Thursday, May 22, 2008

Looking for a house..

We spent about a year looking for a house. We cared about the standard stuff.. is it enough room, are the schools OK, is it close enough to work, and, since it's the San Francisco peninsula: how easy will it be to rent out part or all of the house, since meeting the other criteria can pretty much guarantee a big mortgage payment.

During this whole time we never thought much about the potential for "greening", and it was low on our priorities list. Fortunately, we lucked out and it turned out that the house we bought will be pretty straight forward for putting up solar panels and wiring them into the house. I wanted to take this moment to fire up a quick list of what to look for when buying a house, relative to the "greenability" of the house.

  • Clear south view with no shade on at least one south facing roof surface a couple of hundred square feet big. See the previous post for more info on this one.

  • Roofing material: composite shingles are easiest to work with... spanish tile can be a nightmare. BUT, if the roof needs to be redone anyway (i.e. it's old, it's shake, it's got problems) the new roof will probably be composite shingles and you can coordinate with your roofer to install the necessary standoffs and flashing for the system before the new shingles are applied. If a roof is more than 5 or 10 years old, it's a gray area, because the solar panels will outlive the roof, and at one point you'll probably have to take down your system, re-roof, then re-install your (at that point older) solar panels. Not that this is a showstopper, but it will create extra work that you have to think about.

  • Roofing support structure: most houses built after the 1950's are fine.. but if you have your eye on that Victorian mansion then better have a structural engineer check it out before adding extra loads!

  • Existing electrical system: fuses=bad, breakers=good. The main breaker would be nice to be bigger than or equal to 100 amps. This is also not a showstopper, but you'll probably need to plan on upgrading the service if you have fuses or less than 100 amp service, so expect more costs.

  • Existing insulation, appliances, windows & doors: maybe this is a no-brainer, but if you don't at least try to become as efficient as possible *before* going solar, you're still kind of throwing away dollars (and watts!) Look for dual paned windows, weatherstripping, and energy star appliances. Attic insulation should be at least as tall as the attic joists. In-wall insulation is more rare, but can be retrofitted pretty easily by companies that will spray old newspaper into your walls. (this is on our to-do list)

  • Heating, ventilation, air conditioning: again look for efficiency, and the ability to split into separate heating zones is quite useful, so you don't have to heat the whole house when you're only using 1 room.

  • Landscaping: look for native, drought resistant plants that don't take a lot of water. It's becoming more common, but still isn't really well advertised.

All in all, most of these can be retrofitted for some cost, but the south facing roof may not be possible due to pure geography and location of neighbors trees and 2nd floors and the like. Even trees on your own property can cause trouble, and there is a hefty fine for removing a tree without a permit in many cities. Anyway, trees are great and add incredible value to a property, don't plan on removing a tree to make a solar system "work".. it's probably not going to pay off.

Friday, May 16, 2008

Step 1 - Site Selection

Site selection is extremely critical, since solar panels take up space, and space is a premium in California. Most California homeowners can't afford to simply clear out a field and plant an array of solar panels there. We have to work with existing structures, existing trees, and to be cost effective we usually must mount the panels flush on the roof surface.

The first step the pros usually take is to look at an aerial photo of the property on google maps. The best mounting locations are on south and west facing roofs. Shade is enemy number one, so look for tall buildings and trees that might cast shade on the spot you picked out. The rule of thumb is that the object should be at least twice as far away as it is taller than your spot. So if your roof is 10 feet tall, and your neighbor's tree to the south is 20 feet tall, it better be at least 20 feet away! Otherwise that site is automatically ruled out, pick a different roof surface. The critical time to be 100% shade free is between high noon and 6pm in the summer months, as this is when electricity is in highest demand and is thus the most costly. So look for shade objects to the south and west of your site in the aerial photo.

I can't stress enough how important it is that the spot you pick be shade free. Even a small shadow from a power line or a tall trunk of a palm tree can be enough to basically wipe out production of a full string of panels. It has to do with the way the panels are electrically built: bypass diodes inside the module will cause the production to go to zero in a shadow.

Installation is also possible on flat roofs and patio covers, but I would consult a structural engineer to feel confident on anything other than an existing pitched roof with shingles or tiles over 2x4 or similar rafters.

Now that you're through doing the initial work on google maps, and are fairly confident you have a spot (or a few spots) that are decent candidates, it's time to get up on the roof and take a closer look. On a sunny weekend, go to your candidate sites at 9AM, noon, 3PM, 6PM and note where you see shadows falling. Avoid those spots that catch shade as much as possible! If there's too many shadows, eliminate that candidate and move on to the next one.

In the next step I'll go over advanced site selection, and we'll break out the tools that will help to really solidify what makes a great site.

Wednesday, May 14, 2008

First Post

The purpose of this blog is two-fold:

  1. Provide people with a reference for how to design and build their own grid tied PV Solar electric system in California (including design and implementation tips, as well as how to take full advantage of incentives and tax credits)

  2. Document my own photovoltaic electricity generation intertie system, from the planning and design through the build, tie in, and eventually performance info

Stay tuned for more!