Solar and Three-Phase

[npstone]

I'm looking into having solar installed on my shop/garage roof, which is south facing and is open with no tree or other shading. I like the idea of producing some of my own electricity, offsetting/eliminating my electricity bill, and the tax credit is definitely a bonus. Two things came up when talking to the installer:

1) The house and the shop are on separate utility meters, and to get the metered offset, they have to be combined, otherwise any offset would only be applied to one or the other. Currently, my house electricity usage is about 3 times that of the shop (~$150/month average for the house, and ~$65/month average for the shop). Combining the two into one meter will cost a bit more, but nothing prohibitive, and my goal is to offset about 90%-95% of my total electricity use.

2) It turns out the shop has 3-phase power supplied to it. I had no idea. This is rural Montana, so no reason why I would have expected it there. There is no wiring for three phase equipment in the building, and it doesn't look like any had ever been hooked up. I don't expect to personally use any 3-phase equipment in the shop. I mainly use it for lighter duty vehicle maintenance, some wood work and some welding. It turns out that I'd need to add $2k-3k$ in additional equipment in order to address the 3-phase, combine the meters and add the solar.

So, I'm looking for some general thoughts on what to do. Solar installer suggested getting rid of the 3-phase and saving the money. Other option would be to keep it for potential future users, or even myself, and just have the solar cover the house electricity. Any thoughts?

 

[LXCam]

Damn I've give my left nut for three phase in my shop. But for you I'm with your sparky. For go the 3ph, combine your services and take advantage of the solar. The only downside would be the distance from your house meter to the shop. If it's a long distance it may take a long time for the savings to offset the cost of a new feeder from your panel.

 

[theoldwizard1]

... my goal is to offset about 90%-95% of my total electricity use.

How many panels is that and how much will those panels cost ?

... just have the solar cover the house electricity. Any thoughts?

That is where I would start.

I think the cost of the solar panels and inverter controllers might scare you !

 

[wyliesdiesels]

86ing the shop service and put in a feeder from the house may get pricey depending on length of wire.

U will most likely have to get a new panel unless the shop's current main service panel can easily be converted to a subpanel.

I would leave the services as is and just do solar for the house.

Can u take some pics of the shop panels and post em here.

 

[npstone]

How many panels is that and how much will those panels cost ?

We have a couple of different estimates on the number of panels and the costs, but have a rough idea of what we are looking at.

I think the cost of the solar panels and inverter controllers might scare you !

I've seen the price, I'm aware, and that is why I'm trying to figure whether it my be worth just doing the house.

 

[npstone]

In order to 86 the shop service and put in a feeder from the house may get pricey depending on length of wire.

U will most likely have to get a new panel unless the shop's current main service panel can be eqsily converted to a subpanel.

I would leave the services as is and just do solar for the house.

Can u take some pics of the shop panels and post em here.

I'm nothing close to en electrician, and will be leaving this to the pros, but I suspect you are right, in the new panel. The feeder from the powerline is in the air, so no burying lines, but the cost of new wire may be in there too.

I'm leaning toward just covering the house electricity, like you suggest. I'll try to post a panel pic tomorrow. -6 out there tonight...

 

[npstone]

Damn I've give my left nut for three phase in my shop.

Thanks for the offer, but I think I'll pass...

 

[matt_i]

Damn I've give my left nut for three phase in my shop.

You can keep your nut and buy a Phase Perfect It isn't cheap but you'll have 3phase and can take it anywhere in the country with you should you ever move. That could be a potential selling point you could list, seriously. Its a $5k-10k investment depending on where you live. I get that if you never use the capability and have to pay an additional service charge monthly it isn't really helping.

Just to add some actual content, since presumably your house will be low-amp loads, isn't that a better use of the solar with the idea of using your own generated power? Or is it just to give you a cost-offset by sinking as much energy as possible back into the grid? Either makes sense for different reasons but I'm not sure what your intent is.

 

[Git]

Net metering question

What do you normally pay for electricity (per kWh) and how much will you get for electricity going back onto the grid.

Sounds like it would eliminate a lot of headaches by just looking at the house and forget about the shop. Is there a cap on how big of a system you can install - tied to your annual usage for example. What is your annual usage?

 

[wyliesdiesels]

Net metering question

What do you normally pay for electricity (per kWh) and how much will you get for electricity going back onto the grid.

Sounds like it would eliminate a lot of headaches by just looking at the house and forget about the shop. Is there a cap on how big of a system you can install - tied to your annual usage for example. What is your annual usage?

All that varies by area and PoCo...

