Looking for charge controller and batteries for off-grid?

[pinwheels]

The proverbial "friend of a friend" has 175W 24V PV panels (BP4175) for $200. That's like $1.15/W. They may be used, not new. Apparently, he got stuck with them as they don't meet the long-term degradation standards for CEC tax credits. Their loss. That's about $1.15/W.

Anyway, I'm putting together an off-grid 12V back-up system for radios, computer, and hopefully keep a refrigerator going during an extended outage. I'm looking for appropriately sized batteries and an MPPT charge controller. Any suggestions?? I'll probably get two (350W total) and stick a 1000W inverter on it at some point to drive (hopefully_ a refrigerator, laptop, misc.). So . . .

I'm looking for an MPPT charge controller capable of nominal 24V input and ~30-40A output (preferably programmed for different cell types like AGM vs. flooded). Also looking for batteries (preferably AGM, but costs could get prohibitive) - 12V, 200+Ah. Anybody got suggestions?

[GrizzlyGuy]

How many of the BP4175 panels will you be using, and how long will the wire run be between the panels and the charge controller/batteries?

If it is a long run, you can reduce loss by connecting the panels in series to get a higher output voltage and that will result in less loss in your wire run (loss is I^2 * R so higher voltages and lower currents result in less loss). If you do that, then you'd want to choose a MPPT controller capable of handling the higher input voltage.

Since you will be running radios from your system, the amount of RF/EMI noise generated by the charge controller is something else you should consider. The Xantrex XW-SCC looks like a good candidate:

The Xantrex XW is the only solar charge controller that meets FCC class B requirements for RF/EMI noise. It is the controller that we recommend for any larger solar powered systems for radio or cell phone sites. It is also the only MPPT controller that reads the actual measured input current from the array.

Specs are here. It will handle 150V of open circuit solar panel voltage, and the BP4175 panels have an open circuit voltage of about 35V. This means that you could wire up to 4 panels in series for minimum loss.

[pinwheels]

I was orginally planning on one or two panels. One is enough to power radios. I thought two would cover a refrigerator. Then I did the math. A refrigerator uses 2-3 kWh/day, meaning 400 - 600 Watts from PV after losses in cable, charge controller, battery and inverter, and 250 Ah/day out of the batteries. This is gonna get expensive! I may skip the refrigerator idea and go back to one panel. BTW, it's going to be about 50 ft from panel to controller.

[problemchild]

I was orginally planning on one or two panels. One is enough to power radios. I thought two would cover a refrigerator. Then I did the math. A refrigerator uses 2-3 kWh/day, meaning 400 - 600 Watts from PV after losses in cable, charge controller, battery and inverter, and 250 Ah/day out of the batteries. This is gonna get expensive! I may skip the refrigerator idea and go back to one panel. BTW, it's going to be about 50 ft from panel to controller.

Might want to look into solar friendly refrigerators that use less power.

[pinwheels]

Got a new plan. Will add more in an hour or so . . .

[pinwheels]

This was getting too expensive to justify the extra cost for just-in-case battery backup for extended outages. On the other hand, if I drop all but about 200Ah of battery for radio operation with a small charge controller, but put in enough panels and a grid-tie inverter sized to drive the refrigerator and a few other things during daylight hours only if grid power is off, the refrigerator can (I think) stay cold enough to preserve food overnight. I can also drop my utility bill by a reasonable fraction on an ongoing basis. That's the new plan. Now, I need to do some research on power consumption when the compressor is running to figure minimum inverter size needed, and find out what I'm then looking at for inverter costs.

So, modifying my initial post, anybody with recommendations for sources of grid tie inverters in the 1-2 kW range?

[odysseus]

I was orginally planning on one or two panels. One is enough to power radios. I thought two would cover a refrigerator. Then I did the math. A refrigerator uses 2-3 kWh/day, meaning 400 - 600 Watts from PV after losses in cable, charge controller, battery and inverter, and 250 Ah/day out of the batteries. This is gonna get expensive! I may skip the refrigerator idea and go back to one panel. BTW, it's going to be about 50 ft from panel to controller.

Yes it is, and keep in mind too that the startup needs of a common refrigerator to begin the compressor can be double that. Really for appliances like that you should have a gas generator in the mix.

[pinwheels]

Just found another problem to deal with . Apparently, for the safety of utility workers, inverters in grid-tie systems have to shut down if utility power is lost to prevent creating a shock hazard for utility workers. If I'm going to try to feed the entire service entrance, this means the disconnect has to be on the utility side of the box (between the meter and the distribution panel). Can this be done?

