Thursday, January 12, 2012

A Rough Cut Take on the 70% Rule

A new 70% rule took effect January 1st in Germany. This rule limits the amount of backfeed from a PV system to 70% of the system's peak rating. This means a 10 kW system would only be allowed to backfeed a maximum of 7 kW. This new rule has been put in place to limit the costs of expanding the grid to accommodate peak PV. The annual losses to PV system owners are projected to be an acceptable 1 to 3%.

You kinda have to wonder, why 70%? Maybe it's because the annual losses are minimized. If that's the case you'd have to figure this may be the beginning of something. Perhaps next year the 70% rule will become a 60% rule and a 50% rule the year after.

Another thing to wonder about is why does a home with a 20 kW system get to backfeed 14 kW when a home with a 10 kW system may only backfeed 7 kW? This doesn't seem equitable.

All and all I like the rule. This rule does at least two things. First off, it limits the effect of PV peak on the grid and it does so at minimal cost. Second off, this rule may end up encouraging customers to use energy management systems (EMS) to utilize that 1 to 3% of lost production. And if the 70% rule with its 1 to 3% losses doesn't work maybe the 60% rule with its 10 to 15% losses will.

But then I think... if regulators want people to buy EMS systems why not simply mandate them? But then I think... well, the EMS systems aren't quite smart and cheap enough yet - maybe this is a transition strategy designed to encourage the adoption of EMS systems. Sorta like mandating that cars come with seatbelts, waiting several years for people to get used to them and then forcing people to wear them whether they want to or not. Kinda makes sense... Those damned Germans and their master plans.

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