Solar load calculating in SLV

hyperviktor · February 2019

I'm trying to calculate solar load for a holiday home and wondering what are typical systems in the area ? We'll be building near Blanca.

The base of my calculation is our current energy use in a very small 600sqft flat. This includes all household use ( tv, sound system, computers, ipads, cooking, washing, lighting etc. ) except heating which is not part of our use at the moment.

The total comes to about 12kWh / day. How typical this system would be ? Should I combine solar and wind or is it better to have one system to cover all energy use ?

I'd definitely add a normal generator as well when it's needed as a backup / alternative system.

EDIT : Anyone has experience with LG solar panels ?

BB. · February 2019

Blanca, Murcia, Spain?

Anyway... Energy usage is a highly personal set of choices. "Typical" starting points I like to use:

500-1,000 Watt*Hours per day (15-30 kWH per month): LED lighting, Laptop computer/small fan, RV/Caravan Water Pump, cell phone charger
3,300 WH per day (100 WH per month): LED Lighting, efficient refrigerator, clothes washing machine, Laptop/LED TV, small well pump, cell charger, small fan.
10,000 WH per day (300 kWH per month): Very efficient modern (North American Home) with natural gas/propane/wood for heating, cooking, and hot water
500-1,000 kWH per month. Typical North American Home
1,000-3,000 kWH per month. Lots of electrical devices (heating, air conditioning, cooking, hot water, etc.). Lots of A/C in Texas, etc.

Typically, I would suggest either a 1,000 WH per day system or 3,300 WH per day system. A 3.3 kWH per day system is enough power for a very energy efficient family to have a near-normal electrical existence.

A 12 kWH per day is ~360 kWH per month. What I would suggest is a normal/fairly efficient North American home. In the US, an off grid solar power system, very roughly, costs around USD $1.00 to $2+ per kWH for full time 9+ months per year--This includes upfront capital costs and maintenance (new batteries every 5-7 years, new controllers+inverters every 10+ years, etc.). For a holiday home (say ~3 months during the summer), since power is "lost" the rest of the year, your $/kWH costs go up (less energy to spread your costs across).

I would humbly suggest the "largest" system that usually makes economic sense for an off grid home/summer place is ~3.3 kWH per day.

Just to give you a "quick rule of thumb" design for a 3.3 kWH per day system in Murcia Spain... Battery bank suggest 2 days storage and 50% maximum discharge (about "optimum" for flooded cell lead acid battery bank):

3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank

And for solar array, two calculations, one based on size of battery bank and rate of charge and second based on your loads and hours of sun per day.

Based on 5% to 13% rate of charge (5% good for summer/weekend cabin, 10%+ better for full time off grid system):

647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "cost effective" maximum

And based on a fixed array, tilted to best average harvest:

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

Murcia Spain, facing south, 52 degrees from vertical (best year round harvest)... Note, I cannot paste the table below--Bug in new forum software.

You say summer home... Suggest March through September is 5.10 or more hours per day average (break even).

3,300 WH per day * 1/0.52 off grid system efficiency * 1/5.10 hours of sun March-September minimum = 1,244 Watt array "break even"

You may get away with ~1,218 to 1,244 Watt array (using conservation for "bad weather" and/or a genset for "extra power").

And, if you want a relatively easy to maintain system, ~2,437 Watt array would be really nice (you want to plan on using ~50% to 65% of your "predicted" generation for your base loads).

And for a 647 AH @ 24 volt batt battery bank, I would be suggesting a ~1,620 Watt to 3,240 Watt AC inverter (not to exceed ~3.3 kWatt) as a good fit for this system. (smaller inverters "waste" less power when running smaller AC load).

I will stop here for the moment... Let me know what you think and any questions you may have.

As always do several paper designs before buying any equipment.

-Bill

mike95490 · February 2019

First, is it worth a full up solar install for a couple weeks use ? i'd say use a small efficient generator as a cost factor. Figure your security issues, is some vandal going to steal your solar gear while you are gone the other 50 weeks ?

