solar electricity

EHH week 17: resilient design

Most houses are totally dependent on municipal utilities for power and water, what a friend of mine calls “life support.”  Cut the utilities, and the occupants are left to freeze in the dark while their food rots. 

 

A major goal for Harvest House’s owners is to be able to withstand all nature’s calamities in their house.  In the Seattle area these include earthquakes, floods, and wind.  In December 2006, a wind storm left over 1 million without power, some for as long as 5 days. 

 

This house was designed by the structural engineer, Harriott Smith Valentine, to the strength of a critical facility, like a hospital or an airport control tower.  The building is superinsulated, has a root cellar to store food, and has four huge tanks in the basement to store rainwater.  Without any operating equipment, the occupants will have shelter, warmth, food, and water. 

 

Factor in its solar energy systems, and this house can enable its occupants to live in complete comfort for at least 3 weeks.  With both photovoltaic (solar electric) panels and solar hot water tubes, which are backed up by batteries and a propane generator, the lights will glow, the refrigerator will stay cold, the oven can warm, the heat will flow, and the water will be potable.  By rationing their usage of electricity, they could live independently for many months.

 

With climate change ratcheting up the frequency and intensity of storms and droughts, there is a growing interest in what Alex Wilson calls Resilient Homes.  Alex and Jerelyn Wilson of Building Green visited Eastside Harvest House in October 2011.

EHH week 23: PV system

With the array rack in place, it was time to install the PV panels.  Each one is 4 feet by 4 feet and secured to a special stairstep bracket that allows air to pass around it to help keep it cool.  Ironically, the hotter the panels are, the less power they generate.  The bracket also provides a nifty chase for the wiring that runs from the back of each panel.  The brackets are bolted to aluminum rails which in turn are bolted to the steel pipe rack.  Simple.

 

The panels are Silicon Energy Cascade SiE195, made about an hour away in Marysville, Washington.  They arrive in tidy flat stacks and are absolutely gorgeous.  They have no aluminum frame like most PV panels.  And they don’t have a white PVC backing, so they look great from below, which is how the homeowners will see them.  The cells are spaced apart a little bit, so you can actually see the sky through the glass gaps.

 

The electricity they generate is fed to two DC to AC inverters, SMA America Sunny Boy 8000-US (grey), which send electrons to the utility grid and to four AC to DC inverters, Sunny Island 5048-US (yellow).  The yellow inverters charge the 24 on-site sealed-lead-acid batteries, Sun Xtender PVX-12150HT, that live in cabinets in the garage.  If the power grid goes out, like it did for 300,000 people during a blizzard a few weeks ago in January 2012, the batteries can keep this house humming along.

EHH week 22: PV rack

The Eastside Harvest House is aiming to be a net-zero energy building.  That means that it will generate on site at least 100% of the energy it uses on site.  All the energy the homeowners use for heating, hot water, air conditioning, lighting, cooking, fans, pumps, computers—everything—is expected to be 15,500 kWh (kilowatt hours) for a whole year. 

 

To generate that much electricity, they need to install a 17 kW (kilowatt) PV (photovoltaic) system.  A fixed 1 kW PV array tilted at a near optimum 25 degree angle from the horizontal and facing due south generates about 980 kWh annually in the Seattle area, even with our notoriously cloudy weather. 

 

That means we need a 60 foot long by 24 foot tall array.  We can’t use the roof of the house or garage because they face the wrong direction, aren’t steep enough, and are too small.  So the solar contractor built a custom rack from steel pipe.  It runs over the garage and is partly supported by the garage roof.  The rest lands on concrete footings on the ground, each at a different height which required precise lengths of pipe.

 

The rack made use of standard pipe fittings to make it relatively easy to weld together in the shop and then assemble with bolts in the field.  It is powdercoated black to stand up to the weather and look sleek.  A structural engineer made sure it can resist strong winds trying to send the PV panels into the neighbor’s yard.

Smart design begins here.