Introduction: Figure 1 is a photo of the EDTEK SolBlu combined heat and power (CHP), solar concentrator unit. The Solar Combined Heat and Power System demonstrates the field operational feasibility of the EDTEK SolBlu solar concentrator systems. These systems are designed to intercept sunlight and convert it electrical and thermal energy. The thermal energy is usually collected in the form of hot water; however, the systems could produce steam if desired (at the expense of a slightly lower electrical efficiency). EDTEK was selected by the California Energy Commision to demonstrate the efficiency of this technology. An array of fifteen units will be deployed with combined electrical and thermal loads and monitored over a one-year period on the San Diego State University(SDSU) Campuses. Each 4 dish unit will generate 11 kWh of electricity and 29.5 kWh( or 100,000 BTU’s) of thermal output per day.
Twenty university campuses were surveyed as prospective sites for the demonstration. The SDSU was selected because of its reliable, unobstructed sunlight, available thermal and electrical loads and easy access for interested viewers.
Overall SDSU System Description: A block diagram of the overall SolBlu system is presented in Figure 2. The SolBlu units intercept sunlight and convert it to electricity and thermal energy. The thermal energy is transferred to circulating water via an internal stainless steel liquid-to-liquid heat exchanger. The heat exchanger receives cool water from the external thermal load and transfers the heat gained from cooling the solar PV array to it. The energy is then transferred to the thermal load by means of the circulated water. The electrical energy converted by the solar arrays is sent to the inverters as 24-volt, 40 amp DC power(this can easily be adjusted to 600 volts if desired for commercial installations). The inverters convert it to 120 volt AC power and direct it onto the utility grid or to the battery charger which charges the SolBlu “house keeping” batteries that provide standby power to the SolBlu control computers during the off sun hours. The power converted by the arrays, both thermal and electric, is monitored by flow meters/thermocouples and voltage/current meters respectively. The data are transmitted to a local computer for analysis and storage.
Figure 2.
SolBlu specifications and site requirements: The specifications for the SolBlu are listed in figure 3. The SolBlu unit consists of an array of four 56-inch diameter parabolic dishes each of which converts 250 watts of electric power and 800 watts of thermal power yielding a total of 1 kw and 3.2 kw respectively for the unit.
| Each dish diameter: |
56 inches |
| 4 Dish collection aperture: |
68.4 sq.ft. |
Maximum solar energy intercepted
(this is measured for every second its on the sun): |
6,352 watts |
Electrical capacity
(measured every second on the sun): |
1,200 watts |
| Conversion efficiency: |
25% (vs. 10-15% with flat panels) |
| Electricity produced: |
4,015 kWh per year |
| Thermal energy produced: |
37 Million BTU’s per year |
| Hot water produced: |
140 gallons per day @ 140 F
assuming 50 F starting temperature |
| Collection efficiency: |
89% |
| System Efficiency: |
75% (electricity 25% H2O 50%) |
| Primary Solar concentration ratio: |
2400:1 |
| Reflector: |
Glass protected Aluminum |
| Tracking : |
2- Axis( altitude and azimuth) |
| Control: |
on board computer |
| Sunlight: |
Direct (not dispersed) |
| Night and weather protection: |
Ground facing stowage |
| Wind protection: |
Drives to turn edge on | |
 |
Figure 3.
Given the above specifications, the installation site must provide reliable, unobstructed sunlight over an area of 30 ft (east-to-west) by 20 ft for each of the SolBlu units. This area provides for 30 ft spacing between units in the east-to-west direction and 20 ft spacing in the north-to-south direction. The site must provide structural strength to support about 250 lbs per unit and to sustain the lateral and lifting forces that will be experienced due to storm winds. In addition to the physical requirements, the site ideally will provide a thermal load in the form of circulating water with hot water storage and a point for tying the electrical inverter to the utility grid. If no water load is available, heat will be automatically discharged from the system directly to the atmosphere.