Justice KOURLIS
delivered the opinion of the Court.
Phoenix Power Partners, L.P. (Phoenix) appeals a judgment of the district court affirming Orders of the Colorado Public Utilities Commission (PUC). This court has direct appellate jurisdiction under section 40-6-115(5), 11 C.R.S. (1997). Phoenix challenges the PUC’s ruling, as affirmed by the district court, that certain amendments to a contract between Phoenix and Public Service Company of Colorado (PSCo) were so substantial as to create a new contract not entitled to grandfathered benefits. Phoenix also contests the ruling that the new contract must be submitted to PSCo in accordance with established bidding procedures. We now conclude that the district court correctly determined that the amendments created a new contract, and that the new contract would have to comport with the bidding procedures. Accordingly, we affirm the judgment of the district court.
[361]*361I.
In 1988, Phoenix’s predecessor in interest, Montrose Partners, Ltd.,1 (Montrose/Phoe-nix) entered into a power purchase agreement with PSCo whereby Montrose/Phoenix agreed to sell energy and capacity2 to PSCo from a hydro-electric plant it proposed to build in Montrose, Colorado. The Montrose facility was to be a qualifying small power production facility under the Public Utility Regulatory Policies Act of 1978 (PURPA). See Pub.L. No. 95-617, 92 Stat. 3117 (1978).
In order to place the facts of this case in context, we begin with a brief review of PURPA and its related regulations. Congress enacted PURPA in 1978, in response to a nationwide energy crisis. The purpose of PURPA was to reduce reliance on foreign oil, and on fossil fuels generally, by encouraging energy efficient cogeneration3 technologies and by stimulating the development of renewable, non-traditional energy resources. See 16 U.S.C. §§ 796, 2601 (1994). PURPA directed the Federal Energy Regulatory Commission (FERC) to adopt rules necessary to encourage utilities to purchase power from qualifying cogeneration and small power production facilities.4 See 16 U.S.C. § 824a-S(a)(1994). The rates for these purchases were to be just and reasonable to electricity consumers and were not to exceed the incremental cost to the utility of alternative electric energy. See 16 U.S.C. § 824a-3(b)(1994). PURPA also required that state regulatory authorities implement the FERC rules for electric utilities within their jurisdictions. See 16 U.S.C. § 824a-3(f)(l)(1994).
In 1980, FERC promulgated rules defining small power production facilities and cogen-eration facilities. See 18 C.F.R. §§ 292.203 to 292.206 (1997). The term “qualifying facility” or “QF” is used herein to describe either of these two types of PURPA-qualified facilities. The FERC rules require electric utilities to purchase energy and capacity from qualifying facilities. See 18 C.F.R. § 292.303 (1997)(“Each electric utility shall purchase ... any energy and capacity which is made available from a qualifying facility”). FERC adopted the “full avoided cost” approach to setting rates for purchases from qualifying facilities. Under this approach, the utility sets rates based upon the cost that the utility would have incurred in building its own power plant or purchasing a like amount of power from a non-qualifying facility. See 18 C.F.R. §§ 292.304(b)(2), 292.101(b)(6) (1997).
In 1982, the PUC adopted rules implementing the FERC rules. See Rules Implementing Sections 201 and 210, PURPA, Small Power Production and Cogeneration Facilities, 4 C.C.R. § 723-19 (adopted 1982 and as amended) (the Colorado QF Rules). The Colorado QF Rules parallel the FERC rules in requiring electric utilities to purchase power from QF’s at rates based on the full avoided cost. See 4 C.C.R. § 723-19, Rules 1.207, 3.401. In order to facilitate financing of QF projects, the avoided cost rate calculated at the inception of the contract can be fixed or “locked in” for the full term of the contract.5 See 18 C.F.R. 292.304(d)(2) (1997); 4 C.C.R. § 723-19, Rule 3.507.
Initially, PSCo. set its QF avoided costs administratively and filed tariffs establishing capacity payments derived from these administratively determined avoided costs. Over the next few years, numerous QF developers approached PSCo seeking to sell electricity at the rates set by tariff. By 1987, PSCo reported to the PUC that continued mandatory QF purchases would result in excess [362]*362capacity in the system during the years 1991 through 1993. Payments for excess or unnecessary capacity would translate into higher rates for consumers. Consequently, PSCo sought approval for a moratorium on its obligation to purchase QF power.
