Author: Desislava Georgieva
Published On: 17/06/2022

My name is Ilian Iliev and for 22 years I have small photovoltaic plants. I have been through all kinds of vicissitudes.

Lately, my mission has been to explain why, if you decide to use the roof or the facade of your home to install PV modules, it is better to take advantage of the unattractive option: To use the produced electricity mainly for your own needs and sell to the grid only the surplus, instead of the tempting offer of electricity suppliers , who give you a preferential price if you accept an offer to buy you 100% of the produced electricity. During one of these explanations, my interlocutor said to me: ‘Yes, I understand you, but I will put in much more power than I consume and so I will get money to pay my bill’.

At this point I was disarmed and felt a lack of argument. However, this gave me the idea to prepare the present text for similar cases. Thus came this example, which is based on a real case from February 2022.

In the month of February, a household owning a small system of eight photovoltaic panels with a maximum capacity of 1.2 kWh peak consumed 100 kWh of electricity, which it paid by invoice to the power distribution company at a price of 0.41645lv per kilowatt (the free market price) per kilowatt. Note: All households that have or will install PV capacity become part of the free market. That is, you pay a total of 41.55 BGN for the electricity supplied. We will exclude any additional charges from the invoice, for delivery, VAT and a number of other charges that are derived and not directly relevant to the example. At the same time, the PV modules you have installed have produced 74 kWh of electricity. Of these, you were able to use 30 sq. m. for household needs and 44 sq. m. were fed into the grid of the electricity distribution company. This means that your electricity consumption for the month in question was actually 130 sq. and not 100 as invoiced). So 130 sq. at 0,41645 BGN would make a bill of 54,14 BGN. Or as a consequence of having a PV on the roof you will have saved 12,59 BGN. But this is not all.

In that same month as already noted you have given the grid 44 sq. m. which the energy company will pay you at 0,11 BGN per kilowatt (the price is fixed by the AUP). That is, you will get 4,84 BGN. If we relate all this to the monthly budget of the household we come up with the following: in the expense part we put 41,55 BGN and in the income part 17,43 BGN. The monthly balance for energy will be (- 24,12)lv.

However, if we assume that we have accepted the offer of the energy company – to buy us all the electricity produced by the photovoltaics at a preferential price of BGN 0.19 per kilowatt, then the bill becomes as follows. Sold to the energy company all 74 sq. m. at 0,19 BGN will bring us an income of 14,06 BGN. That is, our sectional balance for energy will be (- 40,08)lv. That is, if you install your own system you will have earned (though not cash) for the month in question 15.96 pence.

To give my friend an answer, I will assume that the PV output is not 1 but 5 kilowatts. I will have to speculate here because I don’t have data for 5 kilowatts, I will extrapolate the data. The electricity used by the household remains constant: 130 sq. ft. at 0.41645 will make a 54.14 lv. payment. Assume that a 5 sq. system will produce 370 sq. of electricity (all things being equal to our one kilowatt system in the example above), which you will sell at 0.19 lv. This means that you will receive an income of 70,30 lv. That is, the monthly balance for energy will be +£16.16.

The example confirms my friend’s logic. With the income I will pay my expense. Except that in the first case one kilowatt brings an income of 17,43 BGN, and in the second case it is from 1 kilowatt our income is 3,23 BGN (total income of 16,16 BGN divided by 5 kilowatts), The cost to build a PV system can vary between 1400 BGN and 2000 BGN per kW/kilowatt. I’ll leave it to you to calculate the cost-effectiveness of either option relative to the cost of the investment you would make. What I will say, however, is that the more you use the electricity produced by your PV to meet your household needs, the more you will increase the efficiency of your investment.

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