Maybe a SMALL system 1 panel for a couple RV / Camper 12V LED lights and a single battery ?

hyperviktor · February 2019

Hi Bill,

Lot's of info, thanks. I got the link on the city-data forum, forgot to detail location - San Luis Valley, Blanca, CO

By holiday home I meant few month in a year maybe but not necessarily summer - I'm sure we'd spend some winter time there too.

The 12 kWh is what we currently use so guess we'd need that much - this excludes heating or water pumping or any additional stuff. Would that be too big of a solar system or maybe too expensive?

Mike - is theft a typical issue in rural areas ? I might be better of with a generator, haven't really thought about and noise maybe an issue but price is definitely much lower - our 33 storey building has run off a generator a few times so for a small house should be easy to get one.

softdown · February 2019

It is Blanca, Colorado at 37 degrees latitude. I suggested he kindly ask this board for solar information. For one thing, among others, this board has yet to go fill tilt "dark side". I can't believe how ugly the internet has grown in the past number of years....but I digress.

BB. · February 2019

A smaller system to run at night, any alarms you may wish, etc... Solar can make sense.

If purely a few weekends here and there (including winter)--It can be difficult to justify full off grid solar. And for many places (especially as you go farther north, winter harvest can be very poor for solar).

For example, a 1,000 Watt*Hour per day system and using a propane refrigerator (a few folks have gotten their from a RV wrecking yard--Make sure they have outside air, and especially exhaust). 1-2 lbs of propane per day for the fridge... And most people need propane for cooking and heating anyway (unless you are using wood for heating). Use a 12 volt RV pump.

Run a small genset for a few weekends/trips (Honda eu2000i if your loads are not large) and a Kill-a-Watt type energy meter to see how much power you really need. Or rent/borrow a 4 kWatt generator or so if you need larger.

More or less, solar power costs, very roughly, ~10x utility power, so look at your loads in that light (your 500 kWH per month or $100 @ $0.20 per kWH electric bill is all of a sudden a $1,000 per month at $2.00 per kWH. To run a genset (fuel) is probably (very roughly) roughly $1.00 per kWH (assuming loads and genset are well matched).

If you know what you want in the cabin... You could run your home through a Kill-a-Watt type meter (LED LIghting, laptop computer, cell phone charger, etc.) and simulate your energy usage.

Likely, for now, a genset plus a small battery system (say 2-4 "golf cart" batteries 6 volts @ 200 AH, makes a 12 volt @ 200 or 400 AH battery bank) with a 300 Watt TSW AC 12 volt inverter (to run stuff at night, quite times). You can use a smallish solar panel to float the battery bank when you are not there (use the genset during the day to a quick daily charge while running the rest of the cabin)... Or even add enough solar panels to make the small battery system stand-alone:

400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 753 Watt nominal array

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

Picking Colorado Springs as an example... Fixed array, best year round tilt, works out to December at 4.36 hours of sun per day (longer term average--Not bad number of hours per day for deep winter) and over >5 hours of sun per day for non-winter seasons:

753 Watt array * 0.52 off grid AC system derating * 4.36 hours of sun per day (Dec) = 1,707 Watt*Hours per Dec "average" Day
753 Watt array * 0.61 off grid DC system derating * 4.36 hours of sun per day (Dec) * 1/12 volt battery bank = 167 AH @ 12 volts per "avg December day"

That is not bad for running a "cabin" (no refrigerator/using ice box or propane powered refrigerator).

Again, energy usage is a highly personal set of choices. I highly suggest that conservation (turning stuff off not being used, buying the most efficient version of appliances, and , for example, a laptop at ~30 Watts vs a desktop computer that can run ~300 Watts) is cheaper than building a larger system to generate the power.

-Bill

hyperviktor · February 2019

Basically we'd stay ther for a month or so at times whenever we'd feel like switching the city for the country. It's not planned as a cabin but as a holiday home, around 600sqft / two storeys.

