Sunday, March 28, 2010

Photo voltaic revisited

Since I started "greening" my house this past year, I have had a lot of people asking me questions about it. First, I don't really see this as a "green" project as much as a "I hate contributing to the political mess involved in using imported oil" mess. A long term investment in my home as well as reducing my electric bill are two of the other advantages. Being "green" is a nice to have, but not my one of the primary motivators.

I'm about to add the next phase to the roof; an additional 15 panels and inverters. This should reduce my average Hawaiian Electric Company (HECO) bill down to around around $8.00. That is the "monthly connection fee".

Here are the answers to a lot of the questions:
  • The system uses SunPower 220 P/V panels that are around 5' long by 2.5' feet wide and Enphase 190 DC to AC micro-inverters. Each panel has its own inverter.
  • The system "wakes up" as soon as the first light shines on it (around 6:45AM)
  • Optimal power production occurs between about 9AM and 3PM. A 6 hour daily window; though the system produces power as long as there is some light.
  • During a typical day, each panel produces around 1KWH. So, 15 panels usually produce between 14 and 16KWH in the winter. However, I have had several 19KWH days.
  • The total system cost was around $28,000 including the mounting on the roof and all of the electrical work necessary to tie 3 separate P/V circuits (just 15A breakers) in to the house. The 3 separate circuits was a design decision that I made.
  • If you want to come by and see the system, sure, come on by. But there is not much to "see" besides some circuit breakers and the panels themselves. The real interesting stuff is in the software which you can see from where you are sitting. The Enphase software allows you to view my system's out in near-realtime. Well, about a 30-45 minute delay. See McBee Photovoltaic system.
  • For the 2009 tax year, I'll get approximately $19,000 in tax credits (state and federal). Thus, the actual out-of-pocket cost for the first year is around $9,000.
  • Actual "payback" at the current cost of electricity (around $0.24 / KWH) is around 7 years.
  • If you are considering this and have the sunlight available, do solar hot water first. Second, put in a "low flow" pool pump (if you have a pool). Both of those provide a better return on investment. I have both; P/V was the next logical step.
  • The panels are on the south-facing side of my roof. They take up about 1/4 of the south facing roof space. For the most part, my neighbors cannot see them.
  • I financed the first year and most of it back from the tax credits. The remainder, I paid back from my savings account.
  • I am adding 15 additional panels next month and am using SunPower's "no interest and no financing for a year" program to finance them as well.
  • I picked the SunPower 220 panels and Enphase micro-inverters because liked the idea of the panels functioning independently. The sizing of the panels and the inverters was confirmed by the vendor (Sunetric Solar Power of Hawaii).
  • The vendor (Sunetric) did ALL of the installation work including the electrical work, permitting, HECO paperwork, and mounting the panels. I just watched and took pictures. :-)
  • There are NO batteries; I am not 'off-the-grid'. Maybe in Phase 3 I'll do that for some critical house-hold things such as the refrigerator, microwave, and a few outlets.
  • On average, I "push back" to HECO around 6 to 8KWH per day of electricity that is then used somewhere else on the grid.
  • At night, I use power just like everyone else. HECO gives me "credit" for the power I sent to them during the day. The idea is to "size" the system so that it generates in about 6 hours the total amount of power you need for 24 hours. HECO only gives a 'credit' for the power. If I consistently generate more power than I need each day, HECO wins. They will NOT pay me for the excess power I produce; only a one year credit.
  • If the commercial power fails, my P/V array shuts down. That is a feature of the inverter. The inverters have to have an "A/C push" from the utility otherwise they don't work. This is so that if HECO shuts off power on my street, I don't keep pushing power out and shock their lineman (line-person?)



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