SolarAndWood said:
So, to do grid tie you need to use certified installers in NY. What is the idea with DIY? You install the system, run DC in the house for whatever you can and then charge the batteries when you don't have enough sun with power from the utility? Or do you go off grid and then make up for the low periods with a generator? When I look at the solar analysis of my site, I would need some big damn batteries to store the power I generate in July to use in January?
Hi,
My system is a regular grid-tie system. I did the install, but it was under a permit and inspected and signed off. The utility then installed a new net meter. So, its just like any professionally installed system. Montana (and I think most states) does not require a certified installer.
The installation is very straight forward if you have done much of any wiring before.
The system is described in mind numbing detail here:
http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm
As you know, when there is a power outage, a regular grid tied system goes down and does not provide any power even if the sun is shining. The grid tie inverters test for the presence of the grid power all the time, and if its not there they shut down until the grid comes back. This is required to get the UL approval for a grid tied inverter. There are grid tied systems that provide battery backup during power outages, but they add a fair bit of cost, and you have to maintain a battery pack that just about wipes out any savings the system might generate.
What I am trying strictly for power outage emergencies is to basically rewire some of the PV modules in my grid tie system to drive a normal charge controller, which charges the batteries in my ElecTrack electric tractor. I've added a combination charger/inverter to the ElecTrack, so that we can get 120VAC power from the ElecTrack battery pack in power outages. The advantage of this over just getting a grid tie system with battery backup is that I don't have to maintain an expensive battery pack that is only used during very rare power outages. I can just use the pack in the ElecTrack. I use the ElecTrak for mowing, snowblowing, ...
For a power outage, the way the sequence goes is: 1) I throw the PV system AC disconnect (so the PV system is completely isolated from the grid), 2) I cover the PV panels with a tarp, 3) I rehook 6 of the panels into 2 strings of 3 panels, 4) I hook the two strings to an Xantrex MPPT 150 charge controller (which I bought just for this purpose) - at this point, the PV panels are charging the ElecTrak pack, 5) plug the inverter into the battery pack, and 6) run extension cords to key loads that we need during an emergency (fridge, ...). I figure this will give us about 5 KWH a day no matter how long the power outage goes -- 5 KWH is plenty for the stuff we really need. The ElecTrak battery pack is six 220AH Trojan 105's (just like a lot of golf carts).
This is all easier to do than it sounds -- partly because the panels are on the ground. The rehooking is quite fast because the MC4 connectors are easy to connect and disconnect. Basically the only cost over what I already had for the ElecTrack was the new Xantrex charge controller and some wire -- about $500 total. I do have to admit that part of the appeal was just to see if I could make it all work
If you want to see how addictive these ElecTraks can be, have a look at George's collection:
http://www.myelec-traks.com/
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On the other question about cost of the micro inverters. I've found the same higher prices when you buy only the inverter, but (at least at WholeSale Solar where I buy stuff), the equivalent packages with the micro inverters are actually a little less than the same package with the string inverter. Have no idea why this is true.
Gary