Blank_Stare said:
In a global network, at times when demand is less than what is available, what will we do with the excess energy, if not store it in batteries?
Was working on a response to nikkom and EnumaElish before the rash of posts.
nikkkom said:
Today, "cheap" cells (ones you would buy for a solar power plant, not for comsat) are 20%.
I knew that, where did I get the 8-10w/sqft.? Probably just mindlessly copying it off the internet. Panels that I purchased in 2009 where rated 130 watts had an area of about 8sq ft. so that is 15 watt/sq ft..
EnumaElish said:
Solar is as much about transmission capacity as it is about storage. Vast areas of Earth receive sunlight almost year round. Improve transmission and you will not need storage.
Storage will still be needed. Look at replacing all sources with solar. Take the US. The best place for solar farm is the southwest still only getting about 5 full sun hours equivalent per day with about 16 hours of no to near no power output. Considering that they are located in a restricted section of the country a new power grid will be needed
The power lines will not only have to carry the immediately used energy but also the stored energy which will be 2 to 3 times the energy used during generation. The US has a generating capacity of about 1000G W for a summer day. 8000G Whrs of energy used during the generation period. This will require a storage capacity of from 16000 -24000G w hrs to just carry over to the next day.
Elon Musk of Tesla is selling Li-ion storage cells he call the "POWEWALL" which can store 14K Whrs. He currently sell them form $6200 apiece with installation costing $800 to $2000. An average home would need about four to five of these batteries just to meet the maximum energy requirements. The daily average US energy usage is about 11B kWhrs. which means that the country would need 786 M POWERWALL batteries at a current cost of $4.9T. These batteries cost about $400 per stored kWhr but it is believed that new technology will bring this cost down to $100 per kWhr stored which is the same as the current lead-acid batteries. Actually the usable energy stored in a Lead acid battery is only 1/2 of the maximum since taking more out significantly reduces the life of the battery. So the new technology may be a significant improvement.
As for other storage methods I looked at elevating water and have it drive a turbine since it is technologically straightforward. If you assume that the average home can have a maximum demand of 60 kWhrs (216Mj) per day and are able to elevate the water to a height of 100 m above the generator one would need to pump about 220,000 L which is a sphere about 7.5 m in diameter equivalent to 7.5 4ft x 18ft circular pools. That is for one full day of power, you would need about 1/2 -3/4 of that for the non generating periods There are about 125M households in the US.
If you want to go off the grid you definitely need batteries or other storage device so for a 60 kwhr max daily energy need and maybe a 12Kw instantaneous power requirement requirement would require about 800 sq ft of solar panels for which most houses do not have adequate roof exposure/area so se aside some of your back yard.
One nice think about solar panels if you do not need the power you just don't turn anything on. With a generator running with no draw you still use energy . You must turn it off. when not using electricity.
For the more eastern part of the country where clouds are prevalent you might want 3 days of backup power or about 12 POWEWALL batteries or 150 deep cycle lead acid batteries.
Rambled a bit but all said and done I think solar will be just one of many power sources we will be using into the foreseeable future. Some countries will use more and some less.