 

[LXCam]

You can keep your nut and buy a Phase Perfect It isn't cheap but you'll have 3phase and can take it anywhere in the country with you should you ever move. That could be a potential selling point you could list, seriously. Its a $5k-10k investment depending on where you live. I get that if you never use the capability and have to pay an additional service charge monthly it isn't really helping.

Just to add some actual content, since presumably your house will be low-amp loads, isn't that a better use of the solar with the idea of using your own generated power? Or is it just to give you a cost-offset by sinking as much energy as possible back into the grid? Either makes sense for different reasons but I'm not sure what your intent is.

Bud I've been a sparky since the early eighties and had my contractors lic since 88. I'm pretty familiar with all the viable options. But I do appreciate the effort

 

[npstone]

Net metering question

What do you normally pay for electricity (per kWh) and how much will you get for electricity going back onto the grid.

Sounds like it would eliminate a lot of headaches by just looking at the house and forget about the shop. Is there a cap on how big of a system you can install - tied to your annual usage for example. What is your annual usage?

My utility is Northwestern Energy and we're paying about $0.12 per kWh. Montana has a net metering law that requires a 1:1 offset, so my "sale" price to the utility is the same. The cap on grid tied systems is 50kW, so I'm not going to be anywhere close to that.

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[Git]

So then what difference does it make if your shop is not on your solar?

Lets say for example, you were going to install 30 panels on your house and 15 on the shop. Since your at 1:1 - you can just install all 45 panels (if you have room) on your house. You will get paid for the excess energy from the house at the same rate your shop will use electricity. That way you can leave the shop completely as is.

(In California, we are limited to a maximum of 120% of annual usage - that is why I asked, because we couldn't do that)

I would be looking at more efficient panels to cut down on the roof space needed - like the LG 320's

 

[theoldwizard1]

The cap on grid tied systems is 50kW, so I'm not going to be anywhere close to that.

So how are they going to "limit" you ?

The small grid tie inverters actually BACKFEED your house through a 120V or 240V plug. They can do this because they "sense" an AC voltage at the plug and actually "mirror" its voltage and frequency. No voltage at the plug, no output from your solar array.

Interesting foot note, if you gave a generator connected via an interlock to your panel, your grid tie will "help" with the oad !

 

[npstone]

So then what difference does it make if your shop is not on your solar?

Lets say for example, you were going to install 30 panels on your house and 15 on the shop. Since your at 1:1 - you can just install all 45 panels (if you have room) on your house. You will get paid for the excess energy from the house at the same rate your shop will use electricity. That way you can leave the shop completely as is.

(In California, we are limited to a maximum of 120% of annual usage - that is why I asked, because we couldn't do that)

My understanding is that I can only offset 100% of annual usage per meter. Since the house and shop are on separate meters, I'd need two complete solar systems for each (inverter and all) or tie both together under one meter, which then brings in the 3-phase issue.

I would be looking at more efficient panels to cut down on the roof space needed - like the LG 320's

I've got plenty of roof space on the shop, not very much on the house that is south facing.

 

[Git]

I am going to assume that "50kw" is actually 50 kWh DC - which would be the size of the system, which would produce around 80,000 kWh annually. A typical house averages around 11,000 kWh annually.

One of the problems when you have extremely large systems is when the system goes off line for the night - the electrical company now has to ramp up their production to make up for it. It's called the 'duck curve'

 

[Git]

My understanding is that I can only offset 100% of annual usage per meter. Since the house and shop are on separate meters, I'd need two complete solar systems for each (inverter and all) or tie both together under one meter, which then brings in the 3-phase issue.



I've got plenty of roof space on the shop, not very much on the house that is south facing.

Well - that changes things, that is why I asked if your were capped. Back to square one

 

[npstone]

So how are they going to "limit" you ?

I have no idea, I'm just basing that of what the statute says:

SUMMARY
Montana's net-metering law, enacted in July 1999, applies to all customers of investor-owned utilities. Systems up to 50 kilowatts (kW) in capacity that generate electricity using solar, wind or hydropower are eligible. No limit on enrollment or statewide installed capacity is specified. Utilities may not require customer-generators to comply with any additional standards or requirements beyond those established by the National Electric Code, National Electrical Safety Code, Institute of Electrical and Electronic Engineers (IEEE), and Underwriters Laboratories (UL).

Net excess generation (NEG) is credited to the customer's next monthly bill. The customer may choose to start the net metering period at the beginning of January, April, July or October to match seasonal farming cycles. At the beginning of the year -- either in January, April, July or October, depending on the customer's choice -- any remaining unused kilowatt-hour (kWh) credits accumulated during the previous year are granted to the utility.

 

[npstone]

Well - that changes things, that is why I asked if your were capped. Back to square one

Yep.