Why utilites will pay a premium for rooftop solar

A power company rang me up last week offering to increase my rooftop solar (RTS) feed-in tariff if I switched my contract to them. My first thought was that this was a marketing ploy but, on reflection, this did not make sense. Why would a power company want a customer who produces about as much power as the household consumes?

By contrast, others are claiming that ordinary householders are subsidising rich rooftop solar owners. For example, Mark McArdle, (Queensland Minister for Energy and Water Supply) issued a media statement saying “the QCA analysis showed the solar bonus scheme currently added $26 per year to everyone’s annual electricity bill, which will increase to $90 next year if an application by Energex to the Australian Energy Regulator was successful.”

He added, “Rooftop solar costs are projected to add more than $240 per year to average electricity bills within five years.” (These claims were based on the previous government’s feed in tariff of 44¢/kWh)

If rooftop solar really was driving up household bills, a power company that was paying a premium to buy more rooftop solar power would have to increase their charges to pay for this premium. Not an aid to competing in a cutthroat market.

So what is rooftop solar actually doing to household power bills in Queensland? And how high could the feed-in tariff go before it really would be increasing household power bills?

In the detailed section below, a comparison of demand and revenue vs time of day for 2008 and 2012 is used to answer the above questions. The quick answers are:

1. Rooftop solar is actually saving the “typical Queensland household” (without PV) $65/yr.

2. The feed-in tariff would have to rise above 96¢/kWh before rooftop solar actually stopped saving households (and power companies) money. Power companies can actually become more competitive by locking in extra contracts for the supply of rooftop solar, even if it means paying the small premium that was offered to me.

3. It is difficult to say what effect rooftop solar would have on household bills in five years’ time. My guess is that investment in rooftop solar will be justified at feed-in tariffs below what householders will be paying for power and that it will still be saving households money.

The Queensland government may actually believe that their decision to drop the feed-in tariff to a mere 8¢/kWh for new contracts will save householders money by killing investment in rooftop solar.

Smarter governments should be encouraging the steady growth of rooftop solar. They should also be seeking ways of using market forces to set the minimum feed-in tariff for new contracts. Both actions would help drive down household bills and boost employment.

Smarter governments might also consider the use of competitive tendering to set up contracts for the supply of rooftop solar power as one way of achieving both of the above aims. They might also consider allowing the use of alternative commercial models to make competitive tendering easier in addition to other advantages such as providing a small boost to the income of homeowners who can’t afford to install rooftop solar. (One possibility would have PV owners leasing roof area from householders.)

DETAILS:

If the feed-in tariff for rooftop solar is higher than what householders are paying for power it looks, at first glance, as though it would push up household bills. However, the reality is more complex. What really counts is the price of the power rooftop solar is replacing. Solar PV produces power during the high demand part of the day. Part of the power mix at this time comes from very expensive sources such as peaking generators that may only run for a limited amount of time during the year. It is these expensive sources of power that rooftop solar should replace. Moreover, added capacity from rooftop solar will increase downward market pressure on prices in general.

Despite the size of the feed-in tariff, it is quite possible that rooftop solar is actually driving down the average household power bill.

Figs 1 and 2 come from RenewEconomy. These graphs compare Queensland demand and revenue vs time of day for 2008 and 2012. This period is important for this discussion. RTS grew dramatically between 2008 and 2012.

The graphs exclude data for RTS

Fig 1 shows that average demand only differed during the time of day when rooftop solar would have been producing power. For this reason, it is not unreasonable to assume that the differences between 2008 and 2012 figures were due to its growth. We can also assume that the amount of rooftop solar for 2008 was small enough to be ignored in calculations.

Data taken from the smoothed curves was used to estimate changes in daily demand, revenue and price for non-rooftop solar. Between 2008 and 2012 there was:

1. A 1.87% drop in demand. (2.67 gWh/day).

2. A massive 31.3% drop in the daily revenue received by non-rooftop solar generators ($2.059 million/day)

3. A 30% reduction in the average price paid to non-rooftop solar generators. (1.41¢kWh)

Little wonder that the power generation industry is not completely enthusiastic about rooftop solar.

It is not clear how Mark McArdle’s $26/yr increase in a typical household power bills was calculated. If it is assumed that rooftop solar at 44¢kWh was simply replacing other domestic power at 23¢kWh and changes in the price of non-rooftop solar power were ignored:

1. The power bill increase would have been $26/yr for a household consuming 0.34 kWh/day of rooftop solar power.

2. The “typical household” would have an average power consumption of 18.2 kWh/day if rooftop solar was 1.87 per cent of the total.

18.2 kWh/day is about what might be expected for a typical household. This supports the idea that the $26/yr figure did not take account of the effect of rooftop solar on the non-rooftop solar power price. When this saving is included in the calculation, rooftop solar at 44¢kWh actually reduces the typical power bill by $65/year. It was estimated that the feed-in tariff would have to go  above 97¢kWh before rooftop solar increased the typical household power bill.

If governments are going to make intelligent decisions about rooftop solar it is important the calculations being used to guide these decisions are taking account of the effect of rooftop solar on non-rooftop solar power prices.

The RenewEconomy article had graphs for a number of other states. These graphs looked similar to the Queensland graphs. Further calculations would need to be done to be certain that rooftop solar was saving householders money in these other states.