Thursday, May 19, 2011

1 MWh on the Clock

A bit of a milestone today.  Since fitting the "proper" OFGEM generation meter back in March last year, the AC power generated (consumed) from my solar panels has been ticking up.

Today, it passed the 1000 kWh (1 MWh) mark.  But amazingly, a full 153kWh of that total was generated just last month!  May is shaping up pretty well too, having made 114kWh this May, compared to only 92kWh last May.


  1. Hi Bodger
    Have you done a flow chart on how much you have invested and what
    kwhs you have gained from the system.

  2. Welcome and thanks to the 1st commentator ever to this blog (excluding one unintelligable spam post I deleted the other week O_o ).

    Ha hahaha... How much I've spent on this Frankenstein system is one of the few parameters I don't keep close tabs on :D

    But a quick tot up last night suggests about £8200 on the current kit in service. That includes the last lot of panels that aren't in service fully yet, and excludes the cost of the ones just taken out of service, along with a bunch of other "stuff" relegated to the "spares bin". Very little actually gets thrown away or sold off; there's enough gear laying about the "lab" to build a whole new 130W system :D

    There's no easy way to calculate ROI on this system, as the embodied "investment" has fluctuated (up *and* down), while the "rate of return" has grown as the system got bigger due to higher utilisation of the capacity of some of the expensive components (the charge controllers and inverters) and the panels have got a lot cheaper. Two years ago I was paying £250 for second hand 80W panels, the last lot only cost £118 each.

    But in pure financial terms, it's a car crash :D 1MWh of electricity is only "worth" about £96. I did receive about £250 in FIT payments for the year 2010-2011 though (more on that soon...).

    Off grid PV (or any kind of off grid power, for that matter) is hugely expensive and never "pays back", mostly because the very expensive batteries are a consumable. The ones I have now only cost £500 as they are a bunch of second hand ones.

    The "pay back" is you get to live without grid power. Most of the experiment has been in trying to answer the question "how much PV do you need to live off grid?". The answer is, "lots" :/ . I measure "success" and ROI in terms of what percentage of total electricity used in our house was generated by the solar system. The lifetime (of the system) offset of grid power is only 13% so far. But the best month was last month (53% of all power used in April was solar power), and the first week of this month (May) was the best weekly offset ever (72% of demand was provided by solar).

    With the solar power also being used to heat water, it also offsets some use of gas too. I can't quantify that offset, other than some days we don't use any gas for water heating and other days we use "some" gas. The hot water tank is effectively another "battery", as it can absorb spare energy from the solar system (that isn't stored in the electrical batteries), and release it later at night, in the form of hot water.