Analysis | Physics of Energy Project Group 4

BATTERY STORAGE WALL

After reviewing the costs and effectiveness, the reality is that adding Tesla Power Wall 2 batteries for storage is not feasible.

Batteries require maintenance and have a finite lifetime, typically 10 years or less (when used as a backup energy source). When on a continuous charge-discharge, the life of the batteries will decrease significantly. They were not designed to be used on a day to day cycle.

A large physical space is needed for the batteries, control systems and power equipment. Roughly a 15’x 30’ rated room with mechanical cooling and ventilation. There is nowhere near enough room for this to be implemented with the number of walls proposed.

Batteries, controls, and electrical power systems are required. Tesla 13.5kWH (5kW continuous load) Power Wall 2 units are $7500 each. A system that could cover the entire output difference of the 143 EV chargers (952kW) and the small canopy (134kW) PV is about 818 kW, or 164 wall units, for a total of $1.23M.

Custom, larger sized systems may be less costly rather than using the smaller Tesla units. We also must add to each of these the cost of installation and power equipment at 30-40% of the battery equipment costs.

Energy Consumption and Generation

Energy = Power*time = I(Current)*V(Voltage)*time

A Level 2 EV charger outputs 40 amps and 208 volts. With structure operation of 92hr/week, this is maximum output per charger of 765 kWh/week.

Base and Perimeter PV solar at 200 W/m2 peak output = 257 kW

Average weekly PV energy generation = 8,330 kWh/week

10% of spaces required to be EV charging ready:

41 EV spaces * 0.9(assuming average EV space occupancy 90% for all 41 spaces while open) * 765 kWh/week

= 28,000 kWh/week energy consumption by EV charging stations

35% of spaces required EV capable:

143 EV spaces in use * 0.8(assuming 80% EV occupancy of the 143 spaces) * 765 kWh/week

= 87,500 kWh/week energy consumption of operation of all spaces required to sized and wired to be EV charging capable

100% of spaces EV capable:

368 spaces * 0.7(assuming 70% EV occupancy of the 368 spaces) * 765 kWh/week

= 197,000 kWh/week energy consumption of operation if all spaces in the garage support EV charging

10% in use:

With current downtown EV charging rates of $1.50/hour and the assumed 90% space occupancy, weekly EV revenue = $1.50 * .9 * 41 spaces * 92 hours/week

=$5,100 - $0.15/kWh(price of electricity) * (28,000kWh - 8,000kWh)

= $2,100 per week after energy costs subtracted

35% in use:

With assumed 80% occupancy of the 143 EV spaces, weekly EV revenue = $1.50 * 0.8 * 143 spaces * 92 hours

= $15,800 - $0.15/kWh * (87,500kWh - 8,000kWh) = $3,900 per week after energy costs subtracted

100% in use:

With assumed 70% occupancy of the 368 EV spaces, weekly EV revenue = $1.50 * 0.7 * 368 spaces * 92 hours

= $35,500 - $0.15/kWh * (197,000kWh - 8,000kWh) = $7,200 per week after energy costs subtracted

10% in use:

This 20,000 kWh/week (28,000 - 8,000) energy consumption would add 0.09% to SLO’s non-residential weekly electricity consumption (1110 GWh in 2017).

California’s electric energy comes mainly from plants using the natural gas combined cycle which emits ⅓ kg of carbon dioxide into the atmosphere per kWh generated. 200,000 kWh/week of electricity use results in the emision of 6,700 kg of CO2 per week but when considering the average gasoline car emits twice the carbon per mile of a hybrid and 3 times as much as battery electric vehicle, they are saving at least as much from being added to the greenhouse gasses.

35% in use:

The estimated 79,500 kWh/week energy draw of 35% of the spaces in use would add 0.37% to non-residential and 0.23% to total SLO grid load on average (SLO total electricity consumption in 2017 was 1780 GWh).

The spaces’ carbon footprint would be 26,500kg of CO2 per week (again, being used to power vehicles which greatly reduce travel emissions by replacing internal combustion engine vehicles).

100% in use:

The estimated 189,000 kWh/week energy draw of 100% of the spaces in use would add 0.89% to non-residential and 0.55% to total SLO grid load on average.

The spaces’ carbon footprint would be 63,000kg of CO2 per week.

EV Space Costs and Revenue

Grid Load and Environmental Impact

CONCLUSIONS

After our analysis, we have come to the conclusion that the best photovoltaic system for the garage would be to cover the base and perimeter with solar panels. This is the maximum panel area we can achieve without creating a full roof (which would require taking out an entire floor of parking due to building codes) and gives the energy production used in the above calculations. Any type of battery storage would not be feasible. There is simply not enough room and the costs are too high. It is notable that none of the cases of 10%, 35%, or 100% EV spaces in the garage add a significant load to the city grid and would not lose money from their energy costs, as is shown above. However, the reality is that offering more charging stations will require more room in the building to be allotted to PG&E hardware. Furthermore, incentivizing charging during the day can be done by making prices more visible to the consumer. By using the app ChargePoint, the city already meters the EV charging station uses. To make customers more inclined to charge during the day, offering a discounted price during daylight hours would make consumers more inclined to charge their cars downtown instead of at home. Also letting consumers know that they are saving both money and the planet by charging during the day can greatly influence consumer behavior in the favor of San Luis Obispo's ultimate goal of being carbon neutral.