Solar Power

Just ran across a story about solar power that may be the perfect example of the problems with solar power for majority use.

Many espouse the virtues of solar power but few deal openly with its dirty secrets. Namely cost of putting a system together and the length of time it takes for the system to 'pay for itself'. The name of this site is the axiom at work here. TANSTAAFL. And while the idea of solar power being a free lunch is prevalent it just is not true at this point. Lets start with some basic numbers.

1) The average power usage for a home today is ~15 kilowatt hours (kw-hr for short) per day
2) The average energy of the sun is ~1kw per square meter. Thus an hour of full sunlight nets 1kw-hr per square meter of surface exposed to sunlight.
3) The average conversion efficiency of readily available solar panels ~15%. So on average 1 square meter of solar panels nets (1000*.15) or about 150 watts per square meter. So it takes about 7 panels (6.7) to develop 1kw of energy.
4) The average cost per watt for solar panels is ~$4. So 1kw worth of production costs $4000.
5) The average length of peak sunlight per day is ~6 hours a day. So to achieve 15kw/hr of energy production per day you need 15/6 or 2.5 of those 1kw arrays. 2.5 * 6.7 = 16.75. That is the size of your array in square meters at 15% conversion efficiency needed to provide the average power consumption for an average house on an average sunny day. 16.75 * 150 = 2,512.5 and that is 2512.5 watts of power during peak production. As I just mentioned a watt of solar panel power production costs about $4 a watt so that means the cost of that array is roughly 2,512.5 * 4 or 10,050 dollars for just the solar collectors to power the average home.

At this point solar pundits are fast to point out that this is a one time cost. IE solar panel lifespans are measured in decades so yes you pay $10k now but you never pay again for the power they produce. The assured life span of most panels produced is 20 years. Ironically the time it is expected for such panels to pay for themselves in terms of the energy they produce is also 20 years (refer to the linked story for just one example).

Is this true ? Well yes depending on a variety of factors. The most important of course being the cost of grid generated energy. Right now the national average sits at around 10 cents per kw-hr. At an average production rate of 6 hours a day a 1kw solar array will generate 60 cents worth of energy a day over the course of a year (the 6 hours accounts for cloudy days and long summer days in most areas). So 365 days in the year times *6 hours of sunlight on average *.10 cents of electricity produced per hour = a grand total of $219 of electricity produced per year by a 1kw solar array. At $4 a watt that is a 4000 dollar array so the expected time for the array to pay for itself is 4000/219 = 18.26. Call it 18 years and 3 months.

This is, to put it mildly, a rather large pill for most people to swallow. Essentially it means swapping monthly costs for a large up front cost. Even so if you are thinking on a long enough term this still seems relatively appealing. After all many panels made in the 70's as this technology really began to emerge for the first time are still kicking along just fine so it isn't unreasonable to expect your array to last long enough that you will indeed be better off than if you just stayed on the grid. After those 18 years and 3 months you are still producing energy and the system has paid for itself. Well not quite. If it were as simple as buying just the panels this might be the case. However, you also have to mount them properly. You have to wire them up to the house electrical system which will require an inverter to turn the power generated by the array into a useable form, ie 110-220 AC or some flavor of DC based on your appliance choices . If you want a stand alone system you also will have to have a battery bank for storing the energy generated during the day for use at night.

Frankly a true standalone system at current grid costs will never be a cost effective solution at average consumption levels barring a serious breakthrough in battery technology or a serious drop in replacement cost. Even if you are going for the hybrid setup like those in the article you still have to deal with the cost of installation, wiring and inverter which for all intents and purposes makes the pay back term 20 years if not more... especially if you also have a battery bank to contend with as both of those examples did. And that is if NO extra costs are incurred during that length of time... highly highly unlikely. At the least you will replace the inverter and batteries at least once. Not to consider other non cost issues like maintenance. Yes there are some additional costs to grid connections but by and by they are very small baring a need for major re-wiring. By comparison it is probably possible to entirely re-wire a house for the cost of a good inverter or even a minimal battery bank, either of which can easily run a couple thousand bucks or more. Finally to really build an independent system you will almost certainly still have to have a gas/diesel/propane etc powered generator to use during the worst periods of no sunlight. A battery backup system to provide this level of independence is just not very realistic... at least not without a major change in the way people consume energy. That is an option for the rabid fringe... but is never going to appeal to the average Joe if they have a choice.

Now I just used a lot of weasel words that proponents will jump all over so lets deal with them. First average use can be reduced significantly with the use of more efficient appliances and better insulation in construction of a home. True. But Energy efficient appliances cost more money. Significantly more money than their energy guzzling counterparts. In fact at current energy costs the extra cost is almost never justified in light of the expected life span of the appliance. If you don't believe me find the cost of your electricity on your bill then go to the home depot and compare power consumption rates on those yellow tags between cheaper units and the uber energy efficient ones and figure out how long it would take the most costly appliance to pay for the difference in energy savings alone. Just to give you an idea the difference in refrigerators if often more than $100 but the difference in yearly energy consumption is rarely more than 100 kw-hr per year. At 10 cents than means 10 years for the appliance to pay for just the cost difference over the other model much less the length of time it would take to justify buying a new model over one you already own in the first place.

Can appliances last that long ? Certainly. Can that kind of purchase affect the overall cost of a solar system if you design the whole house around that idea ? Defiantly. IE if you fill the house with these more costly appliances you can save a significant amount on the array because it won't have to be so big. But if you are not careful you generally just wind up shifting the cost around to different columns. Not to mention completely outfitting your house with new appliances generally only happens when buying a new home.... which is about the only time the extra cost has any chance of being justified.

Don't get me wrong. I am actually a big fan of solar power. However I think those promoting home solar power systems are for the most part pretty shady characters feeding off the eco paranoia that many hold towards our current energy system. When they start being up front about the fact solar is in fact often far more expensive than grid power then I will lend them more credence. The people in this story did this because they like the technology and felt it was personally worth it to install their systems. There is much to be said for energy independence and for reducing the need we have for hydrocarbon fuel usage. But TANSTAAFL. Solar panels have to be produced, batteries have to be disposed of or recycled properly. The process of both is not nearly as green as most people think and those that do understand it tend to simply pass it off as the lesser of two evils. The thing that concerns me about that line of thought is that really... we don't understand the effects of our current energy system on the environment much less one that is only theorized about. In general I think the eco conscious will become a lot smarter when they accept that energy production and consumption on the scale of the human race is ALWAYS going to be something to contend with no matter how we do it.

For example go take the US average yearly energy consumption and apply that to the 15% efficiency rate and 6 hour average of sunlight per day and figure out just how big the array would have to be to supply that power. How much space would we have to cover with solar panels? It is a frightening number I assure you... but please find it for yourself. Now consider if there might not be any potential impacts from intercepting that much sunlight and changing the rates of reflection and absorption on such a scale.... we already know that there are impacts due to such things. Just ask any meteorologist about the urban heating effect.

Now there are some things that could change all this. Size requirements will go down if efficiency increases. I think 25-35% is what is needed. At 50% it will flat out take off especially if the cost of production remains more linked to size than to power production... that is to say if as the efficiency goes up the effective cost per watt of production goes down. Just as a practical matter in terms of making this a smart financial decision the cost per watt has got to go down, or the cost per kw-hr has to go up. The point at which it will attract the common persons interest in my opinion is when it not only costs as much as a car... but can pay for itself over a grid connection in a similar amount of time to most car loans... IE 6 years or less.