Inherited a solar problem

I recently landed a job with the local school system. During the interview I was asked about Geothermal and solar, and replied I had some experience. Friday I was put in charge of all of the schools that have these systems. The big concern was lack of storage for the solar. Investigation found that they don't have any. Each string makes 480 VAC and has it's own inverter, and the power is sold directly to the power company to offset usage. Now they are digging around to find where those credits are, or even if the power company knows we are putting power back into the grid (I'm sure they do). We have 5 schools like this and 5 more being built in the very near future. Since my tiny bit of experience trumps their zero experience, I guess I have inherited the headache.

 

Forget about solar power storage this is green washing ignorance by people who don't understand how any of this works.
Trust me you don't need or want storage, plus you are completely set up wrong to ever even think about tieing in any kind of storage directly to the solar.
It actually looks pretty good.
I'm assuming it's all functional?

Easiest way to test the strings would be to get a fluke325 meter or any one that will read DC amps and go check all the DC wires for current during the day.
I'm assuming this is all passively controlled with no individual string monitoring?

 

THEY thought they had storage, not me.
I checked about twenty strings for AC amps off the inverters, all running 4-5.2 amps, so it seems to be working.

 

Since they are grid fed - does the local power Co do net metering (do the meters run 'backwards" or do they have a meter to record power fed back to grid?

The Power Co may have State or local restrictions...
Also - in many of the these near scams, the power Co will buy back any 'surplus' power at Wholesale rates. Hence the question on the net metering.

IMO, anything other than net metering is a ripoff of the local taxpayers.

Lastly, what kind of synchronous inverters are in use? It may be possible to install a 'pilot' unit that allows local use of the power in the event of a larger grid failure - a hellva lot less expensive than adding storage.

Ok, I see now that you are in SC.
The rates and pricing for SCE&G’s net metering program depend on your current electric rate, which depends on your property type. Most likely, you fall under one of SCE&G’s residential service rates for individually metered private residences and apartments. Net metering works the same for all residential rates – every kilowatt hour (kWh) produced by your system that you don’t use is fed back to the grid. Every kWh sent to the grid earns you a credit that you can use towards your bill the next month at the same rate as your current electric service.

At the end of the year you may not have used all of the credits you accumulated. SCE&G will pay for that excess electric production at the cost they would have spent to supply the power themselves.

So it looks like you have net metering. Maybe,

2018 South Carolina Electric & Gas (SCE&G) Net Metering Rates | EnergySage

and
Net Metering Gets a Lifeline in South Carolina

For your skool systems to be able to operate in "Island" mode may require new inverters. In this case, maybe talk with the outfit that did the installation. There are multiple issues, include automatic grid-isolation switches that are part of the full equation....

Good luck!

For visitors who haven't looked at grid-tie (synchronous inverters) systems
Solar Grid Tie Basics

Beating the Achilles Heel of Grid-Tied Solar Electric Systems

 

Do they have any ground source geothermal?

 

I am a retired industrial electrician (Caterpillar, UAW) I worked at two facilities, Mt. Joy and Aurora. Mt Joy was only ten years newer than aurora. but was orders of magnitude younger as far as energy use and generation. Kenny Hauer (my boss at Mt Joy) was constantly looking for ways to save money, The people at aurora were constantly looking for ways to spend it. Aurora had about a million square feet (111,111 meters squared) of FLAT roof and adamantly refused to even consider solar collection. That's >2Kw per square meter or >200kw for total roof. That site was big enough for wind mills.

 

Follow the Money, Read the contract!

 

YEP

 

is this tied into the grid (grid tie system) ? it must be or else where is all that power going.

 

My bosses thought they stored and used, or at least used, the power. I had the displeasure of telling them that there was no storage or usage capability. Next I have to investigate how it is fed back to the power company, and find out if we are indeed being credited for what we return to the grid. Thankfully there is a layer of muckety-mucks above my pay grade that will have to digest what I find out and answer for it.
They do have synchronous inverters and grid-tie breakers, but I have yet to find any CTs that they may be metering with. I have a power company dude that is supposed to call me Tuesday and maybe shed some light on the methods they are using.
Supposedly, this was a big deal at inception and a special program was initiated.
And yes, these buildings also have closed loop geothermal with a cooling tower, hot water reclaim, a loop fed chiller, and tons of individual water-source heat pumps, another part of the puzzle that no one has a clue about, but the primary reason I got hired.

 

And maybe the reason you are let go.

 

Typical solar isolation numbers are 1KW per Meter sq. Typical numbers for South Carolina for an entire day vary from 2.6 KW/sqM to 6.3 KW/sqM. (flat surface).

Exactly the office that pays for the power, knows if they have net metering, or just ask the power company.

It is grid tied.

There is usage capability in the sense that the current is used first by the school, and if there is excess to feeds back to the power company, the CT is the power meter itself, typically a special meter because some meters don't run backwards.

It is a big deal, lots of room for the collectors, no home owners association to nix the plan, and if the power company is buying back the power at the same rate they are charging for a KWH, then pay back is around 10-15 years, depending on if the utility offered an incentive or not, I believe that all utilities were mandated to have 5% renewable by 2020. The downside for a school is that there is no 30% off their taxes at the end of they year, however there may have been other State and Federal incentives to do this installation, which I suspect there was or it wouldn't have gotten done.

No reason to have battery backup, this is not a Bug out Location, the power goes off the lights go off, you send the students home for the day, week, month, forever.

Rancher

 

Add to that the fact that batteries, used or not, still need replacement from time to time. So the staggering initial cost would be only the beginning of many. Think you're right about the generator.

 

Yep.....everything he said....plus, if there are any 'carbon credits' ( If that's the credit you were talking about), they likely belong to the power company as part of the interconnect agreement. That's the way TVA does it here in Tennessee.

There is no storage because it would have doubled (or more) the initial price of the installation....you not only would have had batteries, but charge controllers out the wa-zoo and hybrid inverters to grid tie and go off grid in a grid down situation.

Most likely, it's setup so the power generated is used first at the location, and any excess flows back to the grid for dollar credit on the bill. Read the contract to see. HERE, ours was initially set up that way, then they flipped to all power goes thru a separate meter, for which we are paid, then onto the grid. Our use flows in thru another meter, for which we are billed. Production is compared to use to decide if there is a bill or a credit.

 

They cannot dictate what you plug in .
IMO If you need storage ,
build a battery bank and create alternative wiring and lighting .
Battery chargers on selected banks on each structure run that structures lighting ,independently of the grid tied lighting . that way when the grid goes down you won't notice it .Battery chargers cannot back feed into the grid .
You can add inverters from each battery bank for running computers an such . Being isolated from the grid there is no danger of some worker being electrocuted working on a damaged grid tied circuit.
And you need not disturb the present solar grid tie system at all .

 

I run an inverter from my shop trailer solar panel battery system on an 120 volt extension cord to the house 100 feet away ( higher voltage has less loss over distance) that drives a 12 volt battery charger to a battery bank at the house for the 12 volt DC lighting through out the house .
On extreme over cast days and no wind for the mill I plug into the grid to run the battery charger at the house . and still my on grid consumption is at a minimum compared to my neighbors.
What is the problem with that ?