The Economics of our SunAmps
We use 2 × SunAmp PVs for our HW system in a household of 3 people.
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According to our water bills, our consumption is about 83 ltr per person per day. Our pattern of use is pretty even across the year: more showers in the summer; an occasional shared bath in the winter.
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The year round average temperature of our rising main is 11.3 °C (Oh, the wonders of logging everything in a DB and knowing how to do SQL subqueries).
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The H/W manifold is mixed to 53°C (perhaps a little too hot for kiddies but we are an adult household).
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I estimate that ~40% of our water is run as hot. (The washing machine and dishwasher, bogs, etc. are cold fill.)
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Cranking these number into a heat calculator, this gives a total heating requirement of just under 5 kWh / day + another 1 kWh / day heat loss as the SunAmps are tight side-by-side and amazingly insulated. (I don't separately meter the SunAmps, but a quick sanity check of my actual half-hourly electricity meter readings would indicate this figure is about 20% too high, but let us stick with this figure for estimating purposes.
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All heating is done at cheap rate tariff ( fixed at 9.66 p / kWh inc VAT) so this costs us ~ £211 p.a.
- Using an ASHP to supply the SunAmps at 40 °C, say, would drop this to 2.5 + 1 kWh saving us less than £100 p.a. or about £1K over 10 years.
So in our case if we decide to install an ASHP, there aren't enough savings to make it worth installing an extra pump, a buffer tank and a two temperature ASHP to use it to (part) heat the DHW.
We will stick to Keep It Simple Stupid.
A couple of caveats here:
- I think our pattern of water use would be very different with children in the household.
- We have a fixed price deal until end 2022. We are going to see a big hike in our next tariff, but I feel that this will settle down in the longer term, so I am ignoring this for now.
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