Experimental solar panel that heats the air in the house in times of crisis.
In this period where the energy crisis is making itself felt even in industrialized countries, this air solar panel can make a significant contribution to the domestic economy; the low cost of production makes it suitable even in developing states as well as in isolated areas where there is no electricity grid, please refer to the link above for a detailed description.
The low production cost also lends itself to implementation in developing countries, and being autonomous it can also be installed in areas without electricity.
Economic solution that pays for itself in a few months, on a sunny day it provides up to 8 hours of air in Sicily, at an average temperature of 50 degrees centigrade, with a volume of 150m2/hour in December/January.
The solar panel is 6 meters by one meter by 20 cm, made with polyurethane-insulated sheet metal panels and a honeycomb polycarbonate front; it faces south and is inclined by 65%, to optimize production in the cold season.
The panel can also be made vertically, of any size, and placed close to a south-facing wall.
There are two 15cm diameter air inlets at the bottom ends with fans, one takes air from the house, the other filtered from outside.
The two outlets are taken in the middle and at the end of the panel, in such a way as to uniform the air flow, fans should not be placed on the hot side as they do not last, the two pipes flow into a larger one and sent into the house, with a low outlet At floor level in the corridor, a fan at the outlet mixes the hot air with that of the house and pushes it throughout the room.
A T-shaped connection pipe has been placed in the two outlets and in the air inlet from the house with a movable circular bulkhead inside to switch from winter to summer mode; in summer the heat is thrown out to avoid overheating of the panel.
The cold air taken from outside is filtered with plastic fabric of the type used in kitchen hood filters.
The “cold” air taken from the house is brought from the opposite side of the panel with an internal duct at the bottom made of honeycomb polycarbonate, this allows a uniform flow of air inside the panel; in this way the air inlet and outlet are on the same side of the house, near the end of the internal corridor.
A smaller panel can also have only one inlet and one outlet, you can choose to take the cold air only from inside the house, only from the outside or from both; if it is also taken from the outside, a passive exit must be provided in the house, at floor height, far from the entrance to expel excess air, the closure can be with slats with a push opening towards the outside.
A 150W solar panel charges the 12V batteries to power the fans, a 15V power supply from the mains charges the batteries at times when the sun is weak, in the morning, in the evening, during the passage of clouds, so the battery is always charged; in areas where there is no electricity, a larger panel and larger batteries can be mounted.
The battery also powers the 12V external porch lights in the evening.
An electronic circuit designed by me controls everything and is connected to the WiFi system for displaying production statistics. If you want, instead of the circuit you can put a normal thermostat and two normal solar battery chargers for a few euros, but having no more WiFi connection and statistics.
At the end of December 2022 and the beginning of January 2023, the panel produced an average of 22 KW/h per day, with an average power of 3.4 KW, and remained on for an average of 6.5 hours with an average temperature of the air produced of 50 degrees centigrade and a air volume of approximately 150m2/hour; it was a warm winter and the outside temperature averaged 12 degrees centigrade, so the delta was around 40 degrees; considering the current cost of electricity (0.46 euro/KW) the saving is around 10 euros per day.
30 days statistics
The “Outside temperature” in the graph is measured behind the panel and therefore significantly higher than the surrounding air during the day, the same as it at night.
The control circuit includes the management of a pre-heating water pipe, but the function is not currently used, on average it would provide hot water at 60 degrees but for half the hours it provides hot air at 50 degrees, on cloudy days it does not manages to bring the temperature above the minimum 55 degrees expected; hydraulic part absent, therefore flow statistics unknown.
The current fan and charger intervention settings are as follows:
Turns on air fans if > 40°C
Turns off air fans if < 35°C Turns on water pump if > 55°C
Turns off water pump if < 50°C
Charger Voltage: 12.6V (-0.2 +0.4)
Panel Voltage: 14.0V (-0.2 +0.4)
Technical considerations resulting from experimentation
-The fans of the thermal panel must only be on the cold air inlet, they don’t last long on the hot outlet even if declared for high temperatures.
-The entrance and exit of the thermal panel must be on opposite corners, if you make the entrance in the center in a vertical panel you need to distribute the cold air laterally, with an obstacle above the duct.
-For each square meter of thermal panel you need at least 15W of fans (from 200 m2/h), 20W is better, do not go below 10W or the temperature exceeds 70 degrees centigrade, overheating the plastic parts.
-The power of the electric solar panel must be double the maximum load of the fans, the control circuit absorbs approximately 2W.
-The battery must be of the same wattage as the panel or higher, it is necessary to keep the fans turned on even during the passage of a cloud or with mist.
-The final outlet fan, in the house, must be kept 3 centimeters beyond the outlet or it will not push the air forward due to the centrifugal force. If it is completely recessed, the air will come out laterally but it is more efficient as it sucks in the air. from the panel, increasing the flow; the engine is thermally stressed and must be supplied with cold air.
-Each additional meter of 15cm diameter pipe requires 5W more fan to avoid reducing the flow rate.
-You can take part of the cold air from the outside to create overpressure inside the house, in this case the two fans must have the same power also taking into account the length of the pipes: for example 6m2 panel, 4m internal cold pipe, 0m external cold hose, 5m hot hose: external cold 36W fan, internal cold 54W fan.
-To increase power, fans of the same power can be placed one after the other, in series and not in parallel. The pressure drop in the tube should not be ignored.