I plan to use the same electrical equipment as we have here, here's a few things to give an idea :

-washing machine/dryer

-fridge/freezer 250l fresh / 93l frozen

-55" tv, bluray, amplifier, playstation

-laptop,ipad, ihpones ( my desktop runs at 550watts + monitor but I probably wouldn't need it )

-cooker and owen - both around 2kw if i'm right

-boiler - 60 liters - around 3kw

-lighting throughout

-water pump(s)

-----------------------

A few things that are used for very short times :

hair dryer, toaster, coffee machine, electric toothbrush,vacuum cleaner

My 12kWh is based on the above.

Heating would be central by some other means, wood or gas maybe but the pump still would need some power.

mcgivor · February 2019

Anything that heats or cools will push demands, consider gas for cooking, clothes dryer and water heating. Refrigerator choose an inverter type to minimize surge, inverter pumps and washing machines are also available. Conservation will greatly reduce the costs of the installation, not to mention the battery replacement costs in the future.

BB. · February 2019

There are several major calculations/estimates that you need to make:

Peak Watts (the most power/appliances you expect to run at the same time--May include starting surges--such as a well pump)
Watt*Hours per day (Water heater--3 kWatts * 2 hours per day = 6 kWH = 6,000 WH per day+all other loads)
Genset fuel (propane, gasoline, diesel, or try no genset at all)

Assuming 12 kWH per day, and 4.6 hours per day of sun (no trees, not in deep valley, etc.--Clear southern exposure), you can begin with a "nominal" system design (2 days storage, 50% max discharge for battery bank, and at least 10% minimum rate of charge).

12,000 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 1,176 AH @ 48 VDC

Then 10% rate of charge:

1,176 AH * 59 volts charging * 1/0.77 panel derating * 0.10 rate of charge = 9,011 Watt array nominal

Size of solar array based on hours of sun per day and loads:

12,000 WH per day * 1/0.52 off grid AC system eff * 1/4.36 hours of sun per day (Dec) = 5,293 Watt array (Dec "break even").

Assuming you want to keep generator use low, then 9,011 Watt array would work very nicely (batteries are expensive and easy to "murder", solar panels are cheap and last 20-40 years). Such a system would supply:

9,011 Watt array * 0.52 AC system eff * 4.36 hours of sun per day (Dec) = 20,430 WH = 20.4 kWH per day

Which is good, you should "plan" on using ~50-65% of your predicted harvest per day... Some days you will get more, other days you will get less.

The "maximum" AC inverter for a 1,176 AH @ 48 VDC battery bank would be ~12 kWatt (1 kWH per 100 AH of 48 VDC bank capacity). So, ~6 kW to 12 kW AC inverter would be nice (if you can run on a 6 kW inverter, that saves money and wasted energy). The surge capacity of most good quality AC inverters is ~2x rated capacity (for seconds to a couple minutes).

Now figure out what you need (like 2x $600 MPPT solar charge controllers, a 6-12 kWatt hybrid/off grid AC inverter, 9,000 Watt array, 1,176 AH @ 48 VDC battery bank, array mounts, wiring, etc.).

Not looking for "exact match" to my sizing numbers--Just using the exact number so you can follow my math. Anything solar, +/- 10% is basically "the same".

Cost out the system and see if this is within your ball park or not.

You can use our host--Good pricing and good product to get a "nominal price" to get started:

www.solar-electric.com

Create a login, if you want. I guess they do have some lower pricing if you have a login.

-Bill

softdown · February 2019

I'm fighting, and losing to, alligators right now. I think there may be power poles not too far from your property. Utility power is far, far cheaper than solar power if the hook up fee is tenable. Wish I was in a better position to evaluate things for you. I seem to be losing my Florida home to heartless Lee County over a technicality - an expired roof permit (expired month ago while difficult tenant was being evicted).

hyperviktor · March 2019

Does anyone know if there's a forum about using generators as a constant power source for a house or shall I ask question here ? I'm trying to figure if there's a type of generator that one can run 24/7 to power a house - well, at least I know they exist but it seems very difficult to find anything. I know it's possible but wasn't able to find any real information, not even sure what I'm looking for - continuous or prime generator ?

