Use of solar energy directly for household needs (without converting into electricity) Student: Ophir Arad

for such a complicated and relevant problem, there is not a one, single, ultimate solution - espcially because new and emarging solutions are invented every day. those solutions appear due to the shift to renewables, the sharp increse of electricity demand and production, the 'race' for getting to net zero CO2 emmission, the gas crisis in the west because of the war between Ukraine and Russia - and much more reasons.

for the ways of energy usage - I would suggest use the energy mainly thermal energy - that would eventually supply hot air that could heat the water heater or activate the condenser unit or help heat up the refrigerent fluid in Heat Pump or AC systems. therefore it could fulfill most of the residential cooling and heating needs in many world areas - therefore dramtically lower the worldwide energy consumption (in Europe alone, almost 50% of energy cunsumption, 80% of which still based on fossil fuels).

in general, hot air could be easily formed this way and therefore using for many applications - cooking, cooking with a shabbath plate, inflating tires (hot air would be pressurized for and therefore suitable) and etc.

however, among the proposed solution ideas there are some that looks more promising then others.

for solar energy harvesting - PVT systems (PV+Thermal) look the most promising. although incorporating electricity production, those systems also creating heat energy, in a way that cools and benefits the PV, and usually connected to a residential water heater and thermal heating storage. In my vision, this thermal storage unit would be compatible with electricity as well - Therefore allowing heating heat with non used electricity during peak hours - therefore storing it as heat that could be easily used for residential heating and cooling. one of those systems best features is that the Thermal extraction system could be incoporated to existing PV modules - and therefore improve their efficiency, lifespan and space usage. for example, an australian startup 'sunovate' offers a air cooled PVT systems that can be built over existing PV - by a sealed air cassete beneath the existing panels. the company claims the total energy produced by their system is 300% the PV alone.

this idea can be evolved, combined with concentrator optics to acheive even more photons reaching the PV and heating it much more - extracting more electricity and more heat. this proposed "CPVT" (concentrated PVT) systems are being studied and researched nowadays.

for thermal energy stroage systems - one of the most promising solutions is solid 'heat batteries', that contain of sand, bricks, gravel or any solid with low heat conduction and a high melting temperature, that could be heated to verying range of temperatures. those TES could be heated even up to 1000 celsius, and can be stored in huge silos or tanks - therefore supplying "only" several MWh on small scale facillities, with the abilities to reach hundreds of MWh's. It is prefered for those systems to use waste materials, therefore recycling them - such as construction sand, or bricks. moreover, 'grainier' materials such as sand could fir much batter in containers, and get the best use of the shape of the tank - therefore improving contact with heating element, and potentially improving the heat storage. those systems are researched, and expected to use even for seasonal heat storage for countries with long cold winters. for example, a finnish start up company called 'polar night' offers "sand batteries" for industrial applications that can store 10 MW of energy, and last for several months (described as seasonal stroage).