I've had 2 companies give me an estimate on photovoltaics for my roof. I want about 125% current electricity capacity because in 4-5 years when a car dies I want replace it with a plug in electric to charge off of my house. Going grid tied. To get125ish % would have to get 327 watt panels.
Both outfits told me I'm at 80% for sun. I had one tree cut down and a few branches trimmed. Roof faces almost dead south. Most of paneled area would be at 28 degree pitch.
Company A said get central inverter Power maximizer
(broken link removed to http://www.tigoenergy.com/data_sheets/MM_ES_datasheet.pdf).
Co B said get micro inverters instead and get creative with a couple different string set ups.
Anyone have any experience with either? Don't want disappointment due to shading knocking down productivity because lots of panels are tied together.
Hi,
Not an expert on this, but I do have a system that uses the Enphas micro inverters.
Just looking at the Tigo manual, it appears that while there is a Tigo ES unit at each PV module there is also a central inverter that they don't provide. So, (I guess) the Tigo units play with the output of each PV module to mazimize its power output, but the output from the Tigo modules is DC and the modules are strung together in a series string and go to a standard string inverter. The advantage is that each panel gets its own optimization (which could be quite helpful for mixed shade), and you get the internet reporting and monitoring of the system right down to the individual PV module.
Install manual for Tigo: (broken link removed to http://www.tigoenergy.com/manuals/install_manual_maximizer.pdf)
With the micro-inverter system, a micro inverter goes on each PV module, and it converts the DC output of the PV module to grid ready 240VAC, which goes right to your circuit breaker box. Each micro inverter is a complete grid-tie inverter.
One thing you could do with the micro-inverter approach is you could initially go for just 100% of your electrical demand, and then add the additional modules when you get the EV. With the micro-inverters, you can use whatever PV modules are the best deal at that time -- they don't have to be the same as the original PV modules. The Tigo system may also allow mixing modules (don't know). A lot of net-metering setups won't pay you for power you produce over what you use on a yearly basis -- they let you accumulate excess power in summer months to apply to low winter months, but at the end of the year its all zeroed out and you don't get paid for your surplus at the end of year. But, it depends on what your utilities rules are.
As far as I know, the Enphase mico-inverters (the most popular brand) only handle PV modules up to 260 watts, so not sure how that's going to work with the 300 watt panels?
Wonder what "getting creative with a couple different string set ups" means? When installers start talking about "getting creative", I get worried
This is my system -- it will give you an idea how an Enphase micro-inverter system goes together:
http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm
This is Doug's bigger Enphase system that uses the new cabling system:
http://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm
It does sound like you have a mixed shading issue, and a system that has optimization for each panel would be a definite plus for you.
This is a bit with my own experience with shading:
http://www.builditsolar.com/Projects/PV/EnphasePV/Shading.htm
Very minor in my case, but there is some info there on the differences between how a string inverter and micro-inverters cope with mixed shade.
Gary
