I've been tossing around the idea of doing a solar system for some time now, I was primarily set on doing a grid tie only system to supplement my power bill but have come up with a different idea.  I would like to do a off-grid system in my on grid house.  I use several 220v high load tools such as welders on a normal basis so I don't see going completely off grid as a viable solution.

The idea here is to remove all auxiliary circuits from the main (on-grid) breaker panel and move them to a off-grid breaker panel completely separate from the grid.

Then connect the panels to inverter/charger and a battery bank.  The idea here being that all the lights/outlets other than high drawl appliances (A/C, oven, dryer, welders etc) be connected to the off grid system.  And all those appliance connected to the on-grid system.

This would allow me to run "half" the house off solar and the other "half" on grid.

It would also allow me to have power to essentials if the grid ever went down for any reason (unlike a grid tie). mind you the only thing I consider essential in that circumstance would be a way to charge emergency items, maybe a light or two, and a fridge to keep my beer cold




Does anyone have any thoughts or potential problems with a system like this?

Your ultimate goal should be to reduce your dependency on electricity from the power company. By installing enough pv you should be able to control your future cost of electricity for your home.I am having difficult in understanding your reasoning. A grid-tied system with battery backup would be the better way to go. Redistributing your critical loads off of a dedicated load center will simplify your installation.

Posted By acwizard on 21 Oct 2011 12:32 PM
Your ultimate goal should be to reduce your dependency on electricity from the power company. By installing enough pv you should be able to control your future cost of electricity for your home.I am having difficult in understanding your reasoning. A grid-tied system with battery backup would be the better way to go. Redistributing your critical loads off of a dedicated load center will simplify your installation.

"enough pv" for my house would require around $10-15k up front cost with me doing the install myself and having my electrician friend wire the box. For $3k up front I could have a useable PV system to run the essentials in my home. Dependency on the grid is a concern of mine. If times got rough and I had to shut the power off to my house for some reason I know that I would have enough to power the essentials for a small upfront cost. And be non reliant on fossil fuel to power a generator for similar effect.

Email me. I'm going to take half my house off grid as well. I don't agree that it needs to cost that much to get started. I picked up a Sunnyboy3000US that was one year old for $500, and we can now find panels in the neighborhood of $1.10 per watt. I'm seeing a huge trend and possible price war starting up. Right now, I don't have enough panels to get the Sunnyboy going. My electric bill for July shot up to $550 and I freaked out, ran around the house removing any excess lights from the ceiling, and making sure everything else was either 13w or 18w cfl's, and made sure things were turned off all month long in August, and my August bill came in at $625. Seems I had the pool pump running for 6 hours in the middle of the night without realizing it. That put me in Tier 5. Around here, Tier 1 is 12cents per kwh. Tier 2=14cents, Tier 3=23cents, Tier 4=26cents, and Tier 5 is a whopping 30cents per kwh. So, I've decided to pick up a secondary pump for daily circulation and filtering, and install a bypass valve so that I can still use the 2hp pump for the spa, vacuuming, etc. The new half horse power pump should only use about 600w or so, and between that and pulling some of the appliances off the grid, I should be able to stay in Tier 1 which is 12cents per Kwh here in Southern California. My goal is to cut my electric bill down to $60 per month or less. Without adding solar yet, I've got it down to about $140 for this month. SCE's tier system is pure theft, and I don't find it acceptable. Anyway, I think by combining conservation and smart shopping, you can pull half your house (or at least enough to keep your bill very low) off the grid for around $3000. I'd be interested in your ideas. -Tom ([email protected])

Pm'd

What part of the country are you in, and how long of an off-grid period are you planning for? This makes a big difference as to how practical the battery backup is. eg, if you are in the Pacific Northwest, and you're planning to have backup in case of extended power outage due to earthquake or other natural disaster, then battery might not be practical. (you wouldn't get more than about 1 sun-hour/day in the depths of winter)

Even in grid tied systems panel costs are no longer the dominating cost factor- the "rest of system" (mounting, wiring, inverter etc.) is now more than 50%. With off-grid the cost & maintenance of batteries becomes a whole 'nuther cost factor.

Unless you're truly dedicated to going off-grid you get more bang per buck out of grid-tied, since without buy more panel & rack for the money you would have spent on batteries. If you ARE dedicated to going off-grid it's usually cost effective to spend a significant chunk of money up-front on efficiency measures to keep the system size down. The size & cost of the PV array & batteries it take to run even your typical Energy Star refrigerator for a week of cloudy weather is daunting.

