Grid Connect Systems:
The high voltage DC current is supplied to an inverter, which synchronizes with the utility and converts the energy into AC electricity for the home or business. In most cases the system will be net metered. When the sun is shining, the first priority of the inverter is to power any electrical loads in the building. If an excess amount of energy is being produced then the meter spins backwards and the electricity is sent out onto the utility grid. When there is not enough sunlight to power all the electrical loads, then electricity is drawn from the utility grid as needed. At the end of the month, after all the ins and outs of the electrical usage and solar production, the utility meter shows the net usage. In the event of utility power failure the solar system automatically and instantaneously shuts down. When utility power returns it will test the grid and the automatically restart solar production
Grid Connect with Battery Backup
In areas where power outages are frequent, or buildings have electrical loads that must stay powered, there is the option of battery back-up. The system functions like a traditional utility intertie system, however there is a battery bank that powers loads when the utility power fails. A critical load panel, that usually includes water pumps, heating systems, lighting and sometimes freezers and computer servers is powered by an inverter. The critical loads run off the batteries and solar power until utility power is restored. The system then automatically returns to normal functioning.
Off Grid Solar:
In off grid systems we use large banks of lead acid batteries to store the electricity that is produced by the panels. When electricity is needed in the home, the inverter draws from the batteries or panels and turns the DC into AC electricity. These systems are more demanding to design and cost more due to batteries and additional electrical components.
This technology is just starting to take hold in the market. It is not appropriate for most residential and business installations. However, it combines the advantages of high efficiency utility interconnect inverters with the independence of off grid. This approach is used mostly in villages, islands and small off grid communities.
Solar Thermal Systems: A Basic Explanation
Part of sunlight is thermal energy. This is evident to anyone that has walked across pavement or hopped into the car on a sunny hot day. Solar thermal systems are designed to efficiently capture this energy and use it to heat domestic hot water and occasionally heat living space. This is done by putting heat absorbing metal plates in sunny locations and circulating fluid through them. Due to the cold climate of the North East, a majority of installations are closed loop systems. Thermal collectors, both flat plate and evacuated tube, absorb the heat in sunlight. The energy is transferred from absorber plates inside the collectors into propylene glycol, a -50F heat transfer solution. The glycol is then circulated through a heat exchanger in a solar storage tank where cold incoming water is heated for domestic use. Solar Thermal systems are preheat systems that operate in series with your existing heating source. There is usually no need to alter the existing hot water heating system. If the water in the solar storage tank is hotter than the temperature setting in the primary tank, then the solar heated water passes through without further heating. If the water in the solar storage tank is cooler than the temperature setting in the primary tank then additional heating is provided.
In some installations large tanks of water and sand beds are used to store heat gathered from the collectors. This heat is then distributed to domestic hot water, indoor swimming pools and radiant heating slabs.