In Decision No. C87-1690 (Dec. 16, 1987)(the Moratorium Decision), the PUC authorized a temporary moratorium on purchases from QF’s, but exempted certain contracts from the moratorium by operation of a grandfather clause. The PUC specifically exempted from the moratorium the pending contract with Montrose/Phoenix and required PSCo to continue negotiating with Mont-rose/Phoenix in good faith. The PUC reserved the right to approve or disapprove any resulting contract on the basis of whether or not it contributed to the excess capacity and cost problems that prompted the moratorium. Shortly after the moratorium was granted, the PUC approved a biennial bidding process to establish avoided costs for future power purchases from QF’s. See In re Public Serv. Co. of Colo., 93 Pub. Util. Rep. 4th 384, 399 (June 9, 1988)(Dec. No.C88-726).
On April 6, 1988, Montrose/Phoenix and PSCo signed a fifteen-year contract under which PSCo would purchase approximately 48.5 Megawatts of capacity from a qualifying water-powered small power production facility to be built in Montrose (the 1988 Agreement). The 1988 Agreement was based upon the 1987 tariffs and was not subject to the new bidding procedure for setting avoided costs because of the grandfather provision in the Moratorium Decision. See Dec. No. C87-1690 (Dec. 16, 1987). Hence, the contract purchase rate was determined by PSCo’s filed 1987 tariffs reflecting PSCo’s administratively set avoided costs. Under the terms of the 1988 Agreement, power deliveries were to begin no earlier than April 1992. The PUC approved the contract on June 29, 1988 in its Decision Number C88-792.
Montrose/Phoenix began to encounter significant difficulties with the federal permitting process and, in November 1991, negotiated an amendment extending the earliest delivery date to September, 1994 (the 1991 Amendment). The 1991 Amendment also reduced the capacity from 48.5 to 43.5 megawatts. The PUC approved the 1991 Amendment at an open meeting in December of 1991.
Permitting difficulties associated with the Montrose site continued, and in 1992, Mont-rose/Phoenix and PSCo began to negotiate further amendments to the 1988 Agreement. In March of 1993, Phoenix6 and PSCo entered into an agreement purporting to amend and restate the 1988 Agreement (the 1993 Amendment). The parties executed the 1993 Amendment in the form of a full contract, some 133 pages in length including exhibits, and restated their entire agreement including the changes.
The 1993 Amendment changed the location of the plant from Montrose to Greeley, and the method of power generation from a water-powered facility to a natural gas-fired cogeneration facility. The waste heat from the Greeley facility would have been used to heat and cool the University of Northern Colorado (UNC) campus. The 1993 Amendment also slightly changed the contemplated capacity. The maximum capacity output at the Montrose hydro-electric plant would have depended upon the varying flows of the Un-compahgre River. As a result, capacity would have averaged about 35 megawatts in summer and 43.5 megawatts in winter. The Greeley site offered a steady 43.5 megawatts of capacity throughout the year. This feature would have allowed PSCo to dispatch, or schedule, the output more dependably and was a benefit to PSCo over the Montrose site. The price also changed somewhat. The Greeley site, because of its greater dis-patchability, commanded a higher rate under the 1987 tariffs than the Montrose site.7
[363]*363In accordance with the language of the agreement itself, and with PUC rules and decisions, PSCo submitted the 1993 Amendment to the PUC for approval. The staff of the PUC raised concerns about the 1993 Amendment, suggesting that the proposed changes were so significant and numerous as to create a new contract, not entitled to the grandfathered status granted to the 1988 Agreement. The staff report further noted that as a proposed new contract for QF power, Phoenix would have to compete for the right to sell its power in the bidding system established for QF’s by Decision Number C88-726. The PUC set the matter for hearing before an Administrative Law Judge (ALJ) on October 14,1993.
Both Phoenix and PSCo took the position at the hearing that the 1993 Amendment was, in fact, simply an amended version of the existing and approved 1988 Agreement. Therefore, under the grandfather provision of the Moratorium Order, they argued that the PUC’s only function should be to determine whether the changes, compared to the original agreement, would benefit ratepayers. Phoenix and PSCo both presented evidence that the 1993 Amendment significantly improved the financial consequences of the original deal for PSCo and consequently for its ratepayers.
Moreover, Phoenix argued that the PUC’s analysis of whether the 1993 Amendment fell within the scope of the grandfathered 1988 Agreement should be governed by the purpose and language of the Moratorium Order. The need for the moratorium arose out of excess capacity. The PUC exempted certain contracts from the impact of the moratorium, provided that they did not exacerbate the capacity problem. Phoenix asserted that the PUC had already determined that the eapacity offered under the 1988 Agreement was, in fact, needed by PSCo. Basically the same capacity was contemplated under the 1993 Amendment, although generated in a different manner and from a different location. Phoenix contended that because the changes would benefit the ratepayers, without contributing to the capacity problem, there was no basis for PUC rejection.
The practical impact of any decision as to whether the 1993 Amendment was grandfathered or created a new contract revolves around price. The price set in the 1987 tariffs for QF power is higher than the price for comparable power in 1993. If Phoenix were offering a new contract, the price would have to comport with 1993 standards and would need to follow the bidding procedure. If the 1993 Amendment related back to the grandfathered contract, PSCo had a legal obligation to pay the. 1987 tariffed rates which were “locked in” under PURPA and Colorado QF Rules.
The ALJ, in his recommendations to the PUC, concluded that the 1993 Amendment created a new contract.8 The PUC adopted the' ALJ’s ruling. The PUC found that the parties had altered the essential elements of the 1988 Agreement and created a new contract by changing the technology, location, fuel source, legal entities and capacity payment.
The district court affirmed the PUC’s finding of a new contract. Like the PUC, the court considered the change in location, technology and legal entity to be dispositive. The court held that the PUC’s ruling was just, reasonable and in accordance with the evidence. Phoenix now appeals the judgment of the district court directly to this [364]*364court under the provisions of section 40-6-115(5).
II.
Judicial review of a PUC order is governed by section 40-6-115, 11 C.R.S. (1997), which provides in pertinent part that decisions may be reviewed “to determine whether the commission has regularly pursued its authority ... and whether the decision of the commission is just and reasonable and whether its conclusions are in accordance with the evidence.” § 40-6-115(3), 11 C.R.S. (1997); see also Boulder Airporter, Inc. v. Rocky Mountain Shuttlines, Inc., 918 P.2d 1118, 1120 (Colo.1996). Questions of law are to be decided by the courts, and PUC rulings in this regard, while entitled to respectful consideration, are not controlling. See § 40-6-115(8)(“the district court shall decide all relevant questions of law”); Union Rural Elec. Ass’n Inc. v. Public Utils. Comm’n, 661 P.2d 247, 251 (Colo.1983).
One of the principal areas of contention between the parties to this ease involves the interrelationship between PURPA and general contract law. Phoenix argues that, under PURPA, the PUC had limited jurisdiction to review the 1993 Amendment solely for the purpose of determining whether it benefited ratepayers or whether, under the Moratorium Decision, it exacerbated the capacity problem. The PUC argues, on the other hand, that PURPA did not even become applicable until the PUC determined whether the 1993 Amendment was the same contract as the one approved in 1988.
We agree with the PUC. Before considering the PUC’s obligations and restrictions under PURPA and the Moratorium Decision, we must first determine whether the 1993 Amendment in fact represents the same contract to which the PUC granted the grandfathered rights. Hence, the case first presents a question of contract law: namely, whether the 1993 Amendment created a new contract, or whether it related back to and reaped benefits afforded to the 1988 Agreement.
We look then to Colorado contract law to answer the question. Under contract law, if the 1993 Amendment works a novation of the 1988 Agreement, it will be deemed to constitute a new contract. A novation extinguishes a previously existing contract by substituting a new contract or obligation. See Moffat County State Bank v. Told, 800 P.2d 1320, 1323 (Colo.1990). There are four requirements for a novation: (1) a previous valid contract, (2) agreement between the parties to abide by the new contract, (3) a valid new contract, and (4) extinguishment of the old contract by substitution of the new one.9 See id. The parties need not expressly manifest their intent to accomplish a novation, but a novation may be inferred from the facts and circumstances surrounding the transaction. See id.
In this case, the 1988 Agreement represents the previous valid contract sufficient to meet the first requirement of the novation test. The 1993 Amendment constitutes an agreement between PSCo and Phoenix, binding on both parties, satisfying the second requirement. The controversy concerns whether the 1993 Amendment created a new contract, thereby superseding the old one, or whether it merely amended the 1988 Agreement.
In Told, this court noted that evidence of a novation exists when “the new contract is so radically different from the old one that it necessarily supersedes it as an entirety.” See id. (quoting Elliott v. Whitney, 215 Kan. 256, 524 P.2d 699, 704 (1974)). [365]*365We conclude that if the essential elements or terms of the contract have been transformed, a new contract will be deemed to supersede the old. The specific facts surrounding the contractual relationship dictate whether or not terms are essential to the agreement. See, e.g., American Mining Co. v. Himrod-Kimball Mines Co., 124 Colo. 186, 190, 235 P.2d 804, 807 (1951)(noting that what constitutes “essential terms” varies widely among jurisdictions and should be determined in each case from the particular circumstances of the transaction); Federal Lumber Co. v. Wheeler, 643 P.2d 31, 36 (Colo.1981)(finding that the house built by a contractor differed so greatly from that specified in the original plan that the original plan did not constitute a contract between the parties because it did not contain the essential terms of the contract for the resulting house).
Phoenix argues that the only essential terms of the contract were price,10 capacity and term. Even if that were the correct analysis, we observe that both price and capacity have changed between the 1988 Agreement and the 1993 Amendment. The record, however, reflects that many more of the changed contract terms are essential and of serious significance both to the parties and tp the PUC. See, e.g., Re Jersey Cent. Power & Light Co., 143 Public Util. Rep. 4th, 188, 194 (May 11, 1993)(rejeeting amendments to a previously approved QF power purchase agreement because a change in location and facility type were not “in conformity with the scope” of the regulatory commission’s previous approval). Further, we view the proper analysis as one that is more expansive. When viewing the 1993 Amendment as a whole, we note that virtually every contract term is altered, albeit some more significantly than others, with the result that the 1993 Amendment differs radically from the 1988 Agreement.
The 1988 Agreement contemplated a category 4C11 water-powered facility, dependent upon the flow of the river for capacity availability, classified under PURPA as a small power production facility and located in Montrose, Colorado. The 1993 Amendment contemplated a category 4A natural gas-fired facility, offering a steady capacity with greater dispatchability, classified under PURPA as a cogeneration facility, located in Greeley, Colorado, and also servicing the UNC campus with its recaptured waste heat.
The Greeley location is much closer to PSCo’s load centers, which proximity increases the reliability of the generation. Further, the gas-fired plant is capable of providing greater dispatch control than the hydro-electric plant. Dispatch control enhances reliability of supply and may improve economic efficiency in operation. Reliability and economic efficiency are important issues between the parties and are proper areas of concern to the PUC. As stated above, the category 4A dispatchability feature triggers a different, higher tariffed rate. In testimony before the PUC, the staff explained that it harbors special concerns about the pricing structure for category 4A plants. Specifically, the PUC described what it termed a “fundamental flaw” with the category 4A QF’s regarding the under-utilization of dis-patchable QF’s below an 80% factor. Hence, while it cannot be said definitively that these changes create a better or worse deal for PSCo and ratepayers, they clearly present substantial and important considerations affecting the basis of the bargain between the parties.
We also note, as did the ALJ, that the proposed heating and cooling of the UNC campus creates what could be considered a subsidization by ratepayers of the cost of electricity to UNC. This too represents a significant change and is an issue of legitimate concern to the PUC in examining the basic terms of the agreement.
Aside from these significant changes, additional terms were altered. Substantial con[366]*366struction on the Montrose plant was to begin by January 1, 1993; substantial construction on the Greeley plant was to begin by June 1, 1993. Both the maintenance provisions and the security deposit were changed under the 1993 Amendment. The amount of capacity which PSCo was obligated to purchase increased under the 1993 Amendment, which in turn increased the total amount of money PSCo would pay over the term of the contract. The only relatively significant item left unchanged was the fifteen-year term with delivery beginning in September, 1994.12 Hence, virtually all of the terms, and certainly the essential terms, of the original contract were changed.
Finally, a novation also requires extin-guishment of the old contract and substitution of the new one. Phoenix argues that its previous obligation to sell electricity to PSCo, and PSCo’s corresponding obligation to purchase, has not been extinguished. Phoenix cites Colowyo Coal Co. v. City of Colorado Springs, 879 P.2d 438 (Colo.App.1994) for the proposition that mere modification of certain contract terms will not accomplish a novation. In Colowyo, a coal mining company entered into a long-term contract with the city of Colorado Springs to supply coal for its electrical power generation plants. Eleven years into the contract, the parties agreed to reduce the fixed contract price and extend the contract term. See Colowyo, 879 P.2d at 443. The court of appeals found that the later amendments evidenced an intent to modify rather than replace the existing contract. See id. The court considered both the fact that the contract language described an intent to amend and restate the original contract, and the fact that only two of the contract terms were altered. See id. The court also noted that a contract’s meaning must be gleaned from the entire document, rather than from isolated portions. See id. at 445.
In this case, far more than just two contract terms were altered, and all amendments predated the beginning of performance of any existing obligations. We agree with the district court that considering the 1993 Amendment as a whole, the PUC made a just and reasonable determination that the 1993 Amendment created a new contract. Accordingly, because we agree that the 1993 Amendment represents a different contract from the 1988 Agreement, it is not entitled to the grandfathered status of the 1988 Agreement.
III.
Phoenix further argues that even if the 1993 Amendment creates a new contract, then the PUC must calculate and assign to the new contract PSCo’s 1993 avoided cost purchase price and enforce this new contract. Phoenix claims that under PURPA and the Colorado QF Rules, Phoenix has a right to sell QF energy and capacity to PSCo, and a right to be paid the avoided cost purchase price applicable to the year in which the contract is executed.
This argument overstates any rights of Phoenix regarding the sale of QF power. The PUC has previously rejected the proposition that QF’s have an absolute right to sell QF power to utilities. First, in its Moratorium Decision, the PUC specifically found that the decision to allow a temporary suspension of PSCo’s obligation to purchase QF capacity did not violate PURPA. See Dec. No. C87-1690. The Moratorium Decision also reinforced the PUC’s own Rule 4.503 authorizing the PUC to relieve PSCo of its obligation to purchase QF power where proposed contracts create safety, capacity or reliability problems. See id. The time for challenging that decision has passed, and the validity of the conclusions underlying that decision are not before the court.
Second, the PUC, in Decision Number C88-726, established and approved a bidding process for setting QF avoided costs and obtaining new QF power. In Decision Number C88-726, the PUC recognized that certain QF developers were in the process of negotiations with PSCo. The PUC provided that if those developers had not reached agreement before December 31, 1988, then [367]*367they, along with any other new QF developers, were required to follow the new bidding procedures. See Dec. No. C88-726. Since we have concluded that the 1993 Amendment created a proposed new contract as of 1993, that new contract must comply with the bidding process because it has no grandfathered rights.
In Decision No. C88-726, the PUC again specifically addressed and rejected the argument that the bidding procedures violated PURPA and its related regulations. Indeed FERC has found that the use of bidding procedures for establishing QF avoided costs is consistent with PURPA. See Southern California Edison Co., 70 FERC ¶ 61,215, 1995 WL 169000 (1995)(requiring the California Public Utilities Commission to allow all potential energy producers to compete with QF’s in a bidding system for establishing avoided costs); see also, Freehold Cogeneration Assocs. v. Board of Regulatory Commr’s, 44 F.3d 1178, 1182 (3d Cir.1995) (referring to New Jersey Board of Regulatory Commissioners’ decision to establish bidding procedures for QF contracts). Again, that PUC decision is not before us.
In the case that is before us, the PUC found that if Phoenix wished to sell its QF energy and capacity under the new 1993 Agreement, it must submit its contract into the bidding process just like any other potential developer. The PUC found that, “the effective procedure for determination of Public Service’s avoided costs” under the Phoenix contract was the bidding process. Dec. No. C95-245. Further, the PUC concluded that “PURPA, the FERC QF Rules, and the [Colorado QF Rules] do not compel Public Service to purchase all capacity and energy offered to it by [Phoenix]” nor do they require the PUC to set a 1993 avoided cost purchase price for Phoenix outside the established bidding process. Id.
We agree with the district court that this conclusion by the PUC is just and reasonable. See Lucero v. Climax Molybdenum Co., 732 P.2d 642, 645-46 (Colo.1987)(noting that courts should give deference to the statutory interpretation of an agency charged ■with administration of a statute); Public Utils. Comm’n v. Grand Valley Rural Power Lines, Inc., 167 Colo. 257, 261, 447 P.2d 27, 28 (1968)(holding that the PUC is the proper authority for interpreting its own rules and decisions and such interpretation will not be overturned unless clearly erroneous).
Accordingly, as we have concluded that the 1993 Amendment constituted a new contract, and the PUC has previously established a bidding procedure the validity of which is not before the court for all proposed QF contracts not exempted from the moratorium, the PUC correctly ruled that the new contract must follow the bidding procedures.
IV.
The 1993 Amendment diverged so significantly from the 1988 Agreement as to constitute a new contract that was not entitled to the grandfathered rights applicable to the 1988 contract. That new contract must be submitted into the bidding process along with other proposed QF contracts. We therefore affirm the district court’s ruling upholding the PUC’s decisions.
SCOTT, J., dissents.