I assume calculations are similar to the solar calculations - what stuff would be running simultaneously and then get something that delivers over that number, so it wouldn't be running on full power.

BB. · March 2019

There is a forum that talks about older equipment and some modern engines (?)

https://www.smokstak.com/forum/

Generally, I would suggest that your steady state loads should range from 30% to 80% rated genset power.

For gasoline, propane,etc. Gensets, they are most fuel efficient over 50% load. Below 50% load, they use almost as much fuel per hour as at 50% rated load.

Inverter generators are more efficient down to around 25% rated load

Diesel cycle engines more fuel efficient at even low loads.

However, depending on brand, model, and age, diesels should be run at 40% to 60% rated load long term (older best 60%, newer perhaps down to 40%).

Gasoline, many folks prefer for very cold climates as easier to start and run (a bit of preheat makes thing easier).

Diesels and propane have issues with cold.

A hybrid system where you run from inverter+battery bank during low power usage (night, midday), and run the genset during heavy energy usage (evenings when coming, doing home work etc.) and charge the battery bank at the same time (keep genset efficiently loaded). That has reduced fuel usage by something like 50% for some villages in Africa (as I recall).

Bill

softdown · March 2019

The above hybrid system is quite logical. Really, really wild ass guess assuming your system is energy efficient: Four golf cart batteries (~$400 plus cables) power house for ~12 hours/day. Genset does the rest.

BB states that propane struggles in the cold? That would be news to me but BB does his homework.

With a 500 gallon (they might allow smaller) propane tank one can buy propane in August, last few years, for less than $1.25/gallon. Propane burns clean and lasts forever.

Your demands lean towards the unique side: 24/7 occupation for 1-2 months/year.

Came close to looking at your property for you. "Fighting alligators" for awhile.... Pretty sure there are several decent residences in your close by area.

You can find "flammability range" of diesel, gas and propane here: https://www.propanecarbs.com/propane.html

mike95490 · March 2019

Real cold areas, propane is reluctant to boil off in the tank to give you gas vapor. That's the only issue with it.

I ran for a week, with a minimal battery bank, using a eu2000 into my hybrid inverter and all normal daytime and nightime loads worked fine, the inverter gen cycled up and down all night as the fridges came on and off. I used a remote tank to get 20 hr runtimes and changed oil with synthetic oil.

Using a battery and inverter gives you quite a bit more flexibility than having to stay within the generators limits. i doubt a small generator can run a fridge and start a 2nd one. I have 2 fridges & a deep freeze.

if you must only use generator, everready just released a nice looking inverter genset, but it's pull start only. I guess if it's always on 24/7 you only need to start it after a oil change every 50 hours.

https://www.energizergenerators.com/ezv7500.html

BB. · March 2019

Regarding propane in cold... Pulling vapor (gas) from the propane tank can lower the temperature of the tank, and if it already well below freezing, smaller tanks (and very dold tanks) will not vaporize well enough to supply the genset.

And larger gensets use liquid propane and have an onboard vaporizer that uses the heat (engine coolant) to vaporize, which can reduce the issues of trying to vaporize propane (other gaseous loads such as cooking, hot water, and heating will cause the tank to run cold too).

Believe me, I live near San Francisco California--I do not know cold. Just summarizing the issues I have read about and tried to help people with here on the forum.

As I always say, the details matter. Do not buy/install equipment without first working the issues out with a pencil and paper (and check with experienced people who can help).

Details like the size of a propane tank (larger tanks, less issues with vaporization). And the newest "hybrid AC inverters" which have generator support.

You can, for example, get a 4 kWatt genset and plug it into an 8 kWatt AC inverter (plus large enough battery bank, typically ~800 AH @ 48 volt minimum for an 8 kW inverter)...

Run the house off the inverter, and loads from zero to 8 kWatt (16 kW surge). Start the genset when battery gets low (auto start, or run full time), and the inverter will support the house loads, and draw power from the genset up to rated load (i.e., program 3.5 kWatt max load from genset. If your loads are light and battery is charged, the Hybrid Inverter passes power from the genset to your loads.

