Going Solar! Part 2

Last time I wrote about our solar system, I wrote mostly about the process of getting solar on our roof, but not much about the system itself.  So, this is more on the system and the science!  I've wanted solar since I was my kids' age, so this process has been really cool to see unfold on our rooftop. 

Solar science is really interesting, and it's gave me even more incentive to understand more about electricity and how it is delivered.  Particularly direct current (DC).  I understand alternating current (AC) pretty well, but I'm a little fuzzy on how DC works!

DC vs AC

Direct current has a lot more variation in its delivery than alternating current.  Direct current - think simple battery circuits - are completely determined by the amount of energy a device is pulling -or the panels are pushing- through the system.  Instead of a fixed number of volts, the power is pulled in based entirely on need instead of being pulsed through a system.  Direct current is like a plumbing drain.  When the toilet flushes, the water leaves at the speed it leaves based on the toilet, not the supply.  

Alternating current is more like a pulse.  The voltage is static, and the amperage maxes out based on what circuits and wiring are available.  I wrote a lot more about that here.  

Solar systems use both.  Solar panels collect energy using direct current while homes and the power grid all operate in an alternating current system.

The Panels

We started with a roof that had very little coverage from surrounding trees or buildings, so solar was an easy choice to add here.  Our proximity to the alley and the neighbors means that almost none of our roof can be shaded, and with two nearly unobstructed gable sides there was plenty of surface area to add a large rooftop system.  Our system is 17 KW, and will produce between 12 and 17 KWs yearround. 

The panels are really cool!  Our system manufacturer is Enphase, and they use microinverter technology to convert the energy from direct current to alternating current before the energy leaves the roof.  The microinverter is great, because if there ever is a problem with a panel, it can be isolated without taking down the entire system.  

Connecting to the Grid

Once the power is off the roof, it goes into the AC controller.  It's only job is to combine the energy from the microinverters.  Then it goes into the system disconnect.  There are two switches in case there is any reason to shut down the entire system.  One controls the solar panels and the other controls the transfer switch in an emergency.  

There is a similar system disconnect on our electric meter.  Since we're in Minnesota, our main breaker panel is indoors.  To meet a shift in fire code, there needs to be an exterior shut off for all electric systems; here that is at the meter.  

Our system can run independently of the power grid as well which is what the biggest component in the system handles.  The transfer switch that will eventually have a back-up battery installed. It also allows the panels to feed the house directly if we have an outage during the day.  Next to the transfer switch is the modem.  This puts out a signal so we can monitor our energy use and help diagnose any issues.

The last piece is the load shedder.  This turns off selected breakers at our panel should we need to run without grid connection.  It can disconnect up to four 120V breakers, or two 240V breakers.  I chose to disconnect our heat pump and our water heater.  If we ever lose power in extreme cold, we can run the fireplaces at much lower wattage. Since the load shedder has an upper limit of 40 amps, I couldn't cut power to the entire HVAC system, but without the heat pump, that system will alert us to any issues.

Bureaucracy

This system relied on a lot of moving parts, and even though it was installed back in May, we had to wait for the power company to sign off on the inter-connected system.  Getting any interconnected solar system -especially one this size- requires a lot of coordination.  Luckily, we worked with an electrician who managed all the moving parts very, very well.  There is still a certain amount of "hurry up and wait" with these systems.  

Permitting needs to be approved through both the city and the power company, and that can take a long time to get through all the different steps and individual contracts.   Our house is now a residential solar producer, so beyond just permits, we have an interconnection contract with the power company.  The permitting process took us a couple months, and the final sign off process took nearly two months.  It's a long game, but definitely worth it!

As always, I advocate working with the permitting departments.  Both the city and the power company had some tweaks: the city wanted a minor change to the meter's internal wiring, and the power company supplied us with a new meter.  Without a bi-directional meter, it wouldn't be able to count our production numbers correctly. Looking at the new one, I can tell exactly how much power we've purchased, and how much we've sold back.  It's pretty cool! 

So, after about six months of intense planning with our electricians, we finally have a solar system up, running, and making us a little bit of cash.  I can't say it hasn't been frustrating, and after a false-start with the wrong company, I do have to say that we landed in a much better place.  I can hardly wait to see how the numbers shake out in the next few years!