Category: tech tips


Electric cars like the Nissan Leaf could be a real game changer.  After crunching some numbers, I calculated that the cost per mile driven in a Nissan Leaf could be noticeably cheaper than a comparable gas vehicle.

This is an exciting development for the solar industry since you can produce the electricity for driving your electric car with a solar PV array. This makes electricity a more significant competitor to oil and could help increase solar implementation rates for consumers.

I ran the following calculations on the cost to drive 10000 miles per year in an electric car compared to a 30 mpg gas engine car.  Here are my findings.

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Flat vs. Tilted Arrays

flat array                      tilted array

One of the most unfortunate mistakes made in PV system design is the flat mounted array.  You should ALWAYS mount modules in a tilted configuration. Lets explore the benefits of the tilted array…

1) More power production results from better sun angle - Modules tilted up toward the southern horizon in the northern hemisphere (or towards the north in the southern hemisphere) will produce considerably more power than modules that are flat.

2) Sheeting of rain water promotes module cleaning - Tilting your array promotes sheeting of rain to clean the modules.  Flat modules are a wonderful catch basin and turn into a a shallow puddle every time it rains.  An even bigger problem can result  View Full Article »

Shade mitigation products like micro-inverters and energy maximizers are the hottest new products in solar.enphase

Enphase micro-inverters provide a convenient solution for dc-ac conversion, shade mitigation, and module level power production monitoring.  Micro-inverters convert DC to AC power at each and every module in the array.  This eliminates the difficult process of string sizing and reduces the problems related to more dangerous high voltage dc strings.

tigoThe Tigo Energy Maximizer dc-dc power optimizer offers shade mitigation, module level mpp tracking, module level production monitoring and they work with any string inverter (SMA, KACO, Fronius, PV Powered, Xantrex etc..).  An additional important benefit of dc-dc power optimizers is they cut the string voltage down to module level voltage if the AC power is lost.  This means that when your main breaker is off, the high voltage strings drop to module level voltage making pv system servicing easier and safer. View Full Article »

The devastating effects of shade

Even small amounts of shade can cause MAJOR power interruption in a solar array.

If you shade only one cell in a module you will likely see a 33% power reduction from that module. If you shade a row of cells in one module, you will see a devastating 90% power reduction. The even bigger problem is that every module in the series string will see the same power reduction.  So when that chimney casts a shadow over one row of cells on the last module in a string of 13, you lose 90% of the power to ALL 13 modules

Most experienced site assessors use the Solmetric Suneye or Solar Pathfinder to determine shading problems before determining how large an array can be mounted in the desired location.

Micro-Inverters (like Enphase) and energy maximizers like the Tigo system can help minimize the power loss due to shading, but solar pros agree that every effort should be made to ensure ALL modules are shade free between the hours of 9AM and 3PM.

ps. even shadows from power lines and bird poop (especially pigeons!) can cause a noticeable power reduction.