Friday, April 24, 2015

Which Solar (Hot water or PV)?

Hot Water Collector or PV System? Which one has the shortest return on Investment (ROI)?

To arrive at a conclusion, I'll be working out some real-life scenarios (based on my family needs).
I have made the following assumptions in the calculations below:

Water Heater.

--> Based on a family of 5.
--> Electric element for both the Solar water heater (SWH) and Electric water heater (EWH) system has been specified as 2KW. This element can be slightly higher for an EWH but average for a SHW system. I've seen SWH installed with a 4KW element. To keep things simple, I'll be working out the consumption using the same 2KW heating element in both cases.
--> My water heating requirements actually reflect ALL my hot water requirements because I'm feeding hot water from the SWH to the washing machine as well, thus eliminating the need to switch on the washing machine heating element. Therefore the SWH will be supplying hot water for all my needs and not only for the bath/kitchen facets. This is not a very common scenario and in fact that's why I use quite a lot of hot water.
--> I'll be using the EWH for 804.5 hours a year while I'll be needing the SWH electric element (when the sun doesn't shine) for 286.5 hours a year.
--> I'm basing the unit of electricity on the 2013 prices, i.e. Eur0.16 per KWH.
--> I have sized the SWH to 200 litres and the EWH to 80 litres.

SWH electrical heating element average use. Note that for a whole 6 months of the year, I won't be needing to assist my hot water production with electricity.
Jan - 2Hrs x 31days = 62Hrs
Feb - 2Hrs x 28days  =56Hrs
Mar - 1Hr x 31days = 31Hrs
Apr - 0Hrs
May - 0Hrs
Jun - 0Hrs
Jul - 0Hrs
Aug - 0Hrs
Sep - 0Hrs
Oct - 0.5Hrs x 31days = 15.5Hrs
Nov - 2Hrs x 30days = 60Hrs
Dec - 2Hrs x 31days = 62Hrs
Total of 286.5Hrs

EWH average use. (Including the Washing machine heating element)
Jan - 3Hrs x 31days = 93Hrs
Feb - 3Hrs x 28days  =84Hrs
Mar - 3Hrs x 31days = 93Hrs
Apr - 2Hrs x 30Days = 60Hrs
May - 1.5Hr x 31Days = 46.5Hrs
Jun - 1Hr x 30Days = 30Hrs
Jul - 1Hr x 31Days = 31Hrs
Aug - 1Hr x 31Days = 31Hrs
Sep - 2Hr x 30 Days = 60Hrs
Oct - 3Hrs x 31days = 93Hrs
Nov - 3Hrs x 30days = 90Hrs
Dec - 3Hrs x 31days = 93Hrs
Total of 804.5Hrs

Yearly Calculations
SWH. 2KW (Electrical Element) x 286.5Hrs = 573KWH x Eur0.16 = Eur91.68
EWH 2KW (Electrical Element) x 804.5Hrs = 1609KWH x Eur0.16 = Eur257.44
Yearly difference of Eur165.76

There are several SWH heaters on the market and their prices vary quite a lot depending on certifications, brand etc. I'll be taking an average of Eur1200 for a SWH while Eur120 for an 80 litre EWH. Taking into consideration the grants currently available for SWH, we can reduce the prices to Eur800.

Therefore, Eur800 - Eur120 = Eur680 difference.
Using the yearly operating difference cost of Eur165.76, it will take 4 years to break even the SWH against the EWH. 

(I have not taken into account the yearly maintenance fees which are charged by RE suppliers to service the SWH. Unfortunately, the charges are quite high when normally only the cathode rod needs to be replaced!)


--> Sized the system to 2KW. 9 panels x 235 Watts each.
--> Feed-in tariff of Eur0.25 per KW (based on 2013 prices).

Yearly Calculations
9 PV @ 235W each = 2115W (Peak Output)
2115W x 0.77 (derating factor) x 5 (average daily hours of sunshine) =  8142.75W or 8KW
Daily average generation = 8KWH x Eur0.25 = Eur2
Yearly, Eur2 x 365days = Eur730

Initial cost. Eur6000 (including government grant (2010))
The payback for the PV system is Eur6000 / Eur730 = 8.2 years.

(I have not taken into account the meter charges).

From the calculations above, 4 years are needed to break-even a SWH while 8.2 years for a PV system. Something to keep in mind however is that normally a SWH is accompanied by a 5-year warranty while a PV system will have 5 years warranty on the inverter and a 20-25 year limited warranty on the PV panel output.
In my opinion, I'm not really worried about the PV panels' warranty, simply because the PV panels are very reliable and I already have experience with some 10 year old panels (and their output is still as new) but I'm more concerned about the inverter. The inverter is a complex electronics device which works every single day (as long as the sun shines) under high loading conditions (90%-100%) of its rated capacity. This places stress on the electronic components and although brand SMA (for example) have a solid product, in my opinion it's the weakest link in a PV system.
Note: Nowadays more electronics are being added to the PV systems to improve their efficiency such as Power Boosters or Power Converters. In my opinion, the more electronics are added, the more prone to failure the system becomes. I'll be more inclined to add an extra panel or two to increase the PV output than add more electronics!

From the calculations above, a SWH will pay back itself in less time than a PV system. So why is it that people still opt to install a PV system before a SWH or even not install a SWH but go for a PV system only? Maybe a PV system is more attractive? is it because it is also cool to produce your own electricity? Well, in my opinion, the answer is simple ignorance due to the lack of information from the governments & RE companies.
RE suppliers in Malta should know more than everyone else that s SWH ROI is better than a PV system. Nonetheless, they still fail to provide this information. Could it be that the profit margin is better on a PV system?
Another point is that the government grants have failed in this regard. The government should have encouraged families to first install a SWH  and then give a better grant to help install a PV system.

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