If you have a big surge, it lets the genset supply 3.5 kWatts, and the AC inverter will supply the rest of the surge (using the battery bank).

And if the battery bank needs charging, the Hybrid inverter will "share" loads and battery charging from the 3.5 kW genset.

This works with and without solar power.

This allows you to run a smaller genset (>50% loads) for your "average loads", and the inverter+battery bank to supply the higher short term loads (well pump, microwave, electric kettle, electric stove) from genset+battery (discharging). And once you turn the loads off, the "extra genset" power is used to recharge the battery bank.

Once the bank is full, the genset is shut down until the batteries are discharge over the next day or so (start charging around 75% to 50% State of charge).

If you are away from the place for months at a time, you probably want either (or both) a small array to "float" the battery bank (flooded cell lead acid batteries need charging ~once per month at ~75F/25C)--And/or use AGM batteries... They have lower self discharge and only need to be recharged (when stored) every ~6 months.

-Bill

softdown · March 2019

I know there are homes in the area. It would sure be convenient if one sold you power via, say, #6 copper wires. I keep things simple to get a point across. Of course the wires might need to be #2 or could be OK at #10. 220 volt crosses terrain pretty efficiently.

softdown · March 2019

I could do a simple and "smallish" 24 volt system for about $2000. Just tossing that out there.... Delete the comment if I'm breaking the rules. This lot is about 20 miles from me.

A full time residence is normally starting around $25,000 for solar - that can go to $50,000 for a larger more sophisticated system. This board has images of systems that likely costs a lot more than $50,000 - for the well heeled.

Solar is not cheap at all. Figure it costs at least 3 times more than grid power for a full time user. Most will pay at least 5 times more if a pro does the sales and install.

hyperviktor · March 2019

Thanks all the input, generator seems the way to go for now. Still no luck finding the right type as most generators are described as backup or so, although i'm guessing it would only need to run maybe around half a day and rest half a day so I could get pretty much anything - looking at generac / hyundai etc.

softdown · March 2019

Do your oil changes to get decent life out of a generator. Low RPM diesel is the go to genset for full timers in northern environs. Honda is a revered name in inverter generators by the way. Use gas for cooking and heating. I'd just use Buddy propane heaters for your application - unless you want to go upscale. These projects always take a lot more time and costs a lot more money than anticipated.

softdown · March 2019

FWIW I got banned at C-D for "discussing moderator actions". Can't keep them in line anymore it seems. Nice enough board in spite of the power hungry mods.

Estragon · March 2019

IMHO, using a standby generator (generac et al) in a prime generator application is likely to be frustrating, and probably more expensive long term.

There are generators designed to run more or less 24/7/365, but they tend to be bigger than needed for a single home. Onan/Cummins and others do make small(ish), prime(ish) generators. Something like a 7kw 1800rpm diesel.

softdown · March 2019

https://forum.solar-electric.com/discussion/comment/395855#Comment_395855

Been thinking about this since it is only 20 miles away. Thinking I would do affordable gensets and replace as needed. It will take awhile to figure out how much time will be spent there. Is crime a threat? Generators are attractive to opportunists. I took the wheels and handles off my ~550 pound generator for that reason.

BB. · March 2019

Also depends power needs over the entire year...

If you need burglar alarm, exterior motion detectors, basement water pump, etc. -- Then a battery based solar power system can help provide the basic power needs when nobody is there (oversize the solar array to carry through bad weather--I.e., overdesign).

Then the next question, if you provide for basic services when nobody is there--A little larger and can it run LED lighting, laptop, TV at night and avoid overnight genset runtime???

-Bill

softdown · March 2019

The mods are now going over old posts of mine and hitting me when their delicate sensitivities are offended. So if you need to reach me - this is the place. Or softears at msn dot com

Mods - BB is a rare one. Most others are into power and control.

Solar load calculating in SLV

Comments

Murcia Spain, facing south, 52 degrees from vertical (best year round harvest)... Note, I cannot paste the table below--Bug in new forum software.

You say summer home... Suggest March through September is 5.10 or more hours per day average (break even).

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