Planning Stages of a Grid Tied System

Cool BreezeCool Breeze Registered Users Posts: 13 ✭✭
I'm back after a bit of a hiatus. It's good to be back!

As the title suggests, I am *still* in the planning stages of a grid tied system. I live in a rural area of Vancouver Island BC Canada and experience frequent winter storms that knocks power out for anywhere from 4 hrs - 2 days. During the last major storm both ways out were block by trees fallen over power lines, there was no power for 2 days, and our power authority was no where to be seen while they fixed the power for the more populated areas. Not really surprising really. We were fine though as we have a propane stove for heat, and our house was prewired to hook up to our 8000W Costco special generator.

What I would like to do is to stay grid tied and not bother with trying to produce everything we use. Power is cheap here in BC. But I want to have a backup plan for when the storms hit. Hopefully the batteries can carry us through the shorter power failures(ala UPS) without needing to haul out the generator. I don't expect to have enough capacity, and I don't want to drain the battery bank too low(lower than 70-75%) by trying to last for the long power outages. In those cases I would be monitoring the battery bank and flash up the generator at a set point. I also don't need to power everything. I have baseboard heat and electric hot water, so I don't plan on power those. I would only power the essentials like fridge, freezer, septic pump, well pump, lights, etc.

So, with those parameters in place I explain my plan. I am drawn to the Outback Radian series of Inverter/Chargers for their impressive range of mode options. I'd like to have an array around 4kW(panels to be determined), use two Midnite 150 charge controllers, a Radian 4048E inverter/charger, and an approximate 400Ah 48V battery bank consisting of good bang for the buck 6V cells(brand/model to be determined). When my Costco generator kicks the bucket I plan on upgrading to a low rpm, liquid cooled, diesel generator with an automatic transfer switch that the Radian can control. I have my eye on a particular Aurora generator that does 3000/4000W.

I'm a bit backwards in explaining all of the equipment I want to use without talking about the loads I want to run. Let me do that now, because therein lies my first question.

Loads: (waiting on kill-a-watt to test freezer and oven as no labels or info on web)
Fridge 816.5W
Propane Stove(electricity needed for the oven)
Coffee Pot/Grinder 1025W/85W
Microwave 1500W
Freezer
Phone 12W
Cable Modem 96W
Wifi 180W
1 hp well pump 2254W
1/2 hp jet pump 1380 W
1/2 hp septic pump 1380W
Well UV light 12W
Laptop Charger 35W
Phone Chargers(2) 36W
Lights(CFL or LED) 300W

Generally speaking that's about all we should need to power to keep on with getting to school/work. We have found that for whatever reason, if the power goes out, many times we will still have high speed internet with the generator power. So, we have been able to check on the status of the power restoration and pass the time watching Netflix.

If I add together the constant loads like fridge, freezer, phone, modem, wifi, 1/3-1/2 lights, etc, I would estimate that I am near 1500-2000W. That doesn't leave a whole lot of head room on the Radian 4048E for intermittent loads like a coffee pot, microwave, or my big fear: the well pump. With the well pump the running watts are 2254, but starting watts are likely at least double: 4508W. I do realize that the Radian can surge for a short period of time, but if I have 1500W constant, then it surges to just over 6kW, will the Radian trip off? Or can it handle this? I need to get this figured out at this stage, because if the Radian 4kW can't handle this scenario, I'll need to be upsizing the entire rig to the 8kW version.

Second question: If I have an undersized generator that is insufficient to fully power my loads, will the Radian use the generator power and take the rest from the batteries? Or will it ignore the generator and just use the batteries? I ask this because of my thought of buying the 3000/4000W diesel generator I mentioned before.

Third question: With a constant load of 1500-2000W and then intermittent loads on top of that, is this a safe rate to be discharging a battery bank? I understand that you don't want to discharge too quickly or else you can risk damage to your batteries. How do you determine the proper rate for a 400Ah battery bank?

Thanks,

CB

Comments

  • DanS26DanS26 Solar Expert Posts: 237 ✭✭✭
    IMO I think you should step back from your current design options.....especially away from anything that includes batteries.

    You are grid tied and with inexpensive POCO power. Be glad for that.  Start with a design that incorporates a straight transformerless GTI and a pad mounted, LP fueled standby generator properly sized for critical loads or for the entire house. Then bury a 500 gal LP tank next to it and fill it with inexpensive, long term storage LP gas.
    18.2kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • Cool BreezeCool Breeze Registered Users Posts: 13 ✭✭
    I've definitely given that option some thought. The advantages being simplicity, less maintenance of batteries, cost savings. 

    That be said, I'm a bit of a prepper. I live in an area prone to earthquakes and risk of tsunami. Now, if there's a big earthquake and tsunami it's anybodies guess whether or not my house will get taken out. But, if I win that bet, I want to be prepared to last for a couple weeks until emergency services can get back into the area. In a Katrina class emergency it'll take months for things to get back to 'normal'. So, I'd like to go the solar route with some battery storage, supplemented with Gen Support for big loads and charging for a longer term approach.

