On June 8 Warren Buffett revealed that Berkshire Hathaway Inc‘s (NYSE: BRK-B  ) subsidiary MidAmerican Energy (recently renamed Berkshire Hathaway Energy) has invested $15 billion into solar and wind projects. Buffett added, “there’s another $15 billion ready to go, as far as I’m concerned.”

Buffett’s giant, exploding money pile
Well for one thing, Berkshire Hathaway is swimming in cash, $55.45 billion to be exact, a record high for the company and up an impressive 32% in just the last year.

BRK.B Cash and Equivalents (Quarterly) data by YCharts.

Of course, that fact’s not very surprising if you realize Buffett’s cash-spewing conglomerate is generating over $2 billion per month in free cash flow.

Buffett’s enthusiasm for renewable energy is also easy to understand in the context of his 2013 shareholder letter where he told investors, “we will always maintain supreme financial strength, operating with at least $20 billion of cash equivalents.”

Buffett’s big solar bets
Among many of Berkshire Hathaway Energy’s titles is the third largest owner of solar assets in the country, behind only possible buyout target Next Era Energy Inc (NYSE: NEE  ) andFirst Solar Inc (NASDAQ: FSLR  ) .

This is a result of three major solar investments totaling $6.02 billion. The first was the 550 MW Topaz solar farm in Tempe, Ariz., the largest solar project in the world at the time, which Buffett bought from its builder First Solar in 2011 for $2 billion. The project ultimately cost $2.4 billion and required Berkshire to issue $1.1 billion in bonds due 2039.

The second project, the 579-MW Antelope Valley project, is currently the largest solar project in the world, built by SunPower Corporation  (NASDAQ: SPWR  ) , and bought by Berkshire Hathaway Energy for $2 billion in January of 2013. To complete the project, Berkshire Hathaway Inc issued $700 million in bonds. The power generated will be enough to power 400,000 California homes and is under a 20-year power purchase agreement (PPA) withEdison International  (NYSE: EIX  )  for “well-above-market prices.”

Source: SEIA.org (Solar Energy Industries Association).

The final project is the 290 MW Agua Caliente project, a $1.8 billion solar project built by First Solar and owned 49% by Berkshire Hathaway Energy and 51% by NRG Energy Inc (NYSE:NRG  ) . The project was partially funded by a $967 million loan from the U.S. Department of Energy and has a 25-year PPA to sell power to utility PG&E Corporation (NYSE: PCG  ) .

Source: Energy.gov.

$15 billion is a drop in the bucket
I think it’s fair to say Mr. Buffett has some deep pockets and isn’t afraid to write big checks. With Berkshire Hathaway Inc now the fifth largest company in the world, with a market cap of $343 billion, and the company generating $25 billion a year in free cash flow, the company’s ability to grow fast enough to keep up with the market is being threatened by the possibility of drowning in its own rivers of cash.

Which brings me back to why Buffett is so enamored with renewable energy. Specifically, there are two reasons Berkshire is targeting this particular area of the energy sector.

First, the global energy infrastructure market is pretty much the only ocean large enough to let Berkshire grow quickly in. For example, according to the International Energy Agency (IEA), between 2012 and 2035, the world will invest $6.4 trillion in renewable energy as part of a $48 trillion in total energy infrastructure and energy efficiency initiatives needed to meet energy demands of a growing world.

On scales such as these, Buffett’s $15 billion renewable pledge, $30 billion energy investment plan, or even his willingness to make a $50 billion acquisition seem paltry, which is exactly why Buffett is leading Berkshire deeper into the energy sector. It’s one of the final growth frontiers left to a company that has nearly run out of worlds to conquer.

Sweet, sweet, tax breaks
The second major reason Buffett loves renewable energy, especially solar power, is the 30% solar tax credit and accelerated depreciation schedule, known as the Modified Accelerated Cost-Recovery System, which allows Berkshire to write off the depreciation in just five years.

How much does this really make a difference? Well, if Berkshire were to invest $15 billion into the solar project through 2016 (the tax credit is set to decline to 10% for utility scale solar projects at the end of that year), the company would be able to accrue $4.5 billion in tax write-offs over five years, or $900 million annually.

For a company starting to run out of ways to grow, investments into clean energy that provide these kind of tax benefits (and automatic shareholder wealth creation), as well as decades of predictable cash flows, are simply too good to pass up. No wonder Buffett can’t seem to get enough.

How can I cash in on this?
There are three easy ways for long-term investors to join the solar bonanza. The first, easiest, and least risky is to own shares of Berkshire Hathaway, which is trading at its historic 21-year average P/E ratio and 22.5% above the level at which Buffett is willing to buy back shares (1.2 times book value).

With analysts expecting 8.5% earnings growth from the company over the next five years, and shares fairly priced, investors shouldn’t expect mind-blowing returns, but you also aren’t likely to lose your shirts, either (the stock is 71% less volatile than the S&P 500).

Two more speculative investments into solar are SunPower and First Solar, two of the largest manufacturers of solar panels (and both profitable, a rarity in this industry) and builders of the massive utility-scale solar projects Buffett is so found of buying — and hinting that he’ll be buying a lot more of.