The limiting factor on peak loads of things like your welder is usually the inverter, not the batteries. But you may already have peak loads higher than those- investigate the peak startup surge of your beer-cooler- it's typically several times greater than the draw when the compressor is already spinning at speed.

For emergencies & off-grid & peak loads, $500-1000 buys a lot of peak capacity in the form of a portable gas generator- a fraction of the panel/ inverter/battery it would take to serve those loads.

I am not sure I understand.  If your utility/State allows netmetering (meter spins backwards when you produce more than you use) why would you set up an offgrid system? You would lose the power the panels are generating when the batteries are full and you are not using it.

There are systems that are grid tied with battery backup for only the critical circuits. Having two seperate electrical systems is asking for issues, from ground loops to complying with NEC requirements.

Posted By OCWingNut on 24 Oct 2011 06:28 PM
  August bill came in at $625. Seems I had the pool pump running for 6 hours in the middle of the night without realizing it. That put me in Tier 5. Around here, Tier 1 is 12cents per kwh. Tier 2=14cents, Tier 3=23cents, Tier 4=26cents, and Tier 5 is a whopping 30cents per kwh. So, I've decided to pick up a secondary pump for daily circulation and filtering, and install a bypass valve so that I can still use the 2hp pump for the spa, vacuuming, etc. The new half horse power pump should only use about 600w or so, and between that and pulling some of the appliances off the grid, I should be able to stay in Tier 1 which is 12cents per Kwh here in Southern California. My goal is to cut my electric bill down to $60 per month or less. Without adding solar yet, I've got it down to about $140 for this month. SCE's tier system is pure theft, and I don't find it acceptable. Anyway, I think by combining conservation and smart shopping, you can pull half your house (or at least enough to keep your bill very low) off the grid for around $3000. I'd be interested in your ideas. -Tom ([email protected])

If you haven't already bought the smaller pool pump, look hard at Pentair's Intelliflo VF

I've done three of them, in one case cutting pool pump power use by 90% (verified 3 different ways) while LENGTHENING hours of operation.

Another client went from 23 kwh / day down to 7 and they have a complicated pool with SPA, floor cleaners, elevated solar panels, etc.

I am going to second Engineers idea about the Pentair pump. We have a job presently where a VF pump is being installed. The pump is expensive but SCE does offer a rebate which will help with the cost.

Our home is set up in a split manner. Most of the loads are on the inverter panel while the big stuff is on the main panel. The invterter panel is fed from a xantrex 6048 which is in turn fed from the grid or solar / batteries. If the grid goes down I don't even notice. If I am making power from PV it just offsets the load from the grid panel and if there is no solar it can pull all the power from the grid. I did this primarily to have a true UPS system, cost wise your far better off with a grid tied no backup and use a genset. I looked in to larger automatic backup genset systems in the $5k range and for twice that I have a system that can handle the loads I need and has a potential payback offsetting power from the PV where a genset never does.

The one thing I would get is a larger inverter that can also grid tie so when you add more panels it can handle it. The only thing my inverter can do is start my 3 ton geo unit. I can start it on grid and move it to the inverter once it is running, but not start it. So get a good big true sine wave inverter, it is the heart of a system like this.

The invterter panel is fed from a xantrex 6048 which is in turn fed from the grid or solar / batteries.

How long have you had that little beauty online and how is your bank set up?

The inverter has been in place and operational since May of 2008 when we moved in (we designed and had it built). I haven't had any issues with the inverter. I have toyed with the idea of adding a second 6048 to be able to start the geo unit, but haven't needed to yet. I think this is a situation for the amount of times I have wished I could start the geo system it isn't worth it. The longest we have been without power in this location was 3 days and had no issues with heat or power during that time. I do believe if I could stagger the motor starts I might be able to do it, but haven't tried yet. My next purchase will likely be another 4 200w panels. I cut the description below from another post.

"Our current system consists of eight Kyocera KC 125w panels and 4 Evergreen ES 205w panels wired in three banks totaling 1.8 kw. I have #2 run from the solar panels to the charge controller, about 50 feet. The charge controller is an Outback MX-60 which converts and regulates the 68v solar system power to feed the 48v battery bank. The battery bank consist of eight Deka AGM 8A8D's wired in series/parallel for 490 amps at 48vdc, or approximately 24kw. The batteries in turn feed the Xantrex XW 6048. The inverter is connected to a large sub panel, almost everything in then house with the exception of the large pool equipment and 4 ton geothermal system."