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Bitcoin versus batteries

9 January 2018

Confused by the title of today's column? Don't worry, let me explain.

An increasing number of people are fitting photovoltaic arrays (PVAs) to their houses in order to generate their own electricity from the sun. Solar power is a safe, low-cost form of renewable energy that some countries (such as Germany and China) have embraced with great enthusiasm.

One of the problems with fitting your own house out with PVAs is that you tend to end up with a surplus of power which, unfortunately, coincides with periods of lowest use.

The long days of summer deliver lots of energy to your PVAs but also mean that aside perhaps from running an air-conditioner, we don't actually use nearly so much power in December through February, as we do during the winter months.

So what do you do with the excess power?

Well Tesla will sell you a big battery that you can bolt to the wall of your house and into which some of the surplus energy can be poured.

Unfortunately, if you run an energy-efficient house and have a good-sized PVA then you will still find that you've got more energy than you can use.

One option has always been to backfeed that energy into the national grid and get paid for it.

Some countries, until recently, even offered to buy that surplus energy at a pretty good rate and it was this backfeed which made PVAs so attractive in certain parts of the world.

However, that's changed now and few countries offer to pay more than a token amount for the energy that you might be generating but not actually need. This has blown the economics of fitting solar generate all to hell in many cases.

So if you can't sell it to the grid for a sensible price and you can't afford to blow tens of thousands of dollars on a house-full of batteries, is there another option?

Well hell yes there is -- and it's called Bitcoin!

Now not being a Bitcoin maven, I had to do some Googling to get the numbers for today's column but here's what I found:

According to this page, it takes about 49,000KWH to mine a single bitcoin -- at least it did back in September of 2017.

Now as of last night (when I wrote this column) a single bitcoin was worth NZ$22,151.143 (check today's rate here)

So, if we had a PVA setup and it was generating an energy surplus that couldn't be stored or used by your house then if you used that energy to mine bitcoins then the effective return rate on that energy would be around 45 cents per KWH.

Wow... with the best deal I could find for selling that excess power back to the grid was a paltry paltry 8 cents per KW/H so using that power to mine Bitcoin would (in theory) return almost six times as much!

Of course there are a few flies in this ointment...

Firstly, the economics will vary wildly, depending on the current value of a Bitcoin. Secondly, as time goes on, the amount of energy needed to mine a coin will increase so the return rate will drop (all else being equal).

Most importantly however, this equation doesn't include the capital cost of the hardware you'll need to mine your Bitcoins -- and that can be significant, especially if you want to suck up all the surplus power around mid-day when your solar array is fair squirting out the watts.

However, if you've already got a mining rig, and have a roof covered in PVAs, and Bitcoin remains high, you'd be stupid not to consider mining as a far more lucrative option to simply getting a crappy 8 cents per unit from your power company.

The economics get even better if you're "off grid" because, to get your 8 cents from the power company, you'll need to get connected and pay all those awful line-fees and other daily charges that account for such a huge percentage of today's power accounts.

So what do readers think?

Might it be worth knocking up a Beowulf cluster of Raspberry Pis to mine Bitcoin with your surplus energy?

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