Solar Systems Connected to the Grid - Rules?

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Power

There have been several reports in the news papers recently about solar PV systems in Karnataka getting connected to the grid and injecting power into the electric grid when they produce more than they need.  Today's Bangalore Mirror had a news item (click here) about a city resident who claims to inject power back to BESCOM.  Though he claims that it is done for free, if the power goes back through his meter, he may actually be getting a rebate by having the meter run slow or even backwards, something known as net metering. The discussion in Praja on SB's blog earlier on this topic can be found here.

BESCOM MD, Mr. Manivannan is quoted as welcoming the move whole heartedly, though his actual quote expresses reservations on the issue. The quote is reproduced below.

"P Manivannan, managing director, Bescom welcomes the move whole-heartedly. “I think the trend is slowly picking up in Bangalore. At a time when we are facing enough power-related problems, this is perhaps the best way to get the quantity of power you require. However, when it comes to supplying generated power back to the Bescom grid, there is a problem as one cannot guarantee the same quantity of power on a 24X7 basis. The fluctuation in supply to the grid affects other customers as a specific load will be allocated to them. Further, you cannot compel the owner to limit its consumption to a certain level.”

This story brings up several important issues that needs to be addressed.  The price of solar PV has dropped sharply and continues to do so following several factors, such as glut of polysilicon raw material in the market, entry tof chinese manufacturers in this area, economic slowdown and withdrawal/reduction of subsidies and benefits in European markets.  This makes it increasingly cheaper for people to buy panels for their use.  However, when such systems are connected to the grid and actually push power back, several precautions need to be taken.

As Mr. Manivannan clearly notes, power is available from solar systems based on when the sun shines.  So matching load and demand can become a problem as number of such systems increase.  The grid is now maintained through a very carefully performed process of load forecasting and having power generation or putting in for buying power so that sufficient capacity is always available to match the demand profile. When there is a mismatch, you have load shedding. Solar and wind systems make power when the sun shines or the wind blows.  However, there also other issues that need to be kept in mind when people connect their solar systems to the grid. Some of these factors in brief are as follows.

  1. Limit on single phase generation: If there are many such micro generators (as we can call small solar PV panel installations) and their supply is not balanced among the phases, the network can become imbalanced.
  2. Generation quantity limits - The power generated should not impact the voltage beyond a limit and the generated power must be within limits of the load sanctioned for the installation since wires are sixed accordingly.
  3. Occupational safety:  Clear standards need to be defined and safety precautions in place so that in the event of a network outage or undervoltage issue or power being shutdown for maintenance, there is no power fed back into the grid through the PV.  This can cause serious disruptions or even cause injury or death to maintenance staff. THe system operator (BESCOM) must be aware of all microgeneration installations in an area.
  4. Quality of electricity:  There are strict criteria so that having multiple generation sources does not impact the quality of electricity available in the grid. This includes the issue of harmonics (distortion of the Sine wave AC signal) and EMC (ElectroMagnetic Compatibility) requirements.

Going by the reports in the press, it is important that BESCOM look into framing rules for such installations (not sure how easy it is or if BESCOM can do it independently without involving the KERC and other bodies) and to notify the public that such random ad-hoc installations are not allowed. The BM article certainly made it sound as if it is not a big deal to plug your solar panel back to the grid.

Discussion on Praja itself on this topic has been around making a neighborhood micro-grid which then interfaces to BESCOM supply.  All these are good ideas, although there is a need for standards, suitable equipment and more studies on such concepts.  The grid operator and the grid itself will also have to get a lot smarter as the number of such installations increase.  Currently, I suspect we have sufficient generation deficit that a solar system that produces power probably has not much of an impact.  

However, in countries like Germany where generous laws have led to massive number of installations, the traditional power plants have to adjust to compensate for the variable production from these generators.  Such a situation can impact the Plant Load Factor (PLF) and thereofre the profitability of the traditional generators.

Overall, a complex topic that will not fit into one blog post, but there is a need for our utilities to get proactive to specify rules and plan for such approaches.  Currently, we have massive power generation deficits, encouraging microgenerators may be a good idea and the impact on the grid may be small (somebody needs to do a proper analysis).  However, it is important to plan further along to the future and start framing rules and planning now for a situation where there are large number of microgenerators that can impact the overall grid performance.

Disclaimer: Since this topic intersects with my professional interests,  and I am not allowed to speak for my company on any public forum, all the discussion in this post is based on material available in the public domain and opinions expressed here are my own.