The Array Farm
Since the monastery is over 13 miles from the nearest power line, bringing in commercial electricity would have been tremendously expensive. Instead, the monks decided to use energy from the desert sun to generate their electricity on-site. These solar arrays gather energy throughout the day and store it in batteries. The batteries then provide uninterrupted power to the monastery 24 hours a day.
The monastery's solar electric power system is made up of components which can be grouped into the following four subsystems:
- Energy Collection
- Energy Storage
- Energy Conversion
- Energy Distribution
Each of these subsystems is discussed in detail below.
The sun's energy is collected by PV modules, which convert sunlight into electrical energy. Usually several modules will be interconnected to form an array. This photo shows one such array, consisting of twelve PV modules mounted on a tracker. The tracker follows the sun throughout the day, making sure that the modules are pointed directly towards it. This allows the maximum amount of energy to be collected by each module. The 12 modules together produce a peak power output of 900 watts, the same amount of power needed to light nine 100-watt light bulbs. There were originally 8 trackers added at the monastery, but four new trackers have now been installed to meet increasing energy demand. If purchased from a utility, the energy from these 12 trackers would cost over $250 per month.
Batteries produce direct current or DC electrical energy, but the electricity needed for typical home appliances is alternating current or AC. This problem is solved by using an inverter, which takes energy from the batteries and produces utility grade AC electric power. The six inverters at the monastery are grouped into three pairs, and although all three pairs draw from the same battery bank, each pair supplies power to a separate building. If an inverter needs servicing, a transfer switch can be activated, allowing one of the remaining inverters to temporarily handle the loads while the service is being completed.
Since the inverters produce power that is virtually identical to that supplied by a utility, there is really nothing extraordinary about the energy distribution system at the monastery. Here at the distribution panel there is no indication that the electricity is generated with solar power. But beware! Solar power systems have limited capacity, so extraneous electrical loads, such as lights left on or coffee pots left plugged in, may leave you in the dark!
The energy collected by the PV arrays is stored in batteries. By storing the energy in batteries, power is available whenever it is needed, instead of just when the sun is out. The battery bank shown consists of 96 individual cells, which are interconnected to form one big battery. This is generally done in large battery banks for easier handling and maintenance of the batteries. Each cell shown weighs 180 lbs., so the whole bank weighs nearly 9 tons! The bank is fully charged by the arrays each day, but if the sun doesn't shine the bank stores enough energy for nearly three days of use.