts into the hall when heat is needed. The compressor can get its power from electrical network, too. The system will save money notably. The roof can also be arched, as long as the radius of curvature is big enough. Solar panels that have a fixed curvature or suppleness can also be used.made

G. The sunniest wall of a block of flats can be covered with the previously described solar panel. A compressor can draw the warm air down by the wall and push it into the underground heat storage, which could be in the yard, too, for example under the parking area, or even under the street. Normally the sunniest wall has no windows, which makes the installing easy and economical.

H. The fact that heat comes from underground raises the question of radon radiation. However, the pipes carrying heat inside are tight, so that no radon can get into the pipes. It is important to pack all joints between the pipe and the floor material.

I. In the southern latitudes heat can be annoying in the summer and a warm floor can make it even worse. In that case it is best to start collecting heat in the autumn. Or why not store cold air in a piece of land during the winter to cool the air in the summer. This means, of course, that a more complicated pipage and some other devices are needed, which are not described here. There would be a separate compressor for the heat and the cold circuits.The compressor of the cold circuit would also get its energy from the Sun in the summer, and in the winter it would get power perhaps from the network or gravitationally with warm difference, and would be turned on to cool the ground when the temperature sinks below 0o centigrade. A small cellar can be built in the middle of the cold ground, which makes it possible to store food in a cool place even in the heat of the summer. Entrance to the cellar can be either from outside or from inside the house. Considerable amounts of energy are used to produce cooling and coldness in the World.

J. Cheap solar cells to be rolled are needed to be installed on the roofs. The solar cells will produce electricity for batteries. - In future: lithium <~ Li+ ~> silicon nanowires, and a car can go 1000 km by one charging. - Electric cars and mopeds keep air clean and noiseless in towns, and will perhaps increase our lifetime. You can produce electricity for the general network too. Nanolayer keeps solar cells clean. The new technique will need a lot of lithium and perhaps graphene: a miracle material for the future.

Tapani Hakonen

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