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Friday, March 9, 2012

Grid Tie Solar Plug and Play in the US

 

While other countries have commercially available grid tie solar plug and play systems (http://solar-power-station.co.uk/), the US does not.  At least one US company has committed to such a product (http://clarianpower.com/), but it is not yet available.

As part of the US DOE’s SunShot initiative to support a multi-source approach to meeting the country’s energy needs, a meeting was held in Washington, DC on October 27, 2011 to focus on the development of plug-and-play solar technologies in the residential sector. The purpose of the workshop was to identify the current barriers and possible solutions for these technologies. Over 60 people attended the conference, including representatives from utilities, code officials, inverter companies, PV module companies, and installers.

Here is a summary of the results of that meeting:  http://www1.eere.energy.gov/solar/pdfs/solar_plug_play_2011.pdf

Although there seemed to be a lot of off-topic discussions, a few big issues emerged:

1.  How to deal with current permitting requirements for electrical issues. 

Suggestions for dealing with electrical safety issues to avoid permitting and inspections by local code enforcers seemed to be fairly straightforward:

--UL listing for PV system: NEC 90.7 Equipment that is listed “need not be inspected at the time of installation.”
– Develop a standard PV plug at the utility meter (or elsewhere)
– Changes to the National Electrical Code are required (we are on writing code council)
– Smart, PV-ready circuit breakers.

2.  How to deal with current permitting requirements for structural safety issues.

Suggestions for dealing with structural issues such as modules resisting windy conditions and PV systems compromising building structures were less imminent and not as practical.

--Can we build a PV system on a residential home that is
• Light-weight (polymer)
• Requires no roofing penetrations (can’t have roof leaks)
• Requires few (or no) tools to install
– Can we design a PV module/array that fits around a roof like a fitted sheet on a
bed?
– Establish requirements for solar ready houses (standardized roof jacks)
– Consider composites, polymers… integrating frames and mounting systems can dramatically reduce weight.

3. There was also discussion about how to integrate Plug and Play Solar arrays with smart grid issues.

I learned a few things from reading the summit results.  The electrical safety concerns seem to be fairly easily overcome.  Many of the obstacles are not difficult safety barriers, but more code-related.  Limiting the Watt size of plug and play systems on each branch circuit allays overloading concerns.

According to NEC 90.7, UL listing is not required, but if non-UL listed equipment is used it must be inspected at the time of installation.  Some advocated a UL listing for the entire system (modules, wiring, inverters, connectors), while others advocated each component be UL listed. 

There are concerns about using the standard three prong plug to simply plug into an existing outlet.  They talked about developing a USB like plug specific to PV systems so people aren’t exposed to live conductors on the male end of the plug.    I don’t really understand the concerns here.  An anti-islanding grid tie inverter shuts off when it is pulled out of the outlet, effectively cutting off current to the plug, and protecting the user from contact with exposed conductors.  The British system uses a standard outlet connection with anti-islanding China-made inverters.

Given the seeming lack of consensus on the structural issues associated with attaching plug and play to buildings, it seems simply requiring ground mounting makes the most sense.  I think keeping people without fall protection off of roofs is a good thing.  Many commercial solar firms working on roofs don’t even provide fall protection systems to their employees, and there are several deaths from roof falls annually in the business.

As a result of the workshop, in January 2012 the DOE announced a 3 year grant program to fund studies on plug and play solar issues that came up in the workshop:  https://eere-exchange.energy.gov/Default.aspx?Search=plug&SearchType=.  It appears that it will be a few more years before commercial plug and play grid tie systems hit the markets in the US, and with the desire to incorporate smart grid components into the system, more than a simple inverter will be required.

So why is the whole issue of plug and play grid tie solar so important?  A 500 watt back yard grid tie system generates about 650 kWh of electricity each year where I live.  In my local utility area, that translates to about 9% of the average residential customer’s annual electricity use.  Besides saving money for the customers, widespread use of these systems could slow the need for new power plants and drastically reduce carbon emissions.  I also recently read the book “The Big Thirst” by Charles Fishman, and learned that steam generating power plants use over 200 billion gallons of water a day to make steam and cool heat exchangers (http://powerscorecard.org/issue_detail.cfm?issue_id=5).  Solar modules require no water for cooling.

While we wait for commercially available plug and play grid tie systems, DIYers need a UL-listed DC to 120V AC inverter, or guidelines for inspectors when non-UL listed equipment is installed, and code revisions that allow connection to the grid.  If other countries have already overcome plug and play solar obstacles, why can’t we?  As the world becomes flatter and hotter, is a three year wait for plug and play solar that is already available elsewhere acceptable?

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