Also, what happens if the load on the panel is too great to be met? Does the inverter just keep trying (i.e., at reduced voltage), or does it just shut down when output voltage falls below some threshold? I got to find somebody familiar with these things.

[xgi1991]

pinwheels, before you totaly give up on your refigerator idea, get yourself a Kill-a-watt meter off amazon, or locally, I believe RadioShack carrys them. That will tell you exactly what each appliance uses per 24 hour day. My 18 cuft fridge actually came out at 1kwh per day, and it is a few years old, if you have a more modern one, you may be surpriced at what you actually use. You also may consider supplimitting your solar with a small wind generator, they can be had off ebay 50, 175 and 225watt ranges, I have a little 50 watt on my roof that does an outstanding job of helping out my small (but growing)160 watt solar setup. Something else to consider, keep you DC line runs as short as possible, AC has no problem going the distance, my water proof battery box is out-side under my kitchen window, everything is in there charge controller, batteries (420 Ahs), inverter etc, it is a 20 foot run for my panels to that box, from there the AC comes to the house. I do have a 3500 watt generator setting right next to it, but have only had to fire it up a couple times in the past 6 months to get the battery bank top'd off. I will be adding to the system as money allows, but, I do have the power now to keep the food cold for more than a few days, when I get more solar, I will be able to take the frigde off gride totaly, now I mainly just use it when we have one of our frquent power outages. True, it is expensive to get a large system setup, but, just do it a piece at a time, once you get the setup started, it is just a matter of adding more battery bank and more wind/solar as you can afford it.

[pinwheels]

Thanks xgi. I'm not giving up on the refrigerator, but I am giving up on the completely off-grid idea and a lot of the batteries. I've got hourly total household energy use data for a few months, and it looks like the refrigerator is running about 200W, but that's averaged. As odysseus points out, the starting load could be the killer. Various web articles list refrigerator running loads at about 700W, with starting loads as high as 2200W. In a power out situation, the PV panels and inverter need to be able to handle that.

I thought about Kill A Watts, but they don't log peaks, only time-averaged use. Peaks only last maybe 1/2 second.

[xgi1991]

Thanks xgi. I'm not giving up on the refrigerator, but I am giving up on the completely off-grid idea and a lot of the batteries. I've got hourly total household energy use data for a few months, and it looks like the refrigerator is running about 200W, but that's averaged. As odysseus points out, the starting load could be the killer. Various web articles list refrigerator running loads at about 700W, with starting loads as high as 2200W. In a power out situation, the PV panels and inverter need to be able to handle that.

I thought about Kill A Watts, but they don't log peaks, only time-averaged use. Peaks only last maybe 1/2 second.

Totaly off grid is way out of my range as well, but the way I figure it, during SHTF, my highest priority will be refridgeration, ultimate goal, is the whole kitchen with extra power for some low voltage LED lighting and radios. I am considering that my bare minimum. It will grow as time and wife allows I suppose. If you want to talk to someone about total offgrid, got a buddy in Grass Valley, he and his family are doing it big time, pm and I will hook you guys up. It is always nice to talk to someone actually doing it and he is open to sharing the info, he has been off the grid for a couple years now.

[pinwheels]

Totally off-grid is also not an option. The batteries alone would be prohibitive. I'm just trying for basic survival stuff - refrigerator, communications, cooking, heat. Assuming gas isn't shut off, I'm good on several fronts - gas gravity heat (no fan), gas cooktop, gas water heater, propane grill, but I need the PVs to handle the refrigerator. If I were where you and your friend are, I'd be more serious about off-grid. Would likely look into hydro power as well.

Low voltage LEDs are great! I just rewired an outside post lamp for a 1W tower LED and a couple of 1/2W path lamps and landscape lights. 5W total fully replaces ~60W of incandescent and 50W of halogen. No further qualms about running for a few hours every night on a photocell.

[paradox]

It might be cheaper to get a DC refrigerator and run a smaller system.

This place has a few: http://www.eco-fridge.com/

There are other options out there too, but all fairly expensive. I've heard of some people modifying chest freezers to be DC fridges, that might be a good option given how cheap you can find them on craigslist.

[Californio]

A 320 watt solar array rated at 18 amps (16 amps real world) with a 400 amp (4x100 deep cycle) battery bank will drive two 12v units like this:

http://www.amazon.com/gp/product/B002Q6L0KU?ie=UTF8&tag=wwwffsite-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B002Q6L0KU

LED lighting, LED TV/sat receiver, radio and AA charger, limited microwave just fine day in and day out.

It won't be your home refrigerator but it works and has been well tested in the real world for several years. The small pocket freezer does keep ice cream bars.

Honda 2000 watt backup generator, just in case.