Batteries are expensive. They are expensive to buy and often the first component that has to be replaced in a system. Energy storage is, however, very important to any solar-powered (photovoltaic or PV) off-grid system. The reason is simple; solar like most renewable energy sources is not continuous. While the energy is endless during a sunny day, enough energy has to be stored to support your system through the nights and cloudy day. One solution to the expensive battery problem comes to mind is replace the electrical energy storage with the thermal energy storage (TES). The idea for TES is to utilize latent heat to preserve energy that is harvested from the Sun. Latent heat is the heat (or energy) required during phase changes for matters Such as water. In the case of water, certain amount of energy is required to freeze it into ice. This amount of energy can be taken from the Sun through PV cells. When the water is frozen, the energy used in freezing is stored in ice.
|Solar panel rack installed at the SEF August 2016 to power solar ice.|
Calculation to Prove this Concept:
To prove this concept, batteries will be used to compare to water/ice. For example, a typical laptop battery is rated at around 15 volts(V) and 5 ampere-hr(Ahr). According to Ohm’s Law, electric power is equal to current times voltage, P = IV. Power can also be expressed as energy per unit time. Therefore, a typical laptop battery can hold around 75 Watt-hour (Whr) worth of energy, which is about 270,000 Joules (J) or 270 Kilo-joules (kJ). Moving onto the water/ice. The heat of fusion for ice is 333.55 Kilo-Joule per Kilogram (kJ/kg). So to melt 1 kg or 1 liters (L) of ice, one would need to use around 335 kJ of energy. In another word, 1 liter of ice can hold around 335 kJ of energy which is a little more than the typical laptop batteries.
The important takeaway from this is the significant cost difference between a kilogram of ice and a laptop battery; for about equal amount of energy storage, 1 kg of ice cost much lower than a laptop battery.
Plan for using TES:
Obviously, a battery can provide immediate electrical energy which is more useful for electronics and electrical appliances than thermal energy. So how can TES be used? For this experiment group, TES will be used to reduce cost of refrigeration. The idea is
- Ice Cream Bus Project – Upgrading a Bus from a local Ice cream business, Social Ice Cream to have a solar powered system and thermal energy storage
- Thailand Project —- Collaborating with Cal Poly EWB to set up a refrigeration system for a rural village in Thailand using thermal energy storage
- Experimental Project – Experimenting with a commercial freezer with better insulation and less surface area to explore cheaper way of refrigeration
Meet the Members:
- Nathan Heston –
- Wilson Yeh – Fourth Year Electrical Engineering student
- Adeel Ali –
Adeel Ali is a 3rd year Physics major who is passionate about a life of academia. He is working towards pursuing a PhD and becoming a Physics professor in the future.
- Mike Stromecki –