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Green Collar Careers - Grid Tied and Off Grid Power

Off Grid Power is for a building or system that will not be connected to the utility power grid.  While that can simplify some of the inverter complexity and utility connection red tape it also suggests that some back up system will be required when the generation system is inactive.  Usually that means batteries. Off Grid systems generally require a more robust design for the inverter, and may even require a dual inverter system and a battery charger system.

 

Grid Tied Power simplifies the overall system design because the utility power will handle the excess surges from appliances like HVAC systems or well pumps and usually there are no batteries to charge.  Some installations that have frequent power outages may choose battery back ups although less then 3% of the grid tied systems use them.

Grid Tied power has become much more readily accepted by utilities, in fact several utilities offer special bonuses for those who install grid tied renewable energy systems.  For example in Texas one utility will actually pay residential account holders over $2 per installed DC watt of panel and pay for the excess power generated by the system at wholesale rates.  For a 3000 Watt system, that translates to the homeowner receiving a $6000 check from the utility just to install the system.  So why would they do that?  The utility is buying a Carbon Credit at lower cost then they pay for commercial wind turbine Carbon Credits.

In most cases the utility will stipulate minimal specifications for the inverter, breakers, ground and lightning surge protection required for the installation.  In nearly all cases the utility will maintain a listing of qualified inverters and any other protective equipment they require.

In nearly all cases the installer will need to be certified by the utility.  That only applies to the craftsperson who makes the electrical connections not the entire system installation.

In nearly all cases the utility will buy back surplus power at wholesale rates; if through the daylight hours the system generates 6kWh and you only use 2 kWh at the same time, the remaining 4kWh is "in the bank" for you to use later at no extra cost.   However if at the end of the month you produced 100 kWh more then you consumed, they would only pay you a reduced rate of wholesale price.  Wouldn't it be nice to get a check back from the utility provider with the bill?

If the system you're designing is a Grid Tied system, the first place to begin is consulting the available utility services to see what they offer and what they require.  All options must be carefully considered for the customer in this decision as they generally will have a long term contract with the utility particularly in the event the utility purchases the Carbon Credits from them.