System Design Questions

[cr0ntab]

Hey All,

I wanted to get a little feedback about a hybrid solar system design.

I just moved into a home and I know I want solar but I don't have a full years worth of data yet for power consumption.

As for data, we only 1/2 month (Dec) billed (507 kWh) + our current best estimate for this month (1080 kWh)

We're in the winter months so power usage is definitely lower than summer time. In the summer time with the AC going I could easily see us hitting closer to 1400-1500 kWh/mo

Winter

1100 kWh/mo * 6 mo = 6600 kWh

Summer

1500 kWh/mo * 6 mo = 9000 kWh

Yearly average

(6600 kWh + 9000 kWh) / 12 mo = 1300 kWh/mo

With that usage I'm estimating a 10kW solar system at least.

We have a pool and with the pump running all the time it makes the payback for solar that much better.

Goals for my project are:

1. 100% offset of power usage
2. Grid Tied
3. Uninterrupted power in the event of an outage, supplemented with an onsite natural gas backup generator

Because of #3 I don't think I really need a huge battery bank as it's just there to buffer the spin up time of the generator.

I don't need to do anything with peak shaving or anything like that.

I'm located in Southern CA with SCE so we have net metering 2.0

Option 1:

DC coupled hybrid inverter such as the Outback Radian GS8048A or Schneider XW+ 6848

With these I can plug the mains into the inverter and they have a second input for the genset.

My biggest concern (possibly unwarranted?) with this setup is that it's DC coupled. When the grid goes down and the genset kicks in what happens to all that 10kW of solar? Does it go into the batteries? If so I probably will need a pretty large bank of batteries (which I don't really want or need)

Option 2:

This option is me getting more creative. I have a little background in electronics but definitely not on the power side.

Instead, get a vanilla grid tie system that feeds into an automatic transfer switch that the genset connects to.

I then feed a large 10kVA? UPS (this is the battery backup part) which then feeds the home.

More parts and components for sure but I think? it should work out.

My understanding of this system is that when the POCO goes down so does my grid tie solar.

The ATS signals the genset to start and in the mean time the UPS picks up the load of the house.

Genset starts and the ATS flips over and the UPS + home are now powered by the genset.

Option 3:

??? You guys tell me if there is another way

Lastly, and I know a few will remark on this. "Why do you need uninterrupted power to the whole house?"

It's something that I want and I'm tired of having to manage 15 different smaller UPS backups for all the electronics I have in the house.

Besides, lets keep this as a fun design exercise for now.

[ButchDeal]

An 8kw inverter is likely too small for 100% of the house load. Yu can likely leave off electric dryer, water heater, heat pump etc. or you will need a bigger inverter. You can cover most of the lights and outlets in the house it full House you need larger inverter.

as for your cincwe s if the batter, you have it backwards, DC can have a smaller battery as the system has better controller of the barge controllers, but AC coupled will require a larger batter as it has to be able to take full solar charge.

[cr0ntab]

An 8kw inverter is likely too small for 100% of the house load. Yu can likely leave off electric dryer, water heater, heat pump etc. or you will need a bigger inverter. You can cover most of the lights and outlets in the house it full House you need larger inverter.

You raise a good point that I forgot to cover in the original post. Most of my appliances are gas fired (Dryer, Water Heater, Furnace, Oven, etc.) So that definitely reduces the power demand.

By far the largest load on the system is the AC unit at 5kW when it's running.

as for your cincwe s if the batter, you have it backwards, DC can have a smaller battery as the system has better controller of the barge controllers, but AC coupled will require a larger batter as it has to be able to take full solar charge.

Got it, thanks for the clarification on that!

[J.P.M.]

As for usage estimates, I'd start with you've usage in the past at the prior residence and adjust (if necessary) for different A/C loading for summer climate at new vs. old location.

Except for HVAC, most residential usage is more f(use patterns/habits, family size ) than the size of the shelter. If the new house is not as old as the prior house, for the same size, expect a lower HVAC load per degree of temp. diff., inside to outside, after ratioing old to new house areas. It'll be a rough est., but I bet you'll be close.

Get familiar with and run PVWatts. Read all the help screens first. With a reasonably and mostly southerly array orientation, and a common roof slope of 20 degrees or so, and no/little shade, a decent grid tied PV system in most locations in SO. CA will probably generate ~~ 1,600 to 1,700 kWh/year per installed STC kW. So, After you figure out how much you want to generate each year, divide that annual goal by, say, 1,650 kWh/yr. and that'll be a rough 1st est. of array size, in STC kW, making your 10 STC kW size probably in the ballpark for your current annual usage est..

A better payback than running the pool pump all the time will probably be a variable speed pump not running all the time. Believe it.

Sounds like you have nat. gas available. If so, keep using it wherever possible as you write instead of electricity for tasks such as clothes drying, water heating and space heating. Much, much less costly.

Buy a copy of "Solar Power Your Home for Dummies". ~~ 20 bucks cheap. A good primer.

NOMB or concern, but if I was planning for power outages, I'd get a generator and forget fooling around with batteries or trying to make PV work during a power outage. Great hobby maybe, but I'd suggest looking before leaping. Lots of fun design can happen on paper for less time and money commitment. The ready, fire, aim method is usually less cost effective with poorer outcomes.

[cr0ntab]

As for usage estimates, I'd start with you've usage in the past at the prior residence and adjust (if necessary) for different A/C loading for summer climate at new vs. old location.

Except for HVAC, most residential usage is more f(use patterns/habits, family size ) than the size of the shelter. If the new house is not as old as the prior house, for the same size, expect a lower HVAC load per degree of temp. diff., inside to outside, after ratioing old to new house areas. It'll be a rough est., but I bet you'll be close.

Our old residence was in Northern California and didn't have AC. I have family in SoCal and I used their electric bills to help "calibrate" my numbers. My house was built in 1997, so definitely newer than my relatives. I'll factor that in with the calculations.

A better payback than running the pool pump all the time will probably be a variable speed pump not running all the time. Believe it.

Already done!

It was installed on Tuesday, I fixed the programming on Wednesday.

NOMB or concern, but if I was planning for power outages, I'd get a generator and forget fooling around with batteries or trying to make PV work during a power outage. Great hobby maybe, but I'd suggest looking before leaping. Lots of fun design can happen on paper for less time and money commitment. The ready, fire, aim method is usually less cost effective with poorer outcomes.

I actually don't really care about the PV working during an outage. If I can get it, great, if not oh well.

The big concern for me is the spin up time on the generator. It takes a minute or two for it to stabilize and provide usable power.

I don't want to have all my computers and servers go down when this happens as I work from home. (Also, resetting all the clocks again is just annoying :P)

Given that, the only way to go about it is with some form of battery system. (As far as I understand)

Whether it's integrated into the inverter, or some external uninterruptible power supply.

--------

This is definitely an expensive endeavor so I want to put all the options on the table before I purchase anything or sign any contracts.

If nothing else I want to also make sure I understand what I'm being sold, I don't like to just "sign on the line" without understanding things.

I'll give that book a read and I'll start playing with the PVWatts calculator as well.

Thanks for the time and the insight!

[J.P.M.]

Our old residence was in Northern California and didn't have AC. I have family in SoCal and I used their electric bills to help "calibrate" my numbers. My house was built in 1997, so definitely newer than my relatives. I'll factor that in with the calculations.



Already done!

It was installed on Tuesday, I fixed the programming on Wednesday.



I actually don't really care about the PV working during an outage. If I can get it, great, if not oh well.

The big concern for me is the spin up time on the generator. It takes a minute or two for it to stabilize and provide usable power.

I don't want to have all my computers and servers go down when this happens as I work from home. (Also, resetting all the clocks again is just annoying :P)

Given that, the only way to go about it is with some form of battery system. (As far as I understand)

Whether it's integrated into the inverter, or some external uninterruptible power supply.

--------

This is definitely an expensive endeavor so I want to put all the options on the table before I purchase anything or sign any contracts.

If nothing else I want to also make sure I understand what I'm being sold, I don't like to just "sign on the line" without understanding things.

I'll give that book a read and I'll start playing with the PVWatts calculator as well.

Thanks for the time and the insight!

FWIW, you're welcome. None of us being as smart as all of us, I'd suggest questioning everything everyone says, even and maybe especially me, until you understand what's been written.

[Mike90250]

re: Spin Up Time for Generator. You want to get a conventional UPS to plug each appliance into, that you want to protect. That will be much , much less expense than a Hybrid Inverter and a room full of batteries. Get the Generator, plumb it to Nat Gas or Propane, and get an Autostart Module and AutoTransfer switch for it.