Solar Thought Experiment

[keightley]

This may be a worthless thought experiment.  But it may help me understand my electricity needs a bit. And I do realize that I will not even come close to this level of usage living in a Chevy Express.  With that said, here is my thought experiment...

I am looking at my electric bills over the last year.  I currently live in a small two bedroom apartment.  The most power I have used over the year in one day is 38 kWh which is about 1580 watts.   If I wanted to power my apartment completely on solar, what size battery would I need?  What about the size of inverter? 

Keightley

 

[highdesertranger]

I don't know if you mistyped but 38 kwh is 38,000 watts. highdesertranger

 

[keightley]

Yes. I know. 38 kwh per day is 38,000 watts which equals 1580 watts per hour. 38 kwh per day cost me $4

 

[Chuck1]

Rough figure, battery type will change this bigtime.

with system losses, 48VDC 1200Ah Battery at about $14,000

inverter, go with 4000w at $2,200

 

[Surly Biker]

Someone may want to help with your math but not sure how relevant it is.  Let me share my experience. I live full time in a van and rely only on solar for cooking (induction cooker and toaster oven), fridge,lights, laptop, and heater fan.  I collect about 1500Wh per day. That's  about 120Ah. With efficiency losses, I'm sure my actual use is about 80Ah per day.

 

[future_vandweller]

Yes.  I know.  38 kwh per day is 38,000 watts which equals 1580 watts per hour.  38 kwh per day cost me $4

" 38 kwh per day is 38,000 watts.."

38 kWh is 38000 Wh, not 38000 W.

38 kWh/day is extremely high for a two bedroom apartment.

If you install solar to meet this high consumption, you'll be over-designing it.

Here's the math:  assume 5 hrs per day of productive sunshine.  Divide 38 kWh by 5 hrs to get 7.6 kW of AC power.  Add 10% to allow for conversion losses to get 1.1*7.6 = 8.4 kW of solar panel.  At 3$/W installed, this system will cost you 25K$ and with a footprint about 1000 sq ft.

 

[future_vandweller]

" 38 kwh per day is 38,000 watts.."

38 kWh is 38000 Wh, not 38000 W.

38 kWh/day is extremely high for a two bedroom apartment.

If you install solar to meet this high consumption, you'll be over-designing it.

Here's the math:  assume 5 hrs per day of productive sunshine.  Divide 38 kWh by 5 hrs to get 7.6 kW of AC power.  Add 10% to allow for conversion losses to get 1.1*7.6 = 8.4 kW of solar panel.  At 3$/W installed, this system will cost you 25K$ and with a footprint about 1000 sq ft.

Looks like I answered a question you didn't ask!

You need 40 kWh of battery capacity.  At 48 V, this amounts to 833 Ah.  Inverter rating depends on your peak power draw.  It could be a 1500 W or 6000 W, depending on the loads you're using at any moment.

 

[keightley]

You have to factor all the other appliances and electronics one has in an apartment that a van does not have: a oven, microwave, blenders, instant pot, toaster, full size refrigerator, dishwasher, washer/dryer, lights, television, hair dryer, computers, internet modem, alarm clocks, radio, etc. And although my heat is gas, I am pretty sure the furnace requires electricity to turn on and off. In the summer one can add air conditioning. In my particular case I have a 120 gallon aquarium with two canisters, UV sterilizer, light, and air pump that runs 24 hours. Oh... then I have a roommate who likes to leave the lights on for her cat.

Another aspect one has to consider that will not happen when living in a van is passive draw on the electric system. A lot of things that require electricity people leave connected to a plug even though the appliance and/or electronic is off.

So like I said. This is just a thought experiment. It is interesting to know that if I want to keep my lifestyle exactly the way it is yet go completely off-grid it will cost me an up front cost of about $16K. My current cost for electricity is approximately $720 a year. So I will not be building me an off-grid mansion out in the middle of the dessert any time soon. LOL

 

[Chuck1]

It would pay off in 22 years, "but" you will need new battery's in 10 years, now pay off is 36 years, "but you will new battery at the 20 year mark, now payoff is 50 years, and so on.

only way you get a payback is if your on the grid and don't need battery's.

 

[John61CT]

Alternative energy is very cost-effective if implemented by the utilities.

For an individual, grid power will always be a tiny fraction of the true cost of solar without subsidies.

Bottom line unless you can benefit from tax write-offs etc, only use solar where mains power is not available.

 

[Travelmonkey]

Someone may want to help with your math but not sure how relevant it is.  Let me share my experience. I live full time in a van and rely only on solar for cooking (induction cooker and toaster oven), fridge,lights, laptop, and heater fan.  I collect about 1500Wh per day. That's  about 120Ah. With efficiency losses, I'm sure my actual use is about 80Ah per day.

I like these types of post with real world info/experiences.  I would have thought you're your use would be higher b/c induction cookers and toaster ovens are high wattage appliances but I guess you only use either appliance 10 to 20 min a day, right?

I kind of stopped reading at the $4/day daily cost for electricity; that's only $120/month (which seems high for an apartment) which makes the break even in the years (decades as chuck points out).  Shut off some lights and call it a day.  

 

[DLTooley]

The biggest benefit of solar is off-grid low voltage/wattage power. Tieing into the grid with a moderate sized mobile set up would be a good project, as well as a power outage backup. I have not done that.

 

[Zoomyn]

A gallon of gasoline holds.. . 120,000Btu - 47 Horsepower - 35kw worth of energy.. . A Honda or Yamaha 2000 inverter generator in its best form is about 10 to (maybe) 25% efficient depending on load, so a gallon of gas converts to between 3.5 and 9 kilowatt hours power. Anyhow - to match that $4 (38kwh) grid power would cost 4+ gallons of gasoline.

There is no magic to grid power, huge scale of mass production & engineering tricks reduces apparent costs. The law of thirds apply to grid power - 38kwh used? It's transparent to the consumer but the averages equal another 38kwh was lost transmitting power to end use point, and 38kwh generating it - so 118kwh was consumed, or the energy equivalent of 3.4 gallons of gasoline.

Soooo... Conservation and elimination of frivolous and/or parasitic loads is key to renewable energy.

 

[Surly Biker]

I like these types of post with real world info/experiences.  I would have thought you're your use would be higher b/c induction cookers and toaster ovens are high wattage appliances but I guess you only use either appliance 10 to 20 min a day, right?

I kind of stopped reading at the $4/day daily cost for electricity; that's only $120/month (which seems high for an apartment) which makes the break even in the years (decades as chuck points out).  Shut off some lights and call it a day.  

Thanks. You're right, the high current appliances only run for 20-30 minutes per day. I was just trying to give the OP a more reasonable estimate of what a van dweller might need. I run about 80Ah/day but am sure that most readers in this forum run considerably less, probably about 20-30 Ah (250-350W) for fridge, lights,laptop, etc. because they use propane for cooking.

Obviously, no AC, electric heat, clothes washer, etc. I'm just trying to keep it real ...

Actually, it's quite simple to make up a little table to estimate energy use, considering the appliance rating, duty cycle, etc. if yo take the time, most folks will probably end up about in that 20-30Ah/day range.

 

[John61CT]

probably about 20-30 Ah (250-350W) for fridge, lights,laptop, etc.

Fridge on its own can use a lot more than that when temp differential is high.

Under 20AH per day (250wH) only in very mild conditions and thermostat set pretty high.

 

[Spaceman Spiff]

My Norcold 2.1 cu. ft. compressor refrigerator (kept at 34º) uses ~30 AH when highs are in the low 70º, to ~ 45 AH when highs are 90ºF.