Strategies for Using a Photovoltaic System to Achieve Net Zero

We have designed a 1400 square foot 2 bedroom house to build near Platt Park. The levels of energy efficiency are comparable to Passivhaus standards, but our main goal is net zero energy cost.  The only way to achieve this goal is with renewable energy. A photovoltaic (PV) system is the best choice.

Now, we could make some reasonable assumptions about projected energy usage for the house in order to size the PV system.  In reality, it's impossible to predict the actual usage for a house, so let's look at the whole problem for other clues to size the PV system:

1.  The roof size places a practical limit on the system size based on the actual roof size and how much photovoltaics will physically fit on it.

2.  In new construction, Xcel Energy limits the size of your proposed system based on how much energy they think you will use.  They make a very primitive and arbitrary guesstimate, but the good news is that they will let you oversize the system and pay you more than retail for all the energy you collect and put on the grid. Since Xcel pays you retail price for the energy you generate, they get to say what the maximum size is.

3.  For an existing home, Xcel will let you size the system based on your last 12 month's actual energy usage.  They will let you build it 20% larger than that if you really want to (because you're SURE to get an electric car here in the next two years, and you need the extra capacity).  For most homes, the roof will be nowhere large enough to provide all your energy needs with PV

Xcel used to pay a one-time cash rebate on your system as soon as it was installed.  Nowadays, the rebate system is performance-based. Your contract with Xcel simply obligates them to pay you, as the system owner, $0.13 per kwh generated, up to the contract maximum per year for ten years.  The contract maximum is also the expected annual output of your system.  This strategy protects Xcel because if your system doesn't perform as expected, they don't have to pay.  It also gives you a big incentive to get your system functioning properly.

By entering into a typical power purchase agreement (PPA) with a solar leasing company such as Sun Run, you can get in the game immediately with no cash out of pocket

Video: Cold Climate Direct SDHW system with Recirculation Freeze Protection

I've mentioned this system before, and I finally made a video.  Please remember this is the first prototype system, and is intended to be temporary.  (It's ugly.)  Our current thinking is that the system isn't developed enough for general public consumption, but I definitely recommend it for do-it-yourself types in milder climates. It is literally the least expensive and most efficient system with freeze protection possible with off-the-shelf parts.

We've instrumented the prototype system, and are checking all the failure modes this winter and measuring the amount of heat lost due to freeze protection.  The video still raises many questions, so don't hesitate to ask them in the comments section here, or preferably at Youtube.

Smart Light Bulbs?

Phillips has recently introduced their HUE lighting system.   It's a wi-fi based light bulb control system for timing,  brightness and color.

How can you use it around the house to save energy?  Honestly, I can't think of any scenarios that would reap enough savings to justify a $60 bulb.

But in multifamily buildings, there's the hallway lighting to address.  In the middle of the night, the hallways could be dimly lit.  During the day, the lights could be completely off.  This system is competitive with the cost of hardwiring timers and dimmers.   And I've never seen dimmable timers.  You could save at least 30% of your hallway lighting cost.  Still, I'd wait until these bulbs come way down in price.  

Product Design and the Fluidmaster Leak Sentry FAIL

Here's a common sense tip when shopping at Home Depot - be very suspicious of buying any product when all the units on the shelf look like they have been returned:

Notice the shabby condition of all the boxes on the right.  The product is obviously a market failure.

It's a great idea - a toilet valve that alerts you to a flapper valve leak.   But somehow the way Fluidmaster has implemented it has turned off customers in a big way.

The Hydro-Clean model on the left is a copy of the Fluidmaster design, and doesn't appear to work much better.   The boxes are fresh only because it was recently introduced.

Now a little commentary on product design and market testing.   Fluidmaster could have saved themselves this costly market failure if only they had gotten a couple thousand out into the field for well-documented feedback.  They probably tested the heck out of these to make sure they worked as designed, and found it was a robust design.

But here's the problem:   They work DIFFERENTLY than what customers are used to.  Sometimes different gets rejected by the market even when it's better.

LED Lighting Update

IKEA has finally put its purchasing power and design talent toward LED lighting.

I think they hit it out of the park, and did it a year ahead of Home Depot.   In the catalog, they mention that the bulbs never need replacing.   Nice.

http://www.ikea.com/us/en/catalog/categories/departments/living_room/20515/

Solar Thermal for the Masses

For a few years now, I've independently been trying to solve the problem of solar domestic hot water (SDHW) systems that are too expensive.  Here's what I've come up with: a simple and cheap solar hot water system design that at the very least should give manufacturers food for thought.

The Problem:  Even small SDHW systems cost way too much ($6-$8k on average)
Since gas heated water is still very cheap, the average family can only save $30/month with solar.

My Opinion:  The US SDHW industry is in deep trouble now, and will remain so until $2000 systems are available. 

A Solution?:  Bring back Recirculation for Freeze Protection (RFP) in all but the coldest climates in the US.

History:  RFP is still used in many non-freezing climates, so it's still a free option on most solar thermal controllers. It's reliability took a hit in the 80s when many systems froze because power failures often accompanied freezing weather. (Freezing rain will often take down power lines) Because of this, most installers eschewed this method for most climates. Historically, it can't be used with flat plate collectors because in the winter it takes too much energy to prevent the collectors from freezing. (They are pointed at the night sky which is usually colder than -100F on a clear night)

Why This Solution Can Work: A. If Evacuated Tube (ET) collectors are used, the heat required for freeze protection is almost negligible, and B. In case of a power failure, the system will self-freeze-protect by thermosiphoning. C. The outdoor piping is freeze and stagnation tolerant hose.

Yes, the ET collector header can still freeze and break, but the probability will prove to be too low to worry about. (Drainback systems have a few failure modes including freezing, but we still use them because the Mean Time Between Failures (MTBF) is long enough.)

I've tested this system for two winters now, and it works great in Denver. Here's a link to the YouTube tutorial about the system.  http://www.youtube.com/watch?feature=player_detailpage&v=N5hdu9p75Vg

For more info and pricing, here's a link to my presentation at the 2012 ACEEE Hot Water Forum.

100% Off-the-Shelf:  Only  five of the items required must be purchased somewhere besides Home Depot:

1.   The pump:  http://www.sun-pump.com

2.   The Pump Controller:  http://www.sun-pump.com

3.   The Collector:  http://www.solarheatexchangemanufacturing.com/NewFiles/heatpipe.html

4.   The ECV, which is a low power consumption electric ball valve from Taco

5.   A 110V SPDT relay is also needed to control the ECV just right.

Just Say No to Twitter

It's an annoying fad that is a complete waste of time for the average person.   And time is your most important dwindling resource.  So cut it out.