    My thoughts on generators, and I think the research will back me up on this, is that low rpm, liquid cooled, diesel generators, outlast propane generators in the long term. They may be more $$$ up front, but they pay off. Propane has a lower energy density than diesel, but can be stored longer and easier than diesel: true. But, I drive a diesel pickup truck, so rotating diesel through my vehicle to ensure fresh fuel for the generator is easy. 

    ~CB
  • BB.BB. Super Moderators, Administrators Posts: 28,768 admin
    Anything can be done... But for solar power, location is highly important. For example, your winter sun appears to be less than ideal:

    http://solarelectricityhandbook.com/solar-irradiance.html

    Vancouver
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 41° angle
    from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    1.88
     
    3.04
     
    3.86
     
    4.76
     
    4.93
     
    4.90
     
    Jul Aug Sep Oct Nov Dec
    5.31
     
    5.17
     
    4.71
     
    3.06
     
    2.12
     
    1.64
     
    You are looking at 6 months of the year with less than 4 hours of (average noon time equivalent) sun per day.

    While your peak power is important for sizing the AC inverter and battery bank, we also need to know your average power usage per day. (Inverters will typically surge 2x their name plate power rating for a few seconds).

    So--That 815 Watt refrigerator (as an example). The typical refrigerator uses ~120 Watts and a 50% duty cycle (in warm climates/rooms). (also note that a refrigerator may use ~600 Watt peak when defrosting, and upwards of 5x running current to start):
    • 120 Watts * 24 hours per day * 0.50 duty cycle = 1,440 WH per day (or ~525 kWH per year)
    If you are looking for emergency power--You might choose to supply loads at ~3.3 kWH per day (or ~100 kWH per month). Using propane (or other fuel) for heat/cooking/hot water)--A 3.3 kWH (3,300 WH) per day system can supply a "near normal" electric existence for a small/very efficient home+family.

    Otherwise, the standard North American home uses around 600-1,000 kWH per month (more if electric heat and/or air conditioning).

    Either is a perfectly good system to design/install for you... but one will will cost ~6-10x more than the other (installation and maintenance costs).

    Say you pay $0.10 per kWH today for electricity--What would you do if your power where to cost ~$1.00 (+/-) instead (typical cost for off grid/generator power). And with solar, you are paying 10+ years of power bills "up front".

    Energy usage is a highly personal set of choices--What works for me (grid tied+small backup AC genset) may not work for you. A 1,000 kWH per month off grid solar power system may cost your somewhere in the ~USD$100,000 range (taxes, cost of living, shipping costs, etc. will affect your costs).

    We can help you with either system design--But for emergency backup power systems (emergency being ~several days to several weeks)--A backup genset with the fuel of your choice is usually the more cost effective choice.

    You can do a hybrid system... Genset+small (3.3 kWH per day) off grid solar power system. Use the genset during the day/bad weather--And use the small solar power system for evening/nighttime power usage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cool BreezeCool Breeze Registered Users Posts: 13 ✭✭
    edited March 2016 #5
    This has been a big worry of mine Bill, and the reason why I hadn't been able to decide on a solar panel as of yet. We don't get a lot of unobstructed sun here throughout the year, it's true.

    I checked out the site you posted and put in a city closer to mine: Sooke, BC. To put it in perspective, I am right on the Juan de Fuca straight, across from Washington State and close to the San Juan Islands. My weather would be similar to Seattle, WA. My house roof is almost exactly south facing at 176 degrees. These are the numbers I got(worse than the numbers you posted from Vancouver):

    JanFebMarAprMayJun
    1.63
     
    2.78
     
    3.52
     
    4.34
     
    4.75
     
    4.92
     
    JulAugSepOctNovDec
    5.42
     
    5.40
     
    4.78
     
    3.09
     
    1.87
     
    1.43
    Right now as I look out my window it is another grey and dreary, spring day. Pretty typical for this area for much of the spring, fall and winter. I was going to ask for opinions on solar panels that do better at low irradiance(i.e. through clouds), but after doing some research, I don't think they exist. Correct me if I'm wrong, but it looks like at present the best up and coming technology for harnessing low irradiance light in a wide spectrum is thin film transistors. Unfortunately, the panels are small and expensive at this point though. Regular solar panels are very poor to useless unless in totally unobstructed sun, unless you are buying the uber expensive/high efficiency panels that are out of this world expensive. Am I right?  

    So, with this data in mind. What is the conclusion?  Am I in an area where it simply doesn't make sense to pour money into solar panels, batteries and inverters?
  • BB.BB. Super Moderators, Administrators Posts: 28,768 admin
    There is another poster here that has put a large off grid power system in their North West home. I forgot their name--Somebody else can point to their installation?

    If you have access to good water flow--Hydro Electric can be interesting.

    But--In the end, if you do not have much sun for 1/2 the year (and worse, if shading from trees/mountains/etc.)--Solar only works with direct sun. I guess there are some panels that will be slightly more efficient with indirect light--But, 10% better on something that is only getting 5% of the light energy (due to shading)--5.5% output is really not a big deal.

    If the shading is in your control--Then cutting trees around your array would be a place to start.

