In a recent post, I discussed why the US needs, on average, 15,000 additional megawatts (“MW”) of new power plant capacity – each year! – just to keep up with the growth in domestic demand for electricity. How many new power plants have to be built to accommodate this national thirst for energy?   Two power plants a year? Five? Ten?  And what  if all of that new power had to come from renewable energy – say solar – as so many in the green community suggest it should, or more urgently, demand it must!? Is it even technically feasible to satisfy our annual electrical demand growth from solar alone?

Of course, the number of new plants (or generating units) needed to supply 15,000 MW of new capacity each year depends on your technology of choice.

• 15 – Large scale 1,000 MW coal fired or nuclear power plants
• 30 – Medium sized 500 MW natural gas, coal fired or nuclear power plants
• 7,500 – Utility scale 2 MW wind turbines
• 75 million – 200 Watt solar panels.

In reality, 75 million solar panels a year isn’t enough. It’s too low because solar panel manufacturers rate their panels DC whereas our electrical grid uses AC power. Using an approximate conversion factor of 0.85, the real number would closer to 88  million – each year. Are we done? Install 88 million solar panels each year instead of 15 large coal or nuclear plants? Hardly.

There’s the pesky matter of cloudy days when a solar plant can’t produce at full power. That’s the rub with most renewable power including both solar and wind. It’s intermittent and you can’t count on all of it being there when you need it.  On average, a typical solar power plant might have a capacity factor rating of roughly 20%; even lower in locations with less abundant sunlight.  Said differently, you could build a 100 megawatt (“MW”) AC solar facility but on average you could only count on 20 MW (20%) being available on any given day. But there’s a niggling problem with that that word “average”. On a bright, clear sunny summer day that solar plant might  produce 100 MW (100%) power during midday. But on a cloudy day in winter it might only produce 5-10% of peak output. In fact, it might rarely ever produce at exactly the 20 MW average. And then there’s mornings and early evenings when the sun is waxing and waning and only a fraction of the 100 MW nameplate rating is produced. Finally there’s that inconvenient daily event…..called night….when the output of  a solar plant is nil, nada, zip – all night long.

Follow this to its logical conclusion and you might want to have some backup power plants that can fill in for the solar plants when the sun doesn’t shine (or shines less than needed for solar output to meet the electrical demand).  And these backup plants had better be ready when you need them – the very definition of “firm capacity”. Today, firm capacity comes from fossil (mostly natural gas and coal) and nuclear plants. By now you might also be tumbling to the fact that 100% of our electrical needs cannot be met with intermittent renewable energy like solar and wind. Simply stated, until we figure out how to store massive quantities of electrical power economically, we need the kind of firm capacity that can only come from fossil and nuclear power plants.

Please don’t misunderstand me. I’m a big fan of renewable power and solar in particular. I think solar has… (forgive me) a sunny future! However, green energy proponents who oppose all forms of fossil power may be the greenest of green advocates but all too often appear willfully ignorant of the realities of delivering reliable electricity 24×7 to consumers.

Today, regulated utilities, independent power producers, regulatory authorities, politicians and rate payer advocates are all engaged in a healthy debate over what percentage of renewable power is practicable.   There is broad consensus that at least 25% of the our electrical power demand can be met with renewable sources. The “25 by ’25″ resolution recently passed by the House Representatives expresses the sense of the Congress that by the year 2025, at least 25 percent of total U.S. energy will come from renewable, domestically produced sources. Since we’re at approximately 9.5% today (source EIA), if enacted into law, we would need an incremental 15.5% over 16 years.

Let’s assume for a moment that all of this incremental renewable energy were to come from solar (admittedly unrealistic but bear with me here). The US currently produces/consumes approximately 4.1 billion megawatt-hours of electricity annually. 15.5% of this is about 615 million megawatt-hours. Assuming 99% reliability and a 20% solar fleet capacity factor, this would translate into 431,050 megawatts DC of newly installed solar panels. Assuming 200 watt DC panels, we’d need approximately 2.2 billion new panels to hit the 25 by 25 target.  If we built one large 431,050 megawatt DC solar power farm, we would need 3,368 square miles of land (assuming 10 acres per megawatt). To put this into perspective, that’s a square parcel of land 58 miles by 58 miles or approximately 0.1% of the total US land area excluding water bodies. You could circumnavigate this solar plant in roughly 4 hours driving at 60 mph. Imagine this facility being located in the hinterlands of the greater southwestern US. Not too hard to imagine, no?

Ok, so we meet our national mandate of 25 by 25 with a 60 mile square swath of solar panels (of course in reality never all at one location and not with 100% solar). I don’t know about you, but I still want electricity at night and on cloudy or rainy days. So lets talk about backup power for the 25% of energy coming from solar. Backup power would only need to operate at night and partially on some, but not all, days during daylight. This intermediate load resource would have to be the lowest cost to build while also not costing too much to operate. Nukes are VERY expensive to build, difficult to finance,  although cheap to run – not the best fit for  backup. Coal plants are relatively less costly than nukes but more costly to run (and getting costlier if you assume carbon taxes or carbon capture/sequestration) plus they have an enormous carbon footprint that threatens their viability. Just try to permit one today. Good luck. That leaves simple and combined cycle gas turbines burning  natural gas. Least cost to build, much lower carbon footprint than coal, financeable, easily permitted and reasonable cost to operate provided natural gas supplies remain abundant and reasonably priced. The good news is that the long-term natural gas supply picture has improved greatly over the past 2 years and prices have come down accordingly.

So there you have it. Solar, wind and other renewables generating at least 25% of our energy backed up mostly by natural gas and maybe a few more nukes. As coal plants retire, a mix of new renewables and gas fired plants will take their place. The renewables mandate may even increase towards 50% or higher over time. A diversified mix of solar, wind, geothermal, and biomass may even require less backup power than initially thought especially if the electrical grid is expanded. Should large scale power storage becomes feasible, the days of fossil fired power may eventually fade.  Until then, fossil based power generation is going to be part of the mix. Welcome to the future of our electrical supply – real or imagined?