Energy needed for himan survival in urban scenario
How much energy needed to survive in central European climate with very low income?
Depends on location and time of the year.
Let's assume mild winter case scenario. November to February, -0C. Area for living 50m2.
1. Keeping warm temperature inside the house at 16-17C: Compressor heat pump 5A, 220AC=1.1KW with duty cycle 50% is around 500W, or Close to 10KW per day.
2. 1-3KW for cooking, lights and washing machine. Actually for assorted needs it may vary up or down drastically. I'm taking it as an average.
For example having 3 times a day tea or coffee: about 200W already. 1 g of water by 1 degree Celsius or (1 Kelvin) equals 1 calorie. Thus 1 Liter from 20C to 100C boiling stage is 334 720 Joules (335KJ) or 93 Wh, but raising that temperature within say 3 minutes it is 1860W instant power, BUT for 3 min only. It is still the same 93W. Please note: in reality, no way to heat water with 93W source as heat will escape faster then water temperature rise to boiling temperature. Realistically with 80% efficiency it is more like 120Wh.
When we talk about some sort of action like heating water or compressor or electric motor, it is always in Watt hours this signifies for how long that action took place. Because energy used in watts has to be calculate in the account time.
I on purposely use electrical terminology Watts because in most of urban survival we going to use electricity.
If you would try to burn wood to heat 1L of water, it will be in theory if we have around 50% efficiency as during burning lots of head goes to atmosphere and with an average dry wood. At this point we will skip the boring calculations and give you the result: around 0.1Kg or 100g.
But how often can you see people using wood to boil or cook in modern world?
Cooking 3kg or 3L pot meal will be 5 times as much as for boiling 3l water. Thus it is around 1500W of electrical power to cook an average dish for 3 people. Please do not use watt hours the same purpose as watts. I use it very loosely because I can keep tracking of which is which, but inexperienced reader might immediately come to erroneous conclusion by using W and Wh at the same time. I keep adding Watts (integrating) consumption with an idea in mind that this has to be in conjunction of time usage. So I have to come up with a number of Watts over 24hrs period. Example: compressor heat pump is 1000Wh consumption. But it is working only at 50% duty cicle (on 2minutes, off 2 minutes). And we might turn it off for 4 hours. Therefore integrated total for the whole 24hr day we have 20000/2=10000 Watt for 24 hours. Same goes for other consumption points.
Also we are not taking in assumption the transportation. It is assumed the "survival" modality and human will travel by his own power.
Also we assuming food is given, which is very bad assumption. Because cooking food takes lots of energy. But to simplify our calculations, I will be using very simple case scenario. Also this is NOT post apocalyptic scenario but rather low or no income person or a a family with very minimal means for their living. We will discuss other, more isolated/autonomous scenarios later but for now here is my estimates:
Most likely 15KW per day or at most 700W per hour.
2. It it possible to drastically cut down electrical consumption with wood furnace. 1kg wood is about 2.6KW energy
1m2 wood is around 400kg, thus in the -10C winter, for 1 month to heat a small 30m2 house : 30d x 11Kw=330Kw or 330/2.6=127kg of wood or 0.3m3.
As I was writing this, I got very doubtful according to my personal observations. Most likely it is close to 2m3 of wood or 6m3 of branches. to have comfortable +18C during mild winter.
This consumption has to be estimated very scrupulously because each particular usage case may vary 100 times.
For example: people always makes the same value for one light bulb on or a cup a tea boiled in an electric tea kettle. Not really...light bulb is 15W for very bright LED light and tea kettle is 700...2000 watts! Obviously left for 24hr 15W bulb will present 360 Watt and teakettle for 5 minutes with 1000 watt power is only 84W used in 5 min segment. But if it is only 2 hours of light, then it is only 30W
Another thing to conciser is a small "energy thief" (or multiple one) we always have in our houses: it is a charger for the cell phone or something left in the wall outlet constantly plugged. I may not believe, but some of them consume around 1W of energy per hour without any usage. Not much, but it is whole day and 360 days per year... thus it is 9000 watts per year! And imagine your whole house is full of those little or big things constantly left to be powered. It will add up rather quickly. One example from my personal life: I left my house for 8 months. When I came back I could not believe the electric bill! I thought it was a mistake. But after looking at what could consume this energy, I look at the wifi router and security camera. Router 15Watt hour, Camera 10-15 watt hour. Total 30Watt. x24hr x30 days=21600 watt per month! x 8 months= almost 173 Kilo Watt!! Wow! It may be not a big deal with 10 cent per Kilowatt, but think about that. 173 Kilo Watt for just having internet and camera working for 8 months!
Let's assume we are very disciplined people and really really surviving.... So we only use energy to stay alive. Wifi is on for an hour and lights are on only for 2 hours at most. Heater to a minimum level (16-17C) and we use very tricky ways to heat the house (with heat pumps). We eat precooked food (cans) , we don't do much shower (only ones per month) and do hygiene with cold water.
In this case the estimate is around 15KW per day if we don't use any extra sources of heat and around 5KW if we use wood/oil/gas heaters or some sort of extra heater to keep 17-18C
Therefore if you have 6500 Watt solar energy system, you could satisfy your energy needs in mild winters or 1600 watt solar system if you can use carbon fuel heaters.
Please write your comments in the forum section. People will appreciate your real observation.
I will try to come up with simplified calculator for energy usage as we are all living in such a different circumstances and climates that my estimate can be way off chart from your case scenario.