Tech Q & A: Off-Grid System Design

Q: When would it be ideal to implement a tracker like zomeworks into the design?

A: Only when the load is larger in relation to the solar input in the summer. A PV direct well pump is a good example. With the low cost of PV modules it is rare that a tracker will be advantageous.


Q: Are energy star labels based on worst case? For example fridge/freezer on COLDEST setting vs a mid setting? If it isn’t based on coldest, would it increase enough to need to be considered when sizing?

A: As far as I’ve seen they are an expected average. Refrigerators I’ve measured in a normal temperature space, set for normal inside temperature, draw almost exactly what the Energy Star yellow tag says it should. I would expect energy use in refrigerators and freezers to be fairly strongly affected when used in other conditions.


Q: Do you recommend any good wind turbine models for off grid systems?

A: It’s hard to make a case for small wind generators considering the low cost of PV modules. That said, I’d look for a manufacturer that has been in business for a decade or more and has existing systems known to work or otherwise verified. Home Power magazine occasionally evaluates small wind generators and I’d stick to those. This has so far excluded ALL vertical axis machines (VAWT).

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