    You can use batteries+AC inverter to make a "whole house" UPS system (battery charged by AC Mains, Genset, possibly some solar panels)--But many times, you would be better off just making a UPS (unterruptable power supply) system for the computer, TV, and a few lights. And simply reset the washer and microwave when the generator starts up.

    Just to give you someplace to start--If you just wanted 100 kWH per month (3,300 WH per day) in December at 1.42 hours of sun per day:
    • 3,300 WH per day * 1/0.52 off grid system eff * 1/1.42 hours of sun per day = 4,469 Watts of solar array "break even"
    And a 24 volt battery bank that would supply 3,300 WH per day (2 days of storage, 50% maximum battery discharge for long life):
    • 3,300 WH * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storage * 1/0.50 max discharge = 647 AH @ 24 volt battery bank
    The maximum AC inverter I would suggest on that battery bank would be:
    • 647 AH * 24 volts * 1/5 hour discharge rate * 0.85 AC inverter eff = 2,640 Watt AC inverter "maximum"
    And, the "average" load you could support (5 hours a day, 2 days in a row, 50% maximum discharge):
    • 647 AH * 24 volts * 1/20 hour discharge rate * 0.85 AC inverter eff = 660 Watt average load (5 hours per day for two days)
    That gives you some ideas of what a small system would look like. The solar array is obviously way oversized to support winter use--But if you have lots of shading too--That just kills solar array output

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DanS26DanS26 Solar Expert Posts: 237 ✭✭✭
    I've definitely given that option some thought. The advantages being simplicity, less maintenance of batteries, cost savings. 

    That be said, I'm a bit of a prepper. I live in an area prone to earthquakes and risk of tsunami. Now, if there's a big earthquake and tsunami it's anybodies guess whether or not my house will get taken out. But, if I win that bet, I want to be prepared to last for a couple weeks until emergency services can get back into the area. In a Katrina class emergency it'll take months for things to get back to 'normal'. So, I'd like to go the solar route with some battery storage, supplemented with Gen Support for big loads and charging for a longer term approach.

    My thoughts on generators, and I think the research will back me up on this, is that low rpm, liquid cooled, diesel generators, outlast propane generators in the long term. They may be more $$$ up front, but they pay off. Propane has a lower energy density than diesel, but can be stored longer and easier than diesel: true. But, I drive a diesel pickup truck, so rotating diesel through my vehicle to ensure fresh fuel for the generator is easy. 

    ~CB

    Then bury two 1000 gallon LP tanks and have two years supply on hand.   You would still be money ahead of any kind of battery based system.  If two year's supply is not enough then your world is in much bigger problems than your electrical needs.

    Here in the Midwest, empty LP tanks are stacked 30 ft high in tank farms.  The result of the big push of farmers and rural residents going to geothermal.  Now that propane has dropped in price from ~$4.00/gal to ~$.89/gal there is a lot of second guessing going on.
    18.2kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • Cool BreezeCool Breeze Registered Users Posts: 13 ✭✭
    WOW, that is ALOT of solar array and battery bank for a 660 Watt average load. That is probably somewhere in the neighbourhood of $12,000 not including the inverter and other components in our canadian peso. And that average load would not power half of my 'critical' loads!

    Well, I guess I'm officially woken up. Haha. Thanks for the advice :)
  • BB.BB. Super Moderators, Administrators Posts: 28,768 admin
    660 watts for 5 hours for two nights.

    Yes, people wonder if we are a solar forum or not.

    Try to make informed decisions is what we do here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • asadlarik3asadlarik3 Registered Users Posts: 9 ✭✭
    edited March 2016 #10
    ok as i understand your main concern is backup power and you need all the backup options available.

    Your maximum energy requirement including freezer and oven can be around 11-12000 watts.

    If you need every thing to be backed up by inverter you will need 2x8048 radian inverter that can support 14-16000 watts or you can get 1x8048 and 1x4048 for around 10-12000 watts. or maybe start with 1x8048 and upgrade later. you should also consider the massive inrush currents of the pumps you have if they don't have soft start.

    If your inverter is lower than your maximum power requirement then either you should be wary of over your current power usage to keep it with in the inverters range. Or you can put selector switches on your loads, so in normal circumstances they are directly powered by the grid, and when power goes down and say you need to turn the pumps you transfer the pumps to inverter or generator via the selector switch use them and then shift back http://www.mqtekindustrialsupplies.com/Chageover-Switch-Universal-Transfer-Cam-Generator-p/cm5p32.htm

    Now about the generator, it is the same story as the inverter. In addition when generator is used whith inverter it can support the power from batteries but to maximum of the inverter's rated power, So if you select 4000watt inverter and 4000watt generator connected to inverter only, it will produce maximum 4000watts, however lets say you get 4000watt inverter and 6000 watt generator you can now connect this to inverter which will produce 4000watts but also you can connect 2000watt directly to generator, in earlier example lets say you directly power a pump from the generator. Also you cant expect to extract 100% power from these small generators, get some 20-30% above your required generator power. I check the aurora website 4000 watt is at 1800rpm, 8000 watt is at 3600rpm 500usd more but engine in both is same running at different rpms.

    in your case if you workout your inverter you can just add the panels which matches your selected inverter and battery backup that you desire.
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