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Renewable Energy … AC vs DC

All electricity is not the same. We blogged earlier about differences in Voltages, Current, Wire Gauges, Hertz (as European vs American), and we slightly touched on AC and DC power. Now let’s talk about something sexy, RENEWABLE ENERGY.

Solar Photovoltaic (PV) panels harness the energy of the sun. Wind turbines harness the energy of wind. And both create DC (Direct Current) power. But wait, don’t we use AC (Alternating Current) in our homes? So how does that work? Unfortunately, with very poor efficiency.

Solar PV Panels are expensive…after installation, currently around $7-$8/watt, and I’ve heard as low as $6/watt. We know prices are going down all of time and PV panel efficiency is increasing, but let’s look at how things are progressing. The panels, themselves, were about $5/watt back in 2007, now they’re less than $4/watt, and pushing down to $3/watt. You then have to add about $1/watt for an inverter (changing DC power to AC) and then installation cost of around $2/watt. Inverters are mostly made up of coiled copper wire, so unless the commodity cost drastically drops, don’t count on the cost of inverters going down. Installation cost is going to be around the same and the major way you can reduce that (other than having cheap labor) is to make the installation during construction versus an addition to an existing structure. Let’s say some new type of installation procedure is invented and pushes installation cost to $1/watt. So even if you can get solar PV panels down to $1/watt, it will still cost around $3/watt after installation ($1 for panels, $1 for inverter, and $1 for installation).

(Update for 2022 - full cost of solar installation was pushing down towards $3/watt for home installations but have climbed up due to inflation, supply issues, and increasing labor costs. Large scale solar was pushing towards low $2/watt. Costs have risen around $1/watt across the board).

PV Panels are around 20% efficient and getting an extra one or two percent solar efficiency is considered a big improvement, but there are many other places that there is inefficiency. You must invert the power and if you get an inverter that’s 85% efficient, you’re lucky. Now you have AC power available, but anything with electronics is going to change that AC back to DC, i.e. computer, printer, TV, electric cars, etc. and how efficient are most power supplies converting the AC to DC, about 50% (if you’re lucky, but most of them are around 35%). That means 50% of what’s going in is being wasted, mostly turned into heat, which is why they’re hot when you pick them up. Just pick one of those little suckers up and see what the power input is and what the power output is. (Remember, Power is equal to Voltage times Amps. And overseas, those little suckers are twice as inefficient.)

Let’s take an American example. You have PV panels or a wind turbine. You’re losing 15% of power inverting it from DC to AC and then at least 50% on top of that changing it from AC back to DC. Running just a laptop for a 40-hour work week wastes $55 a year (did the math in 2008, about $50 in electricity loses and $5 in air conditioning costs). If you are running desktops in your office, it’s even worse. It’s like paying a really expensive toll when there’s a shortcut that’s faster and almost free.

So why don’t you have the PV panels and wind turbines directly supplying power from DC to DC at 97% efficiency? Well, some unique and smart companies do (i.e. Google for its datacenters and charging electric vehicles) and there are patents out there for over a decade dealing with such issues. Other than that, there’s no reason why. The consumers who are purchasing expensive renewable power can save a great deal of money if they installed such systems, but then again, why would manufacturers want to sell less solar panels per person? It’s the whole Apple vs PC/Microsoft thing, “Why sell many products at a small profit margin when you only have to sell a few at really high prices?”

Many people don’t really care since they are already paying for high inefficiency in their electronic devices and consider that normal. Honestly, who really looks at how inefficient a power supply is? Even most engineers don’t. We just take it as it is and become oblivious to the inefficiency since that’s how it’s always been.

We say you should care, since you’re getting cheated out of money.

Take a look at your electric bill, and you’re most likely already paying for it, i.e. a surcharge on your bill to “help” fund renewable energy incentives. So you’re most likely directly funding incentives for others to purchase renewable energy systems who think they’re doing something great for the environment, when in reality they’re wasting a great deal of your money with inefficiency. And indirectly, your taxes are helping schools and other government institutions purchase renewable energy systems, i.e. my hometown purchased an $18 million renewable energy system for its schools and they say they’re getting it for FREE from the state. When I ask what the dollar cost per watt is, I get blank stares.

There is a decade old patent that can turn existing building electrical wiring to supply both AC and DC power, just by changing the outlet. You can buy a high efficiency converter for your whole building and have it converting AC power from the meter at 95% and connect it to your building circuit panel. Now you can cut your electricity costs by more than 50% for all of your electronic devices requiring DC power. And your solar PV panels and wind turbine can feed your home with little worries on conversion loss. As for electric cars…they’re supposed to be 30% of your homes electric bill. With such a system, you can charge your DC electric car straight from your